Note: Descriptions are shown in the official language in which they were submitted.
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POLYCRYSTALLINE DIAMOND COMPOSITE COMPACT
Field
The invention relates to polycrystalline diamond composite compacts, tools
incorporating same, and methods for making and using same.
Background
Polycrystalline diamond (PCD) is a super-hard, also known as superabrasive
material comprising a mass of inter-grown diamond grains and interstices
between the diamond grains. POD may be made by subjecting an
aggregated mass of diamond grains to an ultra-high pressure and
temperature. A material wholly or partly filling the interstices may be
referred
to as filler material. POD may be formed in the presence of a sintering aid
such as cobalt, which is capable of promoting the inter-growth of diamond
grains. The sintering aid may be referred to as a solvent / catalyst material
for
diamond, owing to its function of dissolving diamond to some extent and
catalyst 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 POD product may be wholly
or partially filled with residual solvent / catalyst material. POD may be
formed
on a cobalt-cemented tungsten carbide substrate, which may provide a
source of cobalt solvent / catalyst for the PCD.
POD 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. For example, POD elements may
be used as cutting elements on drill bits used for boring into the earth in
the oil
and gas drilling industry. In many of these applications the temperature of
the
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POD material may become elevated as it engages a rock formation,
workpiece or body with high energy. Unfortunately, mechanical properties of
POD such as hardness and strength tend to deteriorate at high temperatures,
largely as a result of residual solvent / catalyst material dispersed within
it.
United States patent number 3,745,623 discloses a POD element comprising
a polycrystalline diamond layer bonded to a cemented carbide body
comprising 94 weight percent tungsten carbide and 6 weight percent cobalt.
United States Patent number 4,380,471 discloses the various grades of
cemented tungsten carbide may be used as substrates for POD elements,
including the following grades from the Carboloy range: 44A, 90, 883 and
999, which comprise 6, 10, 6 and 3 weight percent cobalt, respectively.
United States patent number 5,304,342 discusses that for a given application,
it is desirable to provide the stiffest possible WC-Co cemented carbide
substrate, thereby minimizing the deflection of the POD layers and reducing
the likelihood of POD failure. However, if the modulus of elasticity is too
high,
the inserts are prone to break off during drilling.
United States patent number 5,667,028 discusses that as a bit rotates, the
edge of the PDC cutting layer of a POD cutter makes contact and "cuts" away
at a formation being drilled. At the same time portions of the exposed cutter
body also make contact with the formation surface. This contact erodes the
cutter body. It discloses an improved polycrystalline diamond composite
("PDC') drag bit cutter comprising multiple cutting surfaces, at least two of
which are non-abutting, resulting in an enhanced useful life. Fluid erosion of
the PDC cutter may also occur.
United States patent number 5,431,239 discloses a composite stud structure
having different material characteristics across its structural cross section
to
provide the abrasion resistance of hard materials combined with fracture
resistance, called fracture toughness. In one embodiment a stud is comprised
of an inner core of material having higher or enhanced fracture toughness,
such as large-grain-size tungsten carbide or high-cobalt-content tungsten
carbide, surrounded by an outer layer of hard, abrasion resistant material. A
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typical material is low-cobalt, cemented tungsten carbide. Although 6% cobalt
is possible, about 9-12% cobalt is the range preferred. Cobalt content usually
ranges between 6 and 20 percent in cemented tungsten carbides. High
cobalt content is greater than about 15%. Carbide grain size and cobalt
content can both be varied to design for strength or high fracture toughness.
The cutting face is usually manufactured of a superhard material such as
polycrystalline diamond.
United States patent number 6,216,805 discloses a cutting element that
includes a base including an erosion-resistant and abrasion-resistant
material.
A cutting end of the cutting element is configured to have a superabrasive
cutting table secured thereto. In an embodiment, the base is fabricated from
an erosion-resistant and abrasion-resistant material. For example, the base
may comprise carbide (e.g., tungsten carbide) and a binder material (e.g.,
cobalt). When relatively more binder is employed to fabricate base, the
erosion-resistance and abrasion-resistance of base decrease. Cemented
carbide structures that have smaller grains of carbide are also typically more
erosion-resistant and abrasion-resistant, but less tough, ductile, and impact-
resistant, than cemented carbide structures formed with larger grains of
carbide.
United States patent number 6,258,139 discloses a PDC (polycrystalline
diamond compact) with an internal diamond core in the substrate, to provide
additional diamond for exposure when the substrate is sufficiently eroded.
Also disclosed is a PDC with an internal carbide core, which is entirely
enclosed by the diamond region of the PDC cutter, to avoid high tensile
stresses in the diamond region.
Freinkel discloses that WC grain size in the range from 1.6 microns to 2.2
microns results in optimum erosion resistance for cemented WC ("Energy loss
mechanisms in the erosion of cemented WC", Scripta Metallurgica, 23, 1989,
pp. 659-664).
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United States patent number 7,017,677 discusses that existing substrates for
shear cutters are generally formed of cemented tungsten carbide particles
with grain sizes in the range of about 1 to 3 microns and cobalt content in
the
range of about 9 percent to 16 percent by weight, and have hardness in the
range of about 86 Ra to 89 Ra.
