U.S. patent application number 15/017992 was filed with the patent office on 2016-06-09 for cutting tool insert.
The applicant listed for this patent is Iain Patrick GOUDEMOND, John Hewitt LIVERSAGE, Danny Eugene SCOTT. Invention is credited to Iain Patrick GOUDEMOND, John Hewitt LIVERSAGE, Danny Eugene SCOTT.
Application Number | 20160159693 15/017992 |
Document ID | / |
Family ID | 40791236 |
Filed Date | 2016-06-09 |
United States Patent
Application |
20160159693 |
Kind Code |
A1 |
LIVERSAGE; John Hewitt ; et
al. |
June 9, 2016 |
CUTTING TOOL INSERT
Abstract
A polycrystalline diamond (PCD) compact and method for making
the compact are provided. The method includes bringing a first PCD
wafer and a second PCD wafer together at an interface in the
presence of a bonding agent to form an unbonded assembly and
bonding the wafers together at the interface at a pressure and
temperature at which diamond is thermodynamically stable. The first
PCD wafer is more thermally stable than the second PCD wafer.
Inventors: |
LIVERSAGE; John Hewitt;
(Springs, ZA) ; GOUDEMOND; Iain Patrick; (Springs,
ZA) ; SCOTT; Danny Eugene; (Montgomery, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LIVERSAGE; John Hewitt
GOUDEMOND; Iain Patrick
SCOTT; Danny Eugene |
Springs
Springs
Montgomery |
TX |
ZA
ZA
US |
|
|
Family ID: |
40791236 |
Appl. No.: |
15/017992 |
Filed: |
February 8, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12668308 |
Mar 26, 2010 |
9255312 |
|
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PCT/IB2009/051479 |
Apr 8, 2009 |
|
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15017992 |
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Current U.S.
Class: |
428/408 |
Current CPC
Class: |
C04B 2235/427 20130101;
C22C 26/00 20130101; C22C 2204/00 20130101; C04B 37/021 20130101;
C04B 35/52 20130101; Y10T 428/30 20150115; C04B 2237/16 20130101;
C04B 2237/365 20130101; C04B 35/645 20130101; Y10T 156/10 20150115;
B01J 3/065 20130101; C04B 2237/704 20130101; C04B 37/026 20130101;
B01J 2203/0655 20130101; C04B 35/528 20130101; C04B 2237/122
20130101; C04B 2237/123 20130101; C04B 2237/083 20130101; B22F
7/062 20130101; B32B 18/00 20130101; C04B 2237/363 20130101; C04B
35/573 20130101 |
International
Class: |
C04B 35/528 20060101
C04B035/528; B32B 18/00 20060101 B32B018/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 8, 2008 |
ZA |
2008/03078 |
Claims
1. A polycrystalline diamond compact comprising a first layer of
polycrystalline diamond bonded to a second layer polycrystalline
diamond, the first layer of polycrystalline diamond being more
thermally stable and thinner than the second layer of
polycrystalline diamond.
2. A polycrystalline diamond compact according to claim 1 wherein
the first layer of polycrystalline diamond is thermally stable
polycrystalline diamond.
3. A polycrystalline diamond compact according to claim 1 wherein
the second layer of polycrystalline diamond contains a bonding
phase comprising a solvent/catalyst.
4. A polycrystalline diamond compact according to claim 2 wherein
the second layer of polycrystalline diamond contains a bonding
phase comprising a solvent/catalyst.
5. A polycrystalline diamond compact according to claim 1 wherein
the bonding between the two layers is direct diamond-to-diamond
bonding.
6. A polycrystalline diamond compact according to claim 2 wherein
the bonding between the two layers is direct diamond-to-diamond
bonding.
7. A polycrystalline diamond compact according to claim 4 wherein
the bonding between the two layers is direct diamond-to-diamond
bonding.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a division of U.S. patent application
Ser. No. 12/668,308 filed Mar. 26, 2010 which is a 35 U.S.C.
.sctn.371 of PCT/IB2009/051479 filed on Apr. 8, 2009, published on
Oct. 15, 2009 under publication number WO 2009/125355 A and which
claims the benefit of priority under 35 U.S.C. .sctn.119 of South
African Patent Application No. 2008/03078 filed Apr. 8, 2008, the
disclosures of which are incorporated herein by reference in their
entirety.
