U.S. patent application number 15/177401 was filed with the patent office on 2017-03-09 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.
Application Number | 20170067294 15/177401 |
Document ID | / |
Family ID | 46881430 |
Filed Date | 2017-03-09 |
United States Patent
Application |
20170067294 |
Kind Code |
A1 |
Can; Nedret |
March 9, 2017 |
SUPERHARD CONSTRUCTIONS AND METHODS OF MAKING SAME
Abstract
A superhard polycrystalline construction comprises 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; and a non-superhard phase at least
partially filling a plurality of the interstitial regions and
having an associated mean free path. The average grain size of the
superhard grains is less than or equal to 25 microns; and the ratio
of the standard deviation in the mean free path associated with the
non-superhard phase to the mean of the mean free path associated
with the non-superhard phase is greater than or equal to 80% when
measured using image analysis techniques at a magnification of
1000. There is also disclosed a method of forming such a superhard
polycrystalline construction.
Inventors: |
Can; Nedret; (Oxfordshire,
GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Element Six Abrasives S.A. |
Luxembourg |
|
LU |
|
|
Family ID: |
46881430 |
Appl. No.: |
15/177401 |
Filed: |
June 9, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14418026 |
Jan 28, 2015 |
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PCT/EP2013/065997 |
Jul 30, 2013 |
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15177401 |
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61678011 |
Jul 31, 2012 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B22F 2005/001 20130101;
E21B 10/54 20130101; B24D 18/0009 20130101; E21B 10/567 20130101;
B22F 7/06 20130101; E21B 10/5673 20130101; B24D 3/10 20130101; B22F
2999/00 20130101; B22F 2999/00 20130101; C22C 26/00 20130101; C22C
26/00 20130101; B22F 2304/05 20130101 |
International
Class: |
E21B 10/567 20060101
E21B010/567; B22F 7/06 20060101 B22F007/06; B24D 18/00 20060101
B24D018/00; B24D 3/10 20060101 B24D003/10 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 31, 2012 |
GB |
1213596.8 |
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 average grain
size of the superhard grains is less than or equal to 25 microns;
and the ratio of the standard deviation in the mean free path
associated with the non-superhard phase to the mean of the mean
free path associated with the non-superhard phase is greater than
or equal to 80% when measured using image analysis techniques at a
magnification of 1000.
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. (canceled)
4. A superhard polycrystalline construction according to claim 1,
wherein the non-superhard phase comprises a binder phase, the
binder phase comprising 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.
5.-8. (canceled)
9. A superhard polycrystalline construction according to claim 1,
wherein the average grain size of the superhard grains is between
around 8 to 20 microns.
10. A superhard polycrystalline construction according to claim 1
wherein the ratio of the standard deviation in the mean free path
associated with the non-superhard phase to the mean of the mean
free path associated with the non-superhard phase is less than 150%
when measured using image analysis techniques at a magnification of
1000.
11. A superhard polycrystalline construction according to claim 1
wherein the ratio of the standard deviation in the mean free path
associated with the non-superhard phase to the mean of the mean
free path associated with the non-superhard phase is less than 120%
when measured using image analysis techniques at a magnification of
1000.
12. A superhard polycrystalline construction according to claim 1,
wherein the body of polycrystalline superhard material comprises a
first region and a second region adjacent the first region, the
second region being bonded to the first region by intergrowth of
grains of superhard material; the first region comprising a
plurality of alternating strata or layers, each stratum or layer
having a thickness in the range of around 5 to 300 microns; the
second region comprising a plurality of strata or layers, one or
more strata or layers in the second region having a thickness
greater than the thicknesses of the individual strata or layers in
the first region, wherein: the alternating layers or strata in the
first region comprise first layers or strata alternating with
second layers or strata, the first layers or strata being in a
state of residual compressive stress and the second layers or
strata being in a state of residual tensile stress; and one or more
of the layers or strata in the first or second regions comprises:
the mass of superhard grains exhibiting inter-granular bonding and
defining a plurality of interstitial regions therebetween; and the
non-superhard phase at least partially filling a plurality of the
interstitial regions and having an associated mean free path; the
ratio of the standard deviation in the mean free path associated
with the non-superhard phase to the mean of the mean free path
associated with the non-superhard phase is greater than or equal to
80% when measured using image analysis techniques at a
magnification of 1000.
13. A superhard polycrystalline construction according to claim 12,
wherein each stratum or layer in the first region has a thickness
in the range of around 30 to 300 microns, or around 30 to 200
microns.
14. A superhard polycrystalline construction according to claim 12,
wherein the strata or layers in the second region have a thickness
of greater than around 200 microns.
15. A superhard polycrystalline construction according to claim 12,
wherein the layers or strata in the first region comprise two or
more different average diamond grain sizes.
16. A superhard polycrystalline construction according to claim 1,
wherein the body of polycrystalline superhard material comprises a
first region and a second region adjacent the first region, the
second region being bonded to the first region by intergrowth of
diamond grains; the first region comprising a plurality of
alternating strata or layers, each layer or stratum in the first
region having a thickness in the range of around 5 to 300 microns;
one or more of the layers or strata in the first region and/or the
second region comprises: a mass of superhard grains exhibiting
inter-granular bonding and defining a plurality of interstitial
regions therebetween; and a non-superhard phase at least partially
filling a plurality of the interstitial regions and having an
associated mean free path; wherein: the ratio of the standard
deviation in the mean free path associated with the non-superhard
phase to the mean of the mean free path associated with the
non-superhard phase being greater than or equal to 80% when
measured using image analysis techniques at a magnification of
1000.
17.-19. (canceled)
20. A superhard polycrystalline construction according to claim 16,
wherein the alternating layers or strata comprise first layers or
strata alternating with second layers or strata, the first layers
or strata being in a state of residual compressive stress and the
second layers or strata being in a state of residual tensile
stress.
21. A superhard polycrystalline construction according to claim 12,
wherein layers or strata in the first region and/or the second
region comprise one or more of: up to 20 wt % nanodiamond additions
in the form of nanodiamond powder grains; salt systems; borides or
metal carbides of at least one of Ti, V, or Nb; or at least one of
the metals Pd or Ni.
22. A superhard polycrystalline construction according to claim 12,
wherein the PCD structure has a longitudinal axis, the layers or
strata in the first region and/or the second region lying in a
plane substantially perpendicular to the plane through which the
longitudinal axis of the PCD structure extends.
