U.S. patent application number 16/762831 was filed with the patent office on 2020-08-27 for superhard constructions & methods of making same.
This patent application is currently assigned to ELEMENT SIX (UK) LIMITED. The applicant listed for this patent is ELEMENT SIX (UK) LIMITED. Invention is credited to DONG WANG.
Application Number | 20200269321 16/762831 |
Document ID | / |
Family ID | 1000004871159 |
Filed Date | 2020-08-27 |
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United States Patent
Application |
20200269321 |
Kind Code |
A1 |
WANG; DONG |
August 27, 2020 |
SUPERHARD CONSTRUCTIONS & METHODS OF MAKING SAME
Abstract
A super hard polycrystalline construction includes a first
region having a body of thermally stable polycrystalline super hard
material with an exposed surface forming a working surface, and a
peripheral side edge. The polycrystalline super hard material has a
plurality of intergrown grains of super hard material, a second
region forming a substrate to the first region, and a third region
interposed between the first and second regions. The third region
extends across a surface of the second region along an interface,
the third region having a composite material having a first phase
comprising a plurality of non-intergrown diamond grains, the
majority of said diamond grains having a coating comprising
nano-sized cBN particles. There is also disclosed a method of
forming such a construction.
Inventors: |
WANG; DONG; (DIDCOT,
GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ELEMENT SIX (UK) LIMITED |
DIDCOT, OXFORDSHIRE |
|
GB |
|
|
Assignee: |
ELEMENT SIX (UK) LIMITED
DIDCOT, OXFORDSHIRE
GB
|
Family ID: |
1000004871159 |
Appl. No.: |
16/762831 |
Filed: |
December 21, 2018 |
PCT Filed: |
December 21, 2018 |
PCT NO: |
PCT/EP2018/086593 |
371 Date: |
May 8, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B22F 3/14 20130101; C22C
26/00 20130101; B22F 2003/242 20130101; B22F 2005/001 20130101;
C22C 29/08 20130101; C22C 2026/007 20130101; B22F 3/24 20130101;
B22F 7/06 20130101; B22F 2998/10 20130101 |
International
Class: |
B22F 7/06 20060101
B22F007/06; B22F 3/14 20060101 B22F003/14; C22C 29/08 20060101
C22C029/08; C22C 26/00 20060101 C22C026/00; B22F 3/24 20060101
B22F003/24 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 31, 2017 |
GB |
1722318.1 |
Claims
1. A super hard polycrystalline construction comprising: a first
region comprising a body of thermally stable polycrystalline super
hard material having an exposed surface forming a working surface,
and a peripheral side edge, said polycrystalline super hard
material comprising a plurality of intergrown grains of super hard
material; a second region forming a substrate to the first region;
and a third region interposed between the first and second regions;
wherein: the third region extends across a surface of the second
region along an interface, the third region comprising a composite
material having a first phase comprising a plurality of
non-intergrown diamond grains, the majority of said diamond grains
having a coating comprising nano-sized cBN particles.
2. The super hard polycrystalline construction of claim 1, wherein
the coatings of the non-intergrown diamond grains of the third
region have a thickness of between around 100 nm to around 800
nm.
3. (canceled)
4. The polycrystalline super hard construction of claim 1, wherein
the cBN particles coating the diamond grains in the third region
have an average grain size of between around 100 nm to around 200
nm.
5. The polycrystalline super hard construction of claim 1, wherein
the composite material of the third region further comprises a
second phase.
6. The polycrystalline super hard construction of claim 5, wherein
the second phase comprises cBN, and/or WC, and/or wBN.
7. The polycrystalline super hard construction of claim 1, wherein
the coated non-intergrown diamond grains comprise between around 20
vol % to around 98 vol % of the third region.
8. The polycrystalline super hard construction of claim 1, wherein
the third region further comprises a matrix material comprising any
one or more of cobalt, aluminium, and/or nickel, and/or one or more
alloys or compounds thereof.
9. The polycrystalline super hard construction of claim 1, wherein
the working surface is substantially non-planar.
10. The polycrystalline super hard construction of claim 1, wherein
the grains of super hard material of the first region comprise
diamond grains, the first region forming a body of polycrystalline
diamond material.
11. (canceled)
12. The polycrystalline super hard construction of claim 1, wherein
the composite material of the third region is more acid resistant
than polycrystalline diamond material having a binder-catalyst
phase comprising cobalt, and/or more acid resistant than cemented
carbide material.
13. The polycrystalline super hard construction of claim 12,
wherein the composite material of the third region is more
resistant to boiling HCl acid than polycrystalline diamond material
having a binder-catalyst phase comprising cobalt, and/or more
resistant to boiling HCl acid than cemented carbide material.
14. The polycrystalline super hard construction of claim 1, wherein
the second region comprises cemented carbide material.
15. The polycrystalline super hard construction of claim 14,
wherein the cemented carbide material comprises tungsten carbide
particles bonded together by a binder material, the binder material
comprising any one or more of Co, Ni, V or Cr, or an alloy
thereof.
16. The super hard polycrystalline construction of claim 1, wherein
the first region is substantially free of a catalyst material for
diamond.
17. The super hard polycrystalline construction of claim 1, wherein
the thermally stable first region comprises at most 3 weight
percent of inaccessible catalyst material for diamond.
18. The super hard polycrystalline construction of claim 1, wherein
the construction has a longitudinal axis, the thickness of the
third region along a plane parallel to the longitudinal axis being
at least 0.05 mm.
19. A method of forming a super hard polycrystalline construction
comprising: forming a pre-sinter assembly comprising: a first mass
of grains or particles of a super hard material; a source of
catalysing material for the first mass of grains or particles of
super hard material; a further mass comprising diamond grains or
particles coated with nano-sized cBN particles; and a mass of
grains or particles of a material to form a substrate; treating the
pre-sinter assembly at an ultra-high pressure of around 5 GPa or
greater and a temperature to bond together the grains of super hard
material in the first mass to form a first region comprising a body
of interbonded polycrystalline super hard material bonded to a
further region formed of substantially non-interbonded grains or
particles of the super hard material in the further mass; the
further region being bonded to the substrate along an interface,
the further region forming an intermediate region between the first
region and the substrate and comprising a diamond composite
material comprising a plurality of non-intergrown diamond grains
having a coating of nan-sized cBN particles.
20. The method of claim 19, further comprising treating the
polycrystalline super hard construction to remove accessible
residual catalyst/binder material from interstitial spaces between
the interbonded grains of super hard material in the first
region.
21. The method of claim 19, wherein the step of forming the
pre-sinter assembly comprises: providing a mass of diamond grains
or particles and/or cubic boron nitride grains or particles to form
the first mass of grains or particles of super hard material.
