U.S. patent application number 13/534927 was filed with the patent office on 2013-01-03 for polycrystalline superhard construction.
Invention is credited to Nedret Can, Thembinkosi Shabalala.
Application Number | 20130000993 13/534927 |
Document ID | / |
Family ID | 44511887 |
Filed Date | 2013-01-03 |
United States Patent
Application |
20130000993 |
Kind Code |
A1 |
Shabalala; Thembinkosi ; et
al. |
January 3, 2013 |
POLYCRYSTALLINE SUPERHARD CONSTRUCTION
Abstract
A polycrystalline superhard construction comprises a body of
polycrystalline superhard material, and a substrate of hard
material bonded thereto along an interface. The body of
polycrystalline superhard material comprises a first region
abutting the substrate along the interface and a second region
bonded to the first region. The second region defines a rake face,
a cutting edge, a chamfer and at least a part of a flank face, the
cutting edge being defined by an edge of the flank face joined to
the chamfer, the chamfer extending between the cutting edge and the
rake face. The height of the chamfer in a plane parallel to the
plane through which the longitudinal axis of the polycrystalline
superhard construction extends is less than the thickness of the
second region. The first region comprises a material having coarser
grains than the second region. There is also disclosed a method of
making the same.
Inventors: |
Shabalala; Thembinkosi;
(Gauteng, ZA) ; Can; Nedret; (Gauteng,
ZA) |
Family ID: |
44511887 |
Appl. No.: |
13/534927 |
Filed: |
June 27, 2012 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
61503420 |
Jun 30, 2011 |
|
|
|
Current U.S.
Class: |
175/434 ;
51/307 |
Current CPC
Class: |
B01J 2203/062 20130101;
E21B 10/5735 20130101; B01J 2203/0655 20130101; E21B 10/36
20130101; E21B 10/567 20130101; E21B 10/55 20130101; B24D 18/0009
20130101; B01J 3/062 20130101; B01J 2203/0685 20130101; E21B 10/54
20130101 |
Class at
Publication: |
175/434 ;
51/307 |
International
Class: |
E21B 10/46 20060101
E21B010/46; B01J 3/06 20060101 B01J003/06; B24D 3/04 20060101
B24D003/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 30, 2011 |
GB |
1111179.6 |
Claims
1. A polycrystalline superhard construction comprising: a body of
polycrystalline superhard material; a substrate of hard material
bonded to the body of polycrystalline superhard material along an
interface; wherein the body of polycrystalline superhard material
comprises a first region and a second region, the first region
abutting the substrate along the interface and the second region
being bonded to the first region along a further interface, the
second region defining a rake face, a cutting edge, a chamfer and
at least a part of a flank face, the cutting edge being defined by
an edge of the flank face joined to the chamfer, the chamfer
extending between the cutting edge and the rake face; the first
region having a first thickness and the second region having a
second thickness; the chamfer having a height in a plane parallel
to the plane through which the longitudinal axis of the
polycrystalline superhard construction extends, the height of the
chamfer being less than the thickness of the second region; the
first region comprising a material having coarser grains than the
material of the second region.
2. A polycrystalline superhard construction according to claim 1
wherein the thickness of the first region is greater than the
thickness of the second region.
3. A polycrystalline superhard construction according to claim 1,
wherein the thickness of the second region is up to around 600
microns.
4. A polycrystalline superhard construction according to claim 1,
wherein the thickness of the first region is around 1200-1800
microns.
5. A polycrystalline superhard construction according to claim 1,
wherein the thickness of the second region exceeds the height of
the chamfer by around between 100 to 400 microns.
6. A polycrystalline superhard construction according to claim 1,
wherein the height of the chamfer is between around 100-400
microns.
7. A polycrystalline superhard construction according to claim 1,
wherein the body of polycrystalline superhard material comprises
polycrystalline diamond material.
8. A polycrystalline superhard construction according to claim 7,
wherein the average grain size of the diamond grains forming the
second region in the body of polycrystalline diamond material is
between around 0.1 to 10 microns.
9. A polycrystalline superhard construction according to claim 7,
wherein the average grain size of the diamond grains forming the
second region in the body of polycrystalline diamond material is
between around 1 to 8 microns.
10. A polycrystalline superhard construction according to claim 7,
wherein the average grain size of the diamond grains forming the
second region in the body of polycrystalline diamond material is
between around 3 to 6 microns.