23. A superhard polycrystalline construction according to claim 12,
wherein the layers or strata are substantially planar, curved,
bowed or domed.
24. A superhard polycrystalline construction according to claim 12,
wherein the PCD structure has a longitudinal axis, the layers or
strata in the first region and/or the second region lying in a
plane at an angle to the plane through which the longitudinal axis
of the PCD structure extends.
25. A superhard polycrystalline construction according to claim 12,
wherein the volume of the first region is greater than the volume
of the second region.
26. A superhard polycrystalline construction according to claim 12,
wherein one or more of the strata or layers intersect a working
surface or side surface of the PCD structure.
27. A superhard polycrystalline construction according to claim 12,
wherein each strata or layer is formed of one or more respective
PCD grades having a TRS of at least 1,000 MPa; the PCD grade or
grades in adjacent strata or layers having a different coefficient
of thermal expansion (CTE).
28. (canceled)
29. A superhard polycrystalline construction as claimed in claim
12, wherein at least a portion of the first region is substantially
free of a catalyst material for diamond, said portion forming a
thermally stable region.
30.-31. (canceled)
32. A superhard construction according to claim 1 further
comprising: a substrate comprising a periphery and an interface
surface and a longitudinal axis; wherein the body of
polycrystalline superhard material is formed over the substrate and
having an exposed outer surface, a peripheral surface extending
therefrom and an interface surface; wherein one of the interface
surface of the substrate or the interface surface of the body of
polycrystalline superhard material comprises: a plurality of
spaced-apart projections arranged to project from the interface
surface, the interface surface between the spaced-apart projections
being uneven.
33.-50. (canceled)
51. The superhard construction of claim 32, wherein the superhard
construction is a cutter element.
52-74. (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 a superhard
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
superhard 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 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 a superhard 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
diamond or polycrystalline CBN layer.
[0007] In some instances, the substrate may be fully cured prior to
attachment to the superhard 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 superhard material
layer.
[0008] Ever increasing drives for improved productivity in the
earth boring field 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 average grain size of the superhard grains is less than
or equal to 25 microns; and
[0015] the ratio of the standard deviation in the mean free path
associated with the non-superhard phase to the mean of the mean
free path associated with the non-superhard phase is greater than
or equal to 80% when measured using image analysis techniques at a
magnification of 1000.
Viewed from a second aspect there is provided a method of forming a
superhard polycrystalline construction, comprising:
[0016] 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,
[0017] arranging the mass of superhard grains to form a pre-sinter
assembly; and
[0018] treating the pre-sinter assembly in the presence of a
catalyst/solvent material for the superhard grains at an ultra-high
pressure of around 6 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 non-superhard phase has an associated mean free path; and
[0019] wherein:
[0020] the average grain size of the superhard grains is less than
or equal to 25 microns; and
[0021] the ratio of the standard deviation in the mean free path
associated with the non-superhard phase to the mean of the mean
free path associated with the non-superhard phase is greater than
or equal to 80% when measured using image analysis techniques at a
magnification of 1000.
[0022] 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.
[0023] 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.
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
[0024] The present invention will now be described by way of
example and with reference to the accompanying drawings in
which:
[0025] FIG. 1 is a polycrystalline diamond (PCD) structure attached
to a substrate;
[0026] FIG. 2 shows a schematic cross-section view of an example of
a portion of a PCD structure;
[0027] FIG. 3 shows a schematic longitudinal cross-section view of
an example of a PCD element;
[0028] FIG. 4 shows a schematic longitudinal cross-section view of
an example of a PCD element;
[0029] FIG. 5 shows a schematic perspective view of part of an
example of a drill bit for boring into the earth;
[0030] FIG. 6A shows a schematic longitudinal cross-section view of
an example of a pre-sinter assembly for a PCD element;
[0031] FIG. 6B shows a schematic longitudinal cross-section view of
an example of a PCD element;
[0032] FIGS. 7A, 7B, 7C and 7D show schematic cross-section views
of parts of examples of PCD structures;
[0033] FIG. 8 is a perspective view of a cutting element having a
non-planar interface according to one example;
[0034] FIG. 9a is a perspective view of the plurality of
projections of FIG. 8 in free space;
[0035] FIG. 9b is a schematic plan view of the substrate of the
cutting element of FIG. 8;
[0036] FIG. 9c is a schematic cross-sectional view of the substrate
along the axis A-A shown in FIG. 9b;
[0037] FIG. 9d is a schematic perspective view of the substrate of
the cutting element of FIG. 8;
[0038] FIG. 10 is a perspective view of a cutting element according
to an example;
[0039] FIG. 11 is a perspective view of a substrate according to a
further example;
[0040] FIG. 12a is a perspective view of a substrate of a cutting
element according to a further embodiment;
[0041] FIG. 12b is a schematic plan view of the substrate of the
cutting element of FIG. 12a;
[0042] FIG. 12c is a schematic cross-sectional view of the
substrate along the axis A-A shown in FIG. 12b;
[0043] FIG. 13 is an interval plot of chipping height for an
example and two conventional reference cutters;
[0044] FIG. 14 is a plot from a high energy drop test showing pass
rate against drop energy for an example and two conventional
reference cutters; and
[0045] FIG. 15 is a plot of depth of penetration against rate of
penetration for an example and five conventional reference
cutters.
DESCRIPTION
[0046] 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.
[0047] 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.
[0048] 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.
[0049] 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.
[0050] A "catalyst material" for a superhard material is capable of
promoting the growth or sintering of the superhard material.
[0051] The term "substrate" as used herein means any substrate over
which the superhard 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.
[0052] 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.
[0053] Like reference numbers are used to identify like features in
all drawings.
[0054] In an embodiment as shown in FIG. 1, a cutting element 1
includes a substrate 10 with a body of superhard material 12 formed
on the substrate 10. The substrate may be formed of a hard material
such as cemented tungsten carbide. The superhard 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 superhard material opposite the substrate forms
the cutting face 14, which is the surface which, along with its
edge 16, performs the cutting in use.
[0055] At one end of the substrate 10 is an interface surface 17
that interfaces with the body of superhard material 12 which is
attached thereto at this interface surface. The substrate 10 is
generally cylindrical and has a peripheral surface 18 and a
peripheral top edge 19.
[0056] 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.
[0057] 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.
[0058] 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.
[0059] 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.
[0060] The embodiments may consist 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.