22. The method of claim 19, wherein the step of providing the mass
of second phase grains or particles comprises providing a mass of
cBN grains, and/or WC grains and/or wBN grains or particles.
23. The method of claim 19, wherein the intermediate region further
comprises a matrix material comprising any one or more alloys or
compounds of any one or more transition metals including titanium,
zirconium, vanadium, hafnium, tantalum, niobium, chromium,
molybdenum, tungsten, copper, cobalt, nickel, iron, and/or
manganese.
24. The method of claim 23, wherein the one or more alloys or
compounds of any one or more of the transition metals comprises
oxides, nitrides, carbides, carbonitrides, and/or oxycarbides of
said transition metals.
25. The method of claim 19, wherein the matrix material further
comprises aluminium, and/or nickel, and/or one or more alloys or
compounds thereof.
26. The method of claim 19, wherein the grains of super hard
material of the first region comprise diamond grains, the first
region forming a body of polycrystalline diamond material.
Description
FIELD
[0001] This disclosure relates to superhard constructions and
methods of making such constructions, particularly but not
exclusively to constructions comprising polycrystalline diamond
(PCD) structures attached to a substrate, and tools comprising the
same, particularly but not exclusively for use in rock degradation
or drilling, or for boring into the earth.
BACKGROUND
[0002] Polycrystalline super hard materials, such as
polycrystalline diamond (PCD) and polycrystalline cubic boron
nitride (PCBN) may be used in a wide variety of tools for cutting,
machining, drilling or degrading hard or abrasive materials such as
rock, metal, ceramics, composites and wood-containing materials. In
particular, tool inserts in the form of cutting elements comprising
PCD material are widely used in drill bits for boring into the
earth to extract oil or gas. The working life of super hard tool
inserts may be limited by fracture of the super hard material,
including by spalling and chipping, or by wear of the tool
insert.
[0003] Cutting elements such as those for use in rock drill bits or
other cutting tools typically have a body in the form of a
substrate which has an interface end/surface and a super hard
material which forms a cutting layer bonded to the interface
surface of the substrate by, for example, a sintering process. The
substrate is generally formed of a tungsten carbide-cobalt alloy,
sometimes referred to as cemented tungsten carbide and the super
hard material layer is typically polycrystalline diamond (PCD),
polycrystalline cubic boron nitride (PCBN) or a thermally stable
product TSP material such as thermally stable polycrystalline
diamond.
[0004] Polycrystalline diamond (PCD) is an example of a super hard
material (also called a superabrasive material or ultra hard
material) comprising a mass of substantially inter-grown diamond
grains, forming a skeletal mass defining interstices between the
diamond grains. PCD material typically comprises at least about 80
volume % of diamond and is conventionally made by subjecting an
aggregated mass of diamond grains to an ultra-high pressure of
greater than about 5 GPa, and temperature of at least about
1,200.degree. C., for example. A material wholly or partly filling
the interstices may be referred to as filler or binder
material.
[0005] PCD is typically formed in the presence of a sintering aid
such as cobalt, which promotes the inter-growth of diamond grains.
Suitable sintering aids for PCD are also commonly referred to as a
solvent-catalyst material for diamond, owing to their function of
dissolving, to some extent, the diamond and catalysing its
re-precipitation. A solvent-catalyst for diamond is understood be a
material that is capable of promoting the growth of diamond or the
direct diamond-to-diamond inter-growth between diamond grains at a
pressure and temperature condition at which diamond is
thermodynamically stable. Consequently the interstices within the
sintered PCD product may be wholly or partially filled with
residual solvent-catalyst material. Most typically, PCD is often
formed on a cobalt-cemented tungsten carbide substrate, which
provides a source of cobalt solvent-catalyst for the PCD.
[0006] Ever increasing drives for improved productivity in the
earth boring field place ever increasing demands on the materials
used for cutting rock. Specifically, PCD materials with improved
abrasion and impact resistance are required to achieve faster cut
rates and longer tool life.
[0007] One of the factors limiting the success of the
polycrystalline diamond (PCD) abrasive cutters particularly when
used as cutting elements in drill bits for boring into the earth in
the oil and gas drilling industry is the generation of heat due to
friction between the PCD and the work material. This heat causes
the thermal degradation of the diamond layer. The thermal
degradation increases the wear rate of the cutter through increased
cracking and spalling of the PCD layer as well as back conversion
of the diamond to graphite causing increased abrasive wear. In
particular, the high temperatures incurred during operation cause
the residual binder-catalyst, e.g. cobalt, in the diamond matrix to
thermally expand. This thermal expansion is known to cause the
diamond crystalline bonds within the microstructure to be broken at
or near the cutting edge, thereby also operating to reduce the life
of the PCD cutter. Also, in high temperature cutting environments,
the cobalt in the PCD matrix can facilitate the conversion of
diamond back to graphite, which is also known to radically decrease
the performance life of the cutting element.
[0008] Attempts in the art to address the above-noted limitations
have largely focused on the solvent catalyst material's degradation
of the PCD construction by catalytic operation, and removal of the
catalyst material therefrom for the purpose of enhancing the
working life of PCD cutting elements. For example, it is known to
treat the PCD body to remove the solvent catalyst material
therefrom. One known way of doing this involves removing the
solvent catalyst material for example by an acid leaching process.
To obtain the maximum benefit, ideally all of the accessible
residual solvent catalyst should be removed from the PCD material
however, there are many examples in the prior art that acknowledge
the extreme difficulty and problems associated in practice with
fully leaching the PCD material of such residual solvent catalyst.
Firstly, it is known that removing substantially all of the
residual catalyst-binder from the interstitial spaces weakens the
PCD material by as much as 30% so whilst the abrasion resistance of
such a PCD composite may be improved there is a significant
decrease in impact resistance of the composite which reduces the
working life of the composite. Secondly, the substrate portion of
the composite which is typically formed of tungsten carbide is
particularly vulnerable to attack and degradation by the acid used
in techniques such as acid leaching. This is particularly
problematic if the interface between the PCD region and the
substrate is non planar as protruding interface features in the
carbide material would be subject to attack from the acid during
the leaching process thereby weakening the bond between the PCD
material and substrate which could reduce the working life of the
element.
[0009] To address these problems, various leaching profiles have
been developed to remove solvent catalyst material only from
specific regions in the PCD material leaving an amount of residual
catalyst in the PCD material, particularly along the interface with
the substrate to preserve the bond therebetween. However, as
mentioned above, leaving residual catalyst solvent in the cutting
element does not eliminate the problems associated with thermal
degradation due to the mismatch in coefficients of thermal
expansion between the diamond grains and solvent catalyst.
