U.S. patent application number 16/208053 was filed with the patent office on 2019-11-07 for superhard constructions & methods of making same.
This patent application is currently assigned to ELEMENT SIX ABRASIVES S.A.. The applicant listed for this patent is ELEMENT SIX ABRASIVES S.A.. Invention is credited to VALENTINE KANYANTA, MAWEJA KASONDE, MEHMET SERDAR OZBAYRAKTAR.
Application Number | 20190337123 16/208053 |
Document ID | / |
Family ID | 48805593 |
Filed Date | 2019-11-07 |
![](/patent/app/20190337123/US20190337123A1-20191107-D00000.png)
![](/patent/app/20190337123/US20190337123A1-20191107-D00001.png)
![](/patent/app/20190337123/US20190337123A1-20191107-D00002.png)
![](/patent/app/20190337123/US20190337123A1-20191107-D00003.png)
![](/patent/app/20190337123/US20190337123A1-20191107-D00004.png)
![](/patent/app/20190337123/US20190337123A1-20191107-D00005.png)
United States Patent
Application |
20190337123 |
Kind Code |
A1 |
KASONDE; MAWEJA ; et
al. |
November 7, 2019 |
SUPERHARD CONSTRUCTIONS & METHODS OF MAKING SAME
Abstract
A superhard polycrystalline construction has a body of
polycrystalline superhard material having a cutting face and a
substrate bonded to the body of polycrystalline superhard material
along an interface. The substrate has a substrate body and a first
end surface forming the interface, the first end surface of the
substrate having a projection extending from the body of the
substrate into the body of superhard material towards the cutting
face. The projection has an outer peripheral surface around which
the body of polycrystalline superhard material extends. The body of
polycrystalline superhard material has a thickness from the cutting
face along the peripheral side edge to the interface with the
substrate of at least around 4 mm and at least a portion of the
projection has a thickness measured in a plane extending along the
longitudinal axis of the construction of at least around 4 mm.
Inventors: |
KASONDE; MAWEJA; (DIDCOT,
GB) ; KANYANTA; VALENTINE; (DIDCOT, GB) ;
OZBAYRAKTAR; MEHMET SERDAR; (DIDCOT, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ELEMENT SIX ABRASIVES S.A. |
Luxembourg |
|
LU |
|
|
Assignee: |
ELEMENT SIX ABRASIVES S.A.
LUXEMBOURG
LU
|
Family ID: |
48805593 |
Appl. No.: |
16/208053 |
Filed: |
December 3, 2018 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
14892712 |
Nov 20, 2015 |
|
|
|
PCT/EP2014/061267 |
May 30, 2014 |
|
|
|
16208053 |
|
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
E21B 10/567 20130101;
B24D 3/14 20130101; E21B 10/5735 20130101; B24D 3/06 20130101 |
International
Class: |
B24D 3/14 20060101
B24D003/14; B24D 3/06 20060101 B24D003/06; E21B 10/567 20060101
E21B010/567; E21B 10/573 20060101 E21B010/573 |
Foreign Application Data
Date |
Code |
Application Number |
May 31, 2013 |
GB |
1309798.5 |
Claims
1. A superhard polycrystalline construction comprising: a body of
polycrystalline superhard material having a cutting face; and a
substrate bonded to the body of polycrystalline superhard material
along an interface; the construction having a central longitudinal
axis extending therethrough and a peripheral side edge; wherein:
the substrate comprises a substrate body and a first end surface
forming the interface, the first end surface of the substrate
comprising a projection extending from the body of the substrate
into the body of superhard material towards the cutting face, the
projection having an outer peripheral surface, the body of
polycrystalline superhard material extending around the peripheral
outer surface of the projection; wherein the body of
polycrystalline superhard material has a thickness from the cutting
face along the peripheral side edge to the interface with the
substrate of at least around 4 mm; and wherein at least a portion
of the projection has a thickness measured in a plane extending
along the longitudinal axis of the construction of at least around
4 mm.
2. The superhard polycrystalline construction of claim 1, wherein
the projection from the substrate extends to and forms part of the
working face.
3. The superhard polycrystalline construction of claim 1, wherein
the projection from the substrate extends to a distance of around
0.5 mm or less from the cutting face.
