U.S. patent application number 15/031058 was filed with the patent office on 2016-09-01 for superhard constructions and methods of making same.
The applicant listed for this patent is Element Six Abrasives S.A.. Invention is credited to Valentine KANYANTA, Maweja KASONDE, Machele Elizabeth NKADIMENG.
Application Number | 20160251742 15/031058 |
Document ID | / |
Family ID | 49727146 |
Filed Date | 2016-09-01 |
United States Patent
Application |
20160251742 |
Kind Code |
A1 |
KANYANTA; Valentine ; et
al. |
September 1, 2016 |
SUPERHARD CONSTRUCTIONS AND METHODS OF MAKING SAME
Abstract
A superhard polycrystalline construction comprises a body of
polycrystalline superhard material comprising a superhard phase,
and a second phase dispersed in the superhard phase, the superhard
phase comprising a plurality of inter-bonded superhard grains. The
second phase comprises particles or grains that do not chemically
react with the superhard grains, and/or do not inter-grow, and form
between around 1 to 30 volume % or wt % of the body of
polycrystalline superhard material.
Inventors: |
KANYANTA; Valentine;
(Oxfordshire, GB) ; KASONDE; Maweja; (Oxfordshire,
GB) ; NKADIMENG; Machele Elizabeth; (Springs,
ZA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Element Six Abrasives S.A. |
Luxembourg |
|
LU |
|
|
Family ID: |
49727146 |
Appl. No.: |
15/031058 |
Filed: |
October 22, 2014 |
PCT Filed: |
October 22, 2014 |
PCT NO: |
PCT/EP2014/072682 |
371 Date: |
April 21, 2016 |
Current U.S.
Class: |
51/307 |
Current CPC
Class: |
C22C 26/00 20130101;
C22C 29/08 20130101; C22C 2026/005 20130101; C22C 2026/008
20130101; C22C 2026/006 20130101; C22C 2026/007 20130101; C22C
29/005 20130101; E21B 10/567 20130101; C22C 2204/00 20130101; E21B
10/56 20130101 |
International
Class: |
C22C 26/00 20060101
C22C026/00; E21B 10/56 20060101 E21B010/56 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 22, 2013 |
GB |
1318640.8 |
Claims
1. A superhard polycrystalline construction comprising: a body of
polycrystalline superhard material, the body of polycrystalline
superhard material comprising: a superhard phase, and a second
phase dispersed in the superhard phase, the superhard phase
comprising a plurality of inter-bonded superhard grains; wherein
the second phase comprises particles or grains that do not
chemically react with the superhard grains, and/or do not
inter-grow, and form between around 1 to 30 volume % or around 1 to
around 30 wt % of the body of polycrystalline superhard
material.
2. A superhard polycrystalline construction according to claim 1,
wherein the superhard grains comprise natural and/or synthetic
diamond grains, the superhard polycrystalline construction forming
a polycrystalline diamond construction.
3. A superhard polycrystalline construction according to claim 1,
further comprising a non-superhard phase comprising a binder
phase.
4. A superhard polycrystalline construction according to claim 3,
wherein the binder phase comprises cobalt, and/or one or more other
iron group elements, 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. A superhard polycrystalline construction according to claim 3,
wherein the particles or grains of the second phase are such that
they do not dissolve in the binder phase material and thereby
remain unsintered in the body of polycrystalline material and form
defects in the polycrystalline material.
6. A superhard polycrystalline construction according to claim 1,
wherein the second phase particles or grains comprise any one or
more of an oxide material, a carbide material, alumina, zirconia,
yttria, silica, tantalum oxide, cBN, PCBN, hexagonal boron nitride,
tungsten carbide, hafnium carbide, zirconium carbide, silicon
carbide, or any combination thereof.
7.-9. (canceled)
10. A superhard polycrystalline construction according to claim 1,
wherein the second phase particles or grains have a grain size
substantially equal to or between around 1.5 to around 3 times the
average grain size of the superhard grains.
11. A superhard polycrystalline construction according to claim 1,
wherein the second phase particles or grains form between around 1
to around 30 volume % of the body of polycrystalline superhard
material.
12. A superhard polycrystalline construction according to claim 1,
wherein the second phase particles or grains form between around 5
to around 15 volume % of the body of polycrystalline superhard
material.
13. A superhard polycrystalline construction according to claim 1,
wherein at least a portion of the body of superhard material is
substantially free of a catalyst material for diamond, said portion
forming a thermally stable region.
14. A superhard polycrystalline construction as claimed in claim
13, wherein the thermally stable region comprises at most 2 weight
percent of catalyst material for diamond.
15. (canceled)
16. A superhard polycrystalline construction according to claim 1,
wherein the second phase particles or granules have a different
stiffness and/or fracture toughness than that of the superhard
phase.
