U.S. patent application number 14/423780 was filed with the patent office on 2015-11-05 for polycrystalline diamond construction and method of making.
The applicant listed for this patent is Element Six Abrasives S.A.. Invention is credited to Nedret Can.
Application Number | 20150314421 14/423780 |
Document ID | / |
Family ID | 47075082 |
Filed Date | 2015-11-05 |
United States Patent
Application |
20150314421 |
Kind Code |
A1 |
Can; Nedret |
November 5, 2015 |
POLYCRYSTALLINE DIAMOND CONSTRUCTION AND METHOD OF MAKING
Abstract
A superhard polycrystalline construction comprises a body of
polycrystalline superhard material, comprising a mass of superhard
grains exhibiting inter-granular bonding and defining a plurality
of interstitial regions therebetween, the superhard grains having
an associated mean free path and a non-superhard phase at least
partially filling a plurality of the interstitial regions and
having an associated mean free path. The median of the mean free
path associated with the non-superhard phase divided by (Q3-Q1) for
the non-superhard phase being greater than or equal to 0.50, where
Q1 is the first quartile and Q3 is the third quartile; and the
median of the mean free path associated with the superhard grains
divided by (Q3-Q1) for the superhard grains being less than 0.60.
The body of polycrystalline superhard material has a first surface
having a surface topology comprising one or more indentations
therein and/or projections therefrom. There is also disclosed a
method of forming such a construction.
Inventors: |
Can; Nedret; (Oxfordshire,
GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Element Six Abrasives S.A. |
Luxembourg |
|
LU |
|
|
Family ID: |
47075082 |
Appl. No.: |
14/423780 |
Filed: |
August 28, 2013 |
PCT Filed: |
August 28, 2013 |
PCT NO: |
PCT/EP2013/067817 |
371 Date: |
February 25, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61695817 |
Aug 31, 2012 |
|
|
|
Current U.S.
Class: |
51/309 ;
51/307 |
Current CPC
Class: |
B22F 3/14 20130101; C04B
2235/427 20130101; B24D 3/06 20130101; B22F 2999/00 20130101; B24D
18/0009 20130101; B22F 2999/00 20130101; C04B 35/52 20130101; B22F
2005/005 20130101; C22C 26/00 20130101; C22C 2026/005 20130101;
C22C 2026/006 20130101; B22F 2005/001 20130101; B22F 2304/054
20130101; E21B 10/567 20130101; C22C 26/00 20130101 |
International
Class: |
B24D 3/06 20060101
B24D003/06; B24D 18/00 20060101 B24D018/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 31, 2012 |
GB |
1215565.1 |
Claims
1. A superhard polycrystalline construction comprising a body of
polycrystalline superhard material, comprising: a mass of superhard
grains exhibiting inter-granular bonding and defining a plurality
of interstitial regions therebetween, the superhard grains having
an associated mean free path; and a non-superhard phase at least
partially filling a plurality of the interstitial regions and
having an associated mean free path; the median of the mean free
path associated with the non-superhard phase divided by (Q3-Q1) for
the non-superhard phase being greater than or equal to 0.50, where
Q1 is the first quartile and Q3 is the third quartile; and the
median of the mean free path associated with the superhard grains
divided by (Q3-Q1) for the superhard grains being less than 0.60;
wherein the body of polycrystalline superhard material has a first
surface having a surface topology comprising one or more
indentations therein and/or projections therefrom.
2. A superhard polycrystalline construction according to claim 1,
wherein the superhard grains comprise natural and/or synthetic
diamond grains, the superhard polycrystalline construction forming
a polycrystalline diamond construction.
3. A superhard polycrystalline construction according to claim 1,
wherein the non-superhard phase comprises a binder phase.
4. A superhard polycrystalline construction according to claim 3,
wherein the binder phase comprises cobalt, and/or one or more other
iron group elements, or an alloy thereof, and/or one or more
carbides, nitrides, borides, and oxides of the metals of Groups
IV-VI in the periodic table.
5. A superhard polycrystalline construction according to claim 4,
wherein the one or more other iron group elements comprises iron or
nickel.
6-7. (canceled)
8. A superhard polycrystalline construction according to claim 1,
wherein the first surface comprises an external working surface
forming the working or cutting surface of the polycrystalline
construction in use.
9. A superhard polycrystalline construction according to claim 1,
wherein the polycrystalline construction comprises one or more of:
up to 20 wt % nanodiamond additions in the form of nanodiamond
powder grains; salts; borides or metal carbides of at least one of
Ti, V, or Nb; or at least one of the metals Pd or Ni.
10. A superhard polycrystalline construction as claimed in claim 1,
wherein at least a portion of the body of polycrystalline superhard
material is substantially free of a catalyst material for diamond,
said portion forming a thermally stable region.
11. A superhard polycrystalline construction as claimed in claim
10, wherein the thermally stable region extends a depth of at least
50 microns from a surface of the body of polycrystalline superhard
material.
12. A superhard polycrystalline construction as claimed in claim
10, wherein the thermally stable region comprising at most 2 weight
percent of catalyst material for diamond.
13. (canceled)
14. A superhard polycrystalline construction as claimed in claim 1
wherein the median of the mean free path associated with the
non-superhard phase divided by (Q3-Q1) for the non-superhard phase
being greater than or equal to 0.83.
15. A superhard polycrystalline construction as claimed in claim 1
wherein the median of the mean free path associated with the
superhard grains divided by (Q3-Q1) for the superhard grains is
less than 0.47.
16. A superhard polycrystalline construction according to claim 1,
wherein the first surface is substantially free of material from a
canister used in formation of the body of polycrystalline superhard
material.
17. The polycrystalline superhard construction according to claim
16, wherein the first surface is of the same quality as the bulk of
the body of polycrystalline superhard material.
18-22. (canceled)
23. An insert for a machine tool, comprising a cutter structure
joined to an insert base, the cutter structure comprising the
polycrystalline superhard construction as claimed in claim 1, the
surface topology being formed on a first face of the body of
polycrystalline superhard material, the first surface forming a
rake face or a cutting face, and the surface topology of the first
surface forming chip-breaker topology.
