U.S. patent application number 11/939330 was filed with the patent office on 2008-09-04 for hybrid carbon nanotube reinforced composite bodies.
This patent application is currently assigned to SMITH INTERNATIONAL, INC.. Invention is credited to Hong Deng, Anthony Griffo, Madapusi K. Keshavan, Alan W. Lockstedt, Yuelin Shen, Xiayang Sheng, Guodong Zhan, Youhe Zhang.
Application Number | 20080210473 11/939330 |
Document ID | / |
Family ID | 39247775 |
Filed Date | 2008-09-04 |
United States Patent
Application |
20080210473 |
Kind Code |
A1 |
Zhang; Youhe ; et
al. |
September 4, 2008 |
HYBRID CARBON NANOTUBE REINFORCED COMPOSITE BODIES
Abstract
A composite body for cutting tools that includes a ductile
phase; a plurality of carbide particles dispersed the ductile
phase; and a plurality of nanotubes integrated into the composite
body is disclosed. Methods of making such composite bodies and
drill bits formed of such material are also disclosed.
Inventors: |
Zhang; Youhe; (Tomball,
TX) ; Zhan; Guodong; (Spring, TX) ; Sheng;
Xiayang; (Sugar Land, TX) ; Lockstedt; Alan W.;
(Magnolia, TX) ; Shen; Yuelin; (Houston, TX)
; Deng; Hong; (Houston, TX) ; Griffo; Anthony;
(The Woodlands, TX) ; Keshavan; Madapusi K.; (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: |
39247775 |
Appl. No.: |
11/939330 |
Filed: |
November 13, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60858830 |
Nov 14, 2006 |
|
|
|
60917163 |
May 10, 2007 |
|
|
|
Current U.S.
Class: |
175/426 ;
423/440 |
Current CPC
Class: |
B22F 1/0025 20130101;
C22C 26/00 20130101; B22F 2005/001 20130101; C22C 29/06 20130101;
C23C 30/005 20130101; B82Y 30/00 20130101 |
Class at
Publication: |
175/426 ;
423/440 |
International
Class: |
E21B 10/46 20060101
E21B010/46 |
Claims
1. A composite body for cutting tools, comprising: a ductile phase;
a plurality of carbide particles dispersed the ductile phase; and a
plurality of nanotubes integrated into the composite body.
2. The composite body of claim 1, wherein the plurality of carbide
particles comprise at least one of tungsten carbide, tantalum
carbide, titanium carbide, or combinations thereof.
3. The composite body of claim 1, wherein the plurality of
nanotubes comprise carbon nanotubes.
4. The composite body of claim 1, wherein the plurality of
nanotubes comprise inorganic nanotubes.
5. The composite body of claim 4, wherein the inorganic nanotube is
formed by depositing an inorganic coating by atomic layer
deposition on a carbon nanotube and removing the carbon
nanotube.
6. The composite body of claim 1, wherein the plurality of nanotube
materials comprises a coating deposited by atomic layer deposition
disposed thereon.
7. The composite body of claim 6, wherein the coating has a
thickness ranging from about 1 to 10 nm.
8. The composite body of claim 6, wherein the coating comprises at
least one of a metal, ceramic materials, alloys thereof, or
combinations thereof.
9. The composite body of claim 1, wherein the ductile phase
comprises at least one of Fe, Ni, Co, and alloys thereof.
10. The composite body of claim 1, wherein at least one of an end
cap or sidewall of the nanotubes is functionalized.
11. A method of forming a composite body for a cutting tool,
comprising: integrating a plurality of nanotubes in one of a
plurality of carbide particles and a binder phase; mixing the other
of the one of a plurality of carbide particles and a binder phase;
and consolidating the mixture.
12. The method of claim 11, wherein the plurality of nanotubes
comprise carbon nanotubes.
13. The method of claim 11, wherein the integrating comprises at
least one of vapor co-deposition, mixing, spray mixing, ball
milling, electromagnetic levitation, infiltration of a perform, and
extrusion.
14. The method of claim 11, wherein the integrating comprises
dispersing the plurality of nanotubes in the plurality of carbide
particles.
15. The method of claim 11, wherein the integrating comprises
dispersing the plurality of nanotubes into a plurality of binder
particles.
16. The method of claim 11, wherein the integrating comprises
integrating the plurality of nanotubes into an infiltration
binder.
17. The method of claim 11, wherein the consolidating comprises at
least one of infiltration, casting, and sintering.
18. A drill bit, comprising: a bit body, the bit body comprising: a
ductile phase; a plurality of carbide particles dispersed the
ductile phase; and a plurality of nanotubes integrated into the bit
body; and at least one cutting element for engaging the formation
disposed on the bit body.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application, pursuant to 35 U.S.C. .sctn. 119(e),
claims the benefit of U.S. Patent Application No. 60/858,830 filed
on Nov. 14, 2006, and U.S. Patent Application No. 60/917,163 filed
on May 10, 2007, both of which are incorporated by reference in
their entirety
BACKGROUND OF INVENTION
[0002] 1. Field of the Invention
[0003] Embodiments disclosed herein relate generally to composite
materials used in cutting tools.
[0004] 2. Background Art
[0005] Historically, there have been two types of drill bits used
drilling earth formations, drag bits and roller cone bits. Roller
cone bits include one or more roller cones rotatably mounted to the
bit body. These roller cones have a plurality of cutting elements
attached thereto that crush, gouge, and scrape rock at the bottom
of a hole being drilled. Several types of roller cone drill bits
are available for drilling wellbores through earth formations,
including insert bits (e.g. tungsten carbide insert bit, TCI) and
"milled tooth" bits. The bit bodies and roller cones of roller cone
bits are conventionally made of steel. In a milled tooth bit, the
cutting elements or teeth are steel and conventionally integrally
formed with the cone. In an insert or TCI bit, the cutting elements
or inserts are conventionally formed from tungsten carbide, and may
optionally include a diamond enhanced tip thereon.
[0006] The term "drag bits" refers to those rotary drill bits with
no moving elements. Drag bits are often used to drill a variety of
rock formations. Drag bits include those having cutting elements or
cutters attached to the bit body, which may be a steel bit body or
a matrix or composite bit body formed from a matrix material such
as tungsten carbide surrounded by an binder material. The cutters
may be formed having a substrate or support stud made of carbide,
for example tungsten carbide, and an ultra hard cutting surface
layer or "table" made of a polycrystalline diamond material or a
polycrystalline boron nitride material deposited onto or otherwise
bonded to the substrate at an interface surface.
[0007] Thus, some of the primary materials used in the formation of
various components in drill bits, as well as other cutting tools,
include ceramic materials formed from tungsten carbide. In
composites formed with tungsten carbide, for example, the resulting
composite includes the hard particle surrounded by metal binder,
typically cobalt- or copper-based alloys, which acts as a matrix.
