U.S. patent application number 10/927968 was filed with the patent office on 2005-06-23 for superhard mill cutters and related methods.
This patent application is currently assigned to Diamicron, Inc.. Invention is credited to Dixon, Richard H..
Application Number | 20050133277 10/927968 |
Document ID | / |
Family ID | 34682461 |
Filed Date | 2005-06-23 |
United States Patent
Application |
20050133277 |
Kind Code |
A1 |
Dixon, Richard H. |
June 23, 2005 |
Superhard mill cutters and related methods
Abstract
Superhard ball mill cutters and their materials and
manufacturing methods.
Inventors: |
Dixon, Richard H.; (Provo,
UT) |
Correspondence
Address: |
Parsons Behle & Latimer
201 South Main Street, Suite 1800
P. O. Box 45898
Salt Lake City
UT
84111
US
|
Assignee: |
Diamicron, Inc.
|
Family ID: |
34682461 |
Appl. No.: |
10/927968 |
Filed: |
August 27, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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60499026 |
Aug 29, 2003 |
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60498768 |
Aug 29, 2003 |
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60498968 |
Aug 29, 2003 |
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60498709 |
Aug 28, 2003 |
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60498896 |
Aug 29, 2003 |
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60498708 |
Aug 28, 2003 |
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Current U.S.
Class: |
175/426 ;
175/434 |
Current CPC
Class: |
B22F 2005/001 20130101;
B22F 2999/00 20130101; C04B 2235/427 20130101; C22C 26/00 20130101;
B22F 2998/00 20130101; B23C 5/1009 20130101; B23C 2226/125
20130101; B23C 2210/03 20130101; B24D 18/00 20130101; B22F 2998/00
20130101; B23C 2226/315 20130101; B23B 2240/28 20130101; B22F
2999/00 20130101; B22F 7/06 20130101; C04B 35/52 20130101; B22F
1/0014 20130101; B22F 2207/03 20130101; B22F 3/15 20130101; C22C
26/00 20130101; B23H 5/04 20130101; B22F 3/14 20130101 |
Class at
Publication: |
175/426 ;
175/434 |
International
Class: |
E21B 010/36 |
Claims
I claim:
1. A superhard ball end mill cutter comprising: a substrate, a
table of superhard material on said substrate, a plurality of
flutes cut into said superhard material, and cutting edges along
said flutes, said cutting edges being formed of superhard material,
said cutting edges serving to cut or remove material from a
workpiece.
2. A cutter as recited in claim 1 wherein said superhard material
is diamond.
3. A cutter as recited in claim 1 wherein said superhard material
is sintered polycrystalline diamond compact.
4. A cutter as recited in claim 1 wherein said superhard material
is cubic boron nitride.
5. A cutter as recited in claim 1 wherein said superhard material
is sintered polycrystalline cubic nitride compact.
6. A cutter as recited in claim 1 wherein said superhard material
is selected from the group consisting of sintered polycrystalline
diamond and sintered cubic boron nitride
7. A cutter as recited in claim 1 wherein said substrate and said
superhard material form a sintered compact.
8. A cutter as recited in claim 1 wherein said substrate is a
metal.
9. A cutter as recited in claim 1 wherein said table of said
superhard material is sintered polycrystalline diamond made from at
least some diamond feedstock in the size range of 0 to 70
.mu.m.
10. A cutter as recited in claim 1 wherein said table of superhard
material and said substrate are formed generally into a ball
configuration.
11. A cutter as recited in claim 10 wherein said ball is bored to
accept an arbor shank.
12. A cutter as recited in claim 11 further comprising an arbor
shank affixed to said ball in said bore.
13. A cutter as recited in claim 1 further comprising a cutting
relief adjacent said cutting edges, said cutting relief serving to
enhance cutting action of the cutter.
14. A cutter as recited in claim 1 further comprising chemical
bonds between said superhard material and said substrate.
15. A cutter as recited in claim 1 further comprising residual
stresses which tend to retain said superhard material adjacent said
substrate.
16. A superhard ball end mill cutter made by the following process
steps: placing a quantity of superhard material crystals or powder
adjacent a substrate material, applying heat and pressure to said
superhard material and said substrate material to sinter them into
a compact that has a table of sintered superhard material on a
substrate, and forming flutes on said cutter.
17. A superhard ball end mill cutter made by the process steps of
claim 16 wherein said flutes leave a cutting edge formed of
superhard material.
18. A superhard ball end mill cutter made by the process steps of
claim 16 further comprising the step of forming a cutting relief
adjacent said cutting edges to enhance their cutting effect.
19. A superhard ball end mill cutter cutter made by the process
steps of claim 16 wherein the cutter has a gradient transition zone
between said table and said substrate
20. A superhard ball end mill cutter cutter made by the process
steps of claim 16 further comprising the step of sweeping a
solvent-catalyst metal from said substrate material through said
superhard material in order to form bonds between said
solvent-catalyst metal and said superhard material.
21. A superhard ball end mill cutter as recited in claim 16 wherein
said superhard material is sintered polycrystalline diamond.
22. A superhard ball end mill cutter as recited in claim 16 wherein
said superhard material is sintered polycrystalline cubic boron
nitride.
23. A superhard ball end mill cutter made by the process steps of
claim 16 further comprising the step of forming chemical bonds
between said superhard material and said substrate.
24. A superhard ball end mill cutter made by the process steps of
claim 16 further comprising the step of forming residual stresses
in the cutter which tend to retain said superhard material adjacent
said substrate.
Description
[0001] This patent application claims priority to U.S. Provisional
Patent Application Ser. 60/499,026 filed on Aug. 29, 2003; to U.S.
Provisional Patent Application Ser. No. 60/498,768 filed on Aug.
29, 2003; to U.S. Provisional Patent Application Ser. No.
60/498,968 filed on Aug. 29, 2003, to U.S. Provisional Patent
Application Ser. No. 60/498,709 filed on Aug. 28, 2003, to U.S.
Provisional Patent Application Ser. No. 60/498,896 filed on Aug.
29, 2003 and to U.S. Provisional Patent Application Ser. No.
60/498,708 filed on Aug. 28, 2003. Each of the foregoing is hereby
incorporated by reference.
BACKGROUND
[0002] This disclosure relates to methods, materials and
apparatuses for making superhard (i.e., polycrystalline diamond and
polycrystalline cubic boron nitride) components, and other hard
components.
SUMMARY
[0003] Various methods, materials and apparatuses for making
superhard components and other hard components are disclosed.
BRIEF DESCRIPTION OF DRAWINGS
[0004] FIG. 1A depicts a quantity of diamond feedstock adjacent to
a metal alloy substrate prior to sintering of the diamond feedstock
and the substrate to create a PDC.
[0005] FIG. 1B depicts a sintered PDC in which the diamond table,
the substrate, and the transition zone between the diamond table
and the substrate are shown.
[0006] FIG. 1BB depicts a sintered PDC in which there is a
continuous gradient transition from substrate metal through the
diamond table.
[0007] FIG. 1C depicts a substrate prior to use of a CVD or PVD
process to form a volume of diamond on the substrate.
[0008] FIG. 1D depicts a diamond compact formed by a CVD or PVD
process.
[0009] FIG. 1E depicts a device, which may be used for loading
diamond feedstock prior to sintering.
[0010] FIG. 1F depicts a furnace cycle for removal of a binder
material from diamond feedstock prior to sintering.
[0011] FIGS. 1G and 1GA depict a precompaction assembly, which may
be used to reduce free space in diamond feedstock prior to
sintering.
[0012] FIG. 2 depicts the anvils of a cubic press that can be used
to provide a high temperature and high pressure sintering
environment, or for hipping.
[0013] FIGS. 3A-1 through 3A-11 depict controlling large volumes of
powder feedstocks, such as diamond.
[0014] FIGS. 4A-4I1 depict some example superhard constructs.
[0015] FIGS. 5-12 depict preparation of superhard materials for use
in making an articulating diamond-surfaced spinal implant
component.
[0016] FIGS. 13A-13G depict some substrate and superhard material
configurations.
[0017] FIGS. 14-36 depict superhard material preparation before
sintering and removal after sintering.
[0018] FIGS. 37a-37c depict sintering of arcuate superhard
surfaces.
[0019] FIGS. 38-50 depict machining and finishing superhard
articulating diamond-surfaced spinal implant components.
[0020] FIGS. 51A-51D depict a superhard ball end mill cutter.
DETAILED DESCRIPTION
[0021] Reference will now be made to the drawings in which the
various elements of the embodiments will be discussed. Persons
skilled in the design of prosthetic joints and other bearing
surfaces will understand the application of the various embodiments
and their principles to sintering and hipping of superhard and hard
components, including those used in prosthetic joints of all types,
and components of prosthetic joints, anywhere hard, durable or
biocompatabile products are desired, and for devices other than
those exemplified herein.
[0022] Various embodiments of the manufacturing systems, devices,
processes and materials disclosed herein relate to superhard and
hard surfaces and components. More specifically, some relate to
diamond and sintered polycrystalline diamond surfaces (PCD). Some
embodiments make or utilize a polycrystalline diamond compact (PDC)
to provide a very strong, low friction, long-wearing, biocompatible
part or surface. Any surface or devices that experiences wear and
requires strength and durability will benefit from the advances
made here.
[0023] The table below provides a comparison of sintered PCD to
some other materials.
1TABLE 1 COMPARISON OF SINTERED PCD TO OTHER MATERIALS Coefficient
of Thermal Thermal Expansion Specific Hardness Conductivity ("CTE")
Material Gravity (Knoop) (W/m K) (.times.10.sup.-6) Sintered
3.5-4.0 9000 900 1.50-4.8 Polycrystalline Diamond Compact (PDC)
Cubic Boron 3.48 4500 800 1.0-4.0 Nitride Silicon 3.00 2500 84
4.7-5.3 Carbide Aluminum 3.50 2000 7.8-8.8 Oxide Tungsten 14.6 2200
112 4-6 Carbide (10% Co) Cobalt 8.2 43 RC 16.9 Chrome Ti6Al4V 4.43
6.6-17.5 11 Silicon Nitride 3.2 14.2 15-7 1.8-3.7
[0024] In view of the superior hardness of sintered PCD, it is
expected that sintered PCD will provide improved wear and
durability characteristics.
[0025] In a PDC, the diamond table is chemically bonded and
mechanically fixed to the substrate in a manufacturing process that
typically uses a combination of high pressure and high temperature
to form the sintered PCD (see, infra). The chemical bonds between
the diamond table and the substrate are established during the
sintering process by combinations of unsatisfied sp3 carbon bonds
with unsatisfied substrate metal bonds. The mechanical fixation is
a result of shape of the substrate and diamond table and
differences in the physical properties of the substrate and the
diamond table as well as the gradient interface between the
substrate and the diamond table. The resulting sintered PDC forms a
durable modular bearing inserts and joints.
[0026] The diamond table may be polished to a very smooth and
glass-like finish to achieve a very low coefficient of friction.
The high surface energy of sintered PDC causes it to work very well
as a load-bearing and articulation surface when a lubricating fluid
is present. Its inherent nature allows it to perform very well when
a lubricant is absent as well.
[0027] While there is discussion herein concerning PDCs, the
following materials could be considered for forming prosthetic
joint components: polycrystalline diamond, monocrystal diamond,
natural diamond, diamond created by physical vapor deposition,
diamond created by chemical vapor deposition, diamond like carbon,
carbonado, cubic boron nitride, hexagonal boron nitride, or a
combination of these, cobalt, chromium, titanium, vanadium,
stainless steel, niobium, aluminum, nickel, hafnium, silicon,
tungsten, molybdenum, aluminum, zirconium, nitinol, cobalt chrome,
cobalt chrome molybdenum, cobalt chrome tungsten, tungsten carbide,
titanium carbide, tantalum carbide, zirconium carbide, hafnium
carbide, Ti6/4, silicon carbide, chrome carbide, vanadium carbide,
yttria stabilized zirconia, magnesia stabilized zirconia, zirconia
toughened alumina, titanium molybdenum hafnium, alloys including
one or more of the above metals, ceramics, quartz, garnet,
sapphire, combinations of these materials, combinations of these
and other materials, and other materials may also be used for a
desired surface.
[0028] Sintered Polycrystalline Diamond Compacts
[0029] One useful material for manufacturing joint bearing surfaces
is a sintered polycrystalline diamond compact. Diamond has the
greatest hardness and the lowest coefficient of friction of any
currently known material. Sintered PDCs are chemically inert, are
impervious to all solvents, and have the highest thermal
conductivity at room temperature of any known material.
[0030] In some embodiments, a PDC provides unique chemical bonding
and mechanical grip between the diamond and the substrate material.
A PDC, which utilizes a substrate material, will have a chemical
bond between substrate material and the diamond crystals. The
result of this structure is an extremely strong bond between the
substrate and the diamond table.
[0031] A method by which PDC may be manufactured is described later
in this document. Briefly, it involves sintering diamond crystals
to each other, and to a substrate under high pressure and high
temperature. FIGS. 1A and 1B illustrate the physical and chemical
processes involved manufacturing PDCs.
[0032] In FIG. 1A, a quantity of diamond feedstock 130 (such as
diamond powder or crystals) is placed adjacent to a
metal-containing substrate 110 prior to sintering. In the region of
the diamond feedstock 130, individual diamond crystals 131 may be
seen, and between the individual diamond crystals 131 there are
interstitial spaces 132. If desired, a quantity of solvent-catalyst
metal may be placed into the interstitial spaces 132. The substrate
may also contain solvent-catalyst metal.
[0033] The substrate 110 may be a suitable pure metal or alloy, or
a cemented carbide containing a suitable metal or alloy as a
cementing agent such as cobalt-cemented tungsten carbide or other
materials mentioned herein. The substrate 110 may be a metal with
high tensile strength. In a cobalt-chrome substrate, the
cobalt-chrome alloy will serve as a solvent-catalyst metal for
solvating diamond crystals during the sintering process.
[0034] The illustration shows the individual diamond crystals and
the contiguous metal crystals in the metal substrate. The interface
120 between diamond powder and substrate material is a region where
bonding of the diamond table to the substrate must occur. In some
embodiments, a boundary layer of a third material different than
the diamond and the substrate is placed at the interface 120. This
interface boundary layer material, when present, may serve several
functions including, but not limited to, enhancing the bond of the
diamond table to the substrate, and mitigation of the residual
stress field at the diamond-substrate interface.
[0035] Once diamond powder or crystals and substrate are assembled
as shown in FIG. 1A, the assembly is subjected to high pressure and
high temperature as described later herein in order to cause
bonding of diamond crystals to diamond crystals and to the
substrate. The resulting structure of sintered polycrystalline
diamond table bonded to a substrate is called a polycrystalline
diamond compact or a PDC. A compact, as the term is used herein, is
a composite structure of two different materials, such as diamond
crystals, and a substrate metal. The analogous structure
incorporating cubic boron nitride crystals in the sintering process
instead of diamond crystals is called polycrystalline cubic boron
nitride compact (PCBNC). Many of the processes described herein for
the fabrication and finishing of PDC structures and parts work in a
similar fashion for PCBNC. In some embodiments, PCBNC may be
substituted for PDC. It should be noted that a PDC can also be made
from free standing diamond without a separate substrate, as
described elsewhere herein.
[0036] FIG. 1B depicts a PDC 101 after the high pressure and high
temperature sintering of diamond feedstock to a substrate. Within
the PDC structure, there is an identifiable volume of substrate
102, an identifiable volume of diamond table 103, and a transition
zone 104 between diamond table and substrate containing diamond
crystals and substrate material. Crystalline grains of substrate
material 105 and sintered crystals of diamond 106 are depicted.
[0037] On casual examination, the finished compact of FIG. 1B will
appear to consist of a solid table of diamond 103 attached to the
substrate 102 with a discrete boundary. On very close examination,
however, a transition zone 104 between diamond table 103 and
substrate 102 can be characterized. This zone represents a gradient
interface between diamond table and substrate with a gradual
transition of ratios between diamond content and metal content. At
the substrate side of the transition zone, there will be only a
small percentage of diamond crystals and a high percentage of
substrate metal, and on the diamond table side, there will be a
high percentage of diamond crystals and a low percentage of
substrate metal. Because of this gradual transition of ratios of
polycrystalline diamond to substrate metal in the transition zone,
the diamond table and the substrate have a gradient interface.
[0038] In the transition zone or gradient transition zone where
diamond crystals and substrate metal are intermingled, chemical
bonds are formed between the diamond and metal. From the transition
zone 104 into the diamond table 103, the metal content diminishes
and is limited to solvent-catalyst metal that fills the
three-dimensional vein-like structure of interstitial voids,
openings or asperities 107 within the sintered diamond table
structure 103. The solvent-catalyst metal found in the voids or
openings 107 may have been swept up from the substrate during
sintering or may have been solvent-catalyst metal added to the
diamond feedstock before sintering.
[0039] During the sintering process, there are three types of
chemical bonds that are created: diamond-to-diamond bonds,
diamond-to-metal bonds, and metal-to-metal bonds. In the diamond
table, there are diamond-to-diamond bonds (sp3 carbon bonds)
created when diamond particles partially solvate in the
solvate-catalyst metal and then are bonded together. In the
substrate and in the diamond table, there are metal-to-metal bonds
created by the high pressure and high temperature sintering
process. And in the gradient transition zone, diamond-to-metal
bonds are created between diamond and solvent-catalyst metal.
[0040] The combination of these various chemical bonds and the
mechanical grip exerted by solvent-catalyst metal in the diamond
table such as in the interstitial spaces of the diamond structure
diamond table provide extraordinarily high bond strength between
the diamond table and the substrate. Interstitial spaces are
present in the diamond structure and those spaces typically are
filled with solvent-catalyst metal, forming veins of
solvent-catalyst metal within the polycrystalline diamond
structure. This bonding structure contributes to the extraordinary
fracture toughness of the compact, and the veins of metal within
the diamond table act as energy sinks halting propagation of
incipient cracks within the diamond structure. The transition zone
and metal vein structure provide the compact with a gradient of
material properties between those of the diamond table and those of
substrate material, further contributing to the extreme toughness
of the compact. The transition zone can also be called an
interface, a gradient transition zone, a composition gradient zone,
or a composition gradient, depending on its characteristics. The
transition zone distributes diamond/substrate stress over the
thickness of the zone, reducing zone high stress of a distinct
linear interface. The subject residual stress is created as
pressure and temperature are reduced at the conclusion of the high
pressure/high temperature sintering process due to the difference
in pressure and thermal expansive properties of the diamond and
substrate materials.
[0041] The diamond sintering process occurs under conditions of
extremely high pressure and high temperature. According to the
inventors' best experimental and theoretical understanding, the
diamond sintering process progresses through the following sequence
of events: At pressure, a cell containing feedstock of unbonded
diamond powder or crystals (diamond feedstock) and a substrate is
heated to a temperature above the melting point of the substrate
metal 110 and molten metal flows or sweeps into the interstitial
voids 107 between the adjacent diamond crystals 106. It is carried
by the pressure gradient to fill the voids as well as being pulled
in by the surface energy or capillary action of the large surface
area of the diamond crystals 106. As the temperature continues to
rise, carbon atoms from the surface of diamond crystals dissolve
into this interstitial molten metal, forming a carbon solution.
[0042] At the proper threshold of temperature and pressure, diamond
becomes the thermodynamically favored crystalline allotrope of
carbon. As the solution becomes super saturated with respect to
C.sub.d (carbon diamond), carbon from this solution begins to
crystallize as diamond onto the surfaces of diamond crystals
bonding adjacent diamond crystals together with diamond-diamond
bonds into a sintered polycrystalline diamond structure 106. The
interstitial metal fills the remaining void space forming the
vein-like lattice structure 107 within the diamond table by
capillary forces and pressure driving forces. Because of the
crucial role that the interstitial metal plays in forming a
solution of carbon atoms and stabilizing these reactive atoms
during the diamond crystallization phase in which the
polycrystalline diamond structure 106 is formed, the metal is
referred to as a solvent-catalyst metal.
[0043] FIG. 1BB depicts a polycrystalline diamond compact having
both substrate metal 180 and diamond 181, but in which there is a
continuous gradient transition 182 from substrate metal to diamond.
In such a compact, the gradient transition zone may be the entire
compact, or a portion of the compact. The substrate side of the
compact may contain nearly pure metal for easy machining and
attachment to other components, while the diamond side may be
extremely hard, smooth and durable for use in a hostile work
environment.
[0044] In some embodiments, a quantity of solvent-catalyst metal
may be combined with the diamond feedstock prior to sintering. This
is found to be necessary when forming thick PCD tables, solid PDC
structures, or when using multimodal fine diamond where there is
little residual free space within the diamond powder. In each of
these cases, there may not be sufficient ingress of
solvent-catalyst metal via the sweep mechanism to adequately
mediate the sintering process as a solvent-catalyst. The metal may
be added by direct addition of powder, or by generation of metal
powder in situ with an attritor mill or by the well-known method of
chemical reduction of metal salts deposited on diamond crystals.
Added metal may constitute any amount from less than 1% by mass, to
greater than 35%. This added metal may consist of the same metal or
alloy as is found in the substrate, or may be a different metal or
alloy selected because of its material and mechanical properties.
Example ratios of diamond feedstock to solvent-catalyst metal prior
to sintering include mass ratios of 70:30, 85:15, 90:10, and 95:15.
The metal in the diamond feedstock may be added powder metal, metal
added by an attritor method, vapor deposition or chemical reduction
of metal into powder.