BACKGROUND OF THE INVENTION
[0002] THIS invention relates to polycrystalline diamond compacts
and more particularly to a method of manufacturing polycrystalline
diamond compacts.
[0003] A commonly used cutting tool insert for drill bits is one
which comprises a layer of polycrystalline diamond (PCD) bonded to
a cemented carbide substrate. The layer of PCD presents a working
face and a cutting edge around a portion of the periphery of the
working surface. Polycrystalline diamond comprises a mass of
diamond particles containing a substantial amount of direct
diamond-to-diamond bonding.
[0004] U.S. Pat. No. 4,224,380 discloses a compact consisting
essentially of self-bonded abrasive particles with an
interconnected network of pores dispersed throughout. The compact
is produced by bonding a mass of abrasive particles into a
self-bonded body through the use of a sintering aid material under
high pressures and temperatures (HP/HT). The body formed at HP/HT
includes the self-bonded particles with the sintering aid material
(e.g., cobalt or cobalt alloys) infiltrated throughout the body.
The infiltrant is then removed, for example, by immersion of the
body in an aqua regia bath. It has been discovered that the removal
of substantially all of the infiltrant provides an abrasive
particles compact which has substantially improved resistance to
thermal degradation at high temperatures.
[0005] U.S. Pat. No. 4,944,772 discloses a process for fabricating
a supported polycrystalline diamond or CBN compact in general,
though such process is especially adapted to the fabrication of a
thermally-supported polycrystalline diamond or CBN compact. The
process comprises forming a sintered polycrystalline diamond or CBN
compact having a surface and separately forming a cemented carbide
support having a support surface. The compact and support then are
mated at their respective surfaces with a layer of diamond or CBN
crystals having the largest dimension of between about 30 and 500
micrometers interposed between said surfaces. Also, a source of
diamond or CBN catalyst/sintering aid material is associated with
the layer of diamond or CBN crystals. The mated compact and support
then are subjected to HP/HT conditions and for a time adequate for
converting said diamond or CBN crystals into a polycrystalline
diamond or CBN compact and for producing a supported
polycrystalline compact of at least two polycrystalline layers
(i.e. bi-layer compact). Preferably, thermally-stable compacts are
used in the process.
[0006] U.S. Pat. No. 5,127,923 discloses a highly consolidated
abrasive compact which has enhanced particle-to-particle bonding,
increased density and improved thermal stability performance
characteristics and which can be bonded directly to a supporting
substrate. The compact is produced by subjecting a mass of abrasive
particles, e.g., diamond or cubic born nitride, to multiple
pressure cycles at high temperatures. A solvent-catalyst sintering
aid is employed in the initial pressure cycle. The compact then
possesses residual interconnected porosity in the particle mass
which is filled with the solvent-catalyst. Depending upon the
degree of sintering, the solvent-catalyst can be removed by
leaching or other suitable process. The removal of the
solvent-catalyst permits further consolidation and sintering of the
particle mass in subsequent pressure cycles. During the final
pressure cycle, the abrasive mass can be bonded to a supporting
substrate. In addition, a non-catalyst sintering aid, such as
silicon, boron or metals rendered non-catalytic by the addition of
silicon or boron which may form strong and chemically-resistant
carbides, can be used in the second pressure cycle to enhance the
sintering process and create a hard abrasive bonding matrix through
out the particle mass.
[0007] Japan patent publication number JP 59-219500 discloses
chemical treatment of a working surface of a PCD element. This
treatment dissolves and removes the catalyst/solvent matrix in an
area immediately adjacent to the working surface. The invention is
claimed to increase the thermal resistance of the PCD material in
the region where the matrix has been removed without compromising
the strength of the sintered diamond.
[0008] U.S. Pat. Nos. 6,544,308 and 6,562,462 disclose a PCD
element having a body with a working surface. A first volume of the
body remote from the working surface contains a catalyzing
material, and a second volume of the body adjacent to the working
surface is substantially free of the catalyzing material.