The individual hard particles thus are embedded in a matrix of a
relatively ductile metal such that the ductile metal matrix
provides the necessary toughness, while the grains of hard material
in the matrix furnish the necessary wear resistance. The ductile
metal matrix also reduces crack formation and suppresses crack
propagation through the composite material once a crack has been
initiated.
[0008] Many factors affect the durability of a tungsten carbide
composite in a particular application. These factors include the
chemical composition and physical structure (size and shape) of the
carbides, the chemical composition and microstructure of the matrix
metal or alloy, and the relative proportions of the carbide
materials to one another and to the matrix metal or alloy.
Generally, as the tungsten carbide particle size and/or cobalt
content decrease, higher hardness, compressive strength, and wear
resistance, but lower toughness is achieved. Conversely, larger
particle sizes and/or higher cobalt content yields high toughness
and impact strength, but lower hardness.
[0009] Many different types of tungsten carbides are known based on
their different chemical compositions and physical structure.
Depending on the particular application, different types of
carbides, or combinations thereof, may be used. Bit components that
have been formed from tungsten carbide include, for example,
inserts for roller cone bits, cutter substrates for drag bits, bit
bodies, hardfacing, etc. Among the various types of tungsten
carbide commonly used in drill bit bodies or other cutting tool
bodies are cast tungsten carbide, macro-crystalline tungsten
carbide, carburized tungsten carbide, and cemented tungsten carbide
(also known as sintered tungsten carbide).
[0010] One type of tungsten carbide is macro-crystalline carbide.
This material is essentially stoichiometric tungsten carbide
created by a thermite process. Most of the macro-crystalline
tungsten carbide is in the form of single crystals, but some
bicrystals of tungsten carbide may also form in larger particles.
Single crystal stoichiometric tungsten carbide is commercially
available from Kennametal, Inc., Fallon, Nev.
[0011] Carburized carbide is yet another type of tungsten carbide.
Carburized tungsten carbide is a product of the solid-state
diffusion of carbon into tungsten metal at high temperatures in a
protective atmosphere. Sometimes, it is referred to as fully
carburized tungsten carbide. Such carburized tungsten carbide
grains usually are multi-crystalline, i.e., they are composed of
tungsten carbide agglomerates. The agglomerates form grains that
are larger than the individual tungsten carbide crystals. These
large grains make it possible for a metal infiltrant or an
infiltration binder to infiltrate a powder of such large grains. On
the other hand, fine grain powders, e.g., grains less than 5 .mu.m,
do not infiltrate satisfactorily. Typical carburized tungsten
carbide contains a minimum of 99.8% by weight of tungsten carbide,
with a total carbon content in the range of about 6.08% to about
6.18% by weight.
[0012] Cast tungsten carbide, on the other hand, is formed by
melting tungsten metal (W) and tungsten monocarbide (WC) together
such that a eutectic composition of WC and W2C, or a continuous
range of compositions therebetween, is formed. Cast tungsten
carbide typically is frozen from the molten state and comminuted to
a desired particle size.
[0013] A fourth type of tungsten carbide, which has been typically
used in hardfacing, is cemented tungsten carbide, also known as
sintered tungsten carbide. Sintered tungsten carbide comprises
small particles of tungsten carbide (e.g., 1 to 15 microns) bonded
together with cobalt. Sintered tungsten carbide is made by mixing
organic wax, tungsten carbide and cobalt powders, pressing the
mixed powders to form a green compact, and "sintering" the
composite at temperatures near the melting point of cobalt. The
resulting dense sintered carbide can then be crushed and comminuted
to form particles of sintered tungsten carbide.
[0014] For conventional tungsten carbide composites, the mechanical
property of fracture toughness is inversely proportional to
hardness, and wear resistance is proportional to hardness. Although
the fracture toughness of cemented tungsten carbide has been
somewhat improved over the years, it is still a limiting factor in
demanding industrial applications such as high penetration
drilling, where cemented tungsten carbide inserts often exhibit
gross brittle fracture that can lead to catastrophic failure.
Traditional metallurgical methods for enhancing fracture toughness,
such as grain size refinement, cobalt content optimization, and
strengthening agents, have been substantially exhausted with
respect to conventional cemented tungsten carbide.
[0015] Bit bodies formed from either cast or macrocrystalline
tungsten carbide or other hard metal matrix materials, while more
erosion resistant than steel, lack toughness and strength, thus
making them brittle and prone to cracking when subjected to impact
and fatigue forces encountered during drilling. This can result in
one or more blades breaking off the bit causing a catastrophic
premature bit failure. Additionally, the braze joints between the
matrix material and the PDC cutters may crack due to these same
forces. The formation and propagation of cracks in the matrix body
and/or at the braze joints may result in the loss of one or more
PDC cutters. A lost cutter may abrade against the bit, causing
further accelerated bit damage. However, bits formed with sintered
tungsten carbide may have sufficient toughness and strength for a
particular application, but may lack other mechanical properties,
such as erosion resistance.
[0016] Regardless of the type of material used in a particular
drilling or cutting tool application, designers continue to seek
improved properties (such as improved wear resistance, thermal
resistance, fracture toughness etc.) in the ceramic materials.
Further, as the bulk particles used in ceramic materials decrease
in size with the increasing use of nanoparticles (grain sizes less
than 100 nm), observed brittleness has limited potential
applications for the resulting material. It has been known for some
time that the addition of fibrous materials to materials may
increase mechanical properties, such as strength. However,
incorporation of the fibrous materials, such as carbon fibers, has
presented difficulties including resistance to wetting of the
fibers and reaction between the metal and carbide.
[0017] Accordingly, there exists a continuing need for a new
composite or matrix body composition for drill bits and other
cutting tools which has high strength and toughness, while
maintaining other desired properties such as wear and erosion
resistance.
SUMMARY OF INVENTION
[0018] In one aspect, embodiments disclosed herein relate to a
composite body for cutting tools that includes a ductile phase; a
plurality of carbide particles dispersed the ductile phase; and a
plurality of nanotubes integrated into the composite body.
[0019] In another aspect, embodiments disclosed herein relate to a
method of forming a composite body for a cutting tool that includes
integrating a plurality of nanotubes in one of a plurality of
carbide particles and a binder phase; mixing the other of the one
of a plurality of carbide particles and a binder phase; and
consolidating the mixture.
[0020] In yet another aspect, embodiments disclosed herein relate
to a drill bit that includes a bit body and at least one cutting
element for engaging the formation disposed on the bit body,
wherein the bit body includes a ductile phase; a plurality of
carbide particles dispersed the ductile phase; and a plurality of
nanotubes integrated into the bit body.
