U.S. patent application number 14/331547 was filed with the patent office on 2015-06-25 for polycrystalline diamond element.
The applicant listed for this patent is John Hewitt Liversage, Kaveshini Naidoo. Invention is credited to John Hewitt Liversage, Kaveshini Naidoo.
Application Number | 20150174733 14/331547 |
Document ID | / |
Family ID | 40600570 |
Filed Date | 2015-06-25 |
United States Patent
Application |
20150174733 |
Kind Code |
A1 |
Liversage; John Hewitt ; et
al. |
June 25, 2015 |
POLYCRYSTALLINE DIAMOND ELEMENT
Abstract
An embodiment of a PCD insert comprises an embodiment of a PCD
element joined to a cemented carbide substrate at an interface. The
PCD element has internal diamond surfaces defining interstices
between them. The PCD element further comprises a working surface
and a low melting point region adjacent the working surface in
which the interstices are at least partially filled with a low
melting point metallic material having a melting point of less than
about 1,300 degrees centigrade at atmospheric pressure, or less
than about 1,200 degrees centigrade at atmospheric pressure. The
PCD clement includes an intermediate region, the interstices of the
intermediate region being at least partially filled with a catalyst
material for diamond.
Inventors: |
Liversage; John Hewitt;
(Springs, ZA) ; Naidoo; Kaveshini; (Springs,
ZA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Liversage; John Hewitt
Naidoo; Kaveshini |
Springs
Springs |
|
ZA
ZA |
|
|
Family ID: |
40600570 |
Appl. No.: |
14/331547 |
Filed: |
July 15, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13254455 |
Nov 9, 2011 |
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PCT/IB2010/050977 |
Mar 8, 2010 |
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14331547 |
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Current U.S.
Class: |
51/309 |
Current CPC
Class: |
B24D 3/10 20130101; B24D
18/0009 20130101; B22F 2005/001 20130101; E21B 10/5735 20130101;
B22F 2999/00 20130101; C22C 26/00 20130101; B22F 7/06 20130101;
E21B 10/5676 20130101; B22F 2999/00 20130101; B22F 7/06 20130101;
B22F 2207/03 20130101 |
International
Class: |
B24D 3/10 20060101
B24D003/10; E21B 10/567 20060101 E21B010/567; B24D 18/00 20060101
B24D018/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 6, 2009 |
GB |
0903826.6 |
Claims
1. A polycrystalline diamond (PCD) element having internal diamond
surfaces, the internal diamond surfaces defining interstices
between them, the PCD element comprising a working surface, a low
melting point region adjacent the working surface and in which the
interstices are at least partially filled with a low melting point
metallic material having a melting point of less than about 1,300
degrees centigrade at atmospheric pressure, and an intermediate
region extending a distance of between about 5 microns and about
600 microns from a boundary defined by the low melting point
region, the interstices of the intermediate region being at least
partially filled with a catalyst material for diamond.
2. A polycrystalline diamond element according to claim 1, in which
the intermediate region extends a distance from the boundary of at
most about 400 microns.
3. A polycrystalline diamond element according to claim 1, in which
the intermediate region extends a distance from the boundary of at
least about 5 microns.
4. A polycrystalline diamond element according to claim 1, in which
the interstices of the intermediate region are at least 50% filled
with a sintering aid or catalyst material for diamond.
5. A polycrystalline diamond element according to claim 1, in which
the low melting point region extends a depth into the PCD element
from the working surface, the depth being at most about 1,000
microns. PATENT
6. A polycrystalline diamond element according to claim 1, in which
the low melting point region extends a depth into the PCD element
from the working surface, the depth being at least about 5
microns.
7. A polycrystalline diamond element according to claim 1, in which
the low melting point region is in the form of a stratum or
layer.
8. A polycrystalline diamond element according to claim 1, in which
the interstices within the low melting point region are at least
50% filled with the low melting point metallic material.
9. A polycrystalline diamond element according to claim 1, in which
the low melting point metallic material has a melting point lower
than 1,100 degrees centigrade at atmospheric pressure.
10. A polycrystalline diamond element according to claim 1, in
which the low melting point metallic material has a melting point
greater than 600 degrees centigrade at atmospheric pressure.