[0010] Another solution proposed in the art if it is desired to
remove all of the residual solvent catalyst from the PCD material,
is to attach a new substrate to the TS PCD once leached prior to
use as a cutting element. This is typically required due to the
vulnerability of the tungsten carbide substrate to attack and
degradation by the acid used in the conventional leaching
techniques. However, a difficulty also known to exist with such TS
PCD is the challenge associated with attaching the TS body to a new
substrate to form a usable compact. Not only are there problems in
achieving a join that has sufficient strength to withstand the
extreme working conditions such as in drilling applications but
also forming such a join has typically only been possible with
planar interfaces between such pieces. This itself results in
residual stress problems between the joined materials in
application thereby impacting the working life of the compact.
[0011] Additionally, past attempts made to attach such TS PCD to a
substrate by an HPHT process have resulted in crack formation in
the TS PCD and/or delamination between the substrate and TS PCD
body during use, making it unsuitable for use in a cutting and/or
wear environment. Such crack formation is even more problematic
when attempting to attach TS PCD to a substrate where the interface
between the two is nonplanar and therefore has not typically been
deemed viable.
[0012] It is, therefore, desirable that a thermally stable
polycrystalline diamond construction be engineered in a manner that
not only displays improved thermal characteristics, when compared
to conventional PCD, but also has improved fracture toughness
without adversely affecting the material's high strength and
abrasion resistance.
SUMMARY
[0013] Viewed from a first aspect there is provided a super hard
polycrystalline construction comprising: [0014] a first region
comprising a body of thermally stable polycrystalline super hard
material having an exposed surface forming a working surface, and a
peripheral side edge, said polycrystalline super hard material
comprising a plurality of intergrown grains of super hard material;
[0015] a second region forming a substrate to the first region; and
[0016] a third region interposed between the first and second
regions; wherein: [0017] the third region extends across a surface
of the second region along an interface, the third region
comprising a composite material having a first phase comprising a
plurality of non-intergrown diamond grains, the majority of said
diamond grains having a coating comprising nano-sized cBN
particles.
[0018] Viewed from a second aspect there is provided a method of
forming a super hard polycrystalline construction comprising:
[0019] forming a pre-sinter assembly comprising: [0020] a first
mass of grains or particles of a super hard material; [0021] a
source of catalysing material for the first mass of grains or
particles of super hard material; [0022] a further mass comprising
diamond grains or particles coated with nano-sized cBN particles;
and [0023] a mass of grains or particles of a material to form a
substrate; [0024] treating the pre-sinter assembly at an ultra-high
pressure of around 5 GPa or greater and a temperature to bond
together the grains of super hard material in the first mass to
form a first region comprising a body of interbonded
polycrystalline super hard material bonded to a further region
formed of substantially non-interbonded grains or particles of the
super hard material in the further mass; the further region being
bonded to the substrate along an interface, the further region
forming an intermediate region between the first region and the
substrate and comprising a diamond composite material comprising a
plurality of non-intergrown diamond grains having a coating of
nan-sized cBN particles.
[0025] Viewed from a further aspect there is provided a tool
comprising the superhard polycrystalline construction defined
above, the tool being for cutting, milling, grinding, drilling,
earth boring, rock drilling or other abrasive applications.
[0026] The tool may comprise, for example, a drill bit for earth
boring or rock drilling, a rotary fixed-cutter bit for use in the
oil and gas drilling industry, or a rolling cone drill bit, a hole
opening tool, an expandable tool, a reamer or other earth boring
tools.
[0027] Viewed from another aspect there is provided a drill bit or
a cutter or a component therefor comprising the superhard
polycrystalline construction defined above.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] Various versions will now be described by way of example and
with reference to the accompanying drawings in which:
[0029] FIG. 1 is a perspective view of an example of a conventional
PCD cutter element or construction for a drill bit for boring into
the earth;
[0030] FIG. 2 is a schematic cross-section of a conventional
portion of a PCD micro-structure with interstices between the
inter-bonded diamond grains filled with a non-diamond phase
material;
[0031] FIG. 3 is a schematic cross-section of a first example of a
superhard construction;
[0032] FIG. 4 is a schematic cross-section of a second example of a
superhard construction;
[0033] FIG. 5 is a schematic cross-section of a third example of a
superhard construction;
[0034] FIG. 6 is a schematic cross-section of a fourth example of a
superhard construction;
[0035] FIG. 7 is a schematic plan view of the superhard
construction of FIG. 5;
[0036] FIG. 8 is a schematic plan view of the superhard
construction of FIG. 6;
[0037] FIG. 9 is a is a schematic alternative plan view of the
superhard construction of FIG. 5; and
[0038] FIG. 10 is a schematic cross-section of a sixth example of a
super hard construction.
[0039] The same references refer to the same general features in
all the drawings.
DESCRIPTION
[0040] As used herein, a "superhard material" is a material having
a Vickers hardness of at least about 28 GPa. Diamond and cubic
boron nitride (cBN) material are examples of superhard
materials.
[0041] As used herein, a "superhard construction" means a
construction comprising a body of polycrystalline superhard
material. In such a construction, a substrate may be attached
thereto.
[0042] As used herein, polycrystalline diamond (PCD) is a type of
polycrystalline superhard (PCS) material comprising a mass of
diamond grains, a substantial portion of which are directly
inter-bonded (intergrown) with each other and in which the content
of diamond is at least about 80 volume percent of the material. In
one example of PCD material, directly after sintering, interstices
between the diamond grains may be at least partly filled with a
binder material comprising a catalyst for diamond. As used herein,
"interstices" or "interstitial regions" are regions between the
diamond grains of PCD material.
[0043] A "catalyst material" for a superhard material is capable of
promoting the growth or sintering of the superhard material.
[0044] The term "substrate" as used herein means any substrate over
which the superhard material layer is formed. For example, a
"substrate" as used herein may be a transition layer formed over
another substrate.
[0045] As used herein, the term "integrally formed" means regions
or parts are produced contiguous with each other and are not
separated by a different kind of material.
[0046] As used herein, the term "super hard composite" means a
composite material formed of substantially non-intergrown grains of
super hard material in a matrix of binder phase material, for
example less than 3% of the grains of super hard material are
intergrown, and in some instances none of the super hard grains are
intergrown. Whether or not the super hard grains are intergrown may
be determined using conventional methods of SEM or X-ray analysis
of images taken of the construction. In addition, for a
substantially non-intergrown structure, the wear resistance of the
material will be substantially less (that is, worse) than sintered
polycrystalline diamond material having the same average grain size
of diamond grains as the super hard grains in the composite
structure. This may be confirmed using conventional tests such as a
vertical borer test of the material.
