U.S. patent application number 14/407957 was filed with the patent office on 2015-06-18 for superhard constructions and methods of making same.
The applicant listed for this patent is Element Six Abrasives S.A.. Invention is credited to Nedret Can, Humphrey Samkelo Lungisani Sithebe.
Application Number | 20150165590 14/407957 |
Document ID | / |
Family ID | 46640991 |
Filed Date | 2015-06-18 |
United States Patent
Application |
20150165590 |
Kind Code |
A1 |
Can; Nedret ; et
al. |
June 18, 2015 |
SUPERHARD CONSTRUCTIONS AND METHODS OF MAKING SAME
Abstract
A superhard polycrystalline construction comprises a body of
polycrystal-line superhard material formed of a mass of superhard
grains exhibiting inter- granular bonding and defining a plurality
of interstitial regions therebetween, the superhard grains having
an associated mean free path, and a non- superhard phase at least
partially filling a plurality of the interstitial regions and
having an associated mean free path. The median of the mean free
path associated with the non-superhard phase divided by (Q3-Q1) for
the non-superhard phase is greater than or equal to 0.83 where Q1
is the first quartile and Q3 is the third quartile and the median
of the mean free path associated with the superhard grains divided
by (Q3-Q1) for the superhard grains is less than 0.47.
Inventors: |
Can; Nedret; (Oxfordshire,
GB) ; Sithebe; Humphrey Samkelo Lungisani; (Springs,
ZA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Element Six Abrasives S.A. |
Luxembourg |
|
LU |
|
|
Family ID: |
46640991 |
Appl. No.: |
14/407957 |
Filed: |
June 14, 2013 |
PCT Filed: |
June 14, 2013 |
PCT NO: |
PCT/EP2013/062440 |
371 Date: |
December 14, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61660509 |
Jun 15, 2012 |
|
|
|
Current U.S.
Class: |
175/434 ; 51/307;
51/309 |
Current CPC
Class: |
C22C 1/051 20130101;
C04B 35/52 20130101; C04B 2235/3804 20130101; B22F 2005/001
20130101; C04B 2235/3817 20130101; E21B 10/567 20130101; C04B
2235/427 20130101; C22C 26/00 20130101; B22F 7/062 20130101; B24D
3/06 20130101; C04B 2235/3852 20130101 |
International
Class: |
B24D 3/06 20060101
B24D003/06; E21B 10/567 20060101 E21B010/567 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 15, 2012 |
GB |
1210653.0 |
Claims
1. A superhard polycrystalline construction comprising a body of
polycrystalline superhard material formed of: a mass of superhard
grains exhibiting inter-granular bonding and defining a plurality
of interstitial regions therebetween, the superhard grains having
an associated mean free path; a non-superhard phase at least
partially filling a plurality of the interstitial regions and
having an associated mean free path; wherein: the median of the
mean free path associated with the non-superhard phase divided by
(Q3-Q1) for the non-superhard phase is greater than or equal to
0.83, where Q1 is the first quartile and Q3 is the third quartile;
and the median of the mean free path associated with the superhard
grains divided by (Q3-Q1) for the superhard grains is less than
0.47.
2. A superhard polycrystalline construction according to claim 1,
wherein the superhard grains comprise natural and/or synthetic
diamond grains, the superhard polycrystalline construction forming
a polycrystalline diamond construction.
3. A superhard polycrystalline construction according to claim 1,
wherein the non-superhard phase comprises a binder phase.
4. A superhard polycrystalline construction according to claim 3,
wherein the binder phase comprises cobalt, and/or one or more other
iron group elements, or an alloy thereof, and/or one or more
carbides, nitrides, borides, and oxides of the metals of Groups
IV-VI in the periodic table.
5. A superhard polycrystalline construction according to claim 4,
wherein the one or more other iron group elements comprises iron or
nickel.
6. A superhard polycrystalline construction according to claim 1,
further comprising a cemented carbide substrate bonded to the body
of polycrystalline material along an interface.
7. A superhard polycrystalline construction according to claim 6,
wherein the cemented carbide substrate comprises tungsten carbide
particles bonded together by a binder material, the binder material
comprising an alloy of Co, Ni and Cr.
8. A superhard polycrystalline construction according to claim 7,
wherein the tungsten carbide particles form at least 70 weight
percent and at most 95 weight percent of the substrate; the binder
material comprising between about 10 to 50 wt. % Ni, between about
0.1 to 10 wt. % Cr, and the remainder weight percent comprising Co;
and wherein the size distribution of the tungsten carbide particles
in the cemented carbide substrate has the following
characteristics: fewer than 17 percent of the tungsten carbide
particles have a grain size of equal to or less than about 0.3
microns; between about 20 to 28 percent of the tungsten carbide
particles have a grain size of between about 0.3 to 0.5 microns;
between about 42 to 56 percent of the tungsten carbide particles
have a grain size of between about 0.5 to 1 microns; less than
about 12 percent of the tungsten carbide particles are greater than
1 micron; and the mean grain size of the tungsten carbide particles
is about 0.6.+-.0.2 microns.
9. A superhard polycrystalline construction according to claim 8,
wherein the binder additionally comprises between about 2 to 20 wt.
% tungsten and between about 0.1 to 2 wt. % carbon.
10. A method of forming a superhard polycrystalline construction,
comprising: providing a mass of grains of superhard material
comprising a first fraction having a first average size and a
second fraction having a second average size, arranging the mass of
superhard grains to form a pre-sinter assembly; and treating the
pre-sinter assembly in the presence of a catalyst/solvent material
for the superhard grains at an ultra-high pressure of around 5.5
Gpa or greater and a temperature at which the superhard material is
more thermodynamically stable than graphite to sinter together the
grains of superhard material to form a polycrystalline superhard
construction, the superhard grains exhibiting inter-granular
bonding and defining a plurality of interstitial regions
therebetween, a non-superhard phase at least partially filling a
plurality of the interstitial regions; wherein the median of the
mean free path associated with the non-superhard phase divided by
(Q3-Q1) for the non-superhard phase is greater than or equal to
0.83, where Q1 is the first quartile and Q3 is the third quartile
of the mean free path measurements associated with the
non-superhard phase; and the median of the mean free path
associated with the superhard grains divided by (Q3-Q1) for the
superhard grains is less than 0.47, where Q1 is the first quartile
and Q3 is the third quartile of the mean free path measurements
associated with the superhard grains.
