U.S. patent application number 14/778409 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 Rodwell Baloyi, Valentine Kanyanta, Maweja Kasonde.
Application Number | 20160251741 14/778409 |
Document ID | / |
Family ID | 48445085 |
Filed Date | 2016-09-01 |
United States Patent
Application |
20160251741 |
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 non-superhard phase dispersed in the superhard phase, the
superhard phase comprising a plurality of inter-bonded superhard
grains. The non-superhard phase comprises particles or grains that
do not chemically react with the superhard grains and form less
than around 10 volume % of the body of polycrystalline superhard
material. There is also disclosed a method of forming such a
superhard polycrystalline construction.
Inventors: |
Kanyanta; Valentine;
(Oxfordshire, GB) ; Kasonde; Maweja; (Oxfordshire,
GB) ; Baloyi; Rodwell; (Springs, ZA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Element Six Abrasives S.A. |
Luxembourg |
|
LU |
|
|
Family ID: |
48445085 |
Appl. No.: |
14/778409 |
Filed: |
March 31, 2014 |
PCT Filed: |
March 31, 2014 |
PCT NO: |
PCT/EP2014/056463 |
371 Date: |
September 18, 2015 |
Current U.S.
Class: |
51/307 |
Current CPC
Class: |
B24D 18/0009 20130101;
B22F 2005/001 20130101; E21B 10/567 20130101; E21B 10/56 20130101;
C22C 26/00 20130101 |
International
Class: |
C22C 26/00 20060101
C22C026/00; E21B 10/56 20060101 E21B010/56; B24D 18/00 20060101
B24D018/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 31, 2013 |
GB |
1305871.4 |
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
non-superhard phase dispersed in the superhard phase, the superhard
phase comprising a plurality of inter-bonded superhard grains;
wherein the non-superhard phase comprises particles or grains that
do not chemically react with the superhard grains and form less
than around 10 volume % 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,
wherein the non-superhard phase further comprises a binder
phase.
4. A superhard polycrystalline construction according to claim 3,
wherein the binder phase comprises cobalt, and/or one or more other
iron group elements, 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 that do not chemically react with
the superhard grains 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 particles or grains that do not chemically react with
the superhard grains comprise any one or more of an oxide material,
such as an oxide of alumina, zirconia, yttria, silica, or tantalum
oxide, or any combination thereof.
7-9. (canceled)
10. A superhard polycrystalline construction according to claim 1,
wherein the particles or grains that do not chemically react with
the superhard grains have a grain size of around 30% or less of the
grain size of the superhard grains.
11. A superhard polycrystalline construction according to claim 1,
wherein the particles or grains that do not chemically react with
the superhard grains form between around 0.5 to around 5 volume %
of the body of polycrystalline superhard material.
12. A superhard polycrystalline construction according to claim 1,
wherein the particles or grains that do not chemically react with
the superhard grains form between around 0.5 to around 2 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 method of forming a superhard polycrystalline construction,
comprising: providing a mass of particles or grains of superhard
material; providing a mass of non-superhard grains or particles
comprising particles or grains of a material that does not
chemically react with the superhard grains having a grain size of
less than around 30% the grain size of the superhard material;
combining the mass of superhard material and the mass of
non-superhard grains to form a pre-sinter assembly; and treating
the pre-sinter assembly in the presence of a catalyst/solvent
material for the superhard grains at an ultra-high pressure of
around 5.5 GPa or greater and a temperature at which the superhard
material is more thermodynamically stable than graphite to sinter
together the grains of superhard material to form a polycrystalline
superhard construction, the superhard grains exhibiting
inter-granular bonding and defining a plurality of interstitial
regions therebetween, the non-superhard phase being dispersed in
the polycrystalline material and forming less than around 10 vol %
of the body of polycrystalline superhard material, any residual
catalyst/solvent at least partially filling a plurality of the
interstitial regions.
17. A method according to claim 16, wherein the step of providing a
mass of grains of superhard material comprises providing a mass of
diamond grains.
18. A method according to claim 17, 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.
19. (canceled)
20. The method of claim 16, 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.
21. The method of claim 18, 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 %.
22-28. (canceled)
29. The method of claim 16, wherein the step of providing a mass of
non-superhard grains or particles comprising particles or grains of
a material that does not chemically react with the superhard grains
comprises providing a mass of material comprising any one or more
of an oxide, a carbide, zirconia, alumina, yttria, and tantalum
oxide.