17. A method of forming a superhard polycrystalline construction,
comprising: providing a mass of particles or grains of superhard
material; providing a mass of second phase grains or particles
comprising particles or grains of a material that do not chemically
react with the superhard grains, and/or do not inter-grow, and form
between around 1 to 30 volume % of the body of polycrystalline
superhard material; combining the mass of superhard material and
the mass of second phase grains to form a pre-sinter assembly; and
treating the pre-sinter assembly in the presence of a
catalyst/solvent material for the superhard grains at an ultra-high
pressure of around 5 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, the second phase being dispersed
in the polycrystalline material and forming between around 1 to
around 30 vol % of the body of polycrystalline superhard material,
any residual catalyst/solvent at least partially filling a
plurality of the interstitial regions.
18. A method according to claim 17, wherein the step of providing a
mass of grains of superhard material comprises providing a mass of
diamond grains.
19. A method according to claim 18, wherein the step of providing a
mass of diamond grains comprises providing a mass of grains having
a first fraction having a first average size and a second fraction
having a second average size, the first fraction having an average
grain size ranging from about 10 to 60 microns, and the second
fraction having an average grain size less than the size of the
coarse fraction.
20. The method of claim 19, wherein the second fraction has an
average grain size between around 1/10 to 6/10 of the size of the
first fraction.
21. The method of claim 17, wherein the average grain size of the
first fraction is between around 10 to 60 microns, and the average
grain size of the second fraction is between about 0.1 to 20
microns.
22. The method of claim 19, wherein the weight ratio of the first
fraction to the second fraction ranges from about 50% to about 97%,
the weight ratio of the second fraction ranging from about 3% to
about 50 weight %.
23.-27. (canceled)
28. The method of claim 19, wherein the step of providing a mass of
grains of superhard material comprises providing three or more
grain size modes to form a multimodal mass of grains comprising a
blend of grain sizes having associated average grain sizes.
29. (canceled)
30. The method of claim 17, wherein the step of providing a mass of
second phase grains or particles comprises providing second phase
particles or grains comprising any one or more of an oxide
material, a carbide material, alumina, zirconia, yttria, silica,
tantalum oxide, cBN, PCBN, hexagonal boron nitride, tungsten
carbide, hafnium carbide, zirconium carbide, silicon carbide, or
any combination thereof.
31. (canceled)
32. The method of claim 17, wherein the step of combining the
masses of particles or grains comprises coating the superhard
grains or particles with the particles or grains of second phase
material which does not chemically react with the particles or
grains of superhard material.
33.-39. (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 tools comprising the
same, particularly but not exclusively for use in rock degradation
or drilling, or for boring into the earth.
BACKGROUND
[0002] Polycrystalline superhard materials, such as polycrystalline
diamond (PCD) 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 super hard tool
inserts may be limited by fracture of the super hard 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 super hard
material which forms a cutting layer bonded to the interface
surface of the substrate by, for example, a sintering process. The
substrate is generally formed of a tungsten carbide-cobalt alloy,
sometimes referred to as cemented tungsten carbide and the super
hard material layer is typically polycrystalline diamond (PCD), 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 or ultra hard
material) comprising a mass of substantially inter-grown diamond
grains, forming a skeletal mass defining interstices between the
diamond grains. PCD material typically comprises at least about 80
volume % of diamond and is conventionally made by subjecting an
aggregated mass of diamond grains to an ultra-high pressure of
greater than about 5 GPa, and temperature of at least about
1,200.degree. C., for example. A material wholly or partly filling
the interstices may be referred to as filler or binder
material.
[0005] PCD is typically formed in the presence of a sintering aid
such as cobalt, which promotes the inter-growth of diamond grains.
Suitable sintering aids for PCD are also commonly referred to as a
solvent-catalyst material for diamond, owing to their function of
dissolving, to some extent, the diamond and catalysing its
re-precipitation. A solvent-catalyst for diamond is understood be a
material that is capable of promoting the growth of diamond or the
direct diamond-to-diamond inter-growth between diamond grains at a
pressure and temperature condition at which diamond is
thermodynamically stable. Consequently the interstices within the
sintered PCD product may be wholly or partially filled with
residual solvent-catalyst material. Most typically, PCD is often
formed on a cobalt-cemented tungsten carbide substrate, which
provides a source of cobalt solvent-catalyst for the PCD. Materials
that do not promote substantial coherent intergrowth between the
diamond grains may themselves form strong bonds with diamond
grains, but are not suitable solvent-catalysts for PCD
sintering.
[0006] Cemented tungsten carbide which may be used to form a
suitable substrate is formed from carbide particles being dispersed
in a cobalt matrix by mixing tungsten carbide particles/grains and
cobalt together then heating to solidify. To form the cutting
element with a superhard material layer such as PCD, diamond
particles or 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 occurs,
forming a polycrystalline superhard diamond 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 place 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 or tool inserts comprising PCD material are
widely used in drill bits for boring into the earth in the oil and
gas drilling industry. 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.
[0011] The most wear resistant grades of PCD usually suffer from a
catastrophic fracture of the cutter before it has worn out. During
the use of these cutters, cracks grow until they reach a critical
length as which catastrophic failure occurs, namely, when a large
portion of the PCD breaks away in a brittle manner. These long,
fast growing cracks encountered during use of conventionally
sintered PCD, result in short tool life.