4. The superhard polycrystalline construction of claim 1, wherein
the body of polycrystalline superhard material comprises natural
and/or synthetic diamond grains, and/or cubic boron nitride
grains.
5.-10. (canceled)
11. The superhard polycrystalline construction of claim 1, wherein
the body of superhard material comprises polycrystalline diamond
material having interbonded diamond grains and interstices
therebetween; wherein at least a portion of the body of superhard
material is substantially free of a catalyst material for diamond,
said portion forming a thermally stable region.
12. The superhard polycrystalline construction of claim 11, wherein
the depth of the thermally stable region from the cutting face
along the peripheral side edge is at least around 3.5 mm or
greater.
13. The superhard polycrystalline construction of claim 11, wherein
the depth of the thermally stable region from the cutting face
along the peripheral side edge is at least around 4.5 mm or
greater.
14. The superhard polycrystalline construction of claim 1, further
comprising a protective layer over at least a portion of the
cutting face.
15. (canceled)
16. The superhard polycrystalline construction of claim 1, further
comprising one or more interlayers bonded between at least a
portion of the substrate and the body of superhard material.
17. The superhard polycrystalline construction of claim 16, wherein
the one or more interlayers differ from one or other or both of the
other interlayers and/or the body of superhard material in grain
size and/or composition.
18. The superhard polycrystalline construction of claim 16, wherein
one or more of the interlayers comprise(s) one or more of a mixture
of WC and diamond powder(s), a mixture of cBN and diamond
powder(s), and/or a mixture of refractory metal(s) and hard
material powders, the hard material powders comprising one or more
of tungsten, vanadium or molybdenum.
19. (canceled)
20. The superhard polycrystalline construction of claim 1, wherein
the projection comprises a planar central portion spaced from the
body of the substrate by an interconnecting surface.
21. (canceled)
22. The superhard polycrystalline construction of claim 20, wherein
the interconnecting surface is concave.
23. The superhard polycrystalline construction of claim 22, wherein
the interconnecting surface extends from the planar central section
to the peripheral side edge of the construction.
24. (canceled)
25. The superhard polycrystalline construction of claim 20, wherein
the interconnecting surface comprises a first portion extending
from the planar central section to a position spaced from the
peripheral side edge of the construction, the interconnecting
surface further comprising a second portion extending from the
first portion to the peripheral side edge, the projection being
substantially frusto-conical in shape.
26. The superhard polycrystalline construction of claim 25, wherein
the second portion forms a shoulder portion having a length of up
to around 3 mm.
27. The superhard polycrystalline construction of claim 25, wherein
the peripheral outer surface of the projection is inclined at an
angle of up to around 15 degrees from the central longitudinal
axis.
28. The superhard polycrystalline construction of claim 1, wherein
the body of polycrystalline superhard material comprises an annular
portion extending around the peripheral outer surface of the
projection.
29. The superhard polycrystalline construction of claim 28, wherein
the annular portion is continuous around the outer peripheral
surface of the projection.
30. The superhard polycrystalline construction of claim 28, wherein
the annular portion is discontinuous around the outer peripheral
surface of the projection.
31.-62. (canceled)
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 14/892,712, filed on Nov. 20, 2015, which is a
U.S. national phase of International Patent Application No.
PCT/EP2014/061267, filed on May 30, 2014, which claims the benefit
of United Kingdom Patent Application No. 1309798.5, filed on May
31, 2013, each of which is incorporated herein by reference in its
entirety.
FIELD
[0002] 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
[0003] Polycrystalline superhard 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.
[0004] 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, the superhard layer bonded to the substrate in a PCD
cutter element typically having a maximum thickness from the
interface with the substrate to the working surface of around 2
mm.
[0005] 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.
[0006] 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.
[0007] 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 or PCBN,
diamond particles or grains or CBN grains are placed adjacent the
cemented tungsten carbide body in a refractory metal enclosure such
as a niobium enclosure and are subjected to high pressure and high
temperature so that inter-grain bonding between the diamond grains
or CBN grains occurs, forming a polycrystalline superhard diamond
or polycrystalline CBN layer.
[0008] 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.
[0009] 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.
[0010] 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.
[0011] Methods used to improve the abrasion resistance of a PCD
composite often result in a decrease in impact resistance of the
composite.