[0061] In some embodiments, the average grain size of the
aggregated mass of superhard grains is less than or equal to 25
microns. In some embodiments, the average grain size is between
around 8 to 20 microns.
[0062] 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.
[0063] 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.
[0064] As used herein, the term "stress state" refers to a
compressive, unstressed or tensile stress state. Compressive and
tensile stress states are understood to be opposite stress states
from each other. In a cylindrical geometrical system, the stress
states may be axial, radial or circumferential, or a net stress
state.
[0065] The body of superhard material 12 shown in FIG. 1 may, in
some embodiments, be a layered construction or have multiple
regions, as described below and illustrated in FIGS. 2 to 5c. A
first further embodiment is illustrated with reference to FIG. 2,
which shows an example of a PCD structure 12 comprising at least
two spaced-apart compressed regions 21 in compressive residual
stress states and at least one tensioned region 22 in a tensile
residual stress state. The tensioned region 22 is located between
the compressed regions 21 and is joined to them.
[0066] Variations in mechanical properties of the PCD material such
as density, elastic modulus, hardness and coefficient of thermal
expansion (CTE) may be selected to achieve the configuration of a
tensioned region between two compressed regions. Such variations
may be achieved by means of variations in content of diamond
grains, content and type of filler material, size distribution or
mean size of the PCD grains, and using different PCD grades either
on their own or in diamond mixes comprising a mixture of PCD
grades.
[0067] With reference to FIG. 3, a further example of a PCD
structure 12 integrally joined to a cemented carbide support body
10. The PCD structure 12 comprises several compressed regions 21
and several tensioned regions 22 in the form of alternating (or
inter-leaved) strata or layers. The PCD structure 12 may be
substantially cylindrical in shape and located at a working end and
defining a working surface 14. The PCD structure 12 may be joined
to the support body 10 at a non-planar interface 17. The compressed
and tensioned regions 21, 22 have a thickness in the range from
about 5 microns to about 200 or, in some embodiments, 300 microns
and may be arranged substantially parallel to the working surface
14 of the PCD structure 12. A substantially annular region 26 may
be located around a non-planar feature 31 projecting from the
support body 10.
[0068] With reference to FIG. 4, an example of a PCD element 1
comprises a PCD structure 12 integrally joined to a cemented
carbide support body 10 at a non-planar interface 25 opposite a
working surface 14 of the PCD structure 12. The PCD structure 12
may comprise about 10 to 20 alternating compressed and tensioned
regions 21, 22 in the form of extended strata or layers. A region
26 that, in this embodiment, does not contain strata may be located
adjacent the interface 25. The strata 21, 22 may be curved or bowed
and yet generally aligned with the interface 25, and may intersect
a side surface 27 of the PCD structure. Some of the strata may
intersect the working surface 14.
[0069] In some embodiments, the region 26 may be of a substantially
greater thickness than the individual strata or layers 21, 22 and,
in some embodiments, the thickness of the region comprising the
alternating layers 21, 22 may be of a greater thickness than the
thickness of the region 26 adjacent the cemented carbide support
body 10 which forms a substrate for the PCD material.
[0070] In some embodiments, the region 26 adjacent the support body
10 may include multiple layers or strata (not shown) that are of
substantially greater thickness than the individual layers or
strata 21, 22, for example, the layers 21, 22 may have a thickness
in the range from about 5 to 200 microns, and the layers in the
region 26 adjacent the support body 10 may have a thickness of
greater than about 200 microns.
[0071] In some embodiments, such as those shown in FIGS. 2 to 4,
the alternating strata, 21, 22 may have a thickness or thicknesses
in the range of from about 5 to 300 microns with the diamond
material being formed of PCD with two or more different average
diamond grain sizes, for example a mixture of two or more grades of
PCD. For example, strata 21 may be formed of an aggregated diamond
mix having average diamond grain sizes A and B and strata 22 may
also be formed of a diamond mix having average diamond grain sizes
A and B but in a different ratio to that of strata 21. In an
alternative embodiment, the strata 21 may be formed of a diamond
mix having average diamond grain sizes A and B and the strata 22
may be formed of a diamond mix having an average diamond grain size
C. It will be appreciated that any other sequence/mixture of two or
more diamond grain sizes may be used to form the alternating layers
21, 22. In these embodiments, the region 26 adjacent the support
body 10 may be formed of a single layer substantially thicker than
the individual strata 21, 22, for example, greater than around 200
microns. Alternatively, the region 26 may be formed of multiple
layers, individual layers or strata comprising diamond grains of
average grain size A and B, and/or C as used to form the diamond
mixes of the strata 21, 22 or another material or diamond grain
size may be used to form the layers in this region 26 adjacent the
support body 10.
[0072] In some embodiments, the diamond layers or strata 21, 22
and/or strata formed in region 26 adjacent the support body 10 (not
shown), may include, for example, one or more of nanodiamond
additions in the form of nanodiamond powder up to 20 wt %, salt
systems, borides, metal carbides of Ti, V, Nb or any of the metals
Pd or Ni.
[0073] In some embodiments, the strata 21, 22 and/or strata formed
in region 26 adjacent the support body 10 may lie in a plane
substantially perpendicular to the plane through which the
longitudinal axis of the diamond construction 1 extends. The strata
may be planar, curved, bowed, domed or distorted, for example, as a
result of being subjected to ultra-high pressure during sintering.
Alternatively, the alternating strata 21, 22 may be aligned at a
predetermined angle to the plane through which the longitudinal
axis of the diamond construction 1 extends to influence performance
through crack propagation control.
[0074] FIG. 5 is a schematic representation of an example of a
drill bit 39 for boring into the earth into which are inserted a
plurality of cutter elements 1 of the type shown in FIG. 1. The
cutter elements 1 may comprise any of the variations shown in the
remaining figures.
[0075] With reference to FIG. 6A, an example of a pre-sinter
assembly 40 for making a PCD element may comprise a support body
30, a region 46 comprising diamond grains packed against a
non-planar end of the support body 30, and a plurality of
alternating diamond-containing aggregate masses in the general form
of discs or wafers 41, 42 stacked on the region 46. In some
versions, the aggregate masses may be in the form of loose diamond
grains or granules. The pre-sinter assembly may be heated to remove
the binder material comprised in the stacked discs.
[0076] With reference to FIG. 6B, an example of a PCD element 100
comprises a PCD structure 200 comprising a plurality of alternating
strata 210, 220 formed of different respective multimodal grades of
PCD material, and a portion 260 that does not comprise strata. The
portion 260 may be cooperatively formed according to the shape of
the non-planar end of the support body 300 to which it has
integrally bonded during the treatment at the ultra-high pressure.
