U.S. patent application number 12/447779 was filed with the patent office on 2010-01-07 for polycrystalline diamond abrasive compacts.
Invention is credited to Barbara Marielle De Leeuw-Morrison, Cornelis Roelof Jonker, Roger William Nigel Nilen.
Application Number | 20100000158 12/447779 |
Document ID | / |
Family ID | 39201883 |
Filed Date | 2010-01-07 |
United States Patent
Application |
20100000158 |
Kind Code |
A1 |
De Leeuw-Morrison; Barbara Marielle
; et al. |
January 7, 2010 |
POLYCRYSTALLINE DIAMOND ABRASIVE COMPACTS
Abstract
This invention is for a polycrystalline diamond composite
material comprising diamond particles and a binder phase, the
polycrystalline diamond composite material defining a plurality of
interstices and the binder phase being distributed in the
interstices to form binder pools. The invention is characterised in
that there is present in the binder phase a separate tungsten
carbide particulate phase in excess of 0.05 total volume %, but not
greater than 2 volume %, expressed as a % of the total composite
material and that the tungsten carbide particulate phase is
homogenously distributed in the composite material in such a manner
that the relative standard deviation of the tungsten carbide grain
size is less than 1. The invention extends to a method of
manufacturing the composite material and to a polycrystalline
diamond abrasive compact comprising the diamond composite material
for use in cutting or abrading of a substrate or in drilling
applications.
Inventors: |
De Leeuw-Morrison; Barbara
Marielle; (Johannesburg, ZA) ; Jonker; Cornelis
Roelof; (Pretoria, ZA) ; Nilen; Roger William
Nigel; (Dowerglen, ZA) |
Correspondence
Address: |
FROMMER LAWRENCE & HAUG
745 FIFTH AVENUE- 10TH FL.
NEW YORK
NY
10151
US
|
Family ID: |
39201883 |
Appl. No.: |
12/447779 |
Filed: |
October 31, 2007 |
PCT Filed: |
October 31, 2007 |
PCT NO: |
PCT/IB2007/054410 |
371 Date: |
June 30, 2009 |
Current U.S.
Class: |
51/295 ; 51/307;
51/309 |
Current CPC
Class: |
B22F 7/06 20130101; C22C
26/00 20130101; B22F 2005/001 20130101; C22C 2026/006 20130101;
B22F 2998/00 20130101; B22F 7/008 20130101; B22F 2998/00
20130101 |
Class at
Publication: |
51/295 ; 51/307;
51/309 |
International
Class: |
B24D 3/10 20060101
B24D003/10; B24D 11/00 20060101 B24D011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 31, 2006 |
ZA |
2006/09073 |
Claims
1. A polycrystalline diamond composite material comprising diamond
particles and a binder phase, the polycrystalline diamond composite
material defining a plurality of interstices and the binder phase
being distributed in the interstices to form binder pools, wherein
there is present in the binder phase a separate tungsten carbide
particulate phase in excess of 0.05 volume %, but not greater than
2 volume %, expressed as a % of the total composite material and
the tungsten carbide particulate phase being homogenously
distributed in the composite material in such a manner that the
relative standard deviation of the tungsten carbide grain size
(expressed as equivalent circle diameter) is less than 1.
2. A polycrystalline diamond composite material according to claim
1, in which the tungsten carbide particulate phase is present in an
amount not greater than 1.5 volume % expressed as a % of the total
composite material.
3. A polycrystalline diamond composite material according to claim
1, in which the tungsten carbide particulate phase is present in an
amount not less than 0.1 volume % expressed as a % of the total
composite material.
4. A polycrystalline diamond composite material according to claim
1, in which the relative standard deviation of the tungsten carbide
grain size (expressed as equivalent circle diameter) is less than
0.9.
5. A polycrystalline diamond composite material according to claim
1, in which the relative standard deviation of the tungsten carbide
grain size (expressed as equivalent circle diameter) is less than
0.8.
6. A polycrystalline diamond composite material according to claim
1, in which the diamond particles have an average diamond grain
size of less than 25 .mu.m.
7. A polycrystalline diamond composite material according to claim
1, in which the diamond particles have an average diamond grain
size of less than 20 .mu.m.
8. A polycrystalline diamond composite material according to claim
1, in which the diamond particles have an average diamond grain
size of less than 15 .mu.m.