[0009] There is a need for polycrystalline diamond compacts having
excellent thermal stability in use combined with high strength and
fracture resistance, and a cost-effective method for making
them.
SUMMARY OF THE INVENTION
[0010] According to the invention there is provided a method for
making a polycrystalline diamond (PCD) compact, the method
including providing a first PCD wafer; providing a second PCD
wafer, the first PCD wafer being more thermally stable than the
second PCD wafer, bringing the first and second PCD wafers together
at an interface in the presence of a bonding agent to form an
unbonded assembly; and bonding together the first and second PCD
wafers at the interface at a pressure and temperature at which
diamond is thermodynamically stable.
[0011] Both the first and second PCD wafers are in the form of
pre-formed polycrystalline diamond bodies, produced by methods
known in the art. The polycrystalline diamond compact which is
produced has a layer or region of PCD which is more thermally
stable than a second layer or region of PCD. The layers or regions
are bonded along an interface.
[0012] The first and second PCD wafers have major surfaces on each
of opposite sides thereof and the unbonded assembly is generally
made by bringing together a major surface of one of the wafers and
a major surface of the other wafer. The wafers are discrete and
separate from each other prior to the bonding step.
[0013] Preferably the first PCD wafer is substantially free or
devoid of solvent/catalyst for diamond. More preferably the first
PCD element is at least partly porous.
[0014] The thickness of the first PCD wafer or of each first PCD
wafer, if there is more than one, is preferably in the range from
about 100 to 500 micrometers.
[0015] Preferably the bonding agent comprises a solvent/catalyst
for diamond. More preferably the bonding agent is disposed in
interstices within the second PCD wafer. Alternatively or
additionally, bonding agent may be disposed on or proximate a
surface of first PCD wafer a surface of the second PCD wafer, or
surfaces of both the first and second PCD wafers.
[0016] The bonding agent must be present at the interface between
the first and second PCD wafers at some stage during the step of
bonding together the first and second PCD wafers.
[0017] The bonding agent may be provided in the form of a layer,
and disposed intermediate the first and second PCD wafers. Such
bonding agent may comprise a solvent/catalyst for diamond or a
refractory metal capable of reacting with diamond to form a metal
carbide, such as Mo, Nb, Ti, V, Cr, Zr, Hf, Ta or W.
[0018] The bonding step preferably results in direct
diamond-to-diamond bonding between diamond in the first PCD wafer
and diamond in the second PCD wafer.
[0019] When the first PCD wafer is porous, a thermally stable
material or material that does not readily react with diamond, or a
precursor material capable of reacting with diamond to form such a
material, may be disposed proximate the upper surface of the first,
at least porous PCD wafer within the unbonded assembly, with the
purpose of melting and infiltrating into pores within the first PCD
wafer during the bonding step. If, as is preferred, such material
has lower melting point than solvent/catalyst for diamond, it will
infiltrate the first PCD wafer before solvent/catalyst within the
second PCD wafer melts and thus hinder or prevent the
solvent/catalyst from infiltrating into the first PCD wafer. This
preserves the thermal stability of the first PCD element.
[0020] Preferably the ultra-high pressure is in the range from 3
GPa to 7 GPa, more preferably the ultra-high pressure is in the
range from 3 GPa to 5 GPa.
[0021] Preferably the temperature is at least 900 degrees
centigrade, more preferably the temperature is at least 1,000
degrees centigrade.
[0022] Where the bonding agent comprises solvent/catalyst for
diamond, the temperature is preferably such that the
solvent/catalyst will dissolve diamond proximate or in the region
of the interface and remain substantially solid, i.e. the
solvent/catalyst will not substantially liquefy and infiltrate the
first PCD wafer to any significant extent.
[0023] It is thus possible to use temperatures and pressures lower
than would be required to produce a layer of PCD from a mass of
diamond particles. Substantial savings in the cost of manufacture
can be achieved.
[0024] According to a further aspect of the invention the
polycrystalline diamond compact comprises a polycrystalline diamond
(PCD) table having a working surface and a region of thermally
stable polycrystalline diamond (TSPCD) adjacent the working
surface.