24-25. (canceled)
26. A method of forming a superhard polycrystalline construction,
comprising: providing a mass of grains of superhard material; and
treating the pre-sinter assembly in the presence of a
catalyst/solvent material for the superhard grains at an ultra-high
pressure of around 5.5 GPa or greater and a temperature at which
the superhard material is more thermodynamically stable than
graphite to sinter together the grains of superhard material to
form a polycrystalline superhard construction, the superhard grains
exhibiting inter-granular bonding and defining a plurality of
interstitial regions therebetween, a non-superhard phase at least
partially filling a plurality of the interstitial regions; wherein:
the median of the mean free path associated with the non-superhard
phase divided by (Q3-Q1) for the non-superhard phase is greater
than or equal to 0.50, where Q1 is the first quartile and Q3 is the
third quartile of the mean free path measurements associated with
the non-superhard phase; and the median of the mean free path
associated with the superhard grains divided by (Q3-Q1) for the
superhard grains is less than 0.60, where Q1 is the first quartile
and Q3 is the third quartile of the mean free path measurements
associated with the superhard grains; and the method further
comprising forming a non-planar surface topology in a first surface
of the body of polycrystalline diamond material, the surface
topology comprising one or more indentations in and/or projections
extending from the first surface.
27. The method of claim 26, wherein, the step of providing a mass
of grains of superhard material comprises providing a mass of
diamond grains having a first fraction having a first average size
and a second fraction having a second average size, the first
fraction having an average grain size ranging from about 10 to 60
microns, and the second fraction having an average grain size less
than the size of the first fraction.
28-38. (canceled)
39. The method of claim 26, wherein the step of forming the surface
topology comprises: placing an aggregated mass of grains of
superhard material into a canister; placing a ceramic layer formed
of a ceramic material either in direct contact with the aggregated
mass of grains of superhard material, or in indirect contact
therewith wherein the ceramic layer is spaced from the grains by an
interlayer of material, the ceramic layer having a surface with
surface topology, the surface topology imprinting a pattern in the
aggregated mass of grains of superhard material complementary to
the surface topology, the ceramic material and the material of the
interlayer where present being such that they do not react
chemically with the superhard material and/or a sinter catalyst
material for the grains of superhard material; the method further
comprising: subjecting the aggregated mass of grains of superhard
material and ceramic layer to a pressure of greater than around 5.5
GPa in the presence of the sinter catalyst material for the grains
of superhard material at a temperature sufficiently high for the
catalyst material to melt; sintering the grains to form a body of
polycrystalline superhard material having a surface topology
complementary to the surface topology of the ceramic layer; and
removing the ceramic layer and said interlayer if present from the
body of polycrystalline material.
40. A method according to claim 39, wherein the step of placing the
ceramic layer in contact with the grains of superhard material
comprises placing the ceramic material in indirect contact
therewith through the interlayer of material, the interlayer
comprising a coating on the ceramic layer.
41. (canceled)
42. A method according to claim 39, wherein the step of placing the
ceramic material in contact with the grains comprises placing a
ceramic material formed of any one or more of the group of oxide
ceramic materials that are not reduced by carbo-thermal reaction in
contact with the grains.
43. A method according to claim 42, wherein the ceramic material is
formed of any one or more of the group of oxide ceramic materials
comprising magnesia, calcia, zirconia, and/or alumina.
44-45. (canceled)
46. A method according to claim 39, wherein step of forming the
body of polycrystalline superhard material comprises forming a body
having a free outer surface on removal of the ceramic layer
therefrom in which the free outer surface is of the same quality as
the bulk of the body of polycrystalline superhard material.
47-48. (canceled)
49. A method according to claim 39, wherein the step of placing the
mass of superhard grains into a canister comprises placing an
aggregated mass of natural or synthetic diamond grains into the
canister.
50-51. (canceled)
52. A method as claimed in claim 26, further comprising treating
the body of superhard polycrystalline material to remove catalyst
material from interstices between inter-bonded grains in the
superhard material after sintering.
53-56. (canceled)
Description
FIELD
[0001] This disclosure relates to superhard constructions and
methods of making such constructions, particularly but not
exclusively to constructions comprising polycrystalline diamond
(PCD) structures attached to a substrate, and tools comprising the
same, particularly but not exclusively for use in rock degradation
or drilling, or for boring into the earth in the oil and gas
industry.
BACKGROUND
[0002] Polycrystalline diamond (PCD) is an example of a superhard
material (also called a superabrasive material) comprising a mass
of substantially inter-grown diamond grains, forming a skeletal
mass defining interstices between the diamond grains. PCD material
typically comprises at least about 80 volume % of diamond and is
conventionally made by subjecting an aggregated mass of diamond
grains to an ultra-high pressure of greater than about 5 GPa, and
temperature of at least about 1,200.degree. C., for example. A
material wholly or partly filling the interstices may be referred
to as filler or binder material.
[0003] PCD is typically formed in the presence of a sintering aid
such as cobalt, which promotes the inter-growth of diamond grains.
Suitable sintering aids for PCD are also commonly referred to as a
solvent-catalyst material for diamond, owing to their function of
dissolving, to some extent, the diamond and catalysing its
re-precipitation. A solvent-catalyst for diamond is understood be a
material that is capable of promoting the growth of diamond or the
direct diamond-to-diamond inter-growth between diamond grains at a
pressure and temperature condition at which diamond is
thermodynamically stable. Consequently the interstices within the
sintered PCD product may be wholly or partially filled with
residual solvent-catalyst material. Most typically, PCD is often
formed on a cobalt-cemented tungsten carbide substrate, which
provides a source of cobalt solvent-catalyst for the PCD. Materials
that do not promote substantial coherent intergrowth between the
diamond grains may themselves form strong bonds with diamond
grains, but are not suitable solvent-catalysts for PCD
sintering.
