U.S. patent application number 11/594566 was filed with the patent office on 2007-07-05 for microwave sintering.
This patent application is currently assigned to Smith International, Inc.. Invention is credited to Anthony Griffo, Madapusi K. Keshavan, David Slutz.
Application Number | 20070151769 11/594566 |
Document ID | / |
Family ID | 38066752 |
Filed Date | 2007-07-05 |
United States Patent
Application |
20070151769 |
Kind Code |
A1 |
Slutz; David ; et
al. |
July 5, 2007 |
Microwave sintering
Abstract
A carbide composite that includes carbide particles having an
average particle size of less than about 100 nanometers and a
metallic binder disposed around the carbide particles is disclosed.
The carbide composite may also include carbide particles having an
average particle size ranging from 3 to 10 microns.
Inventors: |
Slutz; David; (Bethlehem,
PA) ; Keshavan; Madapusi K.; (The Woodlands, TX)
; Griffo; Anthony; (The Woodlands, TX) |
Correspondence
Address: |
OSHA, LIANG LLP / SMITH
1221 MCKINNEY STREET
SUITE 2800
HOUSTON
TX
77010
US
|
Assignee: |
Smith International, Inc.
Houston
TX
|
Family ID: |
38066752 |
Appl. No.: |
11/594566 |
Filed: |
November 8, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60739703 |
Nov 23, 2005 |
|
|
|
Current U.S.
Class: |
175/426 ;
175/430 |
Current CPC
Class: |
E21B 10/55 20130101;
E21B 10/52 20130101; B22F 3/04 20130101; B22F 2005/001 20130101;
B22F 2998/00 20130101; B22F 2003/1054 20130101; B22F 2998/00
20130101; C22C 29/08 20130101; B22F 3/08 20130101; B22F 3/087
20130101; B22F 3/105 20130101 |
Class at
Publication: |
175/426 ;
175/430 |
International
Class: |
E21B 10/36 20060101
E21B010/36 |
Claims
1. A cutting element comprising: a substrate formed from a carbide
composite, the carbide composite comprising: tungsten carbide
particles; and a metallic binder, wherein the tungsten carbide
particles have a particle size ranging from 10 to 100 nm, and
wherein the carbide composite has a hardness greater than 85
Rockwell A.
2. The cutting element of claim 1, wherein the tungsten carbide
particles having a particle size ranging from 10 to 100 nm comprise
from about 10 to 100 percent of the tungsten carbide particles.
3. A method for making a wear resistant element, comprising:
providing a mixture of green carbide particles and a metallic
binding material; and sintering the mixture with microwave energy
to form a composite having a first carbide region and a second
carbide region, wherein the first carbide region has an average
particle size of less than about 100 nm and the second carbide
region has an average particle size ranging from about 3 to about
10 .mu.m.
4. A carbide composite, comprising: a first carbide having an
average particle size of less than about 100 nm; a second carbide
having an average particle size ranging from about 3 to about 10
.mu.m; and a metallic binder disposed around the carbide
particles.
5. The carbide composite of claim 3, wherein the composite is
formed by a process selected from microwave sintering, plasma
assisted sintering, pressure assisted sintering, explosive
compaction, and rapid omnidirectional compaction.
6. The carbide composite of claim 3, wherein the metallic binder is
selected from cobalt, nickel, iron, and alloys thereof.
7. The carbide composite of claim 3, wherein the carbide composite
comprises from about 10 to about 40 weight percent metallic
binder.
8. The carbide composite of claim 3, wherein the carbide composite
has a hardness greater than about 85 Rockwell A.
9. The carbide composite of claim 3, wherein the first carbide is
in an amount ranging from 10 to 50 percent of the metallic
binder.
10. The method of claim 3, wherein carbide particles of the second
carbide region are surrounded by carbide particles of the first
carbide region.
11. The method of claim 3, wherein the carbide particles of the
first carbide region are uniformly distributed in the metallic
binder phase.
12. A carbide composite, comprising: a first carbide region; a
second carbide region; and a metallic binder phase disposed around
carbide particles of the first and second carbide regions, wherein
the first carbide region has an average particle size less than an
average particle size of the second carbide region, and wherein the
composite is formed by a rapid consolidation process.
13. The carbide composite of claim 12, wherein the composite is
formed by a microwave sintering process.
14. The carbide composite of claim 12, wherein the metallic binder
is selected from cobalt, nickel, iron, and alloys thereof.