[0012] Furthermore, despite their high strength, polycrystalline
diamond (PCD) materials are usually susceptible to impact fracture
due to their low fracture toughness. Improving fracture toughness
without adversely affecting the material's high strength and
abrasion resistance is a challenging task.
[0013] There is therefore a need for a polycrystalline super hard
composite such as a PCD composite that has good or improved
abrasion, fracture and impact resistance and a method of forming
such composites.
SUMMARY
[0014] Viewed from a first aspect there is provided a superhard
polycrystalline construction comprising: [0015] a body of
polycrystalline superhard material, the body of polycrystalline
superhard material comprising: [0016] a superhard phase, and a
second phase dispersed in the superhard phase, the superhard phase
comprising a plurality of inter-bonded superhard grains; [0017]
wherein the second phase comprises particles or grains that do not
chemically react with the superhard grains, and/or do not
inter-grow, and form between around 1 to 30 volume % of the body of
polycrystalline superhard material.
[0018] Viewed from a second aspect there is provided a method of
forming a superhard polycrystalline construction, comprising:
[0019] providing a mass of particles or grains of superhard
material; [0020] providing a mass of second phase grains or
particles comprising particles or grains of a material that do not
chemically react with the superhard grains, and/or do not
inter-grow, and form between around 1 to 30 volume % of the body of
polycrystalline superhard material; [0021] combining the mass of
superhard material and the mass of second phase grains to form a
pre-sinter assembly; and [0022] treating the pre-sinter assembly in
the presence of a catalyst/solvent material for the superhard
grains at an ultra-high pressure of around 5 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, the second phase being dispersed in the
polycrystalline material and forming between around 1 to around 30
vol % of the body of polycrystalline superhard material, any
residual catalyst/solvent at least partially filling a plurality of
the interstitial regions.
[0023] 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.
[0024] 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.
[0025] 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
[0026] The present invention will now be described by way of
example and with reference to the accompanying drawings in
which:
[0027] FIG. 1 is a perspective view of an example PCD cutter
element for a drill bit for boring into the earth;
[0028] FIG. 2 is a schematic cross-section of an example portion of
a PCD microstructure with a second dispersed non-reactive phase in
the material;
[0029] FIG. 3 is a plot showing the results of a vertical borer
test comparing a conventional PCD material, an embodiment of PCD
material comprising 30 vol % (around 30 wt %) second phase
dispersed therein, and an embodiment of PCD material comprising 10
vol % (around 10 wt %) second phase dispersed therein and prepared
according to the described method;
[0030] FIG. 4 is a plot showing the results of a vertical borer
test comparing a conventional PCD material, an embodiment of PCD
material comprising 7.5 wt % second phase dispersed therein, and an
embodiment of PCD material comprising 20 wt % second phase
dispersed therein and prepared according to the described method,
for the conditions where the average grain size of the second phase
material is substantially equal to that of the diamond and where
the average grain size of the second phase material is larger than
that of the diamond grains;
[0031] FIG. 5 is a plot showing the results of a vertical borer
test comparing a conventional PCD material, an embodiment of PCD
material comprising 7.5 wt % second phase dispersed therein, and an
embodiment of PCD material comprising 20 wt % second phase
dispersed therein and prepared according to the described method,
for the conditions where the average grain size of the second phase
material is less than that of the diamond, where the average grain
size of the second phase material is substantially equal to that of
the diamond, where the average grain size of the second phase
material is approximately double that of the diamond, and where the
average grain size of the second phase material is larger than
double that of the diamond grains; and
[0032] FIG. 6 is a plot showing the results of a vertical borer
test comparing a conventional PCD material, an embodiment of PCD
material comprising 7.5 wt % second phase dispersed therein, and an
embodiment of PCD material comprising 20 wt % second phase
dispersed therein and prepared according to the described method,
for the conditions where the average grain size of the second phase
material is less than that of the diamond grains, where the average
grain size of the second phase material is approximately equal to
that of the diamond grains and where the average grain size of the
second phase material is larger than that of the diamond
grains.
[0033] The same references refer to the same general features in
all the drawings.
DESCRIPTION
[0034] 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.
[0035] 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.
[0036] 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 example 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
examples 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.
[0037] A "catalyst material" for a superhard material is capable of
promoting the growth or sintering of the superhard material.
[0038] 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.
[0039] As used herein, the term "integrally formed" regions or
parts are produced contiguous with each other and are not separated
by a different kind of material.
[0040] In an example as shown in FIG. 1, a cutting element 1
includes a substrate 10 with a layer of superhard material 12
formed on the substrate 10. The substrate 10 may be formed of a
hard material such as cemented tungsten carbide. The superhard
material 12 may be, for example, polycrystalline diamond (PCD), 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) and may be suitable, for example, for use as a
cutter insert for a drill bit for boring into the earth.
[0041] 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.
[0042] At one end of the substrate 10 is an interface surface 18
that forms an interface with the superhard material layer 12 which
is attached thereto at this interface surface. As shown in the
embodiment of FIG. 1, the substrate 10 is generally cylindrical and
has a peripheral surface 20 and a peripheral top edge 22.