9. A polycrystalline diamond composite material according to claim
1, in which the binder phase includes a catalyst/solvent for the
diamond.
10. A polycrystalline diamond composite material according to claim
1, in which the binder phase includes cobalt, nickel, iron or an
alloy containing one or more of these metals.
11. A polycrystalline diamond abrasive compact comprising a
polycrystalline diamond composite material according to claim 1, in
the form of a layer bonded to a surface of a cemented carbide
substrate.
12. A polycrystalline diamond abrasive compact according to claim
11 wherein the substrate is cemented tungsten carbide
substrate.
13. A method of manufacturing a polycrystalline diamond composite
material according to claim 1, comprising subjecting a powdered
composition including diamond, finely particulate tungsten carbide
particles uniformly distributed in the composition and present in
an amount of 0.5 to 5 mass % of the composition to conditions of
elevated temperature and pressure suitable for diamond
synthesis.
14. A method according to claim 13 wherein the powdered composition
includes a binder in particulate form.
15. A method according to claim 13, in which the tungsten carbide
particles are present in an amount of 1.0 to 3.0 mass % of the
composition.
16. A method according to claim 13, in which the tungsten carbide
particles have a size of less than 1 .mu.m.
17. A method according to claim 13, in which the tungsten carbide
particles have a size of less than 0.75 .mu.m.
18. A method according to claim 13, in which the powdered
composition is placed on a surface of a cemented carbide
substrate.
19. A method according to claim 13, in which the cemented carbide
substrate is a cemented tungsten carbide substrate.
20. A method according to claim 18, in which the powdered
composition forms a region adjacent the surface of the substrate on
which it is placed and a layer of diamond particles is placed on
the powdered composition.
21. A polycrystalline diamond composite material according to claim
1 substantially as herein described with reference to Example 1 or
Example 2.
22. A method of claim 13 substantially as herein described with
reference to Example 1 or Example 2.
Description
BACKGROUND OF THE INVENTION
[0001] The invention relates to polycrystalline diamond abrasive
compacts and a method of producing polycrystalline diamond abrasive
compacts.
[0002] Polycrystalline diamond abrasive compacts (PDC) are used
extensively in cutting, milling, grinding, drilling and other
abrasive operations due to the high abrasion resistance of the
polycrystalline diamond component. In particular, they find use as
shear cutting elements included in drilling bits used for
subterranean drilling. A commonly used PDC is one that comprises a
layer of coherently bonded diamond particles or polycrystalline
diamond (PCD) bonded to a substrate. The diamond particle content
of these layers is typically high and there is generally an
extensive amount of direct diamond-to-diamond bonding or contact.
Diamond compacts are generally sintered under elevated temperature
and pressure conditions at which the diamond particles are
crystallographically or thermodynamically stable.
[0003] Examples of composite abrasive compacts can be found
described in U.S. Pat. Nos. 3,745,623; 3,767,371 and 3,743,489.
[0004] The PCD layer tends to be relatively brittle and this often
limits the lifespan of the tool in application. Hence the PCD layer
is generally bonded to a metal backing material, serving as a
hard-wearing support for the diamond composite portion. By far the
most common form of the resultant body is a disc of polycrystalline
diamond bonded to a cylinder of cemented carbide such as WC-Co.
Bonding of these two elements is usually achieved in-situ during
the sintering of the diamond powder precursor at high pressure and
temperature (HpHT).
[0005] The PCD layer of this type of abrasive compact will
typically contain a catalyst/solvent or binder phase in addition to
the diamond particles. This typically takes the form of a metal
binder matrix which is intermingled with the intergrown network of
particulate diamond material. This matrix usually comprises a metal
exhibiting catalytic or solvating activity towards carbon such as
cobalt, nickel, iron or an alloy containing one or more such
metals.
[0006] The matrix or binder phase may also contain additional
phases. In typical abrasive compacts of the type of this invention,
these will constitute less than 10 mass % of the final binder
phase. These may take the form of additional separate phases such
as metal carbides which are then embedded in the softer metallic
matrix, or they may take the form of elements in alloyed form
within the dominant metal phase.
[0007] Composite abrasive compacts are generally produced by
placing the components necessary to form an abrasive compact, in
particulate form, on a cemented carbide substrate. The components
may, in addition to ultrahard particles, comprise solvent/catalyst
powder, sintering or binder aid material. This unbonded assembly is
placed in a reaction capsule which is then placed in the reaction
zone of a conventional high pressure/high temperature apparatus.