30. The method of claim 16, wherein the step of combining the
masses of particles or grains comprises admixing the particles or
grains.
31. The method of claim 16, wherein the step of combining the
masses of particles or grains comprises coating the superhard
grains or particles with the particles or grains of non-superhard
material which does not chemically react with the particles or
grains of superhard material.
32. The method of claim 16, wherein the step of providing the mass
of material that does not chemically react with the superhard
grains comprises providing grains or particles to form between
around 0.5 to 5 vol % of the body of polycrystalline 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) 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 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),
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 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 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 superhard 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 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 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
non-superhard phase dispersed in the superhard phase, the superhard
phase comprising a plurality of inter-bonded superhard grains;
[0017] wherein the non-superhard phase comprises particles or
grains that do not chemically react with the superhard grains and
form less than around 10 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 non-superhard grains or
particles comprising particles or grains of a material that does
not chemically react with the superhard grains having a grain size
of less than around 30% the grain size of the superhard material;
[0021] combining the mass of superhard material and the mass of
non-superhard 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 5.5 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 non-superhard phase being
dispersed in the polycrystalline material and forming less than
around 10 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. 2a is a schematic cross-section of an example portion
of a PCD micro-structure with a second dispersed non-reactive phase
in the material;
[0029] FIG. 2b is an expanded view of a section of the schematic
cross-section of the example PCD micro-structure of FIG. 2a;
[0030] FIG. 3 is a plot showing the results of a wear resistance
test comparing the wear resistance of an embodiment with that of a
conventional PCD material;
[0031] FIG. 4 is a plot showing the results of a vertical borer
test comparing a conventional unleached PCD material, a
conventional PCD material leached using an acid treatment, and an
embodiment of PCD material prepared according to the described
method; and
[0032] FIG. 5 is a plot showing the results of a vertical borer
test comparing a conventional unleached PCD material, and a further
embodiment of PCD material.
[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 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.
[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 embodiment 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] FIGS. 2a and 2b are cross-sections through an embodiment of
PCD material forming the superhard layer 12 of FIG. 1 showing,
schematically, the PCD microstructure. A non-reactive phase
comprising particles 30 formed of, for example, ceramic oxides are
dispersed in the diamond phase matrix 32 to act as localised stress
raisers and/or micro-defects. The diamond phase matrix 32 here
refers to conventional PCD formed of diamond grains and a catalyst
binder phase 33 dispersed therein. The non-reactive phase 30 may
comprise an oxide, formed for example, of one or more oxides of
alumina, zirconia, tantalum oxide and yttria. The grain size of the
dispersed non-reactive phase particles 30 may, in some embodiments,
not be greater than 30% of the size of diamond grains. The
non-reactive phase particles 30 may 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. The
non-reactive particles are non-reactive with respect to the
superhard phase, for example, diamond, and may also be non-reactive
with the binder phase such that they are not soluble in the binder
phase and do not adhere to the superhard (eg diamond) particles,
that is, there is substantially no interfacial bonding between the
superhard particles and the non-reactive particles which may be
located, as shown in FIG. 2b between interbonded diamond grains and
in a number of interstitial spaces between interbonded diamond
grains, some of which spaces may be at least partially filled with
residual binder phase.
[0048] In some embodiments, the non-reactive phase particles 30
comprise less than 5 volume % of the sintered PCD material. In
other embodiments, the non-reactive phase particles 30 comprise
less than 3 volume % of the sintered PCD material, or even, in some
cases, less than 1 volume % of the sintered PCD material.
[0049] These disperse non-reactive phase particles 30 may be
localized inside the binder pools or in between diamond grains,
depending on the sizes.
[0050] 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 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.
[0051] 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.
[0052] 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.
[0053] 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.
[0054] Some embodiments consist of 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.
[0055] 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.
[0056] 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.
[0057] 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.
[0058] 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.
[0059] The cutter of FIG. 1 having the microstructure of FIGS. 2a
and 2b may be fabricated, for example, as follows.
[0060] 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 non-reactive phase 30.
[0061] Embodiments of superhard constructions may be made by a
method of preparing a green body comprising grains or particles of
superhard material, non-reactive 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.