11. The method of claim 10, wherein, the step of providing a mass
of grains of superhard material comprisies providing a mass of
diamond grains having a first fraction having a first average size
and a second fraction having a second average size, the first
fraction having an average grain size ranging from about 10 to 60
microns, and the second fraction having an average grain size less
than the size of the first fraction.
12. The method of claim 11, wherein the second fraction has an
average grain size between around 1/10 to 6/10 of the size of the
first fraction.
13. The method of claim 10, wherein the average grain size of the
first fraction is between around 10 to 60 microns, and the average
grain size of the second fraction is between about 0.1 to 20
microns.
14. The method of claim 10, wherein the weight ratio of the first
fraction to the second fraction ranges from about 50% to about 97%,
or the weight % of the second fraction ranging from about 3% to
about 50 weight %.
15. The method of claim 14, wherein the ratio by weight percent of
the first fraction to the second fraction is around 60:40.
16. The method of claim 15, wherein the ratio by weight percent of
the first fraction to the second fraction is around 70:30.
17. The method of claim 16, wherein the ratio by weight percent of
the first fraction to the second fraction is around 90:10.
18. The method of claim 17, wherein the ratio by weight percent of
the first fraction to the second fraction is around 80:20.
19. The method of claim 10, wherein the step of providing a mass of
grains of superhard material comprises providing a mass of grains
in which the grain size distributions of the first and second
fractions do not overlap.
20. The method of claim 10, wherein the step of providing a mass of
grains of superhard material comprises providing three or more
grain size modes to form a multimodal mass of grains comprising a
blend of grain sizes having associated average grain sizes.
21. The method of claim 10, wherein the average grain sizes of the
fractions is separated by an order of magnitude.
22. The method of claim 10, wherein the mass of superhard grains
comprises a first fraction having an average grain size of around
20 microns, a second fraction having an average grain size of
around 2 microns, a third fraction having an average grain size of
around 200 nm and a fourth fraction having an average grain size of
around 20 nm.
23. A tool comprising a superhard polycrystalline construction
according to claim 1, the tool being for cutting, milling,
grinding, drilling, earth boring, rock drilling or other abrasive
applications.
24. A tool according to claim 23, wherein the tool comprises a
drill bit for earth boring or rock drilling.
25. A tool according to claim 23, wherein the tool comprises a
rotary fixed-cutter bit for use in oil and gas drilling.
26. A tool according to claim 23, wherein the tool is a rolling
cone drill bit, a hole opening tool, an expandable tool, a reamer
or other earth boring tools.
27. A drill bit or a cutter or a component therefor comprising the
superhard polycrystalline construction according to claim 1.
28-29. (canceled)
Description
FIELD
[0001] This disclosure relates to superhard constructions and
methods of making such constructions, particularly but not
exclusively to constructions comprising polycrystalline diamond
(PCD) structures attached to a substrate and for use as cutter
inserts or elements for drill bits for boring into the earth.
BACKGROUND
[0002] Polycrystalline superhard materials, such as polycrystalline
diamond (PCD) and polycrystalline cubic boron nitride (PCBN) 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. In particular, tool
inserts in the form of cutting elements comprising PCD material are
widely used in drill bits for boring into the earth to extract oil
or gas. The working life of superhard tool inserts may be limited
by fracture of the superhard material, including by spalling and
chipping, or by wear of the tool insert.
[0003] Cutting elements such as those for use in rock drill bits or
other cutting tools typically have a body in the form of a
substrate which has an interface end/surface and an ultra hard
material which forms a cutting layer bonded to the interface
surface of the substrate by, for example, a sintering process. The
substrate is generally formed of a tungsten carbide-cobalt alloy,
sometimes referred to as cemented tungsten carbide and the ultra
hard material layer is typically polycrystalline diamond (PCD),
polycrystalline cubic boron nitride (PCBN) or a thermally stable
product TSP material such as thermally stable polycrystalline
diamond.
[0004] Polycrystalline diamond (PCD) is an example of a superhard
material (also called a superabrasive material) comprising a mass
of substantially inter-grown diamond grains, forming a skeletal
mass defining interstices between the diamond grains. PCD material
typically comprises at least about 80 volume % of diamond and is
conventionally made by subjecting an aggregated mass of diamond
grains to an ultra-high pressure of greater than about 5 Gpa, and
temperature of at least about 1,200.degree. C., for example. A
material wholly or partly filling the interstices may be referred
to as filler or binder material.
[0005] PCD is typically formed in the presence of a sintering aid
such as cobalt, which promotes the inter-growth of diamond grains.
Suitable sintering aids for PCD are also commonly referred to as a
solvent-catalyst material for diamond, owing to their function of
dissolving, to some extent, the diamond and catalysing its
re-precipitation. A solvent-catalyst for diamond is understood be a
material that is capable of promoting the growth of diamond or the
direct diamond-to-diamond inter-growth between diamond grains at a
pressure and temperature condition at which diamond is
thermodynamically stable. Consequently the interstices within the
sintered PCD product may be wholly or partially filled with
residual solvent-catalyst material. Most typically, PCD is often
formed on a cobalt-cemented tungsten carbide substrate, which
provides a source of cobalt solvent-catalyst for the PCD. Materials
that do not promote substantial coherent intergrowth between the
diamond grains may themselves form strong bonds with diamond
grains, but are not suitable solvent -catalysts for PCD
sintering.
[0006] Cemented tungsten carbide which may be used to form a
suitable substrate is formed from carbide particles being dispersed
in a cobalt matrix by mixing tungsten carbide particles/grains and
cobalt together then heating to solidify. To form the cutting
element with an ultra hard material layer such as PCD or PCBN,
diamond particles or grains or CBN grains are placed adjacent the
cemented tungsten carbide body in a refractory metal enclosure such
as a niobium enclosure and are subjected to high pressure and high
temperature so that inter-grain bonding between the diamond grains
or CBN grains occurs, forming a polycrystalline ultra hard diamond
or polycrystalline CBN layer.
[0007] In some instances, the substrate may be fully cured prior to
attachment to the ultra hard material layer whereas in other cases,
the substrate may be green, that is, not fully cured. In the latter
case, the substrate may fully cure during the HTHP sintering
process. The substrate may be in powder form and may solidify
during the sintering process used to sinter the ultra hard material
layer.
[0008] Ever increasing drives for improved productivity in the
earth boring field place create ever increasing demands on the
materials used for cutting rock. Specifically, PCD materials with
improved abrasion and impact resistance are required to achieve
faster cut rates and longer tool life.