[0043] As used herein, a PCD grade is a PCD material characterised
in terms of the volume content and size of diamond grains, the
volume content of interstitial regions between the diamond grains
and composition of material that may be present within the
interstitial regions. A grade of PCD material may be made by a
process including providing an aggregate mass of diamond grains
having a size distribution suitable for the grade, optionally
introducing catalyst material or additive material into the
aggregate mass, and subjecting the aggregated mass in the presence
of a source of catalyst material for diamond to a pressure and
temperature at which diamond is more thermodynamically stable than
graphite and at which the catalyst material is molten. Under these
conditions, molten catalyst material may infiltrate from the source
into the aggregated mass and is likely to promote direct
intergrowth between the diamond grains in a process of sintering,
to form a PCD structure. The aggregate mass may comprise loose
diamond grains or diamond grains held together by a binder material
and said diamond grains may be natural or synthesised diamond
grains.
[0044] Different PCD grades may have different microstructures and
different mechanical properties, such as elastic (or Young's)
modulus E, modulus of elasticity, transverse rupture strength
(TRS), toughness (such as so-called K.sub.1C toughness), hardness,
density and coefficient of thermal expansion (CTE). Different PCD
grades may also perform differently in use. For example, the wear
rate and fracture resistance of different PCD grades may be
different.
[0045] All of the PCD grades may comprise interstitial regions
filled with material comprising cobalt metal, which is an example
of catalyst material for diamond.
[0046] The PCD structure 12 may comprise one or more PCD
grades.
[0047] FIG. 2 is a cross-section through an example of PCD material
forming the superhard layer 12 of FIG. 1 showing, schematically,
the PCD microstructure. A second phase comprising particles 30 or
agglomerates formed of particles or grains that do not chemically
react with the superhard grains, and/or do not inter-grow, and form
between around 1 to 30 volume (or 1 to 30 weight %) of the body of
polycrystalline superhard material, is dispersed in the diamond
phase matrix 32. The diamond phase matrix 32 here refers to
conventional PCD formed of diamond grains and a catalyst binder
phase dispersed therein. The second phase 30 may comprise, for
example any one or more of an oxide material, a carbide material,
alumina, zirconia, yttria, silica, tantalum oxide, cBN, PCBN,
hexagonal boron nitride, tungsten carbide, hafnium carbide,
zirconium carbide, silicon carbide, or any combination thereof. The
grain size of the dispersed second phase particles 30 may, in some
examples, be the same size as or between around 1.5 to around 3
times greater than the average size of the diamond particles or
grains, for example, around twice the size. The second phase
particles 30 may, for example, be admixed with diamond powder and
then the composite is sintered in the traditional way with, for
example, cobalt infiltration at HPHT to provide the catalyst binder
to form the intergranular bonds between the diamond grains.
[0048] In some examples, the second phase particles 30 comprise
between around 1 to around 30 volume % (or around 1 to around 30 wt
%) of the sintered PCD material. In other examples, the second
phase particles 30 comprise between around 5 to around 15 volume %
(or around 5 to around 50 wt %) of the sintered PCD material, or
even, in some cases, between around 10 to between around 30 volume
% (or around 10 to around 30 wt %) of the sintered PCD
material.
[0049] In some examples, the average size of the grains or
particles forming the second phase 30 is between around 10 microns
to around 350 microns and in some examples below around 125
microns.
[0050] These disperse second phase particles 30 may be localized
inside the binder pools or in between diamond grains, depending on
the sizes.
[0051] The grains of superhard material may be, for example,
diamond grains or particles. In the starting mixture prior to
sintering they 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 examples, 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, the fine
fraction may have an average grain size of between around 1/10 to
6/10 of the size of the coarse fraction, and may, in some examples,
range for example between about 0.1 to 20 microns.
[0052] In some examples, the weight ratio of the coarse diamond
fraction to the fine diamond fraction may range 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 examples, the
weight ratio of the coarse fraction to the fine fraction may range
from about 70:30 to about 90:10.
[0053] In further examples, the weight ratio of the coarse fraction
to the fine fraction may range for example from about 60:40 to
about 80:20.
[0054] In some examples, the particle size distributions of the
coarse and fine fractions do not overlap and in some examples the
different size components of the compact are separated by an order
of magnitude between the separate size fractions making up the
multimodal distribution.
[0055] Some examples consist of a wide bi-modal size distribution
between the coarse and fine fractions of superhard material, but
some examples 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.
[0056] 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.
[0057] In examples where the superhard material is polycrystalline
diamond material, the diamond grains used to form the
polycrystalline diamond material may be natural or synthetic.
[0058] In some examples, 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
examples, the binder/catalyst/sintering aid may be Co.
[0059] 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
examples, the metal carbide is tungsten carbide.
[0060] The cutter of FIG. 1 having the microstructure of FIG. 2 may
be fabricated, for example, as follows.
[0061] As used herein, a "green body" is a body comprising grains
to be sintered and a means of holding the grains together, such as
a binder, for example an organic binder, together with the
additional second phase 30.
