U.S. patent application number 15/520748 was filed with the patent office on 2018-11-22 for superhard constructions & methods of making same.
The applicant listed for this patent is Element Six (UK) Limited. Invention is credited to Nedret Can.
Application Number | 20180334858 15/520748 |
Document ID | / |
Family ID | 52013325 |
Filed Date | 2018-11-22 |
United States Patent
Application |
20180334858 |
Kind Code |
A1 |
Can; Nedret |
November 22, 2018 |
SUPERHARD CONSTRUCTIONS & METHODS OF MAKING SAME
Abstract
A super hard polycrystalline construction comprises a body of
polycrystalline super hard material, said body having an exposed
working surface. The body of polycrystalline super hard material
comprises a first region adjacent the working surface and a second
region adjacent the first region; the first region being more
thermally stable than the second region; and a plurality of
apertures or channels, one or more of said apertures or channels
extending from the exposed working surface of the body into the
second region.
Inventors: |
Can; Nedret; (Oxfordshire,
GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Element Six (UK) Limited |
Oxfordshire |
|
GB |
|
|
Family ID: |
52013325 |
Appl. No.: |
15/520748 |
Filed: |
October 15, 2015 |
PCT Filed: |
October 15, 2015 |
PCT NO: |
PCT/EP2015/073941 |
371 Date: |
April 20, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
E21B 10/573 20130101;
B22F 3/24 20130101; B22F 5/00 20130101; E21B 10/5676 20130101; E21B
10/567 20130101; E21B 10/5735 20130101; B22F 7/062 20130101; B22F
2302/406 20130101; B22F 2005/001 20130101; C22C 26/00 20130101;
B22F 2003/245 20130101 |
International
Class: |
E21B 10/567 20060101
E21B010/567; B22F 7/06 20060101 B22F007/06; B22F 5/00 20060101
B22F005/00; B22F 3/24 20060101 B22F003/24; E21B 10/573 20060101
E21B010/573 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 21, 2014 |
GB |
1418660.5 |
Claims
1. A super hard polycrystalline construction comprising: a body of
polycrystalline super hard material, said body having an exposed
working surface; the body of polycrystalline super hard material
comprising a first region adjacent the working surface and a second
region adjacent the first region; the first region being more
thermally stable than the second region; and a plurality of
apertures or channels, one or more of said apertures or channels
extending from the exposed working surface of the body into the
second region.
2. The construction of claim 1, wherein one or more of said
plurality of apertures or channels are at least partly filled with
a secondary material.
3. The construction of claim 2, wherein the secondary material
comprises one or more of a ceramic, a metal, an alloy or a
refractory metal.
4. The construction of claim 2, wherein the secondary material has
a higher coefficient of thermal expansion than the polycrystalline
super hard material forming the body.
5. (canceled)
6. (canceled)
7. The construction of claim 1, wherein a plurality of said
apertures or channels have differing depths.
8. The construction of claim 1, wherein the body has a peripheral
outer surface extending between the working surface and the
substrate, and wherein one or more of the plurality of apertures or
channels closest to the peripheral outer surface have the greatest
depth of the apertures or channels extending from the working
surface into the second region.
9. The construction of claim 1, wherein the body of super hard
material comprises inter-bonded super hard grains comprising
natural and/or synthetic diamond grains, the super hard
polycrystalline construction forming a polycrystalline diamond
(PCD) construction.
10. The construction of claim 9, wherein the second region of the
body further comprises a non-super hard phase comprising a binder
phase located in interstitial spaces between the inter-bonded
diamond grains.
11. (canceled)
12. (canceled)
13. (canceled)
14. (canceled)
15. The super hard polycrystalline construction according to claim
1, wherein at least a portion of the first region of the body of
super hard material is substantially free of a catalyst material
for diamond, said portion forming a more thermally stable region
than the second region, the more thermally stable first region
comprising at most 2 weight percent of catalyst material for
diamond.
16. (canceled)
17. The super hard polycrystalline construction of claim 1, wherein
the depth of the first region from the working surface and/or a
side surface of the body is greater than around 50 microns.
18. The super hard polycrystalline construction of claim 1, wherein
the depth of the first region from the working surface and/or a
side surface of the body is up to around 1500 microns.
19. (canceled)
20. (canceled)
21. The super hard polycrystalline construction of claim 1, wherein
a number of the apertures or channels extend through the first
region of the body from the working surface and do not extend to
the interface of the first region with the second region.
22. The super hard polycrystalline construction of claim 1, wherein
one or more of the apertures or channels comprises one or more of:
a circular cross-section; a non-circular cross-section; a
curvilinear portion; and/or a substantially straight portion.
23. (canceled)
24. (canceled)
25. The super hard polycrystalline construction of claim 1, wherein
a number of the apertures or channels have a circular
cross-section, and wherein the diameters of one or more of the
apertures or channels closer to the peripheral edge of the body are
less than the diameters of one or more of the apertures or channels
closer to the longitudinal axis of the body.