[0021] Other aspects and advantages of the invention will be
apparent from the following description and the appended
claims.
BRIEF DESCRIPTION OF DRAWINGS
[0022] FIG. 1 shows a microstructure of a conventional tungsten
carbide composite.
[0023] FIG. 2 shows a fluidized bed reactor that may be used in
accordance with one embodiment of the present disclosure.
[0024] FIG. 3 is a perspective side view of a drag bit in
accordance with one embodiment of the present disclosure.
[0025] FIG. 4 is a perspective side view of an impreg bit in
accordance with one embodiment of the present disclosure.
[0026] FIG. 5 is a schematic according to one embodiment of the
present disclosure.
DETAILED DESCRIPTION
[0027] In one aspect, embodiments disclosed herein relate to
composite or matrix bodies used in components of downhole cutting
tools, including drill bits, mining picks, core bits, etc. In
particular, embodiments relate to composite bodies having formed
from tungsten carbide particles surrounded by a ductile metal
matrix binder with a reinforcing nanotubular material.
[0028] In addition, embodiments of the present disclosure provide
composite bodies which are formed from such tungsten carbides
infiltrated by suitable metals or alloys as infiltration binders.
Such a composite body may have high transverse rupture strength and
toughness while maintaining wear and erosion resistance.
Embodiments of the present disclosure are based, in part, on the
determination that the life of a composite bit body is related to
the body's strength (also known as transverse rupture strength),
toughness, and resistance to erosion.
[0029] FIG. 1 illustrates the conventional microstructure of
cemented tungsten carbide. As shown in FIG. 1, cemented tungsten
carbide 10 includes tungsten carbide grains 12 that are bonded to
one another by a metal binder phase 14. As illustrated, tungsten
carbide grains may be bonded to other grains of tungsten carbide,
thereby having a tungsten carbide/tungsten carbide interface,
and/or may be bonded to the metal phase, thereby having a tungsten
carbide/metal interface. The unique properties of cemented tungsten
carbide result from this combination of a rigid carbide network
with a tougher metal substructure. The generic microstructure of
cemented tungsten carbide, a heterogenous composite of a ceramic
phase in combination with a metal phase, is similar in all
cements.
[0030] The relatively low fracture toughness of cemented tungsten
carbide has proved to be a limiting factor in more demanding
applications, such as in roller cone rock bits, hammer bits and
drag bits used for subterranean drilling and the like. It is
possible to increase the toughness of the cemented tungsten carbide
by increasing the amount of metal binder present in the composite.
The toughness of the composite mainly comes from plastic
deformation of the metal phase during the fracture process. Yet,
the resulting hardness of the composite decreases as the amount of
ductile metal increases. Thus, an upper limit on the amount of
metal phase typically exists.
[0031] As evident from FIG. 1, the metal phase is not necessarily
continuous in the conventional cemented tungsten carbide
microstructure, particularly in compositions having a low metal
concentration. Further, while a relatively uniform distribution of
tungsten carbide in a metal matrix is desired, typically inadequate
mixing/infiltration results in agglomerates of tungsten carbide
particles and pools of binder. Thus, a crack propagating through
the composite will often travel through the less ductile tungsten
carbide grains, either transgranularly through tungsten
carbide/metal interfaces or intergranularly through tungsten
carbide/tungsten carbide interfaces. As a result, cemented tungsten
carbide often exhibits gross brittle fracture during more demanding
applications, which may lead to catastrophic failure.
[0032] Generally, embodiments of the present disclosure may include
composite body constructions comprising hard phase particulate
materials and a relatively softer binder phase material, where the
composite body construction is also provided with a reinforcing
nanotube material. A cermet or sintered material formed with a
reinforcing nanotube material may find particular use as cutting
tool composite bodies.
[0033] As used herein, the term "nanotube material" refers to
various materials having having a cylindrical or tubular
configuration with at least one dimension, such as length or
diameter, between 1 and 100 nanometers. Types of nanotubes that may
find use as a reinforcing nanotubes material in the present
disclosure may include carbon nanotubes (CNTs), including both
single-walled (SWNT), double-walled (DWNT), multi-walled (MWNT),
inorganic nanotubes, multibranched nanotubes, and CNT-C.sub.60
hybrids. Additionally, in some embodiments, at least a portion of
the surface of the reinforcing nanotubes may be modified.
[0034] Carbon nanotubes are polymers of pure carbon, which may be
functionalized or otherwise modified. Both SWNTs and MWNTs are
known in the art and the subject of a considerable body of
published literature. Examples of literature on the subject are
Dresselhaus, M. S., et al., Science of Fullerenes and Carbon
Nanotubes, Academic Press, San Diego (1996), and Ajayan, P. M., et
al., "Nanometre-Size Tubes of Carbon," Rep. Prog. Phys. 60 (1997):
1025-1062. The structure of a single-wall carbon nanotube may be
described as a single graphene sheet rolled into a seamless
cylinder whose ends are either open or closed. When closed, the
ends are capped by either half fullerenes or more complex
structures including pentagons.
[0035] Nanotubes frequently exist as "ropes," or bundles of 10 to
100 nanotubes held together along their length by van der Waals
forces, with individual nanotubes branching off and joining
nanotubes of other "ropes." Multi-walled carbon nanotubes are
multiple concentric cylinders of graphene sheets. The cylinders are
of successively larger diameter to fit one inside another, forming
a layered composite tube bonded together by van der Waals forces,
with a typical distance of approximately 0.34 nm between layers, as
reported by Peigney, A., et al., "Carbon nanotubes in novel ceramic
matrix nanocomposites," Ceram. Inter. 26 (2000) 677-683.
[0036] Carbon nanotubes are commonly prepared by arc discharge
between carbon electrodes in an inert gas atmosphere. The product
is generally a mixture of single-wall and multi-wall nanotubes,
although the formation of single-wall nanotubes can be favored by
the use of transition metal catalysts such as iron or cobalt. The
electric are method, as well as other methods for the synthesis of
carbon nanotubes is described in, for example, "Nanometre-Size
Tubes of Carbon," P. M. Ajayan and T. W. Ebbesen, Rep. Prog. Phys.,
60, 1025-1062 (1997).
[0037] Inorganic nanotubes may include those prepared from a range
of materials including boron nitride, silicon nitride, silicon
carbide, dichalcogenides, for example, WS.sub.2, oxides such as
HfO.sub.2 and MoO.sub.3, metallic nanotubes, such as Co and Au, and
materials having a composition B.sub.xC.sub.yN.sub.z, where x, y,
and z may be independently selected from 0 to 4, including for
example, BC.sub.2N.sub.2 and BC.sub.4N, and combinations
thereof.