[0047] FIG. 1 is a schematic view of an example of a conventional
PCD super hard construction such as a cutting element 1 which
includes a substrate 3 with a layer of superhard material 2 formed
on the substrate 3. The substrate 3 may be formed of a hard
material such as cemented tungsten carbide. The superhard material
2 may be, for example, high density polycrystalline diamond (PCD)
comprising at least 80 vol % of interbonded (intergrown) diamond
grains. The cutting element 1 may be mounted into a bit body such
as a drag bit body (not shown) and may be suitable, for example,
for use as a cutter insert for a drill bit for boring into the
earth.
[0048] The exposed top surface of the superhard material opposite
the substrate forms the cutting face 4, also known as the working
surface, which is the surface which, along with its edge 6,
performs the cutting in use.
[0049] At one end of the substrate 3 is an interface surface 8. As
shown in FIG. 1, the substrate 3 is generally cylindrical and has a
peripheral surface 10 and a peripheral top edge 12.
[0050] The working surface or "rake face" 4 of the polycrystalline
composite construction 1 is the surface or surfaces over which the
chips of material being cut flow when the cutter is used to cut
material from a body, the rake face 4 directing the flow of newly
formed chips. This face 4 is commonly also referred to as the top
face or working surface of the cutting element as the working
surface 4 is the surface which, along with its edge 6, is intended
to perform the cutting of a body in use. It is understood that the
term "cutting edge", as used herein, refers to the actual cutting
edge, defined functionally as above, at any particular stage or at
more than one stage of the cutter wear progression up to failure of
the cutter, including but not limited to the cutter in a
substantially unworn or unused state.
[0051] As used herein, "chips" are the pieces of a body removed
from the work surface of the body being cut by the polycrystalline
composite construction 1 in use.
[0052] As used herein, a "wear scar" is a surface of a cutter
formed in use by the removal of a volume of cutter material due to
wear of the cutter. A flank face may comprise a wear scar. As a
cutter wears in use, material may progressively be removed from
proximate the cutting edge, thereby continually redefining the
position and shape of the cutting edge, rake face and flank as the
wear scar forms.
[0053] The substrate 3 is typically formed of a hard material such
as a cemented carbide material, for example, cemented tungsten
carbide.
[0054] As shown in FIG. 2, during formation of a conventional
polycrystalline composite construction 1, the interstices 24
between the inter-bonded grains 22 of super hard material such as
diamond grains in the case of PCD, may be at least partly filled
with a non-super hard phase material. This non-super hard phase
material, also known as a filler material may comprise residual
catalyst/binder material, for example cobalt.
[0055] FIGS. 3 to 10 are schematic cross-sections through examples
of super hard constructions which may have the same outer shape as
the construction 1 of FIG. 1.
[0056] In a first example, as shown in FIG. 3, the superhard
construction 30 includes a layer or region of super hard material
34 forming the rake face or cutting surface 4 and having the
cutting edge 6, a substrate 32 and a region 36 intermediate the
layer of superhard material 34 and the substrate 32. The interface
37 between the substrate and the intermediate region 36 has at
least a portion having an uneven topology. This may be interpreted
as, but not limited to, covering one or more of the surface being
non-uniform, varying, irregular, rugged, not level, and/or not
smooth, and/or with peaks and troughs. Additionally, in the example
shown in FIG. 3, the interface 38 between the layer of super hard
material 34 and the intermediate region 36 is substantially
non-planar.
[0057] In the example of FIG. 3, the intermediate region 36 does
not form part of the working surface but is spaced therefrom by a
region of the super hard material 34. Additionally, the
intermediate region 36 of super hard composite material extends
across the interface 37 with the substrate 32 and spaces the super
hard layer 34 from the substrate 32.
[0058] The example of a super hard construction 40 shown in FIG. 4
differs from that shown in FIG. 3 in that the interface 48 between
the layer of super hard material 44 and the intermediate region 46
is substantially planar.
[0059] The further example of a super hard construction 50 shown in
FIG. 5 differs from that shown in FIG. 3 in that an intermediate
region 56 of a composite material formed of non-interbonded grains
of super hard material, such as diamond grains, that is interposed
between a substrate 52 and layer of super hard material 54 extends
to and forms part of the working surface 4 of the super hard
construction 50. The interface 57 between the intermediate region
56 and the substrate 52 has at least a portion having an uneven
topology and the interface 58 between the intermediate region 56
and the layer of super hard material 54 is also substantially
non-planar, the interface 58 being concavely arcuate.
[0060] FIG. 6 is an example similar to that shown in FIG. 5 with
the exception that the interface 68 between the region or layer of
polycrystalline super hard material 64 and the intermediate region
68 is sloped outwardly from the working surface towards the
substrate 62 rather than concavely curved, and that is shown by the
inclined plane depicted in in cross section in FIG. 6, the
intermediate region 66 thereby comprising a truncated cone
projecting from the substrate 62 and extending through the layer or
region of super hard material 64 to the cutting face, forming part
of the working surface of the super hard construction 60.
[0061] FIG. 7 shows the example construction of FIG. 5 in plan view
and it will be seen that the super hard region or layer 54 forms an
annular portion around the outer peripheral surface of the
intermediate region of composite material 56.
[0062] As shown in the plan views, FIGS. 7 and 8, of the examples
of FIGS. 5 and 6 respectively, the super hard layer or region 54
may form an annular portion around the outer peripheral surface of
the intermediate region 56 of composite material, or the layer or
region of super hard material 64 may be in the form of segments
interposed around the cutting edge with the intermediate region 64.
The advantage of such a construction may be that the construction
may be rotatable after use such that a different cutting edge may
be presented to the surface to be cut and also the segments may act
to confine damage to a limited area of the construction during
use.
[0063] In some examples, such as that shown in FIG. 9, and in
particular those where the intermediate region 74 extends to and
forms part of the cutting face 4, the interface 76 between the
intermediate region 74 and the layer of super hard material 72 may
be ridged or grooved, such ridges or grooves extending, for
example, from the cutting face 4 to the flank face of the
construction.
[0064] In some examples (not shown), the intermediate region may
have the general structure of that shown in FIGS. 5 and 6 but may
not extend all the way to or form part of the working surface. For
example, the intermediate region may extend to a distance of around
0.5 mm or less from the working surface.
[0065] In the further example shown in FIG. 10, the super hard
construction 90 comprises a substrate 92, a layer of super hard
material 94 and an intermediate region 96 between the layer of
super hard material 94 and the substrate 92 spacing the layer of
super hard material 94 from the substrate 92. The interface 97
between the substrate and the intermediate region 96 has at least a
portion having an uneven topology and the interface 98 between the
intermediate region 96 and the layer of super hard material 94 is
also substantially non-planar, and may comprise one or more grooves
or ridges to provide an interlocking fit between the two
layers.
