U.S. patent application number 14/236506 was filed with the patent office on 2014-06-19 for polycrystalline diamond construction and method for making same.
This patent application is currently assigned to ELEMENT SIX LIMITED. The applicant listed for this patent is ELEMENT SIX ABRASIVES S.A., ELEMENT SIX LIMITED. Invention is credited to Nedret Can, Michael Lester Fish.
Application Number | 20140165476 14/236506 |
Document ID | / |
Family ID | 46881516 |
Filed Date | 2014-06-19 |
United States Patent
Application |
20140165476 |
Kind Code |
A1 |
Can; Nedret ; et
al. |
June 19, 2014 |
POLYCRYSTALLINE DIAMOND CONSTRUCTION AND METHOD FOR MAKING SAME
Abstract
A polycrystalline diamond construction comprising a body of
polycrystalline diamond material is formed of a mass of diamond
grains exhibiting inter-granular bonding and defining a plurality
of interstitial regions therebetween, and a non-diamond phase at
least partially filling a plurality of the interstitial regions to
form non-diamond phase pools, the non-diamond phase pools each
having an individual cross-sectional area. The percentage of
non-diamond phase in the total area of a cross-section of the body
of polycrystalline diamond material and the mean of the individual
cross-sectional areas of the non-diamond phase pools in the image
analysed using an image analysis technique at a selected
magnification is less than 0.7, or less than 0.340 microns squared,
or between around 0.005 to 0.340 microns squared depending on the
percentage of non-diamond phase in the total area of the
cross-section of the polycrystalline diamond construction. There is
also disclosed a method of making such a construction.
Inventors: |
Can; Nedret; (Oxfordshire,
GB) ; Fish; Michael Lester; (County Clare,
IE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ELEMENT SIX LIMITED
ELEMENT SIX ABRASIVES S.A. |
County Clare
Luxembourg |
|
IE
LU |
|
|
Assignee: |
ELEMENT SIX LIMITED
County Clare
IE
ELEMENT SIX ABRASIVES S.A.
Luxembourg
LU
|
Family ID: |
46881516 |
Appl. No.: |
14/236506 |
Filed: |
August 1, 2012 |
PCT Filed: |
August 1, 2012 |
PCT NO: |
PCT/EP2012/065082 |
371 Date: |
January 31, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61514414 |
Aug 2, 2011 |
|
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|
61514758 |
Aug 3, 2011 |
|
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61553722 |
Oct 31, 2011 |
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Current U.S.
Class: |
51/309 ; 175/426;
175/428; 175/432; 175/434; 299/105; 51/307 |
Current CPC
Class: |
C22C 2204/00 20130101;
E21B 10/54 20130101; E21B 10/5735 20130101; E21C 35/18 20130101;
C22C 26/00 20130101; E21B 10/567 20130101; B22F 2998/00 20130101;
B22F 7/062 20130101; E21B 10/55 20130101; B22F 3/14 20130101; B22F
3/14 20130101; B22F 2998/00 20130101 |
Class at
Publication: |
51/309 ; 51/307;
175/426; 175/428; 175/432; 299/105; 175/434 |
International
Class: |
B22F 3/14 20060101
B22F003/14; E21B 10/55 20060101 E21B010/55; E21B 10/54 20060101
E21B010/54; E21B 10/573 20060101 E21B010/573; E21C 35/18 20060101
E21C035/18; E21B 10/567 20060101 E21B010/567 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 2, 2011 |
GB |
1113299.0 |
Aug 3, 2011 |
GB |
1113391.5 |
Sep 30, 2011 |
GB |
1116899.4 |
Claims
1. A polycrystalline diamond construction comprising a body of
polycrystalline diamond material formed of: a mass of diamond
grains exhibiting inter-granular bonding and defining a plurality
of interstitial regions therebetween, and a non-diamond phase at
least partially filling a plurality of the interstitial regions to
form non-diamond phase pools, the non-diamond phase pools each
having an individual cross-sectional area, wherein the percentage
of non-diamond phase in the total area of a cross-section of the
body of polycrystalline diamond material is between around 0 to 5%,
and the mean of the individual cross-sectional areas of the
non-diamond phase pools in an analysed image of a cross-section
through the body of polycrystalline material is less than around
0.7 microns squared when analysed using an image analysis technique
at a magnification of around 1000 and an image area of 1280 by 960
pixels.
2. A polycrystalline diamond construction comprising a body of
polycrystalline diamond material formed of: a mass of diamond
grains exhibiting inter-granular bonding and defining a plurality
of interstitial regions therebetween, and a non-diamond phase at
least partially filling a plurality of the interstitial regions to
form non-diamond phase pools, the non-diamond phase pools each
having an individual cross-sectional area, wherein the percentage
of non-diamond phase in the total area of a cross-section of the
body of polycrystalline diamond material is between around 5 to
10%, and the mean of the individual cross-sectional areas of the
non-diamond phase pools in an analysed image of a cross-section
through the body of polycrystalline diamond material is less than
around 0.340 microns squared when analysed using an image analysis
technique at a magnification of around 1000 and an image area of
1280 by 960 pixels.
3. A polycrystalline diamond construction comprising a body of
polycrystalline diamond material formed of: a mass of diamond
grains exhibiting inter-granular bonding and defining a plurality
of interstitial regions therebetween, and a non-diamond phase at
least partially filling a plurality of the interstitial regions to
form non-diamond phase pools, the non-diamond phase pools each
having an individual cross-sectional area, wherein the percentage
of non-diamond phase in the total area of a cross-section of the
polycrystalline diamond construction is between around 10 to 15%,
and the mean of the individual cross-sectional areas of the
non-diamond phase pools in an analysed image of a cross section
through the body of polycrystalline material is less than around
0.340 microns squared when analysed using an image analysis
technique at a magnification of around 3000 and an image area of
1280 by 960 pixels.
4. A polycrystalline diamond construction comprising a body of
polycrystalline diamond material formed of: a mass of diamond
grains exhibiting inter-granular bonding and defining a plurality
of interstitial regions therebetween, and a non-diamond phase at
least partially filling a plurality of the interstitial regions to
form non-diamond phase pools, the non-diamond phase pools each
having an individual cross-sectional area, wherein the percentage
of non-diamond phase in the total area of a cross-section of the
polycrystalline diamond construction is between around 15 to 30%,
and the mean of the individual cross-sectional areas of the
non-diamond phase pools in an analysed image of a cross section
through the body of polycrystalline material is between around
0.005 to 0.340 microns squared when analysed using an image
analysis technique at a magnification of around 10000 and an image
area of 1280 by 960 pixels.
5. A polycrystalline diamond construction according to any one of
the preceding claims, wherein the body of polycrystalline diamond
material has a largest dimension of around 6 mm or greater.
6. A polycrystalline diamond construction according to any one of
the preceding claims, wherein the body of polycrystalline diamond
material has a thickness of around 0.3 mm or greater.
7. The polycrystalline diamond construction according to any one of
the preceding claims, further comprising a substrate bonded to the
body of polycrystalline diamond material along an interface.
8. The polycrystalline diamond construction according to claim 7,
wherein the interface between the substrate and the body of
polycrystalline diamond material is substantially non-planar.
9. The polycrystalline diamond construction according to any one of
claims 7 or 8, wherein the substrate comprises cemented
carbide.
10. The polycrystalline diamond construction according to any one
of claims 7 to 9, wherein the substrate has a thickness at least
equal to or greater than the thickness of the body of
polycrystalline diamond material.
11. A cutter for boring into the earth comprising the
polycrystalline diamond construction according to any one of the
preceding claims.
12. A PCD element for a rotary shear bit for boring into the earth,
for a percussion drill bit or for a pick for mining or asphalt
degradation, comprising the polycrystalline diamond construction of
any one of claims 1 to 10.
13. A drill bit or a component of a drill bit for boring into the
earth, comprising a polycrystalline superhard construction
according to any one of claims 1 to 10.
