U.S. patent application number 14/778448 was filed with the patent office on 2016-09-22 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, Mehmet Serdar Ozbayraktar.
Application Number | 20160271757 14/778448 |
Document ID | / |
Family ID | 48445087 |
Filed Date | 2016-09-22 |
United States Patent
Application |
20160271757 |
Kind Code |
A1 |
Kanyanta; Valentine ; et
al. |
September 22, 2016 |
SUPERHARD CONSTRUCTIONS AND METHODS OF MAKING SAME
Abstract
A superhard polycrystalline construction comprises a body of
polycrystalline superhard material comprising a first superhard
phase having a first average grain size; and a second superhard
phase having a second average grain size. The second superhard
phase is located in one or more channels or apertures in the first
superhard phase, the first superhard phase forming a skeleton in
the body of superhard material. The second superhard phase is
bonded to the first superhard phase by a non-superhard phase and
the first superhard phase differs from the second superhard phase
in average grain size and/or composition. There is also dis closed
a method of making such a superhard polycrystalline
construction.
Inventors: |
Kanyanta; Valentine;
(Oxfordshire, GB) ; Kasonde; Maweja; (Oxfordshire,
GB) ; Ozbayraktar; Mehmet Serdar; (Oxfordshire,
GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Element Six Abrasives S.A. |
Luxembourg |
|
LU |
|
|
Family ID: |
48445087 |
Appl. No.: |
14/778448 |
Filed: |
March 31, 2014 |
PCT Filed: |
March 31, 2014 |
PCT NO: |
PCT/EP2014/056458 |
371 Date: |
September 18, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
E21B 10/567 20130101;
B24D 18/0009 20130101; E21B 10/5676 20130101; B22F 2005/001
20130101; B22F 1/007 20130101; E21B 10/5735 20130101; B22F 5/00
20130101; B22F 2007/066 20130101; C22C 26/00 20130101 |
International
Class: |
B24D 18/00 20060101
B24D018/00; B22F 1/00 20060101 B22F001/00; B22F 5/00 20060101
B22F005/00; E21B 10/567 20060101 E21B010/567; E21B 10/573 20060101
E21B010/573 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 31, 2013 |
GB |
1305873.0 |
Claims
1. A superhard polycrystalline construction comprising: a body of
polycrystalline superhard material, the body of polycrystalline
superhard material comprising: a first superhard phase having a
first average grain size; and a second superhard phase having a
second average grain size; wherein the second superhard phase is
located in one or more channels or apertures in the first superhard
phase, the first superhard phase forming a skeleton in the body of
superhard material, the second superhard phase being bonded to the
first superhard phase by a non-superhard phase; and wherein the
first superhard phase differs from the second superhard phase in
average grain size and/or composition.
2. A superhard polycrystalline construction according to claim 1,
wherein the superhard grains of the first and the second superhard
phases comprise natural and/or synthetic diamond grains, the
superhard polycrystalline construction forming a polycrystalline
diamond construction.
3. A superhard polycrystalline construction according to claim 1,
wherein the non-superhard phase comprises a binder phase.
4. A superhard polycrystalline construction according to claim 3,
wherein the binder phase comprises cobalt, and/or one or more other
iron group elements, 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.
5-7. (canceled)
8. 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.
9. A superhard polycrystalline construction as claimed in claim 8,
wherein the thermally stable region comprises at most 2 weight
percent of catalyst material for diamond.
10. A superhard polycrystalline construction according to claim 1,
wherein the skeleton formed of the first superhard phase comprises
a perforated disc having said plurality of channels and/or
apertures therein, the disc comprising a mass of interbonded
superhard grains, the second superhard phase filling the channels
and/or apertures in the disc.
11. A superhard polycrystalline construction according to claim 10,
wherein the skeleton formed of the first superhard phase comprises
a plurality of stacked perforated discs.
12. A superhard polycrystalline construction according to claim 11,
wherein the discs are aligned such that the second superhard phase
filling the channels and/or apertures form one or more of
alternating sectors, concentric layers or regions, or layers or
regions inclined with respect to the central longitudinal axis of
the discs.
13. (canceled)
14. A superhard polycrystalline construction according to claim 1,
wherein the skeleton comprises two or more channels and/or
apertures therein, the body of polycrystalline superhard material
comprising a working surface, the working surface being formed of
alternating portions of the skeleton and the second superhard phase
located in the two or more channels and/or apertures in the
skeleton.