26. The super hard polycrystalline construction of claim 1, wherein
the depth of the one or more apertures or channels from the working
surface is greater than or equal to around 20 microns.
27. The super hard polycrystalline construction of claim 1, wherein
the depth of the one or more apertures or channels from the working
surface is greater than or equal to around half the depth of the
polycrystalline super hard body.
28. (canceled)
29. The super hard polycrystalline construction of claim 1, wherein
the depth(s) from the working surface of one or more of the
apertures or channels closer to the peripheral edge of the body are
greater than the depth(s) of one or more of the apertures or
channels closer to the longitudinal axis of the body.
30. The super hard polycrystalline construction of claim 1 wherein
the ratio of the depth of the one or more holes or channels to the
equivalent diameter of the hole or channel is around 4:1 or
greater.
31. (canceled)
32. The super hard polycrystalline construction of claim 1 wherein
one or more of the holes or channels extend in a plane
substantially parallel to the plane of the longitudinal axis of the
construction.
33. The super hard polycrystalline construction of claim 1, wherein
one or more of the holes or channels extend in a plane inclined to
the plane of the longitudinal axis of the construction.
34. (canceled)
35. (canceled)
36. (canceled)
37. (canceled)
38. (canceled)
39. A method of forming a superhard polycrystalline construction,
comprising: providing a mass of particles or grains of superhard
material and a mass of particles or grains of hard material to form
a pre-sinter assembly; treating the pre-sinter assembly in the
presence of a catalyst/solvent material for the superhard grains at
an ultra-high pressure of around 5 GPa or greater and a temperature
to sinter together the grains of superhard material to form a body
of polycrystalline superhard material bonded to a substrate formed
of the grains or particles of hard material along an interface to
form a polycrystalline superhard construction, the superhard grains
exhibiting inter-granular bonding and defining a plurality of
interstitial regions therebetween; treating a portion of the
polycrystalline super hard construction to render a first region
more thermally stable than a second region, the first region
forming a first region adjacent a working surface; and forming a
plurality of apertures or channels, one or more of said apertures
or channels extending from the exposed working surface of the body
through the first region and into the second region.
40. (canceled)
41. The method of claim 39, wherein the step of forming a plurality
of apertures or channels comprises forming said apertures or
channels using any one or more of laser ablation, electron beam
drilling, electron discharge machining and dye sinking.
42. The method of claim 39, wherein the step of treating the
polycrystalline super hard construction to form the first region
comprises forming the more thermally stable first region to have a
depth from one or more of the working surface or a peripheral side
surface of between around 50 to around 1500 microns.
43. (canceled)
44. (canceled)
45. (canceled)
46. (canceled)
47. (canceled)
48. (canceled)
Description
FIELD
[0001] This disclosure relates to superhard constructions and
methods of making such constructions, particularly but not
exclusively to constructions comprising polycrystalline diamond
(PCD) structures, 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 superhard materials, such as polycrystalline
diamond (PCD) 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), or
a thermally stable product TSP material such as thermally stable
polycrystalline diamond.
[0004] Polycrystalline diamond (PCD) is an example of a superhard
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. Materials
that do not promote substantial coherent intergrowth between the
diamond grains may themselves form strong bonds with diamond
grains, but are not suitable solvent-catalysts for PCD
sintering.
[0006] Cemented tungsten carbide which may be used to form a
suitable substrate is formed from carbide particles being dispersed
in a cobalt matrix by mixing tungsten carbide particles/grains and
cobalt together then heating to solidify. To form the cutting
element with a superhard material layer such as PCD, diamond
particles or grains are placed adjacent the cemented tungsten
carbide body in a refractory metal enclosure such as a niobium
enclosure and are subjected to high pressure and high temperature
so that inter-grain bonding between the diamond grains occurs,
forming a polycrystalline superhard diamond layer.
[0007] In some instances, the substrate may be fully cured prior to
attachment to the superhard material layer whereas in other cases,
the substrate may be green, that is, not fully cured. In the latter
case, the substrate may fully cure during the HTHP sintering
process. The substrate may be in powder form and may solidify
during the sintering process used to sinter the superhard material
layer.
[0008] Ever increasing drives for improved productivity in the
earth boring field place ever increasing demands on the materials
used for cutting rock. Specifically, PCD materials with improved
abrasion and impact resistance are required to achieve faster cut
rates and longer tool life.
[0009] Cutting elements or tool inserts comprising PCD material are
widely used in drill bits for boring into the earth in the oil and
gas drilling industry. Rock drilling and other operations require
high abrasion resistance and impact resistance. One of the factors
limiting the success of the polycrystalline diamond (PCD) abrasive
cutters is the generation of heat due to friction between the PCD
and the work material. This heat causes the thermal degradation of
the diamond layer. The thermal degradation increases the wear rate
of the cutter through increased cracking and spalling of the PCD
layer as well as back conversion of the diamond to graphite causing
increased abrasive wear.
