U.S. patent application number 10/908040 was filed with the patent office on 2006-10-26 for composite structure having a non-planar interface and method of making same.
Invention is credited to Eric F. Drake, Harold Sreshta.
Application Number | 20060237236 10/908040 |
Document ID | / |
Family ID | 36950501 |
Filed Date | 2006-10-26 |
United States Patent
Application |
20060237236 |
Kind Code |
A1 |
Sreshta; Harold ; et
al. |
October 26, 2006 |
COMPOSITE STRUCTURE HAVING A NON-PLANAR INTERFACE AND METHOD OF
MAKING SAME
Abstract
A composite structure includes a first portion comprising a
first metallic material, a monolayer of particles extending into
and bonded with the first portion, and a second portion comprising
a second material, the second portion bonded with the monolayer of
particles and extending into interstices between the particles. A
method for fabricating a composite structure includes bonding a
monolayer of particles to a first portion comprising a first
metallic material, such that the monolayer of particles extends
into the first portion and bonding a second portion comprising a
second material to the monolayer of particles, such that the second
portion extends into interstices between the particles.
Inventors: |
Sreshta; Harold; (Houston,
TX) ; Drake; Eric F.; (Galveston, TX) |
Correspondence
Address: |
JEFFREY E. DALY;GRANT PRIDECO, L.P.
400 N. SAM HOUSTON PARKWAY EAST
SUITE 900
HOUSTON
TX
77060
US
|
Family ID: |
36950501 |
Appl. No.: |
10/908040 |
Filed: |
April 26, 2005 |
Current U.S.
Class: |
175/426 ;
175/432 |
Current CPC
Class: |
B22F 2998/10 20130101;
C22C 1/1036 20130101; E21B 10/5735 20130101; B22F 3/02 20130101;
B22F 3/26 20130101; B22F 2998/10 20130101; B22F 7/04 20130101; B22F
7/04 20130101; B22F 7/02 20130101 |
Class at
Publication: |
175/426 ;
175/432 |
International
Class: |
E21B 10/36 20060101
E21B010/36 |
Claims
1. A composite structure, comprising: a first portion comprising a
first metallic material; a monolayer of particles extending into
and bonded with the first portion; and a second portion comprising
a second material, the second portion bonded with the monolayer of
particles and extending into interstices between the particles.
2. A composite structure, according to claim 1, wherein at least
some of the particles and the first portion define recesses
exhibiting negative draft angles into which the second portion
extends.
3. A composite structure, according to claim 1, wherein the
monolayer of particles is co-sintered with the first portion.
4. A composite structure, according to claim 1, wherein the
monolayer of particles is bonded to the first portion by
metallurgical neck bonds.
5. A composite structure, according to claim 1, wherein the
monolayer of particles comprises one of the first metallic
material, a chemical variant of the first metallic material, a
metallurgical variant of the first metallic material, a metal, and
a metal alloy.
6. A composite structure, according to claim 1, wherein the first
metallic material comprises a first cemented carbide and the second
material comprises one of a second cemented carbide, a diamond
composite material, a metal, and a metal alloy.
7. A composite structure, according to claim 1, wherein the
monolayer of particles comprises at least one of spherical
particles, oblate spherical particles, cylindrical particles,
rod-shaped particles, and irregular shaped particles.
8. A composite structure, according to claim 1, wherein the first
portion is harder than the second portion.
9. A composite structure, according to claim 1, wherein the first
portion is softer than the second portion.
10. A composite structure, according to claim 1, further comprising
a second monolayer of particles extending into and bonded with the
first portion and a third portion comprising a third material, the
third portion bonded with the second monolayer of particles and
extending into interstices between the particles of the second
monolayer of particles.
11. A composite structure, according to claim 1, wherein the second
portion comprises a densified powder.
12. A composite structure, according to claim 1, wherein the second
portion comprises a solidified metal or metal alloy.
13. An insert for a rock bit, comprising: a substrate comprising a
first metallic material; a plurality of particles bonded with the
substrate; and a densified portion comprising a second material,
the densified portion bonded with the plurality of particles and
extending into interstices between the particles.
14. An insert, according to claim 13, wherein at least some of the
plurality of particles and the substrate define recesses exhibiting
negative draft angles into which the densified portion extends.