United States patent number 7,556,668 discloses an embodiment of a
consolidated hard material made from approximately 75 weight percent hard
particles, such as WC, and approximately 25 weight percent binder material,
such as Co. Also disclosed are polycrystalline diamond compact (PDC)
shear-type cutters wherein hard materials disclosed in the patent may be
used to form a shear cutter substrate that is used to carry a layer or "table"
of
polycrystalline diamond that is formed on it at ultrahigh temperatures and
pressures.
There is a need for polycrystalline diamond compact (PDC) cutter elements
having improved overall erosion resistance without substantially
compromising fracture resistance.
Summary
The invention provides a polycrystalline diamond (PCD) composite compact
element comprising a POD structure bonded to a substrate; wherein at least a
peripheral region of the substrate comprises cemented carbide material
having a mean free path (MFP) characteristic of at least about 0.1 microns
and at most about 0.7 microns, or at most about 0.35 microns; and an elastic
limit of at least about 1.9 GPa. In one embodiment of the invention, the
peripheral region of the substrate may be adjacent at least an area of an
exposed peripheral surface of the substrate.
In some embodiments of the invention, the cemented carbide material may
comprise metal carbide particles and metallic binder material; wherein the
content of the metallic binder material within at least the peripheral region
of
the substrate, or throughout substantially the entire substrate, may be at
least
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about 1 weight percent, at least about 3 weight percent, at least about 5
weight percent or at least about 6 weight percent; and at most about 12
weight percent, at most about 11 weight percent or at most about 10 weight
percent of the cemented carbide material. In some embodiments, the content
of the metallic binder material may be less than 9 weight percent. In one
embodiment of the invention, the cemented carbide material may comprise
metallic binder in the range from about 8 weight percent to about 13 weight
percent of the cemented carbide material.
In some embodiments of the invention, the particles of metal carbide within at
least the peripheral region may have a mean size of at least about 0.1 micron,
at least about 0.5 micron, at least about 1 micron, at least about 3 microns
or
at least about 5 microns; and at most about 20 microns, at most about 10
microns, at most about 2 microns or at most about 1 micron. In one
embodiment of the invention, the cemented carbide material may comprise
metal carbide particles having a mean size in the range from about 1.5
microns to about 3 microns.
In some embodiments of the invention, the metal carbide material may
comprise titanium carbide (TiC), tungsten carbide (WC), tantalum carbide
(TaC) or other refractory metal carbide. In one embodiment of the invention,
the metallic binder material may comprise cobalt (Co), nickel (Ni) or iron
(Fe),
or an alloy containing Co, Fe or Ni. In some embodiments, the metallic binder
material may comprise Co substantially in the face centre cubic (fcc) form or
substantially in the hexagonal close packed (hcp) crystallographic form.
In one embodiment of the invention, the metallic binder material may contain
a low level of carbon and a high level of W. In one embodiment, the metal
carbide grains may be substantially rounded WC grains, substantially without
sharp facets or edges. In one embodiment of the invention, the metallic
binder material may contain a solid solution of tungsten (W) or carbon (C), or
both W and C in Co.
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In some embodiments of the invention, the metallic binder material may
contain particles of chromium carbide (Cr3C2) or vanadium carbide (VC), or
particles of Cr3C2 and VC dispersed therein, and in some embodiments the
combined content of Cr3C2 and VC particles in the metallic binder material
may be less than about 1 weight percent. In one embodiment, the metallic
binder material may comprise Co, Ni and Cr3C2, and in one embodiment, the
metallic binder material may comprise Co and Cr3C2, and may be
substantially free of Ni.
In some embodiments of the invention, the metallic binder material may
comprise a concentration of a refractory metal such as W, Ti, Ta and Cr in the
range from about 5 atomic percent to about 30 atomic percent of the binder
material. In one embodiment, the metallic binder material may comprise Co
containing a high concentration of W, in the range from about 5 atomic
percent to about 30 atomic percent, or in the range from about 10 atomic
percent to about 30 atomic percent. In one embodiment, the lattice constant
of the Co in the binder material may be about 1 % to about 5% greater than
that of pure Co (0.3545 nm).
In some embodiments of the invention, metal carbide or metal-containing
nano-particles having mean size in the range from about 0.1 nm to about 500
nm, or in the range from about 0.1 nm to about 200 nm may be dispersed in
the metallic binder material. The nano-particles dispersed in the metallic
binder material may significantly reinforce or strengthen the binder. In some
embodiments, the content of the nano-particles in the metallic binder material
may be at least 5 volume percent of the metallic binder material. In some
embodiments at least the peripheral region of the cemented carbide substrate
is substantially free of eta-phase.
In some embodiments of the invention, at least a peripheral region of the
cemented carbide substrate, or substantially the entire substrate, may have
magnetic coercivity, Hc, of at most about 700 Oe (Oersted), or equivalently
about 55.7 kA/m, and at least about 100 Oe, or equivalently about 7.96 kA/m,
or at least about 200 Oe, or equivalently about 15.9 kA/m.