[0062] Examples of superhard constructions may be made by a method
of preparing a green body comprising grains or particles of
superhard material, second phase and a binder, such as an organic
binder. The green body may also comprise catalyst material for
promoting the sintering of the superhard grains. The green body may
be made by combining the grains or particles with the
binder/catalyst and forming them into a body having substantially
the same general shape as that of the intended sintered body, and
drying the binder. At least some of the binder material may be
removed by, for example, burning it off. The green body may be
formed by a method including a compaction process, an injection
process or other methods such as molding, extrusion, deposition
modelling methods.
[0063] A green body for the superhard construction may be placed
onto a substrate, such as a pre-formed cemented carbide substrate
to form a pre-sinter assembly, which may be encapsulated in a
capsule for an ultra-high pressure furnace, as is known in the art.
The substrate may provide a source of catalyst material for
promoting the sintering of the superhard grains. In some examples,
the superhard grains may be diamond grains and the substrate may be
cobalt-cemented tungsten carbide, the cobalt in the substrate being
a source of catalyst for sintering the diamond grains. The
pre-sinter assembly may comprise an additional source of catalyst
material.
[0064] In one version, the method may include loading the capsule
comprising a pre-sinter assembly into a press and subjecting the
green body to an ultra-high pressure and a temperature at which the
superhard material is thermodynamically stable to sinter the
superhard grains. In some examples, the green body may comprise
diamond grains and the pressure to which the assembly is subjected
is at least about 5 GPa and the temperature is at least about 1,300
degrees centigrade.
[0065] A version of the method may include making a diamond
composite structure by means of a method disclosed, for example, in
PCT application publication number WO2009/128034 with the
additional step of admixing with the diamond grains, prior to
sintering, the grains/particles of non-reactive phase. A powder
blend comprising diamond particles, second phase particles and a
metal binder material, such as cobalt may be prepared by combining
these particles and blending them together. An effective powder
preparation technology may be used to blend the powders, such as
wet or dry multi-directional mixing, planetary ball milling and
high shear mixing with a homogenizer. In one embodiment, the mean
size of the diamond particles may be at least about 50 microns and
they may be combined with other particles by mixing the powders or,
in some cases, stirring the powders together by hand. In one
version of the method, precursor materials suitable for subsequent
conversion into binder material may be included in the powder
blend, and in one version of the method, metal binder material may
be introduced in a form suitable for infiltration into a green
body. The powder blend may be deposited in a die or mold and
compacted to form a green body, for example by uni-axial compaction
or other compaction method, such as cold isostatic pressing (CIP).
The green body may be subjected to a sintering process known in the
art to form a sintered article. In one version, the method may
include loading the capsule comprising a pre-sinter assembly into a
press and subjecting the green body to an ultra-high pressure and a
temperature at which the superhard material is thermodynamically
stable to sinter the superhard grains.
[0066] After sintering, the polycrystalline super hard
constructions may be ground to size and may include, if desired, a
45.degree. chamfer of approximately 0.4 mm height on the body of
polycrystalline super hard material so produced.
[0067] The sintered article may be subjected to a subsequent
treatment at a pressure and temperature at which diamond is
thermally stable to convert some or all of the non-diamond carbon
back into diamond and produce a diamond composite structure. An
ultra-high pressure furnace well known in the art of diamond
synthesis may be used and the pressure may be at least about 5.5
GPa and the temperature may be at least about 1,250 degrees
centigrade for the second sintering process.
[0068] A further example of a superhard construction may be made by
a method including providing a PCD structure and a precursor
structure for a diamond composite structure, forming each structure
into the respective complementary shapes, assembling the PCD
structure and the diamond composite structure onto a cemented
carbide substrate to form an unjoined assembly, and subjecting the
unjoined assembly to a pressure of at least about 5.5 GPa and a
temperature of at least about 1,250 degrees centigrade to form a
PCD construction. The precursor structure may comprise carbide
particles and diamond or non-diamond carbon material, such as
graphite, second phase particles, and a binder material comprising
a metal, such as cobalt. The precursor structure may be a green
body formed by compacting a powder blend comprising particles of
diamond or non-diamond carbon and particles of carbide material and
compacting the powder blend.
[0069] In some examples, both the bodies of, for example, diamond
and carbide material plus the second phase and sintering
aid/binder/catalyst are applied as powders and sintered
simultaneously in a single UHP/HT process. The mixture of diamond
grains, second phase particles 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 example, the processing
conditions generally involve the imposition for about 3 to 120
minutes of a temperature of at least about 1200 degrees C. and an
ultra-high pressure of greater than about 5 GPa.
[0070] In another example, the substrate may be pre-sintered in a
separate process before being bonded together in the HP/HT press
during sintering of the ultrahard polycrystalline material.
[0071] In a further example, both the substrate and a body of
polycrystalline superhard material are pre-formed. For example, the
bimodal feed of ultrahard grains/particles with second phase
particles and optional carbonate binder-catalyst also in powdered
form are mixed together, and the mixture is packed into an
appropriately shaped canister and is then subjected to extremely
high pressure and temperature in a press. Typically, the pressure
is at least 5 GPa and the temperature is at least around 1200
degrees C. The preformed body of polycrystalline superhard material
is then placed in the appropriate position on the upper surface of
the preform carbide substrate (incorporating a binder catalyst),
and the assembly is located in a suitably shaped canister. The
assembly is then subjected to high temperature and pressure in a
press, the order of temperature and pressure being again, at least
around 1200 degrees C. and 5 GPa respectively. During this process
the solvent/catalyst migrates from the substrate into the body of
superhard material and acts as a binder-catalyst to effect
intergrowth in the layer and also serves to bond the layer of
polycrystalline superhard material to the substrate. The sintering
process also serves to bond the body of superhard polycrystalline
material to the substrate.