[0045] When sintering diamond on a substrate with an interface
boundary layer, it may be that no solvent-catalyst metal from the
substrate is available to sweep into the diamond table and
participate in the sintering process. In this case, the boundary
layer material, if composed of a suitable material, metal or alloy
that can function as a solvent-catalyst, may serve as the sweep
material mediating the diamond sintering process. In other cases
where the desired boundary material cannot serve as a
solvent-catalyst, a suitable amount of solvent-catalyst metal
powder as described herein is added to the diamond crystal feed
stock as described above. This assembly is then taken through the
sintering process. In the absence of a substrate metal source, the
solvent-catalyst metal for the diamond sintering process must be
supplied entirely from the added metal powder. The boundary
material may bond chemically to the substrate material, and may
bond chemically to the diamond table and/or the added
solvent-catalyst metal in the diamond table. The remainder of the
sintering and fabrication process may be the same as with the
conventional solvent-catalyst sweep sintering and fabrication
process.
[0046] For the sake of simplicity and clarity in this patent, the
substrate, transition zone, and diamond table have been discussed
as distinct layers. However, it is important to realize that the
finished sintered object may be a composite structure characterized
by a continuous gradient transition from substrate material to
diamond table rather than as distinct layers with clear and
discrete boundaries, hence the term "compact."
[0047] In addition to the sintering processes described above,
diamond parts suitable for use as modular bearing inserts and joint
components may also be fabricated as solid or free-standing
polycrystalline diamond structures without a substrate. These may
be formed by placing the diamond powder combined with a suitable
amount of added solvent-catalyst metal powder as described above in
a refractory metal can (typically Ta, Nb, Zr, or Mo) with a shape
approximating the shape of the final part desired. This assembly is
then taken through the sintering process. However, in the absence
of a substrate metal source, the solvent-catalyst metal for the
diamond sintering process must be supplied entirely from the added
metal powder. With suitable finishing, objects thus formed may be
used as is, or bonded to metal or other substrates.
[0048] Sintering is a method of creating a diamond table with a
strong and durable constitution. Other methods of producing a
diamond table that may or may not be bonded to a substrate are
possible. At present, these typically are not as strong or durable
as those fabricated with the sintering process. It is also possible
to use these methods to form diamond structures directly onto
substrates suitable for use as modular bearing inserts and joints.
A table of polycrystalline diamond either with or without a
substrate may be manufactured and later attached to a modular
bearing inserts and joints in a location such that it will form a
surface. The attachment could be performed with any suitable
method, including welding, brazing, sintering, diffusion welding,
diffusion bonding, inertial welding, adhesive bonding, or the use
of fasteners such as screws, bolts, or rivets. In the case of
attaching a diamond table without a substrate to another object,
the use of such methods as brazing, diffusion welding/bonding or
inertia welding may be most appropriate.
[0049] Although high pressure/high temperature sintering is a
method for creating a diamond surface, other methods for producing
a volume of diamond may be employed as well. For example, either
chemical vapor deposition (CVD), or physical vapor deposition (PVD)
processes may be used. CVD produces a diamond layer by thermally
cracking an organic molecule and depositing carbon radicals on a
substrate. PVD produces a diamond layer by electrically causing
carbon radicals to be ejected from a source material and to deposit
on a substrate where they build a diamond crystal structure.
[0050] The CVD and PVD processes have some advantages over
sintering. Sintering is performed in large, expensive presses at
high pressure (such as 45-68 kilobars) and at high temperatures
(such as 1200 to 1500 degrees Celsius). It is difficult to achieve
and maintain desired component shape using a sintering process
because of flow of high pressure mediums used and possible
deformation of substrate materials.
[0051] In contrast, CVD and PVD take place at atmospheric pressure
or lower, so there no need for a pressure medium and there is no
deformation of substrates.
[0052] Another disadvantage of sintering is that it is difficult to
achieve some geometries in a sintered PDC. When CVD or PVD are
used, however, the gas phase used for carbon radical deposition can
completely conform to the shape of the object being coated, making
it easy to achieve a desired non-planar shape.
[0053] Another potential disadvantage of sintering PDCs is that the
finished component will tend to have large residual stresses caused
by differences in the coefficient of thermal expansion and modulus
between the diamond and the substrate. While residual stresses can
be used to improve strength of a part, they can also be
disadvantageous. When CVD or PVD is used, residual stresses can be
minimized because CVD and PVD processes do not involve a
significant pressure transition (such from 68 Kbar to atmospheric
pressure in high pressure and high temperature sintering) during
manufacturing.
[0054] Another potential disadvantage of sintering PDCs is that few
substrates have been found that are suitable for sintering.
Tungsten carbide is a common choice for substrate materials.
Non-planar components have been made using other substrates. When
CVD or PVD are used, however, synthetic diamond can be placed on
many substrates, including titanium, most carbides, silicon,
molybdenum and others. This is because the temperature and pressure
of the CVD and PVD coating processes are low enough that
differences in coefficient of thermal expansion and modulus between
diamond and the substrate are not as critical as they are in a high
temperature and high pressure sintering process.
[0055] A further difficulty in manufacturing sintered PDCs is that
as the size of the part to be manufactured increases, the size of
the press must increase as well. Sintering of diamond will only
take place at certain pressures and temperatures, such as those
described herein. In order to manufacture larger sintered
polycrystalline diamond compacts, ram pressure of the press
(tonnage) and size of tooling (such as dies and anvils) must be
increased in order to achieve the necessary pressure for sintering
to take place. But increasing the size and capacity of a press is
more difficult than simply increasing the dimensions of its
components. There may be practical physical size constraints on
press size due to the manufacturing process used to produce press
tooling.
[0056] Tooling for a press is typically made from cemented tungsten
carbide. In order to make tooling, the cemented tungsten carbide is
sintered in a vacuum furnace followed by pressing in a hot isosatic
press ("HIP") apparatus. Hipping should be performed in a manner
that maintains uniform temperature throughout the tungsten carbide
in order to achieve uniform physical qualities and quality. These
requirements impose a practical limit on the size tooling that can
be produced for a press that is useful for sintering PDCs. The
limit on the size tooling that can be produced also limits the size
press that can be produced.
[0057] CVD and PVD manufacturing apparatuses may be scaled up in
size with few limitations, allowing them to produce polycrystalline
diamond compacts of almost any desired size.
[0058] CVD and PVD processes are also advantageous because they
permit precise control of the thickness and uniformity of the
diamond coating to be applied to a substrate. Temperature is
adjusted within the range of 500 to 1000 degrees Celsius, and
pressure is adjusted in a range of less than 1 atmosphere to
achieve desired diamond coating thickness.
[0059] Another advantage of CVD and PVD processes is that they
allow the manufacturing process to be monitored as it progresses. A
CVD or PVD reactor can be opened before manufacture of a part is
completed so that the thickness and quality of the diamond coating
being applied to the part may be determined. From the thickness of
the diamond coating that has already been applied, time to
completion of manufacture can be calculated. Alternatively, if the
coating is not of desired quality, the manufacturing processes may
be aborted in order to save time and money.
[0060] In contrast, sintering of PDCs is performed as a batch
process that cannot be interrupted, and progress of sintering
cannot be monitored. The pressing process must be run to completion
and the part may only be examined afterward.
[0061] A cubic press (i.e., the press has six anvil faces) may be
used for transmitting high pressure to an assembly to under
sintering or hipping. For example, a cubic press applies pressure
along 3 axes from six different directions. Alternatively, a belt
press and a cylindrical cell can be used to obtain similar results.
Other presses that may be used include a piston-cylinder press and
a tetrahedral press. Referring to FIG. 2, a representation of the 6
anvils of a cubic press 3720 is provided. The anvils 3721, 3722,
3723, 3724, 3725 and 3726 are situated around a pressure assembly
3730 to carry out sintering or hipping by use of high temperature
and high pressure. The exact sintering or hipping conditions depend
on the materials used, size of the component being manufactured,
and the material and strength properties desired in the finished
product.
[0062] A cubic press usually relies on six carbide anvils attached
to massive hydraulic cylinders converging simultaneously on a
cube-shaped high-pressure capsule. This tri-axial system generates
an essentially iso-static high-pressure condition, which is
particularly suited to sintering products with complex
3-dimensional geometries. Such a press system will be integrated
with computerized control systems to assure optimal and consistent
pressure, time, and temperature sintering conditions.
[0063] A belt press uses two carbide punches converging upon a
high-pressure capsule contained within a carbide die to generate
the extreme pressure required to sinter polycrystalline products.
Shrink-fitted steel belts pre-stress the inner carbide die,
allowing it to withstand the immense internal pressure that occurs
during sintering.
[0064] A piston-cylinder press is similar to a belt press, with a
high-pressure capsule is contained within the cylindrical bore of a
carbide die. Two free-floating carbide pistons engage within the
bore, pressurizing the capsule when load is applied by conical
carbide anvils. The carbide die is supported by radial hydraulic
pressure rather than a series of steel belts. This allows
simultaneous pressurization of both the inside and outside of the
die. Since this press is essentially a gasketless system, there is
very little material movement within the pressure volume during
pressurization and heating.
[0065] CVD and PVD Diamond
[0066] CVD is performed in an apparatus called a reactor. A basic
CVD reactor includes four components. The first component of the
reactor is one or more gas inlets. Gas inlets may be chosen based
on whether gases are premixed before introduction to the chamber or
whether the gases are allowed to mix for the first time in the
chamber. The second component of the reactor is one or more power
sources for the generation of thermal energy. A power source is
needed to heat the gases in the chamber. A second power source may
be used to heat the substrate material uniformly in order to
achieve a uniform coating of diamond on the substrate. The third
component of the reactor is a stage or platform on which a
substrate is placed. The substrate will be coated with diamond
during the CVD process. Stages used include a fixed stage, a
translating stage, a rotating stage and a vibratory stage. An
appropriate stage must be chosen to achieve desired diamond coating
quality and uniformity. The fourth component of the reactor is an
exit port for removing exhaust gas from the chamber. After gas has
reacted with the substrate, it must be removed from the chamber as
quickly as possible so that it does not participate in other
reactions, which would be deleterious to the diamond coating.
[0067] CVD reactors are classified according to the power source
used. The power source is chosen to create the desired species
necessary to carry out diamond thin film deposition. Some CVD
reactor types include plasma-assisted microwave, hot filament,
electron beam, single, double or multiple laser beam, arc jet and
DC discharge. These reactors differ in the way they impart thermal
energy to the gas species and in their efficiency in breaking gases
down to the species necessary for deposition of diamond. It is
possible to have an array of lasers to perform local heating inside
a high pressure cell. Alternatively, an array of optical fibers
could be used to deliver light into the cell.
[0068] The basic process by which CVD reactors work is as follows.
A substrate is placed into the reactor chamber. Reactants are
introduced to the chamber via one or more gas inlets. For diamond
CVD, methane (CH.sub.4) and hydrogen (H.sub.2) gases may be brought
into the chamber in premixed form. Instead of methane, any
carbon-bearing gas in which the carbon has sp3 bonding may be used.
Other gases may be added to the gas stream in order to control
quality of the diamond film, deposition temperature, gain structure
and growth rate. These include oxygen, carbon dioxide, argon,
halogens and others.
[0069] The gas pressure in the chamber is maintained at about 100
torr. Flow rates for the gases through the chamber are about 10
standard cubic centimeters per minute for methane and about 100
standard cubic centimeters per minute for hydrogen. The composition
of the gas phase in the chamber is in the range of 90-99.5%
hydrogen and 0.5-10% methane.
[0070] When the gases are introduced into the chamber, they are
heated. Heating may be accomplished by many methods. In a
plasma-assisted process, the gases are heated by passing them
through a plasma. Otherwise, the gases may be passed over a series
of wires such as those found in a hot filament reactor.
[0071] Heating the methane and hydrogen will break them down into
various free radicals. Through a complicated mixture of reactions,
carbon is deposited on the substrate and joins with other carbon to
form crystalline diamond by sp3 bonding. The atomic hydrogen in the
chamber reacts with and removes hydrogen atoms from methyl radicals
attached to the substrate surface in order to create molecular
hydrogen, leaving a clear solid surface for further deposition of
free radicals.
[0072] If the substrate surface promotes the formation of sp2
carbon bonds, or if the gas composition, flow rates, substrate
temperature or other variables are incorrect, then graphite rather
than diamond will grow on the substrate.
[0073] There are many similarities between CVD reactors and
processes and PVD reactors and processes. PVD reactors differ from
CVD reactors in the way that they generate the deposition species
and in the physical characteristics of the deposition species. In a
PVD reactor, a plate of source material is used as a thermal
source, rather than having a separate thermal source as in CVD
reactors. A PVD reactor generates electrical bias across a plate of
source material in order to generate and eject carbon radicals from
the source material. The reactor bombards the source material with
high energy ions. When the high energy ions collide with source
material, they cause ejection of the desired carbon radicals from
the source material. The carbon radicals are ejected radially from
the source material into the chamber. The carbon radicals then
deposit themselves onto whatever is in their path, including the
stage, the reactor itself, and the substrate.
[0074] Referring to FIG. 1C, a substrate 140 of appropriate
material is depicted having a deposition face 141 on which diamond
may be deposited by a CVD or PVD process. FIG. 1D depicts the
substrate 140 and the deposition face 141 on which a volume of
diamond 142 has been deposited by CVD or PVD processes. A small
transition zone 143 is present in which both diamond and substrate
are located. In comparison to FIG. 1B, it can be seen that the CVD
or PVD diamond deposited on a substrate lacks the more extensive
gradient transition zone of sintered polycrystalline diamond
compacts because there is no sweep of solvent-catalyst metal
through the diamond table in a CVD or PVD process.
[0075] Both CVD and PVD processes achieve diamond deposition by
line of sight. Means (such as vibration and rotation) are provided
for exposing all desired surfaces for diamond deposition. If a
vibratory stage is to be used, the surface will vibrate up and down
with the stage and thereby present all surfaces to the free radical
source.
[0076] There are several methods, which may be implemented in order
to coat cylindrical objects with diamond using CVD or PVD
processes. If a plasma assisted microwave process is to be used to
achieve diamond deposition, then the object to receive the diamond
must be directly under the plasma in order to achieve the highest
quality and most uniform coating of diamond. A rotating or
translational stage may be used to present every aspect of the
surface to the plasma for diamond coating. As the stage rotates or
translates, all portions of the surface may be brought directly
under the plasma for coating in such a way to achieve sufficiently
uniform coating.
[0077] If a hot filament CVD process is used, then the surface
should be placed on a stationary stage. Wires or filaments
(typically tungsten) are strung over the stage so that their
coverage includes the surface to be coated. The distance between
the filaments and the surface and the distance between the
filaments themselves may be chosen to achieve a uniform coating of
diamond directly under the filaments.
[0078] Diamond surfaces can be manufactured by CVD and PVD process
either by coating a substrate with diamond or by creating a
free-standing volume of diamond, which is later mounted for use. A
free-standing volume of diamond may be created by CVD and PVD
processes in a two-step operation. First, a thick film of diamond
is deposited on a suitable substrate, such as silicon, molybdenum,
tungsten or others. Second, the diamond film is released from the
substrate.
[0079] As desired, segments of diamond film may be cut away, such
as by use of a Q-switched YAG laser. Although diamond is
transparent to a YAG laser, there is usually a sufficient amount of
sp2 bonded carbon (as found in graphite) to allow cutting to take
place. If not, then a line may be drawn on the diamond film using a
carbon-based ink. The line should be sufficient to permit cutting
to start, and once started, cutting will proceed slowly.
[0080] After an appropriately-sized piece of diamond has been cut
from a diamond film, it can be attached to a desired object in
order to serve as a surface. For example, the diamond may be
attached to a substrate by welding, diffusion bonding, adhesion
bonding, mechanical fixation or high pressure and high temperature
bonding in a press.
[0081] Although CVD and PVD diamond on a substrate do not exhibit a
gradient transition zone that is found in sintered polycrystalline
diamond compacts, CVD and PVD process can be conducted in order to
incorporate metal into the diamond table. As mentioned elsewhere
herein, incorporation of metal into the diamond table enhances
adhesion of the diamond table to its substrate and can strengthen
the polycrystalline diamond compact. Incorporation of diamond into
the diamond table can be used to achieve a diamond table with a
coefficient of thermal expansion and compressibility different from
that of pure diamond, and consequently increasing fracture
toughness of the diamond table as compared to pure diamond. Diamond
has a low coefficient of thermal expansion and a low
compressibility compared to metals. Therefore the presence of metal
with diamond in the diamond table achieves a higher and more
metal-like coefficient of thermal expansion and the average
compressibility for the diamond table than for pure diamond.
Consequently, residual stresses at the interface of the diamond
table and the substrate are reduced, and delamination of the
diamond table from the substrate is less likely.
[0082] A pure diamond crystal also has low fracture toughness.
Therefore, in pure diamond, when a small crack is formed, the
entire diamond component fails catastrophically. In comparison,
metals have a high fracture toughness and can accommodate large
cracks without catastrophic failure. Incorporation of metal into
the diamond table achieves a greater fracture toughness than pure
diamond. In a diamond table having interstitial spaces and metal
within those interstitial spaces, if a crack forms in the diamond
and propagates to an interstitial space containing metal, the crack
will terminate at the metal and catastrophic failure will be
avoided. Because of this characteristic, a diamond table with metal
in its interstitial spaces is able to sustain much higher forces
and workloads without catastrophic failure compared to pure
diamond.
[0083] Diamond-diamond bonding tends to decrease as metal content
in the diamond table increases. CVD and PVD processes can be
conducted so that a transition zone is established. However, the
surface may be essentially pure PCD for low wear properties.
[0084] Generally CVD and PVD diamond is formed without large
interstitial spaces filled with metal. Consequently, most PVD and
CVD diamond is more brittle or has a lower fracture toughness than
sintered PDCs. CVD and PVD diamond may also exhibit the maximum
residual stresses possible between the diamond table and the
substrate. It is possible, however, to form CVD and PVD diamond
film that has metal incorporated into it with either a uniform or a
functionally gradient composition.
[0085] One method for incorporating metal into a CVD or PVD diamond
film is to use two different source materials in order to
simultaneously deposit the two materials on a substrate in a CVD of
PVD diamond production process. This method may be used regardless
of whether diamond is being produced by CVD, PVD or a combination
of the two.
[0086] Another method for incorporating metal into a CVD diamond
film chemical vapor infiltration. This process would first create a
porous layer of material, and then fill the pores by chemical vapor
infiltration. The porous layer thickness should be approximately
equal to the desired thickness for either the uniform or gradient
layer. The size and distribution of the pores can be used to
control ultimate composition of the layer. Deposition in vapor
infiltration occurs first at the interface between the porous layer
and the substrate. As deposition continues, the interface along
which the material is deposited moves outward from the substrate to
fill pores in the porous layer. As the growth interface moves
outward, the deposition temperature along the interface is
maintained by moving the sample relative to a heater or by moving
the heater relative to the growth interface. It is imperative that
the porous region between the outside of the sample and the growth
interface be maintained at a temperature that does not promote
deposition of material (either the pore-filling material or
undesired reaction products). Deposition in this region would close
the pores prematurely and prevent infiltration and deposition of
the desired material in inner pores. The result would be a
substrate with open porosity and poor physical properties.
[0087] Laser Deposition of Diamond
[0088] Another alternative manufacturing process that may be used
to produce surfaces and components involves use of energy beams,
such as laser energy, to vaporize constituents in a substrate and
redeposit those constituents on the substrate in a new form, such
as in the form of a diamond coating. As an example, a metal,
polymeric or other substrate may be obtained or produced containing
carbon, carbides or other desired constituent elements. Appropriate
energy, such as laser energy, may be directed at the substrate to
cause constituent elements to move from within the substrate to the
surface of the substrate adjacent the area of application of energy
to the substrate. Continued application of energy to the
concentrated constituent elements on the surface of the substrate
can be used to cause vaporization of some of those constituent
elements. The vaporized constituents may then be reacted with
another element to change the properties and structure of the
vaporized constituent elements.
[0089] Next, the vaporized and reacted constituent elements (which
may be diamond) may be diffused into the surface of the substrate.
A separate fabricated coating may be produced on the surface of the
substrate having the same or a different chemical composition than
that of the vaporized and reacted constituent elements.
Alternatively, some of the changed constituent elements that were
diffused into the substrate may be vaporized and reacted again and
deposited as a coating on the substrate. By this process and
variations of it, appropriate coatings such as diamond, cubic boron
nitride, diamond like carbon, B.sub.4C, SiC, TiC, TiN, TiB, cCN,
Cr.sub.3C.sub.2, and Si.sub.3N.sub.4 may be formed on a
substrate.
[0090] In other manufacturing environments, high temperature laser
application, electroplating, sputtering, energetic laser excited
plasma deposition or other methods may be used to place a volume of
diamond, diamond-like material, a hard material or a superhard
material in a location that will serve as a surface.
[0091] In light of the disclosure herein, those of ordinary skill
in the art will comprehend the apparatuses, materials and process
conditions necessary for the formation and use of high quality
diamond on a substrate using any of the manufacturing methods
described herein in order to create a diamond surface.
[0092] Material Property Considerations
[0093] In areas outside of modular bearing inserts and joints, in
particular in the field of rock drilling cutters, polycrystalline
diamond compacts have been used for some time. Historically those
cutters have been cylindrical in shape with a planar diamond table
at one end. The diamond surface of a cutter is much smaller than
the surface needed in most modular bearing inserts and joints s.