[0038] In a particular embodiment, the average diameter of the
nanotube materials may range from about 1 to 100 nanometers. In
various other embodiments, the reinforcing phase may include SWNTs
having an average diameter of about 1 to 2 nanometers and/or MWNTs
having an average diameter of about 2 to 30 nanometers. Nanotube
materials typically have a very high aspect ratio, that is, the
ratio of length to diameter. In a particular embodiment, the
nanotubes used in the present disclosure may have an aspect ratio
ranging from about 25 to 1,000,000, and preferably from about 100
to about 1,000.
[0039] The surface of the carbon nanotubes may, in one embodiment,
be modified prior to incorporation into the composites of the
present disclosure. In some embodiments, the nanostructured carbon
material is modified by a chemical means to yield derivatized
nanostructured carbon material. As used herein, "derivatization"
refers to the attachment of other chemical entities to the
nanostructured carbon material, which may be by chemical or
physical means including, but not limited to, covalent bonding, van
der Waals forces, electrostatic forces, physical entanglement, and
combinations thereof. In other embodiments, the nanostructured
carbon material is modified by a physical means selected from the
group consisting of plasma treatment, heat treatment, ion
bombardment, attrition by impact, milling and combinations thereof.
In yet other embodiments, the nanostructured carbon material is
modified by a chemical means selected from the group consisting of
chemical etching by acids either in liquid or gaseous form,
chemical etching by bases either in liquid or gaseous form,
electrochemical treatments, and combinations thereof.
[0040] One of ordinary skill in the art would appreciate that
derivatization or functionalization may be desired so as to
increase ease in solubilization and/or disperson of the nanotubes
into at least one of the component phases prior to formation of a
composite material. Functionalization or derivatization may occur
by the incorporation of various chemical moieties on either end
caps and/or sidewalls (either exterior or interior) of the nanotube
materials, or with a coating placed thereon.
[0041] For example, functionalization may occur through covalent
and/or non-covalent functionalization, endcap and/or sidewall
functionalization, exohedral and/or endohedral functionalization
and supramolecular complexation. A variety of functionalized
nanotubes have been developed so as to enable dispersion of the
nanostructures into composite materials, including fluoronanotubes,
carboxy-nanotubes, and various covalently bonded nanotubes,
including amino-CNTs, vinyl-CNTs, epoxy-CNTs. Oxidation of
nanotubes may result in carboxyl, hydroxyl, or carbonyl groups,
which may be further modified via amidation or etherification, for
example. Additionally, functionalization frequently occurs through
an initial fluorination, and then subsequent nucleophilic attack,
or via a free radical reaction to form a covalent carbon-carbon
bond. Further, U.S. Pat. Nos. 7,122,165, 7,105,596, 7,048,999,
6,875,412, 6,835,366, 6,790,425, 2005/0255030, which are all herein
incorporated by reference in their entirety, disclose various
sidewall and endcap functionalizations that may, for example, be
used to assist in integration of nanotubes in a composite body of
the present disclosure.
[0042] Additionally, in another embodiment, the nanotube materials
of the present disclosure may be provided with ultra-thin,
conformal coating thereon. As used herein, "ultra-thin" refers to a
thickness of less than 100 nm. In a particular embodiment, the
ultra-thin coating may have a thickness ranging from about 0.1 to
about 50 nm, from about 0.5 to 35 nm in another embodiment, and
from about 1 to 10 nm in yet another embodiment. "Conformal" refers
to a relatively uniform thickness across the surface of the
particle such that the surface shape of a coated particle is
substantially similar to that of the uncoated particle.
[0043] Depending on the desired application of the nanotube
material, type of nanotube material, and type of particulate
material to which the reinforcing tubular material is added, the
composition of the coatings may vary. In a particular embodiment,
the coating may include a sinterable material including, for
example, metals, metal alloys, ceramic materials, and cermets.
[0044] For example, coatings that may be suitable for use on the
nanotube materials of the present disclosure may include metals and
binary materials, i.e., materials of the form Q.sub.xR.sub.y, where
Q and R represent different atoms and x and y are numbers that
reflect an electrostatically neutral material. Among the suitable
binary materials are various inorganic ceramic materials including
oxides, nitrides, carbides, sulfides, fluorides, and combinations
thereof. Examples of oxides that may find use in the present
disclosure include those such as CoO, Al.sub.2O.sub.3, TiO.sub.2,
Ta.sub.2O.sub.5, Nb.sub.2O.sub.5, ZrO.sub.2, HfO.sub.2, SnO.sub.2,
ZnO, La.sub.2O.sub.3, Y.sub.2O.sub.3, CeO.sub.2, SC.sub.2O.sub.3,
Er.sub.2O.sub.3, V.sub.2O.sub.5, SiO.sub.2, In.sub.2O.sub.3, and
the like. Examples of nitrides that may find use in the present
disclosure include those such as Si.sub.3N.sub.4, AlN, TaN, NbN,
TiN, MoN, ZrN, HfN, GaN, and the like. Examples of carbides that
may find use in the present disclosure include those such as SiC,
WC, and the like. Examples of sulfides that may find use in the
present disclosure include those such as ZnS, SrS, CaS, PbS, and
the like. Examples of fluorides that may find use in the present
disclosure include those such as CaF.sub.2, SrF.sub.2, ZnF.sub.2,
and the like. Among the suitable metal coatings include Pt, Ru, Ir,
Pd, Cu, Fe, Co, Ni, W, and the like. Other types of materials that
may be used to form an ultra-thin conformal coating include those
described in U.S. Pat. No. 6,613,383, which is hereby incorporated
by reference in its entirety. Coatings suitable for use in the
present disclosure may also include mixed structures, such as
TiAlN, Ti3AlN, ATO (AlTiO), coatings including doped metals, such
as ZnO:Al, ZnS:Mn, SrS:Ce, Al.sub.2O.sub.3:Er, ZrO.sub.2:Y, which
may also include other rare earth metals (Ce.sup.3+, Tb.sup.3+,
etc.) for doping or co-doping, or nanolaminates, such as
HfO.sub.2/Ta.sub.2O.sub.5, TiO.sub.2/Ta.sub.2O.sub.5,
TiO.sub.2/Al.sub.2O.sub.3, ZnS/Al.sub.2O.sub.3, and the like.
Further, other inorganic species such as inorganic polymers may be
suitable for coatings of the present disclosure, including
inorganic polymers such as, for example, polysilanes,
polysiloxanes, polystannanes, polyphosphazene, polysulfides, and
hybrid polymers of a grafted inorganic and organic polymer.