15. (canceled)
16. A method of forming a superhard polycrystalline construction,
comprising: providing a first mass of particles or grains of
superhard material for forming a first superhard phase; sintering
the first superhard phase and forming a skeleton having a plurality
of channels and/or apertures therein; providing a second mass of
superhard grains or particles for forming a second superhard phase;
positioning the second mass of superhard grains or particles in one
or more channels and/or apertures in the skeleton formed of the
first superhard phase to form a pre-sinter assembly; wherein the
first superhard phase differs from the second superhard phase in
average grain size and/or composition; 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, wherein the body of polycrystalline superhard
material comprises a working surface, the working surface being
formed of alternating portions of the skeleton and the second
superhard phase located in the plurality of channels and/or
apertures in the skeleton.
17. A method according to claim 16, wherein the step of providing a
first mass of grains of superhard material and a second mass of
superhard material comprises providing a first and second mass of
diamond grains.
18. A method according to claim 17, wherein the step of providing a
first mass and a second mass of diamond grains comprises providing
a first and/or a second 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.
19-28. (canceled)
29. The method of claim 16, wherein the step of providing the first
mass of superhard grains comprises sintering a first body of
superhard grains; and forming the channels and/or apertures therein
after sintering and prior to the step of positioning the second
mass of superhard grains or particles in said channels and/or
apertures.
30. The method of claim 29, wherein the step of forming the
channels and/or apertures comprises forming said apertures and/or
channels using an EDM technique, or a laser ablation technique.
31. The method of claim 29, further comprising treating at least a
portion of the sintered first mass of superhard grains to render
said portion free of a catalyst material for the superhard grains,
said portion forming a thermally stable region.
32. The method of claim 16, wherein the step of providing the first
mass of superhard grains comprises forming a green body comprising
the first mass of superhard particles or grains with said channels
and/or apertures therein using one or more of 3D printing or
injection molding techniques.
33. The method of claim 16, wherein the step of providing a first
mass of superhard grains comprises providing a perforated disc
forming the first mass having said a plurality of apertures and/or
channels therein, the disc comprising a mass of interbonded
superhard grains, the second superhard phase filling the apertures
and/or channels in the disc.
34. The method of claim 33, wherein the first superhard
construction comprises a plurality of stacked perforated discs.
35. The method of claim 34, further comprising aligning the discs
such that the second superhard phase filling the apertures and/or
channels forms one or more of alternating sectors, concentric
layers or regions, or layers or regions inclined with respect to
the central longitudinal axis of said discs, the step of sintering
comprising bonding the discs together by infiltration and reaction
with the non-superhard phase.
36-43. (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 superhard tool inserts may be limited
by fracture of the superhard material, including by spalling and
chipping, or by wear of the tool insert.
[0003] Cutting elements such as those for use in rock drill bits or
other cutting tools typically have a body in the form of a
substrate which has an interface end/surface and a superhard
material which forms a cutting layer bonded to the interface
surface of the substrate by, for example, a sintering process. The
substrate is generally formed of a tungsten carbide-cobalt alloy,
sometimes referred to as cemented tungsten carbide and the
superhard material layer is typically polycrystalline diamond
(PCD), polycrystalline cubic boron nitride (PCBN) or a thermally
stable product TSP material such as thermally stable
polycrystalline diamond.
[0004] Polycrystalline diamond (PCD) is an example of a superhard
material (also called a superabrasive 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 at which catastrophic failure can occur, 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 which are critical for the material's ability
to cut through rock, for example, is a challenging task.
[0013] There is therefore a need for a PCD composite that has good
or improved abrasion resistance, 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 first superhard phase
having a first average grain size; and [0017] a second superhard
phase having a second average grain size; [0018] wherein the second
superhard phase is located in one or more channels or apertures in
the first superhard phase, the first superhard phase forming a
skeleton in the body of superhard material, the second superhard
phase being and bonded thereto the first superhard phase by a
non-superhard phase; and [0019] wherein the first superhard phase
differs from the second superhard phase in average grain size
and/or composition.
[0020] Viewed from a second aspect there is provided a method of
forming a superhard polycrystalline construction, comprising:
[0021] providing a first mass of particles or grains of superhard
material for forming a first superhard phase; sintering the first
superhard phase and forming a skeleton having a plurality of
channels and/or apertures therein; [0022] providing a second mass
of superhard grains or particles for forming a second superhard
phase; [0023] positioning the second mass of superhard grains or
particles in one or more channels and/or apertures in the skeleton
formed of the first superhard phase to form a pre-sinter assembly;
wherein the first superhard phase differs from the second superhard
phase in average grain size and/or composition; and [0024] 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, wherein the body of polycrystalline superhard
material comprises a working surface, the working surface being
formed of alternating portions of the skeleton and the second
superhard phase located in the plurality of channels and/or
apertures in the skeleton.