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In one embodiment of the invention, the metal carbide material may be WC
and the content of the metallic binder is in the range from about 1 to about
12
weight percent, or in the range from about 5 to about 11 weight percent; the
metallic binder comprising Co; wherein the cemented carbide has a magnetic
coercivity up to 17.0 kA/m, up to 9.5 kA/m, up to 8 kA/m, or in the range from
1.6 to 6.4 kA/m; a magnetic moment, 6 in units of micro-Tesla times cubic
meter per kilogram, respectively, as a function of the Co proportion (X) in
weight percent of the cemented carbide in a range of 6 = 0.11 X to 6 = 0.137
X.
In some embodiments of the invention, the POD structure may comprise inter-
bonded diamond grains having a mean size of at least about 0.5 micron, at
least about 2 microns or at least about 4 microns, and in some embodiments,
the POD structure may comprise inter-bonded diamond grains having a mean
size of at most about 20 microns, at most about 15 microns or at most about
microns. In one embodiment, the POD structure may comprise thermally
stable POD material, and may comprise at least a region substantially free of
metal solvent / catalyst material. In some embodiments, the POD structure
may be brazed to the substrate, and in one embodiment, the POD may be
integrally formed with and bonded to the substrate.
A method for making a polycrystalline diamond (PCD) composite compact
element is provided, the method including providing a cemented carbide
substrate comprising particles of a metal carbide and a metallic binder
material; wherein the content of the metallic binder may be at least about 1
weight percent, at least about 3 weight percent, at least about 5 weight
percent or at least about 6 weight percent; and at most about 12 weight
percent, at most about 11 weight percent or at most about 10 weight percent;
providing an aggregated mass of diamond particles, the aggregated mass
including a solvent / catalyst material for diamond; contacting the aggregated
mass with a surface of the substrate to form an unbonded assembly and
sintering the unbonded assembly at a pressure and temperature at which
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diamond is thermodynamically stable to form a POD structure bonded to a
cemented carbide substrate. The temperature may be at least 1,400 degrees
centigrade and the pressure may be at least 5.5 GPa. The method is an
aspect of the invention. In some embodiments of the invention, the pre-sinter
assembly may be subjected to a pressure of at least about 6 GPa, at least
about 6.5 GPa, at least about 7 GPa or even at least about 7.5 GPa.
In one version of the method, at least a peripheral region of the substrate
may
comprise cemented carbide material having a mean free path (MFP)
characteristic of at least about 0.1 microns and at most about 0.7 microns, or
at most about 0.35 microns; and an elastic limit of at least about 1.9 GPa. In
one version, the peripheral region of the substrate may be adjacent at least
an
area of an exposed peripheral surface of the substrate.
A method for making a polycrystalline diamond (PCD) composite compact
element is provided, the method including providing a cemented carbide
substrate in which at least a peripheral region comprises cemented carbide
material having a mean free path (MFP) characteristic of at least about 0.1
microns and at most about 0.7 microns, and an elastic limit of at least about
1.9 GPa; the peripheral region comprising particles of a metal carbide and a
metallic binder material, the content of the metallic binder being at least
about
1 weight percent and at most about 12 weight percent; providing an
aggregated mass of diamond particles; introducing a solvent / catalyst
material for diamond into the aggregated mass; and sintering the aggregated
mass in contact with the substrate at a pressure and temperature at which
diamond is thermodynamically stable to form a POD structure bonded to a
cemented carbide substrate. The method is an aspect of the invention.
In some embodiments, the metallic binder may comprise a solvent / catalyst
for diamond.
In some embodiments of the method, the solvent / catalyst for diamond may
be introduced into the aggregated mass of diamond grains by blending
solvent / catalyst material in powder form with the diamond grains, depositing
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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.
In one embodiment of the invention, the method may include removing
solvent / catalyst material from at least a part of the POD structure,
particularly
a part of the POD structure adjacent a working surface of the POD composite
compact element.
Embodiments of a POD composite compact element according to the
invention may be suitable for an earth boring drill bit, such as a rotary
shear-
cutting bit for use in the oil and gas drilling industry. The POD composite
compact element may be suitable for a fixed-cutter drill bit, rolling cone,
hole
opening tool, expandable tool, reamer or other earth boring tools.
An aspect of the invention provides a tool comprising an embodiment of a
POD composite compact element according to the invention, the tool being for
cutting, milling, grinding, drilling, earth boring, rock drilling or other
abrasive
applications, such as the cutting and machining of metal.
In one embodiment, the tool may comprise a drill bit for earth boring or rock
drilling. In one embodiment, the tool may comprise a rotary shear-cutting bit
for use in the oil and gas drilling industry. In some embodiments, the tool
may
be a rolling cone drill bit, a hole-opening tool, an expandable tool, a reamer
or
other earth boring tools.
Drawings
Non-limiting embodiments of the invention will be described with reference to
the accompanying drawings of which:
FIG 1 shows a schematic diagram of a microstructure of cemented carbide.
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FIG 2 shows a schematic perspective view of an embodiment of a POD
composite compact element.
FIG 3 shows a schematic longitudinal cross-section view of an embodiment of
a POD composite compact element.
FIG 4A shows a schematic perspective view and of an embodiment of a POD
composite compact element.