Thus, polycrystalline diamond cutter geometry and manufacturing
methods are not directly applicable to modular bearing inserts and
joints.
[0094] There is a particular problem posed by the manufacture of a
non-planar diamond surface. The non-planar component design
requires that pressures be applied radially in making the part.
During the high pressure sintering process, described in detail
below, all displacements must be along a radian emanating from the
center of the sphere that will be produced to achieve the
non-planar geometry. To achieve this in high temperature/high
pressure pressing, an isostatic pressure field must be created.
During the manufacture of such non-planar parts, if there is any
deviatoric stress component, it will result in distortion of the
part and may render the manufactured part useless.
[0095] Special considerations that must be taken into account in
making non-planar polycrystalline diamond compacts are discussed
below.
[0096] Modulus
[0097] Most polycrystalline diamond compacts include both a diamond
table and a substrate. The material properties of the diamond and
the substrate may be compatible, but the high pressure and high
temperature sintering process in the formation of a polycrystalline
diamond compact may result in a component with excessively high
residual stresses. For example, for a polycrystalline diamond
compact using tungsten carbide as the substrate, the sintered
diamond has a Young's modulus of approximately 120 million p.s.i,
and cobalt cemented tungsten carbide has a modulus of approximately
90 million p.s.i. Modulus refers to the slope of the curve of the
stress plotted against the stress for a material. Modulus indicates
the stiffness of the material. Bulk modulus refers to the ratio of
isostatic strain to isostatic stress, or the unit volume reduction
of a material versus the applied pressure or stress.
[0098] Because diamond and most substrate materials have such a
high modulus, a very small stress or displacement of the
polycrystalline diamond compact can induce very large stresses. If
the stresses exceed the yield strength of either the diamond or the
substrate, the component will fail. The strongest polycrystalline
diamond compact is not necessarily stress free. In a
polycrystalline diamond compact with optimal distribution of
residual stress, more energy is required to induce a fracture than
in a stress free component. Thus, the difference in modulus between
the substrate and the diamond must be noted and used to design a
component that will have the best strength for its application with
sufficient abrasion resistance and fracture toughness.
[0099] Coefficient of Thermal Expansion ("CTE")
[0100] The extent to which diamond and its substrate differ in how
they deform relative to changes in temperature also affects their
mechanical compatibility. Coefficient of thermal expansion ("CTE")
is a measure of the unit change of a dimension with unit change in
temperature or the propensity of a material to expand under heat or
to contract when cooled. As a material experiences a phase change,
calculations based on CTE in the initial phase will not be
applicable. It is notable that when compacts of materials with
different CTEs and moduluses are used, they will stress differently
at the same stress.
[0101] PCD has a CTE on the order of 2-4 micro inches per inch
(10.sup.-6 inches) of material per degree (.mu.in/in .degree. C.).
In contrast, carbide has a CTE on the order of 6-8 .mu.in/in
.degree. C. Although these values appear to be close numerically,
the influence of the high modulus creates very high residual stress
fields when a temperature gradient of a few hundred degrees is
imposed upon the combination of substrate and diamond. The
difference in coefficient of thermal expansion is less of a problem
in simple planar PDCs than in the manufacture of non-planar or
complex shapes. When a non-planar PDC is manufactured, differences
in the CTE between the diamond and the substrate can cause high
residual stress with subsequent cracking and failure of the diamond
table, the substrate or both at any time during or after high
pressure/high temperature sintering.
[0102] Dilatoric and Deviatoric Stresses
[0103] The diamond and substrate assembly will experience a
reduction of free volume during the sintering process. The
sintering process, described in detail below, involves subjecting
the substrate and diamond assembly to pressure ordinarily in the
range of about 40 to about 68 kilobar. The pressure will cause
volume reduction of the substrate. Some geometrical distortion of
the diamond and/or the substrate may also occur. The stress that
causes geometrical distortion is called deviatoric stress, and the
stress that causes a change in volume is called dilatoric stress.
In an isostatic system, the deviatoric stresses sum to zero and
only the dilatoric stress component remains. Failure to consider
all of these stress factors in designing and sintering a
polycrystalline diamond component with complex geometry (such as
concave and convex non-planar polycrystalline diamond compacts)
will likely result in failure of the process.
[0104] Free Volume Reduction of Diamond Feedstock
[0105] As a consequence of the physical nature of the feedstock
diamond, large amounts of free volume are present unless special
preparation of the feedstock is undertaken prior to sintering. It
is necessary to eliminate as much of the free volume in the diamond
as possible, and if the free volume present in the diamond
feedstock is too great, then sintering may not occur. It is also
possible to eliminate the free volume during sintering if a press
with sufficient ram displacement is employed. It is important to
maintain a desired uniform geometry of the diamond and substrate
during any process that reduces free volume in the feedstock, or a
distorted or faulty component may result.
[0106] Selection of Solvent-Catalyst Metal
[0107] Formation of synthetic diamond in a high temperature and
high pressure press without the use of a solvent-catalyst metal is
not a viable method at this time, although it may become viable in
the future. A solvent-catalyst metal is required to achieve desired
crystal formation in synthetic diamond. The solvent-catalyst metal
first solvates carbon preferentially from the sharp contact points
of the diamond feedstock crystals. It then recrystallizes the
carbon as diamond in the interstices of the diamond matrix with
diamond-diamond bonding sufficient to achieve a solid with 95 to
97% of theoretical density with solvent metal 5-3% by volume. That
solid distributed over the substrate surface is referred to herein
as a polycrystalline diamond table. The solvent-catalyst metal also
enhances the formation of chemical bonds with substrate atoms.
[0108] A method for adding the solvent-catalyst metal to diamond
feedstock is by causing it to sweep from the substrate that
contains solvent-catalyst metal during high pressure and high
temperature sintering. Powdered solvent-catalyst metal may also be
added to the diamond feedstock before sintering, particularly if
thicker diamond tables are desired. An attritor method may also be
used to add the solvent-catalyst metal to diamond feedstock before
sintering. If too much or too little solvent-catalyst metal is
used, then the resulting part may lack the desired mechanical
properties, so it is important to select an amount of
solvent-catalyst metal and a method for adding it to diamond
feedstock that is appropriate for the particular part to be
manufactured.
[0109] Diamond Feedstock Particle Size and Distribution
[0110] The durability of the finished diamond product is integrally
linked to the size of the feedstock diamond and also to the
particle distribution. Selection of the proper size(s) of diamond
feedstock and particle distribution depends upon the service
requirement of the specimen and also its working environment. The
durability of polycrystalline diamond is enhanced if smaller
diamond feedstock crystals are used and a highly diamond-diamond
bonded diamond table is achieved.
[0111] Although polycrystalline diamond may be made from single
modal diamond feedstock, use of multi-modal feedstock increases
both impact strength and wear resistance. The use of a combination
of large crystal sizes and small crystal sizes of diamond feedstock
together provides a part with high impact strength and wear
resistance, in part because the interstitial spaces between the
large diamond crystals may be filled with small diamond crystals.
During sintering, the small crystals will solvate and reprecipitate
in a manner that binds all of the diamond crystals into a strong
and tightly bonded compact.
[0112] Diamond Feedstock Loading Methodology
[0113] Contamination of the diamond feedstock before or during
loading will cause failure of the sintering process. Great care
must be taken to ensure the cleanliness of diamond feedstock and
any added solvent-catalyst metal or binder before sintering.
[0114] In order to prepare for sintering, clean diamond feedstock,
substrate, and container components are prepared for loading. The
diamond feedstock and the substrate are placed into a refractory
metal container called a "can" which will seal its contents from
outside contamination. The diamond feedstock and the substrate will
remain in the can while undergoing high pressure and high
temperature sintering in order to form a polycrystalline diamond
compact. The can may be sealed by electron beam welding at high
temperature and in a vacuum.
[0115] Enough diamond aggregate (powder or grit) is loaded to
account for linear shrinkage during high pressure and high
temperature sintering. The method used for loading diamond
feedstock into a can for sintering affects the general shape and
tolerances of the final part. In particular, the packing density of
the feedstock diamond throughout the can should be as uniform as
possible in order to produce a good quality sintered
polycrystalline diamond compact structure. In loading, bridging of
diamond can be avoided by staged addition and packing.
[0116] The degree of uniformity in the density of the feedstock
material after loading will affect geometry of the PDC. Loading of
the feedstock diamond in a dry form versus loading diamond combined
with a binder and the subsequent process applied for the removal of
the binder will also affect the characteristics of the finished
PDC. In order to properly pre-compact diamond for sintering, the
pre-compaction pressures should be applied under isostatic
conditions.
[0117] Selection of Substrate Material
[0118] The unique material properties of diamond and its relative
differences in modulus and CTE compared to most potential substrate
materials diamond make selection of an appropriate polycrystalline
diamond substrate a formidable task. A great disparity in material
properties between the diamond and the substrate creates challenges
for successful manufacture of a PDC with the requisite strength and
durability. Even very hard substrates appear to be soft compared to
PCD. The substrate and the diamond must be able to withstand not
only the pressure and temperature of sintering, but must be able to
return to room temperature and atmospheric pressure without
delaminating, cracking or otherwise failing.
[0119] Selection of substrate material also requires consideration
of the intended application for the part, impact resistance and
strengths required, and the amount of solvent-catalyst metal that
will be incorporated into the diamond table during sintering.
Substrate materials must be selected with material properties that
are compatible with those of the diamond table to be formed.
[0120] Substrate Geometry
[0121] Further, it is important to consider whether to use a
substrate that has a smooth surface or a surface with topographical
features. Substrate surfaces may be formed with a variety of
topographical features so that the diamond table is fixed to the
substrate with both a chemical bond and a mechanical grip. Use of
topographical features on the substrate provides a greater surface
area for chemical bonds and with the mechanical grip provided by
the topographical features, can result in a stronger and more
durable component.
EXAMPLE MATERIALS AND MANUFACTURING STEPS
[0122] The inventors have discovered and determined materials and
manufacturing processes for constructing PDCs for use in a modular
bearing inserts and joints. It is also possible to manufacture the
invented surfaces by methods and using materials other than those
listed below.
[0123] The steps described below, such as selection of substrate
material and geometry, selection of diamond feedstock, loading and
sintering methods, will affect each other, so although they are
listed as separate steps that must be taken to manufacture a PDC or
a compact of polycrystalline cubic boron nitride, no step is
completely independent of the others, and all steps must be
standardized to ensure success of the manufacturing process.
[0124] Select Substrate Material and/or Solvent-Catalyst Metal
[0125] In order to manufacture any polycrystalline component, an
appropriate substrate should be selected (unless the component is
to be free standing without a substrate).
2TABLE 2 SOME SUBSTRATES FOR PROSTHETIC JOINT APPLICATIONS
SUBSTRATE ALLOY NAME REMARKS Titanium Ti6/4 (TiAlVa) A thin
tantalum ASTM F-1313 barrier may be (TiNbZr) placed on the ASTM
F-620 titanium substrate ASTM F-1580 before loading TiMbHf diamond
feedstock. Nitinol (TiNi + other) Cobalt chrome ASTM F-799 Contains
cobalt, chromium and molybdenum. Wrought product Cobalt chrome ASTM
F-90 Contains cobalt, chromium, tungsten and nickel. Cobalt chrome
ASTM F-75 Contains cobalt, chromium and molybdenum. Cast product.
Cobalt chrome ASTM F-562 Contains cobalt, chromium, molybdenum and
nickel. Cobalt chrome ASTM F-563 Contains cobalt, chromium,
molybdenum, tungsten, iron and nickel. Tantalum ASTM F-560
Refractory metal. (unalloyed) Platinum various Niobium ASTM F-67
Refractory metal. (unalloyed) Maganese Various May include Cr, Ni,
Mg, molybdenum. Cobalt cemented WC Commonly used in tungsten
carbide synthetic diamond production Cobalt chrome CoCr cemented
cemented WC tungsten carbide Cobalt chrome CoCr cemented cemented
CrC chrome carbide Cobalt chrome CoCr cemented cemented SiC silicon
carbide Fused silicon carbide SiC Cobalt chrome CoCrMo A thin
tungsten or molybdenum tungsten/cobalt layer may be placed on the
substrate before loading diamond feedstock. Stainless steel
Various
[0126] The CoCr used as a substrate or solvent-catalyst metal may
be CoCrMo or CoCrW or another suitable CoCr. Alternatively, an
Fe-based alloy, a Ni-based alloy (such as Co--Cr--W--Ni) or another
alloy may be used. Co and Ni alloys tend to provide a
corrosion-resistant component. The preceding substrates and
solvent-catalyst metals are examples only. In addition to these
substrates, other materials may be appropriate for use as
substrates for construction of modular bearing inserts and joints
and other surfaces.
[0127] When titanium is used as the substrate, it is possible to
place a thin tantalum barrier layer on the titanium substrate. The
tantalum barrier prevents mixing of the titanium alloys with cobalt
alloys used in the diamond feedstock. If the titanium alloys and
the cobalt alloys mix, it is possible that a detrimentally low
melting point eutectic inter-metallic compound will be formed
during the high pressure and high temperature sintering process.
The tantalum barrier bonds to both the titanium and cobalt alloys,
and to the PCD that contains cobalt solvent-catalyst metals. Thus,
a PDC made using a titanium substrate with a tantalum barrier layer
and diamond feedstock that has cobalt solvent-catalyst metals can
be very strong and well formed. Alternatively, the titanium
substrate may be provided with an alpha case oxide coating (an
oxidation layer) forming a barrier that prevents formation of a
eutectic metal.
[0128] If a cobalt chrome molybdenum substrate is used, a thin
tungsten layer or a thin tungsten and cobalt layer can be placed on
the substrate before loading of the diamond feedstock in order to
control formation of chrome carbide (CrC) during sintering.
[0129] In addition to those listed, other appropriate substrates
may be used for forming PDC surfaces. Further, it is possible
within the scope of the claims to form a diamond surface for use
without a substrate. It is also possible to form a surface from any
of the superhard materials and other materials listed herein, in
which case a substrate may not be needed. Additionally, if it is
desired to use a type of diamond or carbon other than PCD,
substrate selection may differ. For example, if a diamond surface
is to be created by use of chemical vapor deposition or physical
vapor deposition, then use of a substrate appropriate for those
manufacturing environments and for the compositions used will be
necessary.
[0130] Determination of Substrate Geometry
[0131] A substrate geometry appropriate for the compact to be
manufactured and appropriate for the materials being used should be
selected. In order to manufacture a concave non-planar acetabular
cup, a convex non-planar femoral head, or a non-planar surface, it
is necessary to select a substrate geometry that will facilitate
the manufacture of those parts. In order to ensure proper diamond
formation and avoid compact distortion, forces acting on the
diamond and the substrate during sintering must be strictly radial.
Therefore the substrate geometry at the contact surface with
diamond feedstock for manufacturing an acetabular cup, a femoral
head, or any other non-planar component is generally
non-planar.
[0132] As mentioned previously, there is a great disparity in the
material characteristics of synthetic diamond and most available
substrate materials. In particular, modulus and CTE are of concern.
But when applied in combination with each other, some substrates
can form a stable and strong PDC. The table below lists physical
properties of some substrate materials.
3TABLE 3A MATERIAL PROPERTIES OF SOME SUBSTRATES SUBSTRATE MATERIAL
MODULUS CTE Ti 6/4 16.5 million psi 5.4 CoCrMo 35.5 million psi
16.9 CoCrW 35.3 million psi 16.3
[0133] Use of either titanium or cobalt chrome substrates alone for
the manufacture of non-planar PDCs may result in cracking of the
diamond table or separation of the substrate from the diamond
table. In particular, it appears that the dominant property of
titanium during high pressure and high temperature sintering is
compressibility while the dominant property of cobalt chrome during
sintering is CTE. In some embodiments, a substrate of two or more
layers may be used to achieve dimensional stability during and
after manufacturing.
[0134] In various embodiments, a single layer substrate may be
utilized. In other embodiments, a two-layer substrate may be
utilized, as discussed. Depending on the properties of the
components being used, however, it may be desired to utilize a
substrate that includes three, four or more layers. Such
multi-layer substrates are intended to be comprehended within the
scope of the claims.
[0135] Substrate Surface Topography
[0136] Depending on the application, it may be advantageous to
include substrate surface topographical features on a substrate
that is to be formed into a PDC. Regardless whether a one-piece, a
two-piece of a multi-piece substrate is used, it may be desirable
to modify the surface of the substrate or provide topographical
features on the substrate to increase the total surface area of
diamond to enhance substrate to diamond contact and to provide a
mechanical grip of the diamond table.
[0137] The placement of topographical features on a substrate
serves to modify the substrate surface geometry or contours from
what the substrate surface geometry or contours would be if formed
as a simple planar or non-planar figure. Substrate surface
topographical features may include one or more different types of
topographical features that result in protruding, indented or
contoured features that serve to increase surface, mechanically
interlock the diamond table to the substrate, prevent crack
formation, or prevent crack propagation.
[0138] Substrate surface topographical features or substrate
surface modifications serve a variety of useful functions. Use of
substrate topographical features increases total substrate surface
area of contact between the substrate and the diamond table. This
increased surface area of contact between diamond table and
substrate results in a greater total number of chemical bonds
between diamond table and substrate than if the substrate surface
topographical features were absent, thus achieving a stronger
PDC.
[0139] Substrate surface topographical features also serve to
create a mechanical interlock between the substrate and the diamond
table. The mechanical interlock is achieved by the nature of the
substrate topographical features and also enhances strength of the
PDC.
[0140] Substrate surface topographical features may also be used to
distribute the residual stress field of the PDC over a larger
surface area and over a larger volume of diamond and substrate
material. This greater distribution can be used to keep stresses
below the threshold for crack initiation and/or crack propagation
at the diamond table/substrate interface, within the diamond itself
and within the substrate itself.
[0141] Substrate surface topographical features increase the depth
of the gradient interface or transition zone between diamond table
and substrate, in order to distribute the residual stress field
through a longer segment of the composite compact structure and to
achieve a stronger part.
[0142] Substrate surface modifications can be used to created a
sintered PDC that has residual stresses that fortify the strength
of the diamond layer and yield a more robust PDC with greater
resistance to breakage than if no surface topographical features
were used. This is because in order to break the diamond layer, it
is necessary to first overcome the residual stresses in the part
and then overcome the strength of the diamond table.
[0143] Substrate surface topographical features redistribute forces
received by the diamond table. Substrate surface topographical
features cause a force transmitted through the diamond layer to be
re-transmitted from single force vector along multiple force
vectors. This redistribution of forces traveling to the substrate
avoids conditions that would deform the substrate material at a
more rapid rate than the diamond table, as such differences in
deformation can cause cracking and failure of the diamond
table.
[0144] Substrate surface topographical features may be used to
mitigate the intensity of the stress field between the diamond and
the substrate in order to achieve a stronger part.
[0145] Substrate surface topographical features may be used to
distribute the residual stress field throughout the PDC structure
in order to reduce the stress per unit volume of structure.
[0146] Substrate surface topographical features may be used to
mechanically interlock the diamond table to the substrate by
causing the substrate to compress over an edge of the diamond table
during manufacturing. Dovetailed, non-planar and lentate
modifications act to provide force vectors that tend to compress
and enhance the interface of diamond table and substrate during
cooling as the substrate dilitates radially.
[0147] Substrate surface topographical features may also be used to
achieve a manufacturable form. As mentioned herein, differences in
coefficient of thermal expansion and modulus between diamond and
the chosen substrate may result in failure of the PDC during
manufacturing. For certain parts, the stronger interface between
substrate and diamond table that may be achieved when substrate
topographical features are used can achieve a polycrystalline
diamond compact that can be successfully manufactured. But if a
similar part of the same dimensions is to be made using a substrate
with a simple substrate surface rather than specialized substrate
surface topographical features, the diamond table may crack or
separate from the substrate due to differences in coefficient of
thermal expansion or modulus of the diamond and the substrate.
[0148] Examples of useful substrate surface topographical features
include waves, grooves, ridges, other longitudinal surface features
(any of which may be arranged longitudinally, lattitudinally,
crossing each other at a desired angle, in random patterns, and in
geometric patterns), three dimensional textures, non-planar segment
depressions, non-planar segment protrusions, triangular
depressions, triangular protrusions, arcuate depressions, arcuate
protrusions, partially non-planar depressions, partially non-planar
protrusions, cylindrical depressions, cylindrical protrusions,
rectangular depressions, rectangular protrusions, depressions of
n-sided polygonal shapes where n is an integer, protrusions of
n-sided polygonal shapes, a waffle pattern of ridges, a waffle iron
pattern of protruding structures, dimples, nipples, protrusions,
ribs, fenestrations, grooves, troughs or ridges that have a
cross-sectional shape that is rounded, triangular, arcuate, square,
polygonal, curved, or otherwise, or other shapes. Machining,
pressing, extrusion, punching, injection molding and other
manufacturing techniques for creating such forms may be used to
achieve desired substrate topography. Illustration of example
substrate topographical features is found in U.S. Pat. No.
6,709,463 which is hereby incorporated by reference in its
entirety.
[0149] Although many substrate topographies have been depicted in
convex non-planar substrates, those surface topographies may be
applied to convex non-planar substrate surfaces, other non-planar
substrate surfaces, and flat substrate surfaces. Substrate surface
topographies which are variations or modifications of those shown,
and other substrate topographies which increase component strength
or durability may also be used.