The contents of the reaction capsule are then subjected to suitable
conditions of elevated temperature and pressure to enable sintering
of the overall structure to occur.
[0008] It is common practice to rely at least partially on binder
originating from the cemented carbide as a source of metallic
binder material for the sintered polycrystalline diamond. In many
cases however, additional metal binder powder is admixed with the
diamond powder before sintering. This binder phase metal then
functions as the liquid-phase medium for promoting the sintering of
the diamond portion under the imposed sintering conditions.
[0009] Under typical high pressure, high temperature sintering
conditions, binder metal phase originating from the cemented
carbide substrate will also carry with it appreciable levels of
dissolved species originating from the carbide layer, as it
infiltrates the diamond layer. The amount of dissolved species is
strongly affected by the pressure and temperature conditions of
sintering--where higher temperatures will typically increase the
amount in solution. When the preferred substrate of WC-Co is used,
these are W-based species.
[0010] As it infiltrates in to the PCD region, this dissolved
tungsten material reacts with carbon from the diamond layer, and
can precipitate out as carbide-based phases. Under certain
circumstances, this precipitation from the binder occurs on a large
and uncontrolled scale. It may therefore manifest as massive WC
precipitates of tens and even hundreds of microns in size. They
often form on or near the outer periphery of the PDC body during
synthesis; and they usually, but not always, tend to be spatially
connected with the interface region with the carbide substrate.
However, when they do form, the distribution of these precipitates
tends to be highly inconsistent across the macroscopic PCD layer.
There will be some regions with very little, if any, carbide
precipitates present; and certain areas where the relative volume
occupied by them is extremely high.
[0011] These WC precipitates have been found to severely compromise
the abrasive performance of the compacts, as they reduce mechanical
strength by replacing desirable polycrystalline ultrahard material
with a lower strength phase. Additionally, these defect regions in
the PCD can also act as stress raisers under loading in the
application, which then lead to premature fracturing of the PCD
material.
[0012] U.S. Pat. No. 6,915,866 discusses the formation of these
defects or metal spots and the deleterious effect that they can
have on performance of the compact. In this patent, the addition of
chromium carbide into the PCD layer is claimed to reduce the
formation of these precipitates. However, the use of a foreign
species such as chromium carbide, itself represents the
introduction of an additional chemical and physical inhomogeneity.
It is likely that it too may result in a sub-optimal final
structure. There may also be some lessening of the diamond
composite's resistance to thermal degradation due to the presence
of chromium carbide. A further drawback to the use of chromium
carbide relates to the sinterability of the composite--which is
likely to be hindered to some degree at normal sintering
temperatures, and therefore may demand higher sintering
temperatures than usual in order to achieve an appropriate level of
sintering.
[0013] Some success in reducing the occurrence of these large
precipitates has been demonstrated through a lowering of the
temperatures used in the sintering of the PDC body. However, this
is often not always practicable as this will typically result in
sub-optimal sintering conditions and hence a less well-sintered
PCD.
[0014] A further proposal for reducing the occurrence of large
precipitates lies in avoiding any reliance on substrate-originating
binder phase. In this case, catalytic material is added exclusively
to the PCD powder and infiltration from the carbide substrate is
prevented or inhibited. There are however, significant benefits to
relying, at least in part, on binder infiltrating from the
substrate into the diamond region.
[0015] The use of alternate materials, such as steel, for use in
the substrate has also been explored, although these are typically
difficult to sinter to the PCD layer and do not give the same
performance as the preferred WC-Co substrate.
[0016] The development of an abrasive compact that can achieve
optimal properties of impact and wear resistance in the PCD layer
is highly desirable. The difficulty lies in that these optimal
properties typically occur in a similar sintering environment to
that where massive carbide defects in the PCD layer can arise.
These carbide defects themselves have a highly detrimental effect
on these same required properties. Hence a means of preventing or
inhibiting their formation is highly desirable.
