U.S. patent application number 13/997781 was filed with the patent office on 2013-12-19 for high density polycrystalline superhard material.
This patent application is currently assigned to Element Six Abrasives S.A.. The applicant listed for this patent is Mehmet Serdar Ozbayraktar. Invention is credited to Mehmet Serdar Ozbayraktar.
Application Number | 20130337248 13/997781 |
Document ID | / |
Family ID | 43599051 |
Filed Date | 2013-12-19 |
United States Patent
Application |
20130337248 |
Kind Code |
A1 |
Ozbayraktar; Mehmet Serdar |
December 19, 2013 |
HIGH DENSITY POLYCRYSTALLINE SUPERHARD MATERIAL
Abstract
A polycrystalline superhard material comprises a mass of
diamond, graphite or cubic boron nitride particles or grains bonded
together by ultrathin inter-granular bonding layers, the
inter-granular bonding layers having an average thickness of
greater than about 0.3 nm and less than about 100 nm. There is also
disclosed a method for making such a polycrystalline superhard
material.
Inventors: |
Ozbayraktar; Mehmet Serdar;
(Springs, ZA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Ozbayraktar; Mehmet Serdar |
Springs |
|
ZA |
|
|
Assignee: |
Element Six Abrasives S.A.
Luxembourg
LU
|
Family ID: |
43599051 |
Appl. No.: |
13/997781 |
Filed: |
December 20, 2011 |
PCT Filed: |
December 20, 2011 |
PCT NO: |
PCT/EP11/73463 |
371 Date: |
September 2, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61428054 |
Dec 29, 2010 |
|
|
|
Current U.S.
Class: |
428/216 ;
51/295 |
Current CPC
Class: |
C23C 16/342 20130101;
C04B 35/62884 20130101; B22F 1/025 20130101; C04B 2235/80 20130101;
C04B 35/52 20130101; C04B 2235/781 20130101; C04B 35/522 20130101;
C04B 2235/3873 20130101; C04B 35/62839 20130101; C04B 2235/3817
20130101; B82Y 30/00 20130101; C04B 35/6316 20130101; C04B 35/6303
20130101; C04B 35/62842 20130101; C04B 2235/81 20130101; C23C 16/24
20130101; C04B 2235/3839 20130101; C04B 2235/5436 20130101; C04B
2235/3886 20130101; C04B 2235/5445 20130101; C04B 35/62897
20130101; C04B 2235/786 20130101; C04B 2235/386 20130101; Y10T
428/24975 20150115; C04B 2235/3847 20130101; C04B 2235/427
20130101; C04B 2235/3821 20130101; C04B 2235/3826 20130101; C04B
2235/3843 20130101; C04B 35/645 20130101; C04B 35/5831 20130101;
C23C 16/4417 20130101; C04B 2235/3813 20130101; C04B 2235/3856
20130101; C04B 35/62836 20130101; C04B 2235/85 20130101; C04B
35/62802 20130101; E21B 10/5735 20130101 |
Class at
Publication: |
428/216 ;
51/295 |
International
Class: |
E21B 10/573 20060101
E21B010/573 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 29, 2010 |
GB |
1022033.3 |
Claims
1. A polycrystalline superhard material comprising a mass of
diamond, graphite or cubic boron nitride particles or grains bonded
together by ultrathin inter-granular bonding layers, the
inter-granular bonding layers having an average thickness of
greater than about 0.3 nm and less than about 100 nm.
2. A polycrystalline superhard material according to claim 1,
wherein the average thickness of the inter-granular bonding layers
is less than 20 nm.
3. A polycrystalline superhard material according to claim 1,
wherein the average thickness of the inter-granular bonding layers
is less than 10 nm.
4. A polycrystalline superhard material according to claim 1,
wherein the average particle size of the diamond or cubic boron
nitride particles or grains is from about 50 nanometres to about 50
microns.
5. A polycrystalline superhard material according to claim 1,
wherein the polycrystalline superhard material comprises diamond
and the inter-granular bonding layers comprise diamond.
6. A polycrystalline superhard material according to claim 1,
wherein the polycrystalline superhard material comprises diamond
and the inter-granular bonding layers comprise one or more carbides
of one or more bonding elements selected from the group comprising
Sc, Y, Lu, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, B, Al, Ga, C, Si and
Ge and compounds or alloys of these.