15. The carbide composite of claim 12, wherein the carbide
composite comprises from about 10 to about 40 weight percent
metallic binder.
16. The carbide composite of claim 12, wherein each carbide
particle of the second carbide region is surrounded by carbide
particles of the first carbide region.
17. The carbide composite of claim 12, wherein the carbide
particles of the first carbide region are uniformly distributed in
the metallic binder phase.
18. The carbide composite of claim 12, wherein the first carbide
region comprises carbide particles having an average carbide
particle size less than 100 nm and the second carbide region
comprises carbide particles having an average carbide particle size
from 3 to 10 .mu.m.
19. The carbide composite of claim 12, wherein the first carbide
region is in an amount ranging from 10 to 50 percent of the
metallic binder.
20. The carbide composite of claim 12, further comprising a third
carbide region having a third average particle size.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority, pursuant to .sctn. 119(e),
of U.S. Patent Provisional Ser. No. 60/739,703 filed on Nov. 23,
2005, which is herein incorporated by reference in its
entirety.
BACKGROUND OF INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates generally to applications for
microwave sintering. More specifically, the invention relates to
microwave sintered cutting elements for use in drilling
applications.
[0004] 2. Background Art
[0005] Drill bits used to drill wellbores through earth formations
generally are made within several broad categories of bit
structures, including roller cone bits, and drag or fixed cutter
bits.
[0006] Roller cone rock bits include a bit body adapted to be
coupled to a rotatable drill string and include at least one "cone"
that is rotatably mounted to the bit body. A plurality of cutting
elements are positioned on each cone. Within the category of roller
cone bits, there are two further categories, based on the type of
cutting elements. The cutting elements may be formed from the same
base material as is the cone (typically steel) and are known as
"teeth". These bits are typically referred to as "milled tooth"
bits. Other roller cone bits include "insert" cutting elements that
are press (interference) fit into holes formed and/or machined into
the roller cones. The inserts may be formed from, for example,
tungsten carbide, natural or synthetic diamond, boron nitride, or
any one or combination of hard or superhard materials.
[0007] Drag bits (or fixed cutter) are a type of rotary drill bits
having no moving parts on them. One type of drag bit is known in
the art as a PDC bit. PDC bits include a bit body with a plurality
of blades extending radially therefrom. A plurality of cutting
elements are secured on the blades. The cutting elements may be
formed from any one or combination of hard or superhard materials,
for example, natural or synthetic diamond, boron nitride, and
tungsten carbide.
[0008] Most cutting elements include a substrate of tungsten
carbide, a hard material, interspersed with a binder component,
preferably cobalt, which binds the tungsten carbide particles
together. When used in drilling earth formations, the primary
contact between the tungsten carbide cutting element and the earth
formation being drilled is the outer end of the cutting element.
Tungsten carbide cutting elements tend to fail by excessive wear
because of their softness. Thus, it is beneficial to offer this
region of the cutting element greater wear protection.
[0009] An outer wear layer or crown that includes diamond
particles, such as a polycrystalline diamond, can provide such
improved wear resistance, as compared to the softer tungsten
carbide component. Such a polycrystalline diamond layer typically
includes diamond particles held together by a metal matrix, which
also often consists of cobalt. The attachment of the
polycrystalline diamond layer to the tungsten carbide substrate may
be accomplished by brazing.
[0010] Many different types of tungsten carbides are known based on
their different chemical compositions and physical structure. Of
the various types of tungsten carbide commonly used in drill bits,
cemented tungsten carbide (also known as sintered tungsten carbide)
is typically used in cutting elements for drill bits.
[0011] Cemented tungsten carbide refers to a material formed by
mixing particles of tungsten carbide, typically monotungsten
carbide, and particles of cobalt or other iron group metal, and
sintering the mixture. In a typical process for making cemented
tungsten carbide, small tungsten carbide particles, e.g., 1-15
microns, and cobalt particles are vigorously mixed with a small
amount of organic wax which serves as a temporary binder. An
organic solvent may be used to promote uniform mixing. The mixture
may be prepared for sintering by either of two techniques: it may
be pressed into solid bodies often referred to as green compacts;
alternatively, it may be formed into granules or particles such as
by pressing through a screen, or tumbling and then screened to
obtain more or less uniform particle size.