The alternating strata 210, 220 of different grades of PCD or mixes
of diamond grain sizes or grades are bonded together by direct
diamond-to-diamond intergrowth to form an integral, solid and
stratified PCD structure 200. The shapes of the PCD strata 210, 220
may be curved, bowed or distorted in some way as a result of being
subjected to the ultra-high pressure. In some versions of the
method, the aggregate masses may be arranged in the pre-sinter
assembly to achieve various other configurations of strata within
the PCD structure, taking into account possible distortion of the
arrangement during the ultra-high pressure and high temperature
treatment.
[0077] The strata 21, 22, 210, 220 may comprise different
respective PCD grades as a result of the different mean diamond
grain sizes of the strata. Different amounts of catalyst material
may infiltrate into the different types of discs 410, 420 comprised
in the pre-sinter assembly since they comprise diamond grains
having different mean sizes, and consequently different sizes of
spaces between the diamond grains. The corresponding alternating
PCD strata 21, 22, 210, 220 may thus comprise different,
alternating amounts of catalyst material for diamond. The content
of the filler material in terms of volume percent within the
tensioned region may be greater than that within each of the
compressed regions.
[0078] In one example, the compressed strata may comprise diamond
grains having mean size greater than the mean size of the diamond
grains of the tensioned strata
[0079] Whilst not wishing to be bound by a particular theory, when
the stratified PCD structure is allowed to cool from the high
temperature at which it was formed, the alternating strata
containing different amounts of metal catalyst material may
contract at different rates. This may be because metal contracts
much more substantially than diamond does as it cools from a high
temperature. This differential rate of contraction may cause
adjacent strata to pull against each other, thus inducing opposing
stresses in them.
[0080] The PCD element 100 described with reference to FIG. 6B may
be processed by grinding to modify its shape to form a PCD element
substantially as described with reference to FIG. 4. This may
involve removing part of some of the curved strata to form a
substantially planar working surface and a substantially
cylindrical side surface. Catalyst material may be removed from a
region of the PCD structure adjacent the working surface or the
side surface or both the working surface and the side surface. This
may be done by treating the PCD structure with acid to leach out
catalyst material from between the diamond grains, or by other
methods such as electrochemical methods. A thermally stable region,
which may be substantially porous, extending a depth of at least
about 50 microns or at least about 100 microns from a surface of
the PCD structure, may thus be provided. Some embodiments with 50
to 80 micron thick layers in which this leach depth is around 250
microns have been shown to exhibit substantially improved
performance, for example a doubling in performance after leaching
over an unleached PCD product. In one example, the substantially
porous region may comprise at most 2 weight percent of catalyst
material.
[0081] The use of alternating layers or strata with different grain
sizes through, for example, differences in binder content, may
controllably give a different structure when acid leaching is
applied to the PCD construction 1, 100, especially for the
embodiments in which the binder does not contain V and/or Ti. Such
a structure may be created as a result of different residual
tungsten in each layer during HCl acid leaching. In essence, the
rate of leaching is likely to be different in each layer (unless
HF-containing acid is used) and this may enable preferential
leaching especially at the edges of the PCD material. This may be
more pronounced for layers thicker than 120 microns. This is
unlikely to occur if HF acid leaching were applied to the PCD
material. The reason for this is that, in such a process, the HCl
acid removes Co and leaves behind tungsten, whilst HF acid leaching
would remove everything in the binder composition.
[0082] With reference to FIG. 7A, an example variant of a PCD
structure 200 comprises at least three substantially planar strata
210, 220 strata arranged in an alternating configuration
substantially parallel to a working surface 240 of the PCD
structure 200 and intersecting a side surface 270 of the PCD
structure.
[0083] With reference to FIG. 7B, an example variant of a PCD
structure 200 comprises at least three strata 210, 220 strata
arranged in an alternating configuration, the strata having a
curved or bowed shape, with at least part of the strata inclined
away from a working surface 240 and cutting edge 280 of the PCD
structure.
[0084] With reference to FIG. 7C, an example variant of a PCD
structure 200 comprises at least three strata 210, 220 strata
arranged in an alternating configuration, at least part of the
strata inclined away from a working surface 240 of the PCD
structure and extending generally towards a cutting edge 280 of the
PCD structure.
[0085] With reference to FIG. 7D, an example variant of a PCD
structure 200 comprises at least three strata 210, 220 strata
arranged in an alternating configuration, at least part of some of
the strata being substantially aligned with a working surface 240
of the PCD structure and at least part of some of the strata
generally aligned with a side surface 270 of the PCD structure.
Strata may be generally annular of part annular and substantially
concentric with a substantially cylindrical side surface 270 of the
PCD structure 200.
[0086] The PCD structure may have a surface region proximate a
working surface, the region comprising PCD material having a
Young's modulus of at most about 1,050 MPa, or at most about 1,000
MPa. The surface region may comprise thermally stable PCD
material.
[0087] Some examples of PCD structures may have at least 3, at
least 5, at least 7, at least 10 or even at least 15 compressed
regions, with tensioned regions located between them.
[0088] In some embodiments, each stratum or layer may have a
thickness of at least about 5 microns, in others at least about 30
microns, in others at least about 100 microns, or in others at
least about 200 microns. In some embodiments, each stratum or layer
may have a thickness of at most about 300 microns or at most about
500 microns. In some example embodiments, each stratum or layer may
have a thickness of at least about 0.05 percent, at least about 0.5
percent, at least about 1 percent or at least about 2 percent of a
thickness of the PCD structure measured from a point on a working
surface at one end to a point on an opposing surface. In some
embodiments, each stratum or layer may have a thickness of at most
about 5 percent of the thickness of the PCD structure.
[0089] As used herein, the term "residual stress state" refers to
the stress state of a body or part of a body in the absence of an
externally-applied loading force. The residual stress state of a
PCD structure, including a layer structure may be measured by means
of a strain gauge and progressively removing material layer by
layer. In some examples of PCD elements, at least one compressed
region may have a compressive residual stress of at least about 50
MPa, at least about 100 MPa, at least about 200 MPa, at least about
400 MPa or even at least about 600 MPa. The difference between the
magnitude of the residual stress of adjacent strata may be at least
about 50 MPa, at least about 100 MPa, at least about 200 MPa, at
least about 400 MPa, at least about 600 MPa, at least about 800 MPa
or even at least about 1,000 MPa. In one example, at least two
successive compressed regions or tensioned regions may have
different residual stresses. The PCD structure may comprise at
least three compressed or tensioned regions each having a different
residual compressive stress, the regions arranged in increasing or
decreasing order of compressive or tensile stress magnitude,
respectively.