[0062] 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
embodiments, the superhard grains may be diamond grains and the
substrate may be cobalt-cemented tungsten carbide, the cobalt in
the substrate being a source of catalyst for sintering the diamond
grains. The pre-sinter assembly may comprise an additional source
of catalyst material.
[0063] 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 embodiments, 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.
[0064] 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, non-reactive 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.
[0065] 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.
[0066] 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.
[0067] A further embodiment of a superhard construction may be made
by a method including providing a PCD structure and a precursor
structure for a diamond composite structure, forming each structure
into the respective complementary shapes, assembling the PCD
structure and the diamond composite structure onto a cemented
carbide substrate to form an unjoined assembly, and subjecting the
unjoined assembly to a pressure of at least about 5.5 GPa and a
temperature of at least about 1,250 degrees centigrade to form a
PCD construction. The precursor structure may comprise carbide
particles and diamond or non-diamond carbon material, such as
graphite, non-reactive 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.
[0068] In some embodiments, both the bodies of, for example,
diamond and carbide material plus the non-reactive phase and
sintering aid/binder/catalyst are applied as powders and sintered
simultaneously in a single UHP/HT process. The mixture of diamond
grains, non-reactive 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 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.
[0069] In another embodiment, the substrate may be pre-sintered in
a separate process before being bonded together in the HP/HT press
during sintering of the ultrahard polycrystalline material.
[0070] In a further embodiment, both the substrate and a body of
polycrystalline superhard material are pre-formed. For example, the
bimodal feed of ultrahard grains/particles with non-reactive 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.
[0071] 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.
[0072] 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.
[0073] Similarly, the non-reactive 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.
[0074] In one embodiment, 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
[0075] 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
[0076] In another embodiment, 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.
[0077] 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.
[0078] Embodiments are described in more detail below with
reference to the following examples which are provided herein by
way of illustration only and are not intended to be limiting.
Example 1
[0079] 0.5 g of Zirconia with an average grain size of 1 micron was
added to 50 g of a bimodal diamond powder with an average grain
size of 4 microns. The aggregated mass was ball milled in 60 ml of
methanol with Co--WC milling balls. The ratio of milling
balls:powder was 5:1 and milling was carried out for 1 hour at 90
rpm. 2.1 g of the mixture was placed on top of a pre-formed WC--Co
substrate and sintered under high pressure high temperature HPHT
conditions at 6.8 GPa and 1450.degree. C. The PCD cutter was
recovered, processed and analysed. The results are discussed below
with reference to FIGS. 3 to 5.
Example 2
[0080] 1.5 g of Zirconia with an average grain size of 1 micron was
added to 50 g of a bimodal diamond powder with an average grain
size of 4 microns. The aggregated mass was ball milled in 60 m; of
methanol with Co--WC milling balls. The ratio of milling
balls:powder was 5:1 and milling was carried out for 1 hour at 90
rpm. 2.1 g of the mixture was placed on top of a pre-formed WC--Co
substrate and sintered under high pressure high temperature HPHT
conditions at 6.8 GPa and 1450.degree. C. The PCD cutter was
recovered, processed and analysed.
[0081] The results are discussed below with reference to FIGS. 3 to
5.
Example 3
[0082] 0.25 g of Zirconia with an average grain size of 1 micron
was added to 50 g of a unimodal diamond powder with an average
grain size of 3 microns. The aggregated mass was ball milled in 60
ml of methanol with co-WC milling balls. The ratio of milling
balls:powder was 5:1 and milling was carried out for 1 hour at 90
rpm. 2.1 g of the mixture was placed on top of a pre-formed WC--Co
substrate and sintered under high pressure high temperature HPHT
conditions at 6.8 GPa and 1450.degree. C. The PCD cutter was
recovered, processed and analysed.
[0083] The results are discussed below with reference to FIGS. 3 to
5.
Example 4
[0084] 0.5 g of Zirconia with an average grain size of 1 micron was
added to 50 g of a unimodal diamond powder with an average grain
size of 3 microns. The aggregated mass was ball milled in 60 ml of
methanol with Co--WC milling balls. The ratio of milling
balls:powder was 5:1 and milling was carried out for 1 hour at 90
rpm. 2.1 g of the mixture was placed on top of a pre-formed WC--Co
substrate and sintered under high pressure high temperature HPHT
conditions at 6.8 GPa and 1450.degree. C. The PCD cutter was
recovered, processed and analysed.