[0025] In one preferred form of the invention, the PCD compact
comprises a PCD table and a region of TSPCD wherein the region
comprises a relatively small region of the entire PCD. Thus, in one
form of the invention the thickness of the first PCD wafer does not
exceed 1200 .mu.m. The first layer typically has a minimum
dimension of approximately 100 .mu.m. This layer may be further
accompanied by an additional region of PCD which is not
thermally-stable i.e. it contains metallic catalyst/solvent
phase.
[0026] The first PCD wafer will typically have a thickness and
dimension such that in the abrasive element is the thermally stable
region contributes no more than 60%, preferably less than 50% and
most preferably less than 40% to the overall height or thickness of
the PCD table.
[0027] The first PCD wafer will typically be made of thermally
stable polycrystalline diamond which may be any known in the art.
The thermally stable polycrystalline diamond will preferably be
porous. The pores of the porous structure will generally be
substantially empty, although the pores may contain a material
which does not compromise the thermal stability of the layer. The
thermally stable polycrystalline diamond may be made by various
methods known in the art. Typically, the method will include a HPHT
sintering step, but other methods such as chemical vapour
deposition may be employed. The first PCD wafer, as produced, will
typically have a maximum dimension of 1.5 mm. In the case of a
sintering step, it may include the use of a carbide substrate to
provide mechanical support and/or an infiltration source. The wafer
is then thinned, typically using mechanical means, to provide a
maximum thickness of between approximately 1200 and 250 .mu.m. The
catalyst/solvent binder is then removed from the wafer using
various known leaching technologies.
[0028] The second PCD wafer is typically made of polycrystalline
diamond comprising a bonding phase containing catalyst/solvent. The
second PCD wafer may be made by methods known in the art. The
catalyst/solvent will typically be cobalt, iron or nickel or an
alloy containing such a metal.
[0029] The diamond content of the PCD, whether first or second PCD
wafer, is preferably greater than 80 volume %.
[0030] The second PCD wafer may be bonded to a cemented carbide
substrate. Alternatively, if the second PCD wafer is free standing,
a body of cemented carbide may be brought into contact with a
surface of the second PCD wafer in the unbonded assembly. Bonding
of the second PCD wafer to the cemented carbide substrate will
occur during the bonding step.
[0031] During the bonding step, the thermally stable nature of the
first PCD wafer can be preserved by using lower temperatures at
which the catalyst/solvent remains essentially solid. Various other
means such as passivation, co-infiltration, or infiltration control
can be used; or if re-infiltration occurs, then the metallic
infiltrant can be removed or altered in a subsequent leaching or
treatment step.
[0032] By "working surface" of the PCD cutting element is meant
that surface which is usefully employed in the operation of the
cutter i.e. this will typically include the top surface as well as
the peripheral edge portion, generally the top surface of the more
thermally stable PCD region.
[0033] In one form of this invention a plurality of discrete layers
or wafers of PCD are bonded to one another, to form the resultant
PCD table which is bonded to a substrate, particularly a cemented
carbide substrate. An infiltrant, which could be a conventional
solvent/catalyst, may be included between some or all of respective
layers or wafers, or the stack of wafers and the substrate, or a
combination of these, to allow for re-infiltration of an
appropriate infiltrant during the synthesis process. In one version
of this form of this invention, the discrete layers of PCD have
generally the same composition, such that the PCD table has
generally the same composition as the individual layers or wafers.
In an alternative form of the invention, the individual PCD layers
or wafers have different compositions to form, for instance, a PCD
table with a composition gradient running through its
thickness.
[0034] An advantage of stacking relatively thin porous, thermally
stable PCD elements rather than providing a single relatively
thicker one arises from the fact that removal of solvent/catalyst
binder from the PCD element is an extremely difficult and
time-consuming step. This step is necessary since PCD elements
typically include solvent/catalyst material within interstices
within the PCD structure as a consequence of the manufacture of
sintered diamond bodies. The thicker the PCD element, the more
time-consuming and costly is the step of solvent/catalyst removal,
which step typically involves treating the element in an acid
liquor for several weeks. In addition, the lower the average size
of the diamond grains within a PCD element, which may be required
for improved wear resistance of the PCD element, the longer the
treatment step takes. The method overcomes this problem by
providing thinner PCD elements, which require much less time to
treat, and stacking them.
