U.S. patent application number 11/650860 was filed with the patent office on 2008-07-10 for reinforcing overlay for matrix bit bodies.
This patent application is currently assigned to Smith International, Inc.. Invention is credited to Anthony Griffo, Kumar T. Kembaiyan, Madapusi K. Keshavan, Alysia C. White.
Application Number | 20080164070 11/650860 |
Document ID | / |
Family ID | 39226696 |
Filed Date | 2008-07-10 |
United States Patent
Application |
20080164070 |
Kind Code |
A1 |
Keshavan; Madapusi K. ; et
al. |
July 10, 2008 |
Reinforcing overlay for matrix bit bodies
Abstract
A drill bit that includes a matrix bit body having a reinforcing
overlay thereon and having at least one blade thereon; at least one
cutter pocket disposed on the at least one blade; at least one
cutter disposed in the at least one cutter pocket; and a braze
material disposed between the at least one cutter and the at least
one cutter pocket, wherein the reinforcing overlay comprises
carbide particles and at least one binder and has a melting point
greater than a melting point of the braze material is
disclosed.
Inventors: |
Keshavan; Madapusi K.; (The
Woodlands, TX) ; Kembaiyan; Kumar T.; (The Woodlands,
TX) ; White; Alysia C.; (Fulshear, TX) ;
Griffo; Anthony; (The Woodlands, TX) |
Correspondence
Address: |
OSHA, LIANG LLP / SMITH
1221 MCKINNEY STREET, SUITE 2800
HOUSTON
TX
77010
US
|
Assignee: |
Smith International, Inc.
Houston
TX
|
Family ID: |
39226696 |
Appl. No.: |
11/650860 |
Filed: |
January 8, 2007 |
Current U.S.
Class: |
175/374 |
Current CPC
Class: |
E21B 10/55 20130101;
E21B 10/54 20130101 |
Class at
Publication: |
175/374 |
International
Class: |
E21B 10/46 20060101
E21B010/46 |
Claims
1. A drill bit, comprising: a matrix bit body having a reinforcing
overlay thereon and having at least one blade thereon; at least one
cutter pocket disposed on the at least one blade; at least one
cutter disposed in the at least one cutter pocket; and a braze
material disposed between the at least one cutter and the at least
one cutter pocket, wherein the reinforcing overlay comprises
carbide particles and at least one binder and has a melting point
greater than a melting point of the braze material.
2. The drill bit of claim 1, wherein the at least one binder
comprises at least one of nickel, cobalt, iron, and alloys
thereof.
3. The drill bit of claim 1, wherein the reinforcing overlay has a
hardness greater than about 50 HRc.
4. (canceled)
5. The drill bit of claim 1, wherein the reinforcing overlay has a
thickness ranging from about 0.010 to 0.125 inches.
6. The drill bit of claim 1, wherein the matrix bit body comprises
a matrix of tungsten carbide particles and a second binder.
7. The drill bit of claim 6, wherein the second binder comprises at
least one of nickel, cobalt, iron, and copper.
8. The drill bit of claim 6, wherein the second binder comprises
about 30 to 40 volume percent of the matrix bit body.
9. The drill bit of claim 1, wherein the reinforcing overlay
comprises a plurality of layers.
10. (canceled)
11. The drill bit of claim 1, wherein the reinforcing overlay has a
melting point greater than 1000.degree. C.
12. A drill bit, comprising: a matrix bit body having a reinforcing
overlay thereon and having at least one blade thereon; at least one
cutter pocket disposed on the at least one blade; at least one
cutter disposed in the at least one cutter pocket; and a braze
material disposed between the at least one cutter and the at least
one cutter pocket, wherein the reinforcing overlay comprises
carbide particles and at least one binder and has a hardness
greater than about 50 KRc.
13. (canceled)
14. The drill bit of claim 12, wherein the reinforcing overlay has
a hardness ranging from about 50 to 75 HRc.
15. The drill bit of claim 12, wherein the matrix bit body has a
hardness ranging from about 38 to 45 HRc.
16. The drill bit of claim 12, wherein the reinforcing overlay has
a thickness ranging from about 0.010 to 0.125 inches.
17. The drill bit of claim 12, wherein the matrix bit body
comprises a matrix of tungsten carbide particles and a second
binder.
18. The drill bit of claim 17, wherein the second binder comprises
at least one of nickel, cobalt, iron, and copper.
19. The drill bit of claim 17, wherein the second binder comprises
about 30 to 40 volume percent of the matrix bit body.
20. A method of forming a drill bit, comprising: forming a matrix
bit body having at least one blade thereon, wherein the at least
one blade has at least one cutter pocket disposed thereon; applying
a reinforcing overlay to the formed matrix bit body; and brazing at
least one cutter in the at least one cutter pocket with a braze
material.
21. The method of claim 20, wherein forming the matrix bit body
comprises infiltrating a mold filled with carbide particles with a
first binder.