11. A polycrystalline diamond element according to claim 1, in
which the low melting point metallic material is not capable of
reacting to form a stable carbide at less than 1,000 degrees
centigrade at atmospheric pressure.
12. A polycrystalline diamond element according to claim 1, in
which the low melting point metallic material is Ag, Mg, Cu or Pb
in elemental form or an alloy including any of these elements.
13. A polycrystalline diamond element according to claim 1, in
which the low melting point metallic material is Ag or Cu in
elemental form or an alloy including either of these elements.
14. An insert for a tool, the insert comprising a polycrystalline
diamond element according to claim 1.
15. A tool comprising an insert according to claim 14.
16. A method for making a polycrystalline diamond (PCD) element,
the method including providing a PCD body comprising a sintering
aid within interstices of the PCD body, removing at least some of
the sintering aid from a portion of the polycrystalline diamond
element to form a porous region adjacent a working surface, and
infiltrating or permeating at least a portion of the porous region
with low melting point metallic material having a low melting point
of less than 1,300 degrees centigrade at atmospheric pressure.
17. A method according to claim 16, in which substantially all of
the sintering aid is removed from the polycrystalline diamond
element.
Description
FIELD
[0001] This invention relates to polycrystalline diamond (PCD)
elements, particularly but not exclusively to PCD elements suitable
for use in attack tools and cutters, such as picks and rotary drill
bits, as may be used in the mining, tunnelling, construction and
oil and gas industries to process or degrade pavements, rock
formations and the like, or to bore into the earth.
BACKGROUND
[0002] Cutter inserts for drill bits for use in boring into the
earth may comprise a layer of polycrystalline diamond (PCD) bonded
to a cemented carbide substrate. Such cutter inserts may be
referred to as polycrystalline diamond compacts (PDC).
[0003] PCD is an example of a superhard, also called superabrasive,
material comprising a mass of substantially inter-grown diamond
grains, forming a skeletal mass defining interstices between the
diamond grains. PCD material comprises at least about 80 volume %
of diamond and may be 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 degrees centigrade in
the presence of a sintering aid.
[0004] Suitable sintering aids for PCD may also be referred to as a
catalyst material for diamond. Catalyst material for diamond is
understood to be material that is capable of promoting direct
inter-growth of diamond grains at a pressure and temperature
condition at which diamond is thermodynamically more stable than
graphite. Some catalyst materials for diamond may promote the
conversion of diamond to graphite at ambient pressure, particularly
at elevated temperatures. Examples of catalyst materials for
diamond are cobalt, iron, nickel and certain alloys including any
of these. PCD may be formed on a cobalt-cemented tungsten carbide
substrate, which may provide a source of cobalt catalyst material
for the PCD. The interstices with PCD may at least partly be filled
with a material, which may be referred to as a binder or a filler
material. In particular the interstices may be wholly or partially
filled with catalyst material for diamond.
[0005] Components comprising PCD are 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. For example, PCD bodies are commonly
used as cutter inserts on drill bits used for boring into the earth
in the oil and gas drilling industry. PCD bodies are also used for
machining and milling metal-containing bodies, such as may be used
in the auto manufacturing industry. In many of these applications
the temperature of the PCD material becomes elevated as it engages
a rock formation, workpiece or body with high energy.
[0006] PCD is extremely hard and abrasion resistant, which is the
reason it is the preferred tool material in some of the most
extreme machining and drilling conditions, and where high
productivity is required. A disadvantage of PCD containing certain
catalyst materials for diamond as a filler material may be its
relatively poor thermal stability above about 400 degrees
centigrade. The catalyst material may promote the degradation of
the PCD at elevated temperature, particularly at temperatures
greater than about 750 degrees centigrade, as may be experienced in
manufacture and use of PCD compacts.
[0007] U.S. patent application publication number 2007/0079994
discloses thermally stable diamond-bonded compacts that include a
diamond-bonded body comprising a thermally stable region that
extends a distance below a diamond-bonded body surface. The
thermally stable region has a material microstructure comprising a
matrix first phase of bonded together diamond crystals, and a
second phase interposed within the matrix first phase. The second
phase comprises one or more reaction products formed between one or
more infiltrant material and the diamond crystals at high pressure
I high temperature (HPHT) conditions. The infiltrant or replacement
material may include one or more of the following elements: Si, Cu,
Sn, Zn, Ag, Au, Ti, Cd, Al, Mg, Ga, Ge, which may also be used in
compounds containing conventional solvent-catalyst materials
(transition metals) where the solvent catalyst is rendered inactive
by reaction with another material.