[0045] In a particular embodiment, the coating itself may be a
reagent or catalyst that functions as a sintering aid in the
formation of a cermet composite. Thus, the ultra-thin coating may
provide a high surface area of catalyst or reactive material and/or
provide a means for finely dispersing the coating material. For
example, the tubular materials of the present disclosure may be
coated with a material such as aluminum oxide, which may function
as a sintering aid.
[0046] In a particular embodiment, the ultra-thin, conformal
coating of the present disclosure may be applied on the tubular
materials through atomic layer controlled growth techniques or
atomic layer deposition (ALD). ALD deposition of coatings is
described, for example, in U.S. Pat. No. 6,913,827, which is herein
incorporated by reference in its entirety. ALD methods use
self-limiting surface chemistry to control deposition. Under the
appropriate conditions, deposition may be limited to a small number
of functional groups on the surface, i.e., approximately one
monolayer or .about.1.times.10.sup.15 species per cm.sup.2. ALD
permits the deposition of coatings of up to about 0.3 nm in
thickness per reaction cycle, and thus provide a means for
controlling thickness to extremely fine thicknesses. In these
techniques, the coating may be formed in a series of two or more
self-limited reactions, which in most instances can be repeated to
subsequently deposit additional layers of the coating material
until a desired coating thickness is achieved. In most instances,
the first of these reactions may involve some functional group on
the surface of the particle, such as an M-H, M-O--H, or M-N--H
group, where M represents an atom of a metal or semi-metal. The
individual reactions may be carried out separately and under
conditions such that all excess reagents and reaction products are
removed before concluding the succeeding reaction. The particles
may optionally be treated prior to initiating the reaction sequence
to remove volatile materials that may have absorbed onto the
surface of the particulate materials. This may be readily done by
exposing the particles to elevated temperatures and/or vacuum.
[0047] Additionally, in some instances a precursor reaction may be
performed to introduce desirable functional groups onto the surface
of the tubular material to facilitate a reaction sequence in
creating an ultra-thin coating. Examples of such functional groups
include hydroxyl groups, amino groups, and metal-hydrogen bonds,
which may serve as a site of further reaction to allow formation of
an ultra-thin coating. Functionalization may be achieved through
surface treatments including, for example, water plasma treatment,
ozone treatment, ammonia treatment, and hydrogen treatment.
[0048] Oxide coatings may be prepared on particles having surface
hydroxyl or amine (M-N--H) groups using a binary (AB) reaction
sequence as follows. The asterisk (*) indicates the atom that
resides at the surface of the particle or coating, and Z represents
oxygen or nitrogen. M.sup.1 is an atom of a metal (or semimetal
such as silicon), particularly one having a valence of 3 or 4, and
X is a displaceable nucleophilic group. The reactions shown below
are not balanced, and are only intended to show the reactions at
the surface of the particles (i.e., not inter- or intralayer
reactions).
M-Z-H*+M.sup.1X.sub.n.fwdarw.M-Z-M.sup.1X*+HX (A1)
M-Z-M.sup.1X*+H.sub.2O.fwdarw.M-Z-M.sup.1OH*+HX (B1)
In reaction A1, reagent M.sup.1X.sub.n reacts with one or more
M-Z-H groups on the surface of the particle to create a "new"
surface group having the form -M.sup.1X. M.sup.1 is bonded to the
particle through one or more Z atoms. The -M.sup.1X group
represents a site that can react with water in reaction B1 to
regenerate one or more hydroxyl groups. The groups formed in
reaction B1 can serve as functional groups through which reactions
A1 and B1 can be repeated, each time adding a new layer of M.sup.1
atoms. Atomic layer controlled growth and additional binary
reactions are described in more detail in U.S. Pat. No. 6,613,383,
which is herein incorporated by reference in its entirety.
[0049] A convenient method for applying the ultra-thin, conformal
coating to particulate material is to form a fluidized bed of the
particles, and then pass the various reagents in turn through the
fluidized bed under reaction conditions. Methods of fluidizing
particulate material are well known and are described, for example,
"Nanocoating Individual Cohesitve Boron Nitride Particles in a
Fluidized Bed Reactor," Jeffrey R. Wank, et al., Powder Technology
142 (2004) 59-69. Briefly, the ALD process using a fluidized bed
reactor, illustrated in FIG. 2, is described. Uncoated particles
may be supported on a porous plate or screen 220 within a fluidized
bed reactor 200. A fluidizing gas (such as N.sub.2) may be passed
into the reactor 200 through line 240 and upwardly through the
plate or screen 220, lifting the particles and creating a fluidized
bed. Fluid (gaseous or liquid) reagents may be introduced into the
bed 200 also through line 240 for reaction with the surface of the
particles. The fluidizing gas may also act as an inert purge gas
following each dosing of the particles with reagent for removing
unreacted reagents and volatile or gaseous reaction products.
[0050] If desired, multiple layers of ultra-thin coatings may be
deposited on the particulate material. For example, an intermediate
ultra-thin layer may be applied to provide a surface to which a
desired outer layer can be applied more easily. Where multiple
layers of coating are desired, the multiple layers may possess
identical compositions, or the multiple layers may vary in
composition. It is specifically within the scope of the present
disclosure that the multiple layers may include combinations of any
of the above described coating compositions such, for example,
metal-on-metal, metal-on-oxide, and oxide-on-oxide. One of ordinary
skill in the art would recognize that depending on the compositions
of the applied coating, during any subsequent sintering conditions,
the coating may undergo a number of transitions. For example, an
ALD bi-layer of Al.sub.2O.sub.3/TiO.sub.2, after sintering, may
react and form an aluminum titanate coating. Further, one of
ordinary skill in the art would recognize that there is no
limitation on the combination or number of layers which may be
provided on the particulate material of the present disclosure. It
is also specifically within the scope of the present disclosure
that a subsequent coating layer may be deposited by a method other
than ALD, such as CVD or PVD, for example, on an ALD-deposited
coating.
[0051] Alternatively, a coating may be applied using atomic layer
deposition methods as described above, and the coating may
subjected to one or more reactions to form a modified coating. This
technique may be used, for example, for creating ultra-thin
coatings of various types that are not amenable to deposition using
atomic layer deposition techniques. For example, various types of
ultra-thin oxide coatings can be formed using the atomic layer
deposition techniques described above, and then can be carburized
to convert the oxide to the corresponding carbide.
[0052] The coatings disclosed herein may, in various embodiments,
be either amorphous or crystalline in nature. Further, if a coating
is amorphous in nature and is desirably crystalline, the particle
having the coating thereon may be placed in a furnace at the
appropriate environment for crystallization of the coating. In a
particular embodiment, crystallization may occur in air at
temperature of at least 600.degree. C.