7. A polycrystalline superhard material according to claim 1,
wherein the polycrystalline superhard material comprises diamond
and the inter-granular bonding layers comprise SiC.
8. A polycrystalline superhard material according to claim 1,
wherein the polycrystalline superhard material comprises cBN and
the inter-granular bonding layers comprise cBN.
9. A polycrystalline superhard material according to claim 1,
wherein the polycrystalline superhard material comprises cBN and
the inter-granular bonding layers comprise one or more borides
and/or nitrides of one or more bonding elements selected from the
group comprising Be, Mg, Ca, Sc, Y, Lu, Ti, Zr, Hf, V, Nb, Ta, Cr,
Mo, W, Mn, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn,
B, Al, Ga, In, C, Si, Ge, Sn, Pb, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy,
Ho, Er, Tm, Yb and compounds or alloys of these.
10. A method for making polycrystalline superhard material, the
method including providing a mass of diamond, grahite or cubic
boron nitride particles or grains, depositing ultrathin layers of a
bonding material on respective diamond, graphite or cubic boron
nitride particles or grains, the bonding material being selected so
as to be capable of forming bonds with the diamond, graphite or
cubic boron nitride particles or grains, the average thickness of
the deposited layers of bonding material being greater than about
0.5 nm and less than about 200 nm, consolidating the diamond,
graphite or cubic boron nitride particles or grains and bonding
material to form a green body, and subjecting the green body to a
temperature and pressure at which the diamond, graphite or cubic
boron nitride is thermodynamically stable, sintering and forming
polycrystalline superhard material.
11. A method according to claim 10, wherein the average thickness
of the deposited layers of bonding material is less than about 100
nm.
12. A method according to claim 10, wherein the average thickness
of the deposited layers of bonding material is less than about 50
nm.
13. A method according to claim 10, wherein the average particle
size of the diamond, graphite or cubic boron nitride particles or
grains prior to deposition of the bonding material is from about 50
nanometres to about 50 microns.
14. A method according to claim 10, wherein the polycrystalline
superhard material comprises diamond and the bonding material is
graphite or other non-diamond carbon.
15. A method according to claim 10, wherein the polycrystalline
superhard material comprises diamond and the bonding material
comprises a carbide former selected from the group comprising Sc,
Y, Lu, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, B, Al, Ga, C, Si and Ge
and compounds or alloys of these.
16. A method according to claim 10, wherein the polycrystalline
superhard material comprises diamond and the bonding material
comprises Si or SiC.
17. A method according to any one of claims 10 to 13 claim 10,
wherein the polycrystalline superhard material comprises cBN and
the bonding material comprises hBN.
18. A method according to claim 10, wherein the polycrystalline
superhard material comprises cBN and the bonding material comprises
a boride and/or nitride former selected from the group comprising
Be, Mg, Ca, Sc, Y, Lu, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re,
Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, B, Al, Ga, In,
C, Si, Ge, Sn, Pb, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb
and compounds or alloys of these.
19. A method according to claim 10, wherein the step of subjecting
the green body to a pressure comprises subjecting the green body to
a pressure of between about 5 GPa or more, or 6.8 GPa or more, or
7.7 GPa or more, or between about 8 GPa to about 18 GPa.
20. A wear element comprising a polycrystalline superhard material
according to claim 1.
Description
FIELD
[0001] This disclosure relates to a high density polycrystalline
superhard material, a method of making high density polycrystalline
superhard material, and to a wear element comprising a high density
polycrystalline superhard material.
BACKGROUND
[0002] Cutter inserts for machine and other tools may comprise a
layer of polycrystalline diamond (PCD) or polycrystalline cubic
boron nitride (PCBN) bonded to a cemented carbide substrate. PCD
and PCBN are examples of superhard materials, also called
superabrasive materials, which have a hardness value substantially
greater than that of cemented tungsten carbide.