[0004] Cemented tungsten carbide which may be used to form a
suitable substrate is formed from carbide particles being dispersed
in a cobalt matrix by mixing tungsten carbide particles/grains and
cobalt together then heating to solidify. To form the cutting
element with an ultra hard material layer such as PCD or PCBN,
diamond particles or grains or CBN grains are placed adjacent the
cemented tungsten carbide body in a refractory metal enclosure such
as a niobium enclosure and are subjected to high pressure and high
temperature so that inter-grain bonding between the diamond grains
or CBN grains occurs, forming a polycrystalline ultra hard diamond
or polycrystalline CBN layer.
[0005] In some instances, the substrate may be fully cured prior to
attachment to the ultra hard material layer whereas in other cases,
the substrate may be green, that is, not fully cured. In the latter
case, the substrate may fully cure during the HTHP sintering
process. The substrate may be in powder form and may solidify
during the sintering process used to sinter the ultra hard material
layer.
[0006] 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. The working life of superhard tool inserts may
be limited by fracture of the superhard material, including by
spalling and chipping, or by wear of the tool insert.
[0007] 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.
[0008] Ever increasing drives for improved productivity in the
earth boring field place ever increasing demands on the materials
used for cutting rock. Specifically, PCD materials with improved
abrasion and impact resistance are required to achieve faster cut
rates and longer tool life.
[0009] Cutting elements or tool inserts comprising PCD material are
widely used in drill bits for boring into the earth in the oil and
gas drilling industry where rock drilling and other operations
require high abrasion resistance and impact resistance. One of the
factors limiting the success of the polycrystalline diamond (PCD)
abrasive cutters is the generation of heat due to friction between
the PCD and the work material. This heat causes the thermal
degradation of the diamond layer. The thermal degradation increases
the wear rate of the cutter through increased cracking and spalling
of the PCD layer as well as back conversion of the diamond to
graphite causing increased abrasive wear.
[0010] 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. Methods used to improve the abrasion
resistance of a PCD composite often result in a decrease in impact
resistance of the composite.
[0011] 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.
[0012] 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.
[0013] 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.
[0014] 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.
[0015] Another conventional solution is to remove, typically by
acid leaching, the catalyst/solvent or binder phase from the PCD
material.
[0016] 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.
[0017] It has further been appreciated that cutters and machine
tool cutting inserts having cutting surfaces with shaped topologies
may be advantageous in various applications as the surface features
may be beneficial in use to divert, for example, chips from the
working surface being worked on by the cutter or machine tool,
and/or in some instances to act as a chip breaker. Also, such
surface topologies may produce demonstrably better surface finish
qualities compared to flat surface cutting tool geometries.
However, the extreme hardness and abrasion resistance of materials
such as PCD or PCBN which are typically used as the cutting element
or insert in such applications makes it very difficult and
expensive to machine these materials with desired surface topology
features that may be used, for example, as chip breakers or to
divert the debris generated in use.
[0018] There is a need to provide super-hard bodies of
polycrystalline material such as inserts for cutting or machine
tools having effective performance and to provide a more efficient
method for making bodies of polycrystalline materials for use as
such cutters or inserts. An abrasive compact that can also achieve
improved properties of abrasion resistance, fracture and impact
resistance and a method of forming such composites are highly
desirable.
SUMMARY
[0019] Viewed from a first aspect there is provided a superhard
polycrystalline construction comprising a body of polycrystalline
superhard material, comprising:
a mass of superhard grains exhibiting inter-granular bonding and
defining a plurality of interstitial regions therebetween, the
superhard grains having an associated mean free path; and a
non-superhard phase at least partially filling a plurality of the
interstitial regions and having an associated mean free path; the
median of the mean free path associated with the non-superhard
phase divided by (Q3-Q1) for the non-superhard phase being greater
than or equal to 0.50, where Q1 is the first quartile and Q3 is the
third quartile; and the median of the mean free path associated
with the superhard grains divided by (Q3-Q1) for the superhard
grains being less than 0.60; wherein the body of polycrystalline
superhard material has a first surface having a surface topology
comprising one or more indentations therein and/or projections
therefrom.
[0020] Viewed from a second aspect there is provided a method of
forming a superhard polycrystalline construction, comprising:
[0021] providing a mass of grains of superhard material; and [0022]
treating the pre-sinter assembly in the presence of a
catalyst/solvent material for the superhard grains at an ultra-high
pressure of around 5.5 GPa or greater and a temperature at which
the superhard material is more thermodynamically stable than
graphite to sinter together the grains of superhard material to
form a polycrystalline superhard construction, the superhard grains
exhibiting inter-granular bonding and defining a plurality of
interstitial regions therebetween, a non-superhard phase at least
partially filling a plurality of the interstitial regions; [0023]
wherein: [0024] the median of the mean free path associated with
the non-superhard phase divided by (Q3-Q1) for the non-superhard
phase is greater than or equal to 0.50, where Q1 is the first
quartile and Q3 is the third quartile of the mean free path
measurements associated with the non-superhard phase; and [0025]
the median of the mean free path associated with the superhard
grains divided by (Q3-Q1) for the superhard grains is less than
0.60, where Q1 is the first quartile and Q3 is the third quartile
of the mean free path measurements associated with the superhard
grains; and [0026] the method further comprising forming a
non-planar surface topology in a first surface of the body of
polycrystalline diamond material, the surface topology comprising
one or more indentations in and/or projections extending from the
first surface.
BRIEF DESCRIPTION OF DRAWINGS
[0027] Non-limiting embodiments will now be described by way of
example and with reference to the accompanying drawings in
which:
[0028] FIG. 1 is a schematic drawing of the microstructure of a
body of PCD material; and
[0029] FIG. 2 is a schematic drawing of a PCD compact comprising a
PCD structure bonded to a substrate.
DETAILED DESCRIPTION
[0030] 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.
[0031] As used herein, a "PCD structure" comprises a body of PCD
material.
[0032] 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.
[0033] 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.
[0034] 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.
[0035] 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.
[0036] 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.