[0150] Diamond Feedstock Selection
[0151] It is anticipated that typically the diamond particles used
will be in the range of less than 1 micron to more than 100
microns. In some embodiments, however, diamond particles as small
as 1 nanometer may be used. Smaller diamond particles are preferred
for smoother surfaces. Commonly, diamond particle sizes will be in
the range of 0.5 to 2.0 microns or 0.1 to 10 microns.
[0152] An example diamond feedstock is shown in the table
below.
4TABLE 3B EXAMPLE BIMODAL DIAMOND FEEDSTOCK MATERIAL AMOUNT 4 to 8
micron diamond about 90% 0.5 to 1.0 micron diamond about 9%
Titanium carbonitride powder about 1%
[0153] This formulation mixes some smaller and some larger diamond
crystals so that during sintering, the small crystals may dissolve
and then recrystallize in order to form a lattice structure with
the larger diamond crystals. Titanium carbonitride powder may
optionally be included in the diamond feedstock to prevent
excessive diamond grain growth during sintering in order to produce
a finished product that has smaller diamond crystals.
[0154] Another diamond feedstock example is provided in the table
below.
5TABLE 4 EXAMPLE TRIMODAL DIAMOND FEEDSTOCK MATERIAL AMOUNT Size x
diamond crystals about 90% Size 0.1x diamond crystals about 9% Size
0.01x diamond crystals about 1%
[0155] The trimodal diamond feedstock described above can be used
with any suitable diamond feedstock having a first size or diameter
"x", a second size 0.1x and a third size 0.01x. This ratio of
diamond crystals allows packing of the feedstock to about 89%
theoretical density, closing most interstitial spaces and providing
the densest diamond table in the finished polycrystalline diamond
compact.
[0156] Another diamond feedstock example is provided in the table
below.
6TABLE 5 EXAMPLE TRIMODAL DIAMOND FEEDSTOCK MATERIAL AMOUNT Size x
diamond crystals about 88-92% Size 0.1x diamond crystals about
8-12% Size 0.01x diamond crystals about 0.8-1.2%
[0157] Another diamond feedstock example is provided in the table
below.
7TABLE 6 EXAMPLE TRIMODAL DIAMOND FEEDSTOCK MATERIAL AMOUNT Size x
diamond crystals about 85-95% Size 0.1x diamond crystals about
5-15% Size 0.01x diamond crystals about 0.5-1.5%
[0158] Another diamond feedstock example is provided in the table
below.
8TABLE 7 EXAMPLE TRIMODAL DIAMOND FEEDSTOCK MATERIAL AMOUNT Size x
diamond crystals about 80-90% Size 0.1x diamond crystals about
10-20% Size 0.01x diamond crystals about 0-2%
[0159] In some embodiments, the diamond feedstock used will be
diamond powder having a greatest dimension of about 100 nanometers
or less. In some embodiments some solvent-catalyst metal is
included with the diamond feedstock to aid in the sintering
process, although in many applications there will be a significant
solvent-catalyst metal sweep from the substrate during sintering as
well.
[0160] Solvent Metal Selection
[0161] It has already been mentioned that solvent metal will sweep
from the substrate through the diamond feedstock during sintering
to solvate some diamond crystals so that they may later
recrystallize and form a diamond-diamond bonded lattice network
that characterizes PCD. In the event of making a freestanding
compact of PCD without a substrate, solvent metal may be mixed with
diamond crystals before sintering to achieve the same result. Even
if a substrate is being used, It is possible to include some
solvent-catalyst metal in the diamond feedstock when desired to
supplement the sweep of solvent-catalyst metal from the
substrate.
[0162] Traditionally, cobalt, nickel and iron have been used as
solvent metals for making PCD. Platinum and other materials could
also be used for a binder.
[0163] CoCr may be used as a solvent-catalyst metal for sintering
PCD to achieve a more wear resistant PDC. Infiltrating diamond
particles with Cobalt (Co) metal produces standard PDC. As the
cobalt infiltrates the diamond, carbon is dissolved (mainly from
the smaller diamond grains) and reprecipitates onto the larger
diamond grains causing the grains to grow together. This is known
as liquid phase sintering. The remaining pore spaces between the
diamond grains are filled with cobalt metal.
[0164] In one example, the alloy Cobalt Chrome (CoCr) may be used
as the solvent metal which acts similarly to Co metal. However, it
differs in that the CoCr reacts with some of the dissolved carbon
resulting in the precipitation of CoCr carbides. These carbides,
like most carbides, are harder (abrasion resistant) than cobalt
metal and results in a more wear or abrasion resistant PDC.
[0165] Other metals can be added to Co to form metal carbides as
precipitates within the pore spaces between the diamond grains.
These metals include the following, but not limited to, Ti, W, Mo,
V, Ta, Nb, Zr, Si, and combinations thereof.
[0166] It is important not just to add the solvent metal to diamond
feedstock, but also to include solvent metal in an appropriate
proportion and to mix it evenly with the feedstock. The use of
about 86% diamond feedstock and 15% solvent metal by mass (weight)
has provided good result, other ratios of diamond feedstock to
solvent metal may include 5:95, 10:90, 20:80, 30:70, 40:60, 50:50,
60:40, 65:35, 75:25, 80:20, 90:10, 95:5, 97:3, 98:2, 99:1,
99.5:0.5, 99.7:0.3, 99.8:0.2, 99.9:0.1 and others.
[0167] In order to mix the diamond feedstock with solvent-catalyst
metal, first the amounts of feedstock and solvent metal to be mixed
may be placed together in a mixing bowl, such as a mixing bowl made
of the desired solvent-catalyst metal. Then the combination of
feedstock and solvent metal may be mixed at an appropriate speed
(such as 200 rpm) with dry methanol and attritor balls for an
appropriate time period, such as 30 minutes. The attritor balls,
the mixing fixture and the mixing bowl may be made from the
solvent-catalyst metal. The methanol may then be decanted and the
diamond feedstock separated from the attritor balls. The feedstock
may then be dried and cleaned by firing in a molecular hydrogen
furnace at about 1000 degrees Celsius for about 1 hour. The
feedstock is then ready for loading and sintering. Alternatively,
it may be stored in conditions that will preserve its cleanliness.
Appropriate furnaces that may be used for firing also include
hydrogen plasma furnaces and vacuum furnaces.
[0168] Loading Diamond Feedstock
[0169] Referring to FIG. 1E, an apparatus for carrying out a
loading technique is depicted. The apparatus includes a spinning
rod 151 with a longitudinal axis 152, the spinning rod being
capable of spinning about its longitudinal axis. The spinning rod
151 has an end 153 matched to the size and shape of the part to be
manufactured. For example, if the part to be manufactured is
non-planar, the spinning rod end 153 may be non-planar.
[0170] A compression ring 154 is provided with a bore 155 through
which the spinning rod 151 may project. A die 156 or can is
provided with a cavity 157 also matched to the size and shape of
the part to be made.
[0171] In order to load diamond feedstock, the spinning rod is
placed into a drill chuck and the spinning rod is aligned with the
center point of the die. The depth to which the spinning rod stops
in relation to the cavity of the die is controlled with a set screw
and monitored with a dial indicator.
[0172] The die is charged with a known amount of diamond feedstock
material. The spinning rod is then spun about its longitudinal axis
and lowered into the die cavity to a predetermined depth. The
spinning rod contacts and rearranges the diamond feedstock during
this operation. Then the spinning of the spinning rod is stopped
and the spinning rod is locked in place.
[0173] The compression ring is then lowered around the outside of
the spinning rod to a point where the compression ring contacts
diamond feedstock in the cavity of the die. The part of the
compression ring that contacts the diamond is annular. The
compression ring is tamped up and down to compact the diamond. This
type of compaction is used to distribute diamond material
throughout the cavity to the same density and may be done in stages
to prevent bridging. Packing the diamond with the compaction ring
causes the density of the diamond around the equator of the sample
to be very uniform and the same as that of the polar region in the
cavity. In this configuration, the diamond sinters in a truly
non-planar fashion and the resulting part maintains its sphericity
to close tolerances.
[0174] Controlling Large Volumes of Powder Feedstocks, Such As
Diamond
[0175] The following information provides further instruction on
control and pre-processing of diamond feedstock before sintering.
PDC and Polycrystalline Cubic Boron Nitride (PCBN) powders reduce
in volume during the sintering process. The amount of shrinkage
experienced is dependent on a number of factors such as:
[0176] 1. The amount of metal mixed with the diamond.
[0177] 2. The loading density of the powders.
[0178] 3. The bulk density of diamond metal mix.
[0179] 4. The volume of powder loaded.
[0180] 5. Particle size distribution (PSD) of the powders.
[0181] In most PDC and PCBN sintering applications, the volume of
powder used is small enough that shrinkage is easily managed, as
shown in FIG. 3A-1. FIG. 3A-1 illustrates a can 3A-54 in which can
halves 3A-53 contain a substrate 3A-52 and a diamond table 3A-51.
However, when sintering large volumes of diamond powders in
spherical configurations, shrinkage is great enough to cause
buckling of the containment cans 3A-66 as shown in FIG. 3A-2 and
the cross section of FIG. 3A-3. The diamond has sintered 3A-75 but
the can has buckles 3A-77 and wrinkles 3A-78, resulting in a
non-uniform and damaged part. The following method is an improved
loading, pre-compression, densification, and refractory can sealing
method for spherical and non-planar parts loaded with large volumes
of diamond and/or metal powders. The processing steps are described
below.
[0182] Referring to FIG. 3A4 and its cross section at FIG. 3A-5,
PDC or PCBN powders 3A-911 are loaded against a substrate 3A-99 and
into a refractory metal containment can assembly 3A-913 having can
half skins 3A-910 and a seal 3A-912. Extra powder may be loaded
normal to the seam in the can to accommodate shrinkage.
[0183] Referring to FIG. 3A-6, a can assembly 3A-913 is placed into
a compaction fixture 3A-1014, which may be a cylindrical holder or
slide 3A-1015 with two hemispherical punches 3A-1016 and 3A-1017.
The fixture is designed to support the containment cans and allow
the can half skins 3A-910 to slip at the seam during the pressing
operation.
[0184] Referring to FIG. 3A-7-1, the relationship of the can half
skins 3A-910 with the junction 3A-912 and the punch 3A-1016 is
seen.
[0185] Referring to FIG. 3A-7, illustrates a compaction fixture
3A-1014 with a can 3A-913 placed into a press 3A-1218 and the upper
3A-1016 and lower 3A-1017 punches compress the can assembly 3A-913.
The containment can halves 3A-910 slip past each other preventing
buckling while the powdered feedstock is compressed.
[0186] Referring to FIG. 3A-8, the upper punch 3A-24 and upper
press fitting 3A-25 are retracted and a crimping die 3A-20 is
attached to the cylinder of the compaction fixture 3A-21. The can
assembly 3A-913 rests against the lower punch 3A-22 that is
attached to the lower press fitting 3A-23.
[0187] Referring to FIGS. 3A-9 and 3A-9-1, the lower punch 3A-22 is
raised toward the upper punch 3A-24 driving excess can material
3A-27 into the hemispherical portion of the crimping die 3A-19
folding the excess around the upper can 3A-26.
[0188] Referring to FIG. 3A-10, the lower punch is raised expelling
the can assembly 3A-13 from the cylinder 3A-28 of the compaction
fixture 3A-21.
[0189] Referring to FIG. 3A-11, the can assembly 3A-913 emerges
from pressing operation spherical with high loading density. The
part may then be sintered in a cubic or other press without
buckling or breaking the containment cans as the can half skins
3A-910 are overlapped.
[0190] Binding Diamond Feedstock Generally
[0191] Another method that may be employed to maintain a uniform
density of the feedstock diamond is the use of a binder. A binder
is added to the correct volume of feedstock diamond, and then the
combination is pressed into a can. Some binders that may be used
include polyvinyl butyryl, polymethyl methacrylate, polyvinyl
formol, polyvinyl chloride acetate, polyethylene, ethyl cellulose,
methylabietate, paraffin wax, polypropylene carbonate and polyethyl
methacrylate.
[0192] In one embodiment, the process of binding diamond feedstock
includes four steps. First, a binder solution is prepared. A binder
solution may be prepared by adding about 5 to 25% plasticizer to
pellets of poly (propylene carbonate), and dissolving this mixture
in solvent such as 2-butanone to make about a 20% solution by
weight.
[0193] Plasticizers that may be used include nonaqueous binders
generally, glycol, dibutyl phthalate, benzyl butyl phthalate, alkyl
benzyl phthalate, diethylhexyl phthalate, diisoecyl phthalate,
diisononyl phthalate, dimethyl phthalate, dipropylene glycol
dibenzoate, mixed glycols dibenzoate, 2-ethylhexyl diphenyl
dibenzoate, mixed glycols dibenzoate, 2-ethylhexyl diphenyl
phosphate, isodecyl diphenyl phosphate, isodecyl dipheni phosphate,
tricrestyl phosphate, tributoxy ethyl phosphate, dihexyl adipate,
triisooctyl trimellitate, dioctyl phthalate, epoxidized linseed
oil, epoxidized soybean oil, acetyl triethyl citrate, propylene
carbonate, various phthalate esters, butyl stearate, glycerin,
polyalkyl glycol derivatives, diethyl oxalate, paraffin wax and
triethylene glycol. Other appropriate plasticizers may be used as
well.
[0194] Solvents that may be used include 2-butanone, methylene
chloride, chloroform, 1,2-dichloroethne, trichlorethylene, methyl
acetate, ethyl acetate, vinyl acetate, propylene carbonate,
n-propyl acetate, acetonitrile, dimethylformamide, propionitrile,
n-mehyl-2-pyrrolidene, glacial acetic acid, dimethyl sulfoxide,
acetone, methyl ethyl ketone, cyclohexanone, oxysolve 80a,
caprotactone, butyrolactone, tetrahydrofuran, 1,4 dioxane,
propylene oxide, cellosolve acetate, 2-methoxy ethyl ether,
benzene, styrene, xylene, ethanol, methanol, toluene, cyclohexane,
chlorinated hydrocarbons, esters, ketones, ethers, ethyl benzene
and various hydrocarbons. Other appropriate solvents may be used as
well.
[0195] Second, diamond is mixed with the binder solution. Diamond
may be added to the binder solution to achieve about a 2-25% binder
solution (the percentage is calculated without regard to the
2-butanone).
[0196] Third, the mixture of diamond and binder solution is dried.
This may be accomplished by placing the diamond and binder solution
mixture in a vacuum oven for about 24 hours at about 50 degrees
Celsius to drive out all of the solvent 2-butanone.
[0197] Fourth, the diamond and binder may be pressed into shape.
When the diamond and binder is removed from the oven, it will be in
a clump that may be broken into pieces that are then pressed into
the desired shape with a compaction press. A pressing spindle of
the desired geometry may be contacted with the bound diamond to
form it into a desired shape. When the diamond and binder have been
pressed, the spindle is retracted. The final density of diamond and
binder after pressing may be at least about 2.6 grams per cubic
centimeter.
[0198] If a volatile binder is used, it should be removed from the
shaped diamond prior to sintering. The shaped diamond is placed
into a furnace and the binding agent is either gasified or
pyrolized for a sufficient length of time such that there is no
binder remaining. PDC quality is reduced by foreign contamination
of the diamond or substrate, and great care must be taken to ensure
that contaminants and binder are removed during the furnace cycle.
Ramp up and the time and temperature combination are critical for
effective pyrolization of the binder. For the binder example given
above, the debinding process may be used to remove the binder is as
follows. (Referring to FIG. 1F while reading this description may
be helpful.)
[0199] First, the shaped diamond and binder are heated from ambient
temperature to about 500 degrees Celsius. The temperature may be
increased by about 2 degrees Celsius per minute until about 500
degrees Celsius is reached. Second, the temperature of the bound
and shaped diamond is maintained at about 500 degrees Celsius for
about 2 hours. Third, the temperature of the diamond is increased
again. The temperature may be increased from about 500 degrees
Celsius by about 4 degrees per minute until a temperature of about
950 degrees Celsius is reached. Fourth, the diamond is maintained
at about 950 degrees Celsius for about 6 hours. Fifth, the diamond
is then permitted to return to ambient temperature at a temperature
decrease of about 2 degrees per minute.
[0200] In some embodiments, it may be desirable to preform bound
diamond feedstock by an appropriate process, such as injection
molding. The diamond feedstock may include diamond crystals of one
or more sizes, solvent-catalyst metal, and other ingredients to
control diamond recrystallization and solvent-catalyst metal
distribution. Handling the diamond feedstock is not difficult when
the desired final curvature of the part is flat, convex dome or
conical. However, when the desired final curvature of the part has
complex contours, such as illustrated herein, providing uniform
thickness and accuracy of contours of the PDC is more difficult
when using powder diamond feedstock. In such cases it may be
desirable to preform the diamond feedstock before sintering.
[0201] If it is desired to preform diamond feedstock prior to
loading into a can for sintering, rather than placing powder
diamond feedstock into the can, the steps described herein and
variations of them may be followed. First, as already described, a
suitable binder is added to the diamond feedstock. Optionally,
powdered solvent-catalyst metal and other components may be added
to the feedstock as well. The binder will typically be a polymer
chosen for certain characteristics, such as melting point,
solubility in various solvents, and CTE. One or more polymers may
be included in the binder. The binder may also include an elastomer
and/or solvents as desired in order to achieve desired binding,
fluid flow and injection molding characteristics. The working
volume of the binder to be added to a feedstock may be equal to or
slightly more than the measured volume of empty space in a quantity
of lightly compressed powder. Since binders typically consist of
materials such as organic polymers with relatively high CTEs, the
working volume should be calculated for the injection molding
temperatures expected. The binder and feedstock should be mixed
thoroughly to assure uniformity of composition. When heated, the
binder and feedstock will have sufficient fluid character to flow
in high pressure injection molding. The heated feedstock and binder
mixture is then injected under pressure into molds of desired
shape. The molded part then cools in the mold until set, and the
mold can then be opened and the part removed. Depending on the
final PDC geometry desired, one or more molded diamond feedstock
components can be created and placed into a can for PDC sintering.
Further, use of this method permits diamond feedstock to be molded
into a desired form and then stored for long periods of time prior
to use in the sintering process, thereby simplifying manufacturing
and resulting in more efficient production.
[0202] As desired, the binder may be removed from the injection
molded diamond feedstock form. A variety of methods are available
to achieve this. For example, by simple vacuum or hydrogen furnace
treatment, the binder may be removed from the diamond feedstock
form. In such a method, the form would be brought up to a desired
temperature in a vacuum or in a very low pressure hydrogen
(reducing) environment. The binder will then volatilize with
increasing temperature and will be removed from the form. The form
may then be removed from the furnace. When hydrogen is used, it
helps to maintain extremely clean and chemically active surfaces on
the diamond crystals of the diamond feedstock form.
[0203] An alternative method for removing the binder from the form
involves utilizing two or polymer (such as polyethylene) binders
with different molecular weights. After initial injection molding,
the diamond feedstock form is placed in a solvent bath that removes
the lower molecular weight polymer, leaving the higher molecular
weight polymer to maintain the shape of the diamond feedstock form.
Then the diamond feedstock form is placed in a furnace for vacuum
or very low pressure hydrogen treatment for removal of the higher
molecular weight polymer.
[0204] Partial or complete binder removal from the diamond
feedstock form may be performed prior to assembly of the form in a
pressure assembly for PDC sintering. Alternatively, the pressure
assembly including the diamond feedstock form may be placed into a
furnace for vacuum or very low pressure hydrogen furnace treatment
and binder removal.
[0205] Dilute Binder
[0206] In some embodiments, dilute binder may be added to PCD, PCBN
or ceramic powders to hold form. This technique may be used to
provide an improved method of forming PDC, PCBN, ceramic, or cermet
powders into layers of various geometries. A PDC, PCBN, ceramic or
cermet powder may be mixed with a temporary organic binder. This
mixture may be mixed and cast or calendared into a sheet (tape) of
the desired thickness. The sheet may be dried to remove water or
organic solvents. The dried tape may be then cut into shapes needed
to conform to the geometry of a corresponding substrate. The
tape/substrate assembly may be then heated in a vacuum furnace to
drive off the binder material. The temperature may then be raised
to a level where the ceramic or cermet powder fuses to itself
and/or to the substrate, thereby producing a uniform continuous
ceramic or cermet coating bonded to the substrate.
[0207] Referring to FIG. 5, a die 55 with a cup/can in it 54 and
diamond feedstock 52 against it are depicted. A punch 53 is used to
form the diamond feedstock 52 into a desired shape. Binder liquid
51 is not added to the powder until after the diamond, PCBN,
ceramic or cermet powder 52 is in the desired geometry. Dry powder
52 is spin formed using a rotating formed punch 53 in a refractory
containment can 54 supported in a holding die 55. In another method
shown in FIG. 6, feedstock powder 62 is added to a mold 66. A punch
forms the feedstock to shape. A vibrator 67 may be used help the
powder 62 take on the shape of the mold 66. After the powder
feedstock is in the desired geometry, a dilute solution of an
organic binder with a solvent is allowed to percolate through the
powder granules.