14. A method for making a polycrystalline diamond construction, the
method comprising: providing a mass of diamond grains having a
first average size; arranging the mass of diamond grains to form a
pre-sinter assembly with a body of material for forming a
substrate; and treating the pre-sinter assembly in the presence of
a catalyst material for diamond at an ultra-high pressure of around
7 GPa or greater and a temperature at which diamond is more
thermodynamically stable than graphite to sinter together the
diamond grains and a substrate bonded thereto along an interface to
form an integral PCD construction; the diamond grains exhibiting
inter-granular bonding and defining a plurality of interstitial
regions therebetween, a non-diamond phase at least partially
filling a plurality of the interstitial regions to form non-diamond
phase pools, the non-diamond phase pools each having an individual
cross-sectional area, wherein the percentage of non-diamond phase
in the total area of a cross-section of the body of polycrystalline
diamond material is between around 0 to 5%, and the mean of the
individual cross-sectional areas of the non-diamond phase pools in
the image analysed is less than around 0.7 microns squared when
analysed using an image analysis technique at a magnification of
around 1000 and an image area of 1280 by 960 pixels; or the
percentage of non-diamond phase in the total area of a
cross-section of the body of polycrystalline diamond material is
between around 5 to 10%, and the mean of the individual
cross-sectional areas of the non-diamond phase pools in the image
analysed is less than around 0.340 microns squared when analysed
using an image analysis technique at a magnification of around 1000
and an image area of 1280 by 960 pixels; or the percentage of
non-diamond phase in the total area of a cross-section of the
polycrystalline diamond construction is between around 10 to 15%,
and the mean of the individual cross-sectional areas of the
non-diamond phase pools in the image analysed is less than around
0.340 microns squared when analysed using an image analysis
technique at a magnification of around 3000 and an image area of
1280 by 960 pixels; or the percentage of non-diamond phase in the
total area of a cross-section of the polycrystalline diamond
construction is between around 15 to 30%, and the mean of the
individual cross-sectional areas of the non-diamond phase pools in
the image analysed is between around 0.005 to 0.340 microns squared
when analysed using an image analysis technique at a magnification
of around 10000 and an image area of 1280 by 960 pixels.
15. A method of forming the polycrystalline diamond construction of
any one of claims 1 to 10.
16. A polycrystalline diamond construction substantially as
hereinbefore described with reference to any one embodiment as that
embodiment is illustrated in FIGS. 3 to 10b of the accompanying
drawings.
17. A method of forming the polycrystalline diamond construction
substantially as hereinbefore described with reference to any one
embodiment as that embodiment is illustrated in FIGS. 3 to 10b of
the accompanying drawings.
Description
FIELD
[0001] This disclosure relates to a polycrystalline diamond
construction formed of polycrystalline diamond (PCD) material, a
method for making the same and tools comprising same, particularly
but not exclusively for use in boring into the earth.
BACKGROUND
[0002] Polycrystalline diamond (PCD) material comprises a mass of
inter-bonded diamond grains and interstices between the diamond
grains. A body of PCD material may be made by subjecting an
aggregated mass of diamond grains to a high pressure and
temperature in the presence of a sintering aid which is typically a
metal such as cobalt, nickel, iron or an alloy containing one or
more such metals and which may promote the inter-bonding of diamond
grains. The sintering aid may also be referred to as a catalyst
material for diamond and a binder material. Interstices within the
sintered PCD material may be wholly or partially filled with
residual catalyst material. PCD may be formed on a substrate, such
as a cobalt-cemented tungsten carbide substrate, which may provide
a source of cobalt catalyst material for the PCD.
[0003] PCD material may be used as an abrasive compact in a wide
variety of tools for cutting, machining, milling, grinding,
drilling or degrading hard or abrasive materials such as rock,
metal, ceramics, composites and wood-containing materials. For
example, tool inserts comprising PCD material are widely used
within drill bits used for boring into the earth in the oil and gas
drilling industry.
[0004] In many of these applications, the temperature of the PCD
material may become elevated as it engages rock or other workpieces
or bodies. Mechanical properties of PCD material such as abrasion
resistance, hardness and strength tend to deteriorate at elevated
temperatures, which may be promoted by the residual catalyst
material within the body of PCD material.
[0005] It is desirable to improve the abrasion resistance of a body
of PCD material when used as an abrasive compact in tools such as
those mentioned above, as this allows extended use of the cutter,
drill or machine in which the abrasive compact is located. This is
typically achieved by manipulating variables such as average
diamond particle/grain size, overall binder content, particle
density and the like.
[0006] For example, it is well known in the art to increase the
abrasion resistance of an ultrahard composite by reducing the
overall grain size of the component ultrahard particles. Typically,
however, as these materials are made more wear resistant they
become more brittle or prone to fracture.
[0007] Abrasive compacts designed for improved wear performance
will therefore tend to have poor impact strength or reduced
resistance to spalling. This trade-off between the properties of
impact resistance and wear resistance makes designing optimised
abrasive compact structures, particularly for demanding
applications, inherently self-limiting.
[0008] Additionally, because finer grained structures will
typically contain more solvent/catalyst or metal binder, they tend
to exhibit reduced thermal stability when compared to coarser
grained structures. This reduction in optimal behaviour for finer
grained structures can cause substantial problems in practical
applications where the increased wear resistance is nonetheless
required for optimal performance.
[0009] Prior art methods to solve this problem have typically
involved attempting to achieve a compromise by combining the
properties of both finer and coarser ultrahard particle grades in
various manners within the ultrahard abrasive layer.
[0010] Another conventional solution is to remove, typically by
acid leaching, the catalyst/solvent or binder phase from the PCD
material.
[0011] It is typically extremely difficult and time consuming to
remove the bulk of a metallic catalyst/solvent effectively from a
PCD table, particularly from the thicker PCD tables required by
current applications. Achieving appreciable leaching depths can
take so long as to be commercially unfeasible or require
undesirable interventions such as extreme acid treatment or
physical drilling of the PCD tables.
[0012] The development of an abrasive compact that can achieve
improved properties of impact and fatigue resistance consistent
with coarser grained materials, whilst still retaining good wear
resistance and reduced incidence of cracking is highly
desirable.
SUMMARY
[0013] Viewed from a first aspect there is provided a
polycrystalline diamond construction comprising a body of
polycrystalline diamond material formed of: [0014] a mass of
diamond grains exhibiting inter-granular bonding and defining a
plurality of interstitial regions therebetween, and [0015] a
non-diamond phase at least partially filling a plurality of the
interstitial regions to form non-diamond phase pools, the
non-diamond phase pools each having an individual cross-sectional
area, [0016] wherein the percentage of non-diamond phase in the
total area of a cross-section of the body of polycrystalline
diamond material is between around 0 to 5%, and the mean of the
individual cross-sectional areas of the non-diamond phase pools in
an analysed image of a cross-section through the body of
polycrystalline material is less than around 0.7 microns squared
when analysed using an image analysis technique at a magnification
of around 1000 and an image area of 1280 by 960 pixels.
[0017] Viewed from a second aspect there is provided a
polycrystalline diamond construction comprising a body of
polycrystalline diamond material formed of: [0018] a mass of
diamond grains exhibiting inter-granular bonding and defining a
plurality of interstitial regions therebetween, and [0019] a
non-diamond phase at least partially filling a plurality of the
interstitial regions to form non-diamond phase pools, the
non-diamond phase pools each having an individual cross-sectional
area, [0020] wherein the percentage of non-diamond phase in the
total area of a cross-section of the body of polycrystalline
diamond material is between around 5 to 10%, and the mean of the
individual cross-sectional areas of the non-diamond phase pools in
an analysed image of a cross-section through the body of
polycrystalline diamond material is less than around 0.340 microns
squared when analysed using an image analysis technique at a
magnification of around 1000 and an image area of 1280 by 960
pixels.
[0021] Viewed from a third aspect there is provided a
polycrystalline diamond construction comprising a body of
polycrystalline diamond material formed of: [0022] a mass of
diamond grains exhibiting inter-granular bonding and defining a
plurality of interstitial regions therebetween, and [0023] a
non-diamond phase at least partially filling a plurality of the
interstitial regions to form non-diamond phase pools, the
non-diamond phase pools each having an individual cross-sectional
area, [0024] wherein the percentage of non-diamond phase in the
total area of a cross-section of the polycrystalline diamond
construction is between around 10 to 15%, and [0025] the mean of
the individual cross-sectional areas of the non-diamond phase pools
in an analysed image of a cross section through the body of
polycrystalline material is less than around 0.340 microns squared
when analysed using an image analysis technique at a magnification
of around 3000 and an image area of 1280 by 960 pixels.
[0026] Viewed from a fourth aspect there is provided a
polycrystalline diamond construction comprising a body of
polycrystalline diamond material formed of: [0027] a mass of
diamond grains exhibiting inter-granular bonding and defining a
plurality of interstitial regions therebetween, and [0028] a
non-diamond phase at least partially filling a plurality of the
interstitial regions to form non-diamond phase pools, the
non-diamond phase pools each having an individual cross-sectional
area, [0029] wherein the percentage of non-diamond phase in the
total area of a cross-section of the polycrystalline diamond
construction is between around 15 to 30%, and [0030] the mean of
the individual cross-sectional areas of the non-diamond phase pools
in an analysed image of a cross section through the body of
polycrystalline material is between around 0.005 to 0.340 microns
squared when analysed using an image analysis technique at a
magnification of around 10000 and an image area of 1280 by 960
pixels.
[0031] In some embodiments, the body of polycrystalline diamond
material has a largest dimension of around 6 mm or greater.