[0072] In examples 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.
[0073] 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.
[0074] Similarly, the second phase particles may be introduced by
various means, for example, the diamond grains or particles could
be coated with a non-reacting material prior to sintering.
[0075] In one example, the binder/catalyst such as 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
[0076] 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
[0077] In another example, 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.
[0078] In some examples, 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.
[0079] Versions are described in more detail below with reference
to the following examples which are provided herein by way of
illustration only and are not intended to be limiting.
Example 1
[0080] Powders of the second phase materials are mixed in an
organic binder such as polyvinyl alcohol (PVA) or Poly(methyl
methacrylate) (PMMA) and de-ionised water to form the first slurry.
The slurry is then freeze granulated in liquid nitrogen (liquid
nitrogen is used to freeze the slurry depending on the size of the
nozzle which determines the size of the resulting granules).
[0081] In a first example, cBN powder (grade 9) was mixed with PVA
organic binder and de-ionised water was used to prepare granules
smaller than 350 microns. The water was removed from the granules
during freeze drying. The cBN particles are bonded together by the
organic binder (PVA). The dried powder (granules) was sieved to
recover granules of the desired size, in this example, granules
smaller than around 125 micron were recovered.
[0082] A second slurry of diamond powder with a mixture of
different grain sizes, ranging between around 1 micron to around 40
microns was prepared using a solvent such as ethanol and organic
binder system (B90-S2075) and homogenised in a tubular mixer. B90
is an organic binder mixture to a plasticiser S2075. The binder
used in preparing the granules (e.g. PVA, PMMA) should have little
or no solubility in the solvent used in preparing the
second/diamond slurry (e.g. ethanol).
[0083] The granules prepared from the first slurry are then added
to the second slurry and homogenised to form a dispersion of
granules in the diamond slurry. The amount of the added granules
represents around 5-30% of the total mass of solids in the diamond
slurry. The diamond slurry with added granules was then tape cast
to produce paper with a required thickness. Discs of the prepared
paper were cut and introduced into a Nb cup such that a 2.2 mm PCD
thickness is achieved after HPHT sintering onto a WC--Co
Substrate.
[0084] Pre-composites were pressed by pill technology to form a
green-body, de-binded at 600.degree. C. in an inert atmosphere to
remove organic binders and outgassed above 1000.degree. C. under
vacuum.
[0085] The green body was then sintered under high pressure high
temperature HPHT conditions at 5 GPa and 1400.degree. C. The PCD
cutter was recovered, processed and analysed.
[0086] The results are discussed below with reference to FIG.
3.
Example 2
[0087] In a second example, cBN powder (grade 6) was mixed with PVA
organic binder and de-ionised water in accordance with the method
described in example 1 above and a second slurry of diamond powder
with a mixture of different grain sizes, ranging between around 1
micron to around 10 microns (Grade 6) was prepared using a solvent
such as ethanol and organic binder system (B90-S2075) and
homogenised in a tubular mixer, also as described above. Green
bodies as described above were prepared and sintered and the PCD
cutter recovered. The process was repeated to form cutters with cBN
additions forming 7.5 wt % and 20 wt % of the PCD composite. The
process was also repeated to obtain cutters comprising 7.5 wt % cBN
and 20 wt % cBN where the average grain size of the cBN was
substantially larger than that of the diamond grains, (around 30-45
microns whereas the average diamond grain size was around 6
microns).
[0088] The results are discussed below with reference to FIG.
4.
Example 3
[0089] In a third example, cBN powder (grade 9) was mixed with PVA
organic binder and de-ionised water in accordance with the method
described in example 1 above and a second slurry of diamond powder
with a mixture of different grain sizes, ranging between around 9
micron to around 16 microns (Grade 12) was prepared using a solvent
such as ethanol and organic binder system (B90-S2075) and
homogenised in a tubular mixer, also as described above. Green
bodies as described above were prepared and sintered and the PCD
cutter recovered. The process was repeated to form cutters with cBN
additions forming 7.5 wt % and 20 wt % of the PCD composite. The
process was also repeated to obtain cutters comprising 7.5 wt % cBN
and 20 wt % cBN where the average grain size of the cBN was
substantially equal to that of the diamond grains, (around 12
microns (Grade 12). It was also repeated to obtain cutters
comprising 7.5 wt % cBN and 20 wt % cBN where the average grain
size of the cBN was larger than that of the diamond grains, (around
30 microns (a mixture of Grades 20 and 40) whereas the average
diamond grain size was around 12 microns), and it was also repeated
to obtain cutters comprising 7.5 wt % cBN and 20 wt % cBN where the
average grain size of the cBN was substantially greater than that
of the diamond grains, (around 45 microns (Grade 45) whereas that
of the diamond grains was around 12 microns).