[0208] As shown in FIGS. 7 and 8, one powder layer 88 can be
loaded, and after a few minutes, when the binder is cured
sufficiently at room temperature, another layer 89 can be loaded on
top of the first layer 88. This method is particularly useful in
producing PDC or PCBN with multiple layers of varying powder
particle size and metal content. The process can be repeated to
produce as many layers as desired. FIG. 7 shows a section view of a
spherical, multi-layered powder load using a first layer 88, second
layer 89, third layer 810, and final layer 811. The binder content
should be kept to a minimum to produce good loading density and to
limit the amount of gas produced during the binder removal phase to
reduce the tendency of the containment cans 84 being displaced from
a build up of internal pressure.
[0209] Once all of the powder layers are loaded the binder may be
burned-out in a vacuum oven at a vacuum of about 200 Militorrs or
less and at the time and desired temperature profile, such as that
shown in FIG. 9. An acceptable binder is 0.5 to 5% propylene
carbonate in methyl ethyl keytone. An example binder burn out cycle
that may be used to remove binder is as follows:
9 Time Temperature (minutes) (degrees Centigrade) 0 21 4 100 8 250
60 250 140 800 170 800 290 21
[0210] Gradients
[0211] Diamond feedstock may be selected and loaded in order to
create different types of gradients in the diamond table. These
include an interface gradient diamond table, an incremental
gradient diamond table, and a continuous gradient diamond
table.
[0212] If a single type or mix of diamond feedstock is loaded
adjacent a substrate, as discussed elsewhere herein, sweep of
solvent-catalyst metal through the diamond will create an interface
gradient in the gradient transition zone of the diamond table.
[0213] An incremental gradient diamond table may be created by
loading diamond feedstocks of differing characteristics (diamond
particle size, diamond particle distribution, metal content, etc.)
in different strata or layers before sintering. For example, a
substrate is selected, and a first diamond feedstock containing 60%
solvent-catalyst metal by weight is loaded in a first strata
adjacent the substrate. Then a second diamond feedstock containing
40% solvent-catalyst metal by weight is loaded in a second strata
adjacent the first strata. Optionally, additional strata of diamond
feedstock may be used. For example, a third strata of diamond
feedstock containing 20% solvent-catalyst metal by weight may be
loaded adjacent the second strata.
[0214] A continuous gradient diamond table may be created by
loading diamond feedstock in a manner that one or more of its
characteristics continuously vary from one depth in the diamond
table to another. For example, diamond particle size may vary from
large near a substrate (to create large interstitial spaces in the
diamond for solvent-catalyst metal to sweep into) to small near the
diamond surface to create a part that is strongly bonded to the
substrate but that has a very low friction surface.
[0215] The diamond feedstocks of the different strata may be of the
same or different diamond particle size and distribution.
Solvent-catalyst metal may be included in the diamond feedstock of
the different strata in weight percentages of from about 0% to more
than about 80%. In some embodiments, diamond feedstock will be
loaded with no solvent-catalyst metal in it, relying on sweep of
solvent-catalyst metal from the substrate to achieve sintering. Use
of a plurality of diamond feedstock strata, the strata having
different diamond particle size and distribution, different
solvent-catalyst metal by weight, or both, allows a diamond table
to be made that has different physical characteristics at the
interface with the substrate than at the surface. This allows a PDC
to be manufactured that has a diamond table very firmly bonded to
its substrate.
[0216] Bisquing Processes to Hold Shapes
[0217] If desired, a bisquing process may be used to hold shapes
for subsequent processing of PDCs, PCBN, and ceramic or cermet
products. This involves an interim processing step in High
Temperature High Pressure (HTHP) sintering of PDC, PCBN, ceramic,
or cermet powders called "bisquing." Bisquing may provide the
following enhancements to the processing of the above products:
[0218] A. Pre-sintered shapes can be controlled that are at a
certain density and size.
[0219] B. Product consistency is improved dramatically.
[0220] C. Shapes can be handled easily in the bisque form.
[0221] D. In layered constructs, bisquing keeps the different
layers from contaminating each other.
[0222] E. Bisquing different components or layers separately
increases the separation of work elements increasing production
efficiency and quality.
[0223] F. Bisquing molds are often easer to handle and manage prior
to final assembly than the smaller final product forms.
[0224] Bisquing molds or containers can be fabricated from any high
temperature material that has a melting point higher than the
highest melting point of any mix component to be bisqued. Bisque
mold/container materials that work well are Graphite, Quartz, Solid
Hexagonal Boron Nitride (HBN), and ceramics. Some refractory type
metals (high temperature stainless steels, Nb, W, Ta, Mo, etc) work
well is some applications where bisquing temperatures are lower and
sticking of the bisque powder mix is not a problem. Molds or
containers can be shaped by pressing, forming, or machining, and
may be polished at the interface between the bisque material and
the mold/container itself. Some mold container materials require
glazing and/or firing prior to use.
[0225] FIG. 10 shows an embodiment 1006 for making a cylinder with
a concave relief or trough using the bisquing process. Pre-mixed
powders of PDC, PCBN, ceramic, or cermet materials 1001 that
contain enough metal to undergo solid phase sintering are loaded
into the bisquing molds or containers 1002 and 1004. A release
agent may be required between the mold/container to ensure that the
final bisque form can be removed following furnace firing. Some
release agents that may be used are HBN, Graphite, Mica, and
Diamond Powder. A bisque mold/container lid with an integral
support form 1005 is placed over the loaded powder material to
ensure that the material holds form during the sintering process.
The bisque mold/container assembly is then placed in a hydrogen
atmosphere furnace, or alternately, in a vacuum furnace which is
drawn to a vacuum ranging from 200 to 0 Militorrs. The load is then
heated within a range of 0.6 to 0.8 of the melting temperature of
the largest volume mix metal. A typical furnace cycle is shown in
FIG. 12. Once the furnace cycle is completed and the mold/container
is cooled, the hardened bisque formed powders can be removed for
further HPHT processing. A bisque form of feedstock 1003 is the net
product.
[0226] FIG. 11 shows fabrication 1110 of a bisque form for a full
hemispherical part 1109 that has multiple powder layers 1107a and
1107b. Pre-mixed powders of PDC, PCBN, ceramic, or cermet materials
that contain enough metal to undergo solid phase sintering are
loaded into the bisquing molds or containers 1108. A release agent
may be required between the mold/container to ensure that the final
bisque form can be removed following furnace firing. The bisque
mold/container assembly may then be placed in a vacuum furnace that
is drawn to a vacuum ranging from 200 to 0 Militorrs. The load is
then heated within a range of 0.6 to 0.8 of the melting temperature
of the largest volume mix metal. Once the furnace cycle is
completed and the mold/container is cooled, the hardened bisque
1109 formed powders can be removed for further HPHT processing. An
example of a bisque binder burn-out cycle that may be used to
remove the unwanted materials before sintering is as follows:
10 Time Temperature (hours) (degrees Centigrade) 0 21 0.25 21 5.19
800 6.19 800 10.19 21
[0227] Reduction of Free Volume in Diamond Feedstock
[0228] As mentioned earlier, it may be desirable to remove free
volume in the diamond feedstock before sintering is attempted. The
inventors have found this is a useful procedure when producing
non-planar concave and convex parts. If a press with sufficient
anvil travel is used for high pressure and high temperature
sintering, however, this step may not be necessary. Free volume in
the diamond feedstock will be reduced so that the resulting diamond
feedstock is at least about 95% theoretical density and closer to
about 97% of theoretical density.
[0229] Referring to FIGS. 1GA and 1G, an assembly used for
precompressing diamond to eliminate free volume is depicted. In the
drawing, the diamond feedstock is intended to be used to make a
convex non-planar polycrystalline diamond part. The assembly may be
adapted for precompressing diamond feedstock for making PDCs of
other complex shapes.
[0230] The assembly depicted includes a cube 161 of a pressure
transfer medium. A cube is made from pyrophillite or other
appropriate pressure transfer material such as a synthetic pressure
medium and is intended to undergo pressure from a cubic press with
anvils simultaneously pressing the six faces of the cube. A
cylindrical cell rather than a cube may be used if a belt press is
utilized for this step.
[0231] The cube 161 has a cylindrical cavity 162 or passage through
it. The center of the cavity 162 will receive a non-planar
refractory metal can 170 loaded with diamond feedstock 166 that is
to be precompressed. The diamond feedstock 166 may have a substrate
with it.
[0232] The can 170 consists of two non-planar can halves 170a and
170b, one of which overlaps the other to form a slight lip 172. The
can may be an appropriate refractory metal such as niobium,
tantalum, molybdenum, etc. The can is typically two hemispheres,
one that is slightly larger to accept the other being slid inside
of it to fully enclosed the diamond feedstock. A rebated area or
lip is provided in the larger can so that the smaller can will
satisfactorily fit therein. The seam of the can is sealed with an
appropriate sealant such as dry hexagonal boronitride or a
synthetic compression medium. The sealant forms a barrier that
prevents the salt pressure medium from penetrating the can. The can
seam may also be welded by plasma, laser, or electron beam
processes.
[0233] An appropriately shaped pair of salt domes 164 and 167
surround the can 170 containing the diamond feedstock 166. In the
example shown, the salt domes each have a non-planar cavity 165 and
168 for receiving the can 170 containing the non-planar diamond
feedstock 166. The salt domes and the can and diamond feedstock are
assembled together so that the salt domes encase the diamond
feedstock. A pair of cylindrical salt disks 163 and 169 are
assembled on the exterior of the salt domes 164 and 167. All of the
aforementioned components fit within the bore 162 of the pressure
medium cube 161.
[0234] The entire pyrocube assembly is placed into a press and
pressurized under appropriate pressure (such as about 40-68 Kbar)
and for an appropriate although brief duration to precompress the
diamond and prepare it for sintering. No heat is necessary for this
step.
[0235] Mold Releases
[0236] When making non-planar shapes, it may be desirable to use a
mold in the sintering process to produce the desired net shape.
CoCr metal may used as a mold release in forming shaped diamond or
other superhard products. Sintering the superhard powder feed
stocks to a substrate, the object of which is to lend support to
the resulting superhard table, may be utilized to produce standard
PDC and PCBN parts. However, in some applications, it is desired to
remove the diamond table from the substrate.
[0237] Referring to FIG. 14, a diamond layer 1402 and 1403 has been
sintered to a substrate 1401 at an interface 1404. The interface
1404 must be broken to result in free standing diamond if the
substrate is not required in the final product. A mold release may
be used to remove the substrate from the diamond table. If CoCr
alloy is used for the substrate, then the CoCr itself serves as a
mold release, as well as serving as a solvent-catalyst metal. CoCr
works well as a mold release because its CTE is dramatically
different than that of sintered PDC or PCBN. Because of the large
disparity in the CTEs between PDC and PCBN and CoCr, high stress is
formed at the interface 1501 between these two materials as shown
in FIG. 15. The stress that is formed is greater than the bond
energy between the two materials. When the stress is greater than
the bond energy, a crack is formed at the point of highest stress.
The crack then propagates following the narrow region of high
stress concentrated at the interface. Referring to FIG. 16, in this
way, the CoCr substrate 1601 will separate from the PCD or PCBN
1602 that was sintered around it, regardless of the shape of the
interface.
[0238] Materials other than CoCr can be used as a mold release.
These materials include those metals with high CTEs and, in
particular, those that are not good carbide formers. These are, for
example, Co, Ni, CoCr, CoFe, CoNi, Fe, steel, etc.
[0239] Gradient Layers and Stress Modifiers
[0240] Gradient layers and stress modifiers may be used in the
making of superhard constructs. Gradient layers may be used to
achieve any of the following objectives:
[0241] A. Improve the "sweep" of solvent metal into the outer layer
of superhard material and to control the amount of solvent metal
introduced for sintering into the outer layer.
[0242] B. Provide a "sweep" source to flush out impurities for
deposit on the surface of the outer layer of superhard material
and/or chemical attachment/combination with the refractory
containment cans.
[0243] C. Control the Bulk Modulus of the various gradient layers
and thereby control the overall dilatation of the construct during
the sintering process.
[0244] D. Affect the CTE of each of the various layers by changing
the ratio of metal or carbides to diamond, PCBN or other Superhard
materials to reduce the CTE of an individual gradient layer.
[0245] E. Allow for the control of structural stress fields through
the various levels of gradient layers to optimize the overall
construct.
[0246] F. Change the direction of stress tensors to improve the
outer Superhard layer, e.g., direct the tensor vectors toward the
center of a spherical construct to place the outer layer diamond
into compression, or conversely, direct the tensor vectors from the
center of the construct to reduce interface stresses between the
various gradient layers.
[0247] G. Improve the overall structural stress compliance to
external or internal loads by providing a construct that has
substantially reduced brittleness and increased toughness wherein
loads are transferred through the construct without crack
initiation and propagation.
[0248] Referring to FIG. 17, the liquid sintering phase of PDC and
PCBN is typically accomplished by mixing the solvent sintering
metal 1701 directly with the diamond or PCBN powders 1702 prior to
the HPHT pressing, or (referring to FIG. 18) "sweeping" the solvent
metal 1802 from a substrate 1801 into feedstock powders from the
adjacent substrate during HPHT. High quality PDC or PCBN is created
using the "sweep" process.
[0249] There are several theories related to the increased PDC and
PCBN quality when using the sweep method. However, most of those
familiar with the field agree that allowing the sintering metal to
"sweep" from the substrate material provides a "wave front" of
sintering metal that quickly "wets" and dissolves the diamond or
CBN and uses only as much metal as required to precipitate diamond
or PCBN particle-to-particle bonding. Whereas in a "premixed"
environment the metal "blinds off" the particle-to particle
reaction because too much metal is present, or conversely, not
enough metal is present to ensure the optimal reaction.
[0250] Furthermore, it is felt that the "wave front" of metal
sweeping through the powder matrix also carries away impurities
that would otherwise impede the formation of high quality PDC of
PCBN. These impurities are normally "pushed" ahead of the sintering
metal "wave front" and are deposited in pools adjacent to the
refractory containment cans. FIG. 19 depicts the substrate 1904,
the wavefront 1903, and the feedstock crystals or powder 1902 that
the wavefront will sweep through 1901. Certain refractory material
such as Niobium, Molybdenum, and Zirconium can act as "getters"
that combine with the impurities as they immerge from the matrix
giving additional assistance in the creation of high quality end
products.
[0251] While there are compelling reasons to use the "sweep"
process in sintering PDC and PCBN there are also problems that
arise out of its use. For example, not all substrate metals are as
controllable as others as to the quantity of material that is
delivered and ultimately utilized by the powder matrix during
sintering. Cobalt metal (6 to 13% by volume) sweeping from cemented
tungsten carbide is very controllable when used against diamond or
PCBN powders ranging from 1 to 40 microns particle sized. On the
other hand, cobalt chrome molybdenum (CoCrMo) that is useful as a
solvent metal to make PDC for some applications overwhelms the same
PDC matrix with CoCrMo metal in a pure sweep process sometimes
producing inferior quality PDC. The fact that the CoCrMo has a
lower melting point than cobalt, and further that there is an
inexhaustible supply when using a solid CoCrMo substrate adjacent
to the PDC matrix, creates a non-controllable processing
condition.
[0252] In some applications where it is necessary to use sintering
metals such a CoCrMo that can not be "swept" from a cemented
carbide product, it is necessary to provide a simulated substrate
against the PDC powders that provides a controlled release and
limited supply of CoCrMo for the process.
[0253] These "simulated" substrates have been developed in the
forms of "gradient" layers of mixtures of diamond, carbides, and
metals to produce the desired "sweep" affect for sintering the
outer layer of PDC. The first "gradient layer" Oust adjacent to the
outer or primary diamond layer which will act as the bearing or
wear surface) can be prepared using a mixture of diamond,
Cr.sub.3C.sub.2, and CoCrMo. Depending on the size fraction of the
diamond powder used in the outer layer, the first gradient layers
diamond size fraction and metal content is adjusted for the optimal
sintering conditions.
[0254] Where a "simulated" substrate is used, it has been
discovered that often a small amount of solvent metal, in this case
CoCrMo must be added to the outside diamond layer as catalyst to
"kick-off" the sintering reaction.
[0255] One embodiment utilizes the mix ranges for the outer 2001
and inner 2002 gradient layers of FIG. 20 that are listed in Table
9.
11TABLE 9 DIAMOND DIAMOND Cr.sub.3C.sub.2 GRADIENT (Vol. (Size
Fraction- (Vol. CoCrMo LAYERS Percent) .mu.m) Percent) (Vol.
Percent) Outer 92 25 0 8 Inner 70 40 10 20
[0256] The use of gradient layers with solid layers of metal allows
the designer to match the bulk modulus to the CTE of various
features of the construct to counteract dilatory forces encountered
during the HTHP phase of the sintering process. For example, in a
spherical construct as the pressure increases the metals in the
construct are compressed or dilated radially toward the center of
the sphere. Conversely, as the sintering temperature increases the
metal expands radially away from the center of the sphere. Unless
these forces are balanced in some way, the compressive dilatory
forces will initiate cracks in the outer diamond layer and cause
the construct to be unusable.
[0257] Typically, changes in bulk modulus of solid metal features
in the construct are controlled by selecting metals with a
compatible modulus of elasticity. The thickness and other sizing
features are also important. CTE, on the other hand, is changed by
the addition of diamond or other carbides to the gradient
layers.
[0258] One embodiment, depicted in FIG. 21, involves the use of two
gradient outer layers 2101 and 2102, a solid titanium layer 2104
and an inner CoCrMo sphere 2103. In this embodiment the first
gradient layer provides a "sweep source" of biocompatible CoCrMo
solvent metal to the outer diamond layer. The solid titanium layer
provides a dilatory source that offsets the CTE from the solid
CoCrMo center ball and keeps it from "pulling away" from the
titanium/CoCrMo interface as the sintering pressure and temperature
go from the 65 Kbar and 1400.degree. C. sintering range to 1 bar
and room temperature.
[0259] Where two or more powder based gradient layers are to be
used in the construct it becomes increasingly important to control
the CTE of each layer to ensure structural integrity following
sintering. During the sintering process stresses are induced along
the interface between each of the gradient layers. These high
stresses are a direct result of the differences in the CTE between
any two adjacent layers. To reduce these stresses the CTE of one or
both of the layer materials must be modified.
[0260] The CTE of the a substrate can be modified by either
changing to a substrate with a CTE close to that of diamond (an
example is the use of cemented tungsten carbide, where the CTE of
diamond is approximately 1.8 .mu.m/m-.degree. C. and cemented
tungsten carbide is approximately 4.4 .mu.m/m-.degree. C.), or in
the case of powdered layers, by adding a low CTE material to the
substrate layer itself. That is, making a mixture of two or more
materials, one or more of which will alter the CTE of the substrate
layer.
[0261] Metal powders can be mixed with diamond or other superhard
materials to produce a material with a CTE close to that of diamond
and thus produce stresses low enough following sintering to prevent
delamination of the layers at their interfaces. Experimental data
shows that the CTE altering materials will not generally react with
each other, which allows the investigator to predict the outcome of
the intermediate CTE for each gradient level.
[0262] The desired CTE is obtained by mixing specific quantities of
two materials according to the rule of mixtures. Table 10 shows the
change in CTE between two materials, A and B as a function of
composition (volume percent). In this example, materials A and B
have CTEs of 150 and 600 .mu.In./In.-.degree. F. respectively. By
adding 50 mol % of A to 50 mol % of B the resulting CTE is 375
.mu.in/in-.degree. F.
[0263] One or more of the following component processes is
incorporated into the mold release system:
[0264] 1. An intermediate layer of material between the PDC part
and the mold that prevents bonding of the polycrystalline diamond
compact to the mold surface.
[0265] 2. A mold material that does not bond to the PDC under the
conditions of synthesis.
[0266] 3. A mold material that, in the final stages of, or at the
conclusion of, the PDC synthesis cycle either contracts away from
the PDC in the case of a net concave PDC geometry, or expands away
from the PDC in the case of a net convex PDC geometry.
[0267] 4. The mold shape can also act simultaneously as a source of
sweep metal useful in the PDC synthesis process.
[0268] As an example, a mold release system may be utilized in
manufacturing a PDC by employing a negative shape of the desired
geometry to produce non-planar parts. The mold surface contracts
away from the final net concave geometry, the mold surface acts as
a source of solvent-catalyst metal for the PDC synthesis process,
and the mold surface has poor bonding properties to PDCs.
12TABLE 10 PREDICTED DIMENSIONAL CHANGES IN AN EIGHT INCH LAYERED
CONSTRUCT Final CTE Total Length Dimension A % B % (.mu.
In./In-.degree. F.) Change (In.) (In.) 100 0 150 .0012 7.9988 90 10
195 .0016 7.9984 80 20 240 .0019 7.9981 70 30 285 .0023 7.9977 60
40 330 .0026 7.9974 50 50 375 .0030 7.9970 40 60 420 .0034 7.9966
30 70 465 .0037 7.9963 20 80 510 .0041 7.9959 10 90 555 .0044
7.9956 0 100 600 .0048 7.9952
[0269] FIG. 22 is an illustration of how the above CTE modification
works in a one-dimensional example. The one-dimensional example
works as well in a three-dimensional construct. If the above
materials A and B are packed in alternating layers 2201 and 2202 as
shown in FIG. 22, separately in their pure forms, with their CTEs
of 150 and 600 .mu.In./In.-.degree. F. respectively, they will
contract exactly 150 .mu.In./In.-.degree. F. and 600
.mu.In./In.-.degree. F. for every degree decrease in temperature.