[0008] U.S. patent application publication number 2008/0230280
discloses a PCD construction comprising a first region positioned
remote from a surface and that includes a replacement material. The
replacement material may be a noncatalyzing material that is
disposed within interstitial regions between the diamond crystals
in the first region. The noncatalyzing material can have a melting
temperature of less than about 1,200 degrees centigrade and can be
selected from low melting point metallic materials and/or alloys
including elements, which can include those from Group IB of the
Periodic table, such as copper. It is additionally desired that the
replacement material display negligible or no solubility for
carbon.
[0009] There is a need to provide a polycrystalline diamond (PCD)
element having enhanced thermal stability.
SUMMARY
[0010] A purpose of the invention is to provide a (PCD) element
having enhanced thermal stability.
[0011] A first aspect of the invention provides a polycrystalline
diamond (PCD) element having internal diamond surfaces, the
internal diamond surfaces defining interstices between them, the
PCD element comprising a working surface, a low melting point
region adjacent the working surface and in which the interstices
are at least partially filled with a low melting point metallic
material having a melting point of less than about 1,300 degrees
centigrade at atmospheric pressure, or less than about 1,200
degrees centigrade at atmospheric pressure; and an intermediate
region extending a distance of between about 5 microns and about
600 microns from a boundary defined by the low melting point
region, the interstices of the intermediate region being at least
partially filled with a catalyst material for diamond.
[0012] In one embodiment, the PCD element is bonded to a substrate
at an interface and the intermediate region of the PCD element
extends from the boundary defined by the low melting point region
and the interface. In some embodiments, the intermediate region
extends a distance from the boundary of at most about 400 microns,
at most about 200 microns, at most about 100 microns, at most about
50 microns, at most about 10 microns or even at most about 5
microns. In some embodiments, the intermediate region extends a
distance from the boundary of at least about 5 microns, at least
about 10 microns, at least about 50 microns, at least about 100
microns, or even at least about 200 microns.
[0013] In one embodiment of the invention, the interstices of the
intermediate region are at least 50% filled with a sintering aid or
catalyst material for diamond, such as cobalt.
[0014] In some embodiments, the low melting point region extends a
depth into the PCD element from the working surface, the depth
being at most about 1,000 microns, at most about 500 microns or at
most about 100 microns, In some embodiments, the low melting point
region extends a depth into the PCD element from a working surface,
the depth being at least about 5 microns, at least about 10
microns, at least about 50 microns, at least about 100 microns, or
even at least about 200 microns.
[0015] In one embodiment, the low melting point region is in the
form of a stratum or layer. In some embodiments, the low melting
point region is in the form of a layer or stratum that extends to a
depth of at least about 40 microns, at least about 100 microns or
even at least about 200 microns from a working surface.
[0016] In one embodiment of the invention, the interstices within
the low melting point region are at least 50 percent, at least
about 70 percent, at least about 80 percent or at least about 90
percent filled with the low melting point metallic material.
[0017] In one embodiment of the invention, the low melting point
metallic material has a melting point lower than 1,100 degrees
centigrade at atmospheric pressure.
[0018] In some embodiments of the invention, the low melting point
metallic material has a melting point greater than about 600
degrees centigrade or greater than about 700 degrees centigrade at
atmospheric pressure.
[0019] Embodiments of the invention have the advantage that the low
melting point metallic material does not substantially melt when
the PCD element, is brazed onto a tool carrier at temperatures of
several hundred degrees centigrade.
[0020] In one embodiment of the invention, the low melting point
metallic material is not capable of reacting to form a stable
carbide at less than about 1,000 degrees centigrade at atmospheric
pressure.