[0053] Further, various inorganic nanotubes that may find use in
the composites of the present disclosure may include those formed
using a carbon nanotube as a template, applying a conformal coating
via ALD on the carbon nanotubes, and then removing the carbon
nanotube, such as by etching, to form an inorganic nanotube. Such
inorganic coatings, and thus nanotubes, may include the various
coatings described above. U.S. Pat. No. 7,005,391, which is herein
incorporated by reference in its entirety, discloses the formation
of such inorganic nanotubes' via ALD and subsequent etching of the
underlying carbon nanotube template.
[0054] A hard phase particulate materials that may be used with
reinforcing tubular materials to form the composite materials of
the present disclosure may include various materials used to form
cermet materials having application in the drill bit and cutting
tool industry. In one embodiment, the hard phase materials may
include tungsten carbide particles or other metal carbides, such as
titanium and tantalum carbides, and the like. Among the types of
tungsten carbide particles that may be used to form composite
bodies of the present disclosure include cast tungsten carbide,
macro-crystalline tungsten carbide, carburized tungsten carbide,
and cemented tungsten carbide.
[0055] Suitable particle sizes for the hard phase particulate
material of the present disclosure may range u p to 500 microns in
one embodiment, and from the nanometer range (e.g. about 0.001
microns) to about 500 microns in an other embodiment, and from
about 0.005 to 50 microns in yet another embodiment. In one
embodiment, the particulate materials of the present disclosure
have surface areas ranging from about 0.1 to 200 m.sup.2/g or
more.
[0056] As discussed above, one type of tungsten carbide is
macrocrystalline carbide. This material is essentially
stoichiometric WC in the form of single crystals. Most of the
macrocrystalline tungsten carbide is in the form of single
crystals, but some bicrystals of WC may form in larger particles.
The manufacture of macrocrystalline tungsten carbide is disclosed,
for example, in U.S. Pat. Nos. 3,379,503 and 4,834,963, which are
herein incorporated by reference.
[0057] U.S. Pat. No. 6,287,360, which is assigned to the assignee
of the present invention and is herein incorporated by reference,
discusses the manufacture of carburized tungsten carbide.
Carburized tungsten carbide, as known in the art, is a product of
the solid-state diffusion of carbon into tungsten metal at high
temperatures in a protective atmosphere. Carburized tungsten
carbide grains are typically multi-crystalline, i.e., they are
composed of WC agglomerates. The agglomerates form grains that are
larger than individual WC crystals. These larger grains make it
possible for a metal infiltrant or an infiltration binder to
infiltrate a powder of such large grains. On the other hand, fine
grain powders, e.g., grains less than 5 microns, do not infiltrate
satisfactorily. Typical carburized tungsten carbide contains a
minimum of 99.8% by weight of carbon infiltrated WC, with a total
carbon content in the range of about 6.08% to about 6.18% by
weight. Tungsten carbide grains designated as WC MAS 2000 and
3000-5000, commercially available from H.C. Stark, are carburized
tungsten carbides suitable for use in the formation of the matrix
bit body disclosed herein. The MAS 2000 and 3000-5000 carbides have
an average size of 20 and 30-50 micrometers, respectively, and are
coarse grain conglomerates formed as a result of the extreme high
temperatures used during the carburization process.
[0058] Another form of tungsten carbide is cemented tungsten
carbide (also known as sintered tungsten carbide), which is a
material formed by mixing particles of tungsten carbide, typically
monotungsten carbide, and cobalt particles, and sintering the
mixture. Methods of manufacturing cemented tungsten carbide are
disclosed, for example, in U.S. Pat. Nos. 5,541,006 and 6,908,688,
which are herein incorporated by reference. Sintered tungsten
carbide is commercially available in two basic forms: crushed and
spherical (or pelletized). Crushed sintered tungsten carbide is
produced by crushing sintered components into finer particles,
resulting in more irregular and angular shapes, whereas pelletized
sintered tungsten carbide is generally rounded or spherical in
shape.
[0059] Briefly, in a typical process for making cemented tungsten
carbide, a tungsten carbide powder having a predetermined size (or
within a selected size range) is mixed with a suitable quantity of
cobalt, nickel, or other suitable binder. The mixture is typically
prepared for sintering by either of two techniques: it may be
pressed into solid bodies often referred to as green compacts, or
alternatively, the mixture may be formed into granules or pellets
such as by pressing through a screen, or tumbling and then screened
to obtain more or less uniform pellet size. Such green compacts or
pellets are then heated in a controlled atmosphere furnace 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. Sintering globules of tungsten carbide specifically
yields spherical sintered tungsten carbide. Crushed cemented
tungsten carbide may further be formed from the compact bodies or
by crushing sintered pellets or by forming irregular shaped solid
bodies.
[0060] The particle size and quality of the sintered tungsten
carbide can be tailored by varying the initial particle size of
tungsten carbide and cobalt, controlling the pellet size, adjusting
the sintering time and temperature, and/or repeated crushing larger
cemented carbides into smaller pieces until a desired size is
obtained. In one embodiment, tungsten carbide particles
(unsintered) having an average particle size of between about 0.2
to about 20 microns are sintered with cobalt to form either
spherical or crushed cemented tungsten carbide. In a preferred
embodiment, the cemented tungsten carbide is formed from tungsten
carbide particles having an average particle size of about 0.8 to
about 5 microns. In some embodiments, the amount of cobalt present
in the cemented tungsten carbide is such that the cemented carbide
is comprised of from about 6 to 8 weight percent cobalt.
[0061] Cast tungsten carbide is another form of tungsten carbide
and has approximately the eutectic composition between bitungsten
carbide, W.sub.2C, and monotungsten carbide, WC. Cast carbide is
typically made by resistance heating tungsten in contact with
carbon, and is available in two forms: crushed cast tungsten
carbide and spherical cast tungsten carbide. Processes for
producing spherical cast carbide particles are described in U.S.
Pat. Nos. 4,723,996 and 5,089,182, which are herein incorporated by
reference. Briefly, tungsten may be heated in a graphite crucible
having a hole through which a resultant eutectic mixture of
W.sub.2C and WC may drip. This liquid may be quenched in a bath of
oil and may be subsequently comminuted or crushed to a desired
particle size to form what is referred to as crushed cast tungsten
carbide. Alternatively, a mixture of tungsten and carbon is heated
above its melting point into a constantly flowing stream which is
poured onto a rotating cooling surface, typically a water-cooled
casting cone, pipe, or concave turntable. The molten stream is
rapidly cooled on the rotating surface and forms spherical
particles of eutectic tungsten carbide, which are referred to as
spherical cast tungsten carbide.