[0037] As used herein, a "superhard material" is a material having
a Vickers hardness of at least about 28 GPa. Diamond and cubic
boron nitride (cBN) material are examples of superhard
materials.
[0038] As used herein, a "superhard construction" means a
construction comprising a body of polycrystalline superhard
material. In such a construction, a substrate may be attached
thereto or alternatively the body of polycrystalline material may
be free-standing and unbacked.
[0039] As used herein, PCBN (polycrystalline cubic boron nitride)
material refers to a type of superhard material comprising grains
of cubic boron nitride (cBN) dispersed within a matrix comprising
metal or ceramic. PCBN is an example of a superhard material.
[0040] The term "substrate" as used herein means any substrate over
which the ultra hard material layer is formed. For example, a
"substrate" as used herein may be a transition layer formed over
another substrate. Additionally, as used herein, the terms "radial"
and "circumferential" and like terms are not meant to limit the
feature being described to a perfect circle.
[0041] As used herein, the term "integrally formed" regions or
parts are produced contiguous with each other and are not separated
by a different kind of material.
[0042] Like reference numbers are used to identify like features in
all drawings.
[0043] With reference to FIG. 1, a body of PCD material 10
comprises a mass of directly inter-bonded grains of superhard
material 12 and interstices 14 between the grains 12, which may be
at least partly filled with filler or binder material. FIG. 2 shows
an embodiment of a superhard composite compact 20 for use as a
cutter comprising a body of superhard 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, chromium, 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 superhard material 22 during formation of the
compact 20.
[0044] The compact 20 of FIG. 2 may, in use, be attached to a drill
bit (not shown) for oil and gas drilling operations. The body of
superhard material 10 has a free exposed surface 36, which is the
surface which, along with its edge, performs the cutting in use.
This surface has a non-planar surface topology 38 with surface
features extending from and/or into the free surface. In
embodiments where the compact 20 is to be used as a cutter, for
example for drilling in the oil and gas industry, the surface
topology may be used to direct or divert the rock or earth away
from the drill bit to which the cutter is attached. Alternatively
or additionally, the surface topology may act as a chip breaker
suitable for controlling aspects of the size and shape of chips
formed when the body of polycrystalline superhard material is used,
for example, as a cutter or as an insert for a machine tool to
machine a workpiece. Such topology may include depression and/or
protrusion features, such as radial or peripheral ridges and
troughs, formed on a rake surface of the insert.
[0045] 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.
[0046] In some embodiments, the body of superhard material 22 may
include, for example, one or more of nanodiamond additions in the
form of nanodiamond powder up to 20 wt %, salt systems, borides,
metal carbides of Ti, V, Nb or any of the metals Pd or Ni.
[0047] The grains of superhard material may be for example diamond
grains or particles. In the starting mixture prior to sintering
they may be, for example, bimodal, that is, the feed comprises a
mixture of a coarse fraction of diamond grains and a fine fraction
of diamond grains. In some embodiments, the coarse fraction may
have, for example, an average particle/grain size ranging from
about 10 to 60 microns. By "average particle or grain size" it is
meant that the individual particles/grains have a range of sizes
with the mean particle/grain size representing the "average". The
average particle/grain size of the fine fraction is less than the
size of the coarse fraction, for example between around 1/10 to
6/10 of the size of the coarse fraction, and may, in some
embodiments, range for example between about 0.1 to 20 microns.
[0048] In some embodiments, the weight ratio of the coarse diamond
fraction to the fine diamond fraction ranges from about 50% to
about 97% coarse diamond and the weight ratio of the fine diamond
fraction may be from about 3% to about 50%. In other embodiments,
the weight ratio of the coarse fraction to the fine fraction will
range from about 70:30 to about 90:10.
[0049] In further embodiments, the weight ratio of the coarse
fraction to the fine fraction may range for example from about
60:40 to about 80:20.
[0050] In some embodiments, the particle size distributions of the
coarse and fine fractions do not overlap and in some embodiments
the different size components of the compact are separated by an
order of magnitude between the separate size fractions making up
the multimodal distribution.
[0051] The embodiments consist of at least a wide bi-modal size
distribution between the coarse and fine fractions of superhard
material, but some embodiments may include three or even four or
more size modes which may, for example, be separated in size by an
order of magnitude, for example, a blend of particle sizes whose
average particle size is 20 microns, 2 microns, 200 nm and 20
nm.
[0052] Sizing of diamond particles/grains into fine fraction,
coarse fraction, or other sizes in between, may be through known
processes such as jet-milling of larger diamond grains and the
like.
[0053] In embodiments where the superhard material is
polycrystalline diamond material, the diamond grains used to form
the polycrystalline diamond material may be natural or
synthetic.
[0054] In some embodiments, the binder catalyst/solvent may
comprise cobalt or some other iron group elements, such as iron or
nickel, or an alloy thereof. Carbides, nitrides, borides, and
oxides of the metals of Groups IV-VI in the periodic table are
other examples of non-diamond material that might be added to the
sinter mix. In some embodiments, the binder/catalyst/sintering aid
may be Co.
[0055] The cemented metal carbide substrate may be conventional in
composition and, thus, may be include any of the Group IVB, VB, or
VIB metals, which are pressed and sintered in the presence of a
binder of cobalt, nickel or iron, or alloys thereof. In some
embodiments, the metal carbide is tungsten carbide.
[0056] In some embodiments, both the bodies of, for example,
diamond and carbide material plus sintering aid/binder/catalyst are
applied as powders and are sintered simultaneously in a single
UHP/HT process. The diamond grains and mass of carbide to form the
substrate are placed in an HP/HT reaction cell assembly and
subjected to HP/HT processing. The HP/HT processing conditions
selected are sufficient to effect intercrystalline bonding between
adjacent grains of abrasive particles and, optionally, the joining
of sintered particles to the cemented metal carbide support. In one
embodiment, the processing conditions generally involve the
imposition for about 3 to 120 minutes of a temperature of at least
about 1200 degrees C. and an ultra-high pressure of greater than
about 5 GPa.