FIG 4B shows a schematic longitudinal cross-sectional view of the
embodiment of a POD composite compact element shown in FIG 4A.
FIG 5A shows a schematic perspective view of an embodiment of a POD
composite compact element.
FIG 5B shows a schematic longitudinal cross-sectional view of the
embodiment of a POD composite compact element shown FIG 5B.
FIG 6 shows a perspective view of a tool in the form of a rotary earth-boring
drill bit bearing POD elements as cutting elements thereon.
The references refer to the same respective features in all the drawings.
Detailed description of embodiments
As used herein, a "catalyst material for diamond", also referred to as
"solvent /
catalyst for diamond", is a material that is capable of promoting the
nucleation,
growth or inter-bonding of diamond grains at a pressure and temperature at
which diamond is thermodynamically stable. Catalyst materials for diamond
may be metallic, such as cobalt, iron, nickel, manganese and alloys of these,
or non-metallic.
As used herein, "polycrystalline diamond" (PCD) material comprises a mass
of diamond grains, a substantial portion of which are directly inter-bonded
with
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each other and in which the content of diamond is at least about 80 volume
percent of the material. In one embodiment of POD material, interstices
between the diamond gains 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 POD material. In
embodiments of POD material, interstices or interstitial regions may be
substantially or partially filled with a material other than diamond, or they
may
be substantially empty. As used herein, a "filler" material is a material that
wholly or partially fills pores, interstices or interstitial regions within a
structure,
such as a polycrystalline structure. Thermally stable embodiments of POD
material may comprise at least a region from which catalyst material has been
removed from the interstices, leaving interstitial voids between the diamond
grains. As used herein, a "thermally stable PCD" structure is a POD structure
at least a part of which exhibits no substantial structural degradation or
deterioration of hardness or abrasion resistance after exposure to a
temperature above about 400 degrees centigrade.
As used herein, the "elastic limit" of a material means the stress at which
the
strain of the material attains a value of 0.02% under compressive loading.
As used herein, the "mean free path" (MFP) of a composite material such as
cemented carbide is a measure of the mean distance between the aggregate
carbide grains cemented within the binder material. The mean free path
characteristic of a cemented carbide material can be measured using a
micrograph of a polished section of the material. For example, the
micrograph may have a magnification of about 1500x. With reference to FIG
1, the MFP can be determined by measuring the distance between each
intersection of a line and a grain boundary on a uniform grid. The matrix line
segments, Lm, are summed and the grain line segments, Lg, are summed.
The mean matrix segment length using both axes is the "mean free path".
Mixtures of multiple distributions of tungsten carbide particle sizes can
result
in a wide distribution of MFP values for the same matrix content.
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With reference to FIG 2 and FIG 3, embodiments of POD composite compact
elements 100 may comprise a POD structure 110 bonded to a cemented
carbide substrate 120 comprising particles of a metal carbide and a metallic
binder material; wherein at least a peripheral region 121 of the substrate 120
comprises cemented carbide material having a mean free path (MFP)
characteristic of at least about 0.1 microns and at most about 0.7 microns, or
at most about 0.35 microns; and an elastic limit of at least about 1.9 GPa. In
some embodiments, the content of the metallic binder material within a region
121 of the substrate 120 is in the range from about 1 weight percent to about
12 weight percent, and the particles of metal carbide within the region have a
mean size in the range from about 0.1 micron to about 20 microns.
With reference to FIG 4A and FIG 4B, an embodiment of a POD composite
compact element 100 may comprise a POD structure 110 bonded to a
cemented carbide substrate 120 comprising particles of a metal carbide and a
metallic binder material; wherein substantially the entire substrate 120
comprises cemented carbide material having a mean free path (MFP)
characteristic of at least about 0.1 microns and at most about 0.7 microns, or
at most about 0.35 microns; and an elastic limit of at least about 1.9 GPa.
With reference to FIG 5A and FIG 513, an embodiment of a POD composite
compact element 100 may comprise a POD structure 110 bonded to a
cemented carbide substrate 120 comprising particles of a metal carbide and a
metallic binder material; wherein at least a peripheral region of the
substrate
120 comprises cemented carbide material having a mean free path (MFP)
characteristic of at least about 0.1 microns and at most about 0.7 microns, or
at most about 0.35 microns; and an elastic limit of at least about 1.9 GPa;
and
the POD structure 110 is bonded to the substrate 120 by means of a braze
layer 140.
A desired MFP characteristic can be accomplished several ways known in the
art. For example, a lower MFP value may be achieved by using a lower metal
binder content. A practical lower limit of about 3 weight percent cobalt
applies
for cemented carbide and conventional liquid phase sintering. In an
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embodiment where the cemented carbide substrate is subjected to an ultra-
high pressure, for example a pressure greater than about 5 GPa and a high
temperature (greater than about 1,400 C for example), lower contents of
metal binder, such as cobalt, may be achieved. For example, where the
cobalt content is about 3 weight percent and the mean size of the WC grains
is about 0.5 micron, the MFP would be about 0.1 micron, and where the mean
size of the WC grains is about 2 microns, the MFP would be about 0.35
microns, and where the mean size of the WC grains is about 3 microns, the
MFP would be about 0.7 microns. These mean grain sizes correspond to a
single powder class obtained by natural comminution processes that generate
a log normal distribution of particles. Higher matrix (binder) contents would
result in higher MFP values.