[0062] The standard eutectic mixture of WC and W.sub.2C is
typically about 4.5 weight percent carbon. Cast tungsten carbide
commercially used as a matrix powder typically has a hypocutectic
carbon content of about 4 weight percent. In one embodiment of the
present invention, the cast tungsten carbide used in the mixture of
tungsten carbides is comprised of from about 3.7 to about 4.2
weight percent carbon.
[0063] The various tungsten carbides disclosed herein may be
selected so as to provide a bit that is tailored for a particular
drilling, mining, or other cutting application. For example, the
type, shape, and/or size of carbide particles used in the formation
of a composite bit body may affect the material properties of the
formed composite body, including, for example, fracture toughness,
transverse rupture strength, and erosion resistance.
[0064] The mixture includes preferably at least 80% by weight
carbide of the total matrix powder. While reference is made to
tungsten carbide, other carbides of Group 4a, 5a, or 6a metals may
be used. Although the total carbide may be used in an amount less
than 80% by weight of the matrix powder, such matrix bodies may not
possess the desired physical properties to yield optimal
performance.
[0065] In a composite body, the carbide particles may be surrounded
by a metallic binder. The metallic binder may be formed from a
metallic binder powder and/or an infiltration binder. The metallic
binder powder may be pre-blended with the matrix powder hard
carbide particles. To manufacture a composite body via
infiltration, matrix powder is infiltrated by an infiltration
binder. The term "infiltration binder" herein refers to a metal or
an alloy used in an infiltration process to bond the various
particles of tungsten carbide forms together. Catalyst materials
that may be used to form the relative ductile phase of the various
composites of the present disclosure may include all transition
metals, main group metals and alloys thereof, including various
group IVa, Va, and VIa ductile metals and metal alloys including,
but not limited to Fe, Ni, Co, Cu, Ti, Al, Ta, Mo, Nb, W, V, and
alloys thereof, including alloys with materials selected from C, B,
Cr, and Mn. For example, copper, nickel, iron, and cobalt may be
used as the major constituents in the infiltration binder. Other
elements, such as aluminum, manganese, chromium, zinc, tin,
silicon, silver, boron, and lead, may also be present in the
infiltration binder. In one preferred embodiment, the infiltration
binder is selected from at least one of nickel, copper, and alloys
thereof. In another preferred embodiment, the infiltration binder
includes a Cu--Mn--Ni--Zn alloy.
[0066] In one embodiment, the particulate material comprises
tungsten carbide particles and a metallic binder powder. In a
preferred embodiment, nickel and/or iron powder may be present as
the balance of the matrix powder, typically from about 2% to 12% by
weight. In addition to nickel and/or iron, other Group VIIIB metals
such as cobalt and various alloys may also be used. For example, it
is expressly within the scope of the present invention that Co
and/or Ni is present as the balance of the mixture in a range of
about 2% to 15% by weight. Metal addition in the range of about 1%
to about 12% may yield higher matrix strength and toughness, as
well as higher braze strength. In another preferred embodiment, the
matrix powder comprises nickel in an amount ranging from about 2 to
4 weight percent of the matrix powder and iron in an amount ranging
from about 0.5 to 1.5 weight percent of the matrix powder.
[0067] In another embodiment, the ductile binder phase may include
a compound containing silicon and/or titanium and oxygen, and a
titanate, silicate, or complex oxide of a metal selected from the
group of iron, cobalt, nickel and manganese in another embodiment.
The use of titanates and silicates as binders is described, for
example, in U.S. Pat. No. 5,769,176, which is herein incorporated
by reference in its entirety. In yet another embodiment, the
ductile binder phase may include any of the compositions that may
comprise the ultra-thin coating discussed above.
[0068] In a particular embodiment, the composites of the present
disclosure may be prepared by forming a mixture or blend of a hard
particulate/ceramic powder phase and a metal phase with a nanotube
filler integrated into at least one of the two phases. The amount
of nanotube filler that may be used in the matrix bodies of the
present disclosure may range from about 0.5 to 50 parts by volume
(of the mixture) in one embodiment, and from 1 to 20 parts by
volume in another embodiment. In other embodiments, the nanotube
material may be present in an amount up to 10 percent by volume and
up to 1 percent by volume in yet another embodiment. Alternatively,
the nanotubes may be present in an amount up to one-third of the
metallic binder present in the composite body.
[0069] Integration of the nanotube filler into the matrix body may
include any means as known to those skilled in the art. As used
herein, integration refers to any means for adding the nanotubes to
a component of the composite body such that the nanotubes are a
component of the formed composite body, i.e., by dispersion or
other forms of incorporation of the nanotube filler as known to
those skilled in the art. In some embodiments the nanotubes may be
integrated in such a manner so as to achieve a generally uniform
dispersion of the nanotubes through the formed composite body.
[0070] For example, in one embodiment, blending of the nanotube
fillers with a carbide particulate phase may be accomplished by any
suitable wet mixing technique that will provide a dispersion of the
nanotube filler in the carbide powder. Typically, a homogenous
dispersion, with minimal agglomeration and clumping may be
prepared, for example, by dispersing the components, individually
or as a mixture, in a mixing medium, such as a low molecular weight
alcohol (e.g., ethanol), with an ultrasonic probe, blending the
dispersions of the components that are individually dispersed, and
evaporating the solvent in an ultrasonic bath. Further, the mixing
media may optionally contain a surfactant, as known to those of
skill in the art, that may further promote dispersion of the
nanotubes in the particulate phase. Further, while reference is
made to the wet mixing of the nanotube material with carbide
particles, one of ordinary skill in the art would appreciate that
the nanotubes may alternatively be mixed with a binder phase.
[0071] Further, dry mixing or mixing with other volatile media may
also be used. Mechanical mixing may be performed by ball-milling in
conventional rotary mills that mix the powder mixture with the
assistance of tumbling balls. The sizes of the balls, the number of
balls used per unit volume of powder, the rotation speed of the
mill, the temperature at which the milling is performed, and the
length of time that milling is continued can all vary widely. Best
results may generally be achieved with a milling time ranging from
about 4 hours to about 50 hours. The degree of mixing may also be
affected by the "charge ratio," which is the ratio of the mass of
the balls to the mass of the powder. A charge ratio of from about 5
to about 20 will generally provide proper mixing. The milling may
be performed on the powders while suspended in the liquid
suspending agent referred to above.
[0072] Alternatively, one of ordinary skill in the art would
recognize that other means may be used to integrate or incorporate
nanotubes into the composites of the present disclosure, such as,
for example, vapor co-deposition (in which the nanostructure
material and a particulate phase are sublimed, mixed in the vapor
phase, and then condensed on a substrate), spraying coating of
particles or the infiltration binder (such as that described in
U.S. Patent Publication No. 20030012951, which is herein
incorporated by reference in its entirety), infiltration by
electromagnetic levitation (such as that described in U.S. Patent
Publication No. 2004/0206470, which is herein incorporation by
reference in its entirety), extrusion, either high or regular
shear, (such as that described in U.S. Patent Publication No.