[0009] Cutting elements for use in rock drilling and other
operations require high abrasion resistance and impact resistance.
One of the factors limiting the success of the polycrystalline
diamond (PCD) abrasive cutters is the generation of heat due to
friction between the PCD and the work material. This heat causes
the thermal degradation of the diamond layer. The thermal
degradation increases the wear rate of the cutter through increased
cracking and spalling of the PCD layer as well as back conversion
of the diamond to graphite causing increased abrasive wear.
[0010] Methods used to improve the abrasion resistance of a PCD
composite often result in a decrease in impact resistance of the
composite. There is a need for a PCS composite that has improved
abrasion resistance and impact resistance and a method of forming
such composites.
SUMMARY
[0011] Viewed from a first aspect there is provided a superhard
polycrystalline construction comprising a body of polycrystalline
superhard material formed of: [0012] a mass of superhard grains
exhibiting inter-granular bonding and defining a plurality of
interstitial regions therebetween, the superhard grains having an
associated mean free path; [0013] a non-superhard phase at least
partially filling a plurality of the interstitial regions and
having an associated mean free path; wherein: [0014] the median of
the mean free path associated with the non-superhard phase divided
by (Q3-Q1) for the non-superhard phase is greater than or equal to
0.83, where Q1 is the first quartile and Q3 is the third quartile;
and [0015] the median of the mean free path associated with the
superhard grains divided by (Q3-Q1) for the superhard grains is
less than 0.47.
[0016] In some embodiments, the superhard grains comprise natural
and/or synthetic diamond grains, the superhard polycrystalline
construction forming a polycrystalline diamond construction.
[0017] In some embodiments, the non-superhard phase comprises a
binder phase.
[0018] The binder phase may comprise, for example, cobalt, and/or
one or more other iron group elements, such as iron or nickel, or
an alloy thereof, and/or one or more carbides, nitrides, borides,
and oxides of the metals of Groups IV-VI in the periodic table.
[0019] In some embodiments, the polycrystalline superhard
construction further comprises a cemented carbide substrate bonded
to the body of polycrystalline material along an interface.
[0020] The cemented carbide substrate may, for example, comprise
tungsten carbide particles bonded together by a binder material,
the binder material comprising an alloy of Co, Ni and Cr.
[0021] In some embodiments, the tungsten carbide particles form at
least 70 weight percent and at most 95 weight percent of the
substrate; the binder material comprising between about 10 to 50
wt. % Ni, between about 0.1 to 10 wt. % Cr, and the remainder
weight percent comprising Co; and wherein the size distribution of
the tungsten carbide particles in the cemented carbide substrate
has the following characteristics: [0022] fewer than 17 percent of
the carbide particles have a grain size of equal to or less than
about 0.3 microns; [0023] between about 20 to 28 percent of the
tungsten carbide particles have a grain size of between about 0.3
to 0.5 microns; [0024] between about 42 to 56 percent of the
tungsten carbide particles have a grain size of between about 0.5
to 1 microns; [0025] less than about 12 percent of the tungsten
carbide particles are greater than 1 micron; and [0026] the mean
grain size of the tungsten carbide particles is about 0.6+0.2
microns.
[0027] The binder in the substrate may additionally comprise
between about 2 to 20 wt. % tungsten and between about 0.1 to 2 wt.
% carbon.
[0028] Viewed from a second aspect there is provided a method of
forming a superhard polycrystalline construction, comprising:
[0029] providing a mass of grains of superhard material comprising
a first fraction having a first average size and a second fraction
having a second average size, [0030] arranging the mass of
superhard grains to form a pre-sinter assembly; and [0031] treating
the pre-sinter assembly in the presence of a catalyst/solvent
material for the superhard grains at an ultra-high pressure of
around 5.5 GPa or greater and a temperature at which the superhard
material is more thermodynamically stable than graphite to sinter
together the grains of superhard material to form a polycrystalline
superhard construction, the superhard grains exhibiting
inter-granular bonding and defining a plurality of interstitial
regions therebetween, a non-superhard phase at least partially
filling a plurality of the interstitial regions;
[0032] wherein the median of the mean free path associated with the
non-superhard phase divided by (Q3-Q1) for the non-superhard phase
is greater than or equal to 0.83, where Q1 is the first quartile
and Q3 is the third quartile of the mean free path measurements
associated with the non-superhard phase; and [0033] the median of
the mean free path associated with the superhard grains divided by
(Q3-Q1) for the superhard grains is less than 0.47, where Q1 is the
first quartile and Q3 is the third quartile of the mean free path
measurements associated with the superhard grains.
[0034] In some embodiments, the step of providing a mass of grains
of superhard material comprises providing a mass of diamond grains
having a first fraction having a first average size and a second
fraction having a second average size, the first fraction having an
average grain size ranging from about 10 to 60 microns, and the
second fraction having an average grain size less than the size of
the coarse fraction.
[0035] The second fraction may, for example, have an average grain
size between around 1/10 to 6/10 of the size of the first
fraction.
[0036] In some embodiments, the average grain size of the first
fraction is between around 10 to 60 microns, and the average grain
size of the second fraction is between about 0.1 to 20 microns.
[0037] In some embodiments, the weight ratio of the first fraction
to the second fraction ranges from about 50% to about 97%, the
weight ratio of the second fraction ranging from about 3% to about
50 weight %.
[0038] In some embodiments, the ratio by weight percent of the
first fraction to the second fraction is around 60:40, or around
70:30, or around 90:10, or around 80:20.
[0039] The step of providing a mass of grains of superhard material
may comprises, for example, providing a mass of grains in which the
grain size distributions of the first and second fractions do not
overlap.
[0040] The step of providing a mass of grains of superhard material
may, in some embodiments, comprise providing three or more grain
size modes to form a multimodal mass of grains comprising a blend
of grain sizes having associated average grain sizes.
[0041] In some embodiments, the average grain sizes of the
fractions is separated by an order of magnitude.
[0042] In some embodiments, the mass of superhard grains comprises
a first fraction having an average grain size of around 20 microns,
a second fraction having an average grain size of around 2 microns,
a third fraction having an average grain size of around 200 nm and
a fourth fraction having an average grain size of around 20 nm.
[0043] Viewed from a further aspect there is provided a tool
comprising the superhard polycrystalline construction defined
above, the tool being for cutting, milling, grinding, drilling,
earth boring, rock drilling or other abrasive applications.