11. A polycrystalline superhard construction according to claim 7,
wherein the average grain size of the diamond grains forming the
first region in the body of polycrystalline diamond material is
between around 6 to 20 microns.
12. A polycrystalline superhard construction according to claim 7,
wherein the average grain size of the diamond grains forming the
first region in the body of polycrystalline diamond material is
between around 8 to 17 microns.
13. A polycrystalline superhard construction according to claim 7,
wherein the average grain size of the diamond grains forming the
first region in the body of polycrystalline diamond material is
between around 6 to 17 microns.
14. A polycrystalline superhard construction according to claim 1,
wherein the chamfer angle is approximately 45.degree..
15. A polycrystalline superhard construction according to claim 1,
wherein the interface between the first region and the substrate is
substantially non-planar.
16. A polycrystalline superhard construction according to claim 1,
wherein the substrate comprises cemented carbide.
17. A cutter for boring into the earth comprising the
polycrystalline superhard construction according to claim 1.
18. A PCD element for a rotary shear bit for boring into the earth,
for a percussion drill bit or for a pick for mining or asphalt
degradation, comprising the polycrystalline superhard construction
of claim 1.
19. A drill bit or a component of a drill bit for boring into the
earth, comprising a polycrystalline superhard construction
according to claim 1.
20. A method for making a polycrystalline superhard construction as
claimed in claim 1, the method including: providing a first
plurality of aggregate masses comprising diamond grains having a
first mean size, at least one second aggregate mass comprising
diamond grains having a second mean size; arranging the first
aggregate mass on the second aggregate mass to form a pre-sinter
assembly together with a body of material for forming a substrate;
the first region comprising a material having coarser grains than
the material of the second region; and treating the pre-sinter
assembly in the presence of a catalyst material for diamond at an
ultra-high pressure and high temperature at which diamond is more
thermodynamically stable than graphite to sinter together the
diamond grains and a substrate bonded thereto along an interface to
form an integral PCD construction comprising a first region of PCD
bonded to a second region of PCD, the first region being bonded to
the substrate; the first region having a first thickness and the
second region having a second thickness; the second region defining
a rake face, a cutting edge, and at least a part of a flank face;
the method further comprising: forming a chamfer in the flank face,
the cutting edge being defined by an edge of the flank face joined
to the chamfer, the chamfer extending between the cutting edge and
the rake face, the chamfer having a height in a plane parallel to
the plane through which the longitudinal axis of the superhard
construction extends, the height of the chamfer being less than the
thickness of the second region.
Description
FIELD
[0001] This disclosure relates to a cutter comprising a superhard
construction, particularly but not exclusively for a rotary drill
bit for boring into the earth.
BACKGROUND
[0002] Polycrystalline diamond (PCD) material comprises a mass of
inter-grown diamond grains and interstices between the diamond
grains. PCD material may be made by subjecting an aggregated mass
of diamond grains to a high pressure and temperature in the
presence of a sintering aid such as cobalt, which may promote the
inter-growth of diamond grains. The sintering aid may also be
referred to as a catalyst material for diamond. PCD material may be
formed on a cobalt-cemented tungsten carbide substrate, which may
provide a source of cobalt catalyst material for sintering the PCD
material.
[0003] PCD material may be used in a wide variety of tools for
cutting, machining, drilling or degrading hard or abrasive
materials such as rock, metal, ceramics, composites and
wood-containing materials. For example, tool inserts comprising PCD
material are widely used in drill bits used for boring into the
earth in the oil and gas drilling industry. In many of these
applications, the temperature of the PCD material may become
elevated as it engages rock or other workpiece or body with high
energy. The working life of tool inserts may be limited by fracture
of the superhard material, including by spalling and chipping.
[0004] In use as a cutting element in tools such as those mentioned
above, the body of PCD material normally wears according to the
following progression: smooth wear, woody wear, accelerated wear,
spalling. Spalling usually occurs when the wear scar reaches the
top working surface, and results in catastrophic wear failure.
[0005] As used herein, the term "barrel chipping" refers to
chipping in the body of PCD material below a main wear-scar.
[0006] Smooth wear as used herein refers to wear occurring at the
diamond grain level where individual grains or fractions of grains
are removed.