[0010] Methods used to improve the abrasion resistance of a PCD
composite often result in a decrease in impact resistance of the
composite.
[0011] The most wear resistant grades of PCD usually suffer from a
catastrophic fracture of the cutter before it has worn out. During
the use of these cutters, cracks grow until they reach a critical
length at which catastrophic failure occurs, namely, when a large
portion of the PCD breaks away in a brittle manner. These long,
fast growing cracks encountered during use of conventionally
sintered PCD, result in short tool life.
[0012] Furthermore, despite their high strength, polycrystalline
diamond (PCD) materials are usually susceptible to impact fracture
due to their low fracture toughness. Improving fracture toughness
without adversely affecting the material's high strength and
abrasion resistance is a challenging task.
[0013] There is therefore a need for a superhard composite that has
good or improved abrasion, fracture and impact resistance and a
method of forming such a composite.
SUMMARY
[0014] Viewed from a first aspect there is provided a super hard
polycrystalline construction comprising: [0015] a body of
polycrystalline super hard material, said body having an exposed
working surface; [0016] the body of polycrystalline super hard
material comprising a first region adjacent the working surface and
a second region adjacent the first region; the first region being
more thermally stable than the second region; and [0017] a
plurality of apertures or channels, one or more of said apertures
or channels extending from the exposed working surface of the body
into the second region.
[0018] Viewed from a second aspect there is provided a method of
forming a superhard polycrystalline construction, comprising:
[0019] providing a mass of particles or grains of superhard
material and a mass of particles or grains of hard material to form
a pre-sinter assembly; [0020] treating the pre-sinter assembly in
the presence of a catalyst/solvent material for the superhard
grains at an ultra-high pressure of around 5 GPa or greater and a
temperature to sinter together the grains of superhard material to
form a body of polycrystalline superhard material bonded to a
substrate formed of the grains or particles of hard material along
an interface to form a polycrystalline superhard construction, the
superhard grains exhibiting inter-granular bonding and defining a
plurality of interstitial regions therebetween; [0021] treating a
portion of the polycrystalline super hard construction to render a
first region more thermally stable than a second region, the first
region forming a first region adjacent a working surface; and
[0022] forming a plurality of apertures or channels, one or more of
said apertures or channels extending from the exposed working
surface of the body through the first region and into the second
region.
[0023] 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.
[0024] 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.
[0025] 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
[0026] The present invention will now be described by way of
example and with reference to the accompanying drawings in
which:
[0027] FIG. 1 is a perspective view of an example PCD cutter
element or construction for a drill bit for boring into the
earth;
[0028] FIG. 2 is a schematic cross-section of an example portion of
a PCD micro-structure with interstices between the inter-bonded
diamond grains filled with a non-diamond phase material;
[0029] FIGS. 3a to 3j are plan views of example PCD cutter elements
or constructions;
[0030] FIGS. 4a to 4c are schematic cross-sectional views through
example cutter elements or constructions; and
[0031] FIG. 5 is a sectional perspective view from above of an
example PCD cutter element or construction.
[0032] The same reference numerals refer to the same general
features in all the drawings.
DESCRIPTION
[0033] 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.
[0034] As used herein, a "superhard construction" means a
construction comprising a body of polycrystalline superhard
material. In such a construction, a substrate may be attached
thereto or alternatively the body of polycrystalline material may
be free-standing and unbacked.
[0035] 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 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, 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. In
some examples of PCD material, interstices or interstitial regions
may be substantially or partially filled with a material other than
diamond, or they may be substantially empty. PCD material may
comprise at least a region from which catalyst material has been
removed from the interstices, leaving interstitial voids between
the diamond grains.
[0036] A "catalyst material" for a superhard material is capable of
promoting the growth or sintering of the superhard material.
[0037] 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.
[0038] As used herein, the "integrally formed" regions, parts or
portions are regions, parts or portions produced contiguous with
each other and are not separated by a different kind of
material.
[0039] In an example, as shown in FIG. 1, a cutting element 1
includes a substrate 10 with a layer of superhard material 12
formed on the substrate 10. The substrate 10 may be formed of a
hard material such as cemented tungsten carbide. The superhard
material 12 may be, for example, polycrystalline diamond (PCD), or
a thermally stable product such as thermally stable PCD (TSP). 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.
[0040] The exposed top surface of the superhard material opposite
the substrate forms the cutting face 14, also known as the working
surface, which is the surface which, along with its edge 16,
performs the cutting in use.
[0041] At one end of the substrate 10 is an interface surface 18
that forms an interface with the superhard material layer 12 which
is attached thereto at this interface surface. As shown in the
example of FIG. 1, the substrate 10 is generally cylindrical and
has a peripheral surface 20 and a peripheral top edge 22.