SUMMARY OF THE INVENTION
[0017] According to a first aspect of the invention, there is
provided a polycrystalline diamond composite material comprised of
diamond particles and a binder phase; the polycrystalline diamond
composite material defining a plurality of interstices and the
binder phase being distributed in the interstices to form binder
pools, characterised in that there is present in the binder phase a
separate tungsten carbide particulate phase in excess of 0.05
volume %, preferably not less than 0.1 volume %, but not greater
than 2 volume %, preferably not greater than 1.5%, expressed as a %
of the total composite material and the tungsten carbide
particulate phase being homogenously distributed in the composite
material in such a manner that the relative standard deviation of
the WC grain size (expressed as equivalent circle diameter) is
preferably less than 1, more preferably less than 0.9 and most
preferably less than 0.8.
[0018] The polycrystalline diamond composite material will
generally and preferably form a layer bonded to a surface of a
cemented carbide substrate forming a polycrystalline diamond
abrasive compact. The substrate is preferably a cemented tungsten
carbide substrate.
[0019] The polycrystalline diamond composite material of the
invention may be made by subjecting a powdered composition of
diamond and optionally binder in particulate form to conditions of
elevated temperature and pressure suitable for diamond synthesis.
The powdered composition is preferably characterised by the
presence of finely particulate tungsten carbide particles uniformly
distributed in the composition and present in an amount of 0.5 to 5
mass %, preferably 1.0 to 3.0 mass % of the composition. The
tungsten carbide particles are finely particulate, having a
preferred size of less than 1 .mu.m and more preferably a size of
less than 0.75 .mu.m. The preferred concentration of tungsten
carbide particles also expressed as the number of tungsten carbide
particles per gram of diamond powder mixture is between 10.sup.8
and 10.sup.10, most preferably of the order of 10.sup.9 particles
per gram of diamond.
[0020] The invention extends to the use of the polycrystalline
diamond abrasive compacts described above as abrasive cutting
elements, for example for cutting or abrading of a substrate or in
drilling applications.
DESCRIPTION OF EMBODIMENTS
[0021] The present invention is directed to polycrystalline diamond
composite materials, generally as a layer bonded to a cemented
tungsten carbide substrate forming a polycrystalline diamond
abrasive compact, made under high pressure/high temperature
conditions. These composite materials are characterised in that
they have a binder phase of such metallurgical nature that a
separate precipitated carbide phase is distributed throughout in a
homogenous manner.
[0022] The diamond particles may be natural or synthetic in origin.
The average grain size of the diamond particles is typically in the
range between submicron and tens of microns in size. This invention
has particular application where the average diamond grain size is
less than 25 .mu.m, more preferably less than about 20 .mu.m and
most preferably less than 15 .mu.m.
[0023] To produce the polycrystalline diamond composite material of
the invention, a powdered composition as described above will be
subjected to known temperature and pressure conditions necessary to
produce a diamond abrasive compact. These conditions are typically
those required to synthesize the diamond particles themselves.
Generally, the pressures used will be in the range 40 to 70
kilobars and the temperature used will be in the range 1300.degree.
C. to 1600.degree. C.
[0024] The polycrystalline diamond composite material will
generally be bonded as a layer to a cemented carbide support or
substrate forming a composite abrasive compact. To produce such a
composite abrasive compact, the powdered composition will be placed
on a surface of a cemented carbide body before it is subjected to
the elevated temperature and pressure conditions necessary for
compact manufacture. The cemented carbide support or substrate will
be made of cemented tungsten carbide. The binder metal for such
carbides may be any known in the art such as nickel, cobalt, iron
or an alloy containing one or more of these metals. Typically, this
binder will be present in an amount of 10 to 20% by mass in the
substrate body, but this may be as low as 6% by mass. Some of the
binder metal will generally infiltrate the abrasive compact during
compact formation.
[0025] The polycrystalline diamond composite materials of the
invention have a binder phase present. This binder phase is
preferably a catalyst/solvent for the diamond. Catalyst/solvents
for diamond are well known in the art. The binder is preferably
cobalt, nickel, iron or an alloy containing one or more of these
metals. This binder can be introduced either by infiltration into
the mass of abrasive particles during the sintering treatment, or
in particulate form as a mixture within the mass of abrasive
particles. Infiltration may occur from either a supplied shim or
layer of the binder interposed between the substrate and diamond
layer, or from the carbide support. Typically a combination of
approaches is used.