[0012] The most wear resistant grades of PCD and PCBN used in
cutters usually fail by spalling resulting in a catastrophic
fracture of the cutter before it has worn out. Spalling is
considered to be caused by a crack propagating from working area to
the top free surface of the cutting tool. 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 o PCBN breaks away in a brittle manner. Catastrophic failure of
a component or structure indicates that crack grew to reach the
"critical crack length" of the given structural material. The
"critical crack length" is the acceptable length of crack beyond
which the propagation of the crack becomes uncontrollable leading
to catastrophic failure independently of the remaining non-working
area of the component. The long, fast growing cracks encountered
during use of conventionally sintered PCD and PCBN can therefore
result in shorter tool life.
[0013] Furthermore, despite their high strength, polycrystalline
diamond (PCD) and PCBN 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.
[0014] 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 composites.
SUMMARY
[0015] Viewed from a first aspect there is provided a superhard
polycrystalline construction comprising:
[0016] a body of polycrystalline superhard material having a
cutting face; and
[0017] a substrate bonded to the body of polycrystalline superhard
material along an interface;
[0018] the construction having a central longitudinal axis
extending therethrough and a peripheral side edge; wherein:
[0019] the substrate comprises a substrate body and a first end
surface forming the interface, the first end surface of the
substrate comprising a projection extending from the body of the
substrate into the body of superhard material towards the cutting
face, the projection having an outer peripheral surface, the body
of polycrystalline superhard material extending around the
peripheral outer surface of the projection;
[0020] wherein the body of polycrystalline superhard material has a
thickness from the cutting face along the peripheral side edge to
the interface with the substrate of at least around 4 mm; and
[0021] wherein at least a portion of the projection has a thickness
measured in a plane extending along the longitudinal axis of the
construction of at least around 4 mm.
[0022] Viewed from a second aspect there is provided a method of
forming a superhard polycrystalline construction, comprising:
[0023] providing a first mass of particles or grains of superhard
material;
[0024] admixing the first mass of particles or grains with a binder
material to form a green body;
[0025] placing the green body in contact with a pre-formed
substrate to form a pre-sinter assembly, the pre-formed substrate
having a longitudinal axis and comprising a body portion and a
projection, the projection extending at least in part from the body
portion by around 4 mm or greater as measured in a plane parallel
to the longitudinal axis of the substrate;
[0026] treating the pre-sinter assembly in the presence of a
catalyst/solvent material for the superhard grains at an ultra-high
pressure of around 5.5 GPa or greater and a temperature to sinter
together the grains of superhard material to form a polycrystalline
superhard construction comprising a body of polycrystalline
superhard material having a cutting face; the substrate being
bonded to the body of polycrystalline superhard material along an
interface; wherein the projection extends from the body of the
substrate into the body of superhard material towards the cutting
face, the body of polycrystalline material extending around the
projection; and wherein the body of polycrystalline material has a
thickness from the cutting face along a peripheral side edge of the
construction to the interface with the substrate of at least around
4 mm.
[0027] 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.
[0028] 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.
[0029] 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
[0030] The present invention will now be described by way of
example and with reference to the accompanying drawings in
which:
[0031] FIG. 1 is a perspective view of an example superhard cutter
element for a drill bit for boring into the earth;
[0032] FIGS. 2a to 2e are schematic cross-sections of example
superhard cutter elements with differing interfaces between the
superhard body and substrate attached thereto;
[0033] FIGS. 3a and 3b are schematic cross-sections of further
example superhard cutter elements in which the superhard bodies are
formed of regions comprising differing grain sizes and/or
compositions, the interface between the substrate and the superhard
body being spaced from the working surface of the cutter element in
both examples;
[0034] FIGS. 4a and 4b are schematic cross-sections of further
example superhard cutter elements in which the superhard bodies are
formed of regions comprising differing grain sizes and/or
compositions, the interface between the substrate and the superhard
body extending to the working surface of the cutter element in both
examples;
[0035] FIGS. 5a to 5c are perspective view from above of three
example substrate portions showing the shaped end of the substrate
which is to form the interface with a superhard layer, prior to
attachment to a superhard layer;
[0036] FIG. 6 is a schematic cross-section through an example
superhard cutter element showing the boundary between a leached
portion and an unleached portion of the superhard layer;
[0037] FIG. 7a is a schematic cross-section through a conventional
superhard cutter element showing wear into the substrate through
use;
[0038] FIG. 7b is a schematic cross-section through an example
superhard cutter element showing wear remaining in the superhard
body after use; and
[0039] FIG. 8 is a plot showing the results of a vertical borer
test comparing two conventional leached PCD cutter elements, and an
example PCD cutter element.