[0007] Woody wear as used herein refers to the regime where the
wear-scar becomes irregular at the edges and cracking visible. The
rough appearance of the wear-scar is possibly due to wear processes
at a scale of more than one grain.
[0008] As used herein the term spalling refers to catastrophic
failure due to wear cracks propagating to top of the PCD body
acting as a cutter table.
[0009] Durability here refers to distance cut before cutter
failure. High-durability cutters tend to maintain cutting integrity
but eventually become ineffective due to formation of a very large
wear-scar and hence impractical load application requirements.
Prevention of spalling would increase lifetime/durability of the
cutter and there is therefore a need for a product in which
spalling is partially or completely inhibited and a method of
producing such a cutter.
SUMMARY
[0010] Viewed from a first aspect there is provided a
polycrystalline superhard construction comprising: [0011] a body of
polycrystalline superhard material; [0012] a substrate of hard
material bonded to the body of polycrystalline superhard material
along an interface; [0013] wherein the body of polycrystalline
superhard material comprises a first region and a second region,
the first region abutting the substrate along the interface and the
second region being bonded to the first region along a further
interface, [0014] the second region defining a rake face, a
chamfer, a cutting edge, and at least a part of a flank face, the
cutting edge being defined by an edge of the flank face joined to
the chamfer, the chamfer extending between the cutting edge and the
rake face; [0015] the first region having a first thickness and the
second region having a second thickness; [0016] the chamfer having
a height in a plane parallel to the plane through which the
longitudinal axis of the polycrystalline superhard construction
extends, the height of the chamfer being less than the thickness of
the second region; [0017] the first region comprising a material
having coarser grains than the material of the second region.
[0018] Viewed from a second aspect there is provided a cutter for
boring into the earth comprising the above-mentioned
polycrystalline superhard construction.
[0019] Viewed from a third aspect there is provided a PCD element
for a rotary shear bit for boring into the earth, for a percussion
drill bit or for a pick for mining or asphalt degradation,
comprising the above-described polycrystalline superhard
construction.
[0020] Viewed from a fourth aspect there is provided a drill bit or
a component of a drill bit for boring into the earth, comprising
the above-described polycrystalline superhard construction.
[0021] Viewed from a fifth aspect there is provided a method for
making a polycrystalline superhard construction, the method
comprising: [0022] providing a first plurality of aggregate masses
comprising diamond grains having a first mean size, at least one
second aggregate mass comprising diamond grains having a second
mean size; arranging the first aggregate mass on the second
aggregate mass to form a pre-sinter assembly together with a body
of material for forming a substrate; the first region comprising a
material having coarser grains than the material of the second
region; and [0023] treating the pre-sinter assembly in the presence
of a catalyst material for diamond at an ultra-high pressure and
high temperature at which diamond is more thermodynamically stable
than graphite to sinter together the diamond grains and a substrate
bonded thereto along an interface to form an integral PCD
construction comprising a first region of PCD bonded to a second
region of PCD, the first region being bonded to the substrate; the
first region having a first thickness and the second region having
a second thickness; [0024] the second region defining a rake face,
a cutting edge, and at least a part of a flank face; [0025] the
method further comprising:
[0026] forming a chamfer in the flank face, the cutting edge being
defined by an edge of the flank face joined to the chamfer, the
chamfer extending between the cutting edge and the rake face, the
chamfer having a height in a plane parallel to the plane through
which the longitudinal axis of the superhard construction extends,
the height of the chamfer being less than the thickness of the
second region.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] Non-limiting embodiments will now be described by way of
example and with reference to the accompanying drawings, in
which:
[0028] FIG. 1 is schematic partial cross-section through a first
embodiment of a cutter;
[0029] FIG. 2 is a schematic partial cross-section through the
cutter of FIG. 1 showing progression of a wear scar;
[0030] FIG. 3 is a schematic partial cross-section through the
cutter of FIG. 1 showing further progression of a wear scar;
[0031] FIG. 4a is a side view of a conventional cutter showing the
wear scar for a predetermined number of passes;
[0032] FIG. 4b is a side view of an embodiment of a cutter showing
the wear scar for the same predetermined number of passes as that
applied to the cutter of FIG. 4a;
[0033] FIG. 5a is a side view of the conventional cutter of FIG. 4a
after a further number of passes at which spalling has
occurred;
[0034] FIG. 5b is a side view of the embodiment of a cutter shown
in FIG. 4b after the same number of passes applied to the
conventional cutter of FIG. 5a;
[0035] FIG. 6 is a side view of the embodiment of the cutter of
FIG. 4b after a further number of passes;
[0036] FIG. 7a is a side view of a further conventional cutter
after a predetermined number of passes;
[0037] FIG. 7b is a side view of a further embodiment of a cutter
showing the wear scar for the same predetermined number of passes
as that applied to the cutter of FIG. 7a;
[0038] FIG. 8a is a side view of the conventional cutter of FIG. 7a
after a further number of passes at which spalling has
occurred;
[0039] FIG. 8b is a side view of the embodiment of a cutter shown
in FIG. 7b after the same number of passes applied to the
conventional cutter of FIG. 7a; and
[0040] FIG. 9 is a side view of the embodiment of the cutter of
FIG. 7b after a further number of passes.