For an eight inch block of one inch thick stacked layers the total
change in dimension for a one degree decrease in temperature will
be:
[0270] Material A: (4.times.1 In.).times.(0.00015 In./In.-.degree.
F.).times.1.degree. F.=0.0006 In.
[0271] Material B: (4.times.1 In.).times.(0.00060 In./In.-.degree.
F.).times.1).degree. F.=0.0024 In.
[0272] Total overall length decrease in eight inches=0.0030 In.
[0273] By comparison, each of the layers is modified by using a
mixture of 50% of A and 50% of B, and all eight layers are stacked
into the eight-inch block configuration. Re-calculation of the
overall length decrease using the new composite CTE of 375
.mu.In./In.-.degree. F. from Table II shows:
[0274] Material A+B: (8.times.1 In.).times.(0.000375
In./In.-.degree. F.).times.1.degree. F.=0.0030 In.
[0275] Total overall length decrease in eight inches=0.0030 In.
[0276] The length decrease in this case was accurately predicted
for the one-dimensional construct using one-inch thick layers by
using the rule of mixtures.
[0277] Metals have very high CTE values as compared to diamond,
which has one of the lowest CTEs of any known material. When metals
are used as substrates for PDC and PCBN sintering considerable
stress is developed at the interface. Therefore, mixing low CTE
material with the biocompatible metal for medical implants can be
used to reduce interfacial stresses. One of the best candidate
materials is diamond itself. Other materials include refractory
metal carbides and nitrides, and some oxides. Borides and silicides
would also be good materials from a theoretical standpoint, but may
not be biocompatible. The following is a list of candidate
materials:
13 Carbides Silicides Oxynitrides Nitrides Oxides Oxyborides
Borides Oxycarbides Carbonitrides
[0278] There are other materials and combinations of materials that
could be utilized as CTE modifiers.
[0279] There are also other factors that apply to the reduction of
interface stresses for a particular geometrical construct. The
thickness of the gradient layer, its position in the construct, and
the general shape of the final construct all contribute in
interfacial stress tensor reduction. Geometries that are more
spherical tend to promote interface circumferential failures from
positive or negative radial tensors while geometries of a
cylindrical configuration tend to fail at the layer interfaces
precipitated by bending stress couples.
[0280] The design of the gradient layers respecting CTE and the
amount of contraction that each individual layer will experience
during cooling form the HTHP sintering process will largely dictate
the direction of stress tensors in the construct. Generally, the
designer will always desire to have the outer wear layer of
superhard material in compression to prevent delamination and crack
propagation. In spherical geometries the stress tensors would be
directed radially toward the center of the spherical shape giving
special attention to the interfacial stresses at each layer
interface to prevent failures at these interfaces as well. In
cylindrical geometries the stress tensors would be adjusted to
prevent stress couples from initiating cracks in either end of the
cylinder, especially at the end where the wear surface is
present.
[0281] The following are embodiments that relate to a spherical
geometry wherein combinations of gradient layers and/or solid metal
balls are used to control the final outcomes of the constructs.
FIG. 23 is an embodiment that shows a spherical construct, which
utilizes five gradient layers wherein the composition of each layer
is described in Tables 11 and 12:
14 TABLE 11 DIAMOND Cr3C2 CoCrMo LAYER Size Volume Volume Volume
THICKNESS LAYER (.mu.m) % % % (In.) First 20 92 8 0 .090 (Outer
Layer) 2301 Second 2302 40 70 20 20 .104 Third 2303 70 60 20 20
.120 Forth 2304 70 60 26 26 .138 Fifth 2305 70 25 37.5 37.5
.154
[0282]
15 TABLE 12 DIAMOND Cr3C2 CoCrMo LAYER Size Volume Volume Volume
THICKNESS LAYER (.mu.m) % % % (In.) First 20 100 0 0 .090 (Outer
Layer) 2301 Second 2302 40 70 20 20 .104 Third 2304 70 60 20 20
.120 Forth 2304 70 60 26 26 .138 Fifth 2305 70 25 37.5 37.5
.154
[0283] FIG. 24 is an embodiment that shows a spherical construct,
which utilizes four gradient layers wherein the composition of each
layer is described in Tables 13 and 14.
16 TABLE 13 DIAMOND Cr3C2 CoCrMo LAYER Size Volume Volume Volume
THICKNESS LAYER (.mu.m) % % % (In.) First 20 92 0 8 .097 (Outer
Layer) 2401 Second 2402 40 70 10 20 .125 Third 2403 70 60 20 20
.144 Forth 2404 70 50 25 25 .240
[0284]
17 TABLE 14 DIAMOND Cr3C2 CoCrMo LAYER Size Volume Volume Volume
THICKNESS LAYER (.mu.m) % % % (In.) First 20 100 0 0 .097 (Outer
Layer) 2401 Second 2402 40 70 10 20 .125 Third 2403 70 60 20 20
.144 Forth 2404 70 50 25 25 .240
[0285] FIG. 25 shows an embodiment construct that utilizes a center
support ball with gradient layers laid up on the ball and each
other to form the complete construct. The inner ball of solid metal
CoCrMo is encapsulated with a 0.003 to 0.010 inch thick refractory
barrier can 2504 to prevent the over saturation of the system with
the ball metal during the HTHP phase of sintering. The composition
of each layer is described in Tables 15 and 16.
18 TABLE 15 DIAMOND Cr3C2 CoCrMo LAYER Size Volume Volume Volume
THICKNESS LAYER (.mu.m) % % % (In.) First 20 92 0 8 .097 (Outer
Layer) 2501 Second 2502 40 70 10 20 .125 Third 2503 70 60 20 20
.144 CoCrMo Ball N/A N/A N/A N/A N/A 2505
[0286]
19 TABLE 16 DIAMOND Cr3C2 CoCrMo LAYER Size Volume Volume Volume
THICKNESS LAYER (.mu.m) % % % (In.) First 20 100 0 0 .097 (Outer
Layer) 2501 Second 2502 40 70 10 20 .125 Third 2503 70 60 20 20
.144 CoCrMo Ball N/A N/A N/A N/A N/A 2505
[0287] Predicated on the end use function of the sphere above, the
inner ball may be made of cemented tungsten carbide, niobium,
nickel, stainless steel, steel, or one of several other metal or
ceramic materials to suit the designers needs.
[0288] Embodiments relating to dome shapes are described as
follow:
[0289] FIG. 26 shows a dome embodiment construct that utilizes two
gradient layers 2601 and 2602 wherein the composition of each layer
is described in Tables 17 and 18.
20 TABLE 17 DIAMOND Cr3C2 CoCrMo LAYER Size Volume Volume Volume
TiCTiN THICKNESS LAYER (.mu.m) % % % Volume % (In.) First 20 94 0 6
0.05 .200 (Outer Layer) 2602 Second 2601 70 60 20 20 0.05 .125
[0290]
21 TABLE 18 DIAMOND Cr3C2 CoCrMo LAYER Size Volume Volume Volume
TiCTiN THICKNESS LAYER (.mu.m) % % % Volume % (In.) First 20 100 0
0 0.05 .200 (Outer Layer) 2602 Second 2601 70 60 20 20 0.05
.125
[0291] FIG. 27 shows a dome embodiment construct that utilizes two
gradient layers 2701 and 2702 wherein the composition of each layer
is described in Tables 19 and 20:
22 TABLE 19 DIAMOND Cr3C2 CoCrMo LAYER Size Volume Volume Volume
TiCTiN THICKNESS LAYER (.mu.m) % % % Volume % (In.) First 20 94 0 6
0.05 .128 (Outer Layer) 2702 Second 2701 70 60 20 20 0.05 .230
[0292]
23 TABLE 20 DIAMOND Cr3C2 CoCrMo LAYER Size Volume Volume Volume
TiCTiN THICKNESS LAYER (.mu.m) % % % Volume % (In.) First 20 100 0
0 0.05 .128 (Outer Layer) 2702 Second 2701 70 60 20 20 0.05
.230
[0293] FIG. 28 shows a dome embodiment construct that utilizes
three gradient layers 2801, 2802 and 2803 where the composition of
each layer is described in Tables 21 and 22:
24 TABLE 21 DIAMOND Cr3C2 CoCrMo LAYER Size Volume Volume Volume
TiCTiN THICKNESS LAYER (.mu.m) % % % Volume % (In.) First 20 96 0 4
0.05 .168 (Outer Layer) 2801 Second 2802 40 80 10 10 0.05 .060
Third 2803 70 60 20 20 0.05 .130
[0294]
25 TABLE 22 DIAMOND Cr3C2 CoCrMo LAYER Size Volume Volume Volume
TiCTiN THICKNESS LAYER (.mu.m) % % % Volume % (In.) First 20 100 0
0 0.05 .168 (Outer Layer) 2801 Second 2802 40 80 10 10 0.05 .060
Third 2803 70 60 20 20 0.05 .130
[0295] FIG. 29 shows a dome embodiment construct that utilizes
three gradient layers 2901, 2902 and 9803 wherein the composition
of each layer is described in Tables 23 and 24.
26 TABLE 23 DIAMOND Cr3C2 CoCrMo LAYER Size Volume Volume Volume
TiCTiN THICKNESS LAYER (.mu.m) % % % Volume % (In.) First 20 96 0 4
0.05 .065 (Outer Layer) 2901 Second 2902 40 80 10 10 0.05 .050
Third 2903 70 60 20 20 0.05 .243
[0296]
27 TABLE 24 DIAMOND Cr3C2 CoCrMo LAYER Size Volume Volume Volume
TiCTiN THICKNESS LAYER (.mu.m) % % % Volume % (In.) First 20 100 0
0 0.05 .065 (Outer Layer) 2901 Second 2902 40 80 10 10 0.05 .050
Third 2903 70 60 20 20 0.05 .243
[0297] Embodiments relating to Flat Cylindrical shapes are
described as follows:
[0298] FIG. 30 shows a flat cylindrical embodiment construct that
utilizes two gradient layers 3001 and 3002 wherein the composition
of each layer is described in Tables 25 and 26.
28 TABLE 25 DIAMOND Cr3C2 CoCrMo LAYER Size Volume Volume Volume
TiCTiN THICKNESS LAYER (.mu.m) % % % Volume % (In.) First 20 94 0 6
0.05 (Outer Layer) 3001 Second 3002 70 60 20 20 0.05
[0299]
29 TABLE 26 DIAMOND Cr3C2 CoCrMo LAYER Size Volume Volume Volume
TiCTiN THICKNESS LAYER (.mu.m) % % % Volume % (In.) First 20 100 0
0 0.05 (Outer Layer) 3001 Second 3002 70 60 20 20 0.05
[0300] FIG. 31 shows a flat cylindrical embodiment construct that
utilizes three gradient layers 3101, 3102, 3103 wherein the
composition of each layer is described in Tables 27 and 28:
30 TABLE 27 DIAMOND Cr3C2 CoCrMo LAYER Size Volume Volume Volume
TiCTiN THICKNESS LAYER (.mu.m) % % % Volume % (In.) First 20 96 0 4
0.05 (Outer Layer) 3101 Second 3102 40 80 10 10 0.05 Third 3103 70
60 20 20 0.05
[0301]
31 TABLE 28 DIAMOND Cr3C2 CoCrMo LAYER Size Volume Volume Volume
TiCTiN THICKNESS LAYER (.mu.m) % % % Volume % (In.) First 20 100 0
0 0.05 (Outer Layer) 3101 Second 3102 40 80 10 10 0.05 Third 3103
70 60 20 20 0.05
[0302] FIG. 32 shows a flat cylindrical embodiment construct that
utilizes three gradient layers 3201, 3202, 3203 laid up on a CoCrMo
substrate 3204. The cylindrical substrate of solid metal CoCrMo
3204 is encapsulated with a 0.003 to 0.010 inch thick refractory
barrier can 3205 to prevent the over saturation of the system with
the substrate metal during the HTHP phase of sintering. The
composition of each layer is described in Tables 29 and 30:
32 TABLE 29 DIAMOND Cr3C2 CoCrMo LAYER Size Volume Volume Volume
TiCTiN THICKNESS LAYER (.mu.m) % % % Volume % (In.) First 20 96 0 4
0.05 (Outer Layer) 3201 Second 3202 40 80 10 10 0.05 Third 3203 70
60 20 20 0.05 CoCrMo N/A N/A N/A N/A N/A Substrate 3204
[0303]
33 TABLE 30 DIAMOND Cr3C2 CoCrMo LAYER Size Volume Volume Volume
TiCTiN THICKNESS LAYER (.mu.m) % % % Volume % (In.) First 20 100 0
0 0.05 (Outer Layer) 3201 Second 3202 40 80 10 10 0.05 Third 3203
70 60 20 20 0.05 CoCrMo N/A N/A N/A N/A N/A Substrate 3204
[0304] Predicated on the end use function of the cylinder shape of
FIG. 32 the inner substrate could be made of cemented tungsten
carbide, niobium, nickel, stainless steel, steel, or one of several
other metal or ceramic materials to suite the designers needs.
[0305] Embodiments relating to flat cylindrical shapes with
formed-in-place concave features are described as follow:
[0306] FIG. 33 shows an embodiment of a flat cylindrical shape with
a formed in place concave trough or filler support 3303 that
utilizes two gradient layers 3301 and 3302 wherein the composition
of each layer is described in Tables 31 and 32:
34 TABLE 31 DIAMOND Cr3C2 CoCrMo LAYER Size Volume Volume Volume
TiCTiN THICKNESS LAYER (.mu.m) % % % Volume % (In.) First 20 94 0 6
0.05 .156 (Outer Layer) 3301 Second 3302 70 60 20 20 0.05 .060
Filler Support 70 60 20 20 0.05 N/A 3303
[0307]
35 TABLE 32 DIAMOND Cr3C2 CoCrMo LAYER Size Volume Volume Volume
TiCTiN THICKNESS LAYER (.mu.m) % % % Volume % (In.) First 20 100 0
0 0.05 .156 (Outer Layer) 3301 Second 3302 70 60 20 20 0.05 .060
Filler Support 70 60 20 20 0.05 N/A 3303
[0308] FIG. 34 shows an embodiment of a flat cylindrical shape with
a formed in place concave trough or filler support 3403 that
utilizes two gradient layers 3401 and 3402 wherein the composition
of each layer is described in Tables 33 and 34:
36 TABLE 33 DIAMOND Cr3C2 CoCrMo LAYER Size Volume Volume Volume
TiCTiN THICKNESS LAYER (.mu.m) % % % Volume % (In.) First 20 94 0 6
0.05 .156 (Outer Layer) 3401 Second 3402 70 60 20 20 0.05 .060
Filler Support 70 60 20 20 0.05 N/A 3403
[0309]
37 TABLE 34 DIAMOND Cr3C2 CoCrMo LAYER Size Volume Volume Volume
TiCTiN THICKNESS LAYER (.mu.m) % % % Volume % (In.) First 20 100 0
0 0.05 .156 (Outer Layer) 3401 Second 3402 70 60 20 20 0.05 .060
Filler Support 70 60 20 20 0.05 N/A 3403
[0310] FIG. 35 shows an embodiment of a flat cylindrical shape with
a formed in place concave trough or filler support 3504 that
utilizes three gradient layers 3501, 3502, 3503 wherein the
composition of each layer is described in Tables 35 and 36:
38 TABLE 35 DIAMOND Cr3C2 CoCrMo LAYER Size Volume Volume Volume
TiCTiN THICKNESS LAYER (.mu.m) % % % Volume % (In.) First 20 96 0 4
0.05 .110 (Outer Layer) 3501 Second 3502 40 80 10 10 0.05 .040
Third 3503 70 60 20 20 0.05 .057 Filler Support 70 60 20 20 0.05
N/A 3504
[0311]
39 TABLE 36 DIAMOND Cr3C2 CoCrMo LAYER Size Volume Volume Volume
TiCTiN THICKNESS LAYER (.mu.m) % % % Volume % (In.) First 20 100 0
0 0.05 .110 (Outer Layer) 3501 Second 3502 40 80 10 10 0.05 .040
Third 3503 70 60 20 20 0.05 .057 Filler Support 70 60 20 20 0.05
N/A 3504
[0312] FIG. 36 shows an embodiment of a flat cylindrical shape with
a formed in place concave trough or filler support 3604 that
utilizes three gradient layers 3601, 3602, 3603 wherein the
composition of each layer is described in Tables 37 and 38:
40 TABLE 37 DIAMOND Cr3C2 CoCrMo LAYER Size Volume Volume Volume
TiCTiN THICKNESS LAYER (.mu.m) % % % Volume % (In.) First 20 96 0 4
0.05 .110 (Outer Layer) 3601 Second 3602 40 80 10 10 0.05 .040
Third 3603 70 60 20 20 0.05 .057 Filler Support 70 60 20 20 0.05
N/A 3604
[0313]
41 TABLE 38 DIAMOND Cr3C2 CoCrMo LAYER Size Volume Volume Volume
TiCTiN THICKNESS LAYER (.mu.m) % % % Volume % (In.) First 20 100 0
0 0.05 .110 (Outer Layer) 3601 Second 3602 40 80 10 10 0.05 .040
Third 3603 70 60 20 20 0.05 .057 Filler Support 70 60 20 20 0.05
N/A 3604
[0314] Prepare Heater Assembly
[0315] In order to sinter the assembled and loaded diamond
feedstock described above into PCD, both heat and pressure are
required. Heat is provided electrically as the part undergoes
pressure in a press. A heater assembly is used to provide the
required heat.
[0316] A refractory metal can containing loaded and precompressed
diamond feedstock is placed into a heater assembly. Salt domes are
used to encase the can. The salt domes used may be white salt
(NaCl) that is precompressed to at least about 90-95% of
theoretical density. This density of the salt is desired to
preserve high pressures of the sintering system and to maintain
geometrical stability of the manufactured part. The salt domes and
can are placed into a graphite heater tube assembly. The salt and
graphite components of the heater assembly may be baked in a vacuum
oven at greater than 100 degrees Celsius and at a vacuum of at
least 23 torr for about 1 hour in order to eliminate absorbed water
prior to loading in the heater assembly. Other materials that may
be used in construction of a heater assembly include solid or foil
graphite, amorphous carbon, pyrolitic carbon, refractory metals and
high electrical resistant metals.
[0317] Once electrical power is supplied to the heater tube, it
will generate heat required for polycrystalline diamond formation
in the high pressure/high temperature pressing operation.
[0318] Preparation of Pressure Assembly for Sintering
[0319] Once a heater assembly has been prepared, it is placed into
a pressure assembly for sintering in a press under high pressure
and high temperature. A cubic press or a belt press may be used for
this purpose, with the pressure assembly differing somewhat
depending on the type of press used. The pressure assembly is
intended to receive pressure from a press and transfer it to the
diamond feedstock so that sintering of the diamond may occur under
isostatic conditions.
[0320] If a cubic press is used, then a cube of suitable pressure
transfer media such as pyrophillite will contain the heater
assembly. Cell pressure medium may be used if sintering is to take
place in a belt press. Salt may be used as a pressure transfer
media between the cube and the heater assembly. Thermocouples may
be used on the cube to monitor temperature during sintering. The
cube with the heater assembly inside of it is considered a pressure
assembly, and is place into a press a press for sintering.
[0321] Sintering of Feedstock into PCD
[0322] The pressure assembly described above containing a
refractory metal can that has diamond feedstock loaded and
precompressed within is placed into an appropriate press. An
appropriate press is used to create high temperature and high
pressure conditions for sintering.
[0323] To prepare for sintering, the entire pressure assembly is
loaded into a cubic press and initially pressurized to about 40-68
Kbars. The pressure to be used depends on the product to be
manufactured and must be determined empirically. Then electrical
power is added to the pressure assembly in order to reach a
temperature in the range of less than about 1145 or 1200 to more
than about 1500 degrees Celsius. About 5800 watts of electrical
power is available at two opposing anvil faces, creating the
current flow required for the heater assembly to generate the
desired level of heat. Once the desired temperature is reached, the
pressure assembly is subjected to pressure of about 1 million
pounds per square inch at the anvil face. The components of the
pressure assembly transmit pressure to the diamond feedstock. These
conditions are maintained for about 3-12 minutes, but could be from
less than 1 minute to more than 30 minutes. The sintering of PDCs
takes place in an isostatic environment where the pressure transfer
components are permitted only to change in volume but are not
permitted to otherwise deform. Once the sintering cycle is
complete, about a 90 second cool down period is allowed, and then
pressure is removed. The PDC is then removed for finishing.
[0324] Removal of a sintered PDC having a curved, compound or
complex shape from a pressure assembly is simple due to the
differences in material properties between diamond and the
surrounding metals in some embodiments. This is generally referred
to as the mold release system.
[0325] Removal of Solvent-Catalyst Metal from PCD
[0326] If desired, the solvent-catalyst metal remaining in
interstitial spaces of the sintered PCD may be removed. Such
removal is accomplished by chemical leaching as is known in the
synthetic diamond field. After solvent-catalyst metal has been
removed from the interstitial spaces in the diamond table, the
diamond table will have greater stability at high temperatures.
This is because there is no catalyst for the diamond to react with
and break down.
[0327] After leaching solvent-catalyst metal from the diamond
table, it may be replaced by another metal or metal compound to
form thermally stable diamond that is stronger than leached PCD. If
it is intended to weld synthetic diamond or a PDC to a substrate or
to another surface such as by inertia welding, it may be desirable
to use thermally stable diamond due to its resistance to heat
generated by the welding process.