[0021] Embodiments of the invention have the advantage that the low
melting point metallic material does not react with the diamond to
form carbides. The formation of carbide grains may retard the rate
of infiltration of the low melting point metallic material in
manufacture and may create undesirable stresses within the
interstices due to volume changes occurring with the formation of
new phases and compounds. The formation of carbides as a reaction
product of a reaction between the low melting point metallic
material and the diamond of the PCD would necessarily require some
of the surrounding diamond to be sacrificed to the reaction, which
may compromise the integrity of the microstructure.
[0022] In some embodiments of the invention, the low melting point
metallic material is Ag, Mg, Cu or Pb in elemental form or an alloy
including any of these elements, and in some embodiments the low
melting point metallic material is Ag or Cu in elemental form or an
alloy including either of these elements. In one embodiment, the
low melting point metallic material has the characteristic that it
is substantially resistant to oxidation.
[0023] Embodiments of the invention have the advantage of having
enhanced thermal stability without substantially compromising
strength.
[0024] In one embodiment of the invention, the PCD element is
bonded at an interface to a cemented carbide substrate, such as a
cobalt-cemented tungsten carbide substrate, and in one embodiment,
the PCD element is bonded to a hard-metal substrate via a bonding
layer having a coefficient of thermal expansion intermediate that
of the PCD and the hard-metal. In one embodiment, the bonding layer
comprises diamond grains and metal carbide, wherein the diamond
grains are not substantially bonded to each other. In one
embodiment, the PCD element comprises an intermediate region that
is remote from the working surface, in which the interstices are at
least 50% filled with a catalyst material for diamond, the
intermediate region being adjacent the interface and the low
melting point region is remote from the interface.
[0025] A second aspect of the invention provides an insert for a
tool, the insert comprising an embodiment of a PCD element
according to the invention.
[0026] A third aspect of the invention provides a tool comprising
an embodiment of an insert according to the invention.
[0027] In some embodiments, the tool is suitable for machining,
drilling, boring, cutting or otherwise forming or degrading a hard
or abrasive workpiece or other body, such as rock, concrete,
asphalt, metal or hard composite materials. In some embodiments,
the tool is a drill bit for use in earth boring, rock drilling or
rock degradation, as may be used in the oil and gas drilling and
mining industries, and in one embodiment, the tool is a rotary drag
bit for use in earth-boring and rock drilling in the oil and gas
industry.
[0028] A fourth aspect of the invention provides a method for
making a PCD element, the method including providing a PCD body
comprising a sintering aid within interstices of the PCD body,
removing at least some of the sintering aid from a portion of the
polycrystalline diamond element to form a porous region adjacent a
working surface, and infiltrating or permeating at least a portion
of the porous region with low melting point metallic material
having a melting point of less than about 1,300 degrees centigrade
at atmospheric pressure, or less than about 1,200 degrees
centigrade at atmospheric pressure.
[0029] In one embodiment, substantially all of the sintering aid is
removed from the PCD element.
[0030] One embodiment of the method of the invention includes
preventing or avoiding filling the pores within a part of the
porous region with the low melting point metallic material.
[0031] One embodiment of the method of the invention includes
infiltrating a material comprising a catalyst material for diamond,
such as cobalt, into a part of the porous region not filed with the
low melting point metallic material.
[0032] In one embodiment of the invention, a controlled temperature
cycle is employed in such a manner as to allow sufficient or a
certain amount of the low melting point metallic material to be
introduced into the porous region prior to infiltration with the
material comprising a catalyst material for diamond.
DRAWING CAPTIONS
[0033] Non-limiting embodiments will now be described with
reference to the drawings, of which
[0034] FIG. 1 shows a schematic longitudinal cross sectional view
of an embodiment of a PCD element.
[0035] FIG. 2 shows a schematic expanded cross sectional view of a
region of the embodiment shown in FIG. 1.
[0036] FIG. 3A shows schematic perspective views of components used
in an embodiment of a method for manufacturing PCD compacts or
inserts.
[0037] FIG. 3B shows a schematic perspective view of an embodiment
of a PCD compact or insert.
[0038] The same references in all drawings refer to the same
features, unless otherwise indicated.
DETAILED DESCRIPTION OF EMBODIMENTS
[0039] As used herein, a "working surface" of an insert or element
is any part of the insert or element which may in use contact a
workpiece or body being worked. It is understood that any portion
of a working surface is also a working surface.