DETAILED DESCRIPTION OF EMBODIMENTS
[0041] As used herein, a "superhard material" is a material having
a Vickers hardness of at least about 25 GPa. Diamond and cubic
boron nitride (cBN) material are examples of superhard
materials.
[0042] As used herein, a "superhard construction" means a
construction comprising polycrystalline superhard material or
superhard composite material, or comprising polycrystalline
superhard material and superhard composite material.
[0043] As used herein "polycrystalline superhard" (PCS) material
comprises a mass of grains of a superhard material and interstices
between the superhard grains, the content of the superhard grains
being at least about 50 percent of the material by volume. The
grains may comprise diamond or cubic boron nitride (cBN).
[0044] As used herein, polycrystalline diamond (PCD) is a PCS
material comprising a mass of diamond grains, a substantial portion
of which are directly inter-bonded with each other and in which the
content of diamond is at least about 80 volume percent of the
material with "interstices" or "interstitial regions" between the
diamond grains of PCD material.
[0045] As used herein, polycrystalline cubic boron nitride (PCBN)
material is a PCS material comprising a mass of cBN grains
dispersed within a wear resistant matrix, which may comprise
ceramic or metal material, or both, and in which the content of cBN
is at least about 50 volume percent of the material. In some
embodiments of PCBN material, the content of cBN grains is at least
about 60 volume percent, at least about 70 volume percent or at
least about 80 volume percent. Embodiments of superhard material
may comprise grains of superhard materials dispersed within a hard
matrix, wherein the hard matrix preferably comprises ceramic
material as a major component, the ceramic material preferably
being selected from silicon carbide, titanium nitride and titanium
carbo-nitride.
[0046] A cutter 1 according to a first embodiment is shown in FIGS.
1 to 3. The cutter 1 comprises a substrate 2 bonded along an
interface 3 to a body of polycrystalline diamond (PCD) material 4.
The body of PCD material comprises a first region 6 of PCD material
bonded to the substrate 2 and a second region 8 of PCD material
bonded to the first region 6 along a further interface 10. The
exposed surface 12 of the second region 8 forms a rake face 14, a
chamfer 20 extending between the rake face 14 and a cutting edge
16, and at least a part of a flank 18 of the cutter 1, the cutting
edge 16 being defined by the edge of the chamfer 20 and the flank
16.
[0047] The "rake face" 14 of the cutter 1 is the surface or
surfaces over which the chips of material being cut flow when the
cutter 1 is used to cut material from a body, the rake face 14
directing the flow of newly formed chips, and is commonly referred
to as the top face of the cutter. As used herein, "chips" are the
pieces of a body removed from the work surface of the body by the
cutter 1 in use.
[0048] As used herein, the "flank" 18 of the cutter 1 is the
surface or surfaces of the cutter 1 that passes over the surface
produced on the body of material being cut by the cutter 1 and is
commonly referred to as the side or barrel of the cutter. The flank
18 may provide a clearance from the body and may comprise more than
one flank face.
[0049] As used herein, a "cutting edge" 16 is intended to perform
cutting of a body in use. A "rounded cutting edge" is a cutting
edge that is formed by a rounded transition between the rake face
and the flank.