[0057] In some embodiments, the substrate may be pre-sintered in a
separate process before being bonded together in the HP/HT press
during sintering of the ultrahard polycrystalline material.
[0058] In a further embodiment, both the substrate and a body of
polycrystalline superhard material are pre-formed. For example, the
bimodal or multimodal feed of ultrahard grains/particles with
optional carbonate binder-catalyst also in powdered form are mixed
together, and the mixture is packed into an appropriately shaped
canister and is then subjected to extremely high pressure and
temperature in a press. Typically, the pressure is at least 5 GPa
and the temperature is at least around 1200 degrees C. The
preformed body of polycrystalline superhard material is then placed
in the appropriate position on the upper surface of the preform
carbide substrate (incorporating a binder catalyst), and the
assembly is located in a suitably shaped canister. The assembly is
then subjected to high temperature and pressure in a press, the
order of temperature and pressure being again, at least around 1200
degrees C. and 5 GPa respectively. During this process the
solvent/catalyst migrates from the substrate into the body of
superhard material and acts as a binder-catalyst to effect
intergrowth in the layer and also serves to bond the layer of
polycrystalline superhard material to the substrate. The sintering
process also serves to bond the body of superhard polycrystalline
material to the substrate.
[0059] A support body comprising cemented carbide in which the
cement or binder material comprises a catalyst material for
diamond, such as cobalt, may be provided. The support body may have
a non-planar end or a substantially planar proximate end on which
the PCD structure is to be formed and which forms the interface 24.
A non-planar shape of the end may be configured to reduce
undesirable residual stress between the PCD structure 22 and the
support body 30. A cup may be provided for use in assembling the
diamond-containing sheets onto the support body. The first and
second sets of discs may be stacked into the bottom of the cup. In
one version of the method, a layer of substantially loose diamond
grains may be packed onto the uppermost of the discs. The support
body may then be inserted into the cup with the proximate end going
in first and pushed against the substantially loose diamond grains,
causing them to move slightly and position themselves according to
the shape of the non-planar end of the support body to form a
pre-sinter assembly.
[0060] The pre-sinter assembly may be placed into a capsule for an
ultra-high pressure press and subjected to an ultra-high pressure
of at least about 5.5 GPa and a high temperature of at least about
1,300 degrees centigrade to sinter the diamond grains and form a
PCD element comprising a PCD structure integrally joined to the
support body. In one version of the method, when the pre-sinter
assembly is treated at the ultra-high pressure and high
temperature, the binder material within the support body melts and
infiltrates the strata of diamond grains. The presence of the
molten catalyst material from the support body is likely to promote
the sintering of the diamond grains by intergrowth with each other
to form an integral, stratified PCD structure.
[0061] In some versions of the method, the aggregate masses may
comprise substantially loose diamond grains, or diamond grains held
together by a binder material. The aggregate masses of multimodal
grains may be in the form of granules, discs, wafers or sheets, and
may contain catalyst material for diamond and/or additives for
reducing abnormal diamond grain growth, for example, or the
aggregated mass may be substantially free of catalyst material or
additives. In some embodiments, the aggregate masses may be
assembled onto a cemented carbide support body.
[0062] In some embodiments, the pre-sinter assembly may be
subjected to a pressure of at least about 6 GPa, at least about 6.5
GPa, at least about 7 GPa or even at least about 7.5 GPa.
[0063] The one or more indentations in and/or projections 38 from
the free cutting surface 36 of the body of PCD material 22 may be
formed during the sintering process or may, for example, be formed
post-sintering using techniques such as electrical discharge
machining (EDM) or laser ablation to achieve the desired surface
topology to suit the application in which the compact is to be
employed.
[0064] An example method of forming the shaped surface topology
during the sintering process is set out below.
[0065] The aggregated mass of grains of diamond material is placed
into a canister, and a ceramic punch or layer formed of a ceramic
material which does not react chemically with the diamond material
is placed in contact with the aggregated mass of grains of diamond
material, the ceramic layer having a surface with surface topology.
The ceramic material may additionally or alternatively be such that
it does not react chemically with the sinter catalyst material used
to bond the diamond grains to one another during sintering. In some
embodiments, the surface topology of the ceramic material is placed
in direct contact with the diamond grains to imprint a pattern
therein complementary to the surface topology. In other
embodiments, the ceramic material may be in indirect contact with
the grains, being spaced therefrom by a thin layer or a coating to
assist in post sintering separation of the ceramic material from
the sintered superhard diamond material. In such cases, any coating
or additional layer is also formed of a material that does not
react chemically with the superhard material and/or the sinter
catalyst material. The aggregated mass of diamond grains and
ceramic layer are then subjected to an ultra-high pressure of at
least about 5.5 GPa and a temperature of at least about 1,250
degrees centigrade to melt the cobalt comprised in the substrate
body and sinter the diamond grains to each other to form a body of
polycrystalline superhard material having a surface topology
complementary to the surface topology of the ceramic layer. The
ceramic layer is then removed from the body of polycrystalline
material for example by impact.
[0066] The ceramic layer may be easily removed from the body of
polycrystalline material as there is no chemical reaction with the
ceramic material enabling easy separation of the two bodies. Any
residual ceramic may be removed by a light sand blast, resulting in
a good, semi-polished surface finish. The ceramic materials that
may be used to create the surface topology in the superhard
material may include, for example, the group of oxide ceramic
materials that are not reduced by carbo-thermal reaction, including
Magnesia, Calcia, Zirconia, Alumina.
[0067] As mentioned above, in some embodiments, the surface
topology of the ceramic material may be coated with a layer which
directly contacts the grains prior to sintering and which is of a
composition such that it facilitates removal of the ceramic body
from the sintered body of polycrystalline superhard material.
Examples of such a coating may include zirconia, alumina, calcium
carbonate or calcium oxide.
[0068] In alternative embodiments, the ceramic material directly
contacts the grains of polycrystalline superhard material to be
sintered.