[0003] Components comprising PCD are 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. PCD comprises a mass of substantially
inter-grown diamond grains forming a skeletal mass, which defines
interstices between the diamond grains. PCD material comprises at
least about 80 volume % of diamond and may be 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
degrees centigrade in the presence of a sintering aid, also
referred to as a catalyst material for diamond. Catalyst material
for diamond is understood to be material that is capable of
promoting direct inter-growth of diamond grains at a pressure and
temperature condition at which diamond is thermodynamically more
stable than graphite. Some catalyst materials for diamond may
promote the conversion of diamond to graphite at ambient pressure,
particularly at elevated temperatures. Examples of catalyst
materials for diamond are cobalt, iron, nickel and certain alloys
including any of these. PCD may be formed on a cobalt-cemented
tungsten carbide substrate, which may provide a source of cobalt
catalyst material for the PCD. The interstices within PCD material
may at least partly be filled with the catalyst material.
[0004] A well-known problem experienced with this type of PCD
material, however, is that the residual presence of the catalyst
material for diamond, in particular a metallic catalyst material
for diamond, for example Co, Ni or Fe, in the interstices has a
detrimental effect on the performance of the PCD material at high
temperatures. During application, the PCD material heats up and
thermally degrades, largely due to the presence of the metallic
catalyst material that catalyses graphitisation of the diamond and
also causes stresses in the PCD material due to the large
difference in thermal expansion between the metallic catalyst
material and the diamond microstructure.
[0005] Components comprising PCBN are used principally for
machining metals. PCBN material comprises a sintered mass of cubic
boron nitride (cBN) grains. The cBN content of PCBN materials may
be at least about 40 volume %. When the cBN content in the PCBN is
at least about 70 volume % there may be substantial direct contact
among the cBN grains. When the cBN content is in the range from
about 40 volume % to about 60 volume % of the compact, then the
extent of direct contact among the cBN grains is limited. PCBN may
be made by subjecting a mass of cBN grains together with a powdered
matrix phase, to a temperature and pressure at which the cBN is
thermodynamically more stable than the hexagonal form of boron
nitride, hBN.
[0006] GB 2 453 023 discloses an ultra-hard composite construction
comprising an ultra-hard body having a plurality of diamond
crystals bonded to one another by a carbide reaction product. The
carbide reaction product is formed from a carbide former selected
from silicon, boron, titanium, molybdenum or vanadium with diamond
at HPHT conditions. The ultra-hard body resulting from the HPHT
process comprises in the range of from about 40 to 90 percent by
volume diamond. The body may include a further diamond region
positioned along a surface portion of the body and that is
substantially exclusively diamond, having a diamond content of 95
to 99 percent or more.
[0007] There is a need for a high density polycrystalline superhard
material comprising diamond or cubic boron nitride which has a high
thermal stability, thereby enabling high cutting speeds in cutting
applications as well as longer cutter lifetimes in drilling
applications, and greater toughness, all without the need for using
excessive pressures and temperatures.
SUMMARY
[0008] Viewed from a first aspect there is provided a
polycrystalline superhard material comprising a mass of diamond,
graphite or cubic boron nitride particles or grains bonded together
by one or more ultrathin inter-granular bonding layers, the
inter-granular bonding layers having an average thickness of
greater than about 0.3 nm and less than about 100 nm. Such
ultrathin bonding layer(s) may improve toughness.
[0009] In some embodiments, the average thickness of the
inter-granular bonding layers is less than about 20 nm, or less
than about 10 nm, or less than about 5 nm.
[0010] The average particle size of the diamond or cubic boron
nitride particles or grains is from about 50 nanometres to about 50
microns.
[0011] The diamond content of the polycrystalline diamond material
may, in some embodiments, be at least about 90 percent, at least
about 95 percent, or at least about 99 percent of the volume of the
polycrystalline superhard material.
[0012] In some embodiments, the content of the inter-granular
bonding material is at most about 10 volume percent, at most about
5 volume percent, or at most about 1 volume percent of the
polycrystalline superhard material.
[0013] Viewed from a further aspect, there is provided a method for
making polycrystalline superhard material, the method comprising
providing a mass of diamond, graphite or cubic boron nitride
particles or grains, depositing ultrathin layers of a bonding
material on respective diamond, graphite or cubic boron nitride
particles or grains, the bonding material being selected so as to
be capable of forming bonds with the diamond, graphite or cubic
boron nitride particles or grains, the average thickness of the
deposited layers of bonding material being greater than about 0.5
nm and less than about 200 nm, consolidating the diamond, graphite
or cubic boron nitride particles or grains and bonding material to
form a green body, and subjecting the green body to a temperature
and pressure at which the diamond, graphite or cubic boron nitride
is thermodynamically stable, sintering and forming polycrystalline
superhard material.