[0044] The tool may comprise, for example, a drill bit for earth
boring or rock drilling, a rotary fixed-cutter bit for use in the
oil and gas drilling industry, or a rolling cone drill bit, a hole
opening tool, an expandable tool, a reamer or other earth boring
tools.
[0045] Viewed from another aspect there is provided a drill bit or
a cutter or a component therefor comprising the superhard
polycrystalline construction defined above.
BRIEF DESCRIPTION OF THE DRAWINGS
[0046] The present invention will now be described by way of
example and with reference to the accompanying drawings in
which:
[0047] FIG. 1 is a polycrystalline diamond (PCD) structures
attached to a substrate;
[0048] FIG. 2 is a plot showing wear scar depth for two
embodiments; and
[0049] FIG. 3 is a plot of wear scar area against cutting length in
a vertical borer test for an embodiment.
DESCRIPTION
[0050] As used herein, a "superhard material" is a material having
a Vickers hardness of at least about 28 Gpa. Diamond and cubic
boron nitride (cBN) material are examples of superhard
materials.
[0051] As used herein, a "superhard construction" means a
construction comprising a body of polycrystalline superhard
material. In such a construction, a substrate may be attached
thereto or alternatively the body of polycrystalline material may
be free-standing and unbacked.
[0052] As used herein, polycrystalline diamond (PCD) is a type of
polycrystalline superhard (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. In one embodiment
of PCD material, interstices between the diamond grains may be at
least partly filled with a binder material comprising a catalyst
for diamond. As used herein, "interstices" or "interstitial
regions" are regions between the diamond grains of PCD material. In
embodiments of PCD material, interstices or interstitial regions
may be substantially or partially filled with a material other than
diamond, or they may be substantially empty. PCD material may
comprise at least a region from which catalyst material has been
removed from the interstices, leaving interstitial voids between
the diamond grains.
[0053] As used herein, PCBN (polycrystalline cubic boron nitride)
material refers to a type of superhard material comprising grains
of cubic boron nitride (cBN) dispersed within a matrix comprising
metal or ceramic. PCBN is an example of a superhard material.
[0054] A "catalyst material" for a superhard material is capable of
promoting the growth or sintering of the superhard material.
[0055] The term "substrate" as used herein means any substrate over
which the ultra hard material layer is formed. For example, a
"substrate" as used herein may be a transition layer formed over
another substrate. Additionally, as used herein, the terms "radial"
and "circumferential" and like terms are not meant to limit the
feature being described to a perfect circle.
[0056] The superhard construction 1 shown in the FIG. 1 may be
suitable, for example, for use as a cutter insert for a drill bit
for boring into the earth.
[0057] Like reference numbers are used to identify like features in
all drawings.
[0058] In an embodiment as shown in FIG. 1, a cutting element 1
includes a substrate 10 with a layer of ultra-hard material 12
formed on the substrate 10. The substrate may be formed of a hard
material such as cemented tungsten carbide. The ultra-hard material
may be, for example, polycrystalline diamond (PCD), polycrystalline
cubic boron nitride (PCBN), or a thermally stable product such as
thermally stable PCD (TSP). The cutting element 1 may be mounted
into a bit body such as a drag bit body (not shown). The exposed
top surface of the ultra-hard material opposite the substrate forms
the cutting face 14, which is the surface which, along with its
edge 16, performs the cutting in use.
[0059] At one end of the substrate 10 is an interface surface 18
that interfaces with the ultra-hard material layer 12 which is
attached thereto at this interface surface. The substrate 10 is
generally cylindrical and has a peripheral surface 20 and a
peripheral top edge 22.
[0060] The grains of superhard material, such as diamond grains or
particles in the starting mixture prior to sintering may be, for
example, bimodal, that is, the feed comprises a mixture of a coarse
fraction of diamond grains and a fine fraction of diamond grains.
In some embodiments, the coarse fraction may have, for example, an
average particle/grain size ranging from about 10 to 60 microns. By
"average particle or grain size" it is meant that the individual
particles/grains have a range of sizes with the mean particle/grain
size representing the "average". The average particle/grain size of
the fine fraction is less than the size of the coarse fraction, for
example between around 1/10 to 6/10 of the size of the coarse
fraction, and may, in some embodiments, range for example between
about 0.1 to 20 microns.
[0061] In some embodiments, the weight ratio of the coarse diamond
fraction to the fine diamond fraction ranges from about 50% to
about 97% coarse diamond and the weight ratio of the fine diamond
fraction may be from about 3% to about 50%. In other embodiments,
the weight ratio of the coarse fraction to the fine fraction will
range from about 70:30 to about 90:10.
[0062] In further embodiments, the weight ratio of the coarse
fraction to the fine fraction may range for example from about
60:40 to about 80:20.
[0063] In some embodiments, the particle size distributions of the
coarse and fine fractions do not overlap and in some embodiments
the different size components of the compact are separated by an
order of magnitude between the separate size fractions making up
the multimodal distribution.
[0064] The embodiments consists of at least a wide bi-modal size
distribution between the coarse and fine fractions of superhard
material, but some embodiments may include three or even four or
more size modes which may, for example, be separated in size by an
order of magnitude, for example, a blend of particle sizes whose
average particle size is 20 microns, 2 microns, 200 nm and 20
nm.
[0065] Sizing of diamond particles/grains into fine fraction,
coarse fraction, or other sizes in between, may be through known
processes such as jet-milling of larger diamond grains and the
like.
[0066] In embodiments where the superhard material is
polycrystalline diamond material, the diamond grains used to form
the polycrystalline diamond material may be natural or
synthetic.
[0067] In some embodiments, the binder catalyst/solvent may
comprise cobalt or some other iron group elements, such as iron or
nickel, or an alloy thereof. Carbides, nitrides, borides, and
oxides of the metals of Groups IV-VI in the periodic table are
other examples of non-diamond material that might be added to the
sinter mix. In some embodiments, the binder/catalyst/sintering aid
may be Co.
[0068] The cemented metal carbide substrate may be conventional in
composition and, thus, may be include any of the Group IVB, VB, or
VIB metals, which are pressed and sintered in the presence of a
binder of cobalt, nickel or iron, or alloys thereof. In some
embodiments, the metal carbide is tungsten carbide.