15. An insert, according to claim 13, wherein the plurality of
particles is co-sintered with the substrate.
16. An insert, according to claim 13, wherein the plurality of
particles comprises one of the first metallic material, a chemical
variant of the first metallic material, a metallurgical variant of
the first metallic material, a metal, and a metal alloy.
17. An insert, according to claim 13, wherein the first metallic
material comprises a first cemented carbide and the second material
comprises one of a second cemented carbide, a diamond composite
material, a metal, and a metal alloy.
18. An insert, according to claim 13, wherein the plurality of
particles comprises at least one of spherical particles, oblate
spherical particles, cylindrical particles, rod-shaped particles,
and irregular shaped particles.
19. A composite pick, comprising: a tip comprising a first metallic
material; a plurality of particles bonded with the tip; and a
densified portion comprising a second material, the densified
powder bonded with the plurality of particles and extending into
interstices between the particles.
20. A composite pick, according to claim 19, wherein the tip
defines an undulant surface and the plurality of particles is
bonded with the undulant surface.
21. A composite pick, according to claim 19, wherein at least some
of the plurality of particles and the tip define recesses
exhibiting negative draft angles into which the second portion
extends.
22. A composite pick, according to claim 19, wherein the plurality
of particles is co-sintered with the substrate.
23. A composite pick, according to claim 19, wherein the plurality
of particles comprises one of the first metallic material, a
chemical variant of the first metallic material, a metallurgical
variant of the first metallic material, a metal, and a metal
alloy.
24. A composite pick, according to claim 19, wherein the first
metallic material comprises a first cemented carbide and the second
material comprises one of a second cemented carbide, a cemented
carbide and steel mixture, a metal, and a metal alloy.
25. A composite pick, according to claim 20, wherein the plurality
of particles comprises at least one of spherical particles, oblate
spherical particles, cylindrical particles, rod-shaped particles,
and irregular shaped particles.
26. A method for fabricating a composite structure, comprising:
bonding a monolayer of particles to a first portion comprising a
first metallic material, such that the monolayer of particles
extends into the first portion; and bonding a second portion
comprising a second material to the monolayer of particles, such
that the second portion extends into interstices between the
particles.
27. A method, according to claim 26, wherein bonding the monolayer
of particles further comprises co-sintering the monolayer of
particles with the first portion.
28. A method, according to claim 26, wherein bonding the second
portion further comprises: filling the interstices with a powder;
and pressure densifying the powder.
29. A method, according to claim 26, wherein bonding the second
portion further comprises: infiltrating the interstices with a
liquid metal; and allowing the liquid metal to solidify.
30. A method, according to claim 26, further comprising extending
the second portion into recesses defined by the particles and the
first portion.
31. A method, according to claim 30, wherein the recesses exhibit
negative draft angles.
32. A method, according to claim 26, further comprising: bonding a
second monolayer of particles to a first portion, such that the
second monolayer of particles extends into the first portion; and
bonding a third portion comprising a third material to the second
monolayer of particles, such that the third portion extends into
interstices between the particles of the second monolayer of
particles.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to a composite structure including a
non-planar interface and a method of making the composite
structure.
[0003] 2. Description of the Related Art
[0004] Metallic structures often comprise two or more joined
materials that have different properties and characteristics. Often
such disparate materials are joined together into one component
because portions of the component are subjected to different
environments. For example, the body of a drilling bit, such as
those used in oilfield operations, is subjected to high torsion
loads during drilling, while the cutting surfaces thereof encounter
very hard, abrasive materials. Accordingly, rock drilling bit
bodies are generally made of steel, while the cutting surfaces
often comprise tungsten carbide or polycrystalline diamond
composites. Steel provides the material properties required to
endure high torsion loads, while tungsten carbide or
polycrystalline diamond provides deformation- and wear-resistant
material properties. Similar configurations are also found in
mining bits and roadbed milling bits used to break apart old
roadbeds.
[0005] When such disparate materials are joined together, the
mechanical response of the resulting union is affected by the
differences in elastic, plastic, and/or thermal expansion
properties that cause internal residual stresses to develop within
the union, and that cause concentration of applied stress at the
interface, enabling premature failure of the union in service. FIG.