[0040] As used herein, the term "low melting point metallic
material" means metal in elemental or alloy form, which possesses
the characteristic properties of a metal, including high electrical
conductivity, thermal conductivity and fracture toughness. The term
excludes compounds of metals, such as metal carbides, oxides,
nitrides, carbo-nitrides, and other ceramics or inter-low melting
point metallic materials that do not possess metallic
properties.
[0041] As used herein, a catalyst material for diamond is a
material that is capable of promoting the precipitation, growth
and/or sintering-together of grains of diamond under a condition of
pressure and temperature at which diamond is more thermodynamically
stable than graphite. Examples of catalyst materials for diamond
are iron, nickel, cobalt, manganese and certain alloys including
any of these elements. Some catalyst materials for diamond are
capable of promoting the conversion of diamond into graphite at
ambient pressure, particularly at elevated temperatures.
[0042] With reference to FIG. 1 and FIG. 2, an embodiment of a PCD
insert 200 comprises an embodiment of a PCD element 100 joined to a
cemented carbide substrate 220 at an interface 116. The embodiment
of the PCD element 100 has internal diamond surfaces 102, the
internal diamond surfaces 102 defining interstices 104 between
them. The PCD element 100 further comprises a working surface 114
and a low melting point region 111 adjacent the working surface 114
and in which the interstices 104 are at least partially filled with
a low melting point metallic material having a melting point of
less than about 1,300 degrees centigrade at atmospheric pressure,
or less than about 1,200 degrees centigrade at atmospheric
pressure. An intermediate region 112 extends a distance of between
about 5 microns and about 600 microns from a boundary 116, the
interstices 104 of the intermediate region 112 being at least
partially filled with a catalyst material for diamond. In this
embodiment, the boundary is the interface (both indicated by
reference number 116).
[0043] The person skilled in the art will appreciate that PCD
inserts of a wide range of shapes and sizes can be made, depending
on the type of application. The inserts are particularly
advantageous when used in applications where the insert may be
subjected to high temperatures, and therefore where high thermal
stability is important. An especially favoured application is as
inserts for rotary drill bits used for rock drilling and earth
boring in the oil and gas industry.
[0044] With reference to FIG. 3A, an embodiment of a method for
making a PCD element includes providing a PCD insert 300 that has
been manufactured using an ultra-high pressure and high temperature
(HPHT) method well-known in the art. The insert 300 comprises a PCD
element 310 integrally bonded to a cemented carbide hard-metal
substrate 320. The microscopic interstices (not shown) of the PCD
element 310 are substantially filled with cobalt catalyst material.
At least a part of PCD element 310 is detached from the insert 300
to produce a PCD body 311. One way of detaching the PCD element 310
is to grind away the substrate 320. The PCD body 311 is treated to
remove catalyst material from the interstices to produce a porous
and thermally stable PCD element 312. The porous PCD element 312 is
then contacted on one side with a second cemented carbide substrate
340 and on the opposite side with a source 330 of low melting point
metallic material. The source 330 may be in the form of a thin foil
or disc, or powder. The substrate 340 includes tungsten carbide
grains and a cobalt metal binder, the metal binder being capable of
acting as a catalyst material to promote the growth and sintering
of diamond grains. The porous PCD element 312, thus "sandwiched"
between the substrate 340 and the foil or disc 330 is treated at an
ultra-high pressure in excess of about 5 GPa at temperatures
sufficiently high to melt the low melting point metallic material
and to melt the cobalt metal binder of the substrate 340, resulting
in some of it infiltrating into the porous PCD element 312. The
temperature cycle may be controlled in such a manner as to allow
sufficient or a certain amount of the low melting point metallic
material to be introduced into the porous PCD element 312 prior to
the cobalt metal binder material melting and infiltrating into the
porous PCD element 312. After this treatment, the resulting insert
is removed and processed to final dimensions and tolerances to
produce an embodiment of a finished PCD insert 200 shown in FIG.
3B, comprising a PCD element 100 joined to a cemented carbide
substrate 220.
[0045] In one embodiment, the PCD body has a thickness between a
pair of opposite surfaces of at least about 1.5 mm or at least
about 1.8 mm, one of the pair contacted with a source of low
melting point metallic material and the other of the pair contacted
with a source of catalyst material for diamond.