[0050] As used herein, a "wear scar" is a surface of a cutter
formed in use by the removal of a volume of cutter material due to
wear of the cutter. A flank face may comprise a wear scar. As a
cutter wears in use, material may be progressively removed from
proximate the cutting edge, thereby continually redefining the
position and shape of the cutting edge, rake face and flank as the
wear scar forms. As used herein, it is understood that the term
"cutting edge" refers to the actual cutting edge, defined
functionally as above, at any particular stage or at more than one
stage of the cutter wear progression up to failure of the cutter,
including but not limited to the cutter in a substantially unworn
or unused state.
[0051] With reference to FIGS. 1 to 3, the chamfer 20 is formed in
the structure adjacent the cutting edge 16 and flank 18. The rake
face 14 is therefore joined to the flank 18 by the chamfer 20 which
extends from the cutting edge 16 to the rake face 14, and lies in a
plane at a predetermined angle .theta. to the plane perpendicular
to the plane in which the longitudinal axis of the cutter 1
extends. In some embodiments, this chamfer angle is up to around 45
degrees.
[0052] The interface 10 between the first and second regions of PCD
material, 6 and 8, is spaced from the cutting edge 16 which is
defined by the second region 8. Therefore, the thickness of the
second region 8 is greater than the vertical height of the chamfer
20.
[0053] The thickness of the first region 6 of PCD material is
substantially greater than the thickness of the second region 8.
For example, in some embodiments, the thickness of the second
region 8 is up to around 600 microns and the thickness of the first
region 6 is around 1200-1800 microns. In some embodiments, the
thickness of the second region 8 exceeds the vertical chamfer
height by around 100-400 microns and the vertical height of the
chamfer 20 may be, for example, around 400 microns.
[0054] In FIGS. 1 to 3, the hashed lines 22, 24 represent the work
face making an angle .phi. with the longitudinal axis of the cutter
1. This angle .phi. is also referred to as the back-rake angle.
[0055] As the cutter 1 wears, the wear on the cutter 1 is shown by
a shift in the hashed line 22 to the position denoted by the second
hashed line 24. FIG. 1 shows the first stage where all cutting is
carried out by the second region 8 of the body of PCD material. The
first hashed line 22 shows the start of the cut and the second
hashed line 24 shows where the wear has reached the interface 10
between the first and second regions 6, 8 of PCD material. The
initial back rake angle .phi. and its progress shift is thereby
shown in FIG. 1 as the cutter 1 wears during use, the wear-flat
eventually reaching the thicker/softer PCD layer of the first
region 6.
[0056] FIG. 2 shows further wear of the cutter 1 after additional
use and it will be seen that the wear flat proceeds more quickly in
the softer layer of the first region 6 of PCD material than in the
more wear resistant layer of the second region 8 of the body of PCD
material. The wear has therefore progressed into the first region 6
and, as the material of the first region 6 wears faster than the
material of the second region 8, the angle of the cutting face
(denoted by the back rake angle .phi.) gradually decreases so that
the wear of the first region 6 is greater than that of the second
region 8.
[0057] This may have the effect of slowing down the progression of
the wear-flat in the chamfer region 20.
[0058] FIG. 3 shows a further stage where the wear flat has reached
the rake face 14 as it intersects the chamfer 20 and has also
reached the interface 3 of the first region 6 and the substrate 2.
Further wear and retardation of the wear flat in the chamfer region
20 delays the spalling which may occur when the wear flat reaches
the corner of the chamfer 20 as denoted by the second hashed line
24.
[0059] Once the wear reaches the top of the chamfer 20, this could
lead to spalling and, once the wear reaches the interface 3 between
the substrate 2 and the first region 6, the cutter 1 may have
reached the end of its useful working life.
[0060] FIG. 4a is a side view of a conventional cutter showing the
wear scar for a predetermined number of passes. It will be seen
that the wear on this cutter is greater than that on the cutter of
FIG. 4b which is in accordance with a first embodiment for the same
predetermined number of passes as that applied to the cutter of
FIG. 4a.
[0061] FIG. 5a is a side view of the conventional cutter of FIG. 4a
after a further number of passes at which spalling has occurred. It
will be seen that there is extensive spalling damage to the cutter
whilst the cutter of FIG. 4b after the same number of passes
applied to the conventional cutter shows only a small amount of
wear.
[0062] FIG. 6 is a side view of the embodiment of the cutter of
FIG. 4b after a further number of passes with the onset of spalling
behaviour.