[0042] The super hard material may be, for example, polycrystalline
diamond (PCD) and the super hard particles or grains may be of
natural or synthetic origin.
[0043] The substrate 10 may be formed of a hard material such as a
cemented carbide material and may be, for example, cemented
tungsten carbide, cemented tantalum carbide, cemented titanium
carbide, cemented molybdenum carbide or mixtures thereof. The
binder metal for such carbides suitable for forming the substrate
10 may be, for example, nickel, cobalt, iron or an alloy containing
one or more of these metals. Typically, this binder will be present
in an amount of 10 to 20 mass %, but this may be as low as 6 mass %
or less. Some of the binder metal may infiltrate the body of
polycrystalline super hard material 12 during formation of the
compact 1.
[0044] As shown in FIG. 2, during formation of the polycrystalline
composite construction 1, the interstices 24 between the 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,
nickel or iron and may also, or in place of, include one or more
other non-super hard phase additions such as, for example,
Titanium, Tungsten, Niobium, Tantalum, Zirconium, Molybdenum,
Chromium, or Vanadium. In some examples, the content of one or more
of these additional elements within the filler material may be, for
example, about 1 weight % of the filler material in the case of Ti,
about 2 weight % of the filler material in the case of V, and, in
the case of W, the content of W within the filler material may be,
for example, up to about 20 weight % of the filler material.
[0045] PCT application publication number WO2008/096314 discloses a
method of coating diamond particles, to enable the formation of
polycrystalline super hard abrasive elements or composites,
including polycrystalline super hard abrasive elements comprising
diamond in a matrix of material(s) comprising one or more of VN,
VC, HfC, NbC, TaC, Mo.sub.2C, WC. PCT application publication
number WO2011/141898 also discloses PCD and methods of forming PCD
containing additions such as vanadium carbide to improve, inter
alia, wear resistance.
[0046] Whilst wishing not to be bound by any particular theory, the
combination of metal additives within the filler material may be
considered to have the effect of better dispersing the energy of
cracks arising and propagating within the PCD material in use,
resulting in altered wear behaviour of the PCD material and
enhanced resistance to impact and fracture, and consequently
extended working life in some applications.
[0047] In accordance with some examples, a sintered body of PCD
material may be created having diamond to diamond bonding and
having a second phase comprising catalyst/solvent and WC (tungsten
carbide) dispersed through its microstructure together with or
instead of a further non-diamond phase carbide such as VC. The body
of PCD material may be formed according to standard methods, for
example as described in PCT application publication number
WO2011/141898, using HpHT conditions to produce a sintered PCD
table.
[0048] The polycrystalline composite construction 1 when used as a
cutting element may be mounted in use in a bit body, such as a drag
bit body (not shown).
[0049] The substrate 10 may be, for example, generally cylindrical
having a peripheral surface, a peripheral top edge and a distal
free end.
[0050] The working surface or "rake face" 14 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 14 directing the flow of newly
formed chips. This face 14 is commonly also referred to as the top
face or working surface of the cutting element as the working
surface 14 is the surface which, along with its edge 16, 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] As used herein, a PCD grade is a PCD material characterised
in terms of the volume content and size of diamond grains, the
volume content of interstitial regions between the diamond grains
and composition of material that may be present within the
interstitial regions. A grade of PCD material may be made by a
process including providing an aggregate mass of diamond 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 diamond to a pressure and
temperature at which diamond is more thermodynamically stable than
graphite 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 PCD structure. The aggregate mass may comprise loose
diamond grains or diamond grains held together by a binder material
and said diamond grains may be natural or synthesised diamond
grains.
[0054] Different PCD grades 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.
[0055] All of the PCD grades may comprise interstitial regions
filled with material comprising cobalt metal, which is an example
of catalyst material for diamond.
[0056] The PCD structure 12 may comprise one or more PCD
grades.
[0057] The grains of superhard material may be, for example,
diamond grains or particles. In the starting mixture prior to
sintering they may be, for example, bimodal, that is, the feed
comprises a mixture of a coarse fraction of diamond grains and a
fine fraction of diamond grains. In some examples, 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.
[0058] 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 examples, the
weight ratio of the coarse fraction to the fine fraction may range
from about 70:30 to about 90:10.
[0059] 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.
[0060] In some examples, the particle size distributions of the
coarse and fine fractions do not overlap and in some examples the
different size components of the compact are separated by an order
of magnitude between the separate size fractions making up the
multimodal distribution.
[0061] Some examples consist of a wide bi-modal size distribution
between the coarse and fine fractions of superhard 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.
[0062] 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.
[0063] In some examples, the binder catalyst/solvent may comprise
cobalt or some other iron group elements, such as iron or nickel,
or an alloy thereof. Carbides, nitrides, borides, and oxides of the
metals of Groups IV-VI in the periodic table are other examples of
non-diamond material that might be added to the sinter mix. In some
examples, the binder/catalyst/sintering aid may be Co.