[0066] In one or more of the examples, such as those shown in any
one or more of FIGS. 3 to 10, the layer or region of super hard
material 34, 44, 54, 64, 74, 94, prior to final processing and
directly after sintering, may for example have a micro-structure
with interstices between the inter-bonded grains of super hard
material filled with a non-super hard phase material such as that
shown in the representation of conventional PCD in FIG. 2. However,
in the end product, in the case of the super hard grains being
diamond, the interstitial spaces between inter-bonded diamond
grains are substantially free of accessible residual solvent
catalyst that would otherwise be present in the interstitial spaces
and the layer or region of super hard material 34, 44, 54, 64, 74,
94, is considered to be fully leached thermally stable PCD.
[0067] The super hard material of the various examples used to form
the layer or region of super hard material 34, 44, 54, 64, 74, 94,
may be, for example, polycrystalline diamond (PCD) and/or
polycrystalline cubic boron nitride (PCBN) and/or lonsdaleite and
the super hard particles or grains may be of natural and/or
synthetic origin.
[0068] The substrate of the examples, 32, 42, 52, 62, 72, 92 may be
formed of a hard material such as a cemented carbide material and
may include, for example, cemented tungsten carbide, cemented
tantalum carbide, cemented titanium carbide, cemented molybdenum
carbide or mixtures thereof. The binder metal for such carbides
suitable for forming the substrate 32, 42, 52, 62, 72, 92 may be,
for example, nickel, cobalt, iron or an alloy containing one or
more of these metals and may include additional elements or
compounds of other materials such as chromium, or vanadium. This
binder may, for example, be present in an amount of 10 to 20 mass
%, but this may be as low as 6 mass % or less.
[0069] In some examples, the layer or region of polycrystalline
super hard material 34, 44, 54, 64, 74, 94, may be a high density
PCD formed of more than 95 vol % of diamond. Such a PCD body may be
formed using known methods such as by sintering the diamond grains
at sintering pressures of around 8 GPa and above, as described in
US patent application published as US 2010/0084196.
[0070] In some examples, the layer or region of polycrystalline
super hard material 34, 44, 54, 64, 74, 94, may be formed of high
density PCD comprising a sintered mass of nano diamond grains as
set out in US patent application published as US2005/019114.
[0071] In some examples, high density or binderless PcBN, and PcBN
constructions formed from nanomaterials may also be formed
according to known methods.
[0072] In some examples, the layer or region of super hard material
34, 44, 54, 64, 74, 94, may comprise PCBN. Components comprising
PCBN are used principally for machining metals. PCBN material
comprises a sintered mass of cubic boron nitride (cBN) grains. The
cBN content of PCBN materials may be at least about 40 volume %.
When the cBN content in the PCBN is at least about 70 volume %
there may be substantial direct contact among the cBN grains. When
the cBN content is in the range from about 40 volume % to about 60
volume % of the compact, then the extent of direct contact among
the cBN grains is limited. PCBN may be made by subjecting a mass of
cBN particles together with a powdered matrix phase, to a
temperature and pressure at which the cBN is thermodynamically more
stable than the hexagonal form of boron nitride, hBN. PCBN is less
wear resistant than PCD which may make it suitable for different
applications to that of PCD.
[0073] As used herein, a PCD or PCBN grade is a PCD or PCBN
material characterised in terms of the volume content and size of
diamond grains in the case of PCD or cBN grains in the case of
PCBN, the volume content of interstitial regions between the
grains, and composition of material that may be present within the
interstitial regions. A grade of super hard material may be made by
a process including providing an aggregate mass of super hard
grains having a size distribution suitable for the grade,
optionally introducing catalyst material or additive material into
the aggregate mass, and subjecting the aggregated mass in the
presence of a source of catalyst material for the super hard
material to a pressure and temperature at which the super hard
grains are more thermodynamically stable than graphite (in the case
of diamond) or hBN (in the case of CBN), and at which the catalyst
material is molten. Under these conditions, molten catalyst
material may infiltrate from the source into the aggregated mass
and is likely to promote direct intergrowth between the diamond
grains in a process of sintering, to form a polycrystalline super
hard structure. The aggregate mass may comprise loose super hard
grains or super hard grains held together by a binder material. In
the context of diamond, the diamond grains may be natural or
synthesised diamond grains.
[0074] Different grades of super hard material such as
polycrystalline diamond may have different microstructures and
different mechanical properties, such as elastic (or Young's)
modulus E, modulus of elasticity, transverse rupture strength
(TRS), toughness (such as so-called K.sub.1C toughness), hardness,
density and coefficient of thermal expansion (CTE). Different PCD
grades may also perform differently in use. For example, the wear
rate and fracture resistance of different PCD grades may be
different.
[0075] The layer or region 34, 44, 54, 64, 74, 94, of
polycrystalline super hard material shown in the cutter elements
30, 40, 50, 60, 70, 90 of FIGS. 3 to 10 may comprise, for example,
one or more grades of super hard material and may comprise one or
more layers of super hard material which may differ in, for
example, grain size and/or composition of the super hard
material.
[0076] In particular, the grains of super hard material may be, for
example, diamond grains or particles. In the starting mixture prior
to sintering they may be, for example, bimodal, that is, the feed
comprises a mixture of a coarse fraction of diamond grains and a
fine fraction of diamond grains. In some embodiments, the coarse
fraction may have, for example, an average particle/grain size
ranging from about 10 to 60 microns. By "average particle or grain
size" it is meant that the individual particles/grains have a range
of sizes with the mean particle/grain size representing the
"average". The average particle/grain size of the fine fraction is
less than the size of the coarse fraction. For example, the fine
fraction may have an average grain size of between around 1/10 to
6/10 of the size of the coarse fraction, and may, in some examples,
range for example between about 0.1 to 20 microns.
[0077] In some examples, the weight ratio of the coarse diamond
fraction to the fine diamond fraction may range from about 50% to
about 97% coarse diamond and the weight ratio of the fine diamond
fraction may be from about 3% to about 50%. In other embodiments,
the weight ratio of the coarse fraction to the fine fraction may
range from about 70:30 to about 90:10.
[0078] In further examples, the weight ratio of the coarse fraction
to the fine fraction may range for example from about 60:40 to
about 80:20.
[0079] In some examples, the particle size distributions of the
coarse and fine fractions do not overlap and in some embodiments
the different size components of the compact are separated by an
order of magnitude between the separate size fractions making up
the multimodal distribution.
[0080] Some examples consist of a wide bi-modal size distribution
between the coarse and fine fractions of super hard material, but
some examples may include three or even four or more size modes
which may, for example, be separated in size by an order of
magnitude, for example, a blend of particle sizes whose average
particle size is 20 microns, 2 microns, 200 nm and 20 nm.
[0081] Sizing of diamond particles/grains into fine fraction,
coarse fraction, or other sizes in between, may be through known
processes such as jet-milling of larger diamond grains and the
like.