[0063] FIG. 7a is a side view of a further conventional cutter
after a predetermined number of passes and FIG. 7b is a side view
of a further embodiment of a cutter showing the wear scar for the
same predetermined number of passes as that applied to the cutter
of FIG. 7a. It will be seen that in the embodiment shown in FIG.
7b, whilst the wear scar is larger than that shown in FIG. 7a, the
wear is all in the woody region.
[0064] FIG. 8a is a side view of the conventional cutter of FIG. 7a
after a further number of passes at which spalling has occurred.
FIG. 8b is a side view of the embodiment of a cutter shown in FIG.
7b after the same number of passes applied to the conventional
cutter of FIG. 8a. In the embodiment of FIG. 8b, the cutter has
maintained a sharp cutting edge although the wear scar is larger
than that in the cutter of FIG. 8a.
[0065] FIG. 9 is a side view of the embodiment of the cutter of
FIG. 8b after a further number of passes. The cutter has failed due
to the large wear scar although a sharp cutting edge is still
visible.
[0066] The material forming the second region 8 is chosen to be
significantly more wear resistant than the material forming the
first region 6. The significantly lower wear resistance of the
first region 6 assists in enabling a desired wear pattern to be
created in use.
[0067] The cutter 1 may be fabricated as follows.
[0068] As used herein, a "green body" is a body comprising grains
to be sintered and a means of holding the grains together, such as
a binder, for example an organic binder. Embodiments of superhard
constructions may be made by a method including preparing a green
body comprising grains of superhard material and a binder, such as
an organic binder. The green body may also comprise catalyst
material for promoting the sintering of the superhard grains. The
green body may be made by combining the grains with the binder and
forming them into a body having substantially the same general
shape as that of the intended sintered body, and drying the binder.
At least some of the binder material may be removed by, for
example, burning it off. The green body may be formed by a method
including a compaction process, injection or other molding,
extrusion, deposition modelling or other methods. The green body
may be formed from components comprising the grains and a binder,
the components being in the form of sheets, blocks or discs, for
example, and the green body may itself be formed from green bodies.
For example, the green body for the superhard construction may be
formed from distinct green bodies for each of the respective
regions 6, 8, which may be formed separately into generally the
intended shapes of the respective regions and combined to form a
boundary defined by a contact interface.
[0069] One embodiment of a method for making a green body includes
providing tape cast sheets, each sheet comprising a plurality of
diamond grains bonded together by a binder, such as a water-based
organic binder, and stacking the sheets on top of one another and
on top of a support body. Different sheets comprising diamond
grains having different size distributions, diamond content or
additives may be selectively stacked to achieve a desired
structure. The sheets may be made by a method known in the art,
such as extrusion or tape casting methods, wherein slurry
comprising diamond grains and a binder material is laid onto a
surface and allowed to dry. Other methods for making
diamond-bearing sheets may also be used, such as described in U.S.
Pat. Nos. 5,766,394 and 6,446,740. Alternative methods for
depositing diamond-bearing layers include spraying methods, such as
thermal spraying.
[0070] A green body for the superhard construction may be placed
onto a substrate, such as a cemented carbide substrate to form a
pre-sinter assembly, which may be encapsulated in a capsule for an
ultra-high pressure furnace, as is known in the art. The substrate
may provide a source of catalyst material for promoting the
sintering of the superhard grains. In some embodiments, the
superhard grains may be diamond grains and the substrate may be
cobalt-cemented tungsten carbide, the cobalt in the substrate being
a source of catalyst for sintering the diamond grains. The
pre-sinter assembly may comprise an additional source of catalyst
material.
[0071] In one version, the method may include loading the capsule
comprising a pre-sinter assembly into a press and subjecting the
green body to an ultra-high pressure and a temperature at which the
superhard material is thermodynamically stable to sinter the
superhard grains. In one embodiment, the green body may comprise
diamond grains and the pressure is at least about 5 GPa and the
temperature is at least about 1,300 degrees centigrade. In one
embodiment, the green body may comprise cBN grains and the pressure
is at least about 3 GPa and the temperature is at least about 900
degrees centigrade.
[0072] An embodiment of a superhard construction may be made by a
method including providing a PCD structure and a diamond composite
structure, forming each structure into the respective complementary
shapes, assembling the PCD structure and the diamond composite
structure onto a cemented carbide substrate to form an unjoined
assembly, and subjecting the unjoined assembly to a pressure of at
least about 5.5 GPa and a temperature of at least about 1,250
degrees centigrade to form a PCD construction.