[0069] The step of placing the grains of superhard material into
the canister may, in some embodiments, comprise providing a
plurality of sheets comprising the grains and stacking the sheets
in the canister to form the aggregation of superhard grains. In
other embodiments, the grains of superhard material may be
deposited into the canister using sedimentation or electrophoretic
deposition techniques.
[0070] In some embodiments, the ceramic material may be formed, for
example, of any one or more of the group of oxide ceramic materials
that are not reduced by carbo-thermal reaction in contact with the
grains. An example of such materials may include any one or more of
the group of oxide ceramic materials comprising oxides of magnesia,
calcia, zirconia, and/or alumina.
[0071] The steps of placing the materials in the canister may be
reversed or their order changed, for example, the step of placing
the ceramic layer in contact with the aggregated mass of grains may
be after the step of placing the grains into a canister.
Alternatively, the ceramic layer may be placed into the canister
before the grains are placed in the canister.
[0072] The body of polycrystalline diamond material formed by this
method may have a free outer surface 36, on removal of the ceramic
layer therefrom, which is of the same quality as the bulk of the
body of polycrystalline material. This is in contrast, for example,
to conventionally formed PCD in which the PCD layer in direct
contact with the canister material used during sintering is usually
of an inferior quality compared to the bulk PCD due to an
interaction between the diamond, cobalt binder and canister
material. Thus, in conventional PCD cutters, it is usually
necessary to remove the top surface by grinding, sandblasting or
other methods. Such steps are not required in PCD formed according
to one or more embodiments as the body of polycrystalline superhard
material has a surface topology on a first surface, the first
surface being substantially free of material from a canister used
in formation of the body of polycrystalline superhard material.
[0073] The surface topology of the ceramic material may be designed
according to the requirements of a given application of the
polycrystalline body and having regard to the intended shape of the
body depending on its ultimate use. For example, in some
embodiments the surface topology of the ceramic material is
constructed to impart a chamfered edge to the body of
polycrystalline superhard material during sintering.
[0074] In some embodiments, such as those illustrated in FIG. 2,
the body of PCD material 22 may be formed on a substrate 30, the
substrate being placed into the canister prior to sintering, the
body of polycrystalline superhard material 22 bonding to the
substrate 30 during sintering along an interface therebetween. The
interface 24 may be substantially planar, such as shown in FIG. 2,
or it may be substantially non-planar.
[0075] The substrate 30 may, for example, be formed of cemented
carbide material. In some embodiments, the sintered body may have a
thickness of up to around 6000 microns.
[0076] After forming the body of sintered polycrystalline material,
a finishing treatment may be applied to treat the body of
super-hard material 22 to remove sinter catalyst from at least some
of the interstices between the inter-bonded grains. In particular,
catalyst material may be removed from a region of the PCD structure
22 adjacent the working surface or the side surface or both the
working surface and the side surface. This may be done by treating
the PCD structure 22 with acid to leach out catalyst material from
between the diamond grains, or by other methods such as
electrochemical methods. A thermally stable region, which may be
substantially porous, extending a depth of at least about 50
microns or at least about 100 microns from a surface of the PCD
structure 22, may thus be provided. Some embodiments with 50 to 80
micron thick layers in which this leach depth is around 250 microns
have been shown to exhibit substantially improved performance, for
example a doubling in performance after leaching over an unleached
PCD product. In one example, the substantially porous region may
comprise at most 2 weight percent of catalyst material.
[0077] In embodiments where the cemented carbide substrate does not
contain sufficient solvent/catalyst for diamond, and where the PCD
structure is integrally formed onto the substrate during sintering
at an ultra-high pressure, solvent/catalyst material may be
included or introduced into the aggregated mass of diamond grains
from a source of the material other than the cemented carbide
substrate. The solvent/catalyst material may comprise cobalt that
infiltrates from the substrate in to the aggregated mass of diamond
grains just prior to and during the sintering step at an ultra-high
pressure. However, in embodiments where the content of cobalt or
other solvent/catalyst material in the substrate is low,
particularly when it is less than about 11 weight percent of the
cemented carbide material, then an alternative source may need to
be provided in order to ensure good sintering of the aggregated
mass to form PCD.
[0078] Solvent/catalyst for diamond may be introduced into the
aggregated mass of diamond grains by various methods, including
blending solvent/catalyst material in powder form with the diamond
grains, depositing solvent/catalyst material onto surfaces of the
diamond grains, or infiltrating solvent/catalyst material into the
aggregated mass from a source of the material other than the
substrate, either prior to the sintering step or as part of the
sintering step. Methods of depositing solvent/catalyst for diamond,
such as cobalt, onto surfaces of diamond grains are well known in
the art, and include chemical vapour deposition (CVD), physical
vapour deposition (PVD), sputter coating, electrochemical methods,
electroless coating methods and atomic layer deposition (ALD). It
will be appreciated that the advantages and disadvantages of each
depend on the nature of the sintering aid material and coating
structure to be deposited, and on characteristics of the grain.
[0079] In one embodiment, cobalt may be deposited onto surfaces of
the diamond grains by first depositing a pre-cursor material and
then converting the precursor material to a material that comprises
elemental metallic cobalt. For example, in the first step cobalt
carbonate may be deposited on the diamond grain surfaces using the
following reaction:
Co(NO.sub.3).sub.2+Na.sub.2CO.sub.3->CoCO.sub.3+2NaNO.sub.3
[0080] The deposition of the carbonate or other precursor for
cobalt or other solvent/catalyst for diamond may be achieved by
means of a method described in PCT patent publication number
WO/2006/032982. The cobalt carbonate may then be converted into
cobalt and water, for example, by means of pyrolysis reactions such
as the following:
CoCO.sub.3->CoO+CO.sub.2
CoO+H.sub.2->CO+H.sub.2O
[0081] In another embodiment, cobalt powder or precursor to cobalt,
such as cobalt carbonate, may be blended with the diamond grains.
Where a precursor to a solvent/catalyst such as cobalt is used, it
may be necessary to heat treat the material in order to effect a
reaction to produce the solvent/catalyst material in elemental form
before sintering the aggregated mass.