[0069] In some embodiments, both the bodies of, for example,
diamond and carbide material plus sintering aid/binder/catalyst are
applied as powders and sintered simultaneously in a single UHP/HT
process. The mixture of diamond grains and mass of carbide are
placed in an HP/HT reaction cell assembly and subjected to HP/HT
processing. The HP/HT processing conditions selected are sufficient
to effect intercrystalline bonding between adjacent grains of
abrasive particles and, optionally, the joining of sintered
particles to the cemented metal carbide support. In one embodiment,
the processing conditions generally involve the imposition for
about 3 to 120 minutes of a temperature of at least about 1200
degrees C. and an ultra-high pressure of greater than about 5
Gpa.
[0070] In another embodiment, the substrate may be pre-sintered in
a separate process before being bonded together in the HP/HT press
during sintering of the ultrahard polycrystalline material.
[0071] In a further embodiment, both the substrate and a body of
polycrystalline superhard material are pre-formed. For example, the
bimodal feed of ultrahard grains/particles with optional carbonate
binder-catalyst also in powdered form are mixed together, and the
mixture is packed into an appropriately shaped canister and is then
subjected to extremely high pressure and temperature in a press.
Typically, the pressure is at least 5 GPa and the temperature is at
least around 1200 degrees C. The preformed body of polycrystalline
superhard material is then placed in the appropriate position on
the upper surface of the preform carbide substrate (incorporating a
binder catalyst), and the assembly is located in a suitably shaped
canister. The assembly is then subjected to high temperature and
pressure in a press, the order of temperature and pressure being
again, at least around 1200 degrees C. and 5 Gpa respectively.
During this process the solvent/catalyst migrates from the
substrate into the body of superhard material and acts as a
binder-catalyst to effect intergrowth in the layer and also serves
to bond the layer of polycrystalline superhard material to the
substrate. The sintering process also serves to bond the body of
superhard polycrystalline material to the substrate.
[0072] The practical use of cemented carbide grades with
substantially lower cobalt content as substrates for PCD inserts is
limited by the fact that some of the Co is required to migrate from
the substrate into the PCD layer during the sintering process in
order to catalyse the formation of the PCD. For this reason, it is
more difficult to make PCD on substrate materials comprising lower
Co contents, even though this may be desirable.
[0073] An embodiment of a superhard construction may be made by a
method including providing a cemented carbide substrate, contacting
an aggregated, substantially unbonded mass of diamond particles
against a surface of the substrate to form an pre-sinter assembly,
encapsulating the pre-sinter assembly in a capsule for an
ultra-high pressure furnace and subjecting the pre-sinter assembly
to a pressure of at least about 5.5 Gpa and a temperature of at
least about 1,250 degrees centigrade, and sintering the diamond
particles to form a PCD composite compact element comprising a PCD
structure integrally formed on and joined to the cemented carbide
substrate. In some embodiments of the invention, the pre-sinter
assembly may be subjected to a pressure of at least about 6 Gpa, at
least about 6.5 Gpa, at least about 7 Gpa or even at least about
7.5 Gpa.
[0074] The hardness of cemented tungsten carbide substrate may be
enhanced by subjecting the substrate to an ultra-high pressure and
high temperature, particularly at a pressure and temperature at
which diamond is thermodynamically stable. The magnitude of the
enhancement of the hardness may depend on the pressure and
temperature conditions. In particular, the hardness enhancement may
increase the higher the pressure. Whilst not wishing to be bound by
a particular theory, this is considered to be related to the Co
drift from the substrate into the PCD during press sintering, as
the extent of the hardness increase is directly dependent on the
decrease of Co content in the substrate.
[0075] In embodiments where the cemented carbide substrate does not
contain sufficient solvent/catalyst for diamond, and where the PCD
structure is integrally formed onto the substrate during sintering
at an ultra-high pressure, solvent/catalyst material may be
included or introduced into the aggregated mass of diamond grains
from a source of the material other than the cemented carbide
substrate. The solvent/catalyst material may comprise cobalt that
infiltrates from the substrate in to the aggregated mass of diamond
grains just prior to and during the sintering step at an ultra-high
pressure. However, in embodiments where the content of cobalt or
other solvent/catalyst material in the substrate is low,
particularly when it is less than about 11 weight percent of the
cemented carbide material, then an alternative source may need to
be provided in order to ensure good sintering of the aggregated
mass to form PCD.
[0076] Solvent/catalyst for diamond may be introduced into the
aggregated mass of diamond grains by various methods, including
blending solvent/catalyst material in powder form with the diamond
grains, depositing solvent/catalyst material onto surfaces of the
diamond grains, or infiltrating solvent/catalyst material into the
aggregated mass from a source of the material other than the
substrate, either prior to the sintering step or as part of the
sintering step. Methods of depositing solvent/catalyst for diamond,
such as cobalt, onto surfaces of diamond grains are well known in
the art, and include chemical vapour deposition (CVD), physical
vapour deposition (PVD), sputter coating, electrochemical methods,
electroless coating methods and atomic layer deposition (ALD). It
will be appreciated that the advantages and disadvantages of each
depend on the nature of the sintering aid material and coating
structure to be deposited, and on characteristics of the grain.
[0077] In one embodiment of a method of the invention, cobalt may
be deposited onto surfaces of the diamond grains by first
depositing a pre-cursor material and then converting the precursor
material to a material that comprises elemental metallic cobalt.
For example, in the first step cobalt carbonate may be deposited on
the diamond grain surfaces using the following reaction:
Co(NO.sub.3).sub.2+Na.sub.2CO.sub.3.fwdarw.CoCO.sub.3+2NaNO.sub.3
[0078] The deposition of the carbonate or other precursor for
cobalt or other solvent/catalyst for diamond may be achieved by
means of a method described in PCT patent publication number
WO/2006/032982. The cobalt carbonate may then be converted into
cobalt and water, for example, by means of pyrolysis reactions such
as the following:
CoCO.sub.3.fwdarw.CoO+CO.sub.2
CoO+H.sub.2.fwdarw.Co+H.sub.2O
[0079] In another embodiment of the method of the invention, cobalt
powder or precursor to cobalt, such as cobalt carbonate, may be
blended with the diamond grains. Where a precursor to a
solvent/catalyst such as cobalt is used, it may be necessary to
heat treat the material in order to effect a reaction to produce
the solvent/catalyst material in elemental form before sintering
the aggregated mass.
[0080] In some embodiments, the cemented carbide substrate may be
formed of tungsten carbide particles bonded together by the binder
material, the binder material comprising an alloy of Co, Ni and Cr.