[0040] The same references refer to the same general features in
all the drawings.
DESCRIPTION
[0041] 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.
[0042] 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.
[0043] 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 embodiment
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
embodiments of PCD material, interstices or interstitial regions
may be substantially or partially filled with a material other than
diamond, or they may be substantially empty. 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.
[0044] A "catalyst material" for a superhard material is capable of
promoting the growth or sintering of the superhard material.
[0045] 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.
[0046] 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.
[0047] 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.
[0048] In an embodiment 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), a
thermally stable product such as thermally stable PCD (TSP), or
polycrystalline cubic boron nitride (PCBN). 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.
[0049] The exposed surface of the superhard material opposite the
face which forms the interface with the substrate, forms the
cutting face 14 of the cutter element, that is, the surface which,
along with its edge 16, performs the cutting in use.
[0050] 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
embodiment of FIG. 1, the substrate 10 is generally cylindrical and
has a peripheral top edge 20 and a peripheral surface 22.
[0051] 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 superhard material may be made by
a process including providing an aggregate mass of superhard 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 superhard material to a
pressure and temperature at which the superhard 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 superhard
structure. The aggregate mass may comprise loose superhard grains
or superhard grains held together by a binder material. In the
context of diamond, the diamond grains may be natural or
synthesised diamond grains.
[0052] Different grades of superhard 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 K1C 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.
[0053] In the context of PCD, the PCD grades may comprise
interstitial regions filled with material comprising cobalt metal,
which is an example of catalyst material for diamond.
[0054] The polycrystalline superhard structure 12 shown in the
cutter element of FIG. 1 may comprise, for example, one or more PCD
grades.
[0055] FIGS. 2a to 2e are schematic cross-sections through five
embodiments of example polycrystalline superhard cutter elements 1.
The five examples all comprise a substrate 10 extending to a
distance t from the cutting face 14 of the polycrystalline
superhard structure 12, the polycrystalline superhard structure 12
having a thickness h as measured from the cutting face 14 of the
polycrystalline superhard structure 12 along the barrel 13 thereof
to the interface with the substrate 10, the barrel 13 being the
peripheral side edge of the cutter element 1. In these embodiments
shown in FIGS. 2a to 2e, the thickness h is preferably greater than
or equal to around 4 mm. Furthermore, in these embodiments, the
thickness t is preferably less than or equal to around 0.5 mm. In
these embodiments, the polycrystalline superhard layer 12 extends
over the substrate portion at the cutting face 14 and this may be
advantageous as the substrate 10 is thereby protected from chemical
erosion and abrasion during application and also from chemical
attack in the event that the cutter element 1 is subjected to a
treatment such as acid leaching after sintering.
[0056] In some embodiments, and in particular those where the
planar central section 26 of the substrate extends to and forms
part of the cutting face 14, the cutting face 14 or a portion
thereof may be protected against erosion, corrosion or chemical
degradation by attaching or spraying for example a layer of
resistant polymer, oxide, paint, composite materials, onto the
surface. The protective layer(s) may be formed during pre-composite
assembly and bonded on to the cutter surface during HPHT sintering.
Alternatively, the protective layer(s) may be attached to the
cutter surface after sintering and processing and adhered thereto
by surface interaction.
[0057] The five embodiments of FIGS. 2a to 2e differ in the shape
of the end face of the substrate portion 10 which forms the
interface 18 with the polycrystalline superhard structure 12. In
the example shown in FIG. 2a, the end face of the substrate portion
10 which forms the interface 18 is dome shaped with the highest
point 24 of the dome along the longitudinal axis of the cutter
element being spaced from the cutting face 14 by a distance t along
the longitudinal axis of the cutter.