[0090] The results are discussed below with reference to FIG.
5.
Example 4
[0091] In a fourth example, cBN powder (grade 12) was mixed with
PVA organic binder and de-ionised water in accordance with the
method described in example 1 above and a second slurry of diamond
powder with a mixture of different grain sizes, ranging between
around 20 micron to around 25 microns (Grade 22) was prepared using
a solvent such as ethanol and organic binder system (B90-S2075) and
homogenised in a tubular mixer, also as described above. Green
bodies as described above were prepared and sintered and the PCD
cutter recovered. The process was repeated to form cutters with cBN
additions forming 7.5 wt % and 20 wt % of the PCD composite. The
process was also repeated to obtain cutters comprising 7.5 wt % cBN
and 20 wt % cBN where the average grain size of the cBN was
slightly greater than that of the diamond grains (around 30 microns
(a mixture of Grades 20 and 40) whereas the average diamond grain
size was around 22 microns), and it was also repeated to obtain
cutters comprising 7.5 wt % cBN and 20 wt % cBN where the average
grain size of the cBN was substantially greater eg around double
than that of the diamond grains, (around 45 microns (Grade 45)
whereas that of the diamond grains was around 22 microns).
[0092] The results are discussed below with reference to FIG.
6.
[0093] Various samples of PCD material were prepared and analysed
by subjecting the samples to a number of tests. The results of
these tests are shown in FIGS. 3 to 6.
[0094] A number of PCD compacts formed according to Example 1 were
compared in a vertical boring mill test with a commercially
available polycrystalline diamond cutter element having the same
average diamond grain size as that of the two examples tested. The
first example tested included around 10 vol % (in this example
around 10 wt %) second phase (in this example cBN granules) and the
second embodiment tested included around 30 vol % (in this example
around 30 wt %) second phase (in this example cBN granules). In
this test, the wear flat area was measured as a function of the
number of passes of the cutter element boring into the workpiece.
The results obtained are illustrated graphically in FIG. 3. The
results provide an indication of the total wear scar area plotted
against cutting length. It will be seen that the PCD compacts
formed according to example 1 (as denoted by reference lines 100,
102) were able to achieve a significantly greater cutting length
than that occurring in the conventional PCD compact (as denoted by
reference line 104) which was subjected to the same test for
comparison. Furthermore, in the example formed of around 10 wt %
cBN as the second phase (102), a smaller wear scar area than the
conventional PCD compact (104) in this test was achieved.
[0095] A number of PCD compacts formed according to Example 2 were
compared in a vertical boring mill test with a commercially
available polycrystalline diamond cutter element having the same
average diamond grain size as that of the examples tested. The
first version tested included around 7.5 wt % second phase (in this
example Grade 6 cBN granules), the second version tested included
around 20 wt % of Grade 6 cBN granules, the third version tested
included around 7.5 wt % Grade 45 cBN granules and the fourth
version tested included around 20 wt % Grade 45 cBN granules. In
this test, the wear flat area was measured as a function of the
number of passes of the cutter element boring into the workpiece.
The results obtained are illustrated graphically in FIG. 4. It will
be seen that the PCD compacts formed according to Example 2, (as
denoted by reference lines 200,202,203,204) gave end wear scars
(200',202',203',204'). The conventional PCD compact (as denoted by
reference line 205 and wear scar image 205') was subjected to the
same test for comparison. In the version formed of cBN as the
second phase in which the average grain size of the cBN granules
was approximately double that of the average grain size of the
diamond grains (203), a smaller wear scar area than the
conventional PCD compact (104) in this test was achieved where the
average grain size of the diamonds was fine (around 6 microns).
[0096] A number of PCD compacts formed according to Example 3 were
compared in a vertical boring mill test with a commercially
available polycrystalline diamond cutter element having the same
average diamond grain size as that of the examples tested. The
first version tested included around 7.5 wt % second phase (in this
example Grade 9 cBN granules), the second version tested included
around 20 wt % of Grade 9 cBN granules, the third version tested
included around 7.5 wt % Grade 12 cBN granules and the fourth
version tested included around 20 wt % Grade 12 cBN granules. The
fifth version tested included around 7.5 wt % of a mixture of
Grades 20 and 40 cBN granules the sixth version tested included
around 20 wt % of a mixture of Grades 20 and 40 cBN granules, the
seventh version tested included around 7.5 wt % of Grade 45 cBN
granules, and the eighth version tested included around 20 wt % of
Grade 45 cBN granules.
[0097] In this test, the wear flat area was measured as a function
of the number of passes of the cutter element boring into the
workpiece. The results obtained are illustrated graphically in FIG.
5. It will be seen that the PCD compacts formed according to
Example 3, (as denoted by reference lines
300,302,303,304,305,307,308,309) gave end wear scars denoted by
images 300', 302', 303', 304', 305', 307', 308', and 309'
respectively. The conventional PCD compact (as denoted by reference
line 306 and wear scar image 306') was subjected to the same test
for comparison. In the versions formed of cBN as the second phase
in which the average grain size of the cBN granules was
approximately double or greater than that of the average grain size
of the diamond grains, a smaller wear scar area (307-309') than the
conventional PCD compact (306) in this test was achieved where the
average grain size of the diamonds was relatively fine (around 12
microns).