1 illustrates two disparate material portions 102, 104 joined along
an interface 106, which may be planar or non-planar. Such
components are often formed using powder metallurgy techniques. For
example, the material portion 102 may initially comprise a mixture
of steel and tungsten carbide powders and the material portion 104
may comprise a steel powder. The portions 102, 104 may then be cold
isostatically pressed to achieve sufficient densification providing
handling strength and then either hot forged or hot isostatically
pressed to achieve full density. Alternatively, the portion 102 may
initially comprise a sintered cemented carbide and the material
portion 104 may initially comprise a mixture of diamond and metals
powders. The portions 102, 104 may then be hot pressed at very high
pressure to achieve full density.
[0006] In both cases, densification involves the heating of the
portions 102, 104 in contact with one another under high pressure
such that adjacent particles within the portions 102, 104 are
plastically deformed and solid state diffusion bonded, or partially
melted and resolidified.
[0007] Such structures exhibit a mechanical discontinuity along an
interface 106 of the disparate materials. The effects of this
discontinuity on mechanical response of the union typically limit
the useful strength of these structures. For example, if the
portion 102 has a coefficient of thermal expansion (CTE) that is
significantly lower than that of the portion 104, merely cooling
the joined materials from the final densification temperature may
generate sufficient stress at the interface 106 to disbond/disjoin
the portions 102, 104. Even if thermal residual stress in the
joined portions 102, 104 were below the failure threshold, the
application of external loading on the joined portions 102, 104
would result in a concentration of stress at the interface due to
elastic modulus and plastic yielding differences between the
portion 102, 104. The superposition of thermal residual stress and
concentrated load stress may disbond/disjoin the portions 102,
104.
[0008] Various techniques are known to the art for improving the
stress distributions along such disparate material interfaces
(e.g., the interface 106) and, thus, improving the useful strength
of these structures. For example, one technique is to roughen the
interface surface 106 between the disparate materials 102, 104
before joining. Adding topographic complexity in a dimension normal
to the interface surface creates a zone of material that behaves as
though its properties are intermediate the two joined disparate
materials. This configuration is often referred to as a "non-planar
interface", whether the interface is broadly planar or curved. In
one example, illustrated in FIG. 2A, an interface surface 202 of
the portion 104 is roughened prior to joining the portion 102
thereto. Alternatively, as shown in FIG. 2B, localized areas of an
interface surface 204 of the portion 104 are melted, for example,
with an electron beam, laser, or other intense, localized heating
source prior to joining the portion 102 thereto.
[0009] In either case, when the portion 102 is joined to the
portion 104, the material comprising the portion 102 fills the
recesses in the roughened surfaces 202, 204 to further retain the
portions 102, 104 together. While the techniques described in
relation to FIGS. 2A-2B may be effective in improving the strength
of the bond or joint between the portions 102, 104, they each
require additional processing to prepare the interface surfaces
202, 204 for joining. The additional processing may, in some
instances, also be costly. For example, the electron beam, laser,
or other localized, intense heat source equipment used to melt
areas of the interface surface 204 may be very expensive to
purchase, maintain, and operate.
[0010] Other techniques that have been used to aid in retaining
disparate material portions together include machining retention
features in one of the portions and urging material of the other
portion into the features. FIGS. 3A-3C illustrates one particular
example of such a technique. A plurality of radial grooves 302
(only one labeled for clarity) and a circumferential groove 303 are
machined into a face 304 of a cutting blank 306 comprising, for
example, steel. A cutting portion 308, comprising a second
material, e.g., tungsten carbide, polycrystalline diamond, etc., is
formed onto the face 304, such that the cutting portion 308 extends
into the grooves 302, 303. The non-planar interface between the
cutting blank 306 and the cutting portion 308 aids in retaining the
cutting portion 308 on the cutting blank 306, as compared to an
interface that omits the grooves 302, 303. Some designs have
further included undercut grooves, such as illustrated in FIG. 3C,
to further enhance retention of the cutting portion 308 on the
cutting blank 306.