[0058] In the example shown in FIG. 2b, the end face of the
substrate portion 10 which forms the interface 18 has a planar,
coaxially located central section 26 which, at the end face is
circular in cross section having a diameter d. This planar section
26 forms the furthest point of the interface 18 from the body of
the substrate and is spaced from the cutting face 14 by a distance
t along the longitudinal axis of the cutter element 1. The diameter
d of the planar central section 26 of the substrate which forms
part of the interface 18 with the superhard layer is less than the
diameter D of the cutter element 1. The surface 28 of the substrate
extending from the peripheral edge of the planar central section 26
to the peripheral side edge or barrel 13 of the cutter element 1 at
a distance h along the barrel 13 from the cutting face 14, is
concavely curved such that the superhard layer 12 extends across
the planar central section 26.
[0059] The example shown in FIG. 2c differs from that shown in FIG.
2b in that the surface 28 of the substrate extending from the
peripheral edge of the planar central section 26 to the peripheral
side edge of the cutter element 1 is not curved but is instead
sloped, that is shown by the inclined plane depicted in in cross
section in FIG. 2c, the substrate thereby comprising a truncated
cone at the interface end projecting from the body of the substrate
and extending through the layer of superhard material towards the
cutting face 14.
[0060] The example in FIG. 2d differs from that of FIG. 2c in that
the surface of the substrate portion extending from the planar
central section 26 extends in a plane parallel to the central
longitudinal axis of the cutter element for a length equal to (h-t)
and then radially outward to the peripheral side edge, that is to
the barrel 13, of the cutter element 1. Thus, the substrate
includes a coaxially extending cylindrical portion extending within
the body of superhard material, from the body of the substrate
towards the cutting face 14 of the superhard layer. The example in
FIG. 2e differs from that in FIG. 2d in that the surface 28 of the
substrate extending from the planar central section 26 is inclined
at an angle A to the plane parallel to the plane through which the
longitudinal axis of the cutter element extends, the height of the
planar central section being denoted by h' and the radial length of
the portion extending from the planar central section radially to
the barrel 13 of the cutter element is denoted by B. The
intersection 29 between the planar central section 26 and the sides
thereof and between those sides and the radially extending portion
may be curved or meet at a point. Thus the substrate comprises a
truncated cone extending from the body of the substrate towards the
cutting face.
[0061] In these embodiments, the angle A may be between about 0 to
about 15 degrees, and in some embodiments around 5 degrees or less,
and the distance B may be, for example, between about 0 to about 3
mm, and in some embodiments around 2 mm or less.
[0062] FIGS. 3a and 3b show further examples of cutter elements
similar to that shown in FIG. 2e but with the intersections 29
being points and an interlayer 30 being located between either a
portion of the substrate and the superhard layer (as shown in FIG.
3a) or forming the entire interface between the substrate and the
superhard layer (as shown in FIG. 3b). The interlayer 30 may be
comprised of, for example, a different grade of superhard material
to that of the superhard layer 12, and/or, it may be a different
composition to the superhard layer 12.
[0063] In the embodiment shown in FIG. 3a, the interlayer 30 is
positioned between the superhard layer 12 and the substrate 10 and
extends about at least a portion of the planar central section 26.
In this embodiment, the interlayer 30 does not extend to the full
height of the planar central section surface but extends annularly
therearound and is spaced from the cutting face 14. In the example
of FIG. 3b, the interlayer 30 does extend over all of the surface
features of the substrate and spaces the superhard layer 12 from
the substrate 10. In this embodiment, it is the interlayer 30
covering the planar central section that, at its highest point, is
spaced a distance t from the cutting face 14, rather than the
uppermost features of the substrate 10 itself.
[0064] The examples of FIGS. 4a and 4b differ from those shown in
FIGS. 3a and 3b respectively in that in the examples of FIGS. 4a
and 4b the planar central section 26 of the substrate 10 extends to
and forms part of the cutting face 14. The length of the cutter
element from the base of the substrate to the cutting face as
measured along the longitudinal axis of the cutter element is
denoted by H1 and the height of the central section 26 as measured
in a plane parallel to the central longitudinal axis of the cutter
element along the barrel (side edge) of the cutter element is
denoted by H2.
[0065] Multiple interlayers of different grain size and composition
may be included which, in some embodiment, may be substantially
parallel to one another. One or more of such interlayers may
comprise a mixture of WC and diamond powders, a mixture of cBN and
diamond powders, a mixture of refractory metals and super-hard
(such as W, V, Mo) material powders, or any combination thereof.