Changing grain size by mixing different powder classes and altering the
distributions can achieve a whole spectrum of MFP values depending on the
particulars of powder processing and mixing. The exact values would have to
be determined empirically.
The magnetic properties of the cemented carbide material can be related to
important structural and compositional characteristics. The most common
technique for measuring the carbon content in cemented carbides is indirectly,
by measuring the concentration of tungsten dissolved in the binder to which it
is indirectly proportional: the higher the content of carbon dissolved in the
binder the lower the concentration of tungsten dissolved in the binder. The
tungsten content within the binder can be determined from a measurement of
the magnetic moment, 6, or magnetic saturation, MS = 4n6, these values
having an inverse relationship with the tungsten content (Roebuck (1996),
"Magnetic moment (saturation) measurements on cemented carbide
materials", Int. J. Refractory Met., Vol. 14, pp. 419-424.). The following
formula can be used to relate magnetic saturation, Ms, to the concentrations
of W and C in the binder:
MS [C]/[W] x wt.% Co x 201.9 in units of T.m3/kg
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The binder cobalt content within a cemented carbide material can be
measured by various methods well known in the art, including indirect
methods such as such as the magnetic properties of the cemented carbide
material or more directly by means of energy-dispersive X-ray spectroscopy
(EDX), or the most accurate method is based on chemical leaching of Co.
The mean grain size of carbide grains, such as WC grains, can be determined
by examination of micrographs obtained using a scanning electron
microscope (SEM) or light microscopy images of metallurgically prepared
cross-sections of a cemented carbide material body, applying the mean linear
intercept technique, for example. Alternatively, the mean size of the WC
grains can be measured indirectly by measuring the magnetic coercivity of the
cemented carbide material, which indicates the mean free path of Co
intermediate the grains, from which the WC grain size may be calculated
using a simple formula well known in the art. This formula quantifies the
inverse relationship between magnetic coercivity of a Co-cemented WC
cemented carbide material and the Co mean free path, and consequently the
mean WC grain size. Magnetic coercivity has an inverse relationship with
MFP.
An eta-phase composition is understood herein to mean a carbide compound
having the general formula MX M'y CZ, where M is at least one element
selected from the group consisting of W, Mo, Ti, Cr, V, Ta, Hf, Zr, and Nb; M'
is at least one element selected from the group consisting of Fe, Co, Ni, and
C is carbon. Where M is tungsten (W) and M' is cobalt (Co), as is the most
typical combination, then eta-phase is understood herein to mean C03W3C
(eta-1) or C06W6C (eta-2), as well as fractional sub- and super-stoichiometric
variations thereof. There are also some other phases in the W-Co-C system,
such as theta-phases C03W6C2, C04W4C and C02W4C, as well as kappa-
phases C03W9C4 and COW3C (these phases are sometimes grouped in the
literature within a broader designation of eta-phase).
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In some embodiments the cemented carbide substrate is substantially devoid
of eta-phase. The absence of eta-phase may be beneficial to the strength
and fracture toughness of the substrate.
United States Patent Publication Number 2006/0093859 discloses details of a
cemented carbide material comprising tungsten carbide (WC), wherein the
content of the metallic binder is in the range from 5 to 25 weight percent,
the
metallic binder comprising Co; wherein the cemented carbide in at least the
region has a magnetic coercive field strength up to 17.0 kA/m, up to 9.5 kA/m,
up to 8 kA/m, or in the range from 1.6 to 6.4 kA/m; a magnetic moment, 6 in
units of micro-Tesla times cubic meter per kilogram, respectively, as a
function of the Co proportion (X) in weight percent of the cemented carbide in
a range of 6 = 0.11 X to 6 = 0.137 X. An example of a cemented carbide
material having these properties is available from Element Six Hard Materials
GmbH, Germany, under the name of Master GradeTM
The concentration of W in the Co binder depends on the C content. For
example, the W concentration at low C contents is significantly higher. The W
concentration and the C content within the Co binder of a Co-cemented WC
(WC-Co) material can be determined from the value of the magnetic
saturation. The magnetic saturation of a hard metal, of which cemented
tungsten carbide is an example, is defined as the magnetic moment per unit
weight, 6, as well as the induction of saturation per unit weight, 47[6. The
magnetic moment, 6, of pure Co is 16.1 micro-Tesla times cubic metre per
kilogram (J.m3/kg), and the induction of saturation, also referred to as the
magnetic saturation, 4n6, of pure Co is 201.9 J.m3/kg.
In some embodiments, nano-particles having mean size in the range from
about 0.1 nm to about 1 nm and containing cobalt, tungsten and carbon, may
be dispersed within the binder. In one embodiment, particles of type one eta
phase, C03W3C, type two eta phase, C06W6C, and theta phase, C02W4C, in
the fcc crystallographic structure are dispersed in the binder, each having
respective mean size of about 0.213 nm, 0.209 nm and 0.215 nm. The
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presence of these nano-particles can be detected by means of electron
diffraction patterns using high resolution transmission electron microscopy
(HRTEM). Using dark field HRTEM, the nano-particles can be seen as dark
spots. The presence of the nano-particles within the binder may have the
effect of reinforcing the binder.