[0090] In one example, each of the regions may have a mean
toughness of at most 16 MPam1/2. In some embodiments, each of the
regions may have a mean hardness of at least about 50 GPa, or at
least about 60 GPa. Each of the regions may have a mean Young's
modulus of at least about 900 MPa, at least about 950 MPa, at least
about 1,000 or even at least about 1,050 MPa.
[0091] As used herein, "transverse rupture strength" (TRS) is
measured by subjecting a specimen in the form of a bar having width
W and thickness T to a load applied at three positions, two on one
side of the specimen and one on the opposite side, and increasing
the load at a loading rate until the specimen fractures at a load
P. The TRS is then calculated based on the load P, dimensions of
the specimen and the span L, which is the distance between the two
load positions on one side. Such a measurement may also be referred
to as a three-point bending test and is described by D. Munz and T.
Fett in "Ceramics, mechanical properties, failure behaviour,
materials selection" (1999, Springer, Berlin). The TRS
corresponding to a particular grade of PCD material is measured
measuring the TRS of a specimen of PCD consisting of that
grade.
[0092] While the provision of a PCD structure with PCD strata
having alternating compression and tensile stress states tends to
increase the overall effective toughness of the PCD structure, this
may have the effect of increasing the potential incidence of
de-lamination, in which the strata may tend to come apart. While
wishing not to be bound by a particular theory, de-lamination may
tend to arise if the PCD strata are not sufficiently strong to
sustain the residual stress between them. This effect may be
ameliorated by selecting the PCD grades, and the PCD grade or
grades of which the tensioned region in particular is formed, to
have sufficiently high TRS. The TRS of the PCD grade or grades of
which the tensioned region is formed should be greater than the
residual tension that it may experience. One way of influencing the
magnitude of the stress that a region may experience is by
selecting the relative thicknesses of adjacent regions. For
example, by selecting the thickness of a tensioned region to be
greater than that of the adjacent compressive regions is likely to
reduce the magnitude of tensile stress within the tensioned
region.
[0093] The residual stress states of the regions may vary with
temperature. In use, the temperature of the PCD structure may
differ substantially between points proximate a cutting edge and
points remote from the cutting edge. In some uses, the temperature
proximate the cutting edge may reach several hundred degrees
centigrade. If the temperature exceeds about 750 degrees
centigrade, diamond material in the presence of catalyst material
such as cobalt is likely to convert to graphite material, which is
not desired. Therefore, in some uses, the alternating stress states
in adjacent regions as described herein should be considered at a
temperature of up to about 750 degrees centigrade.
[0094] The K1C toughness of a PCD disc is measured by means of a
diametral compression test, which is described by Lammer
("Mechanical properties of polycrystalline diamonds", Materials
Science and Technology, volume 4, 1988, p. 23.) and Miess (Miess,
D. and Rai, G., "Fracture toughness and thermal resistances of
polycrystalline diamond compacts", Materials Science and
Engineering, 1996, volume A209, number 1 to 2, pp. 270-276).
[0095] Young's modulus is a type of elastic modulus and is a
measure of the uni-axial strain in response to a uni-axial stress,
within the range of stress for which the material behaves
elastically. A preferred method of measuring the Young's modulus E
is by means of measuring the transverse and longitudinal components
of the speed of sound through the material, according to the
equation E=2.rho.C.sub.T.sup.2(1+.nu.), where:
.nu.=(1-2 (C.sub.T/C.sub.L).sup.2)/2-2(C.sub.T/C.sub.L).sup.2),
C.sub.L and C.sub.T are respectively the measured longitudinal and
transverse speeds of sound through it and .rho. is the density of
the material. The longitudinal and transverse speeds of sound may
be measured using ultrasonic waves, as is well known in the art.
Where a material is a composite of different materials, the mean
Young's modulus may be estimated by means of one of three formulas,
namely the harmonic, geometric and rule of mixtures formulas as
follows:
E=1/(f.sub.1/E.sub.1+f.sub.2/E.sub.2));
E=E.sub.1.sup.f1+E.sub.1.sup.f2; and
E=f.sub.1E.sub.1+f.sub.2E.sub.2;
in which the different materials are divided into two portions with
respective volume fractions of f.sub.1 and f.sub.2, which sum to
one.
[0096] As described herein, the interface between the body of
superhard material and the substrate may be substantially planar or
non-planar. Examples of non-planar interface designs are described
and illustrated with reference to FIGS. 8 to 12c.
[0097] In the embodiments described herein, when projections or
depressions are described as being formed on the substrate surface,
it should be understood that they could be formed instead on the
surface of the super-hard material layer that interfaces with the
substrate interface surface, with the inverse features formed on
the substrate. Additionally, it should be understood that a
negative or reversal of the interface surface is formed on the
superhard material layer interfacing with the substrate such that
the two interfaces form a matching fit.
[0098] As shown in the embodiment illustrated in FIG. 8, the
cutting element 400 includes the substrate 410 with the layer of
super-hard material 412 formed on the substrate 410. At one end of
the substrate 410 is the interface surface 418 that interfaces with
the superhard material layer 412 which is attached thereto at this
interface surface. The substrate 410 is generally cylindrical and
has a peripheral surface 420 and a peripheral top edge 422. In the
embodiment shown in FIG. 8, the interface surface 418 includes a
plurality of spaced-apart projections 424 that are arranged in a
substantially annular first array and are spaced from the
peripheral edge 422, and a second or inner substantially annular
array of projections 426 that are radially within the first array
424.
[0099] As shown in FIGS. 8 and 9a to 9d, in this embodiment the
spaced-apart projections 424, 426 are arranged in two arrays which
are disposed in two substantially circular paths around a central
longitudinal axis of the substrate 410. However, the invention is
not limited to this geometry, as, for example, the placement of the
projections 424, 426 may be in an ordered non-annular array on the
interface surface 418 or the projections may be randomly
distributed thereon rather than in a substantially circular or
other ordered array. Furthermore, in the embodiments where the
projections are arranged in annular arrays, these may be elliptical
or asymmetrical, or may be offset from the central longitudinal
axis of the substrate 410. Also, whilst the projections 426 of the
inner array are shown to be closer to the outer array 424 than to
the longitudinal central axis of the substrate, in other
embodiments the projections 426 of the inner array may be closer to
the longitudinal central axis.