[0098] A number of PCD compacts formed according to Example 4 were
compared in a vertical boring mill test with a commercially
available polycrystalline diamond cutter element having the same
average diamond grain size as that of the examples tested (Grade 22
having an average grain size of around 22 microns which may be
considered to be coarse grained). The first version tested included
around 7.5 wt % second phase (in this example Grade 12 cBN
granules), the second version tested included around 20 wt % of
Grade 12 cBN granules, the third version tested included around 7.5
wt % of a mixture of Grades 20 and 40 cBN granules and the fourth
version tested included around 20 wt % of a mixture of Grades 20
and 40 cBN granules. The fifth version included around 20 wt %
Grade 45cBN granules. In this test, the wear flat area was measured
as a function of the number of passes of the cutter element boring
into the workpiece. The results obtained are illustrated
graphically in FIG. 6. It will be seen that the PCD compacts formed
according to Example 4, (as denoted by reference lines
400,402,404,408,410) gave end wear scars
(400',402',404',408',410'). The conventional PCD compact (as
denoted by reference line 406 and wear scar image 406') was
subjected to the same test for comparison. In the version formed of
cBN as the second phase in which the average grain size of the cBN
granules was approximately double that of the average grain size of
the diamond grains (410), a smaller wear scar area than the
conventional PCD compact (406) in this test was achieved where the
grain size of the diamonds was coarse (around 22 microns).
[0099] Whilst not wishing to be bound by a particular theory, it is
believed that the fracture performance of PCD may be improved
through the introduction of a second phase comprising particles or
grains that do not chemically react with the superhard grains,
and/or do not inter-grow, and form between around 1 to 30 volume %
or wt % of the body of polycrystalline superhard material in a PCD
matrix according to some embodiments described herein. The second
phase particles of this nature are believed to promote crack
bifurcation or multiple crack fronts in the PCD material in use,
resulting in a redistribution of available strain energy or energy
release rate (G) amongst the various crack tips, and/or favourably
divert cracks in the PCD material. A material that is able to
generate multiple cracks under loading would behave tougher than a
material with only one major crack since multiple crack fronts
ensures that the net energy supplied to the material is divided
between several cracks, resulting in a much slower rate of crack
growth through the material. The end result in application of the
PCD material including such micro-defects is that, in use, the
number of cracks initiated on the wear scar may be increased as
compared to conventional PCD, thus reducing the strain energy
available for each individual crack, hence slowing the growth rate,
and the generation of shorter cracks. The ideal case is where the
wear rate is comparable to the crack growth rate, in which case no
cracks will be visible behind the wear scar thereby forming a
smooth wear scar appearance with no chips or grains pulled out of
the sintered PCD.
[0100] The addition of such a second phase may also have the effect
of increasing the thermal stability of the PCD through the
resultant lower cobalt content in the material of the invention
compared to conventional PCD.
[0101] The size, shape and distribution of these second phase
particles, grains, granules or agglomerates may be tailored to the
final application of the PCD material. It is believed possible to
improve fracture resistance without significantly compromising the
overall abrasion resistance of the material, which is desirable for
PCD cutting tools.
[0102] Thus, it is believed that embodiments may provide a means of
toughening PCD material without compromising its high abrasion
resistance. The concept works by enabling the creation of multiple
crack-fronts or defects which help to redistribute or dissipate the
available fracture energy. These defects may also promote crack
bifurcations, which is another energy dissipation mechanism. The
end result is that there is insufficient energy available to each
individual crack to enable it to propagate quickly and hence this
may significantly slow down the rate of crack growth.
[0103] The vertical borer test results of these engineered
structures show a considerable increase in PCD cutting tool life
compared to conventional PCD, and with no degradation in abrasion
resistance.
[0104] Observation of the wear scar development during testing
showed the material's ability to generate large wear scars without
exhibiting brittle-type micro-fractures (e.g. spalling or
chipping), leading to a longer tool life
[0105] Thus, examples of a PCD material may be formed having that a
combination of high abrasion and fracture performance.
[0106] The PCD element 10 described with reference to FIG. 1 may be
further processed after sintering. For example, 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 which may further enhance the thermal stability of the PCD
element.
[0107] Furthermore, the PCD body in the structure of FIG. 1
comprising a PCD structure bonded to a cemented carbide support
body may be created or finished by, for example, grinding, to
provide a PCD element which is substantially cylindrical and having
a substantially planar working surface, or a generally domed,
pointed, rounded conical or frusto-conical working surface. The PCD
element may be suitable for use in, for example, a rotary shear (or
drag) bit for boring into the earth, for a percussion drill bit or
for a pick for mining or asphalt degradation.
[0108] While various examples 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. For example, the second phase
may be introduced into the PCD in various ways. The dispersed
second phase particles may be localized inside the binder pools or
in between diamond grains, depending on the sizes.
* * * * *