Whilst not wishing to be bound by a particular theory, it is
believed that such interlayers adjacent to the substrate may
eliminate the sudden change in CTE between the substrate and the
superhard layer and thereby assist in inhibiting cracking and/or
delamination of the sintered superhard layer from the substrate by
minimising residual stress between layers of different
compositions.
[0066] When subjected to post-sintering treatments such as acid
leaching to remove residual binder from interstices between the
superhard grains, the layers may introduce different leaching rates
in the cutter resulting in preferential leaching profiles to be
achieved.
[0067] FIGS. 5a to 5c show three examples of the shapes of possible
substrate portions which may form the interface with either an
interlayer 30 or superhard layer 10 (not shown). In FIGS. 5a to 5c,
the planar central portions 26 differ in shape from those of the
other figures in that they have the general shape obtained by
truncating the space between three tangent circles forming a
coaxially located projection from the body of the substrate with a
planar free surface position. In FIG. 5b, the projection from the
substrate to the planar free surface thereof is of substantially
constant cross-sectional area and extends to the barrel 13 of the
cutter element 1. In FIG. 5a the cross-sectional area of the planar
free surface of the projection from the substrate is smaller than
at the base thereof, and the surfaces extending between the
features of the projection to the barrel 13 are curved
concavely.
[0068] In FIG. 5c, this differs from the substrate shown in FIG. 5a
in that the projection extends to a height from the body of the
substrate before decreasing in cross-sectional area to the planar
end surface thereof whilst maintaining the same general shape. The
surface joining the top and bottom of the projection is curved
concavely.
[0069] The projection from the substrate in the examples of FIGS.
5a to 5c is therefore non-conical and non-axisymmetric in shape and
divides the cutting face 14 into three segments which may then be
filled by the polycrystalline superhard material which is separated
from adjacent segments by a core of tougher substrate material and
spokes extending towards the barrel of the cutter. The advantage of
these constructions may be that the cutter is rotatable after use
such that a different cutting edge may be presented to the surface
to be cut and also the segments act to confine damage to a limited
area of the cutter during use.
[0070] FIG. 6 is a schematic cross-section of the cutter of FIG. 2e
which has been subjected to a post sintering treatment such as acid
leaching to remove residual binder from interstices between the
superhard grains forming the polycrystalline superhard layer 12.
The boundary between the leached and unleached portions is denoted
by reference numeral 36 and follows the same general shape of the
interface between the substrate 10 and the superhard layer 12. In
this example, it may be possible to control the leaching profile
such that there is a greater leached volume denoted by L in FIG. 6
than unleached volume of superhard material extending in from the
barrel of the cutter element and the cutting face 14 of the cutter
element may remain unleached or be leached to a depth of, for
example, around 200 microns or less from the cutting face 14. Also,
given the height of the superhard layer 12, it may be possible to
leach the barrel region 13 of the cutter element 1 to a depth of at
least around 3.5 mm and in some embodiments to a depth of around
4.5 mm or greater.
[0071] FIG. 7a is a schematic cross-section through a conventional
PCD cutter 37 formed of a substrate 38 attached to a layer of PCD
material 39 showing wear into the substrate 38 through use. It will
be seen that the wear flat 40 has progressed through both the PCD
layer 39 and the substrate 37.
[0072] FIG. 7b is a schematic cross-section through an example PCD
cutter element showing wear remaining in the PCD body after use.
The cutter shown in FIG. 7a is that of FIG. 3a and it will be seen
that the wear flat 40 is retained in the layer of superhard
material 12 and does not extend into the substrate 10 attached
thereto.
[0073] Thus embodiments of the invention may enable the wear scar
surface of the cutter to be maintained in the layer of superhard
material which is advantageous as the wear scar surface may thereby
be composed of homogeneous material and hence provide uniform
friction across the wear scar surface. Having heterogeneous
material across the wear scar surface as in the conventional cutter
shown in FIG. 7a will result in the wear scar surface being formed
of materials having different coefficients of friction which may
contribute to crack initiation near the wear scar leading to
reduced performance of the cutter and increased susceptibility of
the cutter to failure through spalling.