[0046] One embodiment of the method of the invention includes
heating a source of low melting point metallic material to a
temperature within the range between the melting point of the low
melting point metallic material and the melting point of the
catalyst material, maintaining the temperature within this range
for a period of time sufficient for the infiltration or permeation
of the low melting point metallic material to be completed. In one
embodiment, the temperature is then increased to greater than the
melting point of the catalyst material for a period of time for the
introduction of the catalyst material to be completed.
[0047] One embodiment of the method includes contacting one surface
of a porous PCD body with a source of silver, contacting another
surface of the PCD body with a source of cobalt to form an
assembly, subjecting the assembly to a pressure of at least about
5.5 GPa, heating the assembly to a temperature in the range above
the melting point of silver at the pressure and below the melting
point of cobalt at the pressure, maintaining temperature within
this range for a period of time of at least about 2 minutes or at
least about 3 minutes, and then increasing the temperature to above
the melting point of cobalt at the pressure.
[0048] One embodiment of the method includes contacting one surface
of a porous PCD body with a source of copper, contacting another
surface of the PCD body with a source of cobalt to form an
assembly, subjecting the assembly to a pressure of at least about
5.5 GPa, heating the assembly to a temperature in the range above
the melting point of copper at the pressure and below the melting
point of cobalt at the pressure, maintaining temperature within
this range for a period of time of at least about 1 minute or at
least about 2 minutes, and then increasing the temperature to above
the melting point of cobalt at the pressure.
[0049] In some embodiments, the period of time is at most about 15
minutes or even at most about 10 minutes.
[0050] The sintered PCD body can be produced in an ultra-high
pressure furnace by sintering together diamond grains in the
presence of a catalyst material for diamond at a pressure of at
least about 5.5 GPa and a temperature of at least about 1,300
degrees centigrade. The catalyst material may comprise a
conventional transition metal type diamond catalyst material, such
as cobalt, iron or nickel, or certain alloys thereof. The sintered
PCD body, as a whole or at least a region thereof, may then be
rendered thermally stable, for example, through the removal of the
majority of binder catalyst material from the PCD body or desired
region using acid leaching or another similar process known in the
art.
[0051] The catalyst material present in the PCD body 311 may be
removed by any of various methods known in the art, such as
electrolytic etching, evaporation techniques, acid leaching (for
example by immersion in a liquor containing hydrofluoric acid,
nitric acid or mixtures thereof) or by means of chlorine gas, as
disclosed in international patent publication number WO2007/042920,
or by another method (e.g. as disclosed in South African patent
number 2006100378).
[0052] In one embodiment of the method, a PCD insert similar to PCD
insert 300 in FIG. 3A, is provided. A region adjacent the working
surface of the PCD element is depleted substantially of catalyst
material by means of method known in the art, resulting in the
region being porous. A low melting point metallic material is
introduced into the pores of the porous region. The parameters of
the method of introduction may be controlled to retain porosity
within part of the porous region. A catalyst material is then
infiltrated into the remaining pores of the masked or passivated
region. This may be done by contacting a source of catalyst
material with the working surface of the PCD element, assembling
the PCD insert and the source into a capsule of a kind used for
HPHT sintering of PCD, and subjecting the assembly to an ultra-high
pressure and temperature at which the catalyst material is molten
and the diamond is thermodynamically more stable than graphite. In
some embodiment, the pressure is at least about 5.5 GPa, at least
about 6 GPa or at least about 6.5 GPa. In one embodiment, the
pressure is about 6.8 GPa.