The practical use of cemented carbide grades with substantially lower cobalt
content as substrates for POD inserts is limited by the fact that some of the
Co is required to migrate from the substrate into the POD layer during the
sintering process in order to catalyse the formation of the PCD. For this
reason, it is more difficult to make POD on substrate materials comprising
lower Co contents, even though this may be desirable.
An embodiment of a POD composite compact element may be made by a
method including providing a cemented carbide substrate, contacting an
aggregated, substantially unbonded mass of diamond particles against a
surface of the substrate to form an pre-sinter assembly, encapsulating the
pre-sinter assembly in a capsule for an ultra-high pressure furnace and
subjecting the pre-sinter assembly to a pressure of at least about 5.5 GPa and
a temperature of at least about 1,250 degrees centigrade, and sintering the
diamond particles to form a POD composite compact element comprising a
POD structure integrally formed on and joined to the cemented carbide
substrate. In some embodiments of the invention, the pre-sinter assembly
may be subjected to a pressure of at least about 6 GPa, at least about 6.5
GPa, at least about 7 GPa or even at least about 7.5 GPa.
The hardness of cemented tungsten carbide substrate may be enhanced by
subjecting the substrate to an ultra-high pressure and high temperature,
particularly at a pressure and temperature at which diamond is
thermodynamically stable. The magnitude of the enhancement of the
hardness may depend on the pressure and temperature conditions. In
particular, the harness enhancement may increase the higher the pressure.
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In one embodiment, the substrate may comprise cemented carbide material,
which may comprise cemented carbide WC particles having a mean size in
the range from about 1.5 micron to about 3 micron and Co binder material, the
content of the WC particles being in the range from about 90 weight percent
to about 92 weight percent, and the content of the Co being in the range from
about 8 weight percent to about 10 weight percent of the cemented carbide
material. The cemented carbide material may further comprise particles of
Cr3C2 dispersed in the binder. The content of the Cr3C2 may be in the range
from about 0.1 weight percent and 0.5 weight percent of the cemented
carbide material.
In embodiments where the cemented carbide substrate does not contain
sufficient solvent / catalyst for diamond, and where the POD structure is
integrally formed onto the substrate during sintering at an ultra-high
pressure,
solvent / catalyst material may be included or introduced into the aggregated
mass of diamond grains from a source of the material other than the
cemented carbide substrate. The solvent / catalyst material may comprise
cobalt that infiltrates from the substrate in to the aggregated mass of
diamond
grains just prior to and during the sintering step at an ultra-high pressure.
However, in 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.
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,
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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.
In one embodiment of a method of the invention, 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(NO3)2 + Na2CO3 -> COC03 + 2NaNO3
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 W0/2006/032982. The cobalt carbonate may
then be converted into cobalt and water, for example, by means of pyrolysis
reactions such as the following:
COC03 -> COO + C02
COO + H2 -> Co + H2O
In another embodiment of the method of the invention, 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.
In one embodiment, the cemented carbide substrate may comprise WC
particles having mean size of about 1.4 microns, and a Co-based metallic
binder content of 13 weight percent, and the metallic binder comprises Co, Ni
and Cr3C2, as a non-limiting example in the weight ratio of about 9.79 : 2.95
0.30.
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In one embodiment, the cemented carbide substrate may comprise WC
particles having mean size of about 2.5 microns, and a Co metallic binder
content of 9 weight percent.
In one embodiment, the cemented carbide substrate may comprise WC
particles having mean size of about 2.5 microns, and a Co metallic binder
content of 9 weight percent, and 0.3 weight percent Cr3C2.
In one embodiment, the cemented carbide substrate may comprise WC
particles having mean size of about 0.8 microns, and a Co metallic binder
content of 13 weight percent, and 0.4 weight percent VC and 0.5 weight
percent Cr3C2.
In one embodiment, the cemented carbide substrate may comprise WC
particles having mean size of about 0.8 microns, and a Co metallic binder
content of 10 weight percent, and 0.2 weight percent VC and 0.3 weight
percent Cr3C2.
In one embodiment, the cemented carbide substrate may comprise
microwave sintered WC-Co carbide.
With reference to FIG 6, an embodiment of an earth-boring rotary drill bit,
800,
of the present invention includes, for example, a plurality of cutting
elements
600 as previously described herein with reference to FIG 2, FIG 3, FIG 4A,
FIG 4B, FIG 5A or FIG 5B. The earth-boring rotary drill bit 800 includes a bit
body 802 that is secured to a shank 804 having a threaded connection portion
806 (e.g., a threaded connection portion 806 conforming to industry standards
such as those promulgated by the American Petroleum Institute (API)) for
attaching the drill bit 800 to a drill string (not shown). The bit body 802
may
comprise a particle-matrix composite material or a metal alloy such as steel.
The bit body 802 may be secured to the shank 804 by one or more of a
threaded connection, a weld, and a braze alloy at the interface between them.