[0011] While such techniques often are successful in retaining
disparate materials together, the additional machining steps
required to form the grooves 302, 303 may add substantial cost and
complexity to the finished product. The preferred die-pressing
method for creating irregular or grooved surfaces via powder
fabrication is restricted to geometries that provide positive draft
to allow die withdrawal. Further, it may be difficult to fully fill
the grooves 302, 303, with the second material, especially if they
are narrow or undercut (as illustrated in FIG. 3C).
[0012] As illustrated in FIG. 4, designs have also included
protrusions 402 (only one labeled for clarity) extending from a
first material portion 404 and into a second material portion 406,
forming a non-planar interface 408.
[0013] Yet another technique used to mitigate stress concentrations
along such disparate material interfaces is to employ a "functional
gradient design," as shown in FIG. 5, wherein a third material 502
is disposed in the interface 106 between the two disparate
materials 102, 104. The third material 502 has properties that are
generally between those of the disparate materials 102 and 104. In
other words, the third or gradient material 502 may have, for
example, elastic plastic, thermal expansion properties intermediate
between those of the first disparate material 102 those of the
second disparate material 104. Multiple such intermediate layers or
single graduated layer may be employed to further reduce the
magnitude(s) of disparities of the included interfaces. While such
structures address the property compatibility issues described
above, their complexity often adds prohibitive fabrication cost and
may be incompatible with preferred fabrication methods.
[0014] The present invention is directed to overcoming, or at least
reducing, the effects of one or more of the problems set forth
above.
SUMMARY OF THE INVENTION
[0015] In one aspect of the present invention, a composite
structure is provided. The composite structure includes a first
portion comprising a first metallic material, a monolayer of
particles extending into and bonded with the first portion, and a
second portion comprising a second material, the second portion
bonded with the monolayer of particles and extending into
interstices between the particles.
[0016] In another aspect of the present invention, an insert for a
rock bit is provided. The insert includes a substrate comprising a
first metallic material, a plurality of particles bonded with the
substrate, and a densified portion comprising a second material,
the densified portion bonded with the plurality of particles and
extending into interstices between the particles.
[0017] In yet another aspect of the present invention, a composite
pick is provided. The pick includes a tip comprising a first
metallic material, a plurality of particles bonded with the tip,
and a densified portion comprising a second material, the densified
portion bonded with the plurality of particles and extending into
interstices between the particles.
[0018] In another aspect of the present invention, a method for
fabricating a composite structure is provided. The method includes
bonding a monolayer of particles to a first portion comprising a
first metallic material, such that the monolayer of particles
extends into the first portion and bonding a second portion
comprising a second material to the monolayer of particles, such
that the second portion extends into interstices between the
particles.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The invention may be understood by reference to the
following description taken in conjunction with the accompanying
drawings, in which the leftmost significant digit(s) in the
reference numerals denote(s) the first figure in which the
respective reference numerals appear.
[0020] FIG. 1 is a stylized, cross-sectional side view of a first
conventional composite structure of the prior art.
[0021] FIGS. 2A-2B are stylized, enlarged alternative views of a
portion of the composite structure of prior art FIG. 1.
[0022] FIG. 3A is a top view of a conventional composite cutter of
the prior art.
[0023] FIG. 3B is a cross-sectional view of the conventional
composite cutter of the prior art taken along the line 3B-3B in
FIG. 3A.
[0024] FIG. 3C is a cross-sectional view of the conventional
composite cutter of the prior art taken along the line 3C-3C in
FIG. 3A.
[0025] FIG. 4 is a stylized, cross-sectional side view of a second
conventional composite structure of the prior art.
[0026] FIG. 5 is a stylized, cross-sectional side view of a third
conventional composite structure of the prior art.
[0027] FIG. 6 is a stylized, cross-sectional side view of a first
illustrative embodiment of a composite structure having a
non-planar interface according to the present invention.
[0028] FIG. 7 is a stylized, cross-sectional, enlarged portion of
one illustrative embodiment of the composite structure of FIG. 6
illustrating neck bonds.
[0029] FIG. 8 is a stylized, cross-sectional side view of an
intermediate stage during fabrication of the composite structure of
FIG. 6.
[0030] FIG. 9 is a stylized, cross-sectional side view illustrating
filling fine powder around the particles of the composite structure
intermediate stage of FIG. 8.
[0031] FIG. 10 is a stylized, cross-sectional side view
illustrating densifying the powder of FIG. 9.