[0100] The projections 426 in the second array may be positioned to
radially align with the spaces between the projections 424 in the
first array. The projections 424, 426 and spaces may be staggered,
with projections in one array overlapping spaces in the next array.
This staggered or mis-aligned distribution of three-dimensional
features on the interface surface may assist in distributing
compressive and tensile stresses and/or reducing the magnitude of
the stress fields and/or arresting crack growth by preventing an
uninterrupted path for crack growth.
[0101] As shown in FIGS. 8 and 9a to 9d, in these embodiments, all
or a majority of the projections 424, 426 are shaped such that all
or a majority of the surfaces of the projections are not
substantially parallel to the cutting face 414 of the superhard
material 412 or to the plane through which the longitudinal axis of
the substrate extends. Also, in the embodiments shown in FIGS. 8 to
10 and 12a to 12c, the interface surface 418 in the spaces between
projections is uneven. This may be interpreted as, but not limited
to, covering one or more of these spaces being non-uniform,
varying, irregular, rugged, not level, and/or not smooth, with
peaks and troughs. This arrangement is thought to act to inhibit
uninterrupted crack propagation along the interface surface 418 and
to increase the contact surface area between the interface of the
substrate 410 and the interface of the super hard material layer
412. Furthermore, it is believed that such a configuration acts to
disturb `elastic` wave formation in the material and deflect cracks
at the interface. These spaces or uneven valleys separating each
projection 424, 426 from the adjacent projections may be uniform in
some embodiments and non-uniform in other embodiments.
[0102] The projections 424, 426 may have a smoothly curving upper
surface or may have a sloping upper surface. In some embodiments,
the projections 424, 426 may be slightly trapezoidal or tapered in
shape, being widest nearer the interface surface from which they
project.
[0103] In FIGS. 8 and 9a to 9d, the projections 424, 426 are spaced
substantially equally in/round the respective substantially annular
array, with each projection 424, 426 within a given array having
the same dimension. However, the projections 424, 426 may be formed
in any desired shape, as described above, and spaced apart from
each other in a uniform or non-uniform manner to alter the stress
fields over the interface surface 418. The projections 424 in the
outer array are, as shown in the embodiment of FIGS. 8 and 9,
larger in size than those in the inner array. However, these
relative sizes may be reversed, or the projections 424, 426 in both
arrays could be approximately of uniform size, or a mixture of
sizes.
[0104] In the embodiment shown in FIGS. 8 and 9a to 9d, the outer
array includes double the number of projections 424 than the inner
layer, for example ten and five projections respectively. This
permits the cutter element 400 to have pseudo axi-symmetry thereby
providing freedom in positioning the cutter in the tool or drill
bit in which it is to be used as it would not require specific
orientation. The projections 424, 426 are positioned and shaped in
such a way that they inhibit one or more continuous paths along
which cracks could propagate across the interface surface 418.
Also, in some embodiments, all or the majority of the projections
and/or spaces therebetween do not have any surfaces which are
substantially normal or parallel to any loads expected to be
applied to the cutter element 400 in use, and nor which are
substantially normal or parallel to any exterior surfaces
thereof.
[0105] The arrangement and shape of the projections 424, 426 and
spaces therebetween may affect the stress distributions in the
cutting element 400 and may act to improve the cutting element's
resistance to crack growth, in particular crack growth along the
interface surface 418, for example by arresting or diverting crack
growth across the stress zones in, around and above the projections
424, 426.
[0106] As shown in the embodiment of FIG. 10, the depth of super
hard material in the region around the central longitudinal axis of
the substrate 410 may be substantially the same depth as the depth
of the super hard material at the periphery of the super hard
material layer 412. This may enable the volume and area of super
hard material exposed to the work surface in use not to decrease
significantly with wear progression thereby improving the lifespan
of the cutter element 400. It may also assist in stiffening the
cutter element 400 when loaded in the axial direction. Furthermore,
it may assist in decreasing or substantially eliminating the
possibility of grooving wear formation during use.
[0107] Another embodiment of a substrate 450 and interface surface
451 is shown in FIG. 11. The interface surface 451 of the substrate
450 includes a plurality of adjacent rows of projections 454, each
being substantially pyramidal in shape and abutting one or more
adjacent projections along one side of its base along the surface
450 from which the projections 454 project. In this embodiment, all
or a majority of the projections 454 do not have any surface
substantially parallel to either the cutting face of the super hard
layer (not shown) which will be attached thereto, or the plane
through which the longitudinal axis of the substrate 450 extends.
The projections 454 may be all the same height or some may be of a
greater height than others.
[0108] In a further embodiment (not shown), rather than the entire
interface surface 418, 451 being covered by the projections 454
shown in FIG. 11, only a majority of the interface surface 418, 451
may be covered by the abutting projections 454 and any interface
surface 418, 451 between any projections 454 or not covered by the
projections 454 may be uneven, as described above with respect to
FIGS. 8 to 10.
[0109] A further embodiment of a substrate is shown in FIGS. 12a to
12c. This embodiment differs from that shown in FIGS. 8 to 9d in
that the shape of the projections 424, 426 extending from the
interface surface 418 are of a differing shape and the number of
projections 424 in the outer array are fewer than that shown in
FIG. 8. In the embodiment of FIGS. 12a to 12c, these projections
424, 426 have a peripheral shape having one or more non-planar
faces.
[0110] In one or more of the above-described embodiments, the
features of the interface surfaces 418, 451 may be formed
integrally whilst the substrate is being formed through use of an
appropriately shaped mold into which the particles of material to
form the substrate are placed. Alternatively, the projections and
uneven surfaces of the interface surface 418, 451 may be created
after the substrate has been created or part way through the
creation process, for example by a conventional machining process.
Similar procedures may be applied to the superhard material layer
12 to create the corresponding shaped interface surface for forming
a matching fit with that of the substrate.
[0111] The superhard material layer 12 may be attached to the
substrate by, for example, conventional brazing techniques or by
sintering using a conventional high pressure and high temperature
technique.