[0074] FIG. 8 is a plot showing the results of a vertical borer
test comparing two conventional leached PCD cutter elements, and an
example PCD cutter element.
[0075] The grains of superhard material may be, for example,
diamond grains or particles, or for example, cBN 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 superhard grains and a fine fraction of
superhard grains. In some embodiments, the coarse fraction may
have, for example, an average particle/grain size ranging from
about 10 to 60 microns. By "average particle or grain size" it is
meant that the individual particles/grains have a range of sizes
with the mean particle/grain size representing the "average". The
average particle/grain size of the fine fraction is less than the
size of the coarse fraction, for example between around 1/10 to
6/10 of the size of the coarse fraction, and may, in some
embodiments, range for example between about 0.1 to 20 microns.
[0076] In some embodiments, the weight ratio of the coarse fraction
to the fine fraction ranges from about 50% to about 97% coarse
superhard grains and the weight ratio of the fine fraction may be
from about 3% to about 50%. In other embodiments, the weight ratio
of the coarse fraction to the fine fraction will range from about
70:30 to about 90:10.
[0077] In further embodiments, the weight ratio of the coarse
fraction to the fine fraction may range for example from about
60:40 to about 80:20.
[0078] In some embodiments, the particle size distributions of the
coarse and fine fractions do not overlap and in some embodiments
the different size components of the compact are separated by an
order of magnitude between the separate size fractions making up
the multimodal distribution.
[0079] Some embodiments consist of a wide bi-modal size
distribution between the coarse and fine fractions of superhard
material, but some embodiments may include three or even four or
more size modes which may, for example, be separated in size by an
order of magnitude, for example, a blend of particle sizes whose
average particle size is 20 microns, 2 microns, 200 nm and 20
nm.
[0080] 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.
[0081] In embodiments where the superhard material is
polycrystalline diamond material, the diamond grains used to form
the polycrystalline diamond material may be natural or
synthetic.
[0082] In some embodiments, the polycrystalline superhard material
is PCBN and the superhard particles or grains comprise cBN.
[0083] In some embodiments, the binder catalyst/solvent used to
assist in the bonding of the grains of superhard material such as
diamond grains, may comprise cobalt or some other iron group
elements, such as iron or nickel, or an alloy thereof. Carbides,
nitrides, borides, and oxides of the metals of Groups IV-VI in the
periodic table are other examples of non-diamond material that
might be added to the sinter mix. In some embodiments, the
binder/catalyst/sintering aid may be Co.
[0084] The cemented metal carbide substrate may be conventional in
composition and, thus, may be include any of the Group IVB, VB, or
VIB metals, which are pressed and sintered in the presence of a
binder of cobalt, nickel or iron, or alloys thereof. In some
embodiments, the metal carbide is tungsten carbide.
[0085] The cutter of FIG. 1 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] Embodiments of superhard constructions may be made by a
method of preparing a green body comprising grains or particles of
superhard material, non-reactive phase and a binder, such as an
organic binder. 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] The substrate is preferably pre-formed. In some embodiments,
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 embodiment, 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. A green body
for the superhard construction, which comprises the pre-formed
substrate 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 superabrasive particles, for example in
powder form, are placed inside a metal cup formed, for example, of
niobium, tantalum, or titanium. The pre-formed substrate is placed
inside the cup and 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 of superhard material bonded to the substrate
along the interface therewith.
[0089] 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.
[0090] 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 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. In some embodiments, the pressure to which the
assembly may be subjected is around 5.5-6 GPa, but in some
embodiments it may be around 7.7 GPa or greater. Also, in some
embodiments, the temperature used in the sintering process may be
in the range of around 1400 to around 1500 degrees C.
[0091] 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 with the
additional step of admixing with the diamond grains, prior to
sintering, catalyst material in the form of a metal binder such as
0 to 3 wt % cobalt. A powder blend comprising diamond particles and
the 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 from about 1 to 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.
[0092] 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.
[0093] In the example of PCD, 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.
[0094] 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.