[0032] FIG. 11 is a stylized, cross-sectional side view
illustrating infusing molten metal around the particles of the
composite structure intermediate stage of FIG. 8.
[0033] FIG. 12 is a stylized, cross-sectional, enlarged portion of
one illustrative embodiment of the composite structure of FIG.
6.
[0034] FIG. 13 is a stylized, cross-sectional side view
illustrating various particulate shape embodiments according to the
present invention.
[0035] FIG. 14 is a stylized, cross-sectional side view of a second
illustrative embodiment of a composite structure according to the
present invention.
[0036] FIG. 15 is a perspective view of an exemplary roller-cone
rock bit including inserts or cutters according to the present
invention.
[0037] FIG. 16 is a side view of an exemplary fixed cutter rock bit
including inserts or cutters according to the present
invention.
[0038] FIG. 17 is a perspective view of an illustrative embodiment
of an intermediate stage of a rock bit insert according to the
present invention.
[0039] FIG. 18 is a top view of a first alternative embodiment of
an intermediate stage of a rock bit insert according to the present
invention.
[0040] FIG. 19 is a top view of a second alternative embodiment of
an intermediate stage of a rock bit insert according to the present
invention.
[0041] FIG. 20 is a perspective view of an illustrative embodiment
of a road or mining pick tip according to the present
invention.
[0042] FIG. 21 is a depiction of the macrostructure of one
particular embodiment of a road or mining pick according to the
present invention.
[0043] FIG. 22 is a depiction of a portion of the microstructure of
the road or mining pick of FIG. 21.
[0044] While the invention is susceptible to various modifications
and alternative forms, specific embodiments thereof have been shown
by way of example in the drawings and are herein described in
detail. It should be understood, however, that the description
herein of specific embodiments is not intended to limit the
invention to the particular forms disclosed, but on the contrary,
the intention is to cover all modifications, equivalents, and
alternatives falling within the spirit and scope of the invention
as defined by the appended claims.
DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS
[0045] Illustrative embodiments of the invention are described
below. In the interest of clarity, not all features of an actual
implementation are described in this specification. It will of
course be appreciated that in the development of any such actual
embodiment, numerous implementation-specific decisions must be made
to achieve the developer's specific goals, such as compliance with
system-related and business-related constraints, which will vary
from one implementation to another. Moreover, it will be
appreciated that such a development effort might be complex and
time-consuming but would nevertheless be a routine undertaking for
those of ordinary skill in the art having the benefit of this
disclosure.
[0046] The present invention relates to a structure comprising
disparate materials joined along a non-planar interface that
exhibits, in one illustrative embodiment, an interlocking geometry
and a method for fabricating the structure. While it is not so
limited, the structure of the present invention is particularly
applicable to cemented carbide composites and their incorporation
in layered, functionally graded structures with disparate cemented
carbides, diamond composites, metals, or metal alloys. The
non-planar interface of the present invention allows fabrication of
powder preforms incorporating fully dense elements by direct
pressing or cold isostatic pressing, and powder forging of such
preforms. In particular, the present invention mitigates or avoids
the problem of decompression cracking between fully dense and
powder regions during the unload portion of an isostatic pressing
cycle.
[0047] FIG. 6 depicts one illustrative embodiment of a composite
structure 600 incorporating a non-planar interface according to the
present invention. In this embodiment, the structure 600 comprises
a monolayer of particles 605 (only one labeled for clarity) formed
integrally with a metallic substrate material 610. The particles
605 define an open framework that is substantially filled with a
second material 615. The particles 605 may comprise the same
material as the substrate 610, a chemical or metallurgical variant
of the substrate 610, a metal or a metal alloy. In one embodiment,
shown in FIG. 7, the substrate 610 comprises a sintered powder and
the particles 605 are co-sintered with the substrate 610. In this
embodiment, the particles 605 are attached to the substrate 610
and, in some cases to each other, primarily by metallurgical neck
bonds 705 grown during sintering. In some embodiments, the
particles 605 extend into the substrate 610. Mechanisms that are
operative during neck bond growth include: viscous flow, plastic
flow, evaporation-condensation, volume diffusion, grain boundary
diffusion, and surface diffusion. The particles 605 may be attached
to the substrate 610 by various processes producing metallurgical
bonding, such as liquid phase sintering, solid-state sintering or
diffusion bonding, welding, and brazing. FIG. 8 illustrates an
intermediate configuration, prior to adding the second material 615
to the composite structure 600.