[0035] The invention provides, according to yet another aspect of
the invention, a polycrystalline diamond compact comprising a first
layer of polycrystalline diamond bonded to a second layer of
polycrystalline diamond, the first layer of polycrystalline diamond
being more thermally stable and thinner than the second layer of
polycrystalline diamond.
[0036] Preferably the thickness of the first layer of
polycrystalline diamond is in the range 100 to 500 microns.
[0037] The first layer of polycrystalline diamond preferably
comprises thermally stable polycrystalline diamond, as described
above.
[0038] The second layer of polycrystalline diamond is preferably
polycrystalline diamond containing a bonding phase comprising a
diamond solvent/catalyst, as described above.
[0039] Bonding between the two layers of the polycrystalline
diamond compact is preferably direct diamond-to-diamond
bonding.
[0040] A PCD compact according to the invention and as produced by
the method of the invention is suitable for use in tools for
cutting, machining, boring, drilling or degrading bodies comprising
hard or abrasive materials, such as rock, concrete, asphalt,
ceramic, metal, composites or wood. The PCD compact is particularly
suited to applications in which a working edge of the tool reaches
elevated temperatures in use, particularly the drilling or boring
of rock formations, as may be carried out in the oil and gas
drilling industry. The PCD compact is preferably bonded to a
hard-metal substrate, preferably a cobalt-cemented tungsten carbide
substrate, the more thermally stable first PCD layer being disposed
remotely from the substrate, with a second, less thermally stable
PCD layer being disposed intermediate the first PCD layer and the
substrate. The first PCD layer thus provides a relatively thermally
stable working surface and working edge for engaging the body or
workpiece and improving the overall resilience of the compact
against heating in use. The second PCD layer is preferably more
fracture resistant and stronger than the first PCD layer, and thus
provides robust support for it in use. Interstices within the
second PCD layer are preferably at least partly filled with a metal
or metal alloy, more preferably a metal or metal alloy comprising a
solvent/catalyst for diamond.
[0041] An advantage of the method of the invention is that the
properties of the first and second PCD wafers can be separately
pre-determined, since they are both manufactured separately prior
to being combined. This means that they can be combined without
substantial infiltration of material from one PCD wafer into the
other. In particular, if the second PCD wafer contains a
solvent/catalyst for diamond, it would generally be undesirable for
this material to infiltrate into pores within the first PCD wafer,
when such wafer is porous, since the presence of solvent/catalyst
would substantially reduce its thermal stability. The degree to
which solvent/catalyst would liquefy can be controlled by means of
the temperature used during the bonding step. Preferably, the
temperature would be close enough to the melting point of the
solvent/catalyst material for it to have a solvent/catalyst
function locally proximate the bonding interface, but not for
substantial melting to occur and consequently for molten
solvent/catalyst material to infiltrate into pores within the first
PCD wafer. The temperatures used for the bonding step may therefore
be substantially lower than those that are needed to sinter bulk
PCD, a process that typically requires molten solvent/catalyst to
infiltrate from a hard-metal substrate containing solvent/catalyst
material as a binder. Consequently, a lower pressure could be used
during the bonding step while maintaining a condition wherein
diamond is thermodynamically stable, which is necessary in order to
avoid conversion of diamond into graphite in the presence of a
solvent/catalyst for diamond at a high temperature.
[0042] Another advantage of the invention is that the first PCD
wafer may be relatively thin without risk of fracture during the
bonding step. If the second PCD wafer was sintered during the
bonding step rather than in a separate sintering step, the first
PCD wafer would need to be contacted with an agglomerated mass of
diamond particles during the application of pressure, before the
agglomerated mass had sintered to form a strong, inter-grown PCD
support. This could result in the fracture of the first PCD wafer
during the bonding step. By preparing the second PCD wafer prior to
contacting it with the first PCD wafer, this problem is avoided
since both the second PCD wafer functions as a rigid, stiff support
for the first PCD wafer during this step, which is especially
important if the first PCD wafer is relatively thin.