[0112] The durability of the cutter product including the substrate
and superhard material layer with the aforementioned interface
features and/or the mitigation of elastic stress waves therein may
be further enhanced if the superhard material layer 12 is leached
of catalyst material, either partially or fully, in subsequent
processing, or subjected to a further high pressure high
temperature sintering process. The leaching may be performed whilst
the super hard material layer 12 is attached to the substrate or,
for example, by detaching the super hard material layer 12 from the
substrate, and leaching the detached super hard material layer 12.
In the latter case, after leaching has taken place, the superhard
material layer 12 may be reattached to the substrate using, for
example, brazing techniques or by resintering using a high pressure
and high temperature technique.
[0113] Although particular embodiments have been described and
illustrated, it is to be understood that various changes and
modifications may be made. For example, the substrate described
herein has been identified by way of example. It should be
understood that the super-hard material may be attached to other
carbide substrates besides tungsten carbide substrates, such as
substrates made of carbides of W, Ti, Mo, Nb, V, Hf, Ta, and Cr.
Furthermore, although the embodiments shown in FIGS. 1 to 12c are
depicted in these drawings as comprising PCD structures having
sharp edges and corners, embodiments may comprise PCD structures
having rounded, bevelled or chamfered edges or corners. Such
embodiments may reduce internal stress and consequently extend
working life through improving the resistance to cracking,
chipping, and fracturing of cutting elements through the interface
of the substrate or the super hard material layer having unique
geometries.
[0114] 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.
[0115] 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.
[0116] 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.
[0117] 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 superhard polycrystalline material.
[0118] In a further embodiment, both the substrate and a body of
polycrystalline superhard material are pre-formed. For example, the
bimodal feed of superhard 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.
[0119] 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.
[0120] 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 or greater.
[0121] In a further embodiment, both the substrate and a body of
polycrystalline superhard material are pre-formed. For example, the
bimodal or multimodal feed of superhard grains/particles with
optional carbonate binder-catalyst also in powdered form are mixed
together, and the mixture is packed in alternating layers or strata
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.
[0122] A further example method for making a PCD element is now
described. Aggregate masses in the form of sheets containing
diamond grains held together by a binder material may be provided.
The sheets may be made by a method known in the art, such as by
extrusion or tape casting methods, in which slurries comprising
diamond grains having respective size distributions suitable for
making the desired respective bimodal or multimodal PCD grades, and
a binder material is spread onto a surface and allowed to dry.
Other methods for making diamond-containing 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. The binder material may
comprise a water-based organic binder such as methyl cellulose or
polyethylene glycol (PEG) and different sheets comprising diamond
grains having different size distributions, diamond content or
additives may be provided. For example, at least two sheets
comprising diamond having different mean sizes may be provided and
first and second sets of discs may be cut from the respective first
and second sheets. The sheets may also contain catalyst material
for diamond, such as cobalt, and/or additives for inhibiting
abnormal growth of the diamond grains or enhancing the properties
of the PCD material. For example, the sheets may contain about 0.5
weight percent to about 5 weight percent of vanadium carbide,
chromium carbide or tungsten carbide. In one example, each of the
sets may comprise about 10 to 20 discs.
[0123] A support body comprising cemented carbide in which the
cement or binder material comprises a catalyst material for
diamond, such as cobalt, may be provided. The support body may have
a non-planar end or a substantially planar proximate end on which
the PCD structure is to be formed and which forms the interface. A
non-planar shape of the end may be configured to reduce undesirable
residual stress between the PCD structure and the support body. A
cup may be provided for use in assembling the diamond-containing
sheets onto the support body. The first and second sets of discs
may be stacked into the bottom of the cup in alternating order. In
one version of the method, a layer of substantially loose diamond
grains may be packed onto the uppermost of the discs. The support
body may then be inserted into the cup with the proximate end going
in first and pushed against the substantially loose diamond grains,
causing them to move slightly and position themselves according to
the shape of the non-planar end of the support body to form a
pre-sinter assembly.
[0124] The pre-sinter assembly may be placed into a capsule for an
ultra-high pressure press and subjected to an ultra-high pressure
of at least about 5.5 GPa and a high temperature of at least about
1,300 degrees centigrade to sinter the diamond grains and form a
PCD element comprising a PCD structure integrally joined to the
support body. In one version of the method, when the pre-sinter
assembly is treated at the ultra-high pressure and high
temperature, the binder material within the support body melts and
infiltrates the strata of diamond grains. The presence of the
molten catalyst material from the support body is likely to promote
the sintering of the diamond grains by intergrowth with each other
to form an integral, stratified PCD structure.
[0125] In some versions of the method, the aggregate masses may
comprise substantially loose diamond grains, or diamond grains held
together by a binder material. The aggregate masses of multimodal
grains may be in the form of granules, discs, wafers or sheets, and
may contain catalyst material for diamond and/or additives for
reducing abnormal diamond grain growth, for example, or the
aggregated mass may be substantially free of catalyst material or
additives. In some embodiments, the aggregate masses may be
assembled onto a cemented carbide support body.
[0126] In some embodiments, 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 or even
greater.
[0127] 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.
[0128] 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.
[0129] 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.
[0130] 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->CoCO.sub.3+2NaNO.sub.3
[0131] 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->COO+CO.sub.2
COO+H.sub.2->CO+H.sub.2O
[0132] 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.
[0133] 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: [0134] fewer than 17 percent of the carbide
particles have a grain size of equal to or less than about 0.3
microns; [0135] between about 20 to 28 percent of the tungsten
carbide particles have a grain size of between about 0.3 to 0.5
microns; [0136] between about 42 to 56 percent of the tungsten
carbide particles have a grain size of between about 0.5 to 1
microns; [0137] less than about 12 percent of the tungsten carbide
particles are greater than 1 micron; and [0138] the mean grain size
of the tungsten carbide particles is about 0.6.+-.0.2 microns.
[0139] In some embodiments, the binder additionally comprises
between about 2 to 20 wt. % tungsten and between about 0.1 to 2 wt.
% carbon
[0140] 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): [0141] between about
0.5 to 2.0 wt % cobalt; [0142] between about 0.05 to 0.5 wt. %
nickel; [0143] between about 0.05 to 0.2 wt. % chromium; and [0144]
tungsten and carbon.
[0145] 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.
[0146] The layer of substrate may further comprise free carbon.
[0147] 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, .sigma., 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.Tm.sup.3/kg
[0148] 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.
[0149] 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.
[0150] 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.
[0151] 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.Tm.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.Tm.sup.3/kg.