[0048] The second material 615 may be formed by substantially
filling the open volume between the particles 605 with a fine
metallic powder 905, as shown in FIG. 9, then pressure densifying
the second material 615 (e.g., the fine powder 905), as shown in
FIG. 10. Alternatively, the second material 615 may be formed by
infiltrating the open volume between the particles 605 with liquid
metal and solidifying the metal 1105 as illustrated in FIG. 11, to
form the second material 615 (of FIG. 6). Thus, the second material
615, whether formed using powder or liquid metal techniques,
comprises a densified portion. Note, as depicted in FIG. 12, that
the particles 605 extend from the substrate 610 such that the
particles 605 and the substrate 610 define recesses 1205. The
recesses 1205 exhibit negative draft angles (e.g., the negative
draft angle 1210) or are "undercut." Generally, a draft angle of 90
degrees is neutral. Thus, a draft angle of less than 90 degrees (as
illustrated in FIG. 12) is a negative draft angle. Draft angles
that are greater than 90 degrees are considered positive draft
angles. While the present invention is not so limited, in
particular embodiments, the draft angle may be within a range of
about 3 degrees to about 85 degrees.
[0049] The second material 615 extends into the recesses 1205,
which provides mechanical locking of the second material 615 to the
particles 605. Moreover, the particles 605 provide a tortuous
bonding surface having substantially more bonding area for both the
substrate 610 and the second material 615 as compared to a planar
interface. These factors contribute to improved mechanical
interlocking strength during intermediate processing steps and
increased interfacial strength in the finished structure.
[0050] While the particles 605 are illustrated in FIG. 6 as being
substantially spherical, the present invention is not so limited.
Rather, the particles 605 may take on many other shapes, such as
oblate spheroids 1305, cylinders 1310, and irregular shapes 1315,
as illustrated in FIG. 13, including, for example, acicular,
fibrous, flaky, granular, dendritic, and blocky shapes. Further,
the particles 605 may, in some embodiments, be arranged in a
particular pattern or they may be randomly dispersed on the
substrate material 610.
[0051] Note that substrate 610 may comprise either the "soft" or
"hard" portion of the composite structure 600. For example, wherein
the substrate 610 comprises a cemented carbide and the second
material 615 comprises a polycrystalline diamond material, the
cemented carbide substrate 610 represents the "soft" portion of the
composite structure 600. As illustrated in FIG. 14, the composite
structure 600, for example, may be incorporated into a yet larger
composite structure 1400 including a second monolayer of particles
1405 (only one labeled for clarity) and a third material 1410 that
is softer than the substrate 610. In such a configuration, the
substrate 610 corresponds to the "hard" portion of the composite
couple of the substrate 610 and the third material 1410.
[0052] Particular implementations of the present invention depend
on many scale and property aspects of the components and component
materials. For example, in the case of polycrystalline diamond
composite cutters or insert elements, the desirable thickness of
the particle layer (e.g., the layers of particles 605, 1405)
depends upon the polycrystalline diamond layer thickness and the
shape of the substrate surface. For planar or simply curved
surfaces, a particle size corresponding to about 80% of the
polycrystalline diamond layer thickness may be used. Dimpled,
ribbed, or faceted substrate surfaces may require smaller average
particle sizes or a wider size distribution for conformation to the
substrate surface. Multiple sizes or shapes of particles maybe used
to enhance particle coverage and effective non-planar interface
zone width.
[0053] The non-planar interface structure of the present invention
may be implemented in various products, such as a roller-cone rock
bit 1500, shown in FIG. 15, or a fixed cutter rock bit 1600, shown
in FIG. 16. The rock bits 1500, 1600 comprises a plurality of
polycrystalline diamond coated inserts 1505, 1605, respectively,
(only one labeled in each figure for clarity) that ablate rock
formations during oilfield drilling operations. FIG. 17 illustrates
one particular embodiment of such an insert 1705 at an intermediate
stage of fabrication. The insert 1705 comprises a plurality of
tungsten carbide/cobalt spherical pellets 1710 sintered onto a
cemented carbide substrate 1715 of the same composition. In the
illustrated example, the pellets 1710 have sizes corresponding to a
16/20 mesh. In other embodiments, the pellets 1710 have sizes
corresponding to 80/200 mesh, 40/60 mesh, and 20/30 mesh but may
comprise other sizes depending upon the particular
implementation.