[0073] A version of the method may include making a diamond
composite structure by means of a method disclosed, for example, in
PCT application publication number WO2009/128034 for making a
super-hard enhanced hard-metal material. A powder blend comprising
diamond particles, particles of carbide material and a metal binder
material, such as cobalt may be prepared by combining these
particles and blending them together. Any effective powder
preparation technology may be used to blend the powders, such as
wet or dry multi-directional mixing, planetary ball milling and
high shear mixing with a homogenizer. In one embodiment, the mean
size of the diamond particles may be at least about 50 microns and
they may be combined with other particles simply by stirring the
powders together by hand. In one version of the method, precursor
materials suitable for subsequent conversion into carbide material
or binder material may be included in the powder blend, and in one
version of the method, metal binder material may be introduced in a
form suitable for infiltration into a green body. The powder blend
may be deposited in a die or mold and compacted to form a green
body, for example by uni-axial compaction or other compaction
method, such as cold isostatic pressing (CIP). The green body may
be subjected to a sintering process known in the art for sintering
similar materials without the presence of diamond, such as may be
used to sinter cemented tungsten carbide, to form a sintered
article. For example, the green body may be sintered by means of
hot pressing or spark plasma sintering. The diamond particles may
wholly or partially convert to a non-diamond form of carbon, such
as graphite, depending on the sintering conditions. The sintered
article may be subjected to a subsequent treatment at a pressure
and temperature at which diamond is thermally stable to convert
some or all of the non-diamond carbon back into diamond and produce
a diamond composite structure. An ultra-high pressure furnace well
known in the art of diamond synthesis and the pressure may be at
least about 5.5 GPa and the temperature may be at least about 1,250
degrees centigrade.
[0074] An embodiment of a superhard construction may be made by a
method including providing a PCD structure and a precursor
structure for a diamond composite structure, forming each structure
into the respective complementary shapes, assembling the PCD
structure and the diamond composite structure onto a cemented
carbide substrate to form an unjoined assembly, and subjecting the
unjoined assembly to a pressure of at least about 5.5 GPa and a
temperature of at least about 1,250 degrees centigrade to form a
PCD construction. The precursor structure may comprise carbide
particles and diamond or non-diamond carbon material, such as
graphite, and a binder material comprising a metal, such as cobalt.
The precursor structure may be a green body formed by compacting a
powder blend comprising particles of diamond or non-diamond carbon
and particles of carbide material and compacting the powder
blend.
[0075] The present disclosure may be further illustrated by the
following examples which are not intended to be limiting.
EXAMPLE 1
[0076] In one embodiment, ultra-high pressure and temperature may
be used to sinter the superhard construction at approximately 6.8
GPa or higher. The resulting top layer, namely the second region 8
may comprise sintered fine grains of multimodal diamond, with
average final grain size of, for example, approximately 0.1 to 10
.mu.m, 1 to 8 .mu.m, 3 to 6 .mu.m or 3.5 to 4.5 .mu.m. This second
region 8 may be, for example, between 400 .mu.m and 1000 .mu.m
thick, or between 600 .mu.m and 800 .mu.m thick. The vertical
height of the chamfer 20 may be, for example, between 350 .mu.m and
450 .mu.m, such as around 400 .mu.m. The first region 6 may
comprise less wear resistant sintered coarser grains of multimodal
diamond of average final size of, for example, approximately 6.0 to
20 .mu.m, 8 to 17 .mu.m, 6 to 17 .mu.m or 8.0 to 9.0 .mu.m. This
first region 6 may be, for example between about 1200 .mu.m and
1800 .mu.m thick, such as between about 1400 .mu.m and 1600 .mu.m
thick.
[0077] Such an embodiment of a PCD compact may, for example, be
prepared as follows. 2.5 g of a first multimodal diamond powder mix
having an average particle size of approximately 7 .mu.m and 2.5 g
of a second multimodal diamond powder mix having an average
particle size of approximately 11 .mu.m and 3 weight percent VC-TiC
admix may be prepared and bound into organic tape which is easily
removable by pre-heating, using methods well known in the art.
Sufficient discs of the first tape to form a top sintered layer of
approximately 600 .mu.m final thickness may be placed in a Niobium
canister, and similarly sufficient discs of the second tape to form
the underlying sintered layer of approximately 1600 .mu.m final
thickness may be placed in the canister on top of the first discs.