[0082] As described above, to assist in improving thermal stability
of the sintered structure, the catalysing material may be removed
from a region of the polycrystalline layer adjacent an exposed
surface thereof. Generally, that surface will be on a side of the
polycrystalline layer opposite to the substrate and will provide a
working surface for the polycrystalline diamond layer. Removal of
the catalysing material may be carried out using methods known in
the art such as electrolytic etching, and acid leaching and
evaporation techniques.
[0083] It has been found that multimodal distributions of some
embodiments may assist in achieving a very high degree of diamond
intergrowth while still maintaining sufficient open porosity to
enable efficient leaching.
[0084] Polycrystalline bodies formed according to the
above-described method may have many applications. For example,
they may be used as an insert for a machine tool, in which the
cutter structure comprises the body of polycrystalline superhard
material according to one or more embodiments and the surface
topology of the polycrystalline material in such an application may
be used as a chip-breaker. In such inserts, the cutter structure
which may be joined to an insert base, may have, for example, a
mean thickness of at least 100 microns, and in some embodiments, a
mean thickness of at most 1,000 microns.
[0085] Embodiments are described in more detail below with
reference to the following examples which are provided herein by
way of illustration only and are not intended to be limiting.
Example 1
[0086] This non-limiting example illustrates a method of forming
the surface topology during the sintering process.
[0087] A surface topology configuration may be designed according
to the requirements of a given drilling or machining application
and having regard to the intended shape of a cutter structure or
machine tool insert. A cobalt-cemented carbide substrate body may
be provided and a ceramic plug may be provided, the ceramic plug
having a surface comprising a surface topology that is
complementary (i.e. inverse) to that of the desired surface
topology for the cutter or machine tool insert. A pre-compact
assembly may be prepared by forming a plurality of diamond grains
into an aggregation against the surface of the substrate, and
encapsulating the assembly within a jacket, formed for example of
alumina or other ceramic material. The surface of the ceramic plug
having the desired surface topology to be imparted to the diamond
body on sintering is placed in contact with the diamond grains. The
pre-compact assembly is subjected to an ultra-high pressure of at
least about 5.5 GPa and a temperature of at least about 1,250
degrees centigrade to melt the cobalt comprised in the substrate
body and sinter the diamond grains to each other to form a
composite compact comprising a PCD structure formed joined to the
substrate. After sintering, the ceramic plug may be removed from
the sintered PCD material by, for example, light impact and the PCD
structure may be treated in acid to remove residual cobalt within
interstitial regions between the inter-grown diamond grains.
Removal of a substantial amount of cobalt from the PCD structure is
likely to increase substantially the thermal stability of the PCD
structure and will likely reduce the risk of degradation of the PCD
material. The composite compact thus formed may be further
processed, depending on its intended application. For example, if
it is to be used as a machine tool insert, it may be further
treated by grinding to provide a machine tool insert comprising the
PCD cutter structure having well-defined chip-breaker features.
Example 2
[0088] A quantity of sub-micron cobalt powder sufficient to obtain
2 mass % in the final diamond mixture was initially de-agglomerated
in a methanol slurry in a ball mill with WC milling media for 1
hour. A fine fraction of diamond powder with an average grain size
of 2 .quadrature.m was then added to the slurry in an amount to
obtain 10 mass % in the final mixture. Additional milling media was
introduced and further methanol was added to obtain suitable
slurry; and this was milled for a further hour. A coarse fraction
of diamond, with an average grain size of approximately 20
.quadrature.m was then added in an amount to obtain 88 mass % in
the final mixture. The slurry was again supplemented with further
methanol and milling media, and then milled for a further 2 hours.
The slurry was removed from the ball mill and dried to obtain the
diamond powder mixture.
[0089] The diamond powder mixture was then placed into a suitable
HpHT vessel, adjacent to a tungsten carbide substrate and sintered
at a pressure of around 6.8 GPa and a temperature of about 1500
.quadrature.C.
[0090] The surface topology 38 in the cutting surface 36 of the PCD
body 22 was formed post sintering using EDM techniques. In other
embodiments, the surface topology could have been formed during
sintering using, for example, the techniques described above in
example 1.
Example 3
[0091] A quantity of sub-micron cobalt powder sufficient to obtain
2.4 mass % in the final diamond mixture was initially
de-agglomerated in a methanol slurry in a ball mill with WC milling
media for 1 hour. A fine fraction of diamond powder with an average
grain size of 2 .quadrature.m was then added to the slurry in an
amount to obtain 29.3 mass % in the final mixture. Additional
milling media was introduced and further methanol was added to
obtain a suitable slurry; and this was milled for a further hour. A
coarse fraction of diamond, with an average grain size of
approximately 20 .quadrature.m was then added in an amount to
obtain 68.3 mass % in the final mixture. The slurry was again
supplemented with further methanol and milling media, and then
milled for a further 2 hours. The slurry was removed from the ball
mill and dried to obtain the diamond powder mixture.
[0092] The diamond content of the sintered diamond structure is
greater than 90 vol % and the coarsest fraction of the distribution
may, in some embodiments, be greater than 60 weight % or greater
than weight 70%.
[0093] The surface topology 38 in the cutting surface 36 of the PCD
body 22 was formed post sintering using EDM techniques. In other
embodiments, the surface topology could have been formed during
sintering using, for example, the techniques described above in
example 1.
[0094] The surface topology of the ceramic material may be designed
according to the requirements of a given application of the
polycrystalline body and having regard to the intended shape of the
body depending on its ultimate use. For example, in some
embodiments the surface topology of the ceramic material is
constructed to impart a chamfered edge to the body of
polycrystalline superhard material during sintering.
[0095] In some embodiments, the polycrystalline bodies formed
according to the above-described methods may be used as a cutter
for boring into the earth, or as a PCD element for a rotary shear
bit for boring into the earth, or for a percussion drill bit or for
a pick for mining or asphalt degradation. Alternatively, a drill
bit or a component of a drill bit for boring into the earth, may
comprise the body of polycrystalline superhard material according
to any one or more embodiments.