[0064] The cemented metal carbide substrate may be conventional in
composition and, thus, may be include any of the Group IVB, VB, or
VIB metals, which are pressed and sintered in the presence of a
binder of cobalt, nickel or iron, or alloys thereof. In some
examples, the metal carbide is tungsten carbide.
[0065] The PCD construction 1 may further processed after
sintering. For example, catalyst material may be removed from a
first region of the PCD structure 12 adjacent the working surface
14 or the side surface or both the working surface 14 and the side
surface. This may be done by treating a portion of the PCD
structure with acid to leach out catalyst material from between the
diamond grains, or by other methods such as electrochemical
methods. A thermally stable region, which may be substantially
porous, extending a depth of at least about 50 microns or at least
about 100 microns from a surface of the PCD structure, may thus be
provided which may further enhance the thermal stability of the PCD
element. The more thermally stable region is separated from the
substrate 20 by a less thermally stable second region. The second
region is bonded to the substrate 20 along an interface 170 which
may be substantially planar or non planar. The boundary between the
first region and the second region is denoted by reference numeral
160 in FIGS. 4(a) to 4(c) and this boundary may be substantially
planar or non planar. The depth of the more thermally stable first
region as measured from the working surface 14 may be, for example,
less than around 100 microns, or greater than 100 microns, for
example up to around 1500 microns, up to around 1200 microns, up to
around 750 microns, up to around 650 microns, up to around 450
microns, up to around 350 microns, up to around 300 microns or up
to around 200 microns.
[0066] One or more apertures or channels that extend into the PCD
structure from the working surface 14 are then created in the PCD
to extend beyond the boundary 160 between the first and the second
regions.
[0067] As shown in FIGS. 3a to 3j, the polycrystalline superhard
construction according to some examples comprises a pattern of
apertures or channels 150 one or more of which, as shown in FIGS.
4a to 4c, extend from the working surface 14 of the polycrystalline
superhard body 12 across the boundary 160 between the first and
second regions and into the second region. In some examples, as
shown in FIG. 4(b), one or more apertures or channels may extend
into the substrate 20.
[0068] The apertures or channels 50 may comprise, in some examples,
as shown in FIGS. 3a to 5, an ordered array of apertures or
channels 50 or, in other examples, the channels or apertures 50 may
be randomly arranged or spaced.
[0069] Whilst one or more of the apertures or channels 50 extend(s)
into the second region adjacent the substrate 20, and some may
extend throughout the entire depth of the second region, one or
more additional apertures or channels may extend through only a
portion of the polycrystalline body 12 and terminate in the more
thermally stable first region.
[0070] The shape of one or more of the apertures or channels 50 at
the working surface 14 may be circular and/or non-circular and the
equivalent diameter of the apertures or channels 50 may be
substantially equal for two or more of the channels or
substantially different and may be the same throughout the depth of
the aperture or channel or increasing or decreasing throughout its
depth. In some examples, the minimum depth of one or more of the
apertures or channels 50 is around 20 microns or more.
[0071] In some examples, the smallest dimension of one or more of
the apertures or channels 50, for example the diameter for
apertures or channels having a circular cross-section, is greater
than or equal to around 2 microns. In the event that the aperture
or channel has a non-circular cross-section, the smaller dimension
is the side of a polygon or equivalent diameter.
[0072] In some examples, the ratio of the depth of the aperture or
channel 50 to the equivalent diameter of the aperture or channel is
not less than around 4:1.
[0073] The apertures or channels 50 may extend in a plane
substantially perpendicular to the plane of the working surface 14
or inclined with respect thereto.
[0074] As shown in FIG. 3a, the apertures or channels 50 may have
differing diameters with, for example, the apertures or channels
having the larger diameter being arranged in an annular array
closest to the outer periphery of the construction and one or more
concentrically arranged annular arrays of additional apertures may
be located with decreasing diameters therewithin.
[0075] As shown in FIG. 3b, the apertures or channels 50 may have a
non-circular cross-section and the number of apertures or channels
in each concentrically arranged array may differ with, for example,
fewer apertures being located in the outermost array (as shown for
non-circular cross-sections in FIG. 3b and for circular
cross-sections in FIG. 3f).
[0076] As shown in FIGS. 3c and 3d, a single aperture or channel 50
may be made in the working surface 14 located closest to the
periphery of the construction which is closest to the first contact
point between the construction and the rock in use. This aperture
or channel may have a smaller or larger diameter than other holes
located in its vicinity (see FIGS. 3c and 3d respectively).
[0077] In another example, two apertures or channels 50 are
strategically located not less than around 5 mm apart in the
working surface 14.
[0078] As shown in FIGS. 3c and 3d, there may be a plurality of
additional apertures or channels 50 located around the said
location of the single aperture or channel and these additional
apertures or channels may have differing or the same diameter as
one another and may be, for example, of a smaller diameter than the
single aperture or channel.