[0053] The low melting point metallic materials according to the
invention are substantially inert with respect to diamond and do
not substantially promote its dissolution or degradation at ambient
pressures. They may function as a heat conducting filler within the
PCD element. While wishing not to be bound by any particular
hypothesis, low melting point metallic materials are believed not
to degrade diamond at the high temperatures that may be experienced
in use, i.e. up to about 1,100 degrees centigrade. At temperatures
for which the low melting point metallic material is in the solid
phase, its presence in the interstices may enhance the strength of
the PCD. In addition, the high thermal conductivity of the low
melting point metallic material may further enhance the thermal
stability of the polycrystalline diamond element in comparison to
leached PCD. At temperatures for which the low melting point
metallic material is in or close to the molten phase, stress may be
prevented from building up within the PCD by virtue of the low
melting point metallic material leaking from the interstices as it
thermally expands or melts. Solid metals close to their melting
points generally have greatly reduced yield strength, which reduces
build up of micro-stresses that may arise from a mismatch in the
thermal expansion coefficients. Melting or softening of the metal
may have the additional benefit of lubricating the action of the
polycrystalline diamond element at high temperatures. The low
melting point of the low melting point metallic material means that
relatively low temperatures are required to infiltrate it into a
polycrystalline diamond element in manufacture. In some embodiments
of the method of the invention, the rate and extent of infiltration
may readily be controlled by controlling its viscosity by
controlling the temperature, without need to use very high
temperatures.
EXAMPLES
[0054] The invention will now be described, by way of example only,
with reference to the following non-limiting examples.
Example 1
[0055] A PCD insert having a diameter of about 16 mm and for use in
a rotary drag bit for oil and gas drilling was used as the starting
component. The insert was substantially cylindrical in form and
comprised a PCD layer integrally bonded to a Co-cemented WC
hard-metal substrate. The PCD layer was about 2,3 mm thick and the
diamond grain size distribution was of a multi-modal type,
comprising sintered diamond grains with average grain size of less
than about 20 microns, the interstices between the diamond grains
being filled with Co, a catalyst metal sourced from the hard-metal
substrate during the step of sintering the PCD. Substantially all
of the hard-metal substrate was machined away from the PCD layer,
providing a PCD disc. Substantially all the Co was then removed
from the PCD disc by immersing it in a mixture of hydrofluoric and
nitric acid for several days, resulting in a porous, detached PCD
disc. The PCD disc was heat treated in vacuum in order to remove
(i.e. "outgas") any residual organic impurities that may be
present.
[0056] The porous PCD disc was then re-infiltrated with cobalt from
one side and copper from an opposite side, and simultaneously
re-bonded to a second Co-cemented WC substrate. This
re-infiltration step was carried out at an ultra-high pressure of
greater than about 5 GPa, at which diamond is thermodynamically
stable, and a temperature of about 1,400 degrees centigrade at
which Co is molten at the ultra-high pressure. In order to carry
out this step, a pre-form assembly was prepared, the pre-form
assembly comprising the porous PCD disc placed onto a flat surface
of a cylindrical substrate, and a thin film of copper placed on top
of the porous PCD disc. The copper film was less than 0.5 mm thick
and had been ultrasonically cleaned in an acetone bath.
[0057] The assembly comprising the PCD disc thus "sandwiched"
between the copper foil and the substrate was placed within a
refractory metal jacket, which was subsequently placed within a
ceramic support and subsequently sealed within another metal
casing, as is well known in the art. The pre-form assembly was
assembled into a capsule for an ultra-high pressure furnace and
subjected to the ultra-high pressure and temperature. The
temperature was increased from ambient to the maximum level over a
period of time once the target pressure had been achieved.
[0058] After the re-infiltration step, the insert was removed from
the ultra-high pressure apparatus and the casing and jacketing was
removed. The insert was then sliced into two parts along an axial
plane, producing two cross-sectional surfaces. One of these
surfaces was polished and analysed by means of SEM (scanning
electron microscopy), revealing that the PCD had bonded well with
the substrate and that substantially all of the interstices within
the PCD were filled with copper, cobalt, or a combination of copper
and cobalt. The copper had infiltrated from the flat working
surface to a depth of about 1.7 mm, a region with a depth of about
1.3 mm from the flat working surface being substantially free of
cobalt. The PCD interstices within about 0.2 mm from the substrate
were filled principally with cobalt, although some copper was
evident.
[0059] A second test insert was made as above and subjected to a
wear test, which involved using the insert, suitably prepared as
would be appreciated by the skilled person, to machine a granite
block mounted on a vertical turret milling apparatus. The PCD layer
displayed excellent wear resistance and thermal stability.
Example 2
[0060] A re-infiltrated insert was made using the same process as
in Example 1, the only difference being that a silver foil was used
instead of a copper foil. The insert was also analysed and tested
as in Example 1.