[0014] The diamond particles or grains, prior to deposition of the
bonding material, may have, for example, an average particle or
grain size of from about 50 nanometres to about 50 microns.
[0015] In some embodiments, a multimodal mixture of diamond
particles or grains of varying average particle or grain size may
be provided.
[0016] In some embodiments, the polycrystalline superhard material
may be a stand-alone compact or the polycrystalline superhard
material may be attached to a substrate.
[0017] Sintering may be carried out at pressures of, for example,
about 2.5 GPa or more, or 5 GPa or more, or 6.8 GPa or more, or 7.7
GPa or more, for example between about 8GPa to about 18GPa and
temperatures of about 450 degrees centigrade or more, or 1500
degrees centigrade or more, or 2250 degrees centigrade or more, or
2400 degrees centigrade or more, for sintering times of 10 seconds
or more, or 3 minutes or more, or 30 minutes or more.
[0018] Viewed from another aspect, there is provided a wear element
comprising a polycrystalline superhard material as described
herein.
DETAILED DESCRIPTION
[0019] As used herein, "high density polycrystalline diamond
material" comprises a mass of diamond particles or grains, a
substantial portion of which are bonded to one another and in which
the content of diamond is at least about 90 volume percent of the
material.
[0020] As used herein, "high density polycrystalline cubic boron
nitride material" comprises a mass of cubic boron nitride grains, a
substantial portion of which are bonded to one another and in which
the content of cubic boron nitride is at least about 90 volume
percent of the material.
[0021] As used herein, "epitaxy" in its broadest sense is
understood to include, but not limited to, the deposition of a
polycrystalline or a monocrystalline layer of bonding material. The
epitaxy may be "heteroepitaxy", which is understood to mean that
the superhard material and deposited layers of bonding material
contain different components, or "homoepitaxy", which is understood
to mean that the superhard material and deposited layers of bonding
material contain the same components.
[0022] A "multi-modal size distribution of a mass of grains" is
understood to mean that the grains have a size distribution with
more than one peak, each peak corresponding to a respective "mode".
Multimodal polycrystalline bodies are typically made by providing
more than one source of a plurality of grains, each source
comprising grains having a substantially different average size,
and blending together the grains or particles from the sources.
Measurement of the size distribution of the blended grains
typically reveals distinct peaks corresponding to distinct modes.
When the grains are sintered together to form the polycrystalline
body, their size distribution is further altered as the grains are
compacted against one another and fractured, resulting in the
overall decrease in the sizes of the grains. Nevertheless, the
multimodality of the grains is usually still clearly evident from
image analysis of the sintered article.
[0023] As used herein, a "green body" is an article that is
intended to be sintered or which has been partially sintered, but
which has not yet been fully sintered to form an end product. It
may generally be self-supporting and may have the general form of
the intended finished article.
[0024] As used herein, a "superhard wear element" is an element
comprising a superhard material and is for use in a wear
application, such as degrading, boring into, cutting or machining a
workpiece or body comprising a hard or abrasive material.
[0025] A polycrystalline superhard material is described having a
high density of diamond or cubic boron nitride in its
polycrystalline structure. In some embodiments, a high-purity PCD
or PCD-like material with high diamond density, high degree of
bonding, very little or no free elements or compounds present and
high fracture toughness is provided. In some embodiments, an
analogous high density PCBN material is provided.
[0026] In the case of PCD, in some embodiments, a mass of diamond
particles or grains is provided. A layer of very thin bonding
material is deposited on respective diamond particles or grains
using a suitable method such as sol-gel deposition. To achieve
homoepitaxy, the bonding materials are carbon allotropes such as
graphite, graphene or diamond-like carbon, for example, and to
achieve heteroepitaxy the bonding materials are carbide-forming
elements such as silicon or suitable metals or alloys, for
example.