[0079] As shown in FIGS. 3e and 5, the apertures or channels 50 may
be arranged in a substantially symmetrical distribution with
respect to an axis, radius, side/edge or reference point of the
construction.
[0080] In other examples, the apertures or channels 50 may be
randomly distributed/arranged in the construction.
[0081] In some examples, the apertures or channels 50 may be
located in designated regions or segments of the working surface 14
as shown in FIGS. 3g to 3j, to enable the construction to be
re-used in use by turning the construction to present a new segment
to, for example, the rock being cut. Thus the apertures or channels
50 may be made in a portion of the construction to contain the
damage in one sector of the construction to allow it to be reused.
In one example such a region is delimited by two concentric regions
one being the outer surface of the cutting element and the other
circumference being smaller, for example, and no more than around 4
mm in radius.
[0082] In some examples, the apertures or channels 50 may be
substantially parallel or non-parallel along their depth.
[0083] In some examples, the diameter of one or more of the
apertures or channels 50 may be nano-sized, for example, less than
2 microns. The depth of the nano-sized apertures or channels may,
in some examples, be at least around 20 microns. Furthermore, in
some examples, the ratio of the depth to the equivalent diameter of
the nano-sized holes may be, for example, not less than around
10.
[0084] A number of apertures or channels 50 may be filled with a
secondary material, for example a material which is non leachable
such as a ceramic, metal, alloy, refractories, or combination
thereof. When the apertures or channels are open they act as
reflectors of energy and when there are filled with a secondary
material they may act as energy absorbers. Whilst not wishing to be
bound by theory it is believed that the open apertures or channels
may act as crack barriers, blunting the crack tip and slowing down
the crack growth or propagation by increasing the required energy
for its propagation. The filled apertures or channels are believed
may act as energy absorbers by allowing the crack to progress at a
slower rate thus reducing the risk of catastrophic failure.
[0085] The cutter of FIGS. 1, 3a to 5 having the microstructure of
FIG. 2 may be fabricated, for example, as follows.
[0086] As used herein, a "green body" is a body comprising grains
to be sintered and a means of holding the grains together, such as
a binder, for example an organic binder.
[0087] The green body may also comprise catalyst material for
promoting the sintering of the superhard grains. The green body may
be made by combining the grains or particles with the
binder/catalyst and forming them into a body having substantially
the same general shape as that of the intended sintered body, and
drying the binder. At least some of the binder material may be
removed by, for example, burning it off. The green body may be
formed by a method including a compaction process, an injection
process or other methods such as molding, extrusion, deposition
modelling methods.
[0088] A green body for the superhard construction may be placed
onto a substrate, such as a pre-formed cemented carbide 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.
The substrate may provide a source of catalyst material for
promoting the sintering of the superhard grains. In some
embodiments, the superhard grains may be diamond grains and the
substrate may be cobalt-cemented tungsten carbide, the cobalt in
the substrate being a source of catalyst for sintering the diamond
grains. The pre-sinter assembly may comprise an additional source
of catalyst material.
[0089] In one version, 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 embodiments, 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.
[0090] A version of the method may include making a diamond
composite structure by means of a method disclosed, for example, in
PCT application publication number WO2009/128034. A powder blend
comprising diamond particles, and a metal binder material, such as
cobalt may be prepared by combining these particles and blending
them together. An effective powder preparation technology may be
used to blend the powders, such as wet or dry multi-directional
mixing, planetary ball milling and high shear mixing with a
homogenizer. In one embodiment, the mean size of the diamond
particles may be at least about 50 microns and they may be combined
with other particles by mixing the powders or, in some cases,
stirring the powders together by hand. In one version of the
method, precursor materials suitable for subsequent conversion into
binder material may be included in the powder blend, and in one
version of the method, metal binder material may be introduced in a
form suitable for infiltration into a green body. The powder blend
may be deposited in a die or mold and compacted to form a green
body, for example by uni-axial compaction or other compaction
method, such as cold isostatic pressing (CIP). The green body may
be subjected to a sintering process known in the art to form a
sintered article. In one version, 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.
[0091] After sintering, the polycrystalline super hard
constructions may be ground to size and may include, if desired, a
45.degree. chamfer of approximately 0.4 mm height on the body of
polycrystalline super hard material so produced.
[0092] The sintered article may be subjected to a subsequent
treatment at a pressure and temperature at which diamond is
thermally stable to convert some or all of the non-diamond carbon
back into diamond and produce a diamond composite structure. An
ultra-high pressure furnace well known in the art of diamond
synthesis may be used and the pressure may be at least about 5.5
GPa and the temperature may be at least about 1,250 degrees
centigrade for the second sintering process.