[0328] Manufacture of Concave Surfaces
[0329] An example substrate geometry for manufacturing a concave
spherical, hemispherical or partially spherical polycrystalline
diamond compact can be understood in conjunction with review of
FIGS. 37A-37C. The substrate 601 (and 601a and 601b) may be in the
form of a cylinder with a hemispherical receptacle 602 (and 602a
and 602b) formed into one of its ends. Two substrate cylinders 601a
and 601b are placed so that their hemispherical receptacles 602a
and 602b are adjacent each other, thus forming a spherical cavity
604 between them. A sphere 603 of an appropriate substrate material
is located in the cavity 604. Diamond feedstock 605 is located in
the cavity 604 between the exterior of the sphere 603 and the
concave surfaces of the receptacles 602a and 602b of the substrate
cylinders 601a and 601b. The assembly is placed into a refractory
metal can 610 for sintering. The can has a first cylinder 610a and
a second cylinder 601b. The two cylinders join at a lip 611. After
such an assembly is sintered, the assembly may be slit, cut or
ground along the center line 606 in order to form a first cup
assembly 607a and a second cup assembly 607b. Example substrate
materials for the cylinders 602a and 602b are CoCrMo (ASTM F-799)
and CoCrW (ASTM F-90), and an example substrate material for the
sphere 603 is CoCrMo (ASTM F-799), although any appropriate
substrate material may be used, including some of those listed
elsewhere herein.
[0330] Manufacture of Convex Surfaces
[0331] In this section, examples for manufactureing various convex
superhard surfaces are provided. Referring to FIGS. 13A-13F,
various substrate structures of the invention for making a
generally spherical polycrystalline diamond or polycrystalline
cubic boron nitride compact are depicted. FIGS. 13A and 13B depict
two-layer substrates.
[0332] In FIG. 13A, a solid first sphere 501 of a substrate
material intended to be used as the substrate shell or outer layer
was obtained. The dimensions of the first sphere 501 are such that
the dimension of the first sphere 501 with a diamond table on its
exterior will approximate the intended dimension of the component
prior to final finishing. Once the first sphere 501 of the
substrate is obtained, a hole 502 is bored into its center. The
hole 502 is preferably bored, drilled, cut, blasted or otherwise
formed so that the terminus 503 of the hole 502 is hemispherical.
This may be achieved by using a drill bit or end mill with a round
or ball end having the desired radius and curvature. Then a second
sphere 504 of a substrate material is obtained. The second sphere
504 is smaller than the first sphere 501 and is be placed in hole
502 in the first sphere 501. The substrates materials of spheres
501 and 504 may be selected form those listed in the tables above.
They may also be of other appropriate materials. The second sphere
504 and the hole 502 and its terminus 503 should fit together
closely without excessive tolerance or gap. A plug 505 which may be
of the same substrate material as first sphere 501 is formed or
obtained. The plug 505 has a first end 505a and a second end 505b
and substrate material therebetween in order to fill the hole 502
except for that portion of the hole 502 occupied by the second
sphere 504 adjacent the hole terminus 503. The plug 505 may have a
concave hemispherical receptacle 506 at its first end 505a so that
plug 505 will closely abut second sphere 504 across about half the
spherical surface of second sphere 504. The plug 505 may be
generally cylindrical in shape. The substrate assembly including
one substrate sphere placed inside of another may then be loaded
with diamond feedstock 507 or cubic boron nitride feedstock and
sintered under high pressure at high temperature to form a
spherical polycrystalline diamond compact.
[0333] Referring to FIG. 13B, another substrate geometry for
manufacturing spherical polycrystalline diamond or cubic boron
nitride compacts is depicted. An inner core sphere 550 of
appropriate substrate material is selected. Then an outer substrate
first hemisphere 551 and outer substrate second hemisphere 552 are
selected. Each of the outer substrate first and second hemispheres
551 and 552 are formed so that they each have a hemispherical
receptacle 551a and 552a shaped and sized to accommodate placement
of the hemispheres about the exterior of the inner core sphere 550
and thereby enclose and encapsulate the inner core sphere 550. The
substrates materials of inner core sphere 550 and hemispheres 551
and 552 are preferably selected form those listed in the tables
above or other appropriate materials. With the hemispheres and
inner core sphere assembled, diamond feedstock 553 may be loaded
about the exterior of the hemispheres and high temperature and high
pressure sintering may proceed in order to form a spherical
compact.
[0334] Although FIGS. 13A and 13B depict two-layer substrates, it
is possible to use multiple layer substrates (3 or more layers) for
the manufacture of polycrystalline diamond or polycrystalline
diamond compacts or polycrystalline cubic boron nitride compacts.
The selection of a substrate material, substrate geometry,
substrate surface topographical features, and substrates having a
plurality of layers (2 or more layers) of the same or different
materials depend at least in part on the thermo-mechanical
properties of the substrate, the baro-mechanical properties of the
substrate, and the baro-mechanical properties of the substrate.
[0335] Referring to FIG. 13C, another substrate configuration for
making generally spherical compacts is depicted. The substrate 520
is in the general form of a sphere. The surface of the sphere
includes substrate surface topography intended to enhance fixation
of a diamond table to the substrate. The substrate has a plurality
of depressions 521 formed on its surface. Each depression 521 is
formed as three different levels of depression 521a, 521b and 521c.
The depressions are depicted as being concentric circles, each of
approximately the same depth, but their depths could vary, the
circles need not be concentric, and the shape of the depressions
need not be circular. The depression walls 521d, 521e and 521f are
depicted as being parallel to a radial axis of the depressions
which axis is normal to a tangent to the theoretical spherical
extremity of the sphere, but could have a different orientation if
desired. As depicted, the surface of the substrate sphere 522 has
no topographical features other than the depressions already
mentioned, but could have protrusions, depressions or other
modifications as desired. The width and depth dimensions of the
depressions 521 may be varied according to the polycrystalline
diamond compact that is being manufactured. Diamond feedstock may
be loaded against the exterior of the substrate sphere 520 and the
combination may be sintered at diamond stable pressures to produce
a spherical polycrystalline diamond compact. Use of substrate
surface topographical features on a generally spherical substrate
provides a superior bond between the diamond table and the
substrate as described above and permits a polycrystalline diamond
compact to be manufactured using a single layer substrate. That is
because of the gripping action between the substrate and the
diamond table achieved by use of substrate surface topographical
features.
[0336] Referring to FIG. 13D, a segmented spherical substrate 523
is depicted. The substrate has a plurality of surface depressions
524 equally spaced about its exterior surface. These depressions as
depicted are formed in levels of three different depths. The first
level 524a is formed to a predetermined depth and is of pentagonal
shape about its outer periphery. The second level 524b is round in
shape and is formed to a predetermined depth which may be different
from the predetermined depth of the pentagon. The third level 524c
is round in shape in is formed to a predetermined depth which may
be different from each of the other depths mentioned above.
Alternatively, the depressions may be formed to only one depth, may
all be pentagonal, or may be a mixture of shapes. The depressions
may be formed by machining the substrate sphere.
[0337] Referring to FIG. 13E, a cross section of an alternative
substrate configuration for making a polycrystalline diamond or
polycrystalline cubic boron nitride compact is shown. A compact 525
is shown. The compact 525 is spherical. The compact 525 includes a
diamond table 526 sintered to a substrate 527. The substrate is
partially spherical in shape at its distal side 527a and is
dome-shaped on its proximal side 527b. Alternatively, the proximal
side 527b of the substrate 527 may be described as being partially
spherical, but the sphere on which it is based has a radius of
smaller dimension than the radius of the sphere on which the distal
side 527a of the substrate is based. Each of the top 527c and
bottom 527d are formed in a shape convenient to transition from the
proximal side 527b substrate partial sphere to the distal side 527a
substrate partial sphere. This substrate configuration has
advantages in that it leaves a portion of substrate exposed for
drilling and attaching fixation components without disturbing
residual stress fields of the polycrystalline diamond table. It
also provides a portion of the substrate that does not have diamond
sintered to it, allowing dilatation of the substrate during
sintering without disruption of the diamond table. More than 180
degrees of the exterior of the substrate sphere has diamond on it,
however, so the part is useful as a femoral head or other
articulation surface.
[0338] Referring to FIG. 13F, a cross section of an alternative
substrate configuration for making a polycrystalline diamond
compact is shown. A polycrystalline diamond compact 528 is depicted
having a diamond table 529 and a substrate 530. The substrate has
topographical features 531 for enhancing strength of the diamond to
substrate interface. The topographical features may include
rectangular protrusions 532 spaced apart by depressions 533 or
corridors. The distal side of the substrate is formed based on a
sphere of radius r. The proximal side of the substrate 530b is
formed based on a sphere of radius r', where r>r'. Usually the
surface modifications will be found beneath substantially all of
the diamond table.
[0339] Referring to FIG. 13G, another generally spherical compact
535 is shown that includes a diamond table 536 sintered to a
substrate 536. The substrate is configured as a sphere with a
protruding cylindrical shape. The head 535 is formed so that a
quantity of substrate protrudes from the spherical shape of the
head to form a neck 538 which may be attached to an appropriate
body by any known attachment method. The use of a neck 538
preformed on the substrate that is used to manufacture a
polycrystalline diamond or cubic boron nitride compact 535 provides
an attachment point on the polycrystalline diamond compact that may
be utilized without disturbing the residual stress field of the
compact. The neck 538 depicted is an integral component of a stem
540.
[0340] Any of the previously mentioned substrate configurations and
substrate topographies and variations and derivatives of them may
be used to manufacture a polycrystalline diamond or polycrystalline
cubic boron nitrode compact for use in a variety of fields. In
various embodiments, a single layer substrate may be utilized. In
other embodiments, a two-layer substrate may be utilized, as
discussed. Depending on the properties of the components being
used, however, it may be desired to utilize a substrate that
includes three, four or more layers.
[0341] Segmented and Continuous Superhard Structures
[0342] In this section, the concept of structures which use
segments of hard or superhard materials is discussed. The segments
(or inserts) may present a concave, convex or planar contact area,
as desired, and can simplify construction of products with complex
geometries. Structures with segmented superhard surfaces may be
made by sintering the superhard segments in place on a substrate so
that the segments of superhard material and the substrate form an
integral superhard compact. Or structures with segmented superhard
or hard surfaces may be made by manufacturing the superhard or hard
material in advance, and then installing it in a separate substrate
later by such techniques as friction fit, interference fit,
mechanical interlock, brazing, welding, adhesion, etc. For
comparison, superhard structures with continuous surfaces are also
discussed below. Example segmented and continuous structures are
now discussed.
[0343] The geometry in FIGS. 4A-4B consists of veins or stripes of
bearing material that start from a polar region and migrate outward
with a slight angular propensity. FIG. 4A illustrates a side view
of the head 4A-101. Specifically, the substrate material 4A-104 is
marked by elevated ridges of diamond 4A-102 and recessed troughs
4A-103 between the diamond ridges 4A-102. FIG. 4B is a top view of
FIG. 4A illustrating a pattern of arcuate ridges emanating from a
central location or spherical point. A straight-line version of
this pattern is also possible.
[0344] The geometry of FIGS. 4C-4D consists of undulating lines
that are continuous around the surface of the sphere. FIG. 4C
illustrates a side view of the head with a spherical point 4C-101
such that elevated non-linear ridges of diamond 4C-103 wrap around
the substrate material 4C-102. Like FIGS. 4A and 4B, troughs 4C-104
exist between the diamond ridges 4C-103. FIG. 4D is a top view of
FIG. 4C. A straight line version of this pattern is also
possible.
[0345] Materials for the inserts include but are not limited to
diamond, cubic boron nitride, corbonitride steels, steel,
carbonitrides, borides, nitrides, silicides, carbides, ceramic
matrix composites, fiber reinforced ceramic matrix composites, cast
iron, carbon and alloy steels, stainless steel, roller bearing
steel, tool steel, hard facing alloys, cobalt based alloys, Ni3Al
alloys, surface treated titanium alloys, cemented carbides,
cermets, ceramics, carbon-graphite based materials, fiber
reinforced thermoplastics, metal matrix composites.
[0346] Materials for the substrate include but are not limited to
corbonitride steels, steel, carbonitrides, borides, nitrides,
silicides, carbides, ceramic matrix composites, fiber reinforced
ceramic matrix composites, cast iron, carbon and alloy steels,
stainless steel, roller bearing steel, tool steel, hard facing
alloys, cobalt based alloys, Ni3Al alloys, surface treated titanium
alloys, cemented carbides, cermets, ceramics, carbon-graphite based
materials, fiber reinforced thermoplastics, metal matrix
composites.
[0347] The substrate may be configured such as to place the insert
material into a compressive state sufficient to impart structural
stability to the insert material that heretofore was not present.
The insert material is put into a compressive state by the use of
an interference fit with the surrounding substrate material. By
placing the insert material in this compressive condition the
neutral stress axis in the insert material is displaced in such a
fashion that the bearing material is now capable of sustaining
higher loading while maintaining its structural integrity in
combination with its superior wear properties. This allows for the
use of materials that have very desirable wear properties but
insufficient structural capacity to now be configured in such a
manner as to make them candidates for wear bearings that heretofore
not available for use. The substrate material may be machined or
cast with the desired geometry for the bearing material. The
substrate material is then heated to a pre-determined temperature
and the wear bearing inserts are cooled to a pre-determined
temperature and then the wear bearing insert is pressed into the
substrate. The difference in size of the materials results in the
wear bearing material being in a compressive state.
[0348] FIGS. 4E and 4E-1 depict a spherical structure 4E109 with a
continuous superhard surface. The structure 4E109 depicted may be a
polycrystalline diamond compact that includes a surface volume of
diamond 4E9 on a substrate 4E10. This embodiment includes a
continuous surface layer of diamond, although the diamond surface
may be discontinuous as well.
[0349] FIGS. 4F and 4F1 depict a segmented ball 4F110 with
superhard inserts 4F11 on the surface 4F12 to form a discontinuous
superhard surface. The inserts 4F11 may be located on the substrate
material with great precision and accuracy. The surface of the ball
may be divided into areas of diamond or other superhard material
separate by veins of substrate material. Fabrication of balls with
this vein and patch structure (such as a polyhedral or round
segmented surface) offer some advantages to the manufacturing
process for certain substrate metals as well as provide some
advantages in high impact situations. Each bearing segment of
diamond or superhard material independently accomodate transient
deformations under peak load without resulting in fracture of the
segments of diamond or superhard material.
[0350] FIGS. 4G and 4G1 depict a cross-sectional view of a ball
4G111 with plugs 4G 14. The plugs 4G 14 may be a polycrystalline
diamond compact having a surface of polycrystalline diamond or
other superhard material. The plugs 4G14 may be fixed securely into
receptacles on spherical substrate ball 4G 15 or other desired
structure, or they may be formed as a compact with the substrate.
The plugs or segments may be fashioned as polycrystalline diamond
compacts or other superhard material. Each plug may be a continuous
phase of superhard material, or a compact formed from a bearing
surface of superhard material on a substrate, such as a
polycrystalline diamond compact. The plugs may be bonded, welded,
or mechanically fastened to the substrate structure, preferably in
an appropriate receptacle, leaving a superhard bearing surface
exposed. High quality curvilinear and spherical surface finishes
that are obtained by terminal finishing processes described later
in this document. This approach to segmented bearing surfaces
permits the fabrication of extremely large spherical and or
curvilinear bearing surfaces not possible with continuous bearing
surfaces. Size limitations in the manufacturing of polycrystalline
diamond compact elements might otherwise prevent manufacture of
such large elements.
[0351] FIGS. 4H and 4H1 depict a ball 4H112 constructed of solid or
continuous phase polycrystalline diamond or other superhard
material. This ball 4H112 is made of solid diamond or superhard
material without a separate substrate. The ball 4H112 has a
continuous phase of diamond throughout its interior. Embodiments of
such a continuous phase bearing element may be made from
polycrystalline diamond, polycrystalline cubic boron nitride, or
other superhard material. This structure has certain advantages
from a chemical electromagnetic and structural standpoint.
[0352] FIGS. 4I and 4I1 depict a ball 4I113 with strips, veins or a
discontinuous pattern of diamond 4I17 or another superhard material
located on a substrate 4I18. The diamond on the ball 4I113 surface
may be in a regular or irregular discontinuous pattern in any
desired geometry, such a concentric circles, spirals, latitudinal
or longitudinal lines or otherwise. This structure possesses some
of the advantages common to the segmented bearing surface described
above.
[0353] Finishing Methods and Apparatuses.
[0354] Once a PDC has been sintered, a mechanical finishing process
may be employed to prepare the final product. The finishing steps
explained below are described with respect to finishing a PDC, but
they could be used to finish any other surface or any other type of
component.
[0355] The synthetic diamond industry was faced with the problem of
finishing flat surfaces and thin edges of diamond compacts. Methods
for removal of large amounts of diamond from non-planar surfaces or
finishing those surfaces to high degrees of accuracy for
sphericity, size and surface finish had not been developed in the
prior art.
[0356] Finishing of Superhard Cylindrical and Flat Forms.
[0357] In order to provide a greater perspective on finishing
techniques for curved and non-planar superhard surfaces for modular
bearing inserts and joints, a description of other finishing
techniques is provided.
[0358] Lapping.
[0359] A wet slurry of diamond grit on cast iron or copper rotating
plates are used to remove material on larger flat surfaces (e.g.,
up to about 70 mm. in diameter). End coated cylinders of size
ranging from about 3 mm to about 70 mm may also be lapped to create
flat surfaces. Lapping is generally slow and not dimensionally
controllable for depth and layer thickness, although flatness and
surface finishes can be held to very close tolerances.
[0360] Grinding.
[0361] Diamond impregnated grinding wheels are used to shape
cylindrical and flat surfaces. Grinding wheels are usually resin
bonded in a variety of different shapes depending on the type of
material removal required (i.e., cylindrical centerless grinding or
edge grinding). PDCs are difficult to grind, and large PDC surfaces
are nearly impossible to grind. Consequently, it is desirable to
keep grinding to a minimum, and grinding is usually confined to a
narrow edge or perimeter or to the sharpening of a sized PDC
end-coated cylinder or machine tool insert.
[0362] Electro Spark Discharge Grinding (EDG).
[0363] Rough machining of PDC may be accomplished with electro
spark discharge grinding ("EDG") on large diameter (e.g., up to
about 70 mm.) flat surfaces. This technology typically involves the
use of a rotating carbon wheel with a positive electrical current
running against a PDC flat surface with a negative electrical
potential. The automatic controls of the EDG machine maintain
proper electrical erosion of the PDC material by controlling
variables such as spark frequency, voltage and others. EDG is
typically a more efficient method for removing larger volumes of
diamond than lapping or grinding. After EDG, the surface must be
finish lapped or ground to remove what is referred to as the heat
affected area or re-cast layer left by EDG.
[0364] Wire Electrical Discharge Machining (WEDM).
[0365] WEDM is used to cut superhard parts of various shapes and
sizes from larger cylinders or flat pieces. Typically, cutting tips
and inserts for machine tools and re-shaping cutters for oil well
drilling bits represent the greatest use for WEDM in PDC
finishing.
[0366] Polishing
[0367] Polishing superhard surfaces for modular bearing inserts and
joints to very high tolerances may be accomplished by diamond
impregnated high speed polishing machines. The combination of high
speed and high friction temperatures tends to burnish a PDC surface
finished by this method, while maintaining high degrees of
flatness, thereby producing a mirror-like appearance with precise
dimensional accuracy.
[0368] Finishing A Non-Planar Geometry.
[0369] Finishing a non-planar surface (concave non-planar or convex
non-planar) presents a greater problem than finishing a flat
surface or the rounded edge of a cylinder. The total surface area
of a sphere to be finished compared to the total surface area of a
round end of a cylinder of like radius is four (4) times greater,
resulting in the need to remove four (4) times the amount of PDC
material. The nature of a non-planar surface makes traditional
processing techniques such as lapping, grinding and others unusable
because they are adapted to flat and cylindrical surfaces. The
contact point on a sphere should be a point contact that is
tangential to the edge of the sphere, resulting in a smaller amount
of material removed per unit of time, and a proportional increase
in finishing time required. Also, the design and types of
processing equipment and tooling required for finishing non-planar
objects must be more accurate and must function to closer
tolerances than those for other shapes. Non-planar finishing
equipment also requires greater degrees of adjustment for
positioning the work piece and tool ingress and egress.
[0370] The following are steps that may be performed in order to
finish a non-planar, rounded or arcuate surface.
[0371] 1.) Rough Machining.
[0372] Initially rough out the dimensions of the surface using a
specialized electrical discharge machining apparatus may be
performed. FIG. 38 depicts roughing a PDC sphere 3803. A rotator
3802 is provided that is continuously rotatable about its
longitudinal axis (the z axis depicted). The sphere 3803 to be
roughed is attached to a spindle of the rotator 3802. An electrode
3801 is provided with a contact end 3801a that is shaped to
accommodate the part to be roughed. In this case the contact end
3801a has a partially non-planar shape. The electrode 3801 is
rotated continuously about its longitudinal axis (the y axis
depicted). Angular orientation of the longitudinal axis y of the
electrode 3801 with respect to the longitudinal axis z of the
rotator 3802 at a desired angle .beta. is adjusted to cause the
electrode 3801 to remove material from the entire non-planar
surface of the ball 3803 as desired.
[0373] Thus, the electrode 3801 and the sphere 3803 are rotating
about different axes. Adjustment of the axes can be used to achieve
near perfect non-planar movement of the part to be roughed.