[0082] In some examples, the cemented metal carbide substrate 32,
42, 52, 62, 72, 92 may, for example, be conventional in composition
and, thus, may include any of the Group IVB, VB, or VIB metals,
which are pressed and sintered in the presence of a binder of
cobalt, nickel or iron, or alloys thereof. In some examples, the
metal carbide is tungsten carbide.
[0083] The intermediate region 36, 46, 56, 66, 76, 96 is a
composite material formed of non-interbonded grains of diamond
material, coated with nano-sized cBN particles, and a matrix
material. In some examples, the matrix material further comprises a
second phase such as a material that has a lower hardness than the
hardness of the diamond grains. The additional hard material may,
for example be any one or more of cBN, WC, wBN and the like. In
some examples the matrix material of the intermediate region may
comprise cobalt and/or any one or more alloys or compounds of any
one or more transition metals including titanium, zirconium,
vanadium, hafnium, tantalum, niobium, chromium, molybdenum,
tungsten, copper, cobalt, nickel, iron, and/or manganese. The one
or more alloys or compounds may, for example be any one or more
oxides, nitrides, carbides, carbonitrides, and/or oxycarbides of
said transition metals. In some examples, the matrix material
comprises aluminium, and/or nickel and/or one or more alloys or
compounds thereof.
[0084] In further examples, the matrix material of the intermediate
region comprises any one or more of titanium carbonitride, titanium
diboride, aluminium nitride, aluminium oxide, cobalt, and tungsten
carbide, or alloys or compounds thereof.
[0085] In some examples, the matrix material comprises between
around 5 vol % to around 80 vol % of the material of the
intermediate region, and in some examples comprises between around
5 to 60 vol % thereof, or between around 10 vol % to around 30 vol
% thereof.
[0086] In some examples, the super hard grains in the intermediate
region comprise between around 30 vol % to around 70 vol % of the
material of the intermediate region.
[0087] In some examples, the grains of super hard material in the
intermediate region together with any additional phase to the
matrix material comprises between around 20 vol % to around 95 vol
% of the material of the intermediate region, and in some examples
may be between around 70 vol % to around 90 vol % thereof, or
between around 50 vol % to around 90 vol % thereof, or between
around 30 vol % to around 90 vol % thereof.
[0088] The materials forming the layer or region of super hard
material, the intermediate region and the substrate all have an
associated hardness and, in some examples, the hardness of the
intermediate region is greater than the hardness of the substrate
and less than the hardness of the layer or region of super hard
material.
[0089] In some examples, the intermediate region may comprise two
or more layer or regions differing in composition and/or
construction, such as multiple layers of composite material having
at least the characteristic of non intergrown or non-interbonded
grains of super hard material coated with nano-sized cBN
particles.
[0090] The depth of the layer or region of super hard material 34,
44, 54, 64, 74, 94 from the working surface along the peripheral
side edge of the respective construction 30, 40, 50, 60, 70, 90
may, for example, be at least around 0.3 mm or greater, such as
between around 0.3 mm to around 6.5 mm. Additionally, in some
embodiments, the thickness of the intermediate region 36, 46, 56,
66, 76, 96 along a plane parallel to the longitudinal axis of the
construction may be at least 0.05 mm, for example between around
0.1 mm to around 4 mm, between around 0.3 to around 1 mm, or
between around 0.5 mm to around 0.8 mm.
[0091] In some examples, the thickness of the cBN coating on the
diamond grains in the intermediate region 36, 46, 56, 66, 76, 96 is
between around 100 nm to around 800 nm, in some examples it is
around 200 nm to around 400 nm.
[0092] In any one or more examples, the concentration of super hard
grains in the intermediate region may be graded from the interface
with the layer or region of super hard material to the
substrate.
[0093] Furthermore, in some examples, the layer or region of super
hard material comprises substantially no constituents of the matrix
material of the intermediate region.
[0094] In the superhard polycrystalline constructions according to
any one or more of the examples, the layer or region of super hard
material 34, 44, 54, 64, 72, 84, 94 comprises a thermally stable
material such as thermally stable PCD, and, if the super hard
material comprises diamond grains, may have a diamond content
between around 80 volume % to around 100 volume %. The thermally
stable layer of superhard material may, for example, be
substantially free of all accessible catalyst material for diamond,
said region forming the thermally stable first region, and may, for
example comprise at most around 3 weight percent of catalyst
material for diamond.
[0095] In some examples, the layer of thermally stable super hard
material comprises binderless PCD material and/or CVD diamond
and/or a polycrystalline super hard material formed from
nanodiamond grains.
[0096] In any one or more examples, the intermediate region 36, 46,
56, 66, 86, 96 may be bonded to the layer of superhard material
and/or to a further intermediate region, and/or to the substrate
32, 42, 52, 62, 82, 92 by a brazed joint and/or a sintered joint
along the respective interfaces.
[0097] The grains of superhard material used for making the
thermally stable superhard layer 34, 44, 54, 64, 84, 94 may be, for
example, diamond grains or particles, or for example, lonsdaleite
or cBN grains or particles. As mentioned above, in the starting
mixture prior to sintering they may be, for example, bimodal, that
is, the feed comprises a mixture of a coarse fraction of superhard
grains and a fine fraction of superhard grains.
[0098] In some examples, the binder catalyst/solvent used to assist
in the bonding of the grains of superhard material such as diamond
grains in the sintering process, may comprise cobalt or some other
iron group elements, such as iron or nickel, or an alloy thereof.
Carbides, nitrides, borides, and oxides of the metals of Groups
IV-VI in the periodic table are other examples of non-diamond
material that might be added to the sinter mix. In some examples,
the binder/catalyst/sintering aid may be Co.
[0099] The super hard constructions of the examples shown in FIGS.
3 to 10 may be fabricated, for example, as follows.
[0100] The substrate and intermediate region(s) may be pre-formed.
In some examples, the substrate may be pre-formed by pressing the
green body of grains of hard material such as tungsten carbide into
the desired shape, including the interface features at one free end
thereof, and sintering the green body to form the substrate
element. In an alternative example, the substrate interface
features may be machined from a sintered cylindrical body of hard
material, to form the desired geometry for the interface features.
The substrate may, for example, comprise WC particles bonded with a
catalyst material such as cobalt, nickel, or iron, or mixtures
thereof.
[0101] The intermediate region may be prepared as follows. A mass
of nano-sized cBN particles having, for example, an average
particle size of around 200 nm is obtained. Around 0.5 gram cBN
nano particles are dispersed into 50 ml of an aqueous solution
containing 0.05% polyvinyl alcohol (PVA, Mw 40K). An ultrasonic
probe is introduced to disperse the cBN nano particles. Once fully
dispersed, around 10 g of diamond grits are then added into the
dispersion. The mixture is then freeze dried or spray dried
following a heat treatment at 160.degree. C. for 2 hrs to coat the
diamond grits with the cBN nano particles. The process may be
repeated for example a further two to five times to obtain well
coated diamond grains. SEM imaging may be used to determine the
quality of the coating.