[0093] A further embodiment of a superhard construction may be made
by a method including providing a PCD structure and a precursor
structure for a diamond composite structure, forming each structure
into the respective complementary shapes, assembling the PCD
structure and the diamond composite structure onto a cemented
carbide substrate to form an unjoined assembly, and subjecting the
unjoined assembly to a pressure of at least about 5.5 GPa and a
temperature of at least about 1,250 degrees centigrade to form a
PCD construction. The precursor structure may comprise carbide
particles and diamond or non-diamond carbon material, such as
graphite, and a binder material comprising a metal, such as cobalt.
The precursor structure may be a green body formed by compacting a
powder blend comprising particles of diamond or non-diamond carbon
and particles of carbide material and compacting the powder
blend.
[0094] In some examples, both the bodies of, for example, diamond
and carbide material plus the sintering aid/binder/catalyst are
applied as powders and sintered simultaneously in a single UHP/HT
process. The mixture of diamond grains, and mass of carbide are
placed in an HP/HT reaction cell assembly and subjected to HP/HT
processing. The HP/HT processing conditions selected are sufficient
to effect intercrystalline bonding between adjacent grains of
abrasive particles and, optionally, the joining of sintered
particles to the cemented metal carbide support. In one example,
the processing conditions generally involve the imposition for
about 3 to 120 minutes of a temperature of at least about 1200
degrees C. and an ultra-high pressure of greater than about 5
GPa.
[0095] In another example, the substrate may be pre-sintered in a
separate process before being bonded together in the HP/HT press
during sintering of the ultrahard polycrystalline material.
[0096] In a further example, both the substrate and a body of
polycrystalline superhard material are pre-formed. For example, a
bimodal feed of ultrahard grains/particles and optional carbonate
binder-catalyst also in powdered form are mixed together, and the
mixture is packed into an appropriately shaped canister and is then
subjected to extremely high pressure and temperature in a press.
Typically, the pressure is at least 5 GPa and the temperature is at
least around 1200 degrees C. The preformed body of polycrystalline
superhard material is then placed in the appropriate position on
the upper surface of the preform carbide substrate (incorporating a
binder catalyst), and the assembly is located in a suitably shaped
canister. The assembly is then subjected to high temperature and
pressure in a press, the order of temperature and pressure being
again, at least around 1200 degrees C. and 5 GPa respectively.
During this process the solvent/catalyst migrates from the
substrate into the body of superhard material and acts as a
binder-catalyst to effect intergrowth in the layer and also serves
to bond the layer of polycrystalline superhard material to the
substrate. The sintering process also serves to bond the body of
superhard polycrystalline material to the substrate.
[0097] In examples where the cemented carbide substrate does not
contain sufficient solvent/catalyst for diamond, and where the PCD
structure is integrally formed onto the substrate during sintering
at an ultra-high pressure, solvent/catalyst material may be
included or introduced into the aggregated mass of diamond grains
from a source of the material other than the cemented carbide
substrate. The solvent/catalyst material may comprise cobalt that
infiltrates from the substrate in to the aggregated mass of diamond
grains just prior to and during the sintering step at an ultra-high
pressure. However, in examples where the content of cobalt or other
solvent/catalyst material in the substrate is low, particularly
when it is less than about 11 weight percent of the cemented
carbide material, then an alternative source may need to be
provided in order to ensure good sintering of the aggregated mass
to form PCD.
[0098] Solvent/catalyst for diamond may be introduced into the
aggregated mass of diamond grains by various methods, including
blending solvent/catalyst material in powder form with the diamond
grains, depositing solvent/catalyst material onto surfaces of the
diamond grains, or infiltrating solvent/catalyst material into the
aggregated mass from a source of the material other than the
substrate, either prior to the sintering step or as part of the
sintering step. Methods of depositing solvent/catalyst for diamond,
such as cobalt, onto surfaces of diamond grains are well known in
the art, and include chemical vapour deposition (CVD), physical
vapour deposition (PVD), sputter coating, electrochemical methods,
electroless coating methods and atomic layer deposition (ALD). It
will be appreciated that the advantages and disadvantages of each
depend on the nature of the sintering aid material and coating
structure to be deposited, and on characteristics of the grain.
[0099] In one example, the binder/catalyst such as cobalt may be
deposited onto surfaces of the diamond grains by first depositing a
pre-cursor material and then converting the precursor material to a
material that comprises elemental metallic cobalt. For example, in
the first step cobalt carbonate may be deposited on the diamond
grain surfaces using the following reaction:
Co(NO.sub.3).sub.2+Na.sub.2CO.sub.3->CoCO.sub.3+2NaNO.sub.3
[0100] 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
[0101] 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.
[0102] 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.
[0103] The PCD construction 1 may further processed after
sintering. For example, catalyst material may be removed from a
first region of the PCD structure adjacent the working surface or
the side surface or both the working surface and the side surface
to create the more thermally stable first region leaving residual
solvent catalyst in the interstices of a portion of the PCD
material adjacent the substrate to create the less thermally stable
second region. This may be done by treating the PCD structure with
acid to leach out catalyst material from between the diamond
grains, or by other methods such as electrochemical methods. A
thermally stable region, which may be substantially porous,
extending a depth of at least about 50 microns or at least about
100 microns from a surface of the PCD structure, may thus be
provided which may further enhance the thermal stability of the PCD
element.