[0025] 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.
[0026] 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.
[0027] 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
[0028] The present invention will now be described by way of
example and with reference to the accompanying drawings in
which:
[0029] FIG. 1 is a schematic perspective view of an example PCD
cutter element for a drill bit for boring into the earth;
[0030] FIG. 2 is a plan view of an example of a PCD cutter
element;
[0031] FIG. 3 is a schematic flow diagram of the process of forming
an example PCD cutter element such as that shown in FIG. 2;
[0032] FIG. 4 is a schematic partial cross-section through a
further example of a PCD cutter element;
[0033] FIG. 5a is a schematic partial cross-section through a still
further example of a PCD cutter element;
[0034] FIG. 5b is a plan view of a further example of a PCD cutter
element; and
[0035] FIG. 6 is a plot showing the results of a vertical borer
test comparing two conventional PCD cutters with differing average
diamond grain sizes with the PCD cutter element shown in FIG.
2.
[0036] The same reference numerals refer to the same general
features in all the drawings.
DESCRIPTION
[0037] 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.
[0038] 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.
[0039] 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.
[0040] A "catalyst material" for a superhard material is capable of
promoting the growth or sintering of the superhard material.
[0041] 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.
[0042] 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.
[0043] 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.
[0044] 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.
[0045] 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.
[0046] 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.
[0047] 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.
[0048] All of the PCD grades may comprise interstitial regions
filled with material comprising cobalt metal, which is an example
of catalyst material for diamond.
[0049] The PCD structure 12 may comprise one or more PCD
grades.
[0050] FIG. 2 is a plan view of an embodiment of PCD material
forming the super hard layer 12 of FIG. 1. The superhard layer 12
comprises a first phase of superhard material forming a skeleton or
framework 100 which, in the example in FIG. 2, is in the form of a
spoked disc or section with spokes extending from a central hub
section, and a second superhard phase 120 located between adjacent
spokes.
[0051] The superhard material of the first and second phases 100,
200 may be comprised of inter-bonded grains of superhard material
such as, for example, diamond grains or particles. In each phase,
the starting mixture prior to sintering may be unimodal or
multimodal, for example, bimodal, that is, the feed comprises a
mixture of a coarse fraction of diamond grains and a fine fraction
of diamond grains which are to form one or more of the alternating
layers or strata. 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.
[0052] 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.
[0053] 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.
[0054] 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.
[0055] Some embodiments may comprise 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.
[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 embodiments 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 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.
[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
embodiments, the metal carbide is tungsten carbide.
[0060] The cutter of FIG. 1 may be fabricated, for example, as
shown in the flow diagram of FIG. 3.
[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.
[0062] The mesostructure of the PCD element 200 shown as being
prepared in FIG. 3 is comprised of two PCD phases, the first phase
having a first diamond particle size distribution and the second
phase having a different diamond particle size distribution. As
described above, the different particle size distributions may in
turn be unimodal, comprising a single grade of diamond grains, or
multimodal comprising two or more different grades of diamond
grains or particles. Each material grade powder is prepared
separately by ball milling to produce the particle size
distribution of interest. The individual powders may be mixed by
ball milling with a catalyst binder such as, for example, Co, Ni,
Fe, Mn, Pt, and Ir and/or combinations thereof. In some
embodiments, no additional catalyst binder is included in this
manner.
[0063] As shown in FIG. 3, in a first stage, diamond powder of one
diamond grain size grade is sintered by cobalt infiltration from a
WC substrate at high pressure, preferably above 5 GPa, and high
temperature, preferably above 1400 deg Celsius.
[0064] In another embodiment, powder of one grade of diamond may be
sintered as a solid PCD without infiltration. This is achievable
by, for example, third-generation admixing.
[0065] One or more discs of sintered PCD which are to form the
skeleton or framework in the PCD table 12 may be prepared as above.
The disc(s) is/are then polished and engineered slots or apertures
are cut in the PCD disc(s) to produce the desired skeleton
mesostructure or framework 200 using, for example, an EDM process,
laser abrasion or ablation, or a die sinking process.
[0066] The slots or apertures in the skeleton 200 may take any
shape, as desired for the particular application, such as, for
example, circular, square, rectangular, or polygonal or a mixture
thereof.