[0095] In embodiments where the cemented carbide substrate does not
contain sufficient solvent/catalyst for diamond, and where the PCD
structure is integrally formed onto the substrate during sintering
at an ultra-high pressure, solvent/catalyst material may be
included or introduced into the aggregated mass of diamond grains
from a source of the material other than the cemented carbide
substrate. The solvent/catalyst material may comprise, for example,
cobalt that infiltrates from the substrate into the aggregated mass
of diamond grains just prior to and during the sintering step at an
ultra-high pressure. However, in embodiments where the content of
cobalt or other solvent/catalyst material in the substrate is low,
particularly when it is less than about 11 weight percent of the
cemented carbide material, then an alternative source may need to
be provided in order to ensure good sintering of the aggregated
mass to form PCD.
[0096] 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.
[0097] In one embodiment, 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
[0098] 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
CpO+H.sub.2->Co+H.sub.2O
[0099] In another embodiment, cobalt powder or precursor to cobalt,
such as cobalt carbonate, may be blended with the diamond grains.
Where a precursor to a solvent/catalyst such as cobalt is used, it
may be necessary to heat treat the material in order to effect a
reaction to produce the solvent/catalyst material in elemental form
before sintering the aggregated mass.
[0100] In some embodiments, 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.
[0101] Embodiments are described in more detail below with
reference to the following example which is provided herein by way
of illustration only and is not intended to be limiting.
Example 1
[0102] An aggregated mass of diamond powder with an average grain
size of 12 microns was ball milled in 60 ml of methanol with Co--WC
milling balls. The ratio of milling balls:powder was 5:1 and
milling was carried out for 1 hour at 90 rpm. Once milled, 2.1 g of
the mixture was placed on top of a pre-formed WC--Co substrate. The
pre-formed substrate has a projection extending to about 4 mm from
the end surface of the substrate as shown in FIGS. 2(b) and 2(e).
The substrate and mass of diamond powder were sintered under high
pressure high temperature HPHT conditions at 5.5 GPa and
1450.degree. C. to form a PCD cutter which was recovered, processed
and analysed. The PCD cutter had a PCD thickness from the cutting
surface to the interface with the substrate along the peripheral
side edge of the cutter of around 4 mm.
[0103] The results of the analysis are discussed below with
reference to FIG. 8.
[0104] Various sample of PCD material were prepared and analysed by
subjecting the samples to a number of tests. The results of these
tests are shown in FIG. 8.
[0105] The PCD compact formed according to Example 1 was compared
in a vertical boring mill test with two leached conventional
polycrystalline diamond cutter elements formed of diamond grains
having an average grain size of 12 microns and which were sintered
under pressures of around 5.5 GPa. The conventional PCD cutters in
this test had non-planar interfaces and a thickness of the diamond
table along the peripheral side edge of the cutter of around 2.5
mm. In this test, the wear flat area was measured as a function of
the number of passes of the cutter element boring into the
workpiece. The results obtained are illustrated graphically in FIG.
8. The results provide an indication of the total wear scar area
plotted against cutting length. It will be seen that the PCD
compact formed according to Example 1 denoted by the reference
numeral 54 in FIG. 8, and having a diamond table thickness at the
peripheral edge of the cutter of around 4 mm and projection from
the substrate having a height of around 4 mm was able to achieve a
greater cutting length and smaller wear scar area than that
occurring in both of the conventionally leached PCD compacts
(denoted by reference numerals 50 and 52) which were subjected to
the same test for comparison.
[0106] Whilst not wishing to be bound by a particular theory, it is
believed that crack propagation may be controlled by introducing a
barrier material in the form of the substrate features to slow down
the propagation rate of the crack before the critical length of the
crack is reached and hence avoid spalling of the non-working area
of the superhard material. The protrusion in the substrate has a
higher impact resistance compared to the superabrasive layer and
thereby acts to arrest the cracks to avoid spalling or catastrophic
failure during use of the cutter element.
[0107] The size and shape of the substrate features 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.
[0108] The vertical borer test results of these engineered
structures show a considerable increase in PCD cutting tool life
compared to conventional PCD, and with no degradation in abrasion
resistance.
[0109] 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.
[0110] Thus, embodiments of, for example, a PCD material, may be
formed having a combination of high abrasion and fracture
performance.
[0111] The PCD element 10 described with reference to FIG. 1 may be
further processed after sintering. For example, catalyst material
may be removed from a region of the PCD structure adjacent the
working surface or the side surface or both the working surface and
the side surface. This may be done by treating the PCD structure
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.
[0112] 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.
[0113] 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.
* * * * *