[0012] Such green compacts or particles are then heated in a vacuum
furnace to first evaporate the wax and then to a temperature near
the melting point of cobalt (or the like) to cause the tungsten
carbide particles to be bonded together by the metallic phase.
After sintering, the compacts are crushed and screened for the
desired particle size. Similarly, the sintered particles, which
tend to bond together during sintering, are gently churned in a
ball mill with media to separate them without damaging the
particles. Some particles may be crushed to break them apart. These
are also screened to obtain a desired particle size. The crushed
cemented carbide is generally more angular than the particles which
tend to be rounded.
[0013] Cemented tungsten carbide is classified by grades based on
the grain size of WC and the cobalt content and are primarily made
in consideration of two factors that influence the lifetime of the
tungsten carbide cutting structure; wear resistance and toughness.
As a result, cutting elements known in the art are generally formed
of cemented tungsten carbide with average grain sizes about less
than 3 .mu.m as measured by ASTM E-112 method, cobalt contents in
the range of about 6-16% by weight, and hardness in the range of
about 86 to 91 Ra.
[0014] For a WC/Co system, it is typically observed that the wear
resistance increases as the grain size of tungsten carbide or the
cobalt content decreases. On the other hand, the fracture toughness
increases with larger grains of tungsten carbide and greater
percentages of cobalt. Thus, fracture toughness and wear resistance
(i.e., hardness) tend to be inversely related: as the grain size or
the cobalt content is decreased to improve wear resistance of a
specimen, its fracture toughness will decrease, and vice versa.
[0015] Due to this inverse relationship between fracture toughness
and wear resistance, the grain size of tungsten carbide and cobalt
content are selected to obtain desired wear resistance and
toughness. For example, a higher cobalt content and larger WC
grains are used when a higher toughness is required, whereas a
lower cobalt content and smaller WC grain are used when a better
wear resistance is desired. The relationship between toughness and
wear for carbide composites having varying particle size and cobalt
content is shown in FIG. 1.
[0016] During manufacture of the cutting elements, the materials
are typically subjected to sintering under high pressures and high
temperatures. These manufacturing conditions can lead to potential
problems involving dissimilar elements being bonded to each other
and the diffusion of various components, resulting in residual
stresses induced on the composites. The residual stress induced
composites can often result in insert breakage, fracture or
delamination under drilling conditions.
[0017] Additionally, the combination of the high temperature and
high pressure for the length of time necessary to form the cutting
elements inherently result in grain growth and thus larger carbide
grain sizes. For example, a powder starting with 50 nm WC grains
prior to HTHP sintering may result in a composite having WC grains
larger than 1 .mu.m after sintering. Prior art methods require the
addition of grain growth inhibitors, such as vanadium, chromium, or
compounds including these elements, when a smaller grain size is
desired. However, the use of grain growth inhibitors typically
produces undesirable side effects by altering the physical
characteristics of the sintered carbide product, especially when
the carbide product is to be brazed to a diamond layer or
crown.
[0018] Generally, because a decrease in WC particle size results in
an increase in hardness, wear resistance and transverse rupture
strength of the composites, composites having nanoparticles may be
desirable. However, because of the tendency for grain growth during
the formation of a composite, this results in a limitation on the
ability to obtain nanoparticles. Accordingly, there exists a need
for composites and methods of forming such composites that exhibit
increased wear properties.
SUMMARY OF INVENTION
[0019] In one aspect, the present invention relates to a cutting
element that includes a substrate formed from a carbide composite,
where the carbide composite includes tungsten carbide particles,
and a metallic binder, and where the tungsten carbide particles
have a particle size ranging from 10 to 100 nm, and the carbide
composite has a hardness greater than 85 Rockwell A
[0020] In another aspect, the present invention relates to a method
for making a wear resistant element that includes the steps of
providing a mixture of green carbide particles and a metallic
binding material, and sintering the mixture with microwave energy
to form a composite having a first carbide region and a second
carbide region, wherein the first carbide region has an average
particle size of less than about 100 nm and the second carbide
region has an average particle size ranging from about 3 to about
10 .mu.m.
[0021] In yet another aspect, the present invention relates to a
carbide composite that includes a first carbide having an average
particle size of less than about 100 nm, a second carbide having an
average particle size ranging from about 3 to about 10 .mu.m, and a
metallic binder disposed around the carbide particles.