[0067] In the second stage shown in FIG. 3, the skeleton 200 is
introduced into a niobium cup. A powder mix of the second phase
material 300 such as diamond powder, diamond shredded paper, or,
for example, diamond slurry in inert liquid, is placed into the cup
to fill the open volumes in the skeleton 200 and to form an
interface with a substrate 320 which is placed on top of the
assembly to form a pre-composite. The substrate 320 may be, for
example, a composite of WC, or alumina, and may include a sintering
catalyst such as Co, Ni, Fe, or Mn, for example, which will
infiltrate the skeleton during HPHT sintering.
[0068] The pre-composite is then consolidated to increase the green
body density by methods such as vibration compaction, cold
isostatic pressing, or HIP. In some embodiments, the binder
materials may be removed from the pre-composites by heat treatment
at 650C in an 5%H2/N2 atmosphere.
[0069] The pre-composites may then be outgassed at, for example,
1050 C under vacuum (10.sup.-5 mbar).
[0070] The pre-composite is then sintered in an HPHT process at a
temperature of around 1400 C and a pressure of, for example,
greater than 5 GPa to form a PCD compact such as that shown in FIG.
1.
[0071] In an alternative embodiment, a slurry of diamond or
superhard material powder is prepared in a mixture of alcohol such
as methanol or ethanol and a plasticizer such as DBP. The slurry is
then homogenised in a tubular mixer. A paper of diamond or
superhard material is prepared by casting on a moving table and
dried at about 60 C. The paper thickness may be, for example, 200
micrometres or less. A male structure reproducing the desired
mesostructure is formed on a solid punch, made of, for example, WC,
hardened steel or any high strength material. The punch is used to
create the open spaces/volumes in individual papers which are to
form the mesostructure. A number of individual perforated papers
are stacked together to produce a skeleton mesostructure of
required thickness. The papers are then stacked in a niobium cup
and the method described above for filling the voids in the
mesostructure and sintering to form the PCD compact are
followed.
[0072] In a further alternative embodiment for producing the
skeleton, a green body skeleton of one diamond grade, with a
desired mesostructure, is injection moulded or 3D printed using an
appropriate binder. The open volumes in the skeleton may take any
shape, such as, for example, circular, square, rectangular, or
polygonal, or any desired combination thereof. The skeleton is then
placed in a niobium cup and the method described above for filling
the voids in the mesostructure and sintering to form the PCD
compact are followed.
[0073] In another embodiment the skeleton may be formed as follows.
A male green body skeleton of one diamond graded, with a desired
mesostructure, is injection moulded or 3D printed using an
appropriate binder. A female green body skeleton of one diamond
grade, with a desired mesostructure, is injection moulded or 3D
printed using an appropriate binder. The open volumes in the
skeleton may take any shape, such as circular, square, rectangular,
and polygonal or any combination thereof.
[0074] The male and female parts are assembled, placed on top of a
WC-catalyst substrate in a niobium cup as described in the methods
above and the pre-composite is sintered at HPHT, for example at a
temperature of above 1400 C and pressure above 5 GPa.
[0075] In yet another alternative method, the skeleton may be
prepared as follows. A green body with a desired mesostructure
consisting of alternating material phases is 3D printed using an
appropriate binder. Alternating material phases may be, for
example, PCD of different grades, PCD and an oxide or ceramic or WC
or any other hard metal. The green body is placed on top of a
pre-formed WC-catalyst substrate and sintered at HPHT as described
above.
[0076] In the embodiment where the skeleton or framework 100, 200
is pre-sintered, the skeleton may be subjected to a treatment such
as acid leaching, to remove residual catalyst/binder from some or
substantially all of the interstices between the inter-bonded
diamond grains to reduce the catalyst content therein. This is
prior to the step of subjecting the skeleton to a second HPHT
sintering cycle in which the volumes in the voids or channels in
the skeleton are filled with the second superhard phase. Thus the
skeleton goes through two HPHT sintering cycles (referred to as
double-sintering).
[0077] The starting skeleton disc 100, 200 may be made of a more
abrasive and high impact resistance PCD grade (or material) 300
than that used to fill the voids or channels in the skeleton, or
vice-versa, as desired depending on the intended application of the
sintered PCD compact, the empty volumes of the skeleton disc being
filled with, for example, a diamond powder grade different in
composition and/or particle size from that used in the starting
skeleton green body to achieve the desired construction.
[0078] As described above, the starting skeleton disc may also be
prepared as a green body using 3D printing or injection moulding.
In this case, the insert only goes through one HPHT sintering
cycle.