[0152] 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.
[0153] 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.
[0154] Changing grain size by mixing different powder classes and
altering the distributions may achieve a whole spectrum of MFP
values for the substrate depending on the particulars of powder
processing and mixing. The exact values would have to be determined
empirically.
[0155] In some embodiments, the substrate comprises Co, Ni and
Cr.
[0156] 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.
[0157] 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.
[0158] 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.
[0159] 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.
[0160] 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.
[0161] 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.
[0162] 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.
[0163] To assist in improving thermal stability of the sintered
structure, the catalysing material may be 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.
[0164] Embodiments are described in more detail below with
reference to the following example which is provided herein by way
of illustration only and is not intended to be limiting.
Example 1
[0165] A diamond powder mixture was prepared in the proportions
given in Table 1 below.
TABLE-US-00001 TABLE 1 Grade Grade Grade Grade Grade 2 4 12 22 30
10% 10% 45% 25% 10%
[0166] The diamond powder mixture was then placed into a suitable
HpHT vessel, adjacent to a tungsten carbide substrate with a binder
composition as given in Table 2.
TABLE-US-00002 TABLE 2 Cobalt Nickel Chromium (wt %) (wt %) (wt %)
9.5-10 2.75-3.15 0.25-0.35
and sintered at a pressure of around 6.8 GPa and a temperature of
about 1500 degrees C.
[0167] PDC cutters made with the attributes stated above were made
and tested in a chipping test. The results are shown in FIG. 13.
This test targets edge chipping resistance of sharp cutters by
impacting at energy levels of 5 Joules and was repeated for up to 8
impacts. As shown in FIG. 13, the results of this test confirmed at
a statistically significant level that the embodiment tested had a
higher edge chipping resistance compared to the tested conventional
PDC materials shown in FIG. 13 as Refs 1 and 2.
[0168] In order to test the integrity under impact loading of the
finished PCD compacts formed according to the above example, a high
energy drop test was performed on the cutter and two reference
conventional cutters. The results are shown in the plot of FIG. 14.
It will be seen from FIG. 14 that the cutter according to an
embodiment showed a significantly greater resistance to impact
loading at high energy than the conventional PDC cutters subjected
to the same test, shown as Refs 1 and 2.
[0169] In connection with the above-performed tests, the reference
conventional PCD compacts/cutters tested comprised Refs 1 and 2
which were sintered at a pressure of 5.5 GPa and were formed of a
multi-modal mix of diamond grains with an average grain size of
about 10 microns. The multi modal mix is as set out in Table 3
below:
TABLE-US-00003 TABLE 3 Grade Grade Grade Grade Grade 2 4 6 12 22
Mean grain size 1.7 3.2 4.6 10.1 16.6 micron micron micron micron
micron Refs 1 and 2 5% 16% 7% 44% 28%
For both Refs 1 and 2, the substrate was a tungsten carbide
substrate with 13 wt % Co binder and a tungsten carbide grain size
of predominantly 1 to 4 microns. The magnetic properties of the
substrate prior to sintering were: Magnetic saturation (%): 11.5 to
12.5 Magnetic coercivity (kA/m): 9.0 to 10.5 The differences
between Refs 1 and 2 lay in the non-planar interface designs.
[0170] While laboratory testing showed the PDC cutter an embodiment
to have superior chipping resistance and impact resistance, as
illustrated in FIGS. 13 and 14, the cutter according to an
embodiment is also determined to have significantly longer
durability and good penetration rates, as shown from the test
results of FIG. 15 which is a plot of depth of penetration against
rate of penetration for an embodiment and five conventional
reference cutters. Observation of the cutters once the drill bit
had reached a "dull condition" showed that most of the conventional
cutters had failed due to large wear flats and not due to
catastrophic failure. As the PDC cutter according to an embodiment
had not failed due to catastrophic failure the repair costs to
reuse the drill bit are significantly reduced. For example, such a
cutter could be rotated and re-used in the drill bit for a second
time.
[0171] Example cutters Ex1 to Ex 5 which were subjected to the test
whose results are shown in FIG. 15 are identical to Ref 1, referred
to above in connection with FIGS. 13 and 14 however, the cutter Ex
5 was mounted in a different drill bit design to those of Ex 1 to
Ex 4 for the purposes of this test.
[0172] 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.
[0173] 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.
[0174] 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 "binder
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.
[0175] The binder mean free path measurements and standard
deviations therein 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.
[0176] 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.
[0177] 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). [0178] 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. [0179] 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. [0180] 3. An auto threshold feature was used to
binarise the image and specifically to obtain clear resolution of
the diamond and binder phases. [0181] 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: [0182] a. If too low then resolution of fine
particles is reduced. [0183] b. If too high then: [0184] i.
Efficiency of coarse grain separation is reduced. [0185] ii. High
numbers of coarse grains are cut by the boarders of the image and
hence less of these grains are analysed. [0186] iii. Thus more
images must be analysed to get a statistically-meaningful result.
[0187] 5. Each particle was finally represented by the number of
continuous pixels of which it is formed. [0188] 6. The AnalySIS
software programme proceeded to detect and analyse each particle in
the image. This was automatically repeated for several images.
[0189] 7. Ten SEM images were analyzed using the grey-scale to
identify the binder pools 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.) [0190] 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. [0191] 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. Mean values
were reported for the non-diamond phase mean free paths.
[0192] Also recorded were the standard deviations in the binder
mean free path measurements.
[0193] From this, it was determined that embodiments have a ratio
of the standard deviation of the non-diamond phase mean free path
to the mean of the non-diamond phase mean free path of greater than
80% when the average grain size in the diamond phase is less than
or equal to 25 microns, at a magnification of 1000.times..
[0194] In some embodiments, the ratio of the standard deviation of
the non-diamond phase mean free path to the mean of the non-diamond
phase mean free path is greater than 80% but less than 150% and in
other embodiments is greater than 80% but less than 120%.
[0195] 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. Also, it have been found that the
combination of the following elements in embodiments provides
unexpected additional advantages over any of the individual
components:
1. A multimodal grain size distribution with an average
pre-sintered grain size of approximately less than or equal to 25
microns to give a good wear resistance. 2. A tungsten carbide
substrate having additions of Ni and Cr to provide erosion
resistance. 3. An interface design that minimizes interfacial
stresses. 4. Sintering conditions greater than 6 GPa for improved
composite densification and sintering.
[0196] Whilst 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.
* * * * *