22. The method of claim 20, wherein forming the matrix bit body
comprises hot-pressing carbide particles with a first binder.
23. The method of claim 20, wherein applying the reinforcing
overlay comprises using at least one of a spray-and-fuse, d-gun,
HVOF, and high velocity cold spray.
24. The method of claim 20, wherein the reinforcing overlay
comprises carbide particLes and a second binder selected from at
least one of nickel and cobalt.
25. The method of claim 20, wherein the reinforcing overlay has a
melting point greater than a melting point of the braze
material.
26. The method of claim 20, wherein the forming the matrix bit body
and applying the reinforcing overlay occur simultaneously.
27. The method of claim 20, wherein the applying the reinforcing
overlay occurs prior to the brazing the at least one cutter.
28. The method of claim 20, wherein the applying the reinforcing
overlay occurs after the brazing at least one cutter.
Description
BACKGROUND OF INVENTION
[0001] 1. Field of the Invention
[0002] Embodiments disclosed herein relate generally to PDC bit
bodies. In particular, embodiments disclosed herein relate
generally to PDC matrix bit bodies having a reinforcing overlay
disposed thereon.
[0003] 2. Background Art
[0004] Polycrystalline diamond compact ("PDC") cutters are known in
the art for use in earth-boring drill bits. Typically, bits using
PDC cutters include an integral bit body which may be made of steel
or fabricated from a hard matrix material such as tungsten carbide
(WC). A plurality of PDC cutters is mounted along the exterior face
of the bit body in extensions of the bit body called "blades." Each
PDC cutter has a portion which typically is brazed in a recess or
pocket formed in the blade on the exterior face of the bit
body.
[0005] The PDC cutters are positioned along the leading edges of
the bit body blades so that as the bit body is rotated, the PDC
cutters engage and drill the earth formation. In use, high forces
may be exerted on the PDC cutters, particularly in the
forward-to-rear direction. Additionally, the bit and the PDC
cutters may be subjected to substantial abrasive forces. In some
instances, impact, vibration, and erosive forces have caused drill
bit failure due to loss of one or more cutters, or due to breakage
of the blades.
[0006] As mentioned above, when designing a PDC bit, the bit body
may be selected from a steel bit body and a matrix bit body. While
steel body bits may have toughness and ductility properties which
make them resistant to cracking and failure due to impact forces
generated during drilling, steel is more susceptible to erosive
wear caused by high-velocity drilling fluids and formation fluids
which carry abrasive particles, such as sand, rock cuttings, and
the like. Thus, steel body PDC bits are generally coated with a
more erosion-resistant material, such as tungsten carbide, to
improve their erosion resistance.
[0007] Typically, a hardfacing material is applied, such as by arc
or gas welding, to the exterior surface of the drill bit to protect
the bit against erosion and abrasion, such as by techniques
described U.S. Pat. No. 6,601,475, which is herein incorporated by
reference in its entirety. Hardfacing is typically applied to the
bit prior to brazing of the cutters to the to the bit body. The
hardfacing material typically includes one or more metal carbides,
which are bonded to the steel body by a metal alloy ("binder
alloy"), which is typically a steel alloy. In effect, the carbide
particles are suspended in a matrix of steel forming a layer on the
surface of the steel substrate. The carbide particles give the
hardfacing material hardness and wear resistance, while the matrix
metal provides fracture toughness to the hardfacing. Some typical
methods of application of hardfacing include various welding
techniques, high velocity cold spray methods, plasma spray and
other thermal spray techniques. As improvements in hardfacing
materials and application techniques have been made, hardfacing
materials used on steel bit bodies generally exhibit better erosion
and abrasion resistance than the matrix material used in matrix bit
bodies. Hardfacing materials have also been applied in localized
regions of a bit body, such as, for example, in the area
surrounding the cutter pocket described in U.S. Pat. No. 6,772,849,
which is herein incorporated by reference in its entirety.
[0008] In current bit design practices, over seventy five percent
of PDC bits are made from matrix bit bodies, mainly because a
matrix bit body offers superior erosion resistance as compared to
hardfaced steel bodies. With the advent of improved hardfacing
materials, the hardfacing materials used on steel bit bodies
exhibit better erosion and abrasion resistance as compared to the
matrix material itself. However, one of the primary issues
concerning hardfacing of steel body bits is the bonding and
coverage of the hardfacing material in between pockets and the base
of the pockets. During drilling, fluids seep under the hardfacing
and erode the steel body. In some instances, because of poor
bonding and lack of support, hardfacing material chips off from the
surfaces exposing the steel. Thus, difficulties in obtaining good
and uniform coverage of the bit body are readily apparent and
result in significant erosion of the material, especially in the
area surrounding the cutters and cutter pockets.