[0096] In polycrystalline diamond material, individual diamond
particles/grains are, to a large extent, bonded to adjacent
particles/grains through diamond bridges or necks. The individual
diamond particles/grains retain their identity, or generally have
different orientations. The average grain/particle size of these
individual diamond grains/particles may be determined using image
analysis techniques. Images are collected on a scanning electron
microscope and are analysed using standard image analysis
techniques. From these images, it is possible to extract a
representative diamond particle/grain size distribution.
[0097] Generally, the body of polycrystalline diamond material will
be produced and bonded to the cemented carbide substrate in a HPHT
process. In so doing, it is advantageous for the binder phase and
diamond particles to be arranged such that the binder phase is
distributed homogeneously and is of a fine scale.
[0098] A cross-section through the PCD structure was then examined
micro-structurally by means of a scanning electron microscope
(SEM).
[0099] The homogeneity or uniformity of the sintered structure is
defined by conducting a statistical evaluation of a large number of
collected images. The distribution of the binder phase, which is
easily distinguishable from that of the diamond phase using
electron microscopy, can then be measured in a method similar to
that disclosed in EP 0974566. This method allows a statistical
evaluation of the average thicknesses of the binder phase along
several arbitrarily drawn lines through the microstructure. This
binder thickness measurement is also referred to as the "mean free
path" by those skilled in the art. For two materials of similar
overall composition or binder content and average diamond grain
size, the material which has the smaller average thickness will
tend to be more homogenous, as this implies a "finer scale"
distribution of the binder in the diamond phase. In addition, the
smaller the standard deviation of this measurement, the more
homogenous is the structure. A large standard deviation implies
that the binder thickness varies widely over the microstructure,
i.e. that the structure is not even, but contains widely dissimilar
structure types.
[0100] The binder and diamond mean free path measurements were
obtained for various samples in the manner set out below. Unless
otherwise stated herein, dimensions of mean free path 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.
[0101] 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.
[0102] 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. 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). [0103] 1. A sample piece
of the PCD sintered body is cut using wire EDM and polished. At
least 10 back scatter electron images of the surface of the sample
are taken using a Scanning Electron Microscope at 1000 times
magnifications. [0104] 2. 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. [0105] 3. An auto threshold feature was used to
binarise the image and specifically to obtain clear resolution of
the diamond and binder phases. [0106] 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: [0107] a. If too low then resolution of fine
particles is reduced. [0108] b. If too high then: [0109] i.
Efficiency of coarse grain separation is reduced. [0110] ii. High
numbers of coarse grains are cut by the boarders of the image and
hence less of these grains are analysed. [0111] iii. Thus more
images must be analysed to get a statistically-meaningful result.
[0112] 5. Each particle was finally represented by the number of
continuous pixels of which it is formed. [0113] 6. The AnalySIS
software programme proceeded to detect and analyse each particle in
the image. This was automatically repeated for several images.
[0114] 7. Ten SEM images were analyzed using the grey-scale to
identify the binderpools as distinct from the other phases within
the sample. The threshold value for the SEM was then determined by
selecting a maximum value for binder pools content which only
identifies binder pools and excludes all other phases (whether grey
or white). Once this threshold value is identified it is used to
binarize the SEM image.) [0115] 8. One pixel thick lines were
superimposed across the width of the binarized image, with each
line being five pixels apart (to ensure the measurement is
sufficiently representative in statistical terms). Binder phase
that are cut by image boundaries were excluded in these
measurements. [0116] 9. The distance between the binder pools along
the superimposed lines were measured and recorded--at least 10,000
measurements were made per material being analysed. Median values
were reported for both the non-diamond phase mean free paths and
diamond phase mean free paths. [0117] The distance between the
binder pools along the superimposed lines were measured and
recorded--at least 10,000 measurements were made per material being
analysed. The median value for the non-diamond phase mean free
paths and the diamond phase mean free paths were calculated. The
term "median" in this context is considered to have its
conventional meaning, namely the numerical value separating the
higher half of the data sample from the lower half.
[0118] Also recorded were the mean free path measurements at Q1 and
Q3 for both the diamond and non-diamond phases.
[0119] Q1 is typically referred to as the first quartile (also
called the lower quartile) and is the number below which lies the
25 percent of the bottom data. Q3 is typically referred to as the
third quartile (also called the upper quartile) has 75 percent of
the data below it and the top 25 percent of the data above it.
[0120] From this, it was determined that embodiments have:
alpha >=0.50 and beta <0.60, where alpha is the non-diamond
phase MFP median/(Q3-Q1), which gives a measure of "uniform binder
pool size"; and beta=diamond MFP median/(Q3-Q1) which gives a
measure of "wide grain size distribution"
[0121] In some embodiments it was determined that alpha >=0.83
and beta <0.47.
[0122] While various embodiments have been described with reference
to a number of examples, those skilled in the art will understand
that various changes may be made and equivalents may be substituted
for elements thereof and that these examples are not intended to
limit the particular embodiments disclosed. Various example
arrangements and combinations for cutter structures and inserts are
envisaged by the disclosure. The cutter structure may comprise
natural or synthetic diamond material. Examples of diamond material
include polycrystalline diamond (PCD) material, thermally stable
PCD material, crystalline diamond material, diamond material made
by means of a chemical vapour deposition (CVD) method or silicon
carbide bonded diamond.
[0123] Furthermore, the cutter structure described herein with
reference to one or more embodiments may be used as part of an
insert for a machine tool, comprising the cutter structure with the
superhard polycrystalline construction described herein joined to
an insert base, the surface topology being formed on a first face
of the body of polycrystalline superhard material, the first
surface forming a rake face or a cutting face, and the surface
topology of the first surface forming chip-breaker topology.
[0124] In one or more other embodiments, the superhard
polycrystalline structure described herein may form a PCD element
for one or more of a rotary shear bit for boring into the earth, a
percussion drill bit, or a pick for mining or asphalt
degradation.
* * * * *