[0022] In yet another aspect, the present invention relates to a
carbide composite that includes a first carbide region, a second
carbide region, and a metallic binder phase disposed around carbide
particles of the first and second carbide regions, wherein the
first carbide region has an average particle size less than an
average particle size of the second carbide region, and wherein the
composite is formed by a rapid consolidation process
[0023] Other aspects and advantages of the invention will be
apparent from the following description and the appended
claims.
BRIEF DESCRIPTION OF DRAWINGS
[0024] FIG. 1 shows a graphical comparison of fracture toughness
vs. wear number for conventional carbides.
[0025] FIG. 2 shows a graphical comparison of fracture toughness
vs. wear number for convention carbides and carbides in accordance
with embodiments of the present invention.
[0026] FIG. 3 is a carbide composite made in accordance with one
embodiment of the present invention.
[0027] FIG. 4 is a SEM mircograph of a carbide composite made in
accordance with one embodiment of the present invention.
[0028] FIGS. 5, 5A, and 5B show a roller cone drill bit and
corresponding cutting element made in accordance with one
embodiment of the present invention.
[0029] FIGS. 6 and 6A show a fixed cutter drill bit and
corresponding cutting element made in accordance with one
embodiment of the present invention.
[0030] FIG. 7 shows a cutting element made in accordance with one
embodiment of the present invention.
DETAILED DESCRIPTION
[0031] In one aspect, embodiments of the invention relate to wear
resistant elements and carbide composites having nano-scale carbide
particles. In another aspect, embodiments of the invention relate
to microwave sintered composites. Microwave sintering may provide
for a process of forming a hard composite. As compared to a
conventional high temperature, high pressure (HTHP) sintering
process, such as that disclosed in U.S. Pat. Nos. 4,694,918;
5,370,195; and 4,525,178, sintering using microwave energy may
reduce the pressures used, decrease the applied temperature, and
reduce the sintering time. The microwave sintering process may be
applied to a number of composite materials and may thus form
composites having greater wear resistant properties. Tungsten
carbide, polycrystalline diamond, thermally stable polycrystalline
diamond, silicon carbide, etc, are among the materials suitable for
microwave sintering.
[0032] In one embodiment, a microwave sintered composite made in
accordance with the present invention is a carbide composite having
a carbide particle size on the "nano-scale." As described above, as
the grain size of metal carbides decreases, the wear resistance of
the carbide composite may increase. However, typical processes
involved in the formation of carbide composite present a limitation
on the ability to achieve nano grain carbide particle sizes. As
shown in FIG. 2, carbide composites having nano grain carbide
particles may allow for improved wear properties, as compared to
conventional carbides.
[0033] Carbide composites having nano grain carbide particles may
include carbide particles having a particle size less than 100
nanometers. These small carbide particles may be referred to as
"nano grain" particles or "nanoparticles". In one embodiment, a
carbide composites may be comprised of from about 10 to 100 percent
carbide particles having a particle size less than 100 nanometers.
In another embodiment, the carbide composite may further include at
least one of a coarse grain carbide and a fine grain carbide. As
used herein, a coarse grain carbide is a carbide having an average
carbide particle size between 3 and 10 microns, and a fine grain
carbide is a carbide having an average carbide particle size
between 0.5 and 4 microns. The combination of nano grain and coarse
and/or fine grain carbide may allow for a uniform, gradual, or step
distribution of the carbide particles in the formed composite. A
composite that includes nano grain particles and coarse grain
particles may be formed by microwave sintering, or other rapid
consolidation processes that include plasma assisted sintering,
pressure assisted sintering, explosive compaction, high frequency
induction heating and rapid omnidirectional compaction. Referring
to FIG. 3, a carbide composite according to one embodiment of the
present invention is shown. The carbide composite 30 may include a
mixture of coarse grain carbide particles 32 and nano grain
particles 34, where a core of coarse grain particles 32 are
surrounded by a layer of nano grain particles 34.
[0034] A carbide composite having carbide particles that having a
particle size less than 100 nm may be used to form a substrate of a
cutting element that may be used in drill bit. In one embodiment, a
cutting element that includes carbide particles having a particle
size less than 100 nm may have a hardness greater than 85 Rockwell
A. In other embodiments, the hardness of such composite may be
greater than 87, 89, or 91 Rockwell A. The carbide particles having
a particle size of less than 100 nanometers may comprise from about
10 to 100 percent of the tungsten carbide present in the substrate.