The tungsten carbide particles may form at least 70 weight percent
and at most 95 weight percent of the substrate;. The binder
material may comprise between about 10 to 50 wt. % Ni, between
about 0.1 to 10 wt. % Cr, and the remainder weight percent
comprises Co. The size distribution of the tungsten carbide
particles in the cemented carbide substrate ion some embodiments
has the following characteristics: [0081] fewer than 17 percent of
the carbide particles have a grain size of equal to or less than
about 0.3 microns; [0082] between about 20 to 28 percent of the
tungsten carbide particles have a grain size of between about 0.3
to 0.5 microns; [0083] between about 42 to 56 percent of the
tungsten carbide particles have a grain size of between about 0.5
to 1 microns; [0084] less than about 12 percent of the tungsten
carbide particles are greater than 1 micron; and [0085] the mean
grain size of the tungsten carbide particles is about 0.6.+-.0.2
microns.
[0086] In some embodiments, the binder additionally comprises
between about 2 to 20 wt. % tungsten and between about 0.1 to 2 wt.
% carbon
[0087] A layer of the substrate adjacent to the interface with the
body of polycrystalline diamond material may have a thickness of,
for example, around 100 microns and may comprise tungsten carbide
grains, and a binder phase. This layer may be characterised by the
following elemental composition measured by means of
Energy-Dispersive X-Ray Microanalysis (EDX): [0088] between about
0.5 to 2.0 wt % cobalt; [0089] between about 0.05 to 0.5 wt. %
nickel; [0090] between about 0.05 to 0.2 wt. % chromium; and [0091]
tungsten and carbon.
[0092] In a further embodiment, in the layer described above in
which the elemental composition includes between about 0.5 to 2.0
wt % cobalt, between about 0.05 to 0.5 wt. % nickel and between
about 0.05 to 0.2 wt. % chromium, the remainder is tungsten and
carbon.
[0093] The layer of substrate may further comprise free carbon.
[0094] The magnetic properties of the cemented carbide material may
be related to important structural and compositional
characteristics. The most common technique for measuring the carbon
content in cemented carbides is indirectly, by measuring the
concentration of tungsten dissolved in the binder to which it is
indirectly proportional: the higher the content of carbon dissolved
in the binder the lower the concentration of tungsten dissolved in
the binder. The tungsten content within the binder may be
determined from a measurement of the magnetic moment, a, or
magnetic saturation, M.sub.s=4.pi..sigma., these values having an
inverse relationship with the tungsten content (Roebuck (1996),
"Magnetic moment (saturation) measurements on cemented carbide
materials", Int. J. Refractory Met., Vol. 14, pp. 419-424.). The
following formula may be used to relate magnetic saturation, Ms, to
the concentrations of W and C in the binder:
M.sub.s.varies.[C]/[W].times.wt. % Co.times.201.9 in units of
.mu.T.m.sup.3/kg
[0095] The binder cobalt content within a cemented carbide material
may be measured by various methods well known in the art, including
indirect methods such as such as the magnetic properties of the
cemented carbide material or more directly by means of
energy-dispersive X-ray spectroscopy (EDX), or a method based on
chemical leaching of Co.
[0096] The mean grain size of carbide grains, such as WC grains,
may be determined by examination of micrographs obtained using a
scanning electron microscope (SEM) or light microscopy images of
metallurgically prepared cross-sections of a cemented carbide
material body, applying the mean linear intercept technique, for
example. Alternatively, the mean size of the WC grains may be
estimated indirectly by measuring the magnetic coercivity of the
cemented carbide material, which indicates the mean free path of Co
intermediate the grains, from which the WC grain size may be
calculated using a simple formula well known in the art. This
formula quantifies the inverse relationship between magnetic
coercivity of a Co-cemented WC cemented carbide material and the Co
mean free path, and consequently the mean WC grain size. Magnetic
coercivity has an inverse relationship with MFP.
[0097] As used herein, the "mean free path" (MFP) of a composite
material such as cemented carbide is a measure of the mean distance
between the aggregate carbide grains cemented within the binder
material. The mean free path characteristic of a cemented carbide
material may be measured using a micrograph of a polished section
of the material. For example, the micrograph may have a
magnification of about 1000.times.. The MFP may be determined by
measuring the distance between each intersection of a line and a
grain boundary on a uniform grid. The matrix line segments, Lm, are
summed and the grain line segments, Lg, are summed. The mean matrix
segment length using both axes is the "mean free path". Mixtures of
multiple distributions of tungsten carbide particle sizes may
result in a wide distribution of MFP values for the same matrix
content. This is explained in more detail below.
[0098] The concentration of W in the Co binder depends on the C
content. For example, the W concentration at low C contents is
significantly higher. The W concentration and the C content within
the Co binder of a Co-cemented WC (WC-Co) material may be
determined from the value of the magnetic saturation. The magnetic
saturation 4.pi..sigma. or magnetic moment .sigma. of a hard metal,
of which cemented tungsten carbide is an example, is defined as the
magnetic moment or magnetic saturation per unit weight. The
magnetic moment, .sigma., of pure Co is 16.1 micro-Tesla times
cubic metre per kilogram (.mu.T.m.sup.3/kg), and the induction of
saturation, also referred to as the magnetic saturation,
4.pi..sigma., of pure Co is 201.9 .mu.T.m.sup.3/kg.
[0099] In some embodiments, the cemented carbide substrate may have
a mean magnetic coercivity of at least about 100 Oe and at most
about 145 Oe, and a magnetic moment of specific magnetic saturation
with respect to that of pure Co of at least about 89 percent to at
most about 97 percent.
[0100] A desired MFP characteristic in the substrate may be
accomplished several ways known in the art. For example, a lower
MFP value may be achieved by using a lower metal binder content. A
practical lower limit of about 3 weight percent cobalt applies for
cemented carbide and conventional liquid phase sintering. In an
embodiment where the cemented carbide substrate is subjected to an
ultra-high pressure, for example a pressure greater than about 5
Gpa and a high temperature (greater than about 1,400.degree. C. for
example), lower contents of metal binder, such as cobalt, may be
achieved. For example, where the cobalt content is about 3 weight
percent and the mean size of the WC grains is about 0.5 micron, the
MFP would be about 0.1 micron, and where the mean size of the WC
grains is about 2 microns, the MFP would be about 0.35 microns, and
where the mean size of the WC grains is about 3 microns, the MFP
would be about 0.7 microns. These mean grain sizes correspond to a
single powder class obtained by natural comminution processes that
generate a log normal distribution of particles. Higher matrix
(binder) contents would result in higher MFP values.
[0101] Changing grain size by mixing different powder classes and
altering the distributions may achieve a whole spectrum of MFP
values for the substarte depending on the particulars of powder
processing and mixing. The exact values would have to be determined
empirically.