[0032] In some embodiments, the body of polycrystalline diamond
material has a thickness of around 0.3 mm or greater.
[0033] Viewed from a fifth aspect there is provided a method for
making a polycrystalline diamond construction, the method
comprising: [0034] providing a mass of diamond grains having a
first average size; [0035] arranging the mass of diamond grains to
form a pre-sinter assembly with a body of material for forming a
substrate; and [0036] treating the pre-sinter assembly in the
presence of a catalyst material for diamond at an ultra-high
pressure of around 7 GPa or greater and a temperature at which
diamond is more thermodynamically stable than graphite to sinter
together the diamond grains and a substrate bonded thereto along an
interface to form an integral PCD construction; the diamond grains
exhibiting inter-granular bonding and defining a plurality of
interstitial regions therebetween, a non-diamond phase at least
partially filling a plurality of the interstitial regions to form
non-diamond phase pools, the non-diamond phase pools each having an
individual cross-sectional area, [0037] wherein the percentage of
non-diamond phase in the total area of a cross-section of the body
of polycrystalline diamond material is between around 0 to 5%, and
the mean of the individual cross-sectional areas of the non-diamond
phase pools in the image analysed is less than around 0.7 microns
squared when analysed using an image analysis technique at a
magnification of around 1000 and an image area of 1280 by 960
pixels; or [0038] the percentage of non-diamond phase in the total
area of a cross-section of the body of polycrystalline diamond
material is between around 5 to 10%, and the mean of the individual
cross-sectional areas of the non-diamond phase pools in the image
analysed is less than around 0.340 microns squared when analysed
using an image analysis technique at a magnification of around 1000
and an image area of 1280 by 960 pixels; or [0039] the percentage
of non-diamond phase in the total area of a cross-section of the
polycrystalline diamond construction is between around 10 to 15%,
and the mean of the individual cross-sectional areas of the
non-diamond phase pools in the image analysed is less than around
0.340 microns squared when analysed using an image analysis
technique at a magnification of around 3000 and an image area of
1280 by 960 pixels; or [0040] the percentage of non-diamond phase
in the total area of a cross-section of the polycrystalline diamond
construction is between around 15 to 30%, and the mean of the
individual cross-sectional areas of the non-diamond phase pools in
the image analysed is between around 0.005 to 0.340 microns squared
when analysed using an image analysis technique at a magnification
of around 10000 and an image area of 1280 by 960 pixels.
BRIEF DESCRIPTION OF DRAWINGS
[0041] Non-limiting embodiments will now be described by way of
example and with reference to the accompanying drawings in
which:
[0042] FIG. 1 is a schematic drawing of the microstructure of a
body of PCD material;
[0043] FIG. 2 is a schematic drawing of a PCD compact comprising a
PCD structure bonded to a substrate;
[0044] FIG. 3 is a schematic side view of an example assembly
comprising first and second structures;
[0045] FIG. 4 is a schematic diagram of part of an example pressure
and temperature cycle for making a super-hard construction;
[0046] FIGS. 5 to 9 are schematic diagrams of parts of example
pressure and temperature cycles for making a PCD construction;
and
[0047] FIGS. 10a and 10b are processed images of a micrograph of a
polished section of an embodiment of a body of PCD material at
different diamond densities.
DETAILED DESCRIPTION
[0048] As used herein, "polycrystalline diamond" (PCD) material
comprises 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
gains 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.
Embodiments of PCD material may comprise at least a region from
which catalyst material has been removed from the interstices,
leaving interstitial voids between the diamond grains.
[0049] As used herein, a "PCD structure" comprises a body of PCD
material.
[0050] As used herein, a "metallic" material is understood to
comprise a metal in unalloyed or alloyed form and which has
characteristic properties of a metal, such as high electrical
conductivity.
[0051] As used herein, "catalyst material" for diamond, which may
also be referred to as solvent/catalyst material for diamond, means
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.
[0052] A filler or binder material is understood to mean a material
that wholly or partially fills pores, interstices or interstitial
regions within a polycrystalline structure.
[0053] 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 may be 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. In one
embodiment, the PCD structure may comprise diamond grains having a
multimodal distribution.
[0054] As used herein, the term `total binder area` is expressed as
the percentage of non-diamond phase(s) in the total cross-sectional
area of a polished cross section of the body of PCD material being
analysed.
[0055] With reference to FIG. 1, a body of PCD material 10
comprises a mass of directly inter-bonded diamond grains 12 and
interstices 14 between the diamond grains 12, which may be at least
partly filled with filler or binder material.
[0056] FIG. 2 shows an embodiment of a PCD composite compact 20 for
use as a cutter comprising a body of PCD material 22 integrally
bonded at an interface 24 to a substrate 30. The substrate 30 may
be formed of, for example, cemented carbide material and may be,
for example, cemented tungsten carbide, cemented tantalum carbide,
cemented titanium carbide, cemented molybdenum carbide or mixtures
thereof. The binder metal for such carbides may be, for example,
nickel, cobalt, iron or an alloy containing one or more of these
metals. Typically, this binder will be present in an amount of 10
to 20 mass %, but this may be as low as 6 mass % or less. Some of
the binder metal may infiltrate the body of polycrystalline diamond
material 22 during formation of the compact 20.
[0057] An example of a method for producing the PCD compact 20
comprising the body of PCD material 22, as shown in FIGS. 1 and 2,
is now described with reference to FIGS. 3 to 9. As shown in FIG.
3, a PCD structure (the second structure) 200 is disposed adjacent
a cemented carbide substrate (the first structure) 300, a thin
layer or film 400 of binder material comprising Co connecting
opposite major surfaces of the PCD structure 200 and the substrate
300 to comprise an assembly encased in a housing 100 for an
ultra-high pressure, high temperature press (not shown). The CTE of
the PCD material comprised in the PCD structure 200 is in the range
from about 2.5.times.10-6 per degree Celsius to about 4.times.10-6
per degree Celsius and the CTE of the cobalt-cemented tungsten
carbide material comprised in the substrate 300 is in the range
from about 5.4.times.10-6 per degree Celsius to about 6.times.10-6
per degree Celsius (the CTE values are for 25 degrees Celsius). In
this example, the substrate 300 and the PCD structure 200 contain
binder material comprising Co. It is estimated that PCD material
would have a Young's modulus from about 900 gigapascals to about
1,400 gigapascals depending on the grade of PCD and that the
substrate would have a Young's modulus from about 500 gigapascals
to about 650 gigapascals depending largely on the content and
composition of the binder material.
[0058] FIG. 4 shows a schematic phase diagram of carbon in terms of
pressure p and temperature T axes, showing the line D-G of
thermodynamic equilibrium between diamond and graphite allotropes,
diamond being the more thermally stable in region D and graphite
being the more thermally stable in region G of the diagram. The
line S-L shows schematically the temperature at which the binder
material melts or solidifies at various pressures, this temperature
tending to increase with increasing pressure. Note that this
temperature is likely to be different from that for the binder
material in a pure form because the presence of carbon from the
diamond and or some dissolved WC is expected to reduce this
temperature, since the presence of carbon in solution is expected
to reduce the melting point of cobalt and other metals. The
assembly described with reference to FIG. 3 may be under a first
pressure P1 of about 7.5 gigapascals to about 8 gigapascal and at a
temperature of about 1,450 degrees Celsius to about 1,800 degrees
Celsius, at a condition at which the PCD material has been formed
by sintering an aggregation of diamond grains disposed adjacent the
substrate. There may be no substantial interruption between the
formation of the PCD in situ at the sinter pressure and sinter
temperature on the one hand and subjecting the assembly to the
first pressure P1 on the other; it is the subsequent relationship
between the reduction of the pressure and the temperature at stages
I and II that is the more relevant aspect of the method. At the
sinter temperature, the Co binder material will be molten and
expected to promote the direct inter-growth sintering of the
diamond grains to form the PCD material, the diamond comprised in
the PCD material being thermodynamically substantially more stable
than graphite at the sinter temperature and sinter pressure.
[0059] With further reference to FIG. 4, the pressure and
temperature of the assembly may be reduced to ambient levels in
stages I, II and III. In a particular example, the pressure may be
reduced in stage I from the first pressure P1 to a second pressure
P2 of about 5.5 gigapascals to about 6 gigapascals while reducing
the temperature to about 1,350 degrees Celsius to about 1,500
degrees Celsius to ensure that the pressure-temperature condition
remains such that diamond is more thermodynamically stable than
graphite and that the binder material remains substantially molten.