[0027] The starting mass is sintered at elevated temperature and
pressure conditions as needed for the sintered diamond to be more
thermodynamically stable than graphite. Typically, sintering takes
place at a pressure in excess of about 5 GPa and a temperature in
excess of about 1400.degree. C. However, it will be understood by a
person skilled in the art that suitable conditions from low
pressure (for instance about 2.5 GPa) to about 10 GPa or more (even
up to 25 GPa) and modest temperature (for instance about
450.degree. C.) to about 2400.degree. C. or more in the
diamond-stable region can be used to convert the nano-sized carbon
allotrope to diamond or to cause reaction of the diamond grains
with the carbide-former to form inter-granular bonded layers of
from a few to about 100 atoms thick. In some embodiments, the
pressure conditions are from about 8 GPa to about 10 GPa or, in
other embodiments about 8 GPa to about 18 GPa.
[0028] Excellent bonding in the sintered mass may be achieved by
means of very thin bonded layers of bonding material that form
between the diamond particles or grains, these inter-granular
layers ranging from a few atoms to tens of atoms in thickness. The
resultant material may be highly thermally-stable and tough.
Furthermore utilising reaction bonding as defined above, may result
in a reduction in pressure requirement compared with direct diamond
to diamond conversion which would have significant implications for
commercialisation as cost increases very rapidly and achievable
product size decreases significantly as the pressure requirement is
increased.
[0029] In the case of graphite or other non-diamond carbon as the
bonding material, direct conversion of the very thin layers of
deposited bonding material to diamond will result at sufficient
pressure and temperature, resulting in PCD where the inter-granular
layers have the diamond structure and hence no mismatch on the
particle-layer boundary is expected. In the case of carbide-forming
elements being used as the bonding material, for example silicon or
suitable metals or alloys, reaction-bonded PCD is formed at
sufficient pressure and temperature and the very thin carbide
inter-granular layers will be constrained by the neighbouring
diamond particles to have a structure closer to that of diamond
than that of the free carbide and to have small misfit with the
diamond lattice.
[0030] As a very high percentage volume of the starting material is
already-formed diamond, the need is therefore to transform very
small amounts of carbon, or to react very small amounts of carbide
forming elements or alloys, at the grain boundaries.
[0031] The very thin layers of bonding material may be arranged on
the diamond grains using methods such as, but not limited to,
sol-gel, physical vapour deposition, chemical vapour deposition,
atomic layer deposition, liquid-phase epitaxy, solid-phase epitaxy,
molecular-beam epitaxy or magnetron sputtering. The layers may
partially or completely cover the diamond grains.
[0032] In some embodiments, the average size of the starting
diamond particles or grains may range from about 50 nm to about 50
microns. The average thickness of the starting graphitic, other
carbon or carbide-forming very thin bonding material layers may
range from, for example, about 0.5 nm to about 200 nm. The carbon
binder source may be graphite, or glassy carbon, or graphene, or
any type of fullerene, or diamond-like carbon. The carbide forming
bonding elements may be chosen from, for example, Sc, Y, Lu, Ti,
Zr, Hf, V, Nb, Ta, Cr, Mo, W, B, Al, Ga, C, Si and Ge. In some
embodiments, the bonding material may be silicon or silicon
carbide.
[0033] Combinations (mixtures, alloys, compounds and the like) of
two or more of the carbon binder sources or two or more of the
carbide-forming elements or two or more of the carbides may be
used. In some embodiments, the purity of the starting materials is
selected to assist in the production of PCD with very small flaw
sizes thereby not only improving strength but leading to the option
of transparent PCD material.
[0034] In some embodiments, the average thickness of the newly
grown inter-granular bonded layers may vary from less than 1 nm,
typically from about 0.3 nm, to less than about 100 nm, or less
than about 20 nm, or less than about 10 nm, or less than about 5
nm. The bonded layer material may be diamond, or a carbide
constrained by neighbouring diamond grains to have a crystal
structure closer to that of diamond than to that of the free
carbide, and small amounts of the carbide-forming elements or
alloys may be present.