[0102] In some embodiments, the substrate comprises Co, Ni and
Cr.
[0103] The binder material for the substrate may include at least
about 0.1 weight percent to at most about 5 weight percent one or
more of V, Ta, Ti, Mo, Zr, Nb and Hf in solid solution.
[0104] In further embodiments, the polycrystalline diamond (PCD)
composite compact element may include at least about 0.01 weight
percent and at most about 2 weight percent of one or more of Re,
Ru, Rh, Pd, Re, Os, Ir and Pt.
[0105] A polycrystalline construction according to some embodiments
may have a specific weight loss in an erosion test in a
recirculating rig generating an impinging jet of liquid-solid
slurry below 2.times.10.sup.-3 g/cm.sup.3 at the following testing
conditions: a temperature of 50.degree. C., an impingement angle of
45.degree., a slurry velocity of 20 m/s, a pH of 8.02, a duration
of 3 hours, and a slurry composition in 1 cubic meter water of: 40
kg Bentonite; 2 kg Na2CO3; 3 kg carboxymethyl cellulose, 5
litres
[0106] Some embodiments of a cemented carbide body may be formed by
providing tungsten carbide powder having a mean equivalent circle
diameter (ECD) size in the range from about 0.2 microns to about
0.6 microns, the ECD size distribution having the further
characteristic that fewer than 45 percent of the carbide particles
have a mean size of less than 0.3 microns; 30 to 40 percent of the
carbide particles have a mean size of at least 0.3 microns and at
most 0.5 microns; 18 to 25 percent of the carbide particles have a
mean size of greater than 0.5 microns and at most 1 micron; fewer
than 3 percent of the carbide particles have a mean size of greater
than 1 micron. The tungsten carbide powder is milled with binder
material comprising Co, Ni and Cr or chromium carbides, the
equivalent total carbon comprised in the blended powder being, for
example, about 6 percent with respect to the tungsten carbide. The
blended powder is then compacted to form a green body and the green
body is sintered to produce the cemented carbide body.
[0107] The sintering the green body may take place at a temperature
of, for example, at least 1,400 degrees centigrade and at most
1,440 degrees centigrade for a period of at least 65 minutes and at
most 85 minutes.
[0108] In some embodiments, the equivalent total carbon (ETC)
comprised in the cemented carbide material is about 6.12 percent
with respect to the tungsten carbide.
[0109] The size distribution of the tungsten carbide powder may, in
some embodiments, have the characteristic of a mean ECD of 0.4
microns and a standard deviation of 0.1 microns.
[0110] To assist in improving thermal stability of the sintered
structure, the catalysing material may removed from a region of the
polycrystalline layer adjacent an exposed surface thereof.
Generally, that surface will be on a side of the polycrystalline
layer opposite to the substrate and will provide a working surface
for the polycrystalline diamond layer. Removal of the catalysing
material may be carried out using methods known in the art such as
electrolytic etching, and acid leaching and evaporation
techniques.
[0111] Embodiments are described in more detail below with
reference to the following examples which are provided herein by
way of illustration only and are not intended to be limiting.
EXAMPLE 1
[0112] A quantity of sub-micron cobalt powder sufficient to obtain
2 mass % in the final diamond mixture was initially de-agglomerated
in a methanol slurry in a ball mill with WC milling media for 1
hour. A fine fraction of diamond powder with an average grain size
of 2 .mu.m was then added to the slurry in an amount to obtain 10
mass % in the final mixture. Additional milling media was
introduced and further methanol was added to obtain suitable
slurry; and this was milled for a further hour. A coarse fraction
of diamond, with an average grain size of approximately 20 .mu.m
was then added in an amount to obtain 88 mass % in the final
mixture. The slurry was again supplemented with further methanol
and milling media, and then milled for a further 2 hours. The
slurry was removed from the ball mill and dried to obtain the
diamond powder mixture.
[0113] The diamond powder mixture was then placed into a suitable
HpHT vessel, adjacent to a tungsten carbide substrate and sintered
at a pressure of around 6.8 Gpa and a temperature of about
1500.degree. C.
EXAMPLE 2
[0114] A quantity of sub-micron cobalt powder sufficient to obtain
2.4 mass % in the final diamond mixture was initially
de-agglomerated in a methanol slurry in a ball mill with WC milling
media for 1 hour. A fine fraction of diamond powder with an average
grain size of 2 .mu.m was then added to the slurry in an amount to
obtain 29.3 mass % in the final mixture. Additional milling media
was introduced and further methanol was added to obtain a suitable
slurry; and this was milled for a further hour. A coarse fraction
of diamond, with an average grain size of approximately 20 .mu.m
was then added in an amount to obtain 68.3 mass % in the final
mixture. The slurry was again supplemented with further methanol
and milling media, and then milled for a further 2 hours. The
slurry was removed from the ball mill and dried to obtain the
diamond powder mixture.
[0115] The diamond powder mixture was then placed into a suitable
HpHT vessel, adjacent to a tungsten carbide substrate and sintered
at a pressure of around 6.8 Gpa and a temperature of about 1500
.degree. C.
[0116] The diamond content of the sintered diamond structure is
greater than 90 vol % and the coarsest fraction of the distribution
is greater than 60 weight % and preferably greater than weight
70%.
[0117] In order to test the abrasion resistance of the finished PCD
compacts formed according to the above examples, the diamond layers
were polished and a subjected to a conventional granite turning
test for 3 minutes. The wear scar progression during the machining
process was monitored. The results for both examples are shown in
FIG. 2. It will be seen that the wear scars of the PCD compacts
formed according to examples 1 and 2 above were less than that
occurring in a conventional PCD compact shown as Ref 1 which was
sintered at a pressure of 6.8 GPa and had an average diamond grain
size of around 11.3 microns.
[0118] The PCD compact formed according to Example 2 was then
compared in a vertical boring mill test with commercially available
polycrystalline diamond cutter elements. In this test, the wear
flat area was measured as a function of the number of passes of the
cutter element boring into the workpiece. The results obtained are
illustrated graphically by FIG. 3. The results provide an
indication of the total wear scar area plotted against cutting
length. It will be seen that the PCD compact formed according to
example 2 was able to achieve a greater cutting length and smaller
wear scar area than that occurring in a conventional PCD compacts
which were subjected to the same test for comparison. The
conventional PCD compacts in this test comprised Ref 1 which was
sintered at a pressure of 6.8 GPa and had an average diamond grain
size of around 11.3 microns and Ref 2 which was sintered at a
pressure of 6.8 GPa and had a grain size of around 9.5 microns.