[0026] During the high pressure, high temperature treatment, the
catalyst/solvent material melts and migrates through the diamond
particles, acting as a catalyst/solvent and hence causing the
diamond particles to bond to one another through the formation of
reprecipitated diamond phase. Once manufactured, the composite
material comprises a coherent matrix of diamond particles bonded to
one another, thereby forming a diamond polycrystalline composite
material with many interstices containing binder or
solvent/catalyst material as described above. In essence, the final
composite material therefore comprises a two-phase composite, where
the diamond comprises one phase and the binder the other.
[0027] The applicants have discovered that by introducing finely
particulate tungsten carbide into the unsintered diamond mass as a
dopant at fairly low mass levels prior to sintering, it is possible
to inhibit the subsequent formation of gross carbide-based
precipitates within the binder phase on or after sintering. Whilst
the additional introduction of an undesirable chemical phase into
the system may first appear counter-intuitive, it appears that the
well-distributed presence of these initial particulates in the
pre-sintered mass significantly inhibits the subsequent
uncontrolled formation of gross defects of the same or similar
chemical phases where it may occur. Without being bound by theory,
it is possible that the doped powder mix behaves as a filter,
deliberately drawing out any solute W in a controlled way, and so
reducing the overall concentration. This process then prevents
uncontrolled precipitation of carbide phases elsewhere in the
sintering polycrystalline diamond layer by reducing the available
solute for carbide formation.
[0028] The method for generating composite materials of the
invention is therefore characterized by the initial addition of
finely particulate tungsten carbide to the unsintered diamond
abrasive particle mixture that is used. This may take the form of
admixed separate particles, or may be introduced by the erosive use
of tungsten carbide milling media during diamond powder mix
preparation, where the abrasive action of the diamond particles on
the tungsten carbide milling balls results in the introduction of
the desired levels under fairly strenuous milling conditions.
Deposition through chemical or physical means may be used to
introduce tungsten carbide into the diamond powder mixture.
Sometimes a combination of these methods may be used.
[0029] Typically this tungsten carbide addition will be such as to
produce in the powdered diamond composition, prior to sintering, a
tungsten carbide content in the range of about 0.5 mass % up to
about 5 mass % expressed as a percentage of the unsintered powdered
composition. It has been found that in polycrystalline diamond
materials of the invention with a prevalence for carbide defect
formation, levels of tungsten carbide introduced at 0.7 mass % will
have positive effects. Typically, however, the more preferred range
of addition is from 1.0 to 3 mass %. It should be appreciated
however, that the amount of dopant required to prevent runaway
precipitation will be characteristic of the polycrystalline diamond
composite material being produced. It is therefore anticipated that
different composite materials will have differing optimal levels of
additive within these wider ranges. It has been found that optimal
levels of WC doping for polycrystalline diamond material (PCD of
the invention) occur where the number of WC particles is between
10.sup.8 and 10.sup.10 particles per gram of diamond. The most
preferred range lies in the order of 10.sup.9 (i.e. between
1.times.10.sup.9 9.9.times.10.sup.9 particles per gram of diamond).
When the number of particles lies much below approximately
1.times.10.sup.8 particles per gram of diamond, then the
homogenising effect of the doping process is not optimally
effective.
[0030] It is also preferred that the tungsten carbide particles are
as fine as possible, such that each particle serves as an
effective, yet stable, dopant centre without significantly
interfering with the diamond sintering process. It is preferred
that the average particle size of the WC introduced into the
diamond mixture does not exceed 1 .mu.m; and more preferably does
not exceed 0.75 .mu.m. It is anticipated that where the particles
become too fine in size, the solubility of the WC phase in the
molten catalyst/solvent may result in the complete dissolution of
significant numbers of the particles. The doping effect would then
be substantially compromised. Even in the preferred ranges of the
invention, it is anticipated that some of the particles may
partially dissolve, although this is mitigated by the fact that the
molten catalyst/solvent solution is largely saturated with tungsten
from the carbide substrate.
[0031] It is not necessarily required that the carbide particulate
be introduced throughout the polycrystalline diamond composite
material. Substantial benefits have also been recognised where the
composite material only in the region immediately adjacent to the
substrate interface has been doped with carbide particles. Thus in
this form of the invention, the powdered composition will form a
region immediately adjacent to the substrate interface and a layer
of diamond, optionally with a binder phase in particulate form,
will be placed on the powdered composition. In some cases where the
composite material layer is particularly prone to the formation of
gross carbide precipitates, however, it may be required that all,
or the larger part, of the polycrystalline diamond composite
material be doped. For ease of manufacture, it may also be
preferred that the entire composite material is doped.