Consequently, a nearly perfect non-planar part results from this
process. This method produces PDC non-planar surfaces with a high
degree of sphericity and cut to very close tolerances. By
controlling the amount of current introduced to the erosion
process, the depth and amount of the heat affected zone can be
minimized. In the case of a PDC, the heat affected zone can be kept
to about 3 to 5 microns in depth and is easily removed by grinding
and polishing with diamond impregnated grinding and polishing
wheels.
[0374] Referring to FIG. 39, roughing a convex non-planar PDC 3903
such as an acetablular cup is depicted. A rotator 3902 is provided
that is continuously rotatable about its longitudinal axis (the z
axis depicted). The part 3903 to be roughed is attached to a
spindle of the rotator. An electrode 3901 is provided with a
contact end 3901a that is shaped to accommodate the part to be
roughed. The electrode 3901 is continuously rotatable about its
longitudinal axis (the y axis depicted). Angular orientation of the
longitudinal axis y of the electrode 3901 with respect to the
longitudinal axis z of the rotator 3902 at a desired angle .beta.
is adjusted to cause the electrode 3901 to remove material from the
entire non-planar surface of the cup 3903 as desired.
[0375] In some embodiments, multiple electro discharge machine
electrodes will be used in succession in order to machine a part. A
battery of electro discharge machines may be employed to carry this
out in assembly line fashion. Further refinements to machining
processes and apparatuses are described below.
[0376] Complex positive or negative relief (concave or convex)
forms can be machined into PDC or PCBN parts. This is a standard
Electrical Discharge Machining (EDM) CNC machining center and
suitably machined electrodes accomplish the desired forms.
[0377] FIG. 40 (side view) and FIG. 40a (end view) show an
electrode 4001 with a convex form 4002 machined on the active end
of the electrode 4001, and the electrode base 4005. FIG. 41 (cross
section at 41-41) and FIG. 41a show an electrode 4101 with a
concave form 4102 and base 4105. The opposite ends of the
electrodes are provided with an attachment mechanism at the base
4105 suitable for the particular EDM machine being utilized. There
are a variety of electrode materials that can be utilized such a
copper, copper tungsten, graphite, and combinations of graphite and
metal mixes. Materials best suited for machining PDC and PCBN are
copper tungsten for roughing and pure graphite, or graphite copper
tungsten mixes. Not all EDM machines are capable of machining PDC
and PCBN. Only those equipped with capacitor discharge power
supplies can generate spark intensities with enough power to
efficiently erode these materials.
[0378] The actual size of the machined relief form is usually
machined undersized to allow for a suitable spark gap for the
burning/erosion process to take place. Each spark gap length
dictates a set of machining parameters that must be set by the
machine operator to ensure efficient electrical discharge erosion
of the material to be removed. Normally, two to four electrodes are
prepared with different spark gap allowances. For example, an
electrode using a 0.006 In. spark gap could be prepared for
"roughing," and an "interim" electrode at 0.002 In. spark gap, and
"finishing" electrode at 0.0005 In. spark gap. In each case the
machining voltage (V), peak amperage (AP), pulse duration (P),
reference frequency (RF), retract duration (R), under-the-cut
duration (U), and servo voltage (SV) must be set up within the
machines control system.
[0379] FIG. 42 shows an EDM relief form 4201 sinking operation in a
PDC insert part 4202. Table 39 describes the settings for using a
copper tungsten electrode 4203 for roughing and a graphite/copper
tungsten electrode for finishing. The spark gap 4204 is also
depicted.
42 TABLE 39 Electrode Spark Gap 4203 4204 V AP P RF Roughing .006
-2 7 13 56 Finishing .001 -5 4 2 60
[0380] Those familiar with the field of EDM will recognize that
variations in the parameters shown will be required based on the
electrode configuration, electrode wear rates desired, and surface
finishes required. Generally, higher machining rates, i.e., higher
values of "V" and "AP" produce higher rates of discharge erosion,
but conversely rougher surface finishes.
[0381] Obtaining very smooth and accurate finishes also requires
the use of a proper dielectric machining fluid. Synthetic
hydrocarbons with satellite electrodes as disclosed in U.S. Pat.
No. 5,773,782, which is hereby incorporated by reference, appear to
assist in obtaining high quality surface finishes.
[0382] FIG. 43 shows an embodiment wherein a single ball-nosed
(spherical radiused) EDM electrode 4301 is used to form a concave
relief form 4303 in a PDC or PCBN part 4302. The electrode 4301 is
plunged vertically into the part 4302 and then moved laterally to
accomplish the rest of the desired shape. By programming a CNC
system EDM electrode "cutting path" of the EDM machine, an infinite
variety of concave or convex shapes can be machined. Controlling
the rate of "down" plunging and "lateral" cross cutting, and using
the correct EDM material will dictate the quality of the size
dimensions and surface finishes obtained.
[0383] 2.) Finish Grinding and Polishing.
[0384] Once the non-planar surface (whether concave or convex) has
been rough machined as described above or by other methods, finish
grinding and polishing of a part can take place. Grinding is
intended to remove the heat affected zone in the PDC material left
behind by electrodes.
[0385] In some embodiments of the devices, grinding utilizes a grit
size ranging from 100 to 150 according to standard ANSI B74.16-1971
and polishing utilizes a grit size ranging from 240 to 1500,
although grit size may be selected according to the user's
preference. Wheel speed for grinding should be adjusted by the user
to achieve a favorable material removal rate, depending on grit
size and the material being ground. A small amount of
experimentation can be used to determine appropriate wheel speed
for grinding. Once the spherical surface (whether concave or
convex) has been rough machined as described above or by other
methods, finish grinding and polishing of a part can take place.
Grinding is intended to remove the heat affected zone in the PDC
material left behind by electrodes. Use of the same rotational
geometry as depicted in FIGS. 38 and 39 allows sphericity of the
part to be maintained while improving its surface finish
characteristics.
[0386] Referring to FIG. 44, it can be seen that a rotator 4401
holds a part to be finished 4403, in this case a convex sphere, by
use of a spindle. The rotator 4401 is rotated continuously about
its longitudinal axis (the z axis). A grinding or polishing wheel
4402 is rotated continuously about its longitudinal axis (the x
axis). The moving part 4403 is contacted with the moving grinding
or polishing wheel 4402. The angular orientation 1 of the rotator
4401 with respect to the grinding or polishing wheel 4402 may be
adjusted and oscillated to effect grinding or polishing of the part
(ball or socket) across its entire surface and to maintain
sphericity.
[0387] Referring to FIG. 45, it can be seen that a rotator 4501
holds a part to be finished 4503, in this case a convex non-planar
cup, by use of a spindle. The rotator 4501 is rotated continuously
about its longitudinal axis (the z axis). A grinding or polishing
wheel 4502 is provided that is continuously rotatable about its
longitudinal axis (the x axis). The moving part 4503 is contacted
with the moving grinding or polishing wheel 4502. The angular
orientation .beta. of the rotator 4501 with respect to the grinding
or polishing wheel 4502 may be adjusted and oscillated if required
to effect grinding or polishing of the part across the non-planar
portion of it surface.
[0388] In one embodiment, grinding utilizes a grit size ranging
from 100 to 150 according to standard ANSI B74.16-1971 and
polishing utilizes a grit size ranging from 240 to 1500, although
grit size may be selected according to the user's preference. Wheel
speed for grinding should be adjusted by the user to achieve a
favorable material removal rate, depending on grit size and the
material being ground. A small amount of experimentation can be
used to determine appropriate wheel speed for grinding.
[0389] As desired, a diamond abrasive hollow grill may be used for
polishing diamond or superhard surfaces. A diamond abrasive hollow
grill includes a hollow tube with a diamond matrix of metal,
ceramic and resin (polymer).
[0390] If a diamond surface is being polished, then the wheel speed
for polishing will be adjusted to cause a temperature increase or
heat buildup on the diamond surface. This heat buildup will cause
burnishing of the diamond crystals to create a very smooth and
mirror-like low friction surface. Actual material removal during
polishing of diamond is not as important as removal of sub-micron
sized asperities in the surface by a high temperature burnishing
action of diamond particles rubbing against each other. A surface
speed of 6000 feet per minute minimum is generally required
together with a high degree of pressure to carry out burnishing.
Surface speeds of 4000 to 10,000 feet per minute are believed to be
the most desirable range. Depending on pressure applied to the
diamond being polished, polishing may be carried out at from about
500 linear feet per minute and 20,000 linear feet per minute.
[0391] Pressure must be applied to the work piece to raise the
temperature of the part being polished and thus to achieve the most
desired mirror-like polish, but temperature should not be increased
to the point that it causes complete degradation of the resin bond
that holds the diamond polishing wheel matrix together, or resin
will be deposited on the diamond. Excessive heat will also
unnecessarily degrade the surface of the diamond.
[0392] Maintaining a constant flow of coolant (such as water)
across the diamond surface being polished, maintaining an
appropriate wheel speed such as 6000 linear feet per minute,
applying sufficient pressure against the diamond to cause heat
buildup but not so much as to degrade the wheel or damage the
diamond, and timing the polishing appropriately are all important
and must all be determined and adjusted according to the particular
equipment being used and the particular part being polished.
Generally the surface temperature of the diamond being polished
should not be permitted to rise above 800 degrees Celsius or
excessive degradation of the diamond will occur. Desirable surface
finishing of the diamond, called burnishing, generally occurs
between 650 and 750 degrees Celsius.
[0393] During polishing it is important to achieve a surface finish
that has the lowest possible coefficient of friction, thereby
providing a low friction and long-lasting surface. Once a diamond
or other superhard surface is formed in modular bearing inserts and
joints, the surface may then be polished to an Ra value of 0.3 to
0.005 microns. Acceptable polishing will include an Ra value in the
range of 0.5 to 0.005 microns or less. The parts of the modular
bearing inserts and joints may be polished individually before
assembly or as a unit after assembly. Other methods of polishing
PDCs and other superhard materials may be adapted to work with the
invented modular bearing inserts and joints, with the objective
being to achieve a smooth surface, with an Ra value of 0.01-0.005
microns. Further grinding and polishing details are provided
below.
[0394] FIG. 46 shows a diamond grinding form 4601 mounted to an
arbor 4602, which is in turn mounted into the high-speed spindle
4603 of a CNC grinding machine. The cutting path motion 4604 of the
grinding form 4601 is controlled by the CNC program allowing the
necessary surface coverage requiring grinding or polishing. The
spindle speed is generally related to the diameter of the grinding
form and the surface speed desired at the interface with the
material 4605 to be removed. The surface speed should range between
4,000 and 17,000 feet per minute for both grinding and polishing.
For grinding, the basic grinding media for the grinding form should
be as "free cutting" as practical with diamond grit sizes in the
range of 80 to 120 microns and concentrations ranging from 75 to
125. For polishing the grinding media should not be as "free
cutting," i.e., the grinding form should generally be harder and
denser with grit sizes ranging from 120 to 300 microns and
concentrations ranging from 100 to 150.
[0395] Superhard materials can be more readily removed by grinding
if the actual area of the material being removed is kept as small
as possible. Ideally the bruiting form 4601 should be rotated to
create conditions in the range from 20,000 to 40,000 surface feet
per minute between the part 4605 and the bruiting form 4601.
Spindle pressure between the part 4605 and the bruiting form 4601
operating in a range of 10 to 100 Lbs--force producing an interface
temperature between 650 and 750 degrees Celsius is required.
Cooling water is needed to take away excess heat to keep the part
from possibly failing. The simplest way to keep the grind area
small is to utilize a small cylindrical contact point (usually a
ball form, although a radiused end of a cylinder accomplishes the
same purpose), operating against a larger surface area.
[0396] FIG. 47 shows the tangential area of contact 4620 between
the grinding form 4601 and the substantially larger superhard
material 4621. By controlling the path of the grinding form cutter,
small grooves 4630 (FIG. 48) can be ground into the surface of the
superhard material 4621 removing the material and leaving small
"cusps" 4640 between the adjacent grooves. As the grooves are cut
shallower and closer together the "cusps" 4640 become imperceptible
to the naked eye and are easily removed by subsequent polishing
operations. The cutter line path of the grinding form cutter should
be controlled by programming the CNC system of the grinding machine
to optimize the cusp size, grinding form cutter wear, and material
removal rates.
[0397] Bruiting.
[0398] Obtaining highly polished surface finishes on PDC, PBCN, and
other superhard materials in the range of 0.05 to 0.005 .mu.m can
be obtained by running a PDC form against the surface to be
polished. "Bruiting" or rubbing a diamond surface under high
pressure and temperature against another superhard material
degredates or burns away any positive asperities remaining from
previous grinding and polishing operations producing a surface
finish not obtainable in any other way.
[0399] FIG. 49 shows a PDC dome part 4901 on a holder 4904 and
being "Bruit Polished" using a PDC bruiting form 4902 being rotated
in a high-speed spindle 4903. Ideally the bruiting form should be
rotated in a range from 20,000 to 40,000 surface feet per minute
with the spindle pressure operating in a range of 10 to 100
Lbs--force producing an interface temperature between 650 and 750
degrees Celsius. Angle .alpha. 4905 represents the angular
orientation of the longitudinal axis of the spindle 4903 with
respect to the central axis of the part 4901. Cooling water is
generally required to take away excess heat to keep the part from
failing.
[0400] FIG. 50 shows another embodiment of the bruiting polishing
technique wherein the PDC bruiting form 5001 is controlled through
a complex surface path 5002 by a CNC system of a grinding machine
or a CNC Mill equipped with a high-speed spindle to control the
point of contact 5003 of the form 5001 with a superhard component
5004.
[0401] Use of Cobalt Chrome Molybdenum (CoCrMo) Alloys to Augment
Biocompatibility in PDCS.
[0402] Cobalt and Nickel may be used as catalyst metals for
sintering diamond powder to produce sintered PDCs. The toxicity of
both Co and Ni is well documented; however, use of CoCr alloys
which contain Co and Ni have outstanding corrosion resistance and
avoid passing on the toxic effects of Co or Ni alone. Use of CoCrMo
alloy as a solvent-catalyst metal in the making of sintered PDCs
yields a biocompatible and corrosion resistant material. Such
alloys may be defined as any suitable biocompatible combination of
the following metals: Co, Cr, Ni, Mo, Ti and W. Examples include
ASTM F-75, F-799 and F-90. Each of these will serve as a
solvent-catalyst metal when sintering diamond. Elemental analysis
of the interstitial metal in PDC made with these alloys has shown
that the composition is substantially more corrosion resistant than
PDC made with Co or Ni alone. Interstitial metal in PDC made with
these metals is substantially more corrosion resistant than PDC
made with Co or Ni is and is therefore well suited for medical
applications.
[0403] Carbides as Substrate Materials
[0404] Following known procedures for the production of carbides,
both Ti/TiC (Ti cemented TiC) and Nb/TiC (Nb cemented TiC) can be
manufactured for use as substrate materials in prosthetic joints
(such as femoral heads of prosthetic hip joints) and components
thereof. Ti (or Nb) is mixed with TiC powder and formed into a ball
enclosed by an Nb can. The materials are then formed into a solid
hipping (hot isostatic pressing) in a high pressure press. The
result is either Ti cemented TiC or Nb cemented TiC, producing a
biocompatabile product. The same result could also be achieved by
sintering the Ti (or Nb)+TiC using known sintering procedures such
as those used in the carbide industry. Ti, Nb and TiC have
biocompatible materials and therefore can be used for biomedical
applications such as spinal and hip implants among others.
[0405] Carbide and metal micron powders are added together in a
container with wax and acetone or other appropriate solvent along
with carbide mixing balls. The materials are then milled in an
attritor mill for examples for an appropriate period of time to
thoroughly mix all components and to reduce the material to the
target grain size (the process is controlled to obtain a specific
grain size). After milling the solvent is evaporated off and the
resulting powder is then pressed in a compaction press to the
desired shape. The individual parts are then placed in a furnace
and slowly heated to burn off the wax. Too rapid a wax removal will
cause the parts to have excessive porosity or cause them to
catastrophically fall apart. After removal of the wax, the parts
are then taken up to the sintering temperature and held until
sintering is complete. To minimize or completely eliminate open
porosity, the parts may be hipped in a standard hipping furnace in
which the parts are pressurized to .about.30,000 psi. A more
extreme hipping process is also available called rapid
omnidirectional compaction (ROC). In this process the parts are
rapped in grafoil or graphite paper and placed in a pressure
container with glass powder. The contents are then taken to 125,000
psi and the target temperature where the glass powder melts at
which time it uniformly applies pressure to the part, thus
essentially reducing the porosity to zero.
[0406] The actual temperature for sintering carbides is determined
by the system that one is working in. For tungsten carbide the
temperature is approximately 1200.degree. C. A typical hipping
pressure is 30,000 psi whereas in the ROC process it is
.about.125,000 psi. The target temperature and pressure are
approached slowly over several hours. When the target conditions
are attained they are held for only minutes before the pressure and
temperature are slowly decreased to room temperature and
pressure.
[0407] Material formulations for carbides is determined by the
ultimate use of the material. If toughness is the desired property
then the metal content of the carbide will range upwards of 13 to
>20 weight %. If wear resistance or a low thermal expansion are
the desired properties then the metal content of the carbide will
be <13 weight %.
[0408] Use of Ti and Nb Cemented TiC for use in Prosthetic
Joints
[0409] A sintering and/or hipping process can be used to create Ti
or Nb cemented TiC balls. The balls are then placed in an Nb can
with diamond between the can and the ball. The filled can is then
placed in a high pressure/high temperature press and the diamond is
sintered to the ball. Ti and Nb are useful in this ball production
process because diamond will chemically bond with TiC grains during
the sintering process in a structure that is similar to the
crystalline structure of diamond. The diamond will also chemically
bond to the Ti and Nb because both are good carbide forming
elements. The chemical bonding will increase the adhesion of the
diamond to the substrate (ball core) and prevent the diamond from
delaminating during use. Ti and Nb are used in conjunction with TiC
because their dilatation during the sintering process exceeds that
of their coefficient of thermal expansion (CTE), consequently a
strong ball that does not suffer fracture from residual stress is
produced. The balance between the material properties of the
diamond layer and the core ball or substrate is accomplished by
calculating the volumetric thermal expansion of all components
(=3*CTE*.DELTA.T, where .DELTA.T is the temperature difference
between room temperature and the sintering temperature). Similarly
the volumetric dilatation must be calculated for all components
using the following equation, (-3*p*(1-.nu.))/E; where p is the
sintering pressure, .nu. is Poisson's ratio and E is the elastic
modulus. The CTE and the dilatation are then added together for
each component. The resulting values for each of the components in
the diamond layer are then multiplied by their respective
volumetric ratio in the diamond layer (the volumetric ratio of
diamond to metal is fixed). These two numbers, one for the diamond
and one for the metal, when added together is the total volumetric
change that will occur on coming down from high
pressure/temperature to room temperature for the diamond table. The
is the volumetric change that must be matched by the core. To find
this volume, multiply the combined CTE/dilatation for each of the
two components in the core, Ti and TiC, for example by various
ratios (must add to 1) until the result equals the volumetric
change of the diamond layer. Only the change occurring from high
temperature/pressure to room temperature/pressure is considered
because at the sintering conditions the diamond will sinter around
the once it has fully expanded and dilitated. Thus there will be no
residual stress between them at the sintering conditions. By
balancing the volumetric changes between the core and the diamond
layer, they will both undergo the same volumetric changes on
cooling and depressurization resulting in little or no residual
stress at room temperature/pressure conditions.
[0410] Superhard Ball End Mill Cutter
[0411] Referring to FIGS. 51A-51D, a ball end mill cutter 51A100
may be fabricated using the substrates and materials discussed
herein. For example, a tungsten carbide ball substrate 51A101 may
be sintered into a polysrystalline diamond or polysrystalline cubic
boron nitride compact with a diamond or CBN table 51A102. As an
example, the diamond of CBN table may be 0.050" thick. The compact
may be made from appropriate diamond or CBN feedstock, such as
diamond feedstock in the size range of 0 to 70 .mu.m using
processes described elsewhere herein. The ball 51A103 is then
ground and finished to a final diameter 51A104. It may then be
bored such as by electro discharge machining, to accept an arbor
shank 51A105. The arbor shank may be brazed, bonded, shrink fitted
or otherwise affixed to the bore 51A106. Flutes 51A107 are cut into
the ball, such as by EDM wire machining, grinding or another
appropriate process. This exposes cutting edges 51A108 which cut or
remove material from a workpiece that the ball end mill cutter is
applied to. The cutting edges 51A108 may be enhanced by creating
(such as by grinding) a cutting relief 51A109 back from the cutting
edges to bite or cut more easily into the workpiece that the ball
end mill cutter is used on. The ball end mill cutter may be formed
generally in the shape of a sphere or into any other desired
geometry.
[0412] While the present devices, components thereof, materials
therefore, and manufacturing methods have been described and
illustrated in conjunction with a number of specific
configurations, those skilled in the art will appreciate that
variations and modifications may be made without departing from the
principles herein illustrated, described, and claimed. The present
invention, as defined by the appended claims, may be embodied in
other specific forms without departing from its spirit or essential
characteristics. The configurations described herein are to be
considered in all respects as only illustrative, and not
restrictive. All changes which come within the meaning and range of
equivalency of the claims are to be embraced within their
scope.
* * * * *