[0102] A green body for the superhard construction, which comprises
the pre-formed substrate, a mass of diamond grains coated with the
nano-sized cBN particles to form the intermediate region and the
particles of superhard material such as diamond particles or cubic
boron nitride particles, may be placed onto the substrate, to form
a pre-sinter assembly which may be encapsulated in a capsule for an
ultra-high pressure furnace, as is known in the art. In particular,
the substrate may be placed first into the canister followed by the
coated diamond grains and then the superabrasive particles, for
example in powder form, to form the super abrasive layer, are
placed inside a metal cup formed, for example, of niobium,
tantalum, or titanium. Alternatively, the super abrasive grains for
the super abrasive layer may be placed into the cup first followed
by the coated diamond grains and the pre-formed substrate. The
contents of the cup are then hydrostatically pressed into the
superhard powder such that the requisite powder mass is pressed
around the interface features of the preformed carbide substrate to
form the pre-composite. The pre-composite is then outgassed at
about 1050 degrees C. The pre-composite is closed by placing a
second cup at the other end and the pre-composite is sealed by cold
isostatic pressing or EB welding. The pre-composite is then
sintered to form the sintered body.
[0103] In some examples, the superhard grains for the super
abrasive layer may be diamond grains and the substrate may be
cobalt-cemented tungsten carbide. The pre-sinter assembly may
comprise an additional source of catalyst material such as a disc
containing catalyst material such as cobalt which may be placed
adjacent the diamond grains in the pre-composite assembly.
[0104] In some examples, the binder catalyst/solvent used in the
initial pre-sinter mixture may comprise cobalt or some other iron
group elements, such as iron or nickel, or an alloy thereof.
Carbides, nitrides, borides, and oxides of the metals of Groups
IV-VI in the periodic table are other examples of non-diamond
material that might be added to the sinter mix. In some examples,
the binder/catalyst/sintering aid may be Co.
[0105] In one example, the method may include loading the capsule
comprising a pre-sinter assembly into a press and subjecting the
green body to an ultra-high pressure and a temperature at which the
superhard material is thermodynamically stable to sinter the
superhard grains. In some examples, the green body may comprise
diamond grains and the pressure to which the assembly is subjected
is at least about 5 GPa and the temperature is at least about 1,300
degrees centigrade. In some examples, the pressure to which the
assembly may be subjected is around 5.5-6 GPa, but in some examples
it may be around 7.7 GPa or greater. Also, in some examples, the
temperature used in the sintering process may be in the range of
around 1400 to around 1500 degrees C.
[0106] After sintering, the polycrystalline super hard
constructions may be ground to size and may include, if desired, a
45.degree. chamfer of, for example, approximately 0.4 mm height on
the body of polycrystalline super hard material so produced.
[0107] In the examples where the superabrasive layer comprises
polycrystalline diamond material (PCD), solvent/catalyst for the
diamond grains may be introduced by various methods, including
admixing or blending solvent/catalyst material in powder form with
the diamond grains, depositing solvent/catalyst material onto
surfaces of the diamond grains, or infiltrating solvent/catalyst
material into the aggregated mass from a source of the material,
either prior to the sintering step or as part of the sintering
step, for example from the substrate. Methods of depositing
solvent/catalyst for diamond, such as cobalt, onto surfaces of
diamond grains are well known in the art, and include chemical
vapour deposition (CVD), physical vapour deposition (PVD), sputter
coating, electrochemical methods, electroless coating methods and
atomic layer deposition (ALD). It will be appreciated that the
advantages and disadvantages of each depend on the nature of the
sintering aid material and coating structure to be deposited, and
on characteristics of the grain.
[0108] In one example, the binder/catalyst such as cobalt may be
deposited onto surfaces of the diamond grains which are to form the
superabrasive layer (as opposed to the intermediate region) by
first depositing a pre-cursor material and then converting the
precursor material to a material that comprises elemental metallic
cobalt. For example, in the first step cobalt carbonate may be
deposited on the diamond grain surfaces using the following
reaction:
Co(NO.sub.3).sub.2+Na.sub.2CO.sub.3->CoCO.sub.3+2NaNO.sub.3
[0109] The deposition of the carbonate or other precursor for
cobalt or other solvent/catalyst for diamond may be achieved by
means of a method described in PCT patent publication number
WO/2006/032982. The cobalt carbonate may then be converted into
cobalt and water, for example, by means of pyrolysis reactions such
as the following:
CoCO.sub.3->CoO+CO.sub.2
CoO+H.sub.2->Co+H.sub.2O
[0110] In another example, cobalt powder or precursor to cobalt,
such as cobalt carbonate, may be blended with the diamond grains.
Where a precursor to a solvent/catalyst such as cobalt is used, it
may be necessary to heat treat the material in order to effect a
reaction to produce the solvent/catalyst material in elemental form
before sintering the aggregated mass.
[0111] In some examples, the cemented carbide substrate may be
formed of tungsten carbide particles bonded together by the binder
material, the binder material comprising an alloy of Co, Ni and Cr.
The tungsten carbide particles may form at least 70 weight percent
and at most 95 weight percent of the substrate. The binder material
may comprise between about 10 to 50 wt. % Ni, between about 0.1 to
10 wt. % Cr, and the remainder weight percent comprises Co.
[0112] Examples are described in more detail below with reference
to the following which are provided herein by way of illustration
only and are not intended to be limiting.
Example
1
[0113] The super hard constructions of FIGS. 3 to 10 may be formed
as follows.
[0114] The coated diamond grains which are to form the intermediate
region were made by placing 0.5 gram cBN nano particles having, for
example, an average particle size of around 200 nm are dispersed in
50 ml of an aqueous solution containing 0.05% polyvinyl alcohol
(PVA, Mw 40K). An ultrasonic probe is introduced to disperse the
cBN nano particles. Once fully dispersed, around 10 g of diamond
grits are then added into the dispersion. The mixture is then
freeze dried or spray dried following a heat treatment at
160.degree. C. for 2 hrs to coat the diamond grits with the cBN
nano particles. The process may be repeated for example up to
around five times to obtain well coated diamond grains.
[0115] The dried powder comprising the coated diamond grains was
sieved to form a pre-composite for the intermediate region.
[0116] In preparation of the components to form the PCD layer or
region of the super hard construction, diamond powder with an
average grain size of about 19 microns was mixed in a planetary
ball mill for about 1 hour with 1 wt % Co using methanol media and
tungsten carbide milling balls. After mixing, the powder was sieved
and dried in a rota vapour apparatus to remove the methanol and WC
balls. The dried powder was then returned to the planetary ball
mill for about 5 minutes to remove agglomerates before being sieved
again.