In stage II, the temperature may then be reduced to about 1,100
degrees Celsius to a temperature in the range of about 1,200
degrees Celsius while maintaining the pressure above the line D-G
in the diamond-stable region D to solidify the binder material; and
in stage III the pressure and temperature may be reduced to ambient
levels in various ways. The PCD construction can then be removed
from the press apparatus. Note that the stages I, II and III are
used merely to explain FIG. 4 and there may not be clear
distinction between these stages in practice. For example these
stages may flow smoothly into one another with no substantial
period of maintaining pressure and temperature conditions at the
end of a stage. Alternatively, some or all of the stages may be
distinct and the pressure and temperature condition at the end of a
stage may be maintained for a period.
[0060] In some examples, a pre-sinter assembly for making a PCD or
PCBN construction, for example, may be prepared and provided in
situ at the first pressure P1 as follows. A cup may be provided
into which an aggregation comprising a plurality of diamond or CBN
grains and a substrate may be assembled, the interior shape of the
cup being generally that of the desired shape of the PCD or PCBN
structure (having regard to likely distortion during the sintering
step). The aggregation may comprise substantially loose diamond or
CBN grains or diamond- or CBN-containing pre-cursor structures such
as granules, discs, wafers or sheets. The aggregation may also
include catalyst material for diamond, matrix material for PCBN, or
pre-cursor material for catalyst or matrix material, which may be
admixed with the diamond or CBN grains and or deposited on the
surfaces of the diamond or CBN grains. The diamond or CBN grains
may have a mean size of at least about 0.1 micron and or at most
about 75 microns and may be substantially mono-modal or
multi-modal. The aggregation may also contain additives for
reducing abnormal diamond or CBN grain growth or the aggregation
may be substantially free of catalyst material or additives.
Alternatively or additionally, another source of catalyst or matrix
material such as cobalt may be provided, such as the binder
material in a cemented carbide substrate. A sufficient quantity of
the aggregation may be placed into the cup and then the substrate
may inserted into the cup with a proximate end pushed against the
aggregation. The pre-sinter assembly comprising the aggregation and
the substrate may be encased within a metal jacket comprising the
cup, subjected to a heat treatment to burn off organic binder that
may be comprised in the aggregation, and encapsulated within a
housing (which may be referred to as a capsule) suitable for an
ultra-high pressure press. The housing may be placed in a suitable
ultra-high pressure press apparatus and subjected to a sinter
pressure and sinter temperature to form the assembly comprising a
PCD or PCBN structure adjacent the substrate, connected by a thin
film of molten binder comprising cobalt. In examples such as these,
the sinter pressure may be regarded as the first pressure P1.
[0061] In an example arrangement, a pre-sinter assembly for making
a PCD or PCBN construction may be prepared and provided in a press
apparatus at the first pressure P1 as follows. A PCD or PCBN
structure may be provided pre-sintered in a previous ultra-high
pressure, high temperature process. The PCD or PCBN structure may
contain binder or matrix material comprising cobalt, located in
interstitial regions between the diamond or CBN grains comprised in
the PCD or PCBN material. In the case of PCD material, the PCD
structure may have at least a region substantially free of binder
material. For example, the PCD structure may have been treated in
acid to remove binder material from the interstices at least
adjacent a surface of the PCD structure or throughout substantially
the entire volume of the PCD structure (or variations between these
possibilities), leaving at least a region that may contain pores or
voids. In some examples, voids thus created may be filled with a
filler material that may or may not comprise binder material. The
PCD or PCBN structure may be placed against a substrate and the
resulting pre-construction assembly may be encased within a housing
suitable for an ultra-high pressure press. The housing may be
placed in a suitable ultra-high pressure press apparatus and the
subjected to the first pressure P1 at a temperature at which the
binder material is in the liquid state (at a condition in region D
of FIG. 4).
[0062] Example methods for making an example PCD construction will
be described below with reference to FIGS. 5 to 9. In each figure,
only part of the pressure and temperature cycle is shown, the part
beginning at respective first pressures P1, at which the PCD
material comprised in the construction becomes formed by sintering,
and ending after the temperature has been reduced sufficiently to
solidify the binder material and the pressure has been reduced from
the second pressure P2.
[0063] In some examples, a pre-sinter assembly may be provided,
comprising an aggregation of a plurality of diamond grains located
adjacent a surface of a substrate comprising cobalt-cemented
tungsten carbide. The diamond grains may have a mean size in the
range of about 0.1 to about 40 microns. The pre-sinter assembly may
be encapsulated within a capsule for an ultra-high pressure press
apparatus, into which the capsule may be loaded. The capsule may be
pressurised at ambient temperature to a pressure of at least about
6.5 gigapascals and heated to a temperature in the range of about
1,500 to about 1,600 degrees Celsius, substantially greater than
the melting point (at the pressure) of the cobalt-based binder
material comprised in the substrate and causing the cobalt material
to melt. At this temperature the pre-sinter assembly may be at a
first pressure P1 in the range from about 7.5 to about 10
gigapascals (P1 may be somewhat higher than 7 gigapascals at least
partly as a result of the increase in temperature). The first
pressure P1 and the temperature may be substantially maintained for
at least about 1 minute, or in any event sufficiently long to
sinter together the diamond grains (in these examples, the sinter
pressure will be substantially P1). The pressure may then be
reduced from first pressure P1 through a second pressure P2 in the
range from about 5.5 to about 8.5 gigapascals. The second pressure
may be the pressure at which the binder material begins to solidify
as the temperature is reduced through its solidification
temperature.
[0064] The temperature of the pre-sinter assembly may be reduced
simultaneously with pressure, provided that it remains greater than
the temperature at which the cobalt-based binder material will have
completely solidified. As the pressure is reduced from P2, the
temperature may also be reduced through the solidification line of
the cobalt-based binder material, resulting in the solidification
of the binder material. In these particular examples, the pressure
is substantially continuously reduced from the first pressure P1,
through the second pressure P2 and through the pressure(s) at which
the binder material solidifies, without substantial pause. The rate
of reduction of the pressure and or temperature may be varied or
the rate of the reduction of either or both may be substantially
constant, at least until the cobalt-based binder material has
solidified. The temperature may also be reduced substantially
continuously at least until it is sufficiently low for
substantially all the cobalt-based binder material to have
solidified. The temperature and pressure may then be reduced to
ambient conditions, the capsule removed from the ultra-high
pressure press apparatus and the construction removed from the
capsule. The construction may comprise a sintered PCD structure
formed joined to the substrate, the PCD structure having become
joined to the substrate in the same general step in which the PCD
material was formed by the sintering together of the plurality of
diamond grains. A thin layer rich in cobalt will be present between
the PCD structure and the substrate, joining together these
structures.
[0065] In a particular example method illustrated in FIG. 5, the
first pressure P1 is about 7.6 gigapascals, the temperature at the
first pressure being in the range of about 1,500 to about 1,600
degrees Celsius, and an example second pressure P2 is about 6.8
gigapascals.
[0066] In a particular example method illustrated in FIG. 6, the
first pressure P1 is about 7.7 gigapascals, the temperature at the
first pressure being in the range of about 1,500 to about 1,600
degrees Celsius, and an example second pressure P2 is about 6.9
gigapascals.
[0067] In a particular example method illustrated in FIG. 7, the
first pressure P1 is about 7.8 gigapascals, the temperature at the
first pressure being in the range of about 1,500 to about 1,600
degrees Celsius, and an example second pressure P2 is about 6.9
gigapascals.
[0068] In a particular example method illustrated in FIG. 8, the
first pressure P1 is about 7.9 gigapascals, the temperature at the
first pressure being in the range of about 1,500 to about 1,600
degrees Celsius, and an example second pressure P2 is about 5.5
gigapascals.
[0069] In the example method illustrated in FIG. 9, the first
pressure P1 is about 9.9 gigapascals, the temperature at the first
pressure being about 2,000 degrees Celsius, and an example second
pressure P2 may be about 8.1 gigapascals.
[0070] Note that the line S-L in FIGS. 5 to 9, indicating the
melting and solidification temperatures of cobalt-based binder
material in the presence of carbon, was estimated based on a
calculation using available data. In practice, it may be advisable
not to rely completely on calculated values lying on S-L but to
carry out trial and error experiments to discover the melting and
solidification temperatures for the particular binder material and
pressure being used.
[0071] The method used to measure the pressure and temperature
cycles as illustrated in FIGS. 5 to 9 is measured using so-called
K-type thermocouples and knowledge of the melting temperatures of
copper (Cu) and silver (Ag). Data for the melting points of Cu and
Ag measured using K-type thermocouples up at 60 kilobars was
published by P. W. Mirwald and G. C. Kennedy in an article entitled
"The melting curve of gold, silver and copper to 60-Kbar
pressure--a reinvestigation", published on 10 Nov. 1979 in the
Journal of Geophysical Research volume 84, number B12, pages 6750
to 6756, by The American Geophysical Union. A K-type thermocouple
may also be referred to as a "chromel-alumel" thermocouple, in
which the "chromel" component comprises 90 percent nickel and 10
percent chromium, and the "alumel" component comprises 95 percent
nickel, 2 percent manganese, 2 percent aluminium and 1 percent
silicon. The method includes inserting the junction of a first
K-type thermocouple into a body consisting essentially of Cu and
the junction of a second K-type thermocouple into a body consisting
essentially of Ag, and positioning the two bodies proximate the
pre-sinter assembly within the capsule. The readings from both
thermocouples are recorded throughout at least a part of the
pressure and temperature cycle and the readings processed and
converted to pressure and temperature values according to the
published data.