A tungsten carbide substrate is then placed in the Niobium canister
on top of the second discs, the canister is sealed and then
heat-treated to remove the organic binders. The canister may be
treated at ultra-high pressure and temperature (for example at
approximately 1600.degree. C. and 6.8 GPa or greater). After
sintering, the PCD cutters may be ground to size including a
45.degree. chamfer of approximately 0.4 mm height on the body of
PCD material so produced. Cutters produced according to the above
have been subjected to wear tests (as shown in FIGS. 4b, 5b and 6)
by suitably preparing them as would be appreciated by the skilled
person, to machine a granite block mounted on a vertical turret
milling apparatus and counting the number of passes before failure.
The average number of passes achieved was approximately 65% better
than that of a commercial benchmark, namely that shown and
described above with reference to FIGS. 4a and 5a.
EXAMPLE 2
[0078] In a further embodiment, the second region 8 may comprise
coarse sintered grains of multimodal diamond, with average final
size of approximately 4.5-5.5 .mu.m. In this embodiment, the source
diamond may be admixed with any combination of, for example TiC,
TaC, VC, carbonitrides of Ti, Ta, V, in amounts 1% to 6% by weight.
An example of such an admix is 2-4% TiC-VC. This second region 8
may be, for example between 400 .mu.m and 1000 .mu.m thick, such as
between 600 .mu.m and 800 .mu.m thick. The chamfer angle is
approximately 45.degree. with vertical height of the chamfer 20
being, for example between around 350 .mu.m and 450 .mu.m, such as
around 400 .mu.m. The first region 6 may comprise less wear
resistant sintered coarser grains of multimodal diamond of average
final size of approximately 8.0-9.0 .mu.m. This first region 6 may,
for example, be between about 1200 .mu.m and 1800 .mu.m thick, such
as between about 1400 .mu.m and 1600 .mu.m thick.
[0079] Such an embodiment of a PCD compact may, for example, be
prepared as follows. 2.5 g of two multimodal diamond powder mixes
having average particle sizes of approximately 5 .mu.m and
approximately 11 .mu.m may be prepared and bound into organic tape
easily removed by pre-heating, using methods well known in the art.
Sufficient discs of the first tape to form a top sintered layer of
approximately 600 .mu.m final thickness are placed in a Niobium
canister, and similarly sufficient discs of the second tape to form
the underlying sintered layer of approximately 1600 .mu.m final
thickness are placed in the canister on top of the first discs. A
tungsten carbide substrate is then placed in the Niobium canister
on top of the second discs, the canister is sealed and then
heat-treated to remove the organic binders. The canister may be
treated at ultra-high pressure and temperature (such as
approximately 1600.degree. C. and 6.8 GPa). After sintering, the
PCD cutters may be ground to size including a 45.degree. chamfer of
0.4 mm height on the body of the PCD material. Cutters produced in
this manner were subjected to wear tests by suitably preparing them
as would be appreciated by the skilled person, to machine a granite
block mounted on a vertical turret milling apparatus and counting
the number of passes before failure. The average number of passes
achieved, as illustrated in FIGS. 7b, 8b and 9, outperformed a
corresponding conventional cutter (as shown in FIGS. 7a and 8a)
which had not been surface-treated by a factor of about three.
[0080] Whilst not wishing to be bound by a particular theory, the
above results indicate that more wear-resistant finer-grain PCD
material on less wear-resistant coarser-grain PCD material may
significantly enhance the durability of the cutter produced
according to some embodiments described herein. The wear starts in
the thinner, more wear-resistant layer of the second region 8 and
progresses to the underlying thicker, less wear-resistant layer of
the first region 6 which is bonded to the substrate 2. Unlike in
typical monolayer configurations known in the art, these
configuration may assist in diverting the wear scar downwards into
the barrel of the PCD body, instead of the typical behaviour, in
which the wear-scar generates cracks which move to the free
surfaces of the cutter and result in failure through spalling. This
has the effect that the wear behaviour in cutters according to some
embodiments may remain longer in the smooth to "woody" wear region,
before eventually spalling. Performance may be further improved
when the interface 3 between the body of PCD material and the
substrate 2 is non-planar (not shown).
* * * * *