[0035] In the case of a carbide bonded layer a low degree of
misorientation between the diamond grain and the newly formed layer
is expected due to the layer being very thin, i.e. a misfit angle
of less than approximately 11 degrees is expected. The carbides
have higher coefficient of thermal expansion than diamond, so the
diamond grains in the final product should be under compressive
stress, hence the carbide neck should be in tension favouring
intergranular crack propagation. This should act as a toughening
mechanism.
[0036] Toughness is further enhanced by the nanosized nature of the
bonded inter-layer material. Greater fracture toughness will assist
in the manufacture of higher precision cutting tools that display
less edge chipping of the tool, giving a cleaner and more accurate
cut and more impact resistance. Improved thermal stability is
expected in all cases enabling increased cutting speeds and longer
lifetime in drilling applications.
[0037] In some embodiments, the superhard material is cBN powder
used to synthesise PCBN. The bonding material may be a boride
and/or nitride former in the case of heteroepitaxy or it may be hBN
in the case of homoepitaxy.
[0038] Where the superhard starting material is cBN powder, a
similar approach to that described for PCD synthesis is followed.
In this case very thin bonding material layers of nitride and/or
boride formers are arranged on the primary cBN crystals. The
bonding materials may be chosen from Be, Mg, Ca, Sc, Y, Lu, Ti, Zr,
Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd,
Pt, Cu, Ag, Au, Zn, B, Al, Ga, In, C, Si, Ge, Sn, Pb, La, Ce, Pr,
Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb or compounds/alloys of these.
Alternatively the very thin bonding material layer may be hBN
arranged on the cBN primary crystals and directly converted to PCBN
under appropriate pressure and temperature conditions. Examples of
carbide, nitride, boride and carbonitride binder compounds that can
be used in some embodiments are TiC, TiB.sub.2, TiC.sub.xN.sub.1-x
and TiN.
[0039] Preferred reaction-bonded compounds in the PCD or PCBN very
thin bonded layer region may include but are not limited to: SiC,
Si.sub.3N.sub.4, TiC, TiN, TaC, TaN, TiC.sub.xN.sub.1-x,
TaC.sub.xN.sub.1-x, WC, WN.sub.2, NbC, Nb.sub.2C, and TiB.sub.2. It
is also noted that compounds may be formed on the diamond or cBN
particle or grain surfaces before sintering. This is because
reactions may occur during the arrangement of the bonding material
due to the elevated temperatures used in some of these
processes.
[0040] A method for making polycrystalline superhard material
comprises providing a mass of diamond or cubic boron nitride
particles or grains, depositing ultrathin layers of a bonding
material on respective diamond or cubic boron nitride particles or
grains, the bonding material being selected so as to be capable of
forming bonds with the diamond or cubic boron nitride particles or
grains, and the average thickness of the deposited layers of
bonding material being greater than about 0.5 nm and less than
about 200 nm. The diamond or cubic boron nitride particles or
grains and bonding material are consolidated into a green body,
which green body is then subjected to a temperature and pressure at
which the diamond or cubic boron nitride is more thermodynamically
stable than graphite or hBN, respectively, in order to sinter it
and form polycrystalline diamond or cubic boron nitride
material.
[0041] Prior to deposition of the bonding material, the diamond or
cubic boron nitride particles may have, for example, an average
particle size ranging from about 50 nanometres to about 50
microns.
[0042] The green body, once formed is placed in a suitable
container and introduced into a high pressure high temperature
press. Pressure and heat are applied in order to sinter the diamond
particles together, typically at pressures of 2.5 GPa or more, or
of 5 GPa or more, or of 6.8 GPa or more, or of 7.7 Gpa or more, and
up to about 10 GPa, and temperatures of 450.degree. C. or more, or
1500.degree. C. or more, or 2250.degree. C. or more, or
2400.degree. C. or more, but in some embodiments the pressures may
be up to around 25 GPa.
[0043] Non-limiting examples of polycrystalline superhard materials
will now be described.