[0009] Further, many hardfacing materials used are relatively hard
and brittle. During use of hardfaced bits, a thin coating of the
erosion-resistant material may crack, peel off or wear, exposing
the softer steel body which is then rapidly eroded. This can lead
to loss of PDC cutters as the area around the cutter is eroded
away, causing the bit to fail. Due to the high failure rates caused
by the undercutting of the steel body and poor coverage of
hardfacing near and between the cutter pockets, a typical steel
body bit generally achieve only 1-2 runs per bit.
[0010] The matrix bit body generally is formed by packing a
graphite mold with tungsten carbide powder and then infiltrating
the powder with a molten copper-based alloy binder. For example,
macrocrystalline tungsten carbide and cast tungsten carbide have
been used to fabricate bit bodies. Macrocrystalline tungsten
carbide is essentially stoichiometric WC which is, for the most
part, in the form of single crystals. Some large crystals of
macro-crystalline WC are bi-crystals. Carburized tungsten carbide
has a multi-crystalline structure, i.e., they are composed of WC
agglomerates. 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 W.sub.2C, 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.
[0011] A third 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 for use in
hardfacing.
[0012] 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.
[0013] In designing matrix bit bodies, there is often a compromise
between achieving good wear resistance/hardness and toughness
because wear resistance/hardness and toughness tend to be inversely
related. Efforts to enhance one property usually result in a
trade-off of the other. Thus, it is difficult to achieve both good
wear resistance (especially erosion resistance) in demanding
applications while maintaining adequate toughness. To provide
adequate toughness for many applications, erosion of the matrix bit
body will generally minimize the life of a matrix bit body to 1-3
runs per bit by reducing the capability to rebuild the bit.
Additionally, another issue surrounding the use of matrix bit
bodies involves cracking of the bit body that can result from the
multiple heat cycles that a bit must undergo during brazing.
Furthermore, hardfacing materials which have been conventionally
applied to steel bit bodies to improve wear/erosion resistance have
never been extended to matrix bit bodies because the difference in
the substrate material, i.e., matrix material, has always been
thought to prevent adhesion/bonding of the hardfacing materials to
the matrix body substrate.
[0014] Accordingly, there exists a need for a new matrix body which
has high strength and toughness, resulting in improved ability to
retain blades and cutters, while maintaining other desired
properties such as wear and erosion resistance.
SUMMARY OF INVENTION
[0015] In one aspect, embodiments disclosed herein relate to a
drill bit that includes a matrix bit body having a reinforcing
overlay thereon and having at least one blade thereon; at least one
cutter pocket disposed on the at least one blade; at least one
cutter disposed in the at least one cutter pocket; and a braze
material disposed between the at least one cutter and the at least
one cutter pocket, wherein the reinforcing overlay comprises
carbide particles and at least one binder and has a melting point
greater than a melting point of the braze material.
[0016] In another aspect, embodiments disclosed herein relate to a
drill bit that includes a matrix bit body having a reinforcing
overlay thereon and having at least one blade thereon; at least one
cutter pocket disposed on the at least one blade; at least one
cutter disposed in the at least one cutter pocket; and a braze
material disposed between the at least one cutter and the at least
one cutter pocket, wherein the reinforcing overlay comprises
carbide particles and at least one binder and has a hardness
greater than about 50 HRc.
[0017] In yet another aspect, embodiments disclosed herein relate
to a method of forming a drill bit that includes forming a matrix
bit body having at least one blade thereon, wherein the at least
one blade has at least one cutter pocket disposed thereon; applying
a reinforcing overlay to the formed matrix bit body; and brazing at
least one cutter in the at least one cutter pocket with a braze
material.
[0018] Other aspects and advantages of the invention will be
apparent from the following description and the appended
claims.
BRIEF DESCRIPTION OF DRAWINGS
[0019] FIG. 1 is an illustration of a PDC drill bit.
DETAILED DESCRIPTION
[0020] In one aspect, embodiments disclosed herein relate to a
matrix bit body for a fixed cutter or PDC drill bit having a
reinforcing overlay disposed thereon. Referring to FIG. 1, a fixed
cutter drill bit 10 has a matrix bit body 12 on which a reinforcing
overlay may be disposed (not shown). The lower face of the bit body
12 is formed with a plurality of blades 14, which extend generally
outwardly away from a central longitudinal axis of rotation 16 of
the drill bit. A plurality of PDC cutters 18 are disposed side by
side along the length of each blade. The number of PDC cutters 18
carried by each blade may vary. The PDC cutters 18 are individually
brazed to a stud-like carrier (or substrate), which may be formed
from tungsten carbide, and are received and secured (brazed) within
sockets in the respective blade.
[0021] Matrix Bit Bodies
[0022] As described above, a matrix bit body may include tungsten
carbide particles may be surrounded by a metallic binder. The
matrix bit body may be formed, for example, by packing a graphite
mold with tungsten carbide powder and then infiltrating the powder
with a