[0072] In some examples, the construction may comprise a
polycrystalline cubic boron nitride (PCBN) structure joined to a
cobalt cemented carbide substrate. In some example methods, an
aggregation comprising cubic boron nitride (CBN) grains may be
provided. The CBN grains may have a mean size of at least about 0.1
micron and at most about 30 microns. The aggregation may comprise
tungsten carbide grains and or pre-cursor material for forming a
matrix within which the CBN grains can dispersed in sintered PCBN
material. In some examples, the aggregation may comprise a mixture
of cubic boron nitride powder with a binder material containing Ti,
Al, W or Co and the mixture cast into sheets using a plasticizer
material. In some examples, the super-hard structure may comprise
PCBN material substantially as described in international
application number WO2007049140 and may be manufactured by a method
including providing a powdered composition suitable for the
manufacture of PCBN, the powder comprising at least 80 volume
percent CBN particles and a powdered binder material, and
subjecting the powder composition to attrition milling. The
composition may comprise CBN particles of more than one average
particle size. In various examples, the average size of the CBN
particles may be at most about 12 microns or at most 2 microns. The
binder material may include one or more of phase(s) containing
aluminium, silicon, cobalt, molybdenum, tantalum, niobium, nickel,
titanium, chromium, tungsten, yttrium, carbon and iron. The binder
material may include powder with uniform solid solution of more
than one of aluminium, silicon, cobalt, nickel, titanium, chromium,
tungsten, yttrium, molybdenum, niobium, tantalum, carbon and
iron.
[0073] Various kinds of ultra-high pressure presses may be used,
including belt-type, tetrahedral multi-anvil, cubic multi-anvil,
walker-type or torroidal presses. The choice of press type is
likely to depend on the volume of the super-hard construction to be
made and the pressure and temperature desired for sintering the
super-hard material. For example, tetrahedral and cubic presses may
be suitable for sintering commercially viable volumes of PCD and
PCBN material at pressures of at least about 7 gigapascals or at
least about 7.7 gigapascals.
[0074] Some example methods may include subjecting a PCD or PCBN
construction to a heat treatment at a temperature of at least about
500 degrees Celsius, at least about 600 degrees Celsius or at least
about 650 degrees Celsius for at least about 5 minutes, at least
about 15 minutes or at least about 30 minutes. In some embodiments,
the temperature may be at most about 850 degrees Celsius, at most
about 800 degrees Celsius or at most about 750 degrees Celsius. In
some embodiments, the PCD structure may be subjected to the heat
treatment for at most about 120 minutes or at most about 60
minutes. In one embodiment, the PCD or PCBN structure may be
subjected to the heat treatment in a vacuum. For example, U.S. Pat.
No. 6,517,902 discloses a form of heat treatment for pre-form
elements having a facing table of PCD bonded to a substrate of
cemented tungsten carbide with a cobalt binder. The substrate
includes an interface zone with at least 30 percent by volume of
the cobalt binder in a hexagonal close packed crystal
structure.
[0075] While wishing not to be bound by a particular theory, the
method may result in a reduced likelihood or frequency of cracking
of super-hard constructions because the residual stress within the
construction is reduced.
[0076] Non-limiting examples are described in more detail
below.
Example 1
[0077] A PCD insert for a rock-boring drill bit was made as
described below.
[0078] A pre-sinter assembly was prepared, comprising an
aggregation of a plurality of diamond grains disposed against a
proximate end of a generally cylindrical cemented carbide
substrate. The aggregation comprised a plurality of wafers
comprising diamond grains dispersed within an organic binder
material, the diamond grains having a mean size of at least about
15 microns and at most about 30 microns. The substrate comprised
about 90 weight percent WC grains cemented together by a binder
material comprising Co. The pre-sinter assembly was enclosed in a
metal jacket and heated to burn off the organic binder comprised in
the wafers, and the jacketed, pre-sinter assembly was encapsulated
in a capsule for an ultra-high pressure, high temperature
multi-anvil press apparatus.
[0079] The pre-sinter assembly was subjected to a pressure of about
7.7 gigapascals and a temperature of about 1,550 degrees Celsius to
sinter the diamond grains directly to each other to form a layer of
PCD material connected to the proximate end of the substrate by a
film of molten binder material comprising cobalt from the
substrate. The pressure was reduced to about 5.5 gigapascals and
the temperature was reduced to about 1,450 degrees Celsius,
maintaining conditions at which the diamond comprised in the PCD is
thermodynamically stable (in relation to graphite, a softer
allotrope of carbon) and at which the binder material is in the
liquid phase. The temperature was then reduced to about 1,000
degrees Celsius to solidify the binder material and form a
construction comprising the layer of PCD bonded to the substrate by
the solidified binder material, and the pressure and temperature
were then reduced to ambient conditions.
[0080] The construction was subjected to a heat treatment at 660
degrees Celsius for about 2 hours at substantially ambient pressure
in a substantially non-oxidising atmosphere, and then cooled to
ambient temperature. No cracks were evident in the PCD layer after
the heat treatment.
[0081] The construction was processed by grinding and polishing to
provide an insert for a rock-boring drill bit.
[0082] For comparison, a reference construction was made as
follows. A pre-sinter assembly was prepared as described above in
relation to the example pre-sinter assembly. The pre-sinter
assembly was subjected to a pressure of about 7.7 gigapascal and a
temperature of about 1,550 degrees Celsius to sinter the diamond
grains directly to each other to form a layer of PCD material
connected to the proximate end of the substrate by a film of molten
binder material comprising cobalt from the substrate. The
temperature was reduced to about 1,000 degrees Celsius to solidify
the binder material and form a construction comprising the layer of
PCD bonded to the substrate by the solidified binder material, and
then the pressure and temperature were reduced to ambient
conditions. The construction was subjected to a heat treatment at
660 degrees Celsius for about 2 hours at substantially ambient
pressure in a substantially non-oxidising atmosphere, and then
cooled to ambient temperature. Severe cracks were evident at the
side of the PCD layer after the heat treatment.
Example 2
[0083] A PCD insert for a rock-boring drill bit was made as
described below.
[0084] A pre-sinter assembly was prepared, comprising a PCD
structure having a generally disc-like shape disposed against a
proximate end of a generally cylindrical cemented carbide
substrate. PCD structure had been made in a previous step involving
sintering together an aggregation of a plurality of diamond grains
at an ultra-high pressure of less than about 7 gigapascals and a
high temperature (at which the diamond was thermodynamically more
stable than graphite). The substrate comprised about 90 weight
percent WC grains cemented together by a binder material comprising
Co. The pre-sinter assembly was enclosed in a metal jacket and
heated to burn off the organic binder comprised in the wafers, and
the jacketed, pre-sinter assembly was encapsulated in a capsule for
an ultra-high pressure, high temperature multi-anvil press
apparatus.
[0085] The pre-sinter assembly was subjected to a pressure of about
7.7 gigapascals and a temperature of about 1,550 degrees Celsius to
modify the microstructure of the PCD structure. The pressure was
reduced to about 5.5 gigapascals and the temperature was reduced to
about 1,450 degrees Celsius, maintaining conditions at which the
diamond comprised in the PCD is thermodynamically stable (in
relation to graphite, a softer allotrope of carbon) and at which
the binder material is in the liquid phase. The temperature was
then reduced to about 1,000 degrees Celsius to solidify the binder
material and form a construction comprising the layer of PCD bonded
to the substrate by the solidified binder material, and the
pressure and temperature were then reduced to ambient
conditions.
[0086] The construction was subjected to a heat treatment at 660
degrees Celsius for about 2 hours at substantially ambient pressure
in a substantially non-oxidising atmosphere, and then cooled to
ambient temperature. No cracks were evident in the PCD layer after
the heat treatment.
[0087] The construction was processed by grinding and polishing to
provide an insert for a rock-boring drill bit.
[0088] Certain terms and concepts as used herein will be briefly
explained
[0089] As used herein, "super-hard" means a Vickers hardness of at
least 25 gigapascal. Synthetic and natural diamond, polycrystalline
diamond (PCD), cubic boron nitride (cBN) and polycrystalline cBN
(PCBN) material are examples of super-hard materials. Synthetic
diamond, which is also called man-made diamond, is diamond material
that has been manufactured.