The remaining tungsten carbide may have particle sizes greater than
100 nm, including, but not limited to, carbides with particle sizes
in the range of 0.5 to 4 .mu.m and 3 to 10 .mu.m.
[0035] In one embodiment of the invention, the carbide composite
may include a metal carbide, such as tungsten carbide.
Additionally, the carbide composite may be a sintered tungsten
carbide composite. It is well known that various metal carbide
compositions may be used in addition to tungsten carbide; such
suitable materials include, for example, tantalum carbide or
titanium carbide. Further, references to the use of tungsten
carbide are for illustrative purposes only, and no limitation on
the type of carbide used is intended.
[0036] Within the carbide composite, the metal carbide grains may
be supported within a matrix of a metallic binder. In some
embodiments of the present invention, the metallic binder may be
selected from cobalt, nickel, iron, metal alloys, and mixtures
thereof, preferably cobalt. In other embodiments, the carbide
composite includes from about 10 to about 40 weight percent
metallic binder. In yet other embodiments, the metallic binder may
be selected from cobalt, nickel, iron, titanium, tantalum,
chromium, vanadium, metal alloys, and mixtures thereof.
[0037] In another embodiment, a microwave sintered composite may
include a first region and a second region, where the first region
has an average particle size less than an average particle size of
the second region. In the composite, the carbide particles of the
first region may surround individual carbide particles of the
second region. The carbide particles from the first region may be
uniformly distributed in the matrix of binder materials. Referring
to FIG. 4, a SEM micrograph of a carbide composite made in
accordance with the present invention is shown. Additionally, the
amount of nano grain carbide particles present in some embodiments
of the present invention may range from 10 to 50 weight percent of
the binder material.
[0038] In some embodiments, the first region may include carbide
particles having an average carbide particle size less than 100 nm
and the second region may include carbide particles having an
average particle size between 3 and 10 .mu.m. In other embodiments,
the first region or second regions may include carbide particles
having an average carbide particle size from 0.5 to 4 .mu.m.
[0039] Additionally, the composite may include a third carbide
region having a third average particle size, as well as fourth and
fifth carbide regions having fourth and fifth average particle
sizes. Carbide composites having multimodal particle size
distribution may packed in various packing structures depending on
the distribution as known by one having ordinary skill in the
art.
[0040] In one embodiment, the multiple regions may be formed
simultaneously. In another embodiment, the multiple regions of such
microwave sintered composite may be formed as a step function. Such
step function may allow for a composite having a uniform
consistency to be formed, and then additional regions be
sequentially added to the composite to form a composite having
multiple regions.
[0041] According to some embodiments, the carbide composite formed
by microwave sintering may include multiple regions, each having a
different material composition. A first region may constitute an
outer surface of the carbide composite and the second region may
constitute a body. In one embodiment, a first region may have an
average carbide particle size less than an average carbide particle
size of a second region. In some embodiments, the average carbide
particle size may gradually change from the first region to the
second region. However, in other embodiments, the first region and
the second region are discrete layers within the composite. In
addition to the first and second regions, the carbide composite may
further include a third region disposed between the first region
and second region, where the third region has an average carbide
particle size greater than the first region and less than the
second region. In the microwave sintered carbide having multiple
regions, the first, second, and third carbide regions may each be
selected from average carbide particles sizes of less than 100
nanometers, from 0.5 to 4 .mu.m, and from 3 to 10 .mu.m.
[0042] However, the scope of the present invention is not solely
limited to the formation of carbide composite having nano grain
carbides. Rather it is intended to be within the scope of the
present invention that additional wear resistant materials may be
microwave sintered to form wear resistant elements.
[0043] Wear resistant materials according to embodiments of the
present invention may include polycrystalline diamond, thermally
stable polycrystalline diamond, cubic boron nitride, silicon,
silicon carbide, cermets, other metal carbides, and composites
thereof. These wear resistant materials may be formed by microwave
sintering, and may additionally be used in conjunction with a
carbide composite having nano grain carbides. For example, a
cutting element according to the present invention may include a
carbide composite having a nano grain carbide and a layer of a wear
resistant material selected from microwave sintered polycrystalline
diamond, thermally stable polycrystalline diamond, cubic boron
nitride, silicon, silicon carbide, cermets, other metal carbides,
and composites thereof.