[0032] To distinguish the desired structures of this invention over
those typically observed in similar compacts known in the art, it
is necessary to consider the homogenising effect of this doping on
the overall distribution of the carbide phases in the final
sintered microstructure. As previously discussed, the distribution
of carbide phases in undoped PCD compacts typically manifests in an
uncontrolled and random manner throughout the macroscopic PCD
layer. There will be some areas which show little or no visible
carbide precipitation; and other areas where large carbide-based
gross defects are easily observable. In compacts which are sintered
at lower (typically sub-optimal) temperatures, carbide
precipitation may not be observable at all.
[0033] The composite material of this invention has a
characteristically homogenous or similar-scaled distribution of
tungsten carbide phase particulates in the final microstructure.
Rather than exhibiting a large extreme in carbide particulate grain
size, the size distribution of the carbide phases is
characteristically narrow around the average value, which itself
tends to be typically fine. The narrow breadth of this distribution
can be quantified in statistical terms by the standard deviation,
normalised against the overall average or mean value. Composite
materials of this invention are therefore characterised in having a
standard deviation of the tungsten carbide (WC) phase grain size
(expressed as equivalent circle diameter) that is preferably less
than 1, more preferably less than 0.9 and most preferably less than
0.8. These values are observed across a range of mean WC phase
grain sizes from 0.1 up to 1.5 .mu.m. Typically prior art
polycrystalline diamond abrasive compacts with similar average WC
grain sizes are observed to have relative standard deviations well
in excess of 1.0.
[0034] The measurement of the WC phase grain sizes is carried out
on the final composite focussing on the PCD layer, by conducting a
statistical evaluation of a large number of collected images taken
on a scanning electron microscope. The WC phase grains in the final
microstructure, which are easily distinguishable from the remainder
of the microstructure using electron microscopy, are isolated in
these images using conventional image analysis technology. The
overall area occupied by WC phase is measured; and this area % is
taken to be equivalent to the overall volume % of WC phase(s)
present in the microstructure.
[0035] The average value for the volume % of WC present in the
structures of this invention is decided by the combination of the
WC introduced into the diamond powder mixture as dopant; and the WC
originating from the substrate which precipitates near or onto
these dopant particles. In prior art cutters, two distinct
populations of WC content are typically observable. There are those
with little appreciable overall WC content i.e. where the WC
content lies below 0.05 volume % or certainly significantly below
0.1 volume %; and those with a WC volume % in excess of this
threshold. Typically those with reduced overall WC carbide content
will not be optimally sintered; whilst it is those with WC contents
in excess of 0.1 volume % that suffer from the mass defect
formation previously discussed. Structures of this invention will
typically have WC levels in excess of 0.05 volume %, and more
typically WC levels in excess of 0.1 volume %.
[0036] The size of the WC grains is measured by estimating a circle
equivalent in size or area for each individual grain identified in
the microstructure. The collected distribution of these circles is
then evaluated statistically. The chosen indicative variable is the
diameter of this "equivalent circle", known as the equivalent
circle diameter. An arithmetic average and standard deviation are
then determined from the distribution of these diameters. The
relative or normalised standard deviation value is calculated by
dividing the standard deviation value by the mean value in each
case. Typically magnification levels of 1000 times to 2000 times
are chosen to characteristically represent PCD structures of
interest in this invention, where the average diamond grain size is
submicron up to tens of micron in size.
[0037] The invention will now be illustrated by the following
non-limiting examples:
Example 1
Sample 1A--WC Introduced by Admilling
[0038] A multimodal diamond powder with an average grain size of
approximately 15 .mu.m was milled under typical diamond powder mix
preparation conditions in a planetary ball mill, together with 1%
by mass cobalt powder using WC milling balls. The milling
conditions were monitored so as to maximise the erosion of the WC
milling media allowing the addition of WC to the mixture at an
overall level of 0.7 mass % in the final diamond mixture. The size
of the WC fragment introduced in this manner was typically less
than 0.5 .mu.m. This powder mixture was sintered onto a standard
cemented WC substrate under typical pressure and temperature
conditions in order to produce a polycrystalline diamond layer ell
bonded to the substrate. The resultant sample is designated Sample
A in Table 1 below.