[0090] As used herein, PCBN material comprises grains of cubic
boron nitride (cBN) dispersed within a matrix comprising metal and
or ceramic material.
[0091] PCD material comprises a mass (an aggregation of a
plurality) 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.
Interstices between the diamond grains may be at least partly
filled with a binder material comprising a catalyst material for
synthetic diamond, or they may be substantially empty. Catalyst
material (which may also be referred to as solvent/catalyst
material, reflecting the understanding that the material may
perform a catalytic and or solvent function in promoting the growth
of diamond grains and the sintering of diamond grains) for
synthetic diamond is capable of promoting the growth of synthetic
diamond grains and or the direct inter-growth of synthetic or
natural diamond grains at a temperature and pressure at which
synthetic or natural diamond is thermodynamically more stable than
graphite. Examples of catalyst materials for diamond are Fe, Ni, Co
and Mn, and certain alloys including these. Bodies comprising 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. Various grades of
PCD material may be made. As used herein, a PCD grade is a variant
of 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. Different PCD grades may
have different microstructure and different mechanical properties,
such as elastic (or Young's) modulus E, modulus of elasticity,
transverse rupture strength (TRS), toughness (such as so-called K1C
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.
[0092] Thermally stable PCD material comprises at least a part or
volume of which exhibits no substantial structural degradation or
deterioration of hardness or abrasion resistance after exposure to
a temperature above about 400 degrees Celsius, or even above about
700 degrees Celsius. For example, PCD material containing less than
about 2 weight percent of catalyst metal for diamond such as Co,
Fe, Ni, Mn in catalytically active form (e.g. in elemental form)
may be thermally stable. PCD material that is substantially free of
catalyst material in catalytically active form is an example of
thermally stable PCD. PCD material in which the interstices are
substantially voids or at least partly filled with ceramic material
such as SiC or salt material such as carbonate compounds may be
thermally stable, for example. PCD structures having at least a
significant region from which catalyst material for diamond has
been depleted, or in which catalyst material is in a form that is
relatively less active as a catalyst, may be described as thermally
stable PCD.
[0093] Other examples of superhard materials include certain
composite materials comprising diamond or cBN grains held together
by a matrix comprising ceramic material, such as silicon carbide
(SiC), or cemented carbide material, such as Co-bonded WC material
(for example, as described in U.S. Pat. Nos. 5,453,105 or
6,919,040). For example, certain SiC-bonded diamond materials may
comprise at least about 30 volume percent diamond grains dispersed
in a SiC matrix (which may contain a minor amount of Si in a form
other than SiC). Examples of SiC-bonded diamond materials are
described in U.S. Pat. Nos. 7,008,672; 6,709,747; 6,179,886;
6,447,852; and International Application publication number
WO2009/013713).
[0094] Young's modulus is a type of elastic modulus and is a
measure of the uni-axial strain in response to a uni-axial stress,
within the range of stress for which the material behaves
elastically. A method of measuring the Young's modulus E is by
means of measuring the transverse and longitudinal components of
the speed of sound through the material using ultrasonic waves.
[0095] As used herein, the thickness of the PCD structure 22, 200
or the substrate 30, 300, or some part of the PCD structure or the
substrate is the thickness measured substantially perpendicularly
to the interface 24. In some embodiments, the PCD structure, or
body of PCD material 22, 200 may have a generally wafer, disc or
disc-like shape, or be in the general form of a layer. In some
embodiments, the PCD structure 22, 200 may have a thickness of at
least about 0.3 mm, at least about 0.5 mm, at least about 0.7 mm,
at least about 1 mm, at least about 1.3 mm or at least about 2 mm.
In one embodiment, the PCD structure 22, 200 may have a thickness
in the range from about 2 mm to about 3 mm.
[0096] In some embodiments, the substrate 30, 300 may have the
general shape of a wafer, disc or post, and may be generally
cylindrical in shape. The substrate 30, 300 may have, for example,
an axial thickness at least equal to or greater than the axial
thickness of the body of PCD material 22, 200, and may be for
example at least about 1 mm, at least about 2.5 mm, at least about
3 mm, at least about 5 mm or even at least about 10 mm in
thickness. In one embodiment, the substrate 30, 300 may have a
thickness of at least 2 cm.
[0097] The PCD structure 22, 200 may be joined to the substrate 30,
300 for example only on one side thereof, the opposite side of the
PCD structure not being bonded to the substrate 30, 300.
[0098] In some embodiments, the largest dimension of the body of
PCD material 22, 200 is around 6 mm or greater, for example in
embodiments where the body of PCD material is cylindrical in shape,
the diameter of the body is around 6 mm or greater.
[0099] In some versions of the method, prior to sintering, the
aggregated mass of diamond particles/grains may be disposed against
the surface of the substrate generally in the form of a layer
having a thickness of least about 0.6 mm, at least about 1 mm, at
least about 1.5 mm or even at least about 2 mm. The thickness of
the mass of diamond grains may reduce significantly when the grains
are sintered at an ultra-high pressure.
[0100] The ultrahard particles used in the present process may be
of natural or synthetic origin. The mixture of ultrahard particles
may be multimodal, that it is may comprise a mixture of fractions
of diamond particles or grains that differ from one another
discernibly in their average particle size. Typically the number of
fractions may be: [0101] a specific case of two fractions [0102]
three or more fractions.
[0103] By "average particle/grain size" it is meant that the
individual particles/grains have a range of sizes with the mean
particle/grain size representing the "average". Hence the major
amount of the particles/grains will be close to the average size,
although there will be a limited number of particles/grains above
and below the specified size. The peak in the distribution of the
particles will therefore be at the specified size. The size
distribution for each ultrahard particle/grain size fraction is
typically itself monomodal, but may in certain circumstances be
multimodal. In the sintered compact, the term "average particle
grain size" is to be interpreted in a similar manner.
[0104] As shown in FIG. 1, the bodies of polycrystalline diamond
material produced by an embodiment additionally have a binder phase
present. This binder material is preferably a catalyst/solvent for
the ultrahard abrasive particles used. Catalyst/solvents for
diamond are well known in the art. In the case of diamond, the
binder is preferably cobalt, nickel, iron or an alloy containing
one or more of these metals. This binder may be introduced either
by infiltration into the mass of abrasive particles during the
sintering treatment, or in particulate form as a mixture within the
mass of abrasive particles. Infiltration may occur from either a
supplied shim or layer of the binder metal or from the carbide
support. Typically a combination of the admixing and infiltration
approaches is used.
[0105] During the high pressure, high temperature treatment, the
catalyst/solvent material melts and migrates through the compact
layer, acting as a catalyst/solvent and causing the ultrahard
particles to bond to one another. Once manufactured, the PCD
construction therefore comprises a coherent matrix of ultrahard
(diamond) particles bonded to one another, thereby forming an
ultrahard polycrystalline composite material with many interstices
or pools containing binder material as described above. In essence,
the final PCD construction therefore comprises a two-phase
composite, where the ultrahard abrasive diamond material comprises
one phase and the binder (non-diamond phase), the other.
[0106] In one form, the ultrahard phase, which is typically
diamond, constitutes between 80% and 95% by volume and the
solvent/catalyst material the other 5% to 20%.
[0107] The relative distribution of the binder phase, and the
number of voids or pools filled with this phase, is largely defined
by the size and shape of the diamond grains.
[0108] The binder (non-diamond) phase can help to improve the
impact resistance of the more brittle abrasive phase, but as the
binder phase typically represents a far weaker and less abrasion
resistant fraction of the structure, high quantities will tend to
adversely affect wear resistance. Additionally, where the binder
phase is also an active solvent/catalyst material, its increased
presence in the structure can compromise the thermal stability of
the compact.
[0109] FIGS. 10a and 10b are an example of a processed SEM image of
a polished section of a PCD material, for a diamond intensity of 0
(FIG. 10a) and a diamond intensity of 15 (FIG. 10b) showing the
boundaries between diamond grains. These boundary lines were
provided by image analysis software and were used to measure the
total non-diamond phase (eg binder) surface area in a cross-section
through the body of PCD material and surface area of the individual
non-diamond phase (interstitial) regions which are indicated as
dark areas. The cross-section through the body of PCD material may
be at any orientation through the body of PCD material for the
following analysis to be conducted and results to be achieved. The
image analysis technique is described in more detail below.
[0110] As a non-limiting example, the cross section shown in FIGS.
10a and 10b may be exposed for viewing by cutting a section of the
PCD composite compact by means of a wire EDM. The cross section may
be polished in preparation for viewing by a microscope, such as a
scanning electron microscope (SEM) and a series of micrographic
images of the type shown in FIGS. 5a and 5b may be taken. Each of
the images may be analysed by means of image analysis software to
determine the total binder area and individual binder areas between
the diamond grains. The values of the total binder area and
individual binder area are determined by conducting a statistical
evaluation on a large number of collected images taken on the
scanning electron microscope.