[0079] As described above, the skeleton 100, 200 may be formed of
one or more layers or stacked discs having any desired combination
of voids or channels formed therein, aligned in a particular chosen
configuration. FIGS. 2, 4, 5a and 5b show alternative
configurations for the skeleton, the configuration shown in FIG. 2
being that of a spoked structure such that, in the final sintered
product, the body of superhard material comprises alternating
sectors which may be, for example, concentric vertical layers as
shown in FIG. 2, which may, in other embodiments, be inclined with
respect to the vertical axis as shown in FIG. 4 or regions as shown
in FIGS. 5a an 5b. The alternating sectors, layers or regions are
bonded together by infiltration and reaction with a catalyst
material during a high pressure high temperature sintering.
[0080] As described above, embodiments of either the skeleton 100,
200 and/or the second superhard phase 300 filling the voids or
channels in the skeleton may be made by a number methods of
preparing a green body. The green body or bodies comprise(s) grains
or particles of superhard material, and a binder, such as an
organic binder. The green body or bodies may also comprise catalyst
material for promoting the sintering of the superhard grains. The
green body or bodies may be made by combining the grains or
particles with the binder and forming them into a body having
substantially the same general shape as that of the intended
sintered body, whether that be the skeleton or second superhard
phase which is to fill the channels or voids in the skeleton, and
drying the binder. At least some of the binder material may be
removed by, for example, burning it off. The green body may be
formed by a method including a compaction process, injection or
other methods such as molding, extrusion, deposition modelling
methods.
[0081] The substrate 320 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.
[0082] 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.
[0083] In embodiments where the cemented carbide substrate 320 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.
[0084] 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.
[0085] In one embodiment, the bonder/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
[0086] 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
[0087] 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.
[0088] 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.
[0089] A PCD compact according to an embodiment comprising a
skeleton or framework 100, 200 formed of PCD having an average
diamond grain size of around 4 microns and voids filled with PCD
300 having an average diamond grain sixe of around 22 microns was
compared in a vertical boring mill test with two conventional PCD
cutters formed of diamond having an average grain size of around 4
microns (FG302) and two PCD cutters formed of diamond having an
average grain size of around 22 microns (Quadmodal). The results
are shown graphically in FIG. 6. The results of the test on the PCD
embodiment is the middle line in FIG. 6. 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 provide an
indication of the total wear scar area plotted against cutting
length. It will be seen that the PCD compact formed according to an
embodiment was able to achieve a greater cutting length and smaller
wear scar area than that occurring in the conventional PCD formed
of diamond having an average grain size of 22 microns, and a
greater cutting length and similar wear scar to the conventional
PCD compacts formed of diamonds having a fine grain size of around
4 microns. This means that a longer working life of the tool having
an embodiment cutter is possible for similar wear scar
formation.
[0090] Whilst not wishing to be bound by a particular theory, it is
believed that the functionally graded PCD of embodiments, with
alternating superabrasive phases between the skeleton which has
been double-sintered and the superabrasive material in the voids or
channels of the skeleton or framework, enables the combination of
the high abrasion resistance of one material phase with the high
impact resistance of the other resulting in a PCD material with a
combination of good abrasion, fracture and impact resistance.
Furthermore, it is believed that alternating the single sintered
and double sintered boundaries by filling voids or channels in the
skeleton which has been double-sintered with a superhard phase that
has only been through a single sintering stage may assist in
inhibiting the growth of flaws initiated in the first sintering
process during the second sintering process, which could otherwise
lead to cracks in use, and/or may assist in inhibiting the
initiation of cracks during use. Also, the effect of thermal
expansion of the skeleton or framework during the second sintering
process is believed to be controlled by the presence of the
unsintered second superhard phase which is first sintered during
the second sintering phase. This is also believed to assist in
inhibiting cracks from initiating during use as residual stresses
in the PCD compact 10 may be favourably controlled.
[0091] The PCD elements 10 described with reference to FIGS. 1 and
2 may be processed by grinding to modify their shape. Also,
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. The leaching depth in alternating
sectors, layers or regions will be different due to different
microstructures. This may be used to achieve a preferred leached
profile.
[0092] Furthermore, the PCD body in the structure of FIGS. 1 and 2
comprising a PCD structure bonded to a cemented carbide support
body may be created or finished 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.
[0093] 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, one or
more different manufacturing methods may be used, including but not
limited to EDM cutting and sintering of pre-sintered PCD inserts,
injection moulding or 3D printing of green parts. The pre-sintered
skeleton/perforated disc containing one PCD grade may be prepared
by EDM cutting or laser abrasion or ablation and used in second
stage sintering where a different PCD grade may be used to fill the
empty volumes in the skeleton PCD disc. The result is a
functionally graded PCD material with alternating PCD phases of
different PCD grades.
* * * * *