[0043] A further advantage of the invention is that the
pre-sintering of the first and second PCD wafers prior to the
bonding step is believed to reduce the development of internal
stresses within the PCD compact that arise from combining the
sintering and combining steps where the properties, especially the
thermal properties of the first and second PCD wafers are
substantially different.
[0044] A further advantage of the invention is that the filler
material within interstices within the second PCD wafer may be
selected independently from the binder of substrate, since these
components are pre-sintered prior to the bonding step.
[0045] Yet a further advantage of the invention is that the first
PCD wafer may be treated independently from the substrate and the
second PCD wafer to render it thermally stable. This treatment
typically includes a step of immersing the element in acid for an
extended period of time in order to leach out solvent/catalyst
material from within interstices within it. If this step is carried
out once the first PCD element is bonded to the second PCD wafer,
which may be bonded to a hard-metal substrate, the latter
components need to be masked by some means to prevent them from
being attacked by the acid. This masking process is not technically
trivial and limits the types of leaching treatments which can be
employed without causing significant damage to the portions of the
cutter which must be protected. By treating the first PCD wafer
prior to bonding, this problem is avoided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0046] Non-limiting preferred embodiments will now be described in
more detail, by way of example only, with reference to the drawings
FIGS. 1 and 2, which show schematic diagrams of cross sections of
two embodiments of unbonded assemblies.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0047] In a preferred embodiment of the method described with
reference to FIG. 1, an unbonded assembly, 100, comprising a
thermally stable first PCD element (wafer in shape), 110, a less
thermally stable second PCD element (wafer in shape), 120, and a
hard-metal substrate, 130, is provided. The first PCD element is
disposed remote from the substrate, and the second PCD element is
disposed intermediate the first PCD element and the substrate. The
first PCD element is substantially free or devoid of
catalyst/solvent for diamond and the second PCD element contains a
solvent/catalyst for diamond within internal interstices. The PCD
elements and the substrate are contacted and assembled into a
capsule for use in an ultra-high pressure furnace, as is well known
in the art, and the assembly is subjected to a pressure and
temperature at which diamond is thermodynamically stable. In a
version of the embodiment in which the solvent/catalyst is cobalt,
the pressure is about 5.5 GPa and the temperature is about 1,400
degrees centigrade. In another version of the embodiment the
pressure is 4.5 GPa and the temperature is about 1,200 degrees
centigrade.
[0048] In a preferred embodiment of the method described with
reference to FIG. 2, an unbonded assembly, 100, comprising more
than one thermally stable PCD element, 110, each of which is
referred to in this case as a first PCD element, a less thermally
stable second PCD element, 120, and a hard-metal substrate, 130, is
provided. The first PCD elements are disposed proximate each other
and remote from the substrate, and the second PCD element is
disposed intermediate the first PCD elements and the substrate. The
first PCD elements are substantially devoid of catalyst/solvent for
diamond and the second PCD element contains a solvent/catalyst for
diamond within internal interstices. The PCD elements and the
substrate are contacted and assembled into a capsule for use in an
ultra-high pressure furnace, as is well known in the art, and the
assembly is subjected to a pressure and temperature at which
diamond is thermodynamically stable. In a version of the embodiment
in which the solvent/catalyst is cobalt, the pressure is about 5.5
GPa and the temperature is about 1,400 degrees centigrade.
[0049] The drawings do not show additional shims or sources of
infiltrant which may be included in order to facilitate the bonding
of the PCD elements. These may be inserted at interfaces between
elements.
[0050] The PCD elements, 110 and 120, are produced using an
ultra-high pressure and temperature sintering method, in which
unbonded diamonds are sintered together at a pressure typically in
the range from about 5 GPa to about 8 GPa at a temperature
typically in the range from about 1,300 degrees centigrade to about
1,700 degrees centigrade in the presence of a solvent/catalyst for
diamond, or by means of chemical vapour deposition (CVD). Both
methods are well known in the art. The PCD element may be sliced
from a thicker PCD element by means of electro-discharge machining
or a similar method. The element typically has a diameter
consistent with the final desired diameter of the abrasive element.