[0111] The magnification selected for the microstructural analysis
has a significant effect on the accuracy of the data obtained.
Imaging at lower magnifications offers an opportunity to sample,
representatively, larger particles or features in a microstructure
but may tend to under-represent smaller particles or features as
they are not necessarily sufficiently resolved at that
magnification. By contrast, higher magnifications allow resolution
and hence detailed measurement of fine-scale features but can tend
to sample larger features such that they intersect the boundaries
of the images and hence are not adequately measured. It has been
appreciated that it is therefore important to select an appropriate
magnification for any quantitative microstructural analysis
technique. The appropriateness is therefore determined by the size
of the features that are being characterised. The magnifications
selected for the various measurements described herein are
discussed in more detail below.
[0112] Unless otherwise stated herein, dimensions of total binder
area and individual binder area within the body of PCD material
refer to the dimensions as measured on a surface of, or a section
through, a body comprising PCD material and no stereographic
correction has been applied. For example, the measurements are made
by means of image analysis carried out on a polished surface, and a
Saltykov correction has not been applied in the data stated
herein.
[0113] In measuring the mean value of a quantity or other
statistical parameter measured by means of image analysis, several
images of different parts of a surface or section (hereinafter
referred to as samples) are used to enhance the reliability and
accuracy of the statistics. The number of images used to measure a
given quantity or parameter may be, for example between 10 to 30.
If the analysed sample is uniform, which is the case for PCD,
depending on magnification, 10 to 20 images may be considered to
represent that sample sufficiently well.
[0114] The resolution of the images needs to be sufficiently high
for the inter-grain and inter-phase boundaries to be clearly made
out and, for the measurements stated herein an image area of 1280
by 960 pixels was used.
[0115] In the statistical analysis, 15 images were taken of
different areas on a surface of a body comprising the PCD material,
and statistical analysis was carried out on each image.
[0116] Images used for the image analysis were obtained by means of
scanning electron micrographs (SEM) taken using a backscattered
electron signal. The back-scatter mode was chosen so as to provide
high contrast based on different atomic numbers and to reduce
sensitivity to surface damage (as compared with the secondary
electron imaging mode).
[0117] A number of factors have been identified as being important
for image capturing. These are: [0118] SEM Voltage which, for the
purposes of the measurements stated herein remained constant and
was around 15 kV; [0119] working distance which also remained
constant and was around 8 mm [0120] image sharpness [0121] sample
polishing quality, [0122] image contrast levels which were selected
to provide clear separation of the microstructural features; [0123]
magnification (should be varied according to different diamond
grain size and is as stated below), [0124] number of images
taken.
[0125] Given the above conditions, the image analysis software used
was able to separate distinguishably the diamond and binder phases
and the back-scatter images were taken at approximately 45.degree.
to the edge of the samples.
[0126] The magnification used in the image analysis should be
selected in such a way that the feature of interest is adequately
resolved and described by the available number of pixels. In PCD
image analysis various features of different size and distribution
are measured simultaneously and it is not practical to use a
separate magnification for each feature of interest.
[0127] It is difficult to identify the optimum magnification for
each feature measurement in the absence of a reference measurement
result. It could vary from one operator to another. Therefore, a
procedure is proposed for the selection of the magnification.
[0128] The size of a statistically significant number of diamond
grains in the microstructure is measured and the average value
taken.
[0129] As used herein in relation to grains or particles and unless
otherwise stated or implied, the term "size" refers to the length
of the grain viewed from the side or in cross section using image
analysis techniques.
[0130] The number of pixels that describe this average length is
determined and a range of pixel values are established to fix the
magnification.
[0131] In the image analysis technique, the original image was
converted to a greyscale image. The image contrast level was set by
ensuring the diamond peak intensity in the grey scale histogram
image occurred between 15 and 20. As mentioned above, several
images of different parts of a surface or section were taken to
enhance the reliability and accuracy of the statistics. For
measurements of total non-diamond phase (eg binder) area, the
greater the number of images, the more accurate the results are
perceived to be. For example, about 15000 measurements were taken,
1000 per image with 15 images.
[0132] The steps taken by the image analysis programme may be
summarised in general as follows: [0133] 1. The original image was
converted to a greyscale image. The image contrast level was set by
ensuring the diamond peak intensity in the grey scale histogram
image occurred between 10 and 20. [0134] 2. An auto threshold
feature was used to binarise the image and specifically to obtain
clear resolution of the diamond and binder phases. [0135] 3. The
binder was the primary phase of interest in the current analysis.
[0136] 4. The software, having the trade name analySIS Pro from
Soft Imaging System.RTM. GmbH (a trademark of Olympus Soft Imaging
Solutions GmbH) was used and excluded from the analysis any
particles which touched the boundaries of the image. This required
appropriate choice of the image magnification: [0137] a. If too low
then resolution of fine particles is reduced. [0138] b. If too high
then: [0139] i. Efficiency of coarse grain separation is reduced.
[0140] ii. High numbers of coarse grains are cut by the boarders of
the image and hence less of these grains are analysed. [0141] iii.
Thus more images must be analysed to get a statistically-meaningful
result. [0142] 5. Each particle was finally represented by the
number of continuous pixels of which it is formed. [0143] 6. The
AnalySIS software programme proceeded to detect and analyse each
particle in the image. This can be automatically repeated for
several images. [0144] 7. A large number of outputs was available.
The outputs may be post-processed further, for example using
statistical analysis software and/or carrying out further feature
analysis, for example the analysis described below for determining
the mean of the total binder area for all images and the means of
the individual binder areas.
[0145] If appropriate thresholding is used, the image analysis
technique is unlikely to introduce further errors in measurements
which would have a practical effect on the accuracy of those
measurements, with the exception of small errors related to the
rounding of numbers. In the current analysis, the statistical mean
values of the total binder area and individual binder areas were
used as, according to the Central Limitation Theorem, the
distribution of an average tends to be normal as the sample size
increases, regardless of the distribution from which the average is
taken except when the moments of the parent distribution do not
exist. All practical distributions in statistical engineering have
defined moments, and thus the Central Limitation Theorem applies in
the present case. It was therefore deemed appropriate to use the
statistical mean values.
[0146] The individual non-diamond (eg binder or catalyst/solvent)
phase areas or pools, which are easily distinguishable from that of
the ultrahard phase using electron microscopy, were identified
using the above-mentioned standard image analysis tools. The total
non-diamond phase areas (in square microns) in the analysed
cross-sectional images were determined by summing the individual
binder pool areas within the entire microstructural image area that
was analysed.
[0147] The collected distributions of this data were then evaluated
statistically and an arithmetic average was then determined. Hence
the mean total binder pool area in the surface of the
microstructure being analysed was calculated
[0148] It is anticipated that microstructural parameters may alter
slightly from one area of an abrasive compact to another, depending
on formation conditions. Hence the microstructural imaging is
carried out so as to representatively sample the bulk of the
ultrahard composite portion of the compact.
[0149] Additional non-limiting examples are now described. Three
sets of samples were produced as follows: a multimodal (trimodal)
diamond powder mix with average diamond grain size of approximately
13 .mu.m and 1 weight percent cobalt admix was prepared, in
sufficient quantity to provide approximately 2 g admix per sample.
The admix for each sample was then poured into or otherwise
arranged in a Niobium inner cup. A cemented carbide substrate of
approximately 13 weight percent cobalt content and having a
non-planar interface was placed in each inner cup on the powder
mix. A titanium cup was placed in turn over this structure and the
assembly sealed to produce a canister. The canisters were
pre-treated by vacuum outgassing at approximately 1050.degree. C.,
and divided into three sets which were sintered at three distinct
ultrahigh pressure and temperature conditions in the diamond-stable
region, namely at approximately 5.5 GPa (Set 1), 6.8 GPa (Set 2),
and 7.7 GPa (Set 3). Specifically the canisters were sintered at
temperatures sufficient to melt the cobalt so as to produce PCD
constructions with well-sintered PCD tables and well-bonded
substrates. The technique described above in connection with FIGS.
3 to 9 was applied for the sintering of the canisters at 7.7 GPa
(set 3). The resulting superhard constructions were not subjected
to any post-synthesis leaching treatment.
[0150] Image analysis was then conducted on each of these superhard
constructions using the techniques described above and in
particular the determination of appropriate magnification described
above to determine the mean total binder area in a polished
cross-section and mean cross-sectional binder area for each
sample.
[0151] The experiments may be repeated for different diamond grain
size compositions and the results are set out in Table 1.