[0061] The silver had infiltrated more deeply into the PCD than had
the copper, to a depth of about 2.2 mm from the flat working
surface. This is believed to be due to the lower melting point of
silver and consequently the fact that it would have melted at an
earlier stage than the copper, therefore having more time to
infiltrate the porous PCD before the cobalt melted and began
infiltrating from the opposing direction.
Example 3
[0062] A porous PCD disc can be prepared using the process
described in Example 2, and the silver can be introduced into the
pores prior to the treatment at ultra-high pressure. This can be
done by placing the porous PCD disc into a graphite vessel, and
disposing a silver film on top of it, the silver film having been
ultra-sonically cleaned in an acetone bath. The vessel can then be
placed in a furnace and its contents heated in a vacuum to above
the melting point of the silver, i.e. to about 1,000 degrees
centigrade, causing the silver foil to melt and infiltrate the PCD
disc.
Example 4
[0063] A porous PCD disc can be prepared using the process
described in Example 2 and silver can be introduced into the pores
prior to the treatment at ultra-high pressure by depositing a very
thin film of silver onto a flat surface of the PCD disc by means of
sputtering and then causing it to melt. The mass of the silver
deposited can be calculated to be just sufficient for 10% of the
pores to be filled with silver, and consequently to provide just
enough silver to infiltrate the PCD to a depth of about 10% of its
thickness, i.e. to a depth of about 230 microns from the flat
surface, leaving the remaining pores substantially empty. This mass
could be about 12.5 milligrams. The film thickness should be as
uniform as possible across the PCD surface.
[0064] The silver-coated PCD can then be placed into a graphite
vessel, with the coated surface remote from the base of the
graphite vessel (i.e. on the top surface), and the vessel placed
into a furnace. The vessel and its contents can be heated in a
vacuum to above the melting point of the silver, i.e. to about
1,000 degrees centigrade, causing the silver coating to melt and
infiltrate the PCD disc.
Example 5
[0065] A free-standing fully leached PCD disc was produced
according to a similar process to that disclosed in Example 1.
Diamond powder having a size distribution that can be resolved into
at least two distinct peaks was placed against a cobalt cemented
tungsten carbide substrate, and this assembly was encapsulated in a
refractory metal jacket and subjected to an ultra-high pressure of
at least about 5.5 GPa and a temperature of at least about 1,500
degrees centigrade to sinter the diamond powder into a PCD layer
bonded to the substrate. After sintering the PCD disc was separated
from the substrate by lapping away the carbide base and
substantially all of the cobalt was removed from the interstices of
the PCD by means of leaching in an acid liquor, as is well known in
the art, to form a porous PCD body having a generally disc
form.
[0066] A copper disc was placed against one end of the porous PCD
body and a cobalt cemented tungsten carbide substrate was placed
against the opposite end of the PCD body, and this assembly was
encapsulated within a refractory metal jacket. The porous PCD body
was thus sandwiched between the substrate and the copper disc. The
copper disc had a thickness of about 0.25 mm and diameter
substantially the same as that of the PCD body. The mass of the
copper discs was at around 420 mg, which equates to less than about
10 percent of the volume of the PCD body, and was at a level
considered to be in excess of the volume required to fill the
entire void created during the leaching process.
[0067] The assembly was further encased in a manner known in the
art for HPHT sintering and subjected to a second high pressure
thermal cycle at a temperature of around 1,410 degrees centigrade
and a pressure of around 5.2 GPa. The PCD insert comprising a PCD
layer containing copper and cobalt, and joined to the substrate was
recovered and machined to final specifications to form a PCD cutter
insert.
[0068] The PDC cutter insert was subjected to a milling test, which
involved a high-rotational speed cutting of a granite work piece
and is considered to be a very thermally aggressive test. The
results suggest a dramatic improvement in thermal stability above
that of a control PCD cutter insert, which had not undergone the
process of re-infiltration of copper.
Example 6
[0069] A further material was made using the method disclosed in
Example 5, but by substituting the copper disc with 520 mg of
silver powder. Once again, the mass was chosen to correspond to
around 10 vol % of the fully leached disc. The conditions selected
for the second high pressure thermal cycle were identical to those
used in Example 5. Performance results from this material showed an
improvement in thermal stability above that of non-reinfiltrated
PCD.
* * * * *