[0044] A polycrystalline diamond layer may be formed from a
composite including diamond crystals and a metal catalyst, such as
cobalt. Alternatively, the polycrystalline diamond layer may be
formed from a composite including diamond crystals, cobalt, and
particles of carbides or carbonitrides of the transition metals
selected from the group consisting of W, Ti, Ta, Cr, Mo, Cb, V, Hf,
Zr, and mixtures thereof. A polycrystalline diamond layer includes
individual diamond "crystals" that are interconnected. The
individual diamond crystals thus form a lattice structure. A metal
catalyst, such as cobalt, may be used to promote recrystallization
of the diamond particles and formation of the lattice structure.
Thus, cobalt particles are typically found in the interstitial
spaces in the diamond lattice structure.
[0045] Thermally stable polycrystalline diamond (TSP) may also be
used as a wear resistant material in a cutting element according to
embodiments of the present invention. The manufacture of TSP is
known in the art, but a brief description of one process is
described herein. As mentioned, when formed, a polycrystalline
diamond layer comprises a diamond lattice structure with cobalt
particles often being found within the interstitial spaces in the
diamond lattice structure. Cobalt has a significantly different
coefficient of thermal expansion, as compared to diamond, so upon
heating of the diamond layer, the cobalt will expand, causing
cracks to form in the lattice structure, resulting in deterioration
of the diamond layer.
[0046] In order to obviate this problem, strong acids may be used
to "leach" the cobalt from the diamond lattice structure. Removing
the cobalt causes the diamond layer to become more heat resistant,
but also causes the diamond layer to become more brittle.
Accordingly, in certain cases, only a select portion (measured in
either depth or width) of a diamond layer is leached, in order to
gain thermal stability without losing impact resistance. As used
herein, the term TSP includes both of the above (i.e., partially
and completely leached) compounds.
[0047] Alternatively, TSP may be formed by forming the diamond
layer in a press using a binder other than cobalt, one such as
silicon, which has a coefficient of thermal expansion more similar
to that of diamond than cobalt has. During the manufacturing
process, a large portion, 80 to 100 volume percent, of the silicon
reacts with the diamond lattice to form silicon carbide which also
has a thermal expansion similar to diamond. Upon heating, any
remaining silicon, silicon carbide, and the diamond lattice will
expand at more similar rates as compared to rates of expansion for
cobalt and diamond, resulting in a more thermally stable layer.
[0048] Cubic boron nitride (CBN) refers to an internal crystal
structure of boron atoms and nitrogen atoms in which the equivalent
lattice points are at the corner of each cell. Boron nitride
particles typically have a diameter of approximately one micron and
appear as a white powder. Boron nitride, when initially formed, has
a generally graphite-like, hexagonal plate structure. When
compressed at high pressures (such as 10.sup.6 psi) cubic boron
nitride particles will be formed with a hardness very similar to
diamonds. Accordingly, cubic boron nitride may be used as a wear
resistant material to overlay at least a portion of a carbide
composite in cutting elements according to the present
invention.
[0049] In some embodiments, the wear resistant material may include
cubic boron nitride having an average grain size of about 1.5
.mu.m, where the cubic boron nitride comprised about 50 volume
percent of the wear resistant material. In other embodiments, the
wear resistant material may include cubic boron nitride having an
average grain size of about 2.5 .mu.m, where the cubic boron
nitride comprised about 60 volume percent of the wear resistant
material. The wear resistant material may also comprise a ceramic
or cermet material.
[0050] In yet other embodiments, the wear resistant material may
include a composite of diamond and silicon, silicon carbide, or
other desirable materials. The wear resistant composite may include
either polycrystalline diamond or thermally stable polycrystalline
diamond.
[0051] In some embodiments, microwave sintered composites may be
used in cutting elements for drill bits. In one embodiment, carbide
composites having carbide particles ranging less than 100
nanometers and a metallic binder surrounding the carbide particles
may be included in a cutting element. In another embodiment,
microwave sintered composites including a sintered carbide may be
included in a cutting element. The cutting elements of the present
invention may be used in various types of drill bits, including
roller cone "insert" bits and fixed cutter "PDC" bits.
[0052] Referring to FIG. 5 and 5A, a roller cone "insert" bit 500
having cutting elements according to the present invention is
shown. The bit 500 has a body 504 with legs 506 extending generally
downward, and a threaded pin end 508 opposite thereto for
attachment to a drill string (not shown). Journal shafts (not
shown) are cantilevered from legs 506. Rolling cutters (or roller
cones) 512 are rotatably mounted on journal shafts (not shown).