EXAMPLE 1
[0044] 10 g of crushed diamond of average particle size 0.75 micron
may be cleaned by placing in a furnace and heating at 800 degrees
centigrade for 1 hour in 10% hydrogen in an argon atmosphere. The
diamond powder may then be transferred into a plasma reactor of the
type typically used to deposit diamond-like carbon (DLC), and the
diamond particles may be coated with a coating (not entirely
uniform, but covering most of the surface of the diamond particles)
of DLC of approximately 35 nm thickness. The coated diamond
particles may be transferred to a capsule and subjected to
approximately 8 GPa and 2000 degrees centigrade for approximately
30 seconds at dwell time. The sintered compact may be recovered
from the capsule and high resolution scanning electron microscopy
of a polished section is expected to show diamond grains connected
by layers of diamond of approximately 4-12 nanometres thick. HRTEM
analysis of the composite is expected to confirm that the layers
have a diamond crystal structure. The diamond content of the
sintered compact is expected to be close to 100% by volume.
EXAMPLE 2
[0045] 20 g of diamond of average particle size 2 microns may be
cleaned by placing in a furnace and heating at 800 degrees
centigrade for 1 hour in 10% hydrogen in an argon atmosphere. The
diamond may then be transferred to a radio frequency
plasma-enhanced chemical vapour deposition (rf PECVD) reactor and
subjected to standard conditions for silicon thin film deposition:
the deposition temperature would typically be 200 degrees
centigrade, and silane (SiH.sub.4) and hydrogen (H.sub.2) gases
would be fed into the reactor to maintain a SiH.sub.4 partial
pressure of 0.9 Torr and a [H.sub.2]:[SiH.sub.4] ratio of 80. The
rf power flux would be set at 70 mW/cm.sup.2. After a deposition
time of 500 seconds, the gases would be purged from the reactor
with argon, the reactor cooled and the diamond recovered. 2 g of
the diamond, now coated with a silicon layer of approximately 50
nanometres thick, may then be placed in a capsule in a glove box
under argon atmosphere to prevent oxidation of the silicon layer.
The capsule may be pressed in a high-pressure high-temperature
press at 8 GPa and 1800 degrees centigrade for approximately 15
seconds dwell time at condition. The sintered compact may be
recovered from the capsule and high resolution scanning electron
microscopy of a polished section is expected to show diamond grains
connected by layers of silicon carbide of approximately 4-15
nanometres thick. Analysis of the composite using X-ray diffraction
and the Scherrer calculation is expected to indicate the silicon
carbide layer consisting of crystallites of approximately 4-15
nanometres. The diamond content of the sintered compact is expected
to be approximately 99% by volume.
EXAMPLE 3
[0046] 10 g of crushed cubic boron nitride (cBN) of average
particle size 0.50 micron may be transferred into a chemical vapour
deposition reactor that may be fed with a gas mixture containing
BCl.sub.3--NH.sub.3--H.sub.2--Ar, at flow rates of approximately
BCl.sub.3:0.2 ml/sec; NH.sub.3:1.0 ml/sec; H.sub.2:0.5 ml/sec; Ar:
2 ml/sec. An opaque and semi-crystalline film of boron nitride is
expected to form on the cBN particles after a dwell time of
approximately 5 minutes at 950-1050 degrees centigrade. The coating
is expected to be approximately 45 nm thick. The coated cBN
particles may be transferred to a capsule and subjected to
approximately 6 GPa and 1800-2100 degrees centigrade for
approximately 30 seconds at dwell time. The sintered compact may be
recovered from the capsule and high resolution scanning electron
microscopy of a polished section is expected to show cBN grains
connected by layers of cBN of approximately 4-12 nanometres thick.
HRTEM analysis of the composite is expected to indicate that the
layers have a cBN crystal structure. The cBN content of the
sintered compact is expected to be approximately 95% by volume.
EXAMPLE 4
[0047] 50 g of crushed cubic boron nitride (cBN) of average
particle size 0.1-0.3 micron may be transferred into an atomic
layer deposition reactor and coated with titanium metal using 10-30
cycles of approximately 3 seconds long each to achieve a 3-10
nanometre thick coating of titanium metal on the cBN particles. The
coated cBN particles may be transferred to a capsule and subjected
to approximately 6 GPa and 1800-2100 degrees centigrade for
approximately 30 seconds at dwell time. The sintered compact may be
recovered from the capsule and high resolution scanning electron
microscopy of a polished section is expected to show cBN grains
connected by layers of titanium boride and titanium nitride of
approximately 2-3 nanometres thick. The cBN content of the sintered
compact is expected to be approximately 95% by volume.
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