[0085] The results are discussed below with reference to FIGS. 3 to
5.
Example 5
[0086] 1.5 g of Zirconia with an average grain size of 1 micron was
added to 50 g of a unimodal diamond powder with an average grain
size of 3 microns. The aggregated mass was ball milled in 60 ml of
methanol with Co--WC milling balls. The ratio of milling
balls:powder was 5:1 and milling was carried out for 1 hour at 90
rpm. 2.1 g of the mixture was placed on top of a pre-formed WC--Co
substrate and sintered under high pressure high temperature HPHT
conditions at 6.8 GPa and 1450.degree. C. The PCD cutter was
recovered, processed and analysed.
[0087] The results are discussed below with reference to FIGS. 3 to
5.
[0088] Various sample 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 5.
[0089] The abrasive wear resistance of various PCD samples was
analysed by subjecting the finished PCD samples to a conventional
granite turning test for 3 minutes. The wear scar progression
during the machining process was monitored. The results are shown
in FIG. 3. The wear scar of the PCD compact formed according to
example 1 above with 0.5 vol % zirconia in the finished PCD was
compared with a reference sample (Ref 1) of conventional PCD
without any zirconia additions in the PCD matrix. In addition,
samples were prepared according to embodiments comprising 1 vol %
zirconia in the PCD and 3 vol % zirconia in the PCD.
[0090] It will be seen from the results shown in FIG. 3 that the
addition of small amounts of zirconia improves the wear resistance
of PCD as the wear scar length is less than conventional PCD.
[0091] The PCD compact formed according to Example 1 was compared
in a vertical boring mill test with both leached (Ref Z) and
unleached (Ref NZ) commercially available polycrystalline diamond
cutter elements. In this test, the wear flat area was measured as a
function of the number of passes of the cutter element boring into
the workpiece. The results obtained are illustrated graphically in
FIG. 4. The results provide an indication of the total wear scar
area plotted against cutting length. It will be seen that the PCD
compact formed according to example 1 was able to achieve a greater
cutting length and smaller wear scar area than that occurring in
both leached and unleached conventional PCD compacts which were
subjected to the same test for comparison. The conventional PCD
compacts in this test comprised Ref 2 which was a bimodal mixture
having an average diamond grain size of around 4 microns. Indeed,
FIG. 4 shows a 96% improvement in cutting length was achieved in
the embodiment of PCD compared to a conventional PCD without
zirconia addition.
[0092] Further unleached (NZ) samples of PCD embodiments of Example
3 comprising 0.5 vol % zirconia were compared with a conventional
unleached PCD sample formed of a unimodal diamond feed having an
average diamond grain size of around 3 microns. The results are
shown in FIG. 5. The test showed a 104% improvement in the life of
the cutter compared to a conventional PCD without zirconia
addition.
[0093] 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 the micro-defects and/or stress raisers
in a PCD matrix according to some embodiments described herein. The
micro-defects and/or stress raisers 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. 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.
[0094] The addition of a ceramic non-reactive 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.
[0095] The size, shape and distribution of these micro-defects 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.
[0096] Thus, it is believed that embodiments may provide a means of
toughening PCD material without compromising its high abrasion
resistance. This may be achieved by engineering micro-defects into
the PCD matrix. 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.
[0097] 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.
[0098] 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. A 100% improvement in
cutter tool life, i.e., double the life of conventional untreated
PCD of same average diamond grain size, was noted during
testing.
[0099] Thus, embodiments of a PCD material may be formed having
that a combination of high abrasion and fracture performance.
[0100] 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.
[0101] 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.
[0102] While various embodiments have been described with reference
to a number of examples, those skilled in the art will understand
that various changes may be made and equivalents may be substituted
for elements thereof and that these examples are not intended to
limit the particular embodiments disclosed. For example, the
micro-defects in the form of the non-reactive phase particles may
be introduced into the PCD in various ways and, in some
embodiments, they may be introduced by modifying the HPHT sintering
conditions such that micro-defects are introduced along diamond
grain boundaries through partial sintering of the PCD. These
dispersed non-reactive phase particles may be localized inside the
binder pools or in between diamond grains, depending on the
sizes.
* * * * *