[0119] In polycrystalline diamond material, individual diamond
particles/grains are, to a large extent, bonded to adjacent
particles/grains through diamond bridges or necks. The individual
diamond particles/grains retain their identity, or generally have
different orientations. The average grain/particle size of these
individual diamond grains/particles may be determined using image
analysis techniques. Images are collected on a scanning electron
microscope and are analysed using standard image analysis
techniques. From these images, it is possible to extract a
representative diamond particle/grain size distribution.
[0120] Generally, the body of polycrystalline diamond material will
be produced and bonded to the cemented carbide substrate in a HPHT
process. In so doing, it is advantageous for the binder phase and
diamond particles to be arranged such that the binder phase is
distributed homogeneously and is of a fine scale.
[0121] The homogeneity or uniformity of the sintered structure is
defined by conducting a statistical evaluation of a large number of
collected images. The distribution of the binder phase, which is
easily distinguishable from that of the diamond phase using
electron microscopy, can then be measured in a method similar to
that disclosed in EP 0974566. This method allows a statistical
evaluation of the average thicknesses of the binder phase along
several arbitrarily drawn lines through the microstructure. This
binder thickness measurement is also referred to as the "mean free
path" by those skilled in the art. For two materials of similar
overall composition or binder content and average diamond grain
size, the material which has the smaller average thickness will
tend to be more homogenous, as this implies a "finer scale"
distribution of the binder in the diamond phase. In addition, the
smaller the standard deviation of this measurement, the more
homogenous is the structure. A large standard deviation implies
that the binder thickness varies widely over the microstructure,
i.e. that the structure is not even, but contains widely dissimilar
structure types.
[0122] The binder and diamond mean free path measurements were
obtained for various samples formed according to embodiments in the
manner set out below. Unless otherwise stated herein, dimensions of
mean free path within the body of PCD material refer to the
dimensions as measured on a surface of, or a section through, a
body comprising PCD material and no stereographic correction has
been applied. For example, the measurements are made by means of
image analysis carried out on a polished surface, and a Saltykov
correction has not been applied in the data stated herein.
[0123] In measuring the mean value of a quantity or other
statistical parameter measured by means of image analysis, several
images of different parts of a surface or section (hereinafter
referred to as samples) are used to enhance the reliability and
accuracy of the statistics. The number of images used to measure a
given quantity or parameter may be, for example between 10 to 30.
If the analysed sample is uniform, which is the case for PCD,
depending on magnification, 10 to 20 images may be considered to
represent that sample sufficiently well.
[0124] The resolution of the images needs to be sufficiently high
for the inter-grain and inter-phase boundaries to be clearly made
out and, for the measurements stated herein an image area of 1280
by 960 pixels was used. Images used for the image analysis were
obtained by means of scanning electron micrographs (SEM) taken
using a backscattered electron signal. The back-scatter mode was
chosen so as to provide high contrast based on different atomic
numbers and to reduce sensitivity to surface damage (as compared
with the secondary electron imaging mode). [0125] 1. A sample piece
of the PCD sintered body is cut using wire EDM and polished. At
least 10 back scatter electron images of the surface of the sample
are taken using a Scanning Electron Microscope at 1000 times
magnifications. [0126] 2. The original image was converted to a
greyscale image. The image contrast level was set by ensuring the
diamond peak intensity in the grey scale histogram image occurred
between 10 and 20. [0127] 3. An auto threshold feature was used to
binarise the image and specifically to obtain clear resolution of
the diamond and binder phases. [0128] 4. The software, having the
trade name analySIS Pro from Soft Imaging System.RTM. GmbH (a
trademark of Olympus Soft Imaging Solutions GmbH) was used and
excluded from the analysis any particles which touched the
boundaries of the image. This required appropriate choice of the
image magnification: [0129] a. If too low then resolution of fine
particles is reduced. [0130] b. If too high then: [0131] i.
Efficiency of coarse grain separation is reduced. [0132] ii. High
numbers of coarse grains are cut by the boarders of the image and
hence less of these grains are analysed. [0133] iii. Thus more
images must be analysed to get a statistically-meaningful result.
[0134] 5. Each particle was finally represented by the number of
continuous pixels of which it is formed. [0135] 6. The AnalySIS
software programme proceeded to detect and analyse each particle in
the image. This was automatically repeated for several images.
[0136] 7. Ten SEM images were analyzed using the grey-scale to
identify the binderpools as distinct from the other phases within
the sample. The threshold value for the SEM was then determined by
selecting a maximum value for binder pools content which only
identifies binder pools and excludes all other phases (whether grey
or white). Once this threshold value is identified it is used to
binarize the SEM image.) [0137] 8. One pixel thick lines were
superimposed across the width of the binarized image, with each
line being five pixels apart (to ensure the measurement is
sufficiently representative in statistical terms). Binder phase
that are cut by image boundaries were excluded in these
measurements. [0138] 9. The distance between the binder pools along
the superimposed lines were measured and recorded--at least 10,000
measurements were made per material being analysed. The median
value for the non-diamond phase mean free paths and the diamond
phase mean free paths were calculated. The term "median" in this
context is considered to have its conventional meaning, namely the
numerical value separating the higher half of the data sample from
the lower half.
[0139] Also recorded were the mean free path measurements at Q1 and
Q3 for both the diamond and non-diamond phases.
[0140] Q1 is typically referred to as the first quartile (also
called the lower quartile) and is the number below which lies the
25 percent of the bottom data. Q3 is typically referred to as the
third quartile (also called the upper quartile) has 75 percent of
the data below it and the top 25 percent of the data above it.
[0141] From this, it was determined that embodiments have:
alpha>=0.83 and beta<0.47,
[0142] where
[0143] alpha is the non-diamond phase MFP median/(Q3-Q1), which
gives a measure of "uniform binder pool size"; and
[0144] beta=diamond MFP median/(Q3-Q1) which gives a measure of
"wide grain size distribution"
[0145] It has also been found that multimodal distributions of some
embodiments may assist in achieving a very high degree of diamond
intergrowth while still maintaining sufficient open porosity to
enable efficient leaching.
[0146] While various embodiments have been described with reference
to a number of examples, those skilled in the art will understand
that various changes may be made and equivalents may be substituted
for elements thereof and that these examples are not intended to
limit the particular embodiments disclosed.
* * * * *