The thickness of a first PCD element, 110, may be reduced if
necessary by means of lapping or slicing (for example using EDM),
to provide a maximum thickness of approximately 1200 micrometers.
This is the maximum thickness of PCD that is preferred for being
subject to treatment to remove substantially all solvent/catalyst
contained within the element by means of leaching in acid. Various
methods for removing solvent/catalyst are known in the art, the
most common being immersion of the PCD element into an acid bath
for several days or weeks. Other known methods include electrolytic
etching and evaporation techniques.
[0051] In an embodiment in which a second PCD element is bonded to
a cobalt-cemented cemented carbide substrate, the portion of the
second PCD element adjacent the carbide substrate should have a
grain size that is less than 50 micrometers. Several PCD elements
may be stacked such that their respective average diamond particle
sizes are graded relative to one another and to the uppermost first
PCD element, this grading being within the range from about 0.1 to
30 micrometers. Preferably, the intermediate layers have an average
diamond grain size less than 30 microns.
[0052] During the step of bonding together the PCD wafers and the
substrate, solvent/catalyst material that may be present in the
first layer or the substrate may re-infiltrate voids or pores in
the first PCD wafer, when porous. This can have a detrimental
effect on the thermal stability of the working surface layer.
Re-infiltration can be minimised if as low as possible temperature
is used while still achieving direct diamond-to-diamond bonding
between the PCD wafers. There are several other approaches to
controlling or minimising this effect.
[0053] The first approach is to control the progress of the
infiltrant front as it sweeps upwards into the wafer(s) region;
such that it does not significantly contact the uppermost portions
of the first PCD wafer or wafers. This can be achieved by control
of the temperature and pressure over time during the bonding step,
as would be appreciated by the person skilled in the art.
[0054] A second approach is partially to fill pores within in the
first PCD wafer adjacent the working surface to a desired depth
with a passivation compound or material which effectively hinders
or halts the infiltrant front during the reattachment process.
[0055] A third approach is to co-infiltrate the porous first layer,
typically from the top surface, with an alternative molten
infiltrant material during the reattachment or bonding step. A
material that has a lower melting point than infiltrant sourced
from the substrate is preferred in order to fill the pores before
the substrate infiltrant penetrates from below. However, it can be
desirable to achieve simultaneous infiltration from the top and
bottom of the element or elements. For example, using a similar
process to that described in U.S. Pat. No. 5,127,923, the first PCD
layer or layers may be infiltrated with molten silicon or a
silicon-based compound, resulting in the reactive formation of
silicon carbide within pores as the infiltrant comes into contact
with the diamond network. Other molten infiltrants which are
suitable include metals such as aluminium, magnesium, lead and
other similar metals or alloys containing these metals.
Example 1
[0056] A free-standing first PCD disc comprising bonded diamond
grains having a multimodal size distribution and an average grain
size of about 12 micrometers was prepared by conventional means
using ultra-high pressure and temperature and infiltrated cobalt as
solvent/catalyst sintering aid. The PCD disc was sintered in
contact with a cobalt-cemented tungsten carbide substrate, which
provided the source of cobalt for sintering the PCD and to which
the PCD became integrally bonded during the sintering step. The
substrate was removed by grinding it away, leaving a free-standing
PCD disc. The disc was 17.4 millimetres in diameter and had a
height of about 400 micrometers. The disc was immersed in a mixture
of hydrofluoric and nitric acid for more than 96 hours to remove
substantially all of the cobalt from within interstices within it,
leaving the disc porous, i.e. a polycrystalline diamond with pores
or voids within the polycrystalline structure.
[0057] A second PCD disc, having the same composition as the first
disc, was manufactured in the same way as the first disc, but this
time the substrate was not removed. The second PCD disc had a
thickness of 1 millimetre, and both the PCD and the substrate had a
diameter of 17.4 millimetres. The combined height of the PCD and
substrate was 13 millimetres.