Each roller cone 512 has a plurality of cutting elements 520
mounted thereon. As the roller cone 512 rotates, individual cutting
elements 520 are rotated into contact with the formation and then
out of contact with the formation. In one embodiment, cutting
element 520 may include a carbide composite made in accordance with
the present invention. In another embodiment, cutting element 520
may include a wear resistant element made in accordance with the
present invention
[0053] Referring to FIG. 6 and 6A, a fixed cutter bit and cutting
element according to the present invention is shown. The drag bit
600 has a bit body 602 with a plurality of blades 604 extending
from the central longitudinal axis of rotation 606 of the drill bit
600. A plurality of cutting elements 610 are secured on the blades.
Cutting elements 610 may include a substrate 612 and a wear
resistant cutting portion 614 disposed on the substrate 612. In one
embodiment, substrate 612 may include a carbide composite made in
accordance with the present invention. In another embodiment, the
wear resistant cutting portion 614 may include a sintered
composite, such as microwave sintered polycrystalline diamond made
in accordance with the present invention.
[0054] In some embodiments, the cutting element may include a
carbide composite that has carbide particles having a particle size
of less than about 100 nanometers, a metal binder, and a wear
resistant material overlaying at least a portion of the carbide
composite. As shown in FIG. 5B, a protective coating 522 may be
applied to a surface 524 of a cutting element 520 to, for example,
reduce wear. The protective coating 522 may comprise, for example,
a polycrystalline diamond layer to overlay over a base cutting
element material 526 that comprises a carbide composite that
includes carbide particles having a particle size of less than 100
nanometers.
[0055] Referring to FIG. 7, a cutting element having multiple
carbide regions according to other embodiments of the present
invention is shown. Cutting element 700 may include a first region
702 as the wear surface of the cutting element 700 and a second
region 704 that is the body of the cutting element 700.
Additionally, a third region 706 may be disposed between the first
region 702 and the second region 704. Each region of the cutting
element may include a differing carbide composition such that a
fuctionally graded cutting element is produced.
[0056] Sintering Process
[0057] The sintering process may involve a microwave energy
process. Examples of microwave sintering processes can be found,
for example, in U.S. Pat. Nos. 5,848,348; 6,126,895; and 6,011,248,
which are herein incorporated by reference in their entirety. The
carbide composite and the wear resistant materials may be formed by
the application of heat, such as by sintering of "green" particles
to create intercrystalline bonding between the particles. Briefly,
to form a sintered composite, an unsintered mass of particles is
placed within an enclosure of the reaction cell. If forming a
carbide composite or polycrystalline diamond, for example, a metal
catalyst, such as cobalt, may be included with the unsintered mass
of carbide particles. The reaction cell is then placed under
processing conditions sufficient to cause the bonding between the
carbide particles and binding material. Suitable processing
conditions may include a temperature ranging from 1200 to
1350.degree. C. for 8-20 minutes, with a total cycle time of less
than 2 hours. Application of the sintering processing will cause
metal carbide particles to sinter and form a carbide composite. The
sintering process may also cause diamond crystals, or other
superhard materials, to sinter and form a polycrystalline diamond
layer. Similarly, application of sintering process may cause the
diamond crystals and carbide particles to sinter such that they are
no longer in the form of discrete particles that can be separated
from each other. Further, all of the layers may sinter to each
other.
[0058] In other embodiments, other rapid consolidation processes
that may be used to form composites of the present invention
include plasma assisted sintering, pressure assisted sintering,
explosive compaction, high frequency induction heating and rapid
omnidirectional compaction.
[0059] The composites according to various embodiments of the
present invention may be used in a variety of applications
including, cutting elements for drill bits for drilling earth
formations, tooling blanks, woodworking tools, wear surfaces for a
variety of cutting tools, etc. It should be understood that the
abovementioned applications only serve as an example of the variety
of applications that can use the carbide composites of the present
invention.
[0060] As compared to a conventional sintering process, microwave
sintering and other rapid sintering processes can use lower
sintering temperatures, sintering time, and total cycle time to
achieve a composite having a greater density, hardness, and bending
strength, and lower average grain size.
[0061] While the invention has been described with respect to a
limited number of embodiments, those skilled in the art, having
benefit of this disclosure, will appreciate that other embodiments
can be devised which do not depart from the scope of the invention
as disclosed herein. Accordingly, the scope of the invention should
be limited only by the attached claims.
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