In some embodiments, the bit body 802 may be secured to the shank 804
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indirectly by way of a metal blank or extension between them, as known in the
art.
The bit body 802 may include internal fluid passageways (not shown) that
extend between the face 803 of the bit body 802 and a longitudinal bore (not
shown), which extends through the shank 804 the extension 808 and partially
through the bit body 802. Nozzle inserts 824 also may be provided at the face
803 of the bit body 802 within the internal fluid passageways. The bit body
802 may further include a plurality of blades 816 that are separated by junk
slots 818. In some embodiments, the bit body 802 may include gage wear
plugs 822 and wear knots 828. A plurality of PDC cutting elements of one or
more of embodiments 100, 200, 300 and 400, as previously described herein,
which are generally indicated by reference numeral 600 in FIG 6, may be
mounted on the face 803 of the bit body 802 in cutting element pockets 812
that are located along each of the blades 816. In other embodiments, PDC
cutting elements 700 as previously described with reference to FIG 2, FIG 3,
FIG 4A, FIG 4B, FIG 5A or FIG 5B, or any other embodiment of a PDC cutting
element of the present invention may be provided in the cutting element
pockets 812.
The cutting elements 600 are positioned to cut a subterranean formation
being drilled while the drill bit 800 is rotated under weight on bit (WOB) in
a
bore hole about centreline L800.
Embodiments of PDC cutting elements of the present invention also may be
used as gauge trimmers, and may be used on other types of earth-boring
tools. For example, embodiments of cutting elements of the present invention
also may be used on cones of roller cone drill bits, on reamers, mills, bi-
centre
bits, eccentric bits, coring bits, and so-called hybrid bits that include both
fixed
cutters and rolling cutters.
Embodiments of the invention exhibit enhanced erosion resistance and
sufficient fracture resistance and extended working life potential.
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Embodiments comprising a substrate having magnetic properties according to
the invention have enhanced fracture resistance and high wear resistance.
While wishing not to be bound by a particular theory, micro-structural
features
underlying these magnetic properties may include the amounts of tungsten
and carbon dissolved in the metallic binder, and nano-grained particles
dispersed within the binder, the particles comprising W, C and Co (so-called
eta- or theta-phases).
Embodiments of the invention have the advantage that key properties of the
cemented carbide, such as erosion resistance or fracture toughness are not
deleteriously affected by subjecting it to an ultra-high pressure and
temperature at which diamond is thermodynamically stable.
Embodiments of the invention have the advantage that the absence of eta-
phase therein may be beneficial to the strength and fracture toughness of the
substrate.
Embodiments of the invention have the advantage of comprising a binder
material having enhanced strength. While wishing not to be bound by a
particular theory, high levels of dissolved W or other refractory metal such
as
Ti or Ta in the binder may strengthen the binder. Dissolved W or even other
refractory metal such as Ti or Ta in the binder may have the effect of
increasing the lattice constant of the binder. Embodiments of the invention
have the advantage that they comprise cobalt binder material having
enhanced erosion resistance and strength.
While wishing not to be bound by a particular theory, dissolved W or even of
other refractory metal such as Ti or Ta in cobalt metallic binder may
stabilise
the fcc form of cobalt against conversion to the hcp form, which may have the
effect of improving the strength and erosion resistance of the cobalt binder.
While wishing not to be bound by a particular theory, particles of Cr3C2
dispersed in the metallic binder may increase the yield strength and elastic
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limit of the cemented carbide and inhibit the transformation from the fcc form
of Co to the hcp form, which may improve erosion resistance.
Embodiments of the invention have the advantage of comprising a substrate
with enhanced erosion resistance bonded to a well sintered POD structure
with high diamond grain contiguity.
Embodiments of the invention exhibit enhanced erosion resistance of the
substrates in combination with sufficient fracture resistance.
Embodiments of the invention are described in more detail with reference to
the examples below, which are not intended to limit the invention.
Example 1
A WC-Co substrate was provided, comprising WC grains having mean size of
about 2.5 microns and having a binder content of about 9.3 weight percent,
this value being made up of about 9 weight percent Co and about 0.3 weight
percent Cr2C3. The substrate was generally cylindrical in shape and had a
diameter of about 16 mm and a height of about 13 mm. A layer comprising an
aggregated mass of unbonded diamond grains was deposited onto an end
surface of the substrate to form an unbonded assembly. The diamond grains
had a multimodal size distribution and a mean size of about 7 microns. The
unbonded assembly was mounted within a capsule for an ultra-high pressure
furnace and the capsule was subjected to an ultra-high pressure in the range
from about 5.5 GPa to about 6 GPa and a temperature of about 1,400
degrees centigrade for a period of about 5 minutes to form a sintered POD
composite compact. After sintering, the POD composite compact was
processed to form an insert having a diameter of about 15.9 mm and a POD
structure with thickness in the range of about 1.7 to 2.1 mm.
The mean free path characteristic of the substrate after sintering at the
ultra-
high pressure was estimated to be in the range of about 0.3 micron to about
0.6 micron and the elastic limit was estimated to be in the range from about
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2.0 GPa to about 2.4 GPa. The magnetic coercivity He of the substrate was
estimated to be in the range from about 110 Oe to about 150 Oe, or
equivalently from about 8.7 kA/m to about 11.9 kA/m.