[0054] As noted above, the particles or pellets may take on various
shapes. For example, FIGS. 18-19 illustrate an exemplary insert
comprising rod-shaped or cylindrical tungsten carbide/cobalt
particles 1805 sintered onto a substrate 1810 of the same material.
In FIG. 18, the particles 1805 are arranged in a spiral fashion,
while they are arranged randomly in FIG. 19. Irrespective of the
particle shape and arrangement, the interstices between the
particles or pellets 1710, 1805 are filled with diamond-containing
particle mixes, held in place by a formed can that defines the
final external shape. The assembly is subsequently densified at
high temperature and pressure, achieving full density of the
composite structure.
[0055] Another exemplary implementation of the non-planar interface
structure of the present invention is that of a composite road pick
used for milling roadbeds prior to resurfacing. Such picks are also
used in earth-boring equipment for mining applications. FIG. 20
depicts a sintered, cemented carbide tip 2005 with an integral
particulate non-planar interface layer 2010 disposed on an undulant
surface 2015. In this example, fine nickel particles are coated on
the particulate layer 2010, followed by injection co-molding with a
fugitive-bound mixed cemented carbide and steel powder composite
perform. The assembly is placed in an elastomer mold with steel
powders and a carbide particulate surface layer as described in
U.S. Pat. No. 5,967,248 (which is hereby incorporated by reference
for all purposes) and densified by cold isostatic pressing to
produce a final composite powder preform. The final preform is then
preheated to forging temperature and densified by forging, e.g., in
a hot powder bed. The resulting fully dense functionally-graded
composite tool is then finish machined and heat treated.
[0056] FIG. 21 illustrates the macrostructure of such a composite
road or mining pick 2100, including the cemented carbide tip 2005,
the particulate layer 2010, the undulant surface 2015, the steel
shank 2105 formed during cold isostatic pressing, and the densified
cemented carbide and steel powder 2110. FIG. 20 depicts the
microstructure of the non-planar interface, including the cemented
carbide tip 2005, nickel layer 2005, and the densified cemented
carbide and steel powder 2110.
[0057] In one particular embodiment of the present invention, a
composite structure is provided. The composite structure includes a
first portion comprising a first metallic material, a monolayer of
particles extending into and bonded with the first portion, and a
second portion comprising a second material, the second portion
bonded with the monolayer of particles and extending into
interstices between the particles.
[0058] In another particular embodiment of the present invention,
an insert for a rock bit is provided. The insert includes a
substrate comprising a first metallic material, a plurality of
particles bonded with the substrate, and a densified portion
comprising a second material, the densified portion bonded with the
plurality of particles and extending into interstices between the
particles.
[0059] In yet another particular embodiment of the present
invention, a composite road pick is provided. The road pick
includes a tip comprising a first metallic material, a plurality of
particles bonded with the tip, and a densified portion comprising a
second material, the densified portion bonded with the plurality of
particles and extending into interstices between the particles.
[0060] In another particular embodiment of the present invention, a
method for fabricating a composite structure is provided. The
method includes bonding a monolayer of particles to a first portion
comprising a first metallic material, such that the monolayer of
particles extends into the first portion and bonding a second
portion comprising a second material to the monolayer of particles,
such that the second portion extends into interstices between the
particles.
[0061] This concludes the detailed description. The particular
embodiments disclosed above are illustrative only, as the invention
may be modified and practiced in different but equivalent manners
apparent to those skilled in the art having the benefit of the
teachings herein. Furthermore, no limitations are intended to the
details of construction or design herein shown, other than as
described in the claims below. It is therefore evident that the
particular embodiments disclosed above may be altered or modified
and all such variations are considered within the scope and spirit
of the invention. Accordingly, the protection sought herein is as
set forth in the claims below.
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