TABLE-US-00001 TABLE 1 Grain Binder Size Total Binder Area microns
Area % micron{circumflex over ( )}2 Magnification Mean StdDev 0.01
13.4600 2.2750 8.0699 0.4446 1000x 12.5755 3.1707 8.0223 0.2802
1000x 10.8800 1.8440 6.4004 0.2638 1000x 3.9700 0.7990 10.3135
0.1528 3000x
[0152] It was determined from the above experiments that, for a
total non-diamond phase area (for example binder area) in the range
of around 0 to 5%, it is possible to achieve an associated
individual non-diamond area of less than around 0.7 micon.sup.2, as
determined using an image analysis technique applying a
magnification of around 1000 and analysing an image area of
1280.times.960 pixels, with the largest dimension of the body of
PCD material being around 6 mm or greater. The thickness of the
body of PCD material in these embodiments may be, for example,
around 0.3 mm or greater.
[0153] Furthermore, for a total non-diamond phase area (for example
binder area) in the range of around 5 to 10%, it is possible to
achieve an associated cross-sectional individual non-diamond phase
area of less than around 0.340 micon.sup.2, as determined using an
image analysis technique applying a magnification of between around
1000 and analysing an image area of 1280.times.960 pixels, with the
largest dimension of the body of PCD material being around 6 mm or
greater. The thickness of the body of PCD material in these
embodiments may be, for example, around 0.3 mm or greater.
[0154] Also, for a total non-diamond phase area (for example binder
area) in the range of around 10 to 15%, it is possible to achieve
an associated cross-sectional individual non-diamond phase area of
less than around 0.340 micon.sup.2, as determined using an image
analysis technique applying a magnification of between around 3000
and analysing an image area of 1280.times.960 pixels, with the
largest dimension of the body of PCD material being around 6 mm or
greater. The thickness of the body of PCD material in these
embodiments may be, for example, around 0.3 mm or greater.
[0155] Also, for a total non-diamond phase area (for example binder
area) in the range of around 15 to 30%, it is possible to achieve
an associated cross-sectional individual non-diamond phase area in
the range of around 0.005 to around 0.340 micon.sup.2, as
determined using an image analysis technique applying a
magnification of between around 10000 and analysing an image area
of 1280.times.960 pixels, with the largest dimension of the body of
PCD material being around 6 mm or greater. The thickness of the
body of PCD material in these embodiments may be, for example,
around 0.3 mm or greater.
[0156] Whilst not wishing to be bound by a particular theory, using
the conditions described herein it was determined possible to
achieve total binder areas in the ranges specified above together
with the above-mentioned ranges of associated individual binder
areas. These have been determined to assist generating a more
wear-resistant body of PCD material which, when used as a cutter,
may significantly enhance the durability of the cutter produced
according to some embodiments described herein.
[0157] In addition, various arrangements and combinations are
envisaged for the method by the disclosure, and examples of the
method may further include one or more of the following
non-exhaustive and non-limiting aspects in various
combinations.
[0158] There may be provided a method for making a super-hard
construction comprising:
a first structure joined to a second structure, the first structure
comprising first material having a first coefficient of thermal
expansion (CTE) and a first Young's modulus, and the second
structure comprising second material having a second CTE and a
second Young's modulus; the first CTE and the second CTE being
substantially different from each other and the first Young's
modulus and the second Young's modulus being substantially
different from each other; at least one of the first or second
materials comprising super-hard material; the method including:
forming an assembly comprising the first material, the second
material and a binder material arranged to be capable of bonding
the first and second materials together, the binder material
comprising metal; subjecting the assembly to a sufficiently high
temperature for the binder material to be in the liquid state and
to a first pressure at which the super-hard material is
thermodynamically stable; reducing the pressure to a second
pressure at which the super-hard material is thermodynamically
stable, the temperature being maintained sufficiently high to
maintain the binder material in the liquid state; reducing the
temperature to solidify the binder material; and reducing the
pressure and the temperature to an ambient condition to provide the
super-hard construction.
[0159] In some embodiments, the CTE of one of the first or second
materials is at least about 2.5.times.10-6 per degree Celsius and
at most about 5.0.times.10-6 per degree Celsius and the CTE of the
other of the first or second materials is at least about
3.5.times.10-6 per degree Celsius and at most about 6.5.times.10-6
per degree Celsius, at about 25 degrees Celsius.
[0160] In some embodiments, the Young's modulus of one of the first
or second materials is at least about 500 gigapascals and at most
about 1,300 gigapascals and the Young's modulus of the other of the
first and second materials is at least about 800 gigapascals and at
most about 1,600 gigapascals.
[0161] The Young's moduli of the first and second materials may,
for example, differ by at least about 10%.
[0162] In some embodiments, the CTE of the first and second
materials may, for example, differ by at least about 10%.
[0163] The method may further include sintering an aggregation of a
plurality of grains of the super-hard material in the presence of
sinter catalyst material at a sinter pressure and a sinter
temperature to form the second structure.
[0164] The method may include disposing an aggregation of grains of
super-hard material adjacent the first structure and in the
presence of the binder material to form a pre-sinter assembly;
subjecting the pre-sinter assembly to a sinter pressure and a
sinter temperature to melt the binder material and sinter the
grains of super-hard materials and form the second structure
comprising polycrystalline super-hard material connected to the
first structure by the binder material in the molten state.
[0165] In some embodiments, the first pressure is substantially the
sinter pressure.
[0166] The method may further include providing the first
structure, providing the second structure comprising
polycrystalline super-hard material, disposing the first structure
adjacent the second structure and forming a pre-construction
assembly, and applying a pressure to the pre-construction assembly,
increasing the pressure from ambient pressure to the first
pressure.
[0167] The method may, for example, include subjecting an
aggregation of a plurality of grains of super-hard material to a
sinter pressure and a sinter temperature at which the super-hard
material is capable of being sintered to form the second material,
and reducing the pressure and temperature to an ambient condition
to provide the second structure; the first pressure being
substantially greater then the sinter pressure.
[0168] The second structure may comprise diamond material and the
binder material comprises catalyst material for diamond.
[0169] The first and second structures may each comprise diamond
material and the binder material comprises catalyst material for
diamond.
[0170] In some embodiments, the difference between the second
pressure and the first pressure is at least about 0.5
gigapascal.
[0171] The method may further include subjecting the super-hard
construction to further heat treatment at a treatment temperature
and a treatment pressure at which the super-hard material is
thermodynamically meta-stable.
[0172] The super-hard material may comprise diamond material and
the treatment temperature is at least about 500 degrees Celsius and
the treatment pressure is less than about 1 gigapascal.
[0173] The method may include the step of reducing the pressure
from the first pressure to an intermediate pressure for an holding
period, and then further reducing the pressure from the
intermediate pressure to the second pressure.
[0174] The first pressure may, for example, be at least about 7
gigapascal, the intermediate pressure may be, for example, at least
about 5.5 gigapascals and less than about 10 gigapascals, the
holding period may, for example, be at least about 1 minute and the
second pressure may, for example, be at least about 5.5 gigapascals
and at most about 7 gigapascals.
[0175] The pressure at which the binder material begins to solidify
responsive to the reduction in temperature may, for example, be
substantially equal to the second pressure in some embodiments.
[0176] In other embodiments, the pressure at which the binder
material begins to solidify responsive to the reduction in
temperature may be substantially less than the second pressure.
[0177] In some embodiments, the first structure comprises
cobalt-cemented tungsten carbide material and the second material
comprises PCD material, the CTE of the cemented carbide material
being in the range of about 4.5.times.10-6 to about 6.5.times.10-6
per degree Celsius, the CTE of the PCD material being in the range
of about 3.0.times.10-6 to about 5.0.times.10-6 per degree Celsius;
the Young's modulus of the cemented carbide material being in the
range of about 500 to about 1,000 gigapascals, and the Young's
modulus of the PCD material being in the range of about 800 to
about 1,600 gigapascals; the first pressure being in the range of
about 6 to about 10 gigapascals, and the second pressure being in
the range of about 5.5 to about 8 gigapascals.
[0178] In some embodiments, the pressure at which the cobalt-based
binder material comprised in the cemented carbide material begins
to solidify is equal to the second pressure.
[0179] The second pressure may, for example, be in the range of
about 6.5 to about 7.5 gigapascals.
[0180] In some embodiments, the second structure comprises PCD
material and the method includes subjecting the super-hard
construction to further heat treatment for a treatment period in
the range of about 30 to about 90 minutes at a treatment
temperature in the range of about 550 to about 650 degrees
Celsius.
[0181] The method may include processing the super-hard
construction to provide a tool element. The super-hard construction
may be suitable for an insert for a rock-boring drill bit, for an
impact tool for degrading rock or pavement or for a machine
tool.
[0182] Disclosed methods have the aspect of reducing the likelihood
or frequency of cracking of super-hard constructions, particularly
when subjected to heating in subsequent manufacturing steps or to
elevated temperatures in use.
* * * * *