Example 2
A wear resistant WC-Co substrate having a Co content of about 6.5 weight
percent and low carbon content may be produced according to the teachings
of publication number US2006-0093859. The substrate may be generally
cylindrical in shape and have a diameter of about 16 mm. The coercive field
strength substrate material may be about 7.0 kA/m, the moment of magnetic
saturation, 6, may be about 0.8 J.m3/kg (Ms, 4n6, may be 10.0 J.m3/kg),
the Vickers hardness HV30 may be about 1,100, and the transverse rupture
strength may be about 2,400 MPa. The mean size of the WC grains may be
about 10 microns. Using an optical microscope, the WC grains may have a
rounded appearance. The substrate material may be substantially free of eta-
phase. A thin film sample may be produced for examination by TEM
(transmission electron microscope). The Co lattice constant may be
determined by TEM and X-ray examinations.
The W concentration in the binder of the sample may be in the range from
about 18 to about 19 atomic percent, as determined by means of EDX. TEM
analysis (transmission electron microscope) of a thin film sample of the
substrate material may reveal the presence of nano-grained particles
dispersed in the binder. Electron diffraction analysis may reveal that the
binder comprises tungsten-containing cubic cobalt matrix having face centre
cubic (fcc) structure, the lattice constant of which may be about 0.366 nm.
The electron diffraction analysis may also reveal that the nano-grained
particles have mean size in the range of approximately 3 nm to approximately
nm.
A thermally stable POD disc having diameter of about 16 mm and thickness of
about 2.2 mm may be prepared. Raw material diamond powder may be
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prepared by blending diamond grains from four sources having combined
mean grain size of about 7 microns. The blended mix may be formed into an
aggregated mass and sintered onto a cobalt-cemented cemented tungsten
carbide (WC-Co) substrate at a pressure of about 6.8 GPa and a temperature
of about 1,500 degrees centigrade by means of an ultra-high pressure
furnace, to form a sintered POD composite compact.
The composite compact would comprise a layer of POD integrally bonded
onto the substrate. POD material made as described above would have a
diamond content of about 92 percent by volume ( 1 percent), the balance
being cobalt and minor precipitated phases, the cobalt having infiltrated from
the substrate into the aggregated diamond mass during the sintering step.
The diamond grains within the POD cutting structure would have a multimodal
size distribution with a mean size of about 11 microns ( 5.5 percent),
expressed in terms of equivalent circle diameter. Grain intergrowth and
contact can be expressed in terms of diamond grain contiguity, and the mean
contiguity of the POD would be 62.0 percent ( 1.9 percent). The interstitial
mean free path of the POD would be about 0.7 ( 0.6) microns.
The cemented carbide substrate may then removed from the composite
compact by grinding, leaving an un-backed, free-standing POD disc. The
POD disc may be ground to a thickness of about 2.2 microns and then treated
(leached) in acid to remove substantially all of the cobalt solvent / catalyst
material throughout the entire POD cutting structure.
A foil of active braze material having thickness of about 80 microns and
diameter of about 16 mm may be sandwiched each POD segment and an end
surface of the wear resistant substrate. The braze material comprised by
weight 63.00% Ag, 32.25% Cu and 1.75% Ti, and is available under the trade
name of Cusil ABTM. Prior to brazing, the POD segments may be
ultrasonically cleaned and both the tungsten carbide substrate and the braze
foil were slightly ground and then ultrasonically cleaned. The pre-compact
element assembly may be subjected to heat treatment in a vacuum. The
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temperature may be increased to 920 degrees centigrade over 15 minutes,
held at this level for 5 minutes and then reduced to ambient temperature over
about 8 to 9 hours. A vacuum of at least 10-5 millibar may be maintained
during the heat treatment. Care should be taken to avoid or minimise the
amount of oxygen and other impurities in the furnace environment.
Example 3
A wear resistant WC-Co substrate having a Co content of about 6.5 weight
percent and comprising WC grains having mean size of about 8 microns may
be provided. The substrate may be generally cylindrical in shape and have a
diameter of about 16 mm. The coercive field strength may be about 6.4 kA/m,
the moment of magnetic saturation, 6, may be about 0.95 J.m3/kg (Ms, 4n6,
may be about 11.9 J.m3/kg), the Vickers HV30 hardness may be about
1,140, and the transverse rupture strength may be about 1,950 MPa.
A plurality of diamond grains having multimodal size distribution and mean
size of about 7 microns may be blended with 5 weight percent cobalt powder.
The blended mix may be formed into an unbonded aggregated mass in layer
form against the upper surface of the substrate to form an unbonded
assembly, which may then mounted within a capsule for an ultra-high
pressure furnace. The capsule may be subjected to a pressure of about 5.5
GPa and a temperature of about 1,400 C for a period of about 5 minutes.
After sintering, the first and second substrate elements may be sintered
together and the PCD composite compact may be processed to form an insert
having a diameter of about 15.9 mm and a PCD structure with thickness in the
range of about 1.7 to 2.1 mm.