Sample 1B--WC Introduced by Admixing
[0039] A multimodal diamond powder with an average grain size of
approximately 15 .mu.m was prepared under typical diamond powder
mix preparation conditions in a high shear mixer, together with 1%
by mass cobalt powder in the absence of any WC milling media.
Particulate WC powder was added to this mixture to achieve a level
of 0.7 mass % in the final diamond mixture. The size of the WC
fragment introduced in this manner was typically between 0.35 and
0.7 .mu.m. This powder mixture was sintered onto a standard
cemented WC substrate under typical pressure and temperature
conditions in order to produce a polycrystalline diamond layer
bonded to the substrate. The resultant sample is designated Sample
B in Table 1 below.
Sample 1C--Comparative Sample Produced by Admixing
[0040] A multimodal diamond powder with an average grain size of
approximately 15 .mu.m was prepared under typical diamond powder
mix preparation conditions in a high shear mixer, together with 1%
by mass cobalt powder in the absence of any WC milling media. This
powder mixture was sintered onto a standard cemented WC substrate
under typical pressure and temperature conditions in order to
produce a polycrystalline diamond layer bonded to the substrate.
The resultant sample is designated Sample C in Table 1 below.
[0041] The samples A to C were all subjected to an analysis as
described above to determine the homogeneity of the tungsten
carbide species in the polycrystalline diamond layer of each
sample. The results are set out in Table 1.
TABLE-US-00001 TABLE 1 Mix preparation details Final
microstructure: Amount WC character WC Average Relative ID
Description (mass %) size Volume % sd 1A WC 0.7 <0.5 .mu.m 0.16
0.84 (admilled) 1B WC 0.7 0.35- 0.31 0.55 (admixed) 0.7 .mu.m 1C
Undoped -- -- 0.26 1.2
[0042] It will be noted from the above, that relative standard
deviation of WC grain size for Samples A and B, according to the
invention, was far less than that of Sample C, produced using a
method of the prior art.
[0043] When bulk quantities of PCD materials were then generated
following the compositions of samples 1A, 1B and 1C; a very
significant decrease in the number of carbide precipitate defects
was observed in the materials generated from compositions 1A and
1B. For the same synthesis conditions, the levels of the defect in
the undoped sample C type materials were five times higher than in
those of this invention (sample A and B type materials). The
defects were additionally of much larger scale in the undoped
materials.
Example 2
Sample 2A--WC Introduced by Admilling
[0044] A multimodal diamond powder with an average grain size of
approximately 6 .mu.m was milled under typical diamond powder mix
preparation conditions in a planetary ball mill, together with 1%
by mass cobalt powder using WC milling balls. The milling
conditions were monitored so as to maximise the erosion of the WC
milling media allowing the addition of WC to the mixture at an
overall level of 1.5 mass % in the final diamond mixture. The size
of the WC fragment introduced in this manner was typically less
than 0.5 .mu.m. This powder mixture was sintered onto a standard
cemented WC substrate under typical pressure and temperature
conditions in order to produce a polycrystalline diamond layer ell
bonded to the substrate. The resultant sample is designated Sample
2A in Table 2 below.
Sample 2C--Comparative Sample Produced by Admixing
[0045] A multimodal diamond powder with an average grain size of
approximately 6 .mu.m was prepared under typical diamond powder mix
preparation conditions in a high shear mixer, together with 1% by
mass cobalt powder in the absence of any WC milling media. This
powder mixture was sintered onto a standard cemented WC substrate
under typical pressure and temperature conditions in order to
produce a polycrystalline diamond layer bonded to the substrate.
The resultant sample is designated Sample 2C in Table 2 below.
TABLE-US-00002 TABLE 2 Mix preparation details Final
microstructure: Amount WC character WC Average Relative ID
Description (mass %) size Volume % sd 2A WC 1.5 <0.5 .mu.m 0.54
0.62 (admilled) 2C Undoped -- -- 0.47 1.3
[0046] When bulk quantities of PCD materials were then generated
following the compositions of samples 2A, and 2C; a significant
decrease in the number of carbide precipitate defects was observed
in the materials generated from composition 2A. For the same
synthesis conditions, the levels of the defect in the undoped
sample 2C type materials were at least double those that occurred
in materials of this invention (sample 2A type material).
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