[0117] The pre-composite for the intermediate region was then
placed on top of a cemented tungsten carbide substrate shaped to
provide an interface between the substrate and the intermediate
region at least a portion of which has an uneven topology. The
substrate is also shaped to have a recess therein to receive both
the pre-composite for the intermediate region and the diamond
powder to form the PCD layer, the substrate extending around the
pre-composite for the intermediate region and diamond powder acts
as an infiltration source during the sintering process for the
sintering of the PCD layer.
[0118] About 1.4 grams of the prepared diamond power to form the
PCD layer was placed on the pre-composite for the intermediate
region to form a pre-composite assembly. The assembly was then
placed inside a refractory metal can and the can assembly was
exposed to a de-binding treatment at 500 degrees Celsius under
nitrogen and then vacuum heat treated and sealed at a temperature
of around 1100.degree. C. Subsequently the assembly was sealed and
placed into a high pressure high temperature (HPHT) apparatus. The
assembly was sintered at a pressure of around 8 GPa and a
temperature of around 1550.degree. C. for at least 30 seconds to
form the cutter construction comprising an inter-bonded
polycrystalline diamond (PCD) structure bonded to a substrate
material through an intermediate region formed of non-interbonded
diamond grains and a matrix phase. At least some constituents in
the pre-composite for the intermediate region melt during the HPHT
sintering process. In some examples the sintering time was 20-40
minutes, and in some examples was a number of hours. The diamond
composite structure forming the intermediate region contained about
60% by volume diamond and there was substantially no interbonding
between the diamond grains in the diamond composite structure. The
matrix material of the intermediate region in this example was
determined to include one or more of TiCN, Al.sub.2O.sub.3, and
Al.sub.4O.sub.3.
[0119] The cutter construction was recovered after sintering and
fully processed to a diameter of around 16 mm and an overall height
of around 13 mm with a PCD table thickness of about 1.3 mm
separated from the substrate by the intermediate region formed of a
diamond composite having a thickness of between around 0.7 mm to
0.85 mm. The intermediate region formed of the diamond composite
extended to the peripheral side edge of the construction, the
excess WC forming the substrate during sintering having been
removed to expose the peripheral side edge of the PCD layer and the
intermediate region.
[0120] To render the PCD layer thermally stable, the super hard
construction with the intermediate region and substrate attached
was subjected to a boiling HCl acid leaching treatment for a number
of hours until all accessible residual catalysing material had been
removed from the interstitial spaces between inter-bonded diamond
grains.
[0121] In some examples, the composite material of the intermediate
region is more acid resistant than polycrystalline diamond material
having a binder-catalyst phase comprising cobalt, and/or more acid
resistant than cemented carbide material. The acid resistance of
the material of the intermediate region being more acid resistant
than PCD containing interstitial cobalt and/or WC may be determined
by whether or not it is more resistant to acid damage after 30
hours in a mixture of boiling HCl and water where the HCl forms 20%
and the water the residual 80% of the acid leaching mixture, and
confirming that the material of the intermediate region shows less
than a 10% reduction in its starting weight.
[0122] The materials used to form the intermediate region(s) in the
various examples were separately tested to confirm that the super
hard grains in the material were non-intergrown (non-interbonded)
and therefore were diamond composite materials in the examples and
not considered to be polycrystalline diamond (PCD) material. The
tests performed included vertical boring mill tests with two
leached conventional polycrystalline diamond cutter elements formed
of diamond grains having an average grain size identical to the
grain size in the respective diamond composite materials and which
were sintered under pressures of around 5.5 GPa.
[0123] It was seen that the wear resistance of the diamond
composite material was at least three times less (ie worse) than
that of the conventional PCD which assisted in proving that the
diamond composite materials forming the intermediate region were
not intergrown and therefore were not considered to be
polycrystalline diamond materials. This was also evident from SEM
and X-ray images of the structures which showed the diamond grains
coated with nano-sized cBN particles not to be inter-bonded (ie not
inter-grown) and therefore not classed as PCD material.
[0124] The complete cutter construction itself was brazed to a
steel tool holder and subjected to a vertical turret lathe
test.
[0125] It was be seen that the performance of the example cutter
construction was significantly better than a conventional cutter
formed of a PCD layer bonded to a WC substrate in which the PCD
layer had the same average grain size as the PCD layer of the
example and same PCD layer thickness that had not been subjected to
an acid leaching treatment to remove all of the residual catalyst
from the PCD region.
[0126] Whilst not wishing to be bound by a particular theory, it is
believed that in the examples the composition and structure of the
intermediate region provides a good support to the TS super hard
structure, particularly as, for example, it is known that leaching
conventional PCD typically reduces the strength of the PCD by up to
around 30%. The intermediate region may be shaped to suit the
particular end application of the superhard construction, for
example, to ensure that a large surface area of TS superhard
material may be presented at the cutting edge so that as the wear
scar progresses, the wear is contained in the TS region which is
supported by a tough and strong supporting intermediate region. In
some examples, a protrusion from the intermediate region may have a
higher impact resistance compared to the superhard layer and
thereby act to assist in arresting cracks to avoid spalling or
catastrophic failure during use of the superhard construction.
[0127] The size and shape of the intermediate region and the TS
super hard region may be tailored to the final application of the
superhard material. It is believed possible to improve spalling
resistance without significantly compromising the overall abrasion
resistance of the material, which is desirable for PCD and PCBN
cutting tools.
[0128] Observation of the wear scar development during testing
showed the material's ability to generate large wear scars without
exhibiting brittle-type micro-fractures (e.g. spalling or
chipping), leading to a longer tool life.
[0129] Thus, examples of, for example, a PCD material, may be
formed having a combination of high abrasion and fracture
performance.
[0130] The superhard constructions may be finished by, for example,
grinding, to provide a super hard element which is substantially
cylindrical and having a substantially planar working surface, or a
generally domed, pointed, rounded conical or frusto-conical working
surface. The super hard element may be suitable for use in, for
example, a rotary shear (or drag) bit for boring into the earth,
for a percussion drill bit or for a pick for mining or asphalt
degradation.
[0131] While various versions have been described with reference to
a number of examples, those skilled in the art will understand that
various changes may be made and equivalents may be substituted for
elements thereof and that these examples are not intended to limit
the particular versions disclosed. For example, in some versions
each of the non-intergrown diamond grains in the third region have
a coating comprising nano-sized cBN particles. to render the PCD
thermally stable, the PCD structure with the intermediate region
attached may be subjected to acid to leach out catalyst material
from between the diamond grains, or to other methods of achieving
this, such as electrochemical methods.
* * * * *