[0058] The first, leached PCD disc was placed onto the top surface
of the second PCD disc, and a silicon disc having diameter of 17.4
millimetres was placed onto the upper surface of the first PCD disc
to form an unbonded assembly. The unbonded assembly therefore
comprised a first, thermally stable PCD disc remote from a
substrate, with a second, much less thermally stable PCD disc
intermediate the first PCD disc and the substrate, and integrally
bonded to the substrate, and a silicon disc on top of the first PCD
disc. The unbonded assembly was encapsulated within a jacket
comprising a refractory metal cup, as is known in the art, and
assembled into a capsule used for sintering PCD in a conventional
ultra-high pressure apparatus. The purpose of the silicon was to
infiltrate into the upper porous PCD layer before the cobalt
melted, and to react with the diamond to form silicon carbide,
which is thermally stable. Once formed, the silicon carbide would
prevent substantial infiltration of cobalt from the second,
intermediate PCD disc into the first, upper PCD disc, which it was
intended should remain thermally stable. The assembly was subjected
to an ultra-high pressure of about 5.5 GPa and a temperature of
about 1,400 degrees centigrade for about five minutes to yield a
PCD compact.
[0059] The PCD compact comprised an upper region of thermally
stable PCD, comprising silicon carbide within internal interstices
or pores of an inter-bonded network of sintered diamond grains
bonded to a PCD region comprising cobalt within the interstices.
The bonding at the interface between these two PCD regions was in
the form of direct diamond-to-diamond bonding between diamond in
the first, upper layer and that of the second, lower layer.
Example 2
[0060] A free-standing first, leached PCD disc and a second,
unleached PCD disc bonded to a substrate were prepared as in
example 1.
[0061] A with niobium wafer having diameter of 17.4 millimetres was
placed on onto the top surface of the second PCD disc, and the
first, leached PCD disc was placed onto the niobium wafer, in
effect sandwiching the niobium wafer between the first and second
PCD discs. A copper disc having diameter of 17.4 millimetres was
placed onto the upper surface of the first PCD disc to form an
unbonded assembly. The unbonded assembly therefore comprised a
first, thermally stable PCD disc remote from a substrate, with a
second, much less thermally stable PCD disc intermediate the first
PCD disc and the substrate, and integrally bonded to the substrate,
a niobium wafer intermediate the first and second PCD discs, and a
copper disc on top of the first PCD disc. The unbonded assembly was
encapsulated within a jacket comprising a refractory metal cup, as
is known in the art, and assembled into a capsule used for
sintering PCD in a conventional ultra-high pressure apparatus. The
purpose of the copper was to infiltrate into the upper porous PCD
layer before the cobalt melted, and thus to prevent substantial
infiltration of cobalt from the second, intermediate PCD disc into
the first, upper PCD disc, which it was intended should remain
thermally stable. Copper does not react readily with diamond and
therefore does not compromise the thermal stability of PCD. The
assembly was subjected to an ultra-high pressure of about 5.5 GPa
and a temperature of about 1,200 degrees centigrade for about five
minutes to yield a PCD compact. The temperature was selected to be
higher than the melting point of copper, but lower than that of
cobalt.
[0062] The PCD compact comprised an upper region of thermally
stable PCD, comprising copper within internal interstices of an
inter-bonded network of sintered diamond grains bonded to a PCD
region comprising cobalt within the interstices.
Example 3
[0063] A free-standing first, leached PCD disc and a second,
unleached PCD disc bonded to a substrate were prepared as in
example 1.
[0064] The first, leached PCD disc was placed onto the top surface
of the second PCD disc to form an unbonded assembly. The unbonded
assembly was encapsulated within a jacket comprising a refractory
metal cup, as is known in the art, and assembled into a capsule
used for sintering PCD in a conventional ultra-high pressure
furnace. The assembly was subjected to an ultra-high pressure of
about 5.5 GPa and a temperature of about 1,250 degrees centigrade
for about ten minutes to yield a PCD compact. The temperature was
selected to be as close as practically possible to the melting
point of cobalt, without substantial cobalt melting occurring.
[0065] The PCD compact comprised an upper region of thermally
stable, substantially porous PCD bonded to a lower PCD region
comprising cobalt within the interstices. Direct diamond-to-diamond
bonding between diamond in the first, upper layer and that of the
second, lower layer was evident, and the first PCD layer was
substantially free of cobalt.
* * * * *