20040029706, which is herein incorporated by reference in its
entirety), or infiltration of a perform (such as that described in
U.S. Pat. No. 6,934,600).
[0073] In various embodiments, the nanotubes may be incorporated in
the composite body in such a manner as to form a random
distribution. In other embodiments, however, the nanotubes may be
incorporated in such as manner so that the nanotubes may have an
oriented structure, such as uniform orientation in two dimensions
or three dimensions. U.S. Pat. Nos. 7,105,596 and 6,790,425, which
are herein incorporated by reference in their entirety, discuss the
macroscopic assembly of nanotubes in a structure.
[0074] The composite bodies of the present disclosure may be
prepared by a number of different methods, e.g., by infiltration,
casting, or other sintering techniques, including layered
manufacturing. Further, one of ordinary skill in the art would
appreciate that other methods may be used, such as, for example,
solid state or liquid phase sintering, pneumatic isostatic forging,
spark plasma sintering, microwave sintering, gas phase sintering,
and hot isostatic pressing.
[0075] Infiltration processes that may be used to form a composite
body of the present disclosure may begin with the fabrication of a
mold, having the desired body shape and component configuration. A
mass of carbide particles and, optionally, metal binder powder may
be infiltrated with a molten infiltration binder. In various
embodiments, the nanotube materials may be integrated into the
resulting composite body through at least one of the carbide
particles, the metal binder powder, and the infiltration
binder.
[0076] Alternatively, casting processes may be used, in which a
molten mixture of carbide particles, a binder, and nanotube
particles may be either poured into a mold, or melted within a
mold, and then cooled to cast the composite body. As described
above, the nanotube materials may be integrated into the resulting
composite body through at least one of the carbide particles or
metal binder.
[0077] Layered manufacturing of a composite body involves the
sintering of a first layer of particles together by a layered
manufacturing equipment, after which a second layer of particles is
disposed over the first layer and sintered in selected regions of
the second layer together and to the first layer. The process
repeats to fabricate subsequent layers until the desired part has
been formed from the composite material particles. Once a drill bit
body or other article of manufacture has been fabricated from the
composite body material, the particulate-based part may be
infiltrated with a binder material that binds adjacent particles of
matrix material together, and forms a substantially integral part
that represents the model used to generate the bit body or other
article. U.S. Pat. Nos. 5,544,550 and 5,433,280 discuss the use of
layered manufacturing techniques to form bit bodies. As described
above, the nanotube materials may be integrated into the resulting
composite body through at least one of the carbide particles or
metal binder.
[0078] Composite bodies of the present disclosure may be used in a
number of different applications, such as tools for drilling,
mining, and construction applications, including for example,
composite bodies for drill bits, mining picks, core bits, etc,
where mechanical properties of high fracture toughness, wear
resistance, and hardness are highly desired. Additionally, the
composite body may be used to form bit bodies and/or other wear and
cutting components in such downhole cutting tools as roller cone
bits, percussion or hammer bits, and drag bits, and a number of
different cutting and machine tools.
[0079] Referring to FIG. 3, a drag bit body 30 is formed with
blades 32 at its lower end. A plurality of recesses or pockets 34
are formed in the faces to receive a plurality of conventional
polycrystalline diamond compact cutters 36. The PDC cutters,
typically cylindrical in shape, are made from a hard material such
as tungsten carbide and have a polycrystalline diamond layer
covering the cutting face 37. The PDC cutters are brazed into the
pockets after the bit body 30 has been made. In one embodiment, the
bit body 30 comprises a composite body formed in accordance with
the present disclosure. Methods of making composite or matrix bit
bodies are known in the art and are disclosed for example in U.S.
Pat. No. 6,287,360, which is assigned to the assignee of the
present invention and hereby incorporated by reference in its
entirety.
[0080] A diamond impregnated diamond bit manufactured according to
embodiments of the invention is illustrated in FIG. 4. Referring
now to FIG. 4, a diamond impregnated drill bit 40 includes a shank
44 and a crown 46. Shank 44 may be formed of steel and includes a
threaded pin 48 for attachment to a drill string. Crown 46 has a
cutting face 42 and outer side surface 45. According to one
embodiment, crown 46 is a composite bit body according to one
embodiment of the present invention. Additionally, crown 46 may
optionally include various surface features, such as raised ridges
47 and inserts 49. Once crown 46 is formed, inserts 49 may be
mounted in the sockets (not shown) and affixed by any suitable
method, such as brazing, adhesive, mechanical means such as
interference fit, or the like.
[0081] As described above, matrix bodies of the present disclosure
having reinforcing nanotube materials therein may provide for an
increase in toughness. Referring to FIG. 5, a schematic of the
reinforcing effects of the nanotube material in a matrix body of
the present disclosure is shown. As shown in FIG. 5, as a material
is subjected to a load, and as a crack begins to propagate through
the material, it is postulated that the nanotube materials may
reinforce the composite material in one or more of several
mechanisms. First, incorporation of nanotubes may allow for fiber
bridging 52, i.e., the bridging of the crack wake by the nanotubes.
A toughening effect may also be achieved when the nanotubes either
distributing load from the crack tip while remaining intact,
debonding between the nanotubes and the surrounding material
followed by pull-out 84, and/or fracture of the individual
nanotubes 56 followed by energy adsorption through pull-out of the
broken nanotube. An alternative theory of a toughening mechanism is
crack deflection 58. When a crack propagates through a material, a
nanotube being of greater strength than the surrounding material,
depending on the orientation of the nanotube in the composite,
crack propagation may be deflected away from the axis of highest
stress to a less efficient plane directed by the longitudinal
orientation of the nanotube. This may lead to increased fracture
energy through increased fracture surface area and lower driving
forces due to the reduced resolved normal stresses at the crack
tip.
[0082] Advantageously, embodiments of the present disclosure may
provide for at least one of the following. By incorporating a
reinforcing nanotube material into a composite body, composite
bodies may be formed having an increased toughness. Furthermore,
because the increases in toughness may be obtained by adding
nanotubes, the fracture toughness may be increased without
substantially altering the composition, and thus wear resistance of
the body. Incorporation of coated nanotubes into the composite
material may provide for increased wettability and interfacial
adhesion of the nanotubes within the surrounding metal phase,
thereby resulting in a homogenous dispersion in the composite.
Improvements in creep resistance and stress relaxation in coated
nanotubes may further allow for improved high temperature
performance of reinforced composite structures.
[0083] 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.
* * * * *