[0104] The apertures or channels may then be formed in the PCD
material by, for example, laser ablation, electron beam drilling,
Electron Discharge Machining or dye sinking techniques.
[0105] Various samples of PCD material were prepared and analysed
by subjecting the samples to a number of tests.
[0106] A number of PCD compacts formed according to the above
examples were compared in a vertical boring mill test with a
commercially available polycrystalline diamond cutter elements
having the same average diamond grain size as that of the two
examples tested. It will be seen that the PCD compacts formed
according to examples were able to achieve a significantly greater
cutting length than that occurring in the conventional PCD compact
which was subjected to the same test for comparison.
[0107] Whilst not wishing to be bound by a particular theory, it is
believed that the fracture performance of PCD may be improved
through the introduction of a plurality of apertures or channels
into the body of polycrystalline superhard material in a PCD matrix
comprising a first region which is more thermally stable than a
second region, one or more of which extend into the second region,
according to examples described herein. The apertures or channels
are believed to inhibit or arrest crack propagation in the PCD
material in use, resulting in a redistribution of available strain
energy or energy release rate (G) amongst the various crack tips,
and/or favourably divert cracks in the PCD material. The end result
in application of the PCD material including such apertures or
channels is that, in use, the cracks initiated on the wear scar may
be arrested, thus reducing the strain energy available for each
individual crack, hence slowing the growth rate, and the generation
of shorter cracks. The ideal case is where the wear rate is
comparable to the crack growth rate, in which case no cracks will
be visible behind the wear scar thereby forming a smooth wear scar
appearance with no chips or grains pulled out of the sintered
PCD.
[0108] The addition of apertures or channels 50 may also have the
effect of increasing the thermal stability of the superhard
material such as PCD through the resultant lower cobalt content in
the superhard material compared to conventional PCD.
[0109] The size, shape and distribution of these apertures or
channels 50 may be tailored to the final application of the
superhard material. It is believed possible to improve fracture
resistance without significantly compromising the overall abrasion
resistance of the material, which is desirable particularly for PCD
cutting tools.
[0110] Thus, it is believed that examples may provide a means of
toughening thermally stable PCD material without compromising its
high abrasion resistance. Furthermore, having one or more apertures
or channels extend into the less thermally stable or unleached
region is believed may inhibit or arrest cracks that may otherwise
form underneath the apertures or channels from propagating into the
aperture or channel from below and potentially causing the
construction to spall.
[0111] Furthermore, it is believed that the apertures or channels
may dampen or disperse the incident energy received from the
interaction between the construction and the work piece being cut.
The apertures or channels are believed to dampen/disperse the
energy by reflection (for empty apertures or channels) or
absorption (filled apertures or channels). Also, it is believed
that the apertures or channels may act as a crack barrier hindering
the crack propagation and preventing the catastrophic failure of
the cutting element by spalling, chipping or pull out of block of
grains.
[0112] It is also believed the apertures or channels may have an
effect on the cooling efficiency and thermal stability of the
construction and residual stress therein. It is believed the
apertures or channels may improve the cooling efficiency of the
construction by increasing the transfer surface between the
construction and the coolant used during drilling. Furthermore, the
apertures or channels may allow or assist in unconfined expansion
of material in the bulk of the construction and reduce the residual
stresses therein. The making of the apertures or channels in the
construction may assist in releasing detrimental residual stresses
pre-existing from the manufacturing process of the construction.
For example, the interface between the bulk material of the
construction and the secondary material of filled holes allows
stress accommodation due to thermal expansion mismatch between the
different phases in the bulk of the construction. The apertures or
channels may be filled, for example, with a precursor or secondary
phase material with a CTE higher than the CTE of the
polycrystalline superhard material to induce compressive stresses
in the volume of polycrystalline superhard material.
[0113] The vertical borer test results of these engineered
structures show a considerable increase in PCD cutting tool life
compared to conventional PCD.
[0114] 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
[0115] Thus, examples of a PCD material may be formed having that a
combination of high abrasion and fracture performance.
[0116] Furthermore, the PCD body in the structure of FIG. 1
comprising a PCD structure bonded to a cemented carbide support
body may be created or finished by, for example, grinding, to
provide a PCD 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 PCD
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.
[0117] While various embodiments have been described with reference
to a number of examples, those skilled in the art will understand
that various changes may be made and equivalents may be substituted
for elements thereof and that these examples are not intended to
limit the particular embodiments disclosed. For example, whilst the
examples described and illustrated have been shown to have a
boundary between the first region and the second region and an
interface between the second region and the substrate which is
substantially planar, it will be appreciated that one or both of
these boundaries/interfaces may be non-planar, depending on the
intended end application of the product.
* * * * *