U.S. patent application number 14/367165 was filed with the patent office on 2014-10-23 for methods of forming a superhard structure or body comprising a body of polycrystalline diamond containing material.
This patent application is currently assigned to Element Six Abrasives S. A.. The applicant listed for this patent is Element Six Abrasives S.A.. Invention is credited to Moosa Mahomed Adia, Geoffrey John Davies.
Application Number | 20140311045 14/367165 |
Document ID | / |
Family ID | 45572839 |
Filed Date | 2014-10-23 |
United States Patent
Application |
20140311045 |
Kind Code |
A1 |
Davies; Geoffrey John ; et
al. |
October 23, 2014 |
METHODS OF FORMING A SUPERHARD STRUCTURE OR BODY COMPRISING A BODY
OF POLYCRYSTALLINE DIAMOND CONTAINING MATERIAL
Abstract
A method of producing a free standing PCD comprises forming a
mass of combined diamond particles and precursor compound(s) for
the metals of the metallic network by suspending the diamond
particles in a liquid, and crystallising and/or precipitating the
precursor compounds in the liquid. The mass is then removed from
suspension by sedimentation and/or evaporation to form a dry powder
of combined diamond particles and precursor compound(s). The powder
is subjected to a heat treatment to dissociate and reduce the
precursor compound(s) to form metal particles smaller in size than
the diamond particles to provide a homogeneous mass. This is then
consolidated using isostatic compaction to form a homogeneous
cohesive green body of a pre-selected size and 3-dimensional shape.
The green body is subjected to high pressure and high temperature
conditions such that the metallic material wholly or in part
becomes molten and facilitates diamond particle to particle bonding
via partial diamond re-crystallisation to form a free standing PCD
body.
Inventors: |
Davies; Geoffrey John;
(Springs, ZA) ; Adia; Moosa Mahomed; (Springs,
ZA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Element Six Abrasives S.A. |
Luxembourg |
|
LU |
|
|
Assignee: |
Element Six Abrasives S. A.
Luxembourg
LU
|
Family ID: |
45572839 |
Appl. No.: |
14/367165 |
Filed: |
December 20, 2012 |
PCT Filed: |
December 20, 2012 |
PCT NO: |
PCT/EP2012/076450 |
371 Date: |
June 19, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61578734 |
Dec 21, 2011 |
|
|
|
Current U.S.
Class: |
51/309 |
Current CPC
Class: |
C22C 26/00 20130101;
B24D 18/0009 20130101; B24D 3/10 20130101; C22C 1/1026
20130101 |
Class at
Publication: |
51/309 |
International
Class: |
B24D 3/10 20060101
B24D003/10; B24D 18/00 20060101 B24D018/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 21, 2011 |
GB |
1122066.2 |
Claims
1. A method of producing a free standing PCD body comprising a
combination of intergrown diamond grains forming a diamond network
and an interpenetrating metallic network, not attached to a second
body or substrate made of a different material such as a metal,
cermet or ceramic, the method comprising the steps of: a. forming a
mass of combined diamond particles and precursor compound(s) for
the metals of the metallic network by suspending the diamond
particles in a liquid, and crystallising and/or precipitating the
precursor compounds in the liquid; b. removing the mass from
suspension by sedimentation and/or evaporation to form a dry powder
of combined diamond particles and precursor compound(s); c.
subjecting the powder to a heat treatment to dissociate and reduce
the precursor compound(s) to form metal particles smaller in size
than the diamond particles to provide a homogeneous mass; d.
consolidating the homogeneous mass of diamond particles and
metallic material using isostatic compaction to form a homogeneous
cohesive green body of a pre-selected size and 3-dimensional shape;
and e. subjecting the green body to high pressure and high
temperature conditions such that the metallic material wholly or in
part becomes molten and facilitates diamond particle to particle
bonding via partial diamond re-crystallisation to form a free
standing PCD body; wherein: the diamond network of the PCD body is
formed of diamond grains having a plurality of grain sizes, the
diamond network comprising a grain size distribution having an
average diamond grain size, wherein the largest component of the
diamond grain size distribution is no greater than three times the
average diamond grain size; and the PCD material forming the free
standing PCD body is homogeneous, the PCD body being spatially
constant and invariant with respect to diamond network to metallic
network volume ratio, wherein the homogeneity is measured at a
scale greater than ten times the average grain size and spans the
dimension of the PCD body, the PCD material being macroscopically
residual stress free at said scale.
2. A method according to claim 1 wherein the mass of combined
diamond particles and precursor compound(s) for the metals of the
metallic network is formed by simultaneously or sequentially adding
to the suspension a solution of a metal containing compound and a
solution of a reactive compound such that an insoluble precursor
compound(s) for the metal(s) of the metallic network nucleates and
grows on the surfaces of the diamond particles forming the
precursor compound(s) as particles attached to and decorating the
diamond particle surfaces.
3. A method according to claim 1 wherein the mass of combined
diamond particles and precursor compound(s) for the metals of the
metallic network is formed by crystallizing from solution in the
suspending liquid a soluble precursor compound(s) for the metals of
the metallic network.
4. A method according to claim 2 wherein the precursor compound(s)
for the metal of the metallic network is (are) crystallized and/or
precipitated in a suspension of pre-selected portion of the diamond
particles; the method further comprising after completion of the
crystallization and/or precipitation of the precursor compound(s)
adding the remaining portion of the diamond particles to the
stirred suspension prior to removal of the suspension liquid; and
subsequently applying heat treatment to dissociate and/or reduce
the precursor compound(s) to metallic particles.
5. A method according to claim 4 wherein the portion of diamond
particles for initial combination with the precursor compound(s) is
pre-selected on the basis of diamond particle size and/or diamond
mass proportion.
6-8. (canceled)
9. A method according to claim 1, wherein the liquid suspension
medium is water or an alcohol.
10. (canceled)
11. A method according to claim 2, wherein the precursor
compound(s) is (are) a carbonate, hydroxide, oxalate or
acetate.
12. A method according to claim 3, wherein the precursor
compound(s) is a nitrate.
13-15. (canceled)
16. A method according to claim 2, wherein the precursor
compound(s) is (are) selected from tungstates, molybdates,
tantalates, titanates, niobates, vanadates and stannates.
17-18. (canceled)
19. A method according to claim 2 wherein the precursor is an
amorphous semi-porous oxide.
20. A method according to claim 19 wherein the oxide is selected to
be any one or more of or any permutation of tungstic oxide,
WO.sub.3, molybdic oxide, MoO.sub.3, tantalum pentoxide,
Ta.sub.2O.sub.5, titanium oxide, TiO.sub.2, niobium pentoxide,
Nb.sub.2O.sub.5, and vanadium oxide, V.sub.2O.sub.3.
21. A method according to claim 20 wherein the reactant compound to
form the oxide by reaction with water is an alcoxide of general
formula M(ROH).sub.n, M being a metal and R being an organic
alkane.
22. A method according to claim 2, wherein the mass of diamond
particles and precursor compound(s) is heated in a reducing gas
environment to convert the precursor compound(s) to metallic
particles smaller than the diamond particles.
23. A method according to claim 22 wherein the gaseous environment
contains hydrogen.
24. A method according to claim 22, wherein the temperature and
time of heat treatment is sufficient to generate amorphous
non-diamond carbon where metallic particles decorate and are
attached to the diamond surfaces and/or are in contact with the
diamond surfaces.
25. A method according to claim 22, wherein the temperature and
time of heat treatment is insufficient to generate amorphous
non-diamond carbon where metallic particles decorate and are
attached to the diamond surfaces and/or are in contact with the
diamond surfaces.
26. A method according to claim 2, wherein one or more of the
precursor compound(s) yields one or more transition metal carbides
at the surface of the diamond particles during heat treatment.
27. A method according to claim 26 wherein the precursor
compound(s) yield a metal/metal carbide combination attached to the
diamond surfaces.
28. A method according to claim 27 where the metal/metal carbide
combination is selected from cobalt/tungsten carbide,
cobalt/tantalum carbide or nickel/titanium carbide or any
combination.
29. A method according to claim 1 wherein the green body is
subjected to a pressure in the range of 5 to 10 GPa and to a
temperature in the range 1100 to 2500.degree. C. to form a fully
dense free standing PCD body.
30-31. (canceled)
Description
FIELD
[0001] This disclosure relates to methods of making a superhard
structure or body comprising a body of polycrystalline diamond
containing material and a body made by such methods.
BACKGROUND
[0002] Polycrystalline diamond materials (PCD) as considered in
this disclosure consist of an intergrown network of diamond grains
with an interpenetrating metallic network. This is illustrated
schematically in FIG. 1 which shows the microstructure of PCD
material comprising the intergrown network of diamond grains 1 with
an inter-penetrating metallic network 2 with facets occurring at
the diamond-metal interfaces 3. Each grain has a degree of plastic
deformation 4. Newly crystallized diamond bonds 5 bond the diamond
grains as shown in the inset of this figure. The network of diamond
grains is formed by sintering of diamond powders facilitated by
molten metal catalyst/solvent for carbon at elevated pressures and
temperatures. The diamond powders may have a monomodal size
distribution whereby there is a single maximum in the particle
number or mass size distribution, which leads to a monomodal grain
size distribution in the diamond network. Alternatively, the
diamond powders may have a multimodal size distribution where there
are two or more maxima in the particle number or mass size
distribution, which leads to a multimodal grain size distribution
in the diamond network. Typical pressures used in this process are
in the range of around 4 to 7 GPa but higher pressures up to 10 GPa
or more are also practically accessible and can be used. The
temperatures employed are above the melting point at such pressures
of the metals. The metallic network is the result of the molten
metal freezing on return to normal room conditions and will
inevitably be a high carbon content alloy. In principle, any molten
metal solvent for carbon which can enable diamond crystallization
at such conditions may be employed. The transition metals of the
periodic table and their alloys may be included in such metals.
[0003] Conventionally, the predominant custom and practice in the
prior art is to use the binder metal of hard metal substrates
caused to infiltrate into a mass of diamond powder, after melting
of such binders at the elevated temperature and pressure. This is
infiltration of molten metal at the macroscopic scale of the
conventional PCD construction, i.e., infiltrating at the scale of
millimeters. By far the most common situation in the prior art is
the use of tungsten carbide, with cobalt metal binders as the hard
metal substrate. This inevitably results in the hard metal
substrate being bonded in-situ to the resultant PCD. Successful
commercial exploitation of PCD materials to date has been very
heavily dominated by such custom and practice.
[0004] For the purposes of this disclosure, PCD constructs which
use hard metal substrates as a source of the molten metal sintering
agent via directional infiltration and the bonding in-situ to that
substrate, are referred to as "conventional PCD" constructions or
bodies. This is illustrated in FIG. 2 which is a schematic diagram
of the infiltration process in a conventional PCD body with arrows
indicating the direction and the long range of the infiltration
through 2 to 3 mm of thickness of the PCD layer. The arrows in the
inset 11 indicate again that the range of infiltration transcends
many diamond grains. The PCD layer 6 in a conventional PCD body is
normally of the order of 2 to 3 mm in thickness. The substrate 7 is
predominantly made of tungsten carbide/cobalt alloy. The number 8
indicates approximately the direction of the infiltration of the
cobalt infiltrant through the thickness of the PCD layer during the
high pressure high temperature process. The oval region 11 is at
the interface between the carbide substrate and the PCD layer, and
the inset of FIG. 2 shows schematically an expanded view of region
11 with the diamond grains in this region through which the long
range infiltration of cobalt occurs. The inset highlights the fact
that the directional infiltration transcends many grains through
the thickness of the PCD layer. The diamond grains 9 and 10 may
typically be of varying size in the body and could be made of multi
modal mixes of diamond particles.
[0005] It has been appreciated that this conventional approach to
the manufacture of PCD bodies results in a series of limitations
and constraints which in turn have undesirable consequences in many
applications. These limitations include: [0006] 1. Macroscopic
residual stress distributions (at the scale of the conventional PCD
body i.e. at the scale of millimeters) in the PCD body which
inevitably have deleterious tensile components. [0007] 2. A
dimensional limitation of PCD material layers in the direction of
the infiltration of the molten metal from the substrate. [0008] 3.
Structural and compositional in-homogeneities as a result of
directional molten metal infiltration over a distance of the order
of millimeters. [0009] 4. Significant practical difficulties in
exploiting a broad range of metal alloy compositions and limited
metallurgical compositions which result there from. [0010] 5. Micro
residual stress management at the scale of the diamond micro
structural grain size is limited and impractical. [0011] 6.
Manufacturing degrees of freedom such as grain size distribution,
metal content and metal alloy composition are co-dependent and
cannot readily be independently preselected, chosen or varied.
[0012] The present applicants have appreciated that the limitations
and problems with respect to homogeneity, macroscopic and
microscopic residual stresses, size and shape of the PCD body, and
restricted choice of material composition described above for
conventional PCD bodies or constructions give rise to poor or
inadequate performance in many applications.
[0013] There is a need for the development PCD bodies of any
3-dimensional shape, with high material homogeneity and with the
absence of macroscopic residual stress, and with an expanded choice
of PCD material structure and composition, with attendant micro
residual stress control, all of which are highly desirable.
SUMMARY
[0014] 1. Viewed from a first aspect there is provided a method of
producing a free standing PCD body comprising a combination of
intergrown diamond grains forming a diamond network and an
interpenetrating metallic network, not attached to a second body or
substrate made of a different material such as a metal, cermet or
ceramic, the method comprising the steps of: [0015] a. forming a
mass of combined diamond particles and precursor compound(s) for
the metals of the metallic network by suspending the diamond
particles in a liquid, and crystallising and/or precipitating the
precursor compounds in the liquid; [0016] b. removing the mass from
suspension by sedimentation and/or evaporation to form a dry powder
of combined diamond particles and precursor compound(s); [0017] c.
subjecting the powder to a heat treatment to dissociate and reduce
the precursor compound(s) to form metal particles smaller in size
than the diamond particles to provide a homogeneous mass; [0018] d.
consolidating the homogeneous mass of diamond particles and
metallic material using isostatic compaction to form a homogeneous
cohesive green body of a pre-selected size and 3-dimensional shape;
and [0019] e. subjecting the green body to high pressure and high
temperature conditions such that the metallic material wholly or in
part becomes molten and facilitates diamond particle to particle
bonding via partial diamond re-crystallisation to form a free
standing PCD body; wherein: [0020] the diamond network of the PCD
body is formed of diamond grains having a plurality of grain sizes,
the diamond network comprising a grain size distribution having an
average diamond grain size, wherein the largest component of the
diamond grain size distribution is no greater than three times the
average diamond grain size; and [0021] the PCD material forming the
free standing PCD body is homogeneous, the PCD body being spatially
constant and invariant with respect to diamond network to metallic
network volume ratio, wherein the homogeneity is measured at a
scale greater than ten times the average grain size and spans the
dimension of the PCD body, the PCD material being macroscopically
residual stress free at said scale.
BRIEF DESCRIPTION OF THE FIGURES
[0022] Embodiments will now be described by way of example and with
reference to the accompanying drawings in which:
[0023] FIG. 1 is schematic diagram of the microstructure of PCD
material showing the intergrown network of diamond grains with an
inter-penetrating metallic network with facets occurring at the
diamond-metal interfaces;
[0024] FIG. 2 is a schematic diagram of the infiltration process in
a conventional PCD body with arrows indicating the direction and
the long range of the infiltration through 2 to 3 mm of thickness
of the PCD layer;
[0025] FIG. 3 is a schematic diagram of the very localised or short
range movement of metal during the sintering of diamond particles
to form an embodiment of PCD showing the diamond particles with
well and homogeneously distributed, smaller metal particles;
[0026] FIG. 4 is a graph of cobalt content versus average grain
size of the starting diamond particles for PCD sintered by the
conventional route;
[0027] FIG. 5 is a generalized flow diagram showing two alternative
approaches of embodiments of the method and preferences, laid out
in two columns, for combining diamond powders with appropriate
metals to form a mass of particulate material, which after forming
into a 3-dimensional semi-dense body is subjected to high
temperature and pressure conditions to melt or partially melt the
metal and partially re-crystallize the diamond to create the free
standing PCD body;
[0028] FIG. 6 is a schematic diagram for the method of FIG. 5
column 2;
[0029] FIG. 7 is a cobalt, carbon binary phase diagram;
[0030] FIG. 8 is a schematic representation of a diamond particle
showing metal particles decorating the surface;
[0031] FIGS. 9a and 9b are SEM micrographs of whisker-like crystals
of cobalt carbonate decorating the surfaces of 2 micro meter sized
diamond particles;
[0032] FIGS. 10a and 10b are SEM micrographs of cobalt metal
particles decorating the surfaces of 4 micro meter sized diamond
particles;
[0033] FIG. 11 is a TEM micrograph of a diamond particle decorated
in cobalt metal particles together with a schematic diagram of the
diamond surface;
[0034] FIG. 12 is two SEM micrographs of diamond particles
decorated in cobalt particles and tungsten carbide;
[0035] FIG. 13 is an SEM micrograph showing a multimodal size
distribution of diamond particles which have been co-decorated in
cobalt and tantalum carbide particles;
[0036] FIG. 14 is an embodiment of a 3-dimensional shaped PCD body
intended for use in general applications;
[0037] FIG. 15 is an SEM micrograph of mixed cobalt nickel
carbonate crystals decorating 1 micron diamond particles; and
[0038] FIG. 16 is an SEM micrograph showing 95% cobalt, 5% nickel
alloy metal particles decorating the surfaces of 1 micron diamond
particles.
DETAILED DESCRIPTION
[0039] Prior art methods for making PCD materials are dominated by
the use of substrates of metallic materials which provide a source
of molten metal solvents for carbon which are caused to infiltrate
a mass of diamond particles and via partial diamond
recrystallisation result in diamond particle to particle
intergrowth or sintering. Inevitably, such substrates are bonded to
the resultant PCD material during such manufacturing procedure.
There are many structural compositional and dimensional limitations
and restrictions to the PCD material which follow from the use of
such substrates. These include unavoidable macro residual stress
distributions, PCD material layer thicknesses restricted
practically to about 3 mm or less and limitations in both diamond
to metal ratio and the elemental and alloy composition of the
metal. The limitations of these prior art constructions which have
been appreciated by the present applicants are set out below.
[0040] 1. The residual stress is a distribution of tensile and
compressive stresses in the body of the PCD material. At the scale
related to the diamond grain size, which generally may be
considered to be at the scale of less than ten times the average
diamond grains size, where the coarsest component of grain size is
no greater than three times the average diamond grain size, the
stresses operative may be defined as and referred to as the "micro
residual stress". [0041] At the scale greater than ten times the
average diamond grain size, where the coarsest component of diamond
grain size is less than three times the average diamond grain size,
the stresses operative may be defined as and referred to as the
"macro residual stress". Typically, for very fine PCD grain sizes
this is at a scale greater than a few tens of micro meters. For
coarse grain sized PCD materials, this scale may typically be
greater than a tenth of a millimeter. [0042] In the case of
conventional PCD constructions the bonding of the substrate to the
PCD layer invariably results in a macro residual stress
distribution. This is as a result of the thermo elastic mismatch
between the materials of the PCD layer and the substrate which, as
a result of differential thermal contraction and elastic expansion,
causes the residual stress distribution to form, on return to room
temperature and pressure at the end of the sintering process. In
the general case of metallic substrates, although the overall
average macroscopic stress in the PCD layer is compressive, the
residual stress distribution unavoidably, always has significant
tensile stress components due to bending effects of the bonded PCD
body. These tensile stress components promote crack propagation
leading to early fracture of the PCD body during general mechanical
applications. Early fracture signals the end of life of such a
body. In certain instances, for example when very dissimilar
materials are used for the PCD and the substrate, which can cause
very high residual tensile stresses, fracture may even result from
the manufacturing process alone. This is a contributor to a high
product reject rate even in standard production processes. [0043]
Conventional PCD cutters used in rock drilling applications
comprising a PCD element bonded to a hard metal substrate element
particularly suffer from early fracture problems caused by crack
propagation assisted by the macroscopic residual stresses. Much of
the prior art for such cutters involves disclosures and inventions
aimed at limiting such problems. Aspects such as non-planar
interfaces between the PCD layer and carbide substrate, break-in
chamfers at the PCD cutter leading edge, partial removal of the
metal in the PCD by leaching at the surface, vacuum heat treatment
annealing and, more recently, functional grading of the PCD layer
and the carbide substrate have been developed and exploited to
reduce the magnitude of the tensile component and/or displace these
tensile maxima to positions remote from the free surfaces, and in
so doing favorably alter the crack behavior of cutters. These prior
art approaches have had some effect but do not provide a
comprehensive solution to early fracture problems of this nature
because the tensile components in the macroscopic residual stress
distributions cannot be eliminated. [0044] 2. In principle, with
the conventional approach, one could form a PCD layer on any size
and shape of the substrate. The thickness of such a PCD layer in
the direction of the infiltration is limited in practice by any one
or combination of three possibilities. Firstly, above a thickness
of about 3 mm the tensile component of the residual stress can
become very significant and can be dominant in regard to failure of
the PCD in manufacture or mechanically based applications.
Secondly, a practical limitation in the range of molten metal
infiltration results in insufficient metal for good diamond
sintering to occur beyond a certain thickness of PCD, after which
the desired properties of the material are lost. The infiltration
range depends upon the diamond particle size distribution which
determines the pore size distribution. A limited range in thickness
to a few millimeters before inadequate metal for good diamond
sintering is particularly the case for PCD wholly made from or with
a fine grain component of less than 10 micron particles. Thirdly,
directional infiltration of molten metal sweeps impurities such as
oxygen and its compounds with the melt front. These impurities
concentrate sufficiently at a particular range of thickness where
they can interfere with the diamond sintering mechanisms leading to
very poor quality PCD which now will have inferior properties.
[0045] The second and third factors contribute to inhomogeneity in
both structure and composition of the PCD material. A consequence
of limiting the thickness of the PCD material construction to a
small number of millimeters is that large equi-axed three
dimensional shapes for the PCD material component greater than this
small dimension cannot be made. Thus, the PCD material component of
a three dimensional construction is limited to a thin layer on the
three dimensional substrate shape, no matter its size or shape.
This thickness limitation is only minimally increased in the prior
art by such means as metal powder additions to the starting diamond
powder source layer. This inherently, of its very nature, limits
the PCD material to high metal contents and thus can progressively
compromise the structure and properties, and the homogeneity of
such structures. [0046] 3. Structural and compositional
in-homogeneities as a result of directional molten metal
infiltration, occur discontinuously extending from the substrate
which acts as the source of the molten metal diamond sintering aid
into the PCD layer. In the most common case in which commercially
available standard tungsten carbide cobalt hard metals are used as
the substrate, immediately above the substrate a layer of up to a
few tens of micro meters thick always occurs where nearly all of
the diamond has been taken into solution by the molten cobalt
allowing it to become saturated in dissolved carbon. This layer
will then have low diamond content with little or no intergrowth
between the remaining diamond grains. Above this layer, the molten
cobalt saturated in dissolved carbon can now facilitate dissolution
and re-precipitation of some of the diamond, which provides the
diamond to diamond bonding. Where tungsten carbide cobalt hard
metal substrates are used, the infiltrating molten cobalt often
carries with it tungsten in solution. The tungsten, when it
experiences the carbon now rapidly coming into solution, reacts
with this carbon and solid tungsten carbide crystals precipitate.
The tungsten carbide precipitation being governed by the normal
rules of nucleation and growth of a solid phase in a liquid medium,
results in tungsten carbide precipitates being distributed
inhomogeneously in the metallic network of the PCD. Often, the
tungsten carbide based inhomogeneity can be extreme with regions in
the PCD volume containing areas of many tens of micro meters
across, which are depleted in diamond and have a dominant
population of tungsten carbide precipitates. Such inhomogeneity
severely compromises the properties of PCD material where they
occur, resulting in inferior performance in application. [0047]
Local inhomogeneity in diamond/metal content also arises due to the
directional infiltration being unequal and/or not simultaneous
across the expanse of the boundary area between the PCD and the
substrate. This results in uncontrolled structural/compositional
variations spatially, which cause local variations in PCD
properties and, as such, can be considered as unwanted defects.
[0048] The in-homogeneity described in this section gives rise to
residual stresses at the defined macroscopic scale of the PCD body
by virtue of the thermo elastic property differences between the
adjacent inhomogeneous parts of the material. [0049] 4. Molten
metal infiltration from a substrate to form PCD is limited to the
metal component of said substrate which is molten under appropriate
pressure and temperature conditions for diamond recrystallisation
to occur. The binder metallurgy of practical hard metal materials
is significantly limited and highly dominated by cobalt. This is
particularly the case for tungsten carbide based hard metal
materials which are generally the most highly developed and
superior materials for most applications. More rarely available is
titanium carbide hard metal which, however, is made mainly with
nickel as the binding metal. Using tungsten carbide/cobalt hard
metal material types for PCD substrates, which is overwhelmingly
the normal commercial situation, thus largely restricts such
conventional PCD products to cobalt based metallurgy for the
metallic network in the PCD material layer. The infiltrating cobalt
from such a substrate can only be alloyed with other metals to a
limited extent by adding metal powders to the diamond powder layer
during manufacture. [0050] Alternatively, the prior art teaches the
use of placing thin metal layers between the substrate and the
diamond powder layer. This approach is also limited to available
metals alloys in strip form which of course will have to be alloyed
further in situ by the molten metal infiltrating from the
substrate. [0051] The present applicants have appreciated that both
of the above approaches to metallurgical modification for the PCD
material usually result in alloy inaccuracy and in-homogeneity in
the PCD layer due to the directional infiltration of the substrate
origin metal. Thus, whilst the applicants believe that in principle
any combination of transition metal elements which can enable
diamond crystallization may be used to form the diamond intergrowth
essential for PCD materials and the resultant metal
interpenetrating network, to date only a narrow set of
possibilities have been conventionally exploited and these are
mostly limited to cobalt as the main metallic component.
[0052] It is known that highly specific transition metal alloys
with accurate compositions can exhibit special and remarkable
properties, such as magnetic and thermal expansion properties. With
conventional PCD made by infiltration of the metal component in
total or in part from a substrate it is impractical and often
impossible to specify sufficiently accurately or arrive at chosen
alloys in the PCD material to exploit special and desired
properties of such specific alloys. [0053] 5. Micro residual stress
at the scale of the diamond grain size and associated metal between
the grains arises during the drop to room pressure and temperature
during the manufacturing process. This is due to the thermo-elastic
mismatch between the diamond network and particular metal
interpenetrating network present. Typically, the thermal mismatch
derived residual stress is the dominant effect. The elastic modulus
and thermal expansion coefficient of transition metal alloys are
highly dependent upon the accurate and specific alloy composition.
This is true particularly for the coefficient of thermal expansion.
For example in the iron/nickel system, for very specific alloys
such as invar, Fe, 36% Ni, a linear coefficient minimum of 1.5 ppm
.degree. K.sup.-1 can be obtained which can be compared with the
pure metal values of 12 and 13 ppm .degree. K.sup.-1 for iron and
nickel, respectively. Deviations of 0.1% by weight in this alloy
can result in a doubling of the linear coefficient of expansion,
showing the high sensitivity to the alloy composition. Pure cobalt
has a linear coefficient of expansion of 13 ppm .degree. K.sup.-1
and some of its alloys with iron and nickel also exhibit similar
lowered thermal expansion behavior. The micro residual stress
therefore will vary significantly from place to place in a PCD
material where the alloy is inhomogeneous and not accurately
determined. Thus due to the inhomogeneity and inaccuracy of
metallurgy typical of the conventional PCD approach where
infiltration from a substrate is employed, micro residual stress
management at the scale of the diamond micro structural grain size
is limited and impractical. [0054] 6. In conventional PCD, other
than pressure and temperature conditions, the only real degree of
freedom one has to determine the type of PCD material is to choose
and specify the size distribution of the starting source diamond
powder. In particular, once the diamond starting particle size is
chosen, the metal content of the PCD material layer is restricted
to a limited range. The latter is as a consequence of the bed or
layer of diamond particles being exposed to a large reservoir of
molten metal, in the normally large substrate. PCD materials with
low metal contents cannot be easily accessed. Generally, in
conventional PCD, the metal content of the PCD material increases
inversely with the diamond particle size. Increasing the pressure
of manufacture can decrease the metal content but only to a limited
extent. Therefore, the resultant composition of conventional PCD
material has been restricted and limited and the choice of metal
content and diamond size distribution cannot be independently
pre-selected and made over a wide range. The result is that the
metal content for each chosen diamond size distribution is limited
to a range of about 3 or 4 volume percent around the mean value
which is typically about 6 volume percent for the very coarse
grades and about 13 volume percent for very fine grades such as 1
micron. [0055] This is illustrated by FIG. 4 which is a plot of
cobalt content of PCD materials related to average grain size of
the starting diamond particles for PCD sintered by the conventional
route and shows the limited range of metal content (the field
between the dashed parallel lines, region 1) typical of historical
conventional PCD made with tungsten carbide hard metal substrates.
FIG. 4 also shows that, after many years of development,
conventional PCD is still largely confined to diamond/cobalt ratios
in the band 15 between the dotted lines. This figure also shows the
trend of increasing metal content with average finer grain sizes.
[0056] The present applicants have appreciated that one of the
important limitations for conventional PCD is the inability to
achieve very high diamond contents, i.e., low metal contents,
particularly with fine diamond size distribution. A well
established example of this is 1 micron PCD which has not been made
conventionally with more than 86 to 88 volume percent diamond
content, i.e., less than 12 to 14 volume percent metal content. It
has been empirically determined in the art that increases in
pressure and temperature conditions of conventional PCD manufacture
are capable of lowering the metal content by about 1 to 2 volume
percent. The lower limit of metal content which can readily be
obtained for conventionally made PCD materials with typical
historically exploited diamond particle size distributions is
indicated for such historical conventional PCD materials by the
lower dashed line A-B in FIG. 4. This line corresponds to the
formula y=-0.25x+10, where y is the metal content of the PCD in
volume percent, and x is the average grain size of the PCD material
in micro meters. The field of metal content below this line is not
conventionally accessible using the typical pressures and
temperatures available with the use of the presently developed
commercial high pressure high temperature equipment. As explained
in numbered section 4 above, the metal or alloy composition is also
conventionally limited and difficult to accurately and controllably
vary. Generally, therefore, in the conventional approach, the
manufacturing degrees of freedom such as grain size distribution,
metal content and metal alloy are co-dependent and not readily
independently pre-selected, chosen and varied.
[0057] The limitations and problems with respect to homogeneity,
macroscopic and microscopic residual stresses, size and shape of
the PCD body, and restricted choice of material composition
described above for the prior art conventional PCD bodies or
constructions gives rise to poor or inadequate performance in many
applications.
[0058] The present applicants have appreciated that the development
of free standing PCD bodies of any 3-dimensional shape,
specifically engineered to have high material homogeneity and with
an absence of macroscopic residual stress, and with an
independently pre-selected greatly expanded choice of PCD material
structure and composition, with attendant micro residual stress
control, is highly desirable. Some embodiments described hereunder
are directed at removing or ameliorating the limitations of the
conventional approach to PCD bodies or constructions in which the
possibility of better exploiting the true potential of PCD
materials becomes viable.
[0059] The removal or amelioration of the limitations of
conventional PCD materials makes the applications indicated above
more viable with the potential of new applications becoming
possible for PCD materials.
[0060] A free standing, single volume of PCD material is disclosed
which is homogeneous and free of residual stress at a macroscopic
scale greater than ten times the average grain size, where the
coarsest component of grain size is no greater than three times the
average grain size.
[0061] The free standing nature of this PCD volume or body arises
due to the absence of a bonded substrate of a dissimilar material
to the PCD. The absence of a substrate also means that the molten
metal required for enabling the partial recrystallisation of the
diamond particles to form the particle to particle diamond bonding
does not arise from long range directional infiltration from such a
substrate body. Rather, the required molten metal is provided
solely by an initial homogeneous, intimate and accurate combination
or mass of diamond particles and smaller, pure metal particles,
grains or entities. The details of the methods employed to form
such a mass of diamond and metal particles, which is homogeneous
above a scale related to the average and maximum diamond particle
sizes, together with the means by which the homogeneity is
progressively maintained during consolidation of the mass to form a
so called green body of pre-selected size and shape and subsequent
sintering of the diamond particles at high pressure and
temperature, are described below.
[0062] When the metal particles are exposed to appropriate high
pressure and temperature conditions such that the metal melts, the
molten metal only permeates the surrounding interstices in the
local vicinity of each diamond particle. On exposure of a mass of
such diamond particle/metal combinations to these conditions, this
very short range permeation of the molten metal into the
surroundings of each diamond engenders high homogeneity of diamond
and metal. This is illustrated in FIG. 3 which is a schematic
diagram of the very localised or short range movement of metal
during the sintering of diamond particles in the PCD. It shows the
diamond particles 13 with well and homogeneously distributed,
smaller metal particles 12. The metal movement is depicted by
arrows 14 moving in all directions but only as far as neighbouring
diamond particles. The high purity of the diamond metal combination
also ensured by embodiments of the methods described herein helps
the generation of high homogeneity so that third phase
precipitates, such as oxides and tungsten carbide and the like, may
be avoided.
[0063] The free standing volume or body of homogeneous PCD material
is not bonded in any way to other material bodies during
manufacture, be they of a dissimilar material or of a different
composition and structure of PCD. Macroscopic residual stresses
cannot therefore be generated during return to room pressure and
temperature at the end of the manufacturing process. Such a free
standing PCD body may thus be considered to be macroscopically
stress free at a scale above which it is homogeneous, spatially
invariant and considered to be made of one average property
material. In the context of typical PCD materials, this scale may
be considered to be greater than ten times the average grain size,
where the coarsest component of grain size is no greater than three
times the average grain size. Where the average diamond grain size
is about 10 to 12 micro meters and the maximum grain size is
smaller than about 40 micro meters this scale may be considered to
be above 120 micro meters. Where the average diamond grain size is
about 1 micro meter where the maximum grain size is about 3 micro
meters, this scale may be considered to be above 10 micro
meters.
[0064] The long range directional infiltration of molten metal from
a substrate in conventional PCD manufacture as previously
described, contributes to the dimensions of the PCD in the
direction of the infiltration being limited to about 3 mm. Some
embodiments ensure or assist in the maintenance of diamond and
metal homogeneity at each stage of manufacture of a free standing
PCD body and employ short range permeation of molten metal during
the sintering stage and thereby eliminate or substantially
ameliorate the above-mentioned limitation. Consequently, the
dimensions possible for the free standing, stress free PCD body in
any orthogonal direction is not limited in such a way. Therefore,
it is believed that any desired 3-dimensional shape may be
generated, which is not possible in the conventional PCD prior art.
Moreover, embodiments of the methods described herein may provide
near net size and shape capabilities so that accurate non distorted
free standing PCD bodies may be made.
[0065] The generation of PCD having valuable general shapes where
one direction in the PCD body is significantly greater than any of
the dimensions at right angles to it is believed to be possible.
For example, columnar structures where the cross-sectional area
perpendicular to the axis is circular (cylindrical shaped),
elliptical or any regular or irregular polyhedral shape can be
made.
[0066] Alternatively, general shapes where one direction in the
solid is significantly less than any dimension at right angles to
it may also be readily made, for example, these shapes include
discs and plates. The large faces of the plates may be any regular
or irregular polyhedron.
[0067] The near net shape capability of some of the embodiments of
the methods described herein may allow 3-dimensional solids having
high degrees of symmetry to be made, such as spheres, ellipsoids
(oblate and prolate) and regular solids. The regular solids may
include the five so-called "Platonic" solids, namely the
tetrahedron, cube, octahedron, icosahedron and dodecahedron. The
thirteen semi-regular, so called "Archimedes" solids which include
the cuboctahedron, truncated cube, truncated octahedron, truncated
dodecahedron and truncated tetrahedron may also be made. Moreover,
the generation of other convex polyhedra such as prisms, pyramids
and the like are believed to be possible. In addition, PCD bodies
formed as conical and toroidal shapes may be made, together with
polyhedral toroidal shapes. More generally, any irregular shape
where the solid is bounded by one or more non-straight edge and one
or more non-flat surface may be possible. All of the 3-dimensional
solid shapes described above, be they of high symmetry or irregular
may be modified by forming concave re-entrant surfaces. Such
re-entrant surfaces may be bounded by flat polygonal faces, curved
surfaces, irregular surfaces or any combination of these.
Re-entrant surfaces may have particular value where the free
standing body is required to be mechanically attached to a
foundation or another body. For example, a circumferential groove
may facilitate the use of a split ring for interlocking
purposes.
[0068] Practical dimensions for such 3-dimensional shaped free
standing PCD bodies will however be limited by the dimensions and
design characteristics of the high pressure high temperature
apparatus used to manufacture them. Large high pressure high
temperature systems with a sample volume of greater than 1.0 litre
and with high pressure reaction volumes of dimensions as large as
132 mm in diameter, have been disclosed in the technical literature
(Ref. 5). More recently, it has been established in the art that
high pressure systems with reaction volumes of 2.0 litres or more
are viable. Such systems may be either multi-axial (such as cubic)
systems or belt type system, both of which are known in the art.
The latter belt type systems are favoured and are practically more
amenable to large reaction volumes because of their ability to
maintain pressure by accommodating large volume changes during the
reaction processes.
[0069] Free standing PCD bodies made with in accordance with some
embodiments of the method described herein may be made such that
the largest dimension in any direction in the body may fall within
the range 5 to 150 mm. For example, a free standing PCD body
consisting of a right circular cylinder of 100 mm diameter and 100
mm long will have the largest dimension along a body diagonal of
141.4 mm. Another example is a free standing PCD cube of edge
length 85 mm, which has a face diagonal of 120.2 mm and a body
diagonal of 147.2 mm. Another example of a small free standing PCD
right circular cylinder which has its largest dimension within the
quoted range, has a diameter of 4 mm and a length of 4 mm and a
body diagonal of 5.66 mm.
[0070] Another serious practical difficulty appreciated by the
present applicants leading to limitations in the conventional PCD
prior art is the limited metallurgical scope derived from
infiltration from a substrate. This is true even when metal powders
are added to the PCD starting diamond. The inherent metallurgical
inhomogeneity characteristic of the conventional PCD approach which
is a result of directional infiltration of the required molten
metal in turn results in an inability to permit creation and
choosing of accurate and specific alloy compositions which are the
same from place to place across the volume of the PCD material.
Indeed it is also very difficult for even the diamond to metal
ratio to be invariant across the dimensions of the PCD volume or
layer. It is well known that the properties of alloys are usually
highly dependent upon very specific and accurately made
compositions. Moreover, PCD materials themselves exhibit properties
very dependent upon accurate compositions. The general consequence
therefore of this for conventional PCD is that the true scope of
composition and therefore properties cannot be uniformly achieved
across the dimensions of the conventional PCD volume or layer.
[0071] In contrast, some embodiments of the methods described
herein are unfettered by such inhomogeneity and inaccuracy problems
of composition as very accurate and specific wide ranging alloy
compositions may be chosen and made invariant across the dimensions
of the free standing PCD volume.
[0072] The accuracy in diamond-to-metal ratio characteristic of
some embodiments of the methods described herein results from the
metal or alloy being smaller than the diamond particle sizes, and
being homogeneously distributed and associated with each diamond
particle. This is particularly true for the method where the
metal(s) or alloy(s) of choice are decorated onto or associated
with the surface of each individual diamond particle of the
starting diamond powder. During the high pressure high temperature
phase of the manufacturing process where the metal on each of the
diamond particle surfaces is melted, the molten metal permeates the
interstices between the diamond particles to a very limited range
between the surrounding particles. This ensures that the chosen
diamond to metal ratio is constant and invariant across the
dimensions of the free standing PCD body and homogeneous at a
macroscopic scale. The scale above which this homogeneity and
invariance of composition occurs is dependent upon the grain size
distribution of the PCD material and is smaller for smaller average
grain sizes. For example where the average grain size is 1 micro
meter and the maximum grain size is about 3 micro meters the
material can be considered to be homogeneous and spatially
invariant above about 10 micro meters. More generally, the
macroscopic scale above which the PCD material is considered to be
spatially invariant may be defined as at a scale greater than 10
times the average grain size, where the largest grains are no more
than 3 times the average grain size.
[0073] The accuracy of the alloy composition in some embodiments
described herein may be achievable as a consequence of the use of
molecular precursors for the chosen metals in the methods described
herein. Some of the molecular precursors such as nitrate or
carbonate salts of the metals may be made as mixed crystals or
solid solutions. This is possible in the cases where the metal
salts are isomorphous, i.e., having the same crystallographic
structure. In particular, this is true for the carbonates of some
transition metals such as iron, nickel, cobalt and manganese. Where
the mixed molecular precursor is chemically generated or
precipitated by reacting a solution of soluble salts or compounds,
the accuracy of the specifically chosen metallic element ratio may
be determined by easily provided concentration ratios of the
solutions of the source compounds of the chosen metals. One of the
examples of this is to create a combined mixed solution of metal
nitrates in water and then to precipitate a mixed carbonate
precursor for the chosen alloy by reaction with sodium or ammonium
carbonate solutions. The use of mixed molecular precursors in this
way enables the chosen metal elements to be combined at an atomic
scale. In contrast, the conventional approach to PCD manufacture
necessarily involves alloying by virtue of melts, flowing and
diffusing together which always results in spatial variation and
inaccuracy.
[0074] Precursor compounds which may be dissociated and/or reduced
to metals and alloys are readily available for nearly all the
metals of the periodic table. Those precursors which can be reduced
to metals or metal carbides by reaction with carbon may be
preferred. In particular, the metals of Group VIIIA of the periodic
table can be exploited individually or in fully alloyed
combinations. The metals chosen wholly or in part must however be
capable of facilitating diamond crystallization in order to create
the necessary diamond particle to particle bonding for PCD. An
important implication of this is that the resultant metallic
network of the PCD material has carbon in solid solution usually to
a maximum level as expressed in appropriate metallurgical phase
diagrams. In addition, metallic elements which readily form stable
carbides will also be present in the metallic network as carbide
components. Thus, the metal alloys exploitable in PCD are the high
carbon versions of such metals.
[0075] The free standing PCD bodies of some embodiments described
herein due to the high homogeneity and accuracy of composition may
thus exploit the special properties of highly specific chosen
compositions. For example, the metallic network may be chosen to be
made from controlled expansion alloys which have highly specific
elemental ratios. The thermo elastic properties of the metallic
network may therefore be chosen to be specific from a wide range
but, due to the homogeneity, be the same at all parts of the free
standing PCD body. The range of linear coefficient of thermal
expansion for the metallic network extends from magnitudes typical
of elements such as cobalt (13 ppm .degree. K.sup.-1 at room
temperature) to that typical of low expansion alloys like the high
carbon version of Invar (Fe, 33% Ni, 0.6% C, about 3.3 ppm .degree.
K.sup.-1 at room temperature, ref 4). By accurate choice of the
metallurgy of the metallic network the difference in thermo elastic
properties between the diamond network and the inter-penetrating
metallic network may be accurately chosen and determined. Together
with the metal content which may be independently chosen, such
differences in the thermo elastic properties of the two
inter-penetrating networks generate residual stresses at the scale
of the microstructure during the quench to room conditions at the
end of the manufacturing process. If the dominant stress generating
effect is due to the thermal shrinkage difference and the diamond
expansion coefficient, which is about 1 ppm .degree. K.sup.-1 at
room temperature, the diamond network will be generally
compressively stressed and the metallic network generally under
tension. The magnitude of this micro residual stress may be
considered to be high when the linear coefficient of expansion of
the metallic network is 10 to 14 ppm .degree. K.sup.-1, medium for
a linear coefficient of expansion of 5 to 10 ppm .degree. K.sup.-1
and low for less than 5 ppm .degree. K.sup.-1. Where the PCD body
is homogeneous at a macroscopic scale as previously defined, these
micro residual stresses sum to zero, resulting in the macroscopic
residual stress being considered to be zero and the free standing
PCD body itself to be macroscopically stress free. When alloys with
a coefficient of linear thermal expansion of less than 5 ppm
.degree. K.sup.-1 are used the differences in elastic modulus
between the alloys and diamond become more significant and the
micro residual stress in the metallic network may in fact become
compressive. Low expansion alloys such as iron, 33 weight % nickel,
0.6 weight % carbon which has a literature value of elastic modulus
and coefficient of linear thermal expansion of 150 GPa and 3.3 ppm
.degree. K.sup.-1, respectively, are examples of such alloys.
[0076] PCD bodies where the micro residual stress in the metallic
network has an overall compressive nature form some embodiments and
are now disclosed.
[0077] The understanding of the present applicants is that micro
residual stresses play a significant role in crack initiation and
local crack coalescence during mechanical applications of PCD
materials. This may be considered as a key aspect of wear behaviour
at the particle to particle level. Materials with a low propensity
of micro cracking may hence be developed using the approach and
methods described herein.
[0078] The ability to independently choose and pre-select the metal
content and metallurgical type of the PCD material for the purpose
of micro structural stress management as discussed above is an
example of an important and distinct character of some embodiments,
namely, the ability to independently choose and control the
structural and compositional variables.
[0079] Unlike in the conventional infiltration from a substrate PCD
approach where initial choice of diamond particle size and size
distribution largely fixes or radically limits other variables, the
method of some embodiments described herein allows independent
choices and control of these variables and also the homogeneity of
the end products to be specifically engineered to be high. For
example the metal content, metal type, diamond size and size
distribution may be independently chosen and controlled. As can be
seen in FIG. 4, conventionally when fine grain PCD of about 1
micron average grain size is made by infiltration of metal from a
hard metal substrate, the metal content is restricted to about 12
to 14 volume percent.
[0080] In contrast, some embodiments described herein provide for
the metal content to be chosen independently to the metal type and
be anywhere in the range from about 1 to 20 percent. Similarly,
where a multimodal grain size is chosen for the embodiments of a
PCD body described herein and the average grain size is about ten
micro meters with the maximum grain size about 30 micro meters,
again the metal content may be chosen anywhere in the range from
about 1 to about 20 percent. The metal content for conventional PCD
material being restricted to around and close to 9 volume percent,
as illustrated in FIG. 4, no longer applies. The field of metal
contents below the lower dashed line A-B in FIG. 4 which correspond
approximately to the formula y=-0.25x+10 where y is the metal
content in volume percent and x is the average grain size of the
PCD material in micro meters, may therefore be exploited using the
methods described herein and embodiments of free standing PCD
bodies with metal contents in this field are envisaged.
[0081] The metallic network may be chosen to be most combinations
and permutations of the metals of the periodic table provided that
diamond crystallization can be facilitated by such metals, which
also means that the alloys all have a high carbon content. This
choice is made completely independently of average grain size,
grain size distribution and diamond to metal ratio. Clearly, a
greatly extended range of PCD material types with their attendant
properties can now be accessed. Yet another feature of some
embodiments described herein is that the element tungsten will be
absent unless deliberately included. This is in contrast to the
dominant custom and practice of the conventional prior art PCD
approach where tungsten carbide/cobalt hard metal substrates are
used which inevitably result in tungsten being inhomogeneously
incorporated as tungsten carbide precipitates in the PCD layer.
Some embodiments of the methods described herein assist in allowing
the incorporation of tungsten carbide as an added phase at
controllable and homogeneous levels if such compositions are
chosen. Typically, PCD compositions free of tungsten may, however,
readily be made.
[0082] The metals and alloys which are capable of facilitating
diamond crystallization after melt, include any of and any combined
permutations or alloys of the transition metals of the periodic
table whereby at least one metal does not form stable carbide
compounds at conditions of temperature and pressure appropriate for
diamond crystallization. Typical of these latter metals and
preferred for diamond crystallization processes are the Group VIIIA
metals of the periodic table such as iron, nickel, cobalt and also
the Group VIIA metal manganese. Transition metals which form stable
carbides under typical diamond re-crystallization from metal
solutions conditions include tungsten, titanium, tantalum,
molybdenum, zirconium, vanadium, chromium and niobium. Some
embodiments described herein allow the metallic network in the PCD
body to be accurately chosen combinations of iron, nickel, cobalt
or manganese with the carbides of these elements. Notably, cobalt,
tungsten carbide (WC) combinations ranging from high cobalt content
to low cobalt content may be provided by some embodiments of these
methods.
[0083] A further feature some embodiments occurs as a result of the
absence of macroscopic residual stress, in that manufacturing
pressure and temperature conditions may be widely chosen as
undesirable residual stress distributions from such pressure and
temperature choices does not occur. The conventional PCD approach
suffers from significant increases in residual stress distributions
as higher pressures and temperatures are used causing a high
incidence of cracking and fracture of the PCD parts during
manufacture. Thus, the approach of some embodiments described
herein may allow the ready beneficial use of higher pressures and
temperatures. The benefits may include increased intergrowth of
diamond particles and associated property improvements such as
increases in hardness, strength and thermal properties with
increased diamond to metal ratio. When striving for PCD materials
confined to particularly low metal contents such as 1 or 2 volume
percent, the convenience of using increased pressures and
temperatures may allow fully dense PCD material to be achieved.
[0084] Some embodiments of methods for producing free standing PCD
bodies are described in detail below which covers means of creating
particulate masses of diamond and metals and alloys, followed by
techniques to consolidate these masses into green bodies of
pre-determined shapes and sizes and finally subjecting the green
bodies to high pressure high temperature conditions in order to
sinter the diamond particles.
[0085] Methods to produce the free standing, three dimensional PCD
body or construction, of any shape and up to about 100 mm in any
dimension, which is macroscopically homogeneous in structure and
composition and stress free at a macroscopic scale are described.
This macroscopic scale is dependent upon the grain size
distribution of the PCD material and defined to be greater than ten
times the average grain size, with the maximum grain size being
about three times the average grain size. For most typical so
called coarse grain sized PCD materials this is greater than about
0.2 mm (200 micro meters). For very fine grained PCD materials
close to an average of 1 micron, this scale is above about 10 micro
meters. In order to achieve this, means of combining diamond
powders of predetermined particle size distribution with metals or
metal alloys at least one of which is capable of facilitating
diamond crystallization are required. Typically, but not
exclusively, diamond powders with an average particle size of less
than 20 micro meters may be used. After melting the metals in a
consolidated mass of the combined diamond particles and metals, at
appropriate pressure and temperature conditions, the molten metal
only permeates the mass from each diamond particle into the regions
between immediately surrounding particles. This short range
permeation or infiltration is thought to contribute to and ensure
the homogeneity of the PCD body and in turn may provide for the PCD
body to be macroscopically stress free.
[0086] The approaches and means used to make the mass or
combination of diamond powder and appropriate metals and alloys for
subsequent sintering of the diamond particles at high pressure and
temperature, may provide homogeneity in diamond size distribution,
diamond to metal distribution and metal composition. This
homogeneity of the powder mass or combination may then provide for
the homogeneity of the final sintered PCD material body. Further,
this may be facilitated if, preferably, the form of the metals or
metal alloys is of metal particles, grains or entities which are
smaller than the size of the diamond particles for each chosen size
or size range of diamond particles required to produce PCD with a
chosen desired grain size distribution.
[0087] FIG. 5 is a generalized flow diagram showing alternative
approaches and preferences for combining diamond powders with
appropriate metals to form a mass of particulate material which,
after forming into 3-dimensional semi-dense so-called "green"
bodies, is subjected to high temperature and pressure conditions to
melt or partially melt the metal and partially re-crystallize the
diamond to create the free standing PCD bodies.
[0088] Methods according to one or more embodiments of creating a
starting mass of combined diamond particles and smaller metal(s) or
alloy(s) make use of precursor compounds, which may be dissociated
or reduced to form the sufficiently pure metals and alloys by heat
treatment in controlled environments. Examples of such environments
include vacuum or appropriate gases which have reducing gases
present such as hydrogen or carbon monoxide and the like. These
precursors include compounds such as salts, oxides and
organometallic compounds of the transition metals or any chemical
compound which can be dissociated and or reduced to yield at least
one of the required metals. For final alloy formation these
precursors may be mixed. Alternatively, individual precursor
compounds which contain the elemental combination of the desired
alloys may be used, for example, mixed salts such as iron nickel
cobalt nitrates, Fe.sub.xNi.sub.yCo.sub.z(NO.sub.3).sub.2 where
x+y+z=1, and the like. This will engender highest accuracy of final
alloy atomic composition and homogeneity.
[0089] Ionic compounds such as salts which can be dissociated
and/or reduced to form pure metals may be examples of candidates
for precursors. Examples of some such salts are nitrates,
sulphates, carbonates, oxalates, acetates and hydroxides of the
transition metals.
[0090] Of particular interest for some embodiments are the oxalates
of cobalt and nickel, CoC.sub.2O.sub.4 and NiC.sub.2O.sub.4 which
decompose to the metal in inert atmosphere, such as nitrogen, at
very low temperatures and above such as 310 and 360.degree. C.,
respectively (Ref 1). Such oxalates may be used in hydrated form,
e.g. crystals of CoC.sub.2O.sub.4.2H.sub.2O and
NiC.sub.2O.sub.4.2H.sub.2O or dehydrated form.
[0091] Nitrate salts, in particular cobalt(II) nitrate hexahydrate
crystals, Co(NO.sub.3).sub.2.6H.sub.2O, nickel nitrate hexahydrate
crystals, Ni(II) (NO.sub.3).sub.2.6H.sub.2O and ferrous iron(II)
nitrate hexahydrate crystals, Fe(NO.sub.3).sub.2.6H.sub.2O,
respectively, may, in some embodiments, be preferred as
crystallized precursors for the specific metals. Such nitrate
crystals are easily dehydrated and dissociated at low temperatures
approaching 200.degree. C. and reduced to the pure metals above
temperatures as low as about 350.degree. C. in hydrogen containing
gaseous environments (Ref. 2 and 3).
[0092] Alloy compositions may be obtained by mixing the salts or by
the use of mixed metal single compounds such as mixed salts. For
example co-crystallized nitrates of iron, cobalt and nickel to form
mixed crystals such as Fe.sub.xCo.sub.yNi.sub.z(NO.sub.3).sub.2
where x+y+z=1. One advantage of using such mixed salts may be that,
on dissociation and/or reduction to the metallic state, the metals
will already be mixed at the atomic scale, engendering maximum
homogeneity in regard to alloy composition.
[0093] Carbonates are also excellent precursors for metals such as
iron, nickel, cobalt, copper and manganese. On thermal dissociation
and reduction these salts form particularly finely sized metals,
often down to a few tens of nanometers.
[0094] When metals such as cobalt, nickel, iron, manganese or
copper, are desired to be combined with metals which form stable
carbides during decomposition/reduction and/or diamond sintering,
such as tungsten, molybdenum, chromium, tantalum, niobium,
vanadium, zirconium, titanium and the like, a useful approach is to
use ionic compounds where the former metals form the cation and the
latter carbide forming metals form part of the anion, such as in
tungstates, molybdates, chromates, tantalates, niobates, vanadates,
zirconates and titanates, respectively. Some important examples of
such compounds are cobalt tungstate, CoWO.sub.4, nickel molybdate,
NiMoO.sub.4 and cobalt vanadate, Co.sub.3(VO.sub.4).sub.2,
respectively.
[0095] Intermetallic compounds such as CoSn may also be made by
dissociation/reduction of precursors such as cobalt stannate,
CoSnO.sub.3.
[0096] Examples of oxides which may be used include ferrous and
ferric oxide (Fe.sub.2O.sub.3 and Fe.sub.3O.sub.4), nickel oxide
(NiO), cobalt oxides (CoO and Co.sub.3O.sub.4). The latter oxide,
Co.sub.3O.sub.4, may be produced as micro meter sized aggregates of
20 to 100 nm particles by the decomposition of cobalt carbonate in
air at low temperatures such as 300 to 400.degree. C. For final
alloy formation, these precursors may be mixed.
[0097] Other precursor compounds for the metal(s) or alloy(s) may
be crystallized from solution in liquids where the diamond powder
is present as a solid suspension, FIG. 5 column 1. Some precursor
compounds are soluble in solvent liquids such as water or alcohols
and may be crystallized from such solutions by reduction of
temperature and/or evaporation of the solvent or protocols known in
the art of crystallization from solution, where suitable degrees of
supersaturation and or seeding may be exploited.
[0098] Stable suspensions of desired diamond particle size
distributions anywhere in the range of 0.1 to greater than 30 micro
meters may be obtained when in water or alcohol, particularly when
the suspension is vigorously stirred. After appropriate settling
and decantation followed by drying procedures, a combination of
solid precursor(s) for the metal and diamond results. The
crystallization of the precursor is organized such that the
particle or crystal size is smaller than that of the diamond
powder. Subsequently, dissociation and/or reduction of the
precursor by heat treatment in vacuum or reductive gases generates
a mass of diamond and smaller sized metal particles, grains or
entities. Approaches where diamond suspensions are used,
particularly when they are continuously stirred, may engender
excellent homogeneous mixing with crystallized precursors. The
liquid suspension medium for the diamond and solvent for the
precursor compounds may be water or alcohols such as ethanol and
the like or any appropriate and convenient liquid. Where pure water
is used, preferred precursors for the metals are salts and in
particular nitrates. This is because all metal nitrates have a high
solubility in water and may readily be thermally dissociated and/or
reduced to the pure metal by low temperature heat treatment. Again,
in particular cobalt(II) nitrate hexahydrate crystals,
Co(NO.sub.3).sub.2.6H.sub.2O, nickel nitrate hexahydrate crystals,
Ni(II) (NO.sub.3).sub.2.6H.sub.2O and ferrous iron(II) nitrate
hexahydrate crystals, Fe(NO.sub.3).sub.2.6H.sub.2O, respectively,
may be used, for example, as crystallized precursors for the
specific metals. Such nitrate crystals are easily dehydrated and
dissociated at low temperatures approaching 200.degree. C. and
reduced to the pure metals above temperatures as low as about
350.degree. C. in hydrogen containing gaseous environments (Ref 2
& 3). In addition, many of the metal nitrates may be
co-crystallized as mixed crystals whereby atomic scale mixing of
extremely accurate alloys may be achieved on dissociation and
reduction to the metallic state.
[0099] Another class of precursor compounds for this approach are
the oxalates, M.sub.x(C.sub.2O.sub.4).sub.y, x and y being
dependent upon the valency of the metal M, as the anion is
(C.sub.2O.sub.4).sup.2-. Examples of oxalate salts which may be
used include cobalt oxalate dehydrate crystals,
Co(II)C.sub.2O.sub.4.2H.sub.2O, nickel oxalate dehydrate crystals,
Ni(II)C.sub.2O.sub.4.2H.sub.2O and ferrous iron oxalate dehydrate
crystals, Fe(II)C.sub.2O.sub.4.2H.sub.2O. Ferric oxalate
pentahydrate crystals,
Fe(III).sub.2(C.sub.2O.sub.4).sub.3.5H.sub.2O may also be
crystallized and used in this approach. These compounds may be very
easily decomposed and/or reduced to the pure metal at low
temperatures (Ref 1).
[0100] Transition metal acetate crystals may also be used in this
approach, such as cobalt acetate quadrahydrate,
Co(II)(C.sub.3H.sub.3O.sub.2).sub.2.4H.sub.2O, nickel acetate
quadrahydrate, Ni(II)(C.sub.3H.sub.3O.sub.2).sub.2.4H.sub.2O
crystals and ferrous iron acetate quadrahydrate,
Fe(II)(C.sub.3H.sub.3O.sub.2).sub.2.4H.sub.2O crystals.
[0101] Superior accuracy and homogeneity of diamond to metal
composition ratio, metal alloy composition and purity may be
possible using the above described method. Another approach to
creating a mass or combination of diamond powder and metal(s),
however, involves chemical reaction(s) to form and/or precipitate
the precursor compound(s) for the metal in liquid in the presence
of diamond powder in suspension, as shown in FIG. 5 column 2. Here
the precursor is significantly insoluble in the chosen suspension
liquid. The reactants to form the precipitated precursor are
introduced into the diamond suspension by adding solutions of
soluble compounds. One or more of these solutions is a source of
the desired metal or metals.
[0102] FIG. 6 is a schematic diagram for this approach and
illustrates a solution of a compound which is a source of metal
atoms or ions, 16, is simultaneously added together with a solution
of reactants, 17, to a continuously stirred suspension of diamond
powder, 18. The metal source compound and reactant from solutions
16 and 17 react to form precipitate crystals or compounds which
nucleate and grow on the diamond particle surfaces. These crystals
or compounds then decorate the diamond surfaces and are
precursor(s) for pre-selected metal particles. A representative
diamond particle, 19, is illustrated with a precursor compound, 20,
which decorates the particle surface. Notable examples of this
approach may have the feature of the nucleation and growth of the
precursor compound on the surface of the diamond particles. In this
way the precursor compound(s) for the metal are attached to the
diamond surfaces and may be said to decorate said surfaces. Often
the precursor is discretely distributed and does not form a
continuous coating of the diamond particle surfaces. Some
precursors may however form continuous coats on the diamond
surfaces but on dissociation and reduction to the metallic state,
the metal particles are discrete and discontinuously distributed
and decorate the diamond surfaces. Examples of the latter are
amorphous oxides formed by reaction of metal alkoxides with water,
elaborated upon below.
[0103] To enhance the behavior of nucleation and growth of the
precursor(s) on the surfaces of the diamond particles, the surface
chemistry of the diamond particles may be deliberately chosen and
produced to suit the nucleation of the precursor(s). When the
precursor compound being precipitated has an oxy-anion such as
CO.sub.3.sup.2- or OH.sup.-, or is formed by polycondensation,
hydrophilic diamond surface chemistries based upon oxygen species
such as -OH, --C.dbd.O or --C--O--C-- and the like are appropriate.
Means of accentuating such diamond surface chemistries are well
known in the art and include high intensity ultrasound treatment of
the diamond in water. FIG. 6 includes a schematic representation of
a diamond particle with the surface decorated in a crystalline
precursor compound.
[0104] The precursor compound being a surface decorant or coating,
means that the carbon at the diamond surface in contact with the
precursor may act as an efficient reducing agent for the metal
precursor compound on subsequent heat treatment. This carbothermal
reduction of the precursor may be used solely or in conjunction
with other dissociative or reductive steps such as the use of
hydrogen gas as reducing agent. Where the precursor materials are
in intimate contact with the diamond surfaces as is the case with
this approach, the resultant metal will take in carbon from the
diamond surface and contain carbon in solid solution. Stable
carbides may also form at such conditions. The amount of carbon in
solid solution in the metal decorant is highly dependent upon the
temperature chosen for dissociation and reduction of the precursor.
A guide to the carbon content to be expected for particular metals
and alloys can be obtained by regard to the literature phase
diagrams of the particular metal and alloy with carbon. By way of
example to illustrate this, consider FIG. 7, which is the binary
cobalt, carbon phase diagram. The line labeled AB is the solid
solubility limit of carbon in solid face-centred-cubic cobalt. If
the dissociation, reduction of a precursor for cobalt to obtain the
metal is carried out at 700.degree. C., the carbon content of the
resulting cobalt metal will be given by this line at 700.degree.
C., namely about 0.2 atomic percent carbon, similarly if the
dissociation, reduction is carried out at 1050.degree. C., the
carbon content of the cobalt will be about 0.8 atomic percent
carbon. On quench to room conditions these carbon contents may be
metastably maintained. Thus the carbon content of the resultant
metal on the diamond surfaces may be chosen and predetermined.
[0105] Moreover, if the heat treatment conditions are maintained at
the chosen temperatures for time periods of sufficient length, the
carbon in solid solution in the metal may diffuse through the metal
decorating the surface and progressively transport carbon from the
diamond surface and come out of solution at the metal surface,
forming a deposit of non-diamond carbon. When this occurs, by
choice of temperature and time of the heat treatment, chosen and
controlled predetermined amounts of amorphous and or
nano-crystalline non-diamond carbon may be generated on the metal
surfaces. This non-diamond carbon component of the starting diamond
metal particulate mass may contribute to the efficient
crystallization of diamond which bonds the diamond particle or
grains together in the final PCD body.
[0106] Superior, especially well inter-grown diamond networks may
be produced by control of such a non-diamond carbon component of
the starting mass. Lower temperature conditions for short periods
may also be chosen, guided by the appropriate metal, carbon phase
diagram so that the non-diamond carbon is low or absent.
[0107] FIG. 8 shows schematic representations of a diamond particle
21 and metal particles decorating the surface 22 thereof. The metal
particles may comprise grains or other entities without and with
significant amounts of non-diamond carbon. The metal particles may
have their surfaces covered in amorphous non-diamond carbon, 23,
dependent on the choice of dissociation, reduction temperature.
Temperatures chosen near A in FIG. 7 do not result in detectable
non-diamond carbon. Temperatures chosen near B in FIG. 7, result in
significant formation of non-diamond carbon, which cover the metal
particles.
[0108] A character of the metal decorant particles, grains or
entities which result from this preferred approach is that they are
much smaller than the diamond particles themselves and do not form
a continuous metal coating. The metal decorants are typically from
about 10 to just over 100 nm in size. This may allow very fine, so
called sub-micron diamond particle sizes, from 0.1 to 1 micro meter
to be accurately and homogeneously combined with chosen metals.
This may provide a means of making PCD bodies of extremely fine
diamond grain size less than 1 micro meter.
[0109] A further benefit of this diamond suspension technique is
that it may be readily and conveniently scaled to that required by
commercial PCD manufacturing, where batch quantities of several
kilograms may be required. This may be done by appropriate choice
of suspension vessel sizes in conjunction with, where necessary,
heat treatment furnace designs capable of continuous operation.
[0110] The following are examples of some chemical protocols for
some metals which may be exploited using this reaction based
precursor compound generation approach, where the precursor
nucleates and grows on the diamond surface. These are examples only
and are not intended to be limiting.
[0111] Cobalt is the historically dominant metal used in PCD
material. A very convenient source solute for cobalt is crystalline
pure cobalt nitrate salt, Co(NO.sub.3).sub.2.6H.sub.2O. This is due
to cobalt nitrate's very high solubility in both water and ethyl
alcohol, which are possible solvents and suspension liquids for
some embodiments of the method. Cobalt nitrate in solution reacts
with sodium or ammonium carbonate solution, Na.sub.2Co.sub.3 or
(NH.sub.4).sub.2CO.sub.3, respectively to precipitate cobalt
carbonate crystals, CoCO.sub.3, as indicated in equation (1) below
for the sodium carbonate case.
Co ( NO 3 ) 2 soln + Na 2 CO 3 soln suspension H 2 O diamond CoCO 3
.dwnarw. + 2 NaNO 3 soln ( 1 ) ##EQU00001##
[0112] More generally, the nitrate solutions of any of the
transition metals of the periodic table may be reacted with sodium
or ammonium carbonate solution to precipitate and decorate the
surfaces of diamond particles in suspension with corresponding
water insoluble metal carbonates. The reaction with different
transition metal nitrate solutions may be carried out sequentially
or simultaneously. A mixture of solutions of nitrates may also be
employed to precipitate mixed carbonate crystals, such as
Fe.sub.xNi.sub.yC.sub.zCO.sub.3 where x+y+z=1.
[0113] FIGS. 9a and 9b are scanning electron microscope (SEM)
images of a 2 micro meter diamond particle which has been decorated
in very fine, approximately 100 nm long, whisker like cobalt
carbonate crystals. Whisker-like crystals of cobalt carbonate are
shown as decorating the surfaces of 2 micro meter sized diamond
particles. Cobalt carbonate is a precursor compound for cobalt
metal.
[0114] In order to form cobalt metal as a particulate decoration on
the diamond particle surfaces, such cobalt carbonate decorated
diamond particles may be heated in, for example, a flowing gas
mixture of 10% hydrogen in argon, at a constant temperature chosen
in the range 500 up to 1320.degree. C., for time periods of from
several tens of minutes to a few hours. If the temperature is
maintained below about 850.degree. C. for a chosen short time, no
non-diamond carbon can be detected.
[0115] FIGS. 10a and 10b are SEM images of 4 micro meter sized
diamond particles decorated in about 22 weight % (10 volume %)
cobalt after reduction in 10% hydrogen argon gas mixture at
850.degree. C. The cobalt metal decorating particles or grains vary
from about 10 to 120 nm in size. In this embodiment, no non-diamond
carbon could be detected with SEM or transmission electron
microscope (TEM) techniques.
[0116] FIG. 11 is a TEM micrograph of a diamond particle decorated
in cobalt metal particles, 26, together with a schematic diagram of
the diamond surface, 25. Each cobalt metal particle or grain, 26,
is surrounded by a non-diamond carbon halo, 27 on a hydrogenated
diamond surface, 25. The non-decorated portion of the diamond
surfaces will be hydrogen terminated after such a heat treatment as
The schematic diagram of FIG. 11 shows nano cobalt particles or
grains decorating the surface of a diamond particle after reduction
of cobalt carbonate decorant at 1050.degree. C. for two hours in
flowing 10% hydrogen/argon gas mixture. The hydrogen termination of
the diamond surface where the metal decorant is absent is a useful
feature of the some embodiments of the method when hydrogen heat
treatment is included.
[0117] Insoluble hydroxides may also be precipitated and decorated
onto diamond particle surfaces in suspension. For example nickel
hydroxide, Ni(OH).sub.2, may be generated by the reaction of nickel
nitrate solution with sodium hydroxide solution in water as
indicated in equation (2) below.
Ni ( NO 3 ) 2 soln + 2 NaOH soln suspension H 2 O diamond Ni ( OH )
2 .dwnarw. + 2 NaNO 3 soln ( 2 ) ##EQU00002##
[0118] The precipitative approach may also be applied to precursors
which combine metals such as iron, nickel, cobalt, manganese,
copper and the like as cations with the metals of the periodic
table which may readily form stable carbides such as tungsten,
molybdenum, chromium, tantalum, niobium, vanadium, zirconium,
titanium and the like, as oxy-anions.
[0119] These precursors may include tungstates, molybdates,
chromates, tantalates, niobates, vanadates, zirconates and
titanates. For example, cobalt tungstate Co(WO.sub.4).sub.2 may be
decorated onto diamond particle surfaces by the reaction of cobalt
nitrate solution with sodium tungstate solution in water as
indicated in equation (3).
Co ( NO 3 ) 2 soln + Na 2 WO 4 soln suspension H 2 O diamond CoWO 4
.dwnarw. + 2 NaNO 3 soln ( 3 ) ##EQU00003##
[0120] After reduction of the cobalt tungstate precursor, diamond
decorated cobalt and tungsten carbide results where the atomic
ratio of cobalt and tungsten is 50%. This chemical protocol may be
combined with cobalt carbonate precipitation such that any cobalt
to tungsten atomic ratio in the range 50 to close to 100% may be
generated.
[0121] An alternative chemical protocol to introduce tungsten is to
use the reaction of ammonium paratungstate
(NH.sub.4).sub.10W.sub.12O.sub.41 solution with dilute mineral
acids such nitric acid, HNO.sub.3 to precipitate tungstic oxide,
W0.sub.3 as surface decorant, which in turn is readily reduced in
the presence of diamond to form tungsten carbide particles.
Precipitation of carbonates after that of the tungstic oxide, such
as cobalt carbonate using equation (1), may be done to co-decorate
the diamond surfaces.
[0122] Two SEM micrographs are given in FIG. 12 showing the surface
of diamond particles of about 2 micro meters in size, decorated in
both cobalt, 28, and tungsten carbide, 29, particles after
reduction of such a co-decoration in 10% hydrogen, argon flowing
gas mixture at 1050.degree. C. The precursor used for the cobalt
was cobalt carbonate and the precursor used for the tungsten
carbide was tungstic oxide. TEM microscopy also detected
significant amounts of non-diamond, mainly amorphous carbon forming
a covering on the cobalt particles after such furnace conditions.
Very similar chemical protocols may be used to create decorants
involving molybdenum carbides.
[0123] Where it is desired to generate decorants involving the
carbides of the so called good carbide forming metallic elements
such as, in particular, titanium, tantalum, niobium, vanadium,
zirconium, chromium and the like a preferred chemical route is to
react dry alcoholic solutions of the metal alkoxides with water,
with the diamond powder suspended in alcohol. When this is done,
amorphous, micro-porous coats of the metal oxide form on the
diamond particles. On subsequent heat treatment these oxide coats
form discrete decorations of metal carbide on the diamond particle
surfaces. A general formula for the metal alkoxides is M(OR).sub.n,
where n is dependent upon the valency of the metal M and R is a
alkane group, such as methyl, --CH.sub.3, ethyl,
--CH.sub.2CH.sub.3, isopropyl, --C.sub.3H.sub.7 and the like. The
metal alkoxides reaction with the water to yield hydroxides, as is
given in equations (4), which then undergo polycondensation
reactions to form the amorphous oxide coats as in equation (5).
M ( OR ) n alc . soln + n H 2 O Suspension C 2 H 5 OH diamond M (
OH ) n + n ROH ( 4 ) n - 1 ( OH ) M - OH + HO - M ( OH ) n - 1
suspension C 2 H 5 OH diamond n - 1 ( HO ) M - O - M ( OH ) n - 1 +
H 2 O ( 5 ) ##EQU00004##
[0124] An example reaction for amorphous tantalum oxide,
Ta.sub.2O.sub.5 is given in equation (6) where tantalum ethoxide,
Ta(OC.sub.2H.sub.5).sub.5 is reacted with water in ethyl alcohol,
C.sub.2H.sub.5OH.
2 Ta ( OC 2 H 5 ) 5 alc . soln + 5 H 2 O suspension C 2 H 5 OH
diamomd Ta 2 O 5 .dwnarw. + 10 C 2 H 5 OH ( 6 ) ##EQU00005##
[0125] After forming such micro-porous oxide coats, precursors for
metals such as cobalt, nickel, iron, manganese and the like, such
as carbonates or hydroxides, may be precipitated into and onto the
oxide coats using the chemical reactions already indicated. Cermet
or hard metal like compositions of combined decorations of these
metals with carbides may then be formed by appropriate heat
treatment in reducing environments.
[0126] FIG. 13 shows an SEM micrograph of a multimodal diamond
powder made up of fine diamond particles (about 2 micro meters in
diameter) and coarser particles (from about 15 to 30 micro meters
in diameter), which has been decorated in 5.3 weight % tantalum
carbide (TaC) particles together with 3 weight % cobalt particles.
The precursor for the TaC was amorphous Ta.sub.2O.sub.5 deposited
onto the diamond surfaces by reaction (6). After settling, washing
and drying procedures, the diamond powder was then co-decorated
with cobalt carbonate crystals using the reaction of equation (1).
Subsequently the combined precursors were reduced to form the TaC,
cobalt metal co-decoration of FIG. 13 by heat treatment in flowing
5% hydrogen, nitrogen gas at 1100.degree. C. for 3 hours. It may be
seen in FIG. 13 that both the TaC particles 31 which appear bright
in appearance and the cobalt metal particles 30 which appear duller
in appearance are very much smaller than the diamond particles and
homogeneously cover both the coarse and fine diamond particles.
[0127] Free standing PCD bodies may then be made from masses of
diamond particles such as these, with their decorations of metal,
metal carbide combinations. In such cases the resultant metal,
metal carbide network of the PCD material may have cermet or hard
metal carbide like compositions. Some embodiments of such
compositions include WC/Co, TaC/Co and TiC/Ni.
[0128] Any of these chemical reactions to form the precursor
compound decorants on the diamond particle surfaces may be done in
sequence and applied to the pre-selected diamond powder as a whole
or to any part or component of the diamond powder in appropriate
suspension media.
[0129] The diamond powder components may be based upon mass
fractions or upon size, size distribution or any desired
combination of these. The part or component of the desired diamond
size distribution is first suspended in the liquid medium and the
chosen chemical reaction protocol(s) to decorate that component
with chosen precursor(s) carried out. Subsequently, the remaining
diamond powder component or part is added and suspended. The act of
suspension and attendant vigorous stirring provides an efficient
means of homogeneously mixing the decorated and undecorated
portions of the diamond powder. In this way chosen pre-selected
components of the diamond powder may be decorated in chosen metal
with the other components remaining undecorated after subsequent
dissociation/reduction of the precursor(s) to the metal(s).
[0130] Also, differing amounts of the same precursor may be
decorated onto different mass and/or size fractions of the diamond
powders by sequential adding of the components to the suspension,
reaction vessel.
[0131] Alternatively, different amounts of and/or types of
precursor(s) may be decorated on chosen diamond powder components
in separated suspension vessels. Again a final combination of the
suspensions can provide efficient homogeneous mixing of these
components.
[0132] In addition, any of the diamond powder fractions or
components may be made up of diamond particles differing in respect
to diamond type. Diamond particles of differing type are
distinguished here in regard to the variation in structure and/or
quantity of lattice defects known in the art. In particular
nitrogen related lattice defects are exemplary, which are known to
affect the material properties of diamond. A convenient way to
differentiate diamond type is to use natural diamond as opposed to
standard synthetic diamond, natural diamond having typically
aggregated nitrogen lattice defects as compared to standard
synthetic diamond which contains single atoms of nitrogen
substituting for carbon atoms at levels typically of about 100
ppm.
[0133] These means of associating different amounts and/or
different metal compositions with different diamond fractions or
components may provide a highly accurate and versatile way of
manipulating the diamond sintering mechanisms at the local scale of
the diamond particles and in turn engendering manipulation of
structure and composition at such a scale. For example, if certain
fractions remain free of metal during initial application of load
and heat in the high pressure apparatus, diamond particle, point to
surface contact for the particles of such fractions can be
un-fettered by metal decoration leading to enhanced plastic
deformation of such particles. This in turn may be possible to
facilitate local enhanced diamond to diamond bonding. Further it
may be possible to associate immovable "unmelted" particles with
some diamond particle fractions and not others. For example metal
carbide particles such as tungsten carbide, titanium carbide,
tantalum carbide and the like may be decorated onto and associated
only with a particular size fraction of the diamond. A vast number
of PCD free standing body embodiments with novel compositions,
structures and properties may in this way be generated using such
prepared decorated diamond powder, metal combinations or
masses.
[0134] The homogeneous mass of diamond and metal is consolidated to
form a so-called "green body" of desired size and 3-dimensional
shape. Means of forming a green body include simple die set
compaction, isostatic compaction, gel casting, injection moulding
and the like and any other technique or procedure known in the art.
Where isostatic compaction is used, hot isostatic procedures are
preferred due to superior strength of the green bodies occurring.
Preferences amongst such means to produce green bodies may be
determined by the degree to which each technique can maintain
general compositional and special homogeneity. Temporary organic
binders such as methyl cellulose, polyvinyl alcohol, polyvinyl
bitherol and the like may be employed to aid with green body
integrity and of sufficient strength for practical handling.
[0135] The homogeneous green body is then encapsulated such that it
may be contained and isolated from the pressure and temperature
media and structures of high pressure and high temperature cells,
capsules or reaction chambers as well known in the art of
polycrystalline diamond manufacture. Where the 3-dimensional shape
of the desired PCD body is geometrically simple canisters made from
refractory metals may be used. Where general convex 3-dimensional
shapes of the PCD body are desired, appropriate canisters may be
moulded from refractory metals. The encapsulation material or metal
canisters are preferably organised so that they may be evacuated
and sealed again as had been established and is well known in the
art. Removing atmospheric gases from the porosities of the green
body and sealing the green body's encapsulation materials to
maintain a vacuum in the porosities is a preference. Prior to the
sealing of the encapsulation materials or canisters or temporary
organic binders which may have been employed in forming the green
bodies must be removed by procedures such as heat treatment and the
like.
[0136] The green bodies in their sealed encapsulations are then
assembled into a cell or capsule comprising pressure and
temperature transmitting media and heating element structures as
known in the art. The design of the cell or capsule is chosen so
that pressure and temperature gradients experienced by the green
body at its sintering conditions are minimised. Low shear strength
pressure transmitting materials such as ionic salts often combined
with ceramic powders may be used, for example, sodium chloride
combined with zirconia, ZrO.sub.2. These measures assist in
enabling the homogeneity of the structure and composition of the
green body to be translated into corresponding homogeneity of the
PCD body on sintering. Moreover, in this regard, the pressure and
temperature time cycle may be chosen so that simultaneous and or
symmetrical melting of the metal component in the green body
occurs.
[0137] A further precaution to engender stress free and crack free
standing PCD bodies may be to release the pressure during the end
phase of the manufacturing cycle with the maintenance of sufficient
temperature to maintain the pressure transmitting media of the cell
or capsule in as plastic a state as possible. The homogeneity of
the green body together with the precautions outlined above is
necessary so that the shrinkage during sintering of the diamond
particles is equal in all orthogonal directions. In this way, the
pre-selected 3-dimensional shape of the green body may be
maintained and translated to the final free standing PCD body. In
addition, the degree and magnitude of the equi-directional
shrinkage for each variant or embodiment of PCD material and body
may be empirically determined. Some of the embodiments of the
methods described herein thus may allow free standing, macro stress
free PCD bodies of net or near net size and shape to be
generated.
[0138] This feature of net or near net size and shape may provide
practical and commercial viability and attractiveness as further
sizing and shaping is minimized or not required.
[0139] The green bodies generated by the above methods are
subjected to high pressure, high temperature conditions for
appropriate times to cause sintering of the diamond particles and
form the free standing PCD bodies. Each specific chosen metallic
composition may require specific temperature, pressure and time
cycles to be determined empirically such that the re-crystallized
diamond is of good quality crystal and is largely defect free.
Typical pressure and temperature conditions are in the range of 5
to 15 GPa and in the range of 1200 to 2500.degree. C. respectively.
Preferably pressures in the range 5.5 to 8.0 GPa along with
temperatures in the range 1350 to 2200.degree. C. are used.
[0140] Some embodiments are described in more detail below with
reference to the examples, which are not intended to be
limiting.
EXAMPLES
Example 1
[0141] PCD free standing, macro residual stress free, bodies each
comprising an intergrown diamond network with a monomodal, mean
grain size of close to 1 micro meter with an inter-penetrating
metallic network made up of independently pre-selected alloy made
up of 95 weight % cobalt and 5 weight % nickel were manufactured.
The overall diamond content was pre-selected independently of the
diamond size distribution and alloy composition to be about 93
volume % with the metal being a corresponding 7 volume %. The PCD
body was a right cylinder 13 mm in diameter and 8 mm long. The
method as outlined in FIG. 5 column 2 was used whereby the
precursor for the metallic component of the PCD body was reactively
created in a water liquid suspension of starting diamond particles
and was caused to nucleate and grow on the surfaces of the starting
diamond particles. The following sequential steps and procedures
were carried out in order to so manufacture this PCD free standing
body. [0142] a) A mass of combined diamond particles and metallic
materials was created in the following manner. [0143] 100 g of
monomodal diamond powder of mean particle size of about 1 micro
meter, extending from about 0.75 to 1.25 micro meters, was
suspended in 2.5 litres of de-ionised water. The size distribution
had only one maximum at the average particle size of 1 micro meter.
This type of size distribution had been designated as monomodal.
The diamond powder had previously been produced by crushing and
classifying procedures known in the art, the source material for
which was conventional, commercial synthetic type Ib diamond
abrasive. The diamond powder had also been previously heated in a
mixture of sulphuric acid and nitric acid which after washing in
de-ionised water ensured that the powder was now hydrophilic with a
surface chemistry dominated by oxygen molecular species such as
--OH, --C--O--C--, --C.dbd.O and the like. To the suspension a
mixed aqueous solution of cobalt and nickel nitrate and an aqueous
solution of sodium carbonate were slowly and simultaneously added
while the suspension was vigorously stirred. Equation (7) below was
used to calculate the required amounts of cobalt and nickel
nitrates.
[0143]
0.95Co(NO.sub.3).sub.2+0.05Ni(NO.sub.3).sub.2+Na.sub.2CO.sub.3=Co-
.sub.0.95Ni.sub.0.05CO.sub.3+2NaNO.sub.3 (7) [0144] The mixed
cobalt and nickel nitrate aqueous solution was made by dissolving
89.25 g of cobalt nitrate hexahydrate,
Co(NO.sub.3).sub.2.6H.sub.2O, crystals and 4.71 g of nickel nitrate
hexahydrate, Ni(NO.sub.3).sub.2.6H.sub.2O, crystals in 200 ml of
de-ionised water. In this way the atomic ratio of cobalt:nickel was
95:5. The sodium carbonate aqueous solution was made by dissolving
35 g of sodium carbonate, Na.sub.2CO.sub.3, in 200 ml of de-ionised
water. The mixed cobalt, nickel nitrate and sodium carbonate
reacted to form mixed cobalt nickel carbonate precipitate
crystals.
[0145] The mixed cobalt nickel carbonate precursor, nucleated and
grew on the diamond particle surfaces and formed a discrete set of
particles decorating the surfaces. The sodium nitrate product of
the reaction, equation 7, being highly soluble in water was then
removed by a few repeated cycles of decantation and washing in
de-ionised water. After a final wash in pure ethyl alcohol the
precursor decorated diamond powder was dried under vacuum at
60.degree. C.
[0146] The dried powder was then placed in an alumina ceramic boat
with a loose powder depth of about 5 mm and heated in a flowing
stream of argon gas containing 5% hydrogen. The top temperature of
the furnace was 1050.degree. C. which was maintained for 2 hours
before cooling to room temperature. This furnace treatment
dissociated and reduced the mixed cobalt-nickel carbonate to form
alloy particles decorating the surfaces of the diamond particles.
In this way it was ensured that the alloy metal particles were
always smaller than the diamond particles with the alloy being
homogeneously distributed.
[0147] FIG. 15 is an SEM micrograph showing the fine cobalt nickel
carbonate crystals decorating the 1 micron diamond particle
surfaces. It may be seen that the precursor crystals or particles
are all significantly smaller than the diamond particles.
[0148] FIG. 16 is an SEM micrograph showing the alloy metal
particles decorating the diamond particle surfaces. The alloy metal
particles comprise 95% cobalt, 5% nickel alloy metal particles
which are shown as decorating the surfaces of 1 micron diamond
particles. The conditions of the heat treatment also caused
amorphous non-diamond carbon to form at the surfaces of the
cobalt-nickel alloy particles. The resultant powder mass had a
black appearance. The powder mass was stored under dry nitrogen in
an air-tight container. [0149] b) 4.4 g fractions of the
diamond-metal powder mass were then pre-compacted into a niobium
cylindrical canister using a uni-axial hard metal compaction die. A
second niobium cylindrical canister of slightly larger diameter was
then slid over the first canister in order to surround and contain
the pre-compacted powder mass. The free air in the porosities of
the pre-compacts was then evacuated and the canisters sealed under
vacuum using an electron beam welding system known in the art. The
canister assemblies were then subjected to cold isostatic
compaction at a pressure of 200 MPa to consolidate to a high green
density and to eliminate spatial density variations. In this way
homogeneous green bodies were produced with measured densities of
about 2.7 gcm.sup.-3, which corresponds to a porosity of
approximately 35% by volume. [0150] c) Each encapsulated
cylindrical green body was then placed in an assembly of
compactable ceramic, salt components suitable for high pressure
high temperature treatment as well established in the art. The
material immediately surrounding the encapsulated green body was
made from very low shear strength material such as sodium chloride.
This provides for the green bodies being subjected to pressures
which approach a hydrostatic condition. In this way pressure
gradient induced distortions of the green body may be mitigated.
[0151] The green bodies were subjected to a pressure of 7.5 GPa and
a temperature of approximately 1950.degree. C. for 1 hour using a
belt type high pressure apparatus as well established in the art.
During the end phase of the high pressure high temperature
procedure the temperature was slowly reduced over several minutes
to approximately 750.degree. C., maintained at this value and then
the pressure was reduced to ambient conditions. The high pressure
assembly was then allowed to cool to ambient conditions before
extraction from the high pressure apparatus. This procedure during
the end phase of the high pressure high temperature treatment was
thought to allow the surrounding salt media to remain in a plastic
state during the removal of pressure and so prevent or inhibit
shear forces bearing upon the now sintered PCD body. The final
dimensions of the free standing PCD cylindrical body were then
measured and the shrinkage calculated. [0152] d) SEM image analysis
was undertaken on sectioned and polished samples of the PCD bodies.
These showed a well sintered continuous network of diamond and an
interpenetrating network of metal. There was an absence of other
material phases such as oxides and carbides. In order to assess the
homogeneity of the microstructure, SEM image fields of at least 10
times by 10 times the average grain size for sections and polished
samples taken in both axial and diametral directions were
considered and compared. For this specific example, where the
average grain size was close to 1 micro meter, ten micro meters by
ten micro meters image fields were compared from place to place on
the polished cross-sections. The magnification employed was
.times.10,000. Across the axial section, 9 fields were chosen to be
representative of the centre and the edge positions. In addition,
across the diametral section a further 5 centre to edge positions
were compared. In terms of the image contrast and geometric pattern
of the diamond grains and metal pool, no difference could be seen.
No grains greater than 3 micro meters were found. It was therefore
concluded that the PCD material microstructure was invariant from
image to image showing that the material was homogeneous above this
scale, i.e., above the scale of 10 times the average grain size, in
this particular case above the 10 micro meter scale. As explained
in the previous sections, since this specific example was made from
one composition of PCD material, then it implies that the free
standing PCD body was macroscopically stress free above this scale.
[0153] To check this, a biaxial strain gauge was attached to one
face of a PCD cylinder and the cylinder cut in half midway along
its axis using electro discharge machining (EDM). It was noted that
no change of strain was observed. If the PCD free standing body had
a macroscopic residual stress distribution across its dimension,
then removing half of the body would inevitably have resulted in a
strain response. Since no strain response was observed it was
concluded and confirmed that the free standing body was
macroscopically stress free. [0154] A finite element method was
used in order to numerically assess the micro residual stress
magnitude for this composition of PCD material. The elastic modulus
assumed in the calculations for diamond and the 95% Co-5% Ni alloy
were 1050 and 200 GPa, respectively. The difference in linear
thermal expansion coefficient was 11 ppm .degree. K.sup.-1. The
linear thermal expansion coefficient for this alloy falls within
the range 10 to 14 ppm .degree. K.sup.-1. The micro residual stress
for this particular PCD material would therefore be considered by
the previous definitions to be in the "high" category. The
calculated micro residual principal tensile stress magnitude in the
metallic network using the Finite Element analysis with its
attendant assumptions was 2300 MPa which was consistent with the
micro residual stress being considered as high.
Example 2
[0155] PCD free standing, macro residual stress free, bodies each
comprising an intergrown multimodal diamond network where the grain
size distribution extends from about 2 micro meters to about 30
micro meters with a mean grain size of close to 10 micro meter
together with an inter-penetrating metallic network made up of pure
cobalt were manufactured. The overall diamond content was
pre-selected independently of the diamond size distribution and
metal composition to be about 91 volume % with the metal being a
corresponding 9 volume %. The PCD body was a right cylinder 16 mm
in diameter and 16 mm long. The method outlined in FIG. 5 column 2
was used whereby the precursor for the metallic component of the
PCD body was reactively created in a water liquid suspension of
starting diamond particles and was caused to nucleate and grow on
the surfaces of the starting diamond particles. The following
sequential steps and procedures were carried out in order to so
manufacture this PCD free standing body. [0156] a) A mass of
combined diamond particles and metallic materials was created in
the following manner.
[0157] 100 g of diamond powder was suspended in 2.5 litres of
de-ionised water. The diamond powder comprised 5 separate so-called
monomodal diamond fractions each differing in average particle
size. The diamond powder was thus considered to be multimodal. The
100 g of diamond powder was made up as follows: 5 g of average
particle size 1.8 micro meters, 16 g of average particle size 3.5
micro meters, 7 g of average particle size 5 micro meters, 44 g of
average particle size 10 micro meters and 28 g of average particle
size 20 micro meters. This multimodal particle size distribution
extended from about 1 micro meter to about 30 micro meters.
[0158] The diamond powder had been rendered hydrophilic by prior
acid cleaning and washing in de-ionised water. To the suspension an
aqueous solution of cobalt nitrate and a separate aqueous solution
of sodium carbonate were simultaneously slowly added while the
suspension was vigorously stirred. The cobalt nitrate solution was
made by dissolving 123.5 grams of cobalt nitrate hexahydrate
crystals, Co(NO.sub.3).sub.2.6H.sub.2O, in 200 ml of de-ionised
water. The sodium carbonate solution is made by dissolving 45 g of
pure anhydrous sodium carbonate, Na.sub.2CO.sub.3 in 200 ml of
de-ionised water. The cobalt nitrate and sodium carbonate reacted
in solution as per equation (1), in the presence of the suspended
diamond powder and cobalt carbonate crystals nucleated and grew on
the diamond particle surfaces. The cobalt carbonate precursor
compound for cobalt, took the form of whisker shaped crystals
decorating the diamond particle surfaces identical in form to those
shown in FIGS. 9a and b. The sodium nitrate product of reaction was
removed by a few cycles of decantation and washing in de-ionised
water. The powder was finally washed in pure ethyl alcohol, removed
from the alcohol by decantation and dried under vacuum at
60.degree. C.
[0159] The dried powder was then placed in an alumina ceramic boat
with a loose powder depth of about 5 mm and heated in a flowing
stream of argon gas containing 5% hydrogen. The top temperature of
the furnace was 700.degree. C. which was maintained for 2 hours
before cooling to room temperature. This furnace treatment
dissociated and reduced the cobalt carbonate precursor to form pure
cobalt particles decorating the surfaces of the diamond particles.
In this way it was ensured that the cobalt particles were always
smaller than the diamond particles with the cobalt being
homogeneously distributed. The conditions of the heat treatment
were chosen with reference to the cobalt carbon phase diagram of
FIG. 7. At 700.degree. C. it may be seen that the solid solubility
of carbon in cobalt is low. Thus the formation of amorphous
non-diamond carbon at this temperature is very low and no
non-diamond carbon could be detected in the final diamond-metal
particulate mass. The resultant powder mass had a pale light grey
appearance. The powder mass was stored under dry nitrogen in an
air-tight container. [0160] b) 13.4 g fractions of the
diamond-metal powder mass were then pre-compacted into a niobium
cylindrical canister using a uni-axial hard metal compaction die.
Right cylindrical green bodies with homogeneous porosity
distribution, encapsulated and vacuum sealed in niobium canisters
were then produced using the procedures specified in Example 1. The
diameter and length of each encapsulated green body cylinder were
measured and the diameter and length of each cylindrical green body
itself calculated using knowledge of the wall thicknesses of the
canisters. Both the average diameter and length of the green body
cylinders were calculated to be 18.25 mm. [0161] c) Each of the
encapsulated green bodies was then subjected to high pressure and
high temperature conditions in order to cause diamond particle to
particle bonding via partial diamond recrystallisation. The
procedures specified in Example 1 were used except that the
pressure and temperature conditions were significantly lower,
specifically 5.6 GPa and 1400.degree. C. Again, the temperature
during the return to room pressure at the end stage of the
manufacturing cycle was maintained close to about 750.degree. C.
This precaution was intended to mitigate any possible shear
stresses being applied during the end stage of the cycle. [0162] d)
SEM image analysis was undertaken on sectioned and polished samples
of the PCD bodies. These showed a well sintered continuous network
of diamond and an interpenetrating network of metal. There was an
absence of other material phases such oxides and carbides. Hundred
micro meters by hundred micro meters image fields were compared
from place to place on the polished cross-sections. It was found
that the PCD material microstructure was invariant from image to
image showing that the material was homogeneous above this scale.
This implies that the free standing PCD body is macroscopically
stress free above this scale. [0163] A finite element method was
used in order to numerically assess the micro residual stress
magnitude for this composition of PCD material. The elastic modulus
assumed in the calculations for diamond and the Co metallic network
was 1050 and 200 GPa, respectively. The linear coefficient of
thermal expansion for cobalt is 13 ppm .degree. K.sup.-1, which
falls in the range of 10 to 14 ppm .degree. K.sup.-1. The
calculated micro residual principal tensile stress magnitude in the
metallic network using the Finite Element analysis with its
attendant assumptions was in excess of 2000 MPa which was
consistent with the micro residual stress being considered as
high.
[0164] The dimensions of each final cylindrical PCD free standing
body were measured at various positions along the length of the
cylinders and the squareness was checked. It was evident that only
minimal geometric distortion had occurred indicating the
achievement of near net shape. The average shrinkage of both
diameter and length due to the sintering of the material was 12%.
Knowledge of this shrinkage factor for this particular PCD material
allows the final dimension to be pre-selected, thus making near net
sizing possible.
Example 3
[0165] PCD free standing, macro residual stress free, bodies each
comprising an intergrown diamond network where the grain size
distribution extends from about 2 micro meters to about 30 micro
meters, with a mean grain size of close to 10 micro meter together
with an inter-penetrating metallic network made up of pure cobalt
were manufactured. The overall diamond content was pre-selected
independently of the diamond size distribution and metal
composition to be about 95 volume % with the metal being a
corresponding 5 volume %. The preparation method in this example
was changed compared to that of Example 2 with the intention of
creating favourable micro structural consequences related to degree
of intergrowth and contiguity of the diamond grains. The basis of
the change of preparation method was that the precursor compound
for the metal component of the PCD was decorated onto a
pre-selected portion of the diamond powder. In this example, the
pre-selected portion upon which all of the metal was decorated was
made up of the three coarsest size fractions which also correspond
to about half of the total diamond particle surface area. [0166] a)
A mass of combined diamond particles and metallic materials was
created in the following manner. [0167] Two portions of diamond
powder were used totalling 100 g. One portion of 79 g of diamond
powder made up of 7 g of average particle size 5 micro meters, 44 g
of average particle size 10 micro meters and 28 g of average
particle size 20 micro meters was suspended in 2.5 litres of
de-ionised water. This portion of the diamond powder comprised 3
separate so-called monomodal diamond fractions each differing in
average particle size. The diamond particle surface area of this
portion of the diamond powder corresponded to approximately 50% of
the total surface area of all the powder. The remaining portion of
total mass 21 g of diamond powder made up of 5 g of average
particle size 1.8 micro meters and 16 g of average particle size
3.5 micro meters was retained. To the suspension an aqueous
solution of cobalt nitrate and a separate aqueous solution of
sodium carbonate were simultaneously slowly added while the
suspension was vigorously stirred. The cobalt nitrate solution was
made by dissolving 65.7 g of cobalt nitrate hexahydrate crystals,
Co(NO.sub.3).sub.2.6H.sub.2O, in 200 ml of de-ionised water. The
sodium carbonate solution was made by dissolving 24 g of pure
anhydrous sodium carbonate, Na.sub.2CO.sub.3 in 200 ml of
de-ionised water. It was assumed that the cobalt nitrate and sodium
carbonate reacted in solution as per equation (1). In the presence
of the suspended diamond powder, cobalt carbonate crystals
nucleated and grew on the diamond particle surfaces. While
continuing the stirring of this suspension, the remaining 21 g
portion of diamond powder was added. Since the reaction generating
the cobalt carbonate precursor was complete prior to this addition,
this fine sized diamond powder portion remained un-decorated.
Incorporating this portion in suspension served to homogeneously
mix the two portions of diamond powder. A dry particulate mass of
powder was then made using the washing and drying procedures of
Example 2. [0168] b) Free standing PCD bodies were then made using
this mass of combined diamond and cobalt using the green body
consolidation and high pressure high temperature sintering
procedures as described in Example 2. [0169] c) SEM image analysis
procedures were carried out on sectioned and polished samples. It
was concluded that excellent diamond grain contiguity with good
general homogeneity had resulted.
Example 4
[0170] PCD free standing, macro residual stress free, bodies were
made with the same diamond composition and size distribution as in
Example 2. The metal was pre-selected independently to be 9 volume
percent pure Nickel. As in Example 2, the method as outlined in
FIG. 5 column 2 was used. The following sequential steps and
procedures were carried out in order to so manufacture this PCD
free standing body, differing from Example 2 in that the precursor
compound was a hydroxide as opposed to a carbonate. [0171] a) A 100
g of diamond powder identical to that used in Example 2 was
suspended in 2.5 litres of de-ionised water. While continuously
stirring the suspension, an aqueous solution of nickel nitrate was
slowly added. Simultaneously an aqueous solution of sodium
hydroxide was slowly added. The nickel nitrate solution was made by
adding 96.8 g of nickel nitrate hexahydrate,
Ni(NO.sub.3).sub.2.6H.sub.2O, to 200 ml of de-ionised water. The
sodium hydroxide solution was made by adding 27 g of pure sodium
hydroxide crystals, NaOH, to 200 ml of de-ionised water. Insoluble
nickel hydroxide, Ni(OH).sub.2, was precipitated as per equation
(2), and decorated the surfaces of the diamond particles. In this
case nickel hydroxide was the precursor compound for nickel metal.
A dry mass of the diamond powder decorated in the nickel hydroxide
was then obtained by a few cycles of settling, washing in pure
water and drying under vacuum at 60.degree. C. The mass of diamond
powder decorated in nickel hydroxide was then heated in a vacuum
furnace at a top temperature of 800.degree. C. for 1 hour. The
nickel hydroxide was converted into nickel metal which decorated
the diamond particle surfaces. The solid solubility of carbon in
nickel at 800.degree. C. is low and very little non-diamond
amorphous carbon was formed. The resulting mass had a grey
appearance. [0172] b) Right cylindrical green bodies were then made
using the same procedures as given in Example 2. [0173] c) Each of
the encapsulated green bodies was then subjected to high pressure
and high temperature conditions in order to cause diamond particle
to particle bonding via partial diamond recrystallisation. The
pressure, temperature, time cycle was identical to that of Example
2. [0174] d) SEM image analysis was carried out and showed a well
sintered continuous network of diamond, with homogeneity of diamond
and nickel. There was an absence of other material phases such
oxides and carbides, in particular, indicating the presence of only
pure nickel metal. The SEM images showing fields of about
100.times.120 micro meters taken from various parts of polished
cross sections were identical in regard to the distribution of
diamond and metal. This indicated that above this scale, the
material was homogeneous and could be considered to be
macroscopically stress free.
Example 5
[0175] PCD free standing, macro residual stress free, bodies were
made with the same diamond composition and size distribution as in
Examples 2 and 4. The metal was pre-selected independently to be 9
volume percent of a iron, 33 weight percent nickel alloy. As in
Examples 2 and 4, the method as outlined in FIG. 5 column 2 was
used. The following sequential steps and procedures were carried
out in order to so manufacture this PCD free standing body. The
precursor compound was a mixed ferrous, nickel carbonate. [0176] a)
A 100 g of diamond powder identical to that used in Examples 2 and
4 was suspended in 2.5 litres of de-ionised water. While
continuously stirring the suspension, an aqueous mixed solution of
ferrous nitrate and nickel nitrate was slowly added. Simultaneously
an aqueous solution of sodium carbonate was slowly added. The mixed
ferrous nitrate, nickel nitrate solution was made by adding 79.4 g
of ferrous nitrate hexahydrate crystals,
Fe(NO.sub.3).sub.2.6H.sub.2O, and 37.6 g of nickel nitrate
hexahydrate, Ni(NO.sub.3).sub.2.6H.sub.2O, to 200 ml of de-ionised
water. The sodium carbonate solution was made by adding 44 g of
pure anhydrous sodium carbonate, Na.sub.2CO.sub.3, to 200 ml of
de-ionised water. A mixed ferrous iron, nickel carbonate, of
nominal formula Fe.sub.0.67Ni.sub.0.33CO.sub.3 was precipitated and
decorated the diamond particle surfaces. A dry particulate mass of
diamond decorated in this alloy precursor was then produced by
several cycles of settling decantation and washing in pure water
followed by drying under vacuum at 60.degree. C. The mass of
diamond powder decorated in the mixed carbonate was then heated in
a vacuum furnace at a top temperature of 850.degree. C. for 1 hour.
The mixed carbonate was converted into an iron nickel alloy which
decorated the diamond particle surfaces. A small sample of
resulting particulate mass was taken and dissolved in nitric acid
in order that chemical analysis techniques such as inductively
coupled plasma spectroscopy (ICP) could be applied to determine and
confirm the alloy composition. The alloy was shown to be iron, 33%
nickel and therefore accurately as pre-selected. [0177] b) Right
cylindrical green bodies were then made using the same procedures
as given in Example 2. [0178] c) Each of the encapsulated green
bodies was then subjected to high pressure and high temperature
conditions in order to cause diamond particle to particle bonding
via partial diamond recrystallisation. The pressure, temperature,
time cycle was identical to that of Example 2 and 4. [0179] d) SEM
image analysis was carried out and showed a well sintered
continuous network of diamond, with homogeneity of diamond and
metal alloy. There was an absence of other material phases such
oxides and carbides, in particular, indicating the presence of only
iron nickel alloy metal. The SEM images showing fields of about
100.times.120 micro meters taken from various parts of polished
cross sections were identical in regard to the distribution of
diamond and metal. This indicated that above this scale, the
material was homogeneous and could be considered to be
macroscopically stress free.
[0180] A finite element method was used in order to numerically
assess the micro residual stress magnitude for this composition of
PCD material. It is known from the literature (ref. 4) that iron
33% nickel with 0.6% carbon in solid solution is a low thermal
expansion alloy which exhibits a linear coefficient of thermal
expansion of 3.3 ppm .degree. K.sup.-1 at and near room temperature
which falls within the range of less than 5 ppm .degree. K.sup.-1.
The difference in thermal expansion coefficient between diamond and
this alloy was therefore small. The literature elastic modulus for
this alloy is about 150 GPa. However, the difference in elastic
modulus between diamond and this alloy remains high and is typical
of transition alloys. During the pressure and temperature release,
at the end of the manufacturing cycle, it would therefore be
expected that the residual stress would predominantly originate
from the differential expansion of the metal relative to diamond on
pressure release. The micro residual stress in the metal would then
be compressive in nature. The calculated micro residual principal
compressive stress magnitude in the metallic network using the
Finite Element analysis with its attendant assumptions was in
excess of -2000 MPa. This Finite Element analysis clearly indicates
that using certain accurately produced low expansion alloys that
the micro residual stress can be compressive. This is an aspect of
the present invention.
Example 6
[0181] PCD free standing, macro residual stress free, bodies were
made with the same diamond composition and size distribution as in
Examples 2, 4 and 5. The metallic network was pre-selected
independently to be 9 volume percent of the PCD, and to be a
cobalt, tungsten carbide cermet. This cermet itself was
pre-selected to be made up of 78 volume percent cobalt and 22
volume percent tungsten carbide (66.8 weight percent cobalt, 33.2
weight percent tungsten carbide).
[0182] As in Examples 2, 4 and 5, the method as outlined in FIG. 5
column 2 was used. The following sequential steps and procedures
were carried out in order to so manufacture this PCD free standing
body. The precursor compounds used were cobalt carbonate and
tungstic oxide, WO.sub.3. [0183] a) 100 g of diamond powder
identical to that used in Examples 2, 4 and 5 was suspended in 2.5
litres of de-ionised water. While continuously stirring the
suspension, an aqueous solution of cobalt nitrate was slowly added.
Simultaneously an aqueous solution of sodium carbonate was slowly
added. Cobalt carbonate was precipitated and decorated the diamond
particle surfaces. While maintaining this decorated diamond powder
in suspension, an aqueous solution of ammonium paratungstate was
slowly added. Simultaneously, dilute nitric acid was added.
Tungstic oxide, WO.sub.3, was precipitated and decorated the
diamond particle surfaces. In this way, the diamond surfaces were
co-decorated in both cobalt carbonate and tungstic oxide. The
cobalt nitrate solution was made by adding 96.3 g of cobalt nitrate
hexahydrate crystals, Co(NO.sub.3).sub.2.6H.sub.2O to 200 ml of
de-ionised water. The sodium carbonate solution was made by adding
35.5 g of pure anhydrous sodium carbonate, Na.sub.2CO.sub.3, to 200
ml of de-ionised water. The ammonium paratungstate solution was
made by adding 12.9 g of ammonium paratungstate pentahydrate,
(NH.sub.4).sub.10(W.sub.12O.sub.41).5H.sub.2O to 200 ml of
de-ionised water. The dilute nitric acid solution was made by
adding AR grade concentrated nitric acid to 200 ml of de-ionised
water to provide a concentration of 0.25 mols per litre. The
particulate diamond mass was then washed free of the sodium and
ammonium nitrate by-product of the reaction and any un-reacted
soluble material by several cycles of settling, addition of pure
de-ionised water and decantation. Finally, the diamond particulate
mass, co-decorated in cobalt carbonate and tungstic oxide was dried
under vacuum at 60.degree. C. The dried powder was then placed in
an alumina ceramic boat with a loose powder depth of about 5 mm and
heated in a flowing stream of argon gas containing 5% hydrogen. The
top temperature of the furnace was 1000.degree. C. which was
maintained for 2 hours before cooling to room temperature. This
furnace treatment dissociated and reduced the cobalt carbonate
precursor to form pure cobalt particles. The tungstic oxide
precursor was reduced and the resultant tungsten reacted with some
of the diamond present to form tungsten carbide. The surfaces of
the diamond particles were in this way now co-decorated in cobalt
and tungsten carbide particles. These particles were always smaller
than the diamond particles and extremely well and homogeneously
distributed. [0184] A sample of the particulate mass was heat
treated in acid to dissolve the metallic component and ICP chemical
analysis carried out. The atomic ratio of cobalt to tungsten was
found to be approximately 68% Co, 32% W which is consistent with
the pre-selected choice of cermet composition, namely, 78 volume
percent cobalt and 22 volume percent tungsten carbide. [0185] b)
Right cylindrical green bodies were then made using the same
procedures as given in Example 2. [0186] c) Each of the
encapsulated green bodies was then subjected to high pressure and
high temperature conditions in order to cause diamond particle to
particle bonding via partial diamond recrystallisation. The
procedures specified in Example 1 were used except that the
pressure and temperature conditions were significantly lower,
specifically 5.6 GPa and 1400.degree. C. as used in Example 2.
Again, the temperature during the return to room pressure at the
end stage of the manufacturing cycle was maintained close to about
750.degree. C. This precaution was intended to mitigate any
possible shear stresses being applied during the end stage of the
cycle. [0187] d) SEM image analysis was carried out and showed a
well sintered continuous network of diamond, with an
interpenetrating cermet network comprising fine tungsten carbide
grains bonded with cobalt. There was an absence of other material
phases such oxides. The SEM images showing fields of about
100.times.120 micro meters taken from various parts of polished
cross sections were identical in regard to the distribution of
diamond and cermet network. This indicated that above this scale,
the material was homogeneous and could be considered to be
macroscopically stress free. [0188] A finite element method was
used in order to numerically assess the micro residual stress
magnitude for this composition of PCD material. The linear
coefficient of thermal expansion for the particular cermet network
(66.8 weight percent cobalt, 33.2 weight percent carbide) produced
was estimated from the literature values for cobalt and tungsten
carbide to be 10.6 ppm .degree. K.sup.-1. This falls within the
range of 10 to 14 ppm .degree. K.sup.-1. Similarly, the modulus of
elasticity was estimated to be 360 GPa. The calculated micro
residual tensile stress magnitude in the metallic/cermet network
was in the range 1800 to 2200 MPa which is considered to be in the
high range as expected for this composition of PCD material but,
nevertheless, clearly less than the magnitude calculated for the
cobalt case of Example 2.
Example 7
[0189] PCD free standing bodies each comprising an intergrown
diamond network and an interpenetrating metallic network were made
using a starting diamond powder with an average particle size of
0.5 micro meters. The metallic network was pre-selected to be 11
volume percent of the PCD material with the metal independently
pre-selected to be a 50% by weight nickel, 50% by weight copper
alloy. The PCD body was a right cylinder 13 mm in diameter and 8 mm
long. The method as outlined in FIG. 5 column 2 was used whereby
the precursor for the metallic component of the PCD body was
reactively created in a water liquid suspension of starting diamond
particles and was caused to nucleate and grow on the surfaces of
the starting diamond particles. The following sequential steps and
procedures were carried out in order to so manufacture this PCD
free standing body. [0190] a) 60 g of diamond powder with an
average particle size close to 0.5 micro meters was suspended in
2.0 litres of de-ionised water. While continuously stirring the
suspension, an aqueous mixed solution of copper nitrate and nickel
nitrate was slowly added. Simultaneously an aqueous solution of
sodium carbonate was slowly added. The mixed copper nitrate, nickel
nitrate solution was made by adding 26 g of anhydrous copper
nitrate, Cu(NO.sub.3).sub.2, and 40 g of nickel nitrate
hexahydrate, Ni(NO.sub.3).sub.2.6H.sub.2O, to 200 ml of de-ionised
water. The sodium carbonate solution was made by adding 35 g of
pure anhydrous sodium carbonate, Na.sub.2CO.sub.3, to 200 ml of
de-ionised water. A mixed copper, nickel basic carbonate was
precipitated and decorated the diamond particle surfaces. The 0.5
micro meter powder so decorated with the mixed alkaline carbonate
precursor was then removed from suspension using a laboratory
centrifuge. The material was washed free of the soluble sodium
carbonate by-product by a few cycles of re-suspension in cold
de-ionised water and removal from suspension by centrifuge. The
material was dried under vacuum. The dried powder was then placed
in an alumina ceramic boat with a loose powder depth of about 3 mm
and heated in a flowing stream of argon gas containing 5% hydrogen.
The top temperature of the furnace was 1000.degree. C. which was
maintained for 1 hour before cooling to room temperature. This
furnace treatment dissociated and reduced the mixed copper, nickel
basic carbonate precursor to form pure 50% copper, 50% nickel alloy
particles decorating the surfaces of the diamond particles. [0191]
b) The general procedures used in Example 1 to produce consolidated
and encapsulated right cylinder green bodies were then carried out.
[0192] c) The general procedures used in Example 1 to subject the
green bodies to a pressure of 7.5 GPa at a temperature of
1950.degree. C. for 1 hour were then carried out. [0193] d) SEM
image analysis was carried out on polished sections of the
resulting PCD bodies and showed a well sintered continuous network
of diamond, with an interpenetrating network comprising a single
phase copper nickel alloy.
Example 8
[0194] The PCD material made in Example 2 based upon a multimodal
particle size of diamond starting powder and with 9 volume percent
cobalt was chosen and free standing PCD bodies of the 3-dimensional
shape given in FIG. 14 were produced. FIG. 14 shows a 3-dimensional
shaped PCD body intended for use in general applications. The body
was of 45 mm of overall length. These PCD bodies are intended for
use in general applications where rock removal is required, such as
cutting elements in rotary rock drills or road planing heads. The
bodies had a cylindrical barrel of diameter 25 mm diameter and 25
mm long. The cutting end was designed to have a sloping rounded
chisel shape. The bodies were of 45 mm of overall length. [0195] a)
A quantity of diamond particulate mass decorated with cobalt was
made using the procedures and material quantities using the method
of FIG. 5 column 2 as described in Example 2, paragraph (a) above.
[0196] b) 65 g fractions of the diamond-metal powder mass were then
filled into niobium pre-formed canisters which had been placed in
compaction tooling of the desired geometrical shape. The diamond,
metal powder charge was then compacted using a cylindrical piston.
A second niobium cylindrical canister was then inserted into the
tooling so that its outer surface slid inside the inner cylindrical
wall of the first canister. This pre-compacted green body was then
removed from the compaction tooling and a tungsten carbide hard
metal mandrel inserted into the open end of the second niobium
canister. The free air in the porosities of the pre-compacts was
then evacuated and the canisters sealed under vacuum using an
electron beam welding system known in the art. The canister
assemblies were then subjected to cold isostatic compaction at a
pressure of 200 MPa to consolidate to a high green density and to
eliminate spatial density variations, and thereafter the mandrels
removed. In this way encapsulated, homogeneous green bodies were
produced with measured densities of about 2.6 gcm.sup.-3, which
correspond to a porosity of approximately 35% by volume. [0197] c)
The encapsulated green bodies were then inserted into pre-compacted
semi-sintered high porosity ceramic components mirroring their
shape. This sub-assembly was in turn inserted into a cylindrical
cavity pre-formed in sodium chloride components so that the low
shear strength sodium chloride completely surrounded the green body
containing sub-assembly. The green bodies were then subjected to
high pressure high temperature cycles as well known in the art of
PCD manufacture at appropriate conditions to cause sintering of the
diamond particles and the formation of the PCD free standing
bodies. Typical conditions were about 5.7 GPa and about
1400.degree. C. maintained for 25 minutes. The release of pressure
and return to room temperature was carried out as outlined in
Example 1 paragraph (c) above. [0198] d) A sample of the sintered
free standing PCD bodies was sectioned and polished and examined
using SEM. From comparisons of images taken from various parts of
the sections, it was observed that well-sintered homogeneous PCD
material had been formed. The 3-dimensional geometry as
pre-selected and indicated in FIG. 14 had been maintained with no
significant distortion. By comparing the dimensions of the green
bodies and the final sintered bodies, the dimensional shrinkage was
found to be 12%. Thus, near-net size and shape behaviour was
attained during the manufacture.
Example 9
[0199] PCD free standing, macro residual stress free, bodies each
comprising an intergrown diamond network with a mean grain size of
close to 10 micro meters with an inter-penetrating metallic network
made up of cobalt at 9 volume % were manufactured. The PCD bodies
were chosen to be large discs with the desired diameter of 100 mm
and thickness of 3 mm. [0200] a) A diamond particulate mass
decorated in 9 volume % cobalt particles was produced using the
method of FIG. 5 column 2 and the procedures, chemical protocol and
precursor as specified in Example 2. [0201] b) 95 g fractions of
this mass were then formed into disc green bodies of 106 mm
diameter and 4 mm thick. Each green body was pre-compacted into
niobium canisters using simple floating piston and cylinder
tooling. The green bodies were vacuum degassed and the canisters
sealed using electron beam welding. The dimensions of the green
body were measured correcting for the known wall thicknesses of the
canisters and the green body density was calculated to be 2.7
gcm.sup.-3, which corresponds to approximately 33% porosity by
volume. [0202] c) Each green body was subjected to a pressure,
temperature and time cycle in a large volume belt type high
pressure apparatus known in the art. The specific conditions
employed were typically 5.6 GPa and 1400.degree. C. maintained for
35 minutes. The precautionary measured aimed at mitigating
distortions as outlined in Example 1 were employed. [0203] d) The
resultant free standing green bodies suffered a minimal axially
symmetric distortion whereby the thickness at the centre was about
1% greater than the chosen 3 mm and the thickness at the periphery
of the disc was about 1% less than the chosen 3 mm. The homogeneity
of the diamond-metal particulate mass and the green body density
allows the shrinkage during sintering to be near uniform. The
slight distortion experienced in the PCD discs results from
unavoidable material flow characteristics and is typical of the
high pressure apparatus employed. The distortion is within the
range whereby compensating dimensions of the green body can be
used. This may be done by appropriate slight changes of mass of the
diamond charge and the shape of the compaction tooling. By a series
of empirical trials near-net size and shape large discs of free
standing PCD material can be achieved. After minimal final shaping
and polishing free standing PCD discs 100.5 mm diameter and 2.95 mm
thick were obtained with a final density of 3.9 gcm.sup.-3. [0204]
Image analysis using SEM procedures confirmed the homogeneity of
the PCD material above a scale of about 100 micro meters.
[0205] In summary, there is disclosed in this disclosure a
polycrystalline diamond (PCD) construction or body which is free
standing in that it is not attached or bonded, in any manner during
any stage of the manufacture of the PCD, to a second body or
substrate of a dissimilar material. In particular, a substrate such
as tungsten carbide/cobalt hard metal commonly used in conventional
PCD constructions where the cobalt binder metal is infiltrated into
a mass of diamond powder to facilitate diamond particle-to-particle
sintering is excluded.
[0206] Manufacturing methods whereby the metals required to enable
sintering of the diamond particles are homogeneously combined with
a pre-selected diamond powder of chosen specific size distribution
are also described. These may allow both the amount and specific
metallurgy of the metals to be independently pre-selected and
chosen such that they are independent of the chosen diamond size
and size distribution. Thus, key manufacturing degrees of freedom
such as the diamond grain size distribution, the metal content of
the PCD material and the atomic and alloy composition of the metal
may be chosen and pre-selected independent of one another.
[0207] The PCD body so formed may comprises a single volume of PCD
material which is homogeneous at a macroscopic scale, i.e., above a
scale defined for this invention to be greater than ten times the
average diamond grain size, with the coarsest component of grain
size being three times the average grain size. The homogeneity at
this scale provides for the PCD body to be considered as a
spatially invariant material. At this macroscopic scale the PCD
body is therefore stress free, having an absence of residual
stress. Another consequence of not directionally infiltrating from
a substrate is that the PCD body or construction is dimensionally
unrestricted in this regard in any or all orthogonal directions.
The dimensions in any particular direction are restricted only by
the size of the high pressure apparatus used to manufacture the PCD
body. With the high pressure apparatus known in the art the
dimensions in any or all of the orthogonal directions may be up to
100 mm or more. The PCD body or construction can thus be viewed as
a true 3-dimensional body of any shape and is not restricted to a
layer or plate where one dimension is always of the order of a few
millimeters, as is the case for conventional PCD bodies or
constructs.
[0208] Methods are described where diamond particles are combined
with the metals, alloys or metal/metal carbide combinations for PCD
materials such that the metallic particles, grains or entities are
smaller than the diamond particles. This may ensure the homogeneity
of metal diamond distribution at a scale greater than the diamond
particle or subsequent grain size maximum. The metals, alloys or
metal/metal carbide in the mass are the sole source of the molten
metal necessary and required to cause the sintering of the diamond
particles via partial diamond re-crystallization mechanisms.
[0209] One method to create particulate diamond-metal masses
involves the crystallization of the precursor compound or compounds
for the desired metallic particles from solution where the diamond
powder particles are present in suspension in the solution. The
precursor compound may be formed using any of the crystallization
procedures known in the art, such as using reduction of temperature
and or removal of solvent by evaporation. After total removal of
the solvent, liquid suspension media, a well-mixed intimate
combination of the diamond powder and precursor compound or
compounds for the metal particles is produced. This method uses
precursor compounds which are soluble in the liquid suspension
media. Examples of liquid media or solvents are water and alcohol.
Examples of possible precursor compounds are ionic salts,
particularly the nitrates of the transition metals. In turn, the
precursor compounds are dissociated and reduced to form the
metallic particles by a heat treatment preferably in a reducing
furnace environment.
[0210] Another method, as shown in FIG. 5 column 2, concerns the
chemical reactive generation of the desired precursors for the
desired metallic particles in liquid media with the presence of the
diamond powders in suspension. Such precursors are significantly
insoluble in the suspension media. The precursor compounds may
nucleate and grow on the diamond particle surfaces to form a
particulate decoration of the diamond surfaces with particles or
grains of the precursor compounds. To facilitate the nucleation of
the precursor materials on the diamond surfaces, the surface
chemistry of the diamond particles may be pre-selected and/or
deliberately altered to be hydrophilic and dominated by oxygen
species prior to the suspension decoration with the precursor
compounds.
[0211] In turn, the precursor compounds are dissociated and reduced
by a heat treatment, for example in a reducing furnace environment,
to form metallic particles which decorate the diamond particle
surfaces and do not form a continuous metallic coat. The furnace
environment may be a vacuum or involve flowing gas mixtures
containing at least one gas capable of reducing the precursors or
its dissociative products to the metallic state and/or metal
carbide. Typical reductive gases are hydrogen and carbon monoxide.
The heat treatment conditions may be pre-selected to be
sufficiently high in temperature and of a sufficiently long
duration to cause controlled amounts of amorphous non-diamond
carbon to be formed on the metal and diamond surfaces.
Alternatively, the heat treatment conditions may be pre-selected to
be sufficiently low in temperature and short in time for
non-diamond carbon not to form at a detectable level. For example
when cobalt is used as the PCD metal component, temperatures above
800.degree. C. for times of an hour or more are typical of the
former case. The presence or absence of amorphous non-diamond
carbon together with the control of its amount in the diamond/metal
particulate mass is a degree of freedom which may play a role in
the sintering mechanisms of the diamond particles.
[0212] The metallic particles now decorate the diamond particle
surfaces. This approach may assist in ensuring that the metallic
particles are always smaller than the diamond particles. Examples
of liquid media may include water and alcohols. Some precursors may
be insoluble salts of the transition metals such as carbonates,
oxalates, acetates, tungstates, tantalates, titanates, molybdates,
niobates, and the like. The reactants to reactively form these
precursors are soluble salts in the chosen solvent or suspension
medium. A reactant source of transition metals such as iron,
nickel, cobalt, manganese, chromium, copper and the like may be
nitrate salts. Alternatively, precursor compounds for transition
metals which form stable carbides such as tungsten, molybdenum,
tantalum, titanium, niobium, zirconium and the like may be oxides
generated by the reaction of alkoxide compounds with water in
alcohol suspension media. A reaction to generate tungstic oxide,
WO.sub.3 as a precursor to form tungsten carbide on diamond
particle surfaces may be the reaction of ammonium paratungstate
with dilute mineral acids such as nitric acid in water as solvent
and suspension medium for the diamond.
[0213] Any of these chemical reactions to form the precursor
compound decorants on the diamond particle surfaces may be done in
sequence and applied to the pre-selected diamond powder as a whole
or to any component of the diamond powder in appropriate suspension
media. The diamond powder components may be based upon mass
fractions or upon size, size distribution or any desired
combination of these. Some of the diamond powder components may be
left undecorated.
[0214] The above described methods of preparing the diamond grains
and precursors assist in achieving high homogeneity in the sintered
products.
[0215] Diamond powder fractions or components may also differ in
diamond type, based upon the lattice defect composition and
structure of the diamond crystals. A convenient way of such
differentiation of diamond type between the diamond powder
fractions or components can be to use diamond of natural origin as
opposed to standard synthetic diamond origin. The lattice defects
in natural diamonds are typically and predominantly made up of
aggregated nitrogen impurity atomic structures. In contrast, the
lattice defects in typical synthetic diamonds commercially
crystallized using molten transition metal solvents are
overwhelmingly dominated by single nitrogen atoms which substitute
for individual carbon atoms. Moreover, the overall nitrogen content
in natural diamond is typically an order of magnitude greater than
for such synthetic diamond. PCD materials made with these different
types of diamond exhibit significantly different properties.
Pre-selected combinations of natural and synthetic diamonds may
also be used for purpose.
[0216] In turn, the precursor compounds are dissociated and reduced
to form metallic particles by a heat treatment, for example in a
reducing furnace environment. In this way, different components of
the diamond powder may be decorated in any of the different
metallic particles and to any different degree. Thus the metallic
particles may be pre-selected both in elemental composition and
amount to be associated and decorated onto any chosen sub-component
of the diamond particles. A vast number of PCD free standing body
embodiments with desired compositions, structures and properties
may, in this way, be generated using such prepared decorated
diamond powder, metal combinations or masses.
[0217] The methods involving liquid suspension procedures may have
particular utility in that they may be easily altered in scale and
may allow production quantities of kilograms or more of accurate,
homogeneous combinations of the diamond and metals and metals/metal
carbides to be made. Moreover a notable and valuable characteristic
of one method is that wide ranging combinations of diamond
particles and metals, which may be pre-selected to vary
independently in diamond particle size, metal amount and metal
elemental composition, may be made.
[0218] The masses of diamond particle, metal combinations generated
by the above methods are consolidated into cohesive so called
"green bodies" of a pre-selected size and 3-dimensional shape.
Consolidation may be effected in compaction die arrangements or
isostatic compaction apparatuses as known in the art. Preferably
hot isostatic compaction may be employed. Isostatic compaction
techniques may have the benefit of spatial homogeneity of density
in the green body, which assists in ensuring that the homogeneity
of the starting diamond powder, metal combination is maintained and
in turn engenders directionally equal shrinkage during subsequent
sintering of the diamond particles. Free standing PCD bodies of
near net pre-determined shape may then be made. The degree of
shrinkage on sintering to form the PCD body may be measured for
each specific diamond and metal composition. Such knowledge allows
the size of resultant PCD body to be preselected for each PCD
composition. Free standing PCD bodies of near net pre-determined
size may then be made.
[0219] Temporary organic binders may be employed to provide
cohesion in the green bodies. A special case of this and as an
alternative to isostatic compaction, gel casting techniques may be
employed as known in the art. This technique to form the green
bodies also maintains spatial homogeneity of the diamond and metal
distributions so that directionally equal shrinkage on sintering
may occur, so that the 3-dimensional shape of the green body may be
maintained on formation of the free standing body. There is a large
number of powder, slurry and suspension based consolidation and
green body formation techniques known in the art for material
fabrication from particulate starting materials. In addition to
those already disclosed above, these include injection moulding,
slip casting, electrophoresis enhanced sedimentation, centrifugal
enhanced sedimentation, 3-dimensional printing and many others.
Each of the consolidation and green body making techniques has it
own character in regard to the size of particles it may viably be
applied to and also the degree to which homogeneity including that
of porosity can be maintained. Preferences of techniques to be
applied to make any given 3-dimensional and material embodiments
take such character of the technique into consideration. In
particular, the ability of a technique to be accurate, reproducible
and maintain spatial homogeneity all in regard to porosity is of
importance in the choice of preferred techniques to be used for any
particular embodiment. This consideration is directed at the
achievement of near net size and shape.
[0220] The green bodies generated by the above methods are
subjected to high pressure, high temperature conditions for
appropriate times to cause sintering of the diamond particles and
form the free standing PCD bodies. Typical pressure and temperature
conditions are in the range of 5 to 15 GPa and in the range of 1200
to 2500.degree. C. respectively. Preferably pressures in the range
5.5 to 8.0 GPa along with temperatures in the range 1350 to
2200.degree. C. may be used.
[0221] There is also disclosed a means of managing and controlling
the micro residual stress magnitude of the free standing macro
residual stress free PCD body, i.e., below a scale defined to be
less than ten times the average grain size, where the coarsest
component of grain size is no greater than three times the average
grain size. Above this scale some embodiments provide for the PCD
free standing body to be residual stress free, i.e., macro residual
stress free. The methods disclosed may allow a very wide range of
diamond to metal ratios and accurate metal compositions to be
pre-selected independently of resultant diamond grain size and size
distribution. Thus the relative differences in thermo-elastic
properties between the diamond network and that of the metallic
network can be pre-selected and accurately controlled.
[0222] Often, but not exclusively, the dominant properties in this
regard are the thermal expansion coefficients of the metals in
comparison to that of diamond. In such cases, on return to ambient
conditions of temperature and pressure during the manufacturing
process the relative differences of properties cause the diamond
network to be generally compressed and the metallic network
generally put into a state of tension. For each PCD body material
pre-selected in regard to diamond and overall metal content, the
micro residual stress magnitudes may thus be considered to be high,
medium or low in magnitude by the use of metal compositions with
thermal expansion coefficients in the ranges of 10 to 14, 5 to 10
and less than 5 ppm .degree. K.sup.-1, respectively.
[0223] Some embodiments include the high carbon versions of
controlled expansion transition metal alloys. A notable low
expansion alloy with a very low minimum of linear coefficient of
thermal expansion is an iron, 33 weight % nickel, 0.6 weight %
carbon alloy (ref. 4). This alloy has a literature linear
coefficient of thermal expansion value of 3.3 ppm .degree.
K.sup.-1, which falls into the less than 5 ppm .degree. K.sup.-1
category. This alloy would then be expected to provide a metallic
network in PCD materials where the tensile residual stress
magnitude in the metallic network is low. However, this alloy has
an elastic modulus of approximately 200 GPa, which is very
different and removed from the elastic modulus of the diamond
network, typically 1050 GPa. In such a case, the elastic property
difference should dominate when the manufacturing conditions are
returned to room conditions. The differential expansion of the
diamond and metallic networks on release of pressure should then
result in the metallic network experiencing a compressive micro
residual stress. Thus, where metals of low thermal expansion
coefficients are used it is possible that the residual stress in
the metallic network can become compressive.
[0224] Any or all of the above aspects may provide for the
manufacture of free standing PCD bodies, not attached to a
dissimilar material, comprising a pre-selected combination of
intergrown diamond grains of specific size and size distribution,
in conjunction with an independently pre-selected specific metallic
inter-penetrating network, with an independently pre-selected
specific overall metal to diamond ratio. These primary degrees of
freedom may be independently pre-selected.
[0225] Some embodiments may benefit from removal of the metal from
a chosen depth from the surface of the PCD body or throughout the
volume of the PCD body. This may be done using, for example,
chemical leaching techniques well known in the art.
[0226] In summary, embodiment methods involve, for example, diamond
particle suspension in a liquid and the crystallisation and/or
precipitation of precursor compound for the required metals of the
PCD material to be formed and the subsequent thermal
decomposition/reduction of these precursors to form the metals.
These methods are inherently characterised by the resultant
metallic particles being smaller than the chosen diamond particles.
The described methods involving diamond particle suspensions and
the crystallisation and/or precipitation of precursor compounds for
the metals become more and more practicable and efficient as the
diamond particle sizes become smaller and smaller down to and
including sub-micron sizes. This is due to the precursor compounds
for the metals being influenced in their crystallisation and/or
precipitation by the overall diamond surface area, which becomes
progressively larger as the diamond particles become smaller. In
addition, dissociation/reduction of precursor compounds for metals
readily form very fine and often nano-sized metal particles. The
methods described herein for forming embodiments of free standing
bodies of PCD material thus provide good practicality for PCD
materials with desired very fine diamond grain sizes, particularly
for diamond grain sizes in the sub-micron range.
[0227] This character of these suspension methods, along with the
suspension stirring dynamics, provides for a high degree of
homogeneity of mix of the diamond particles and metallic particles,
and may even approach the ultimate homogeneity in this regard. This
homogeneity of diamond and metal in a particulate mass assists in
the formation of a green body and subsequent free standing PCD body
formed at high pressure high temperature which is homogeneous with
respect to its diamond and metallic composition above a scale
related to the average and maximum grain size of the diamond grain
size of the diamond network and also which spans the dimensions of
the free standing PCD body. This scale can be used to define the
so-called "macroscopic" scale of the PCD material. It has been
experientially determined by the inventors that using the methods
described herein the diamond network to metallic network volume
ratio is spatially constant and invariant above a scale greater
than ten times the average diamond grain size, provided that the
largest component of diamond grain size is no greater than three
times the average diamond grain size. This spatial invariance of
diamond network to metallic network volume ratio at the defined
macroscopic scale, across the dimensional span of the PCD body
means that, at completion of the manufacturing process, the free
standing PCD body will be macroscopically residual stress free.
[0228] Conversely, if the PCD body is inhomogeneous, with the
diamond network to metallic network volume ratio varying from place
to place in the PCD body, the PCD material from place to place will
differ in thermal expansion and elastic properties. These spatial
differences in properties then necessarily lead to a significant
macroscopic residual stress field across the dimensional span of
the PCD body, caused by the spatial differential in contraction,
when the PCD body is returned to room temperature and pressure at
the end of the high temperature high pressure process.
[0229] Free standing PCD bodies of embodiments which are residual
stress free may have considerable benefits in applications
involving mechanical action such as general machining, drilling and
the like. In such applications, the tooling material efficiency is
often governed by crack related processes leading to undesired
fracture behaviour such as chipping and spalling. It is well known
in the art that macroscopic, tool piece dimension spanning,
residual stress fields can easily enhance the propagation of cracks
and thereby increase the occurrence of chipping and spalling. The
absence of macroscopic residual stress fields mitigates such
behaviour and such absence is therefore desirable.
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Ehrhardt, M. Gjikaj, W. Brockner, "Thermal decomposition of cobalt
nitrate compounds: Preparation of anhydrous cobalt (II) nitrate and
its characterization by Infrared and Raman spectra", Thermochimica
Acta, 432 (2005), 36-40. [0232] 3. W. Brockner, C. Ehrhart, M.
Gjikaj, "Thermal decomposition of nickel nitrate hexahydrate,
Ni(NO.sub.3).sub.2.4H.sub.2O", Thermochimica Acta, 456 (2007),
64-68. [0233] 4. E. L. Frantz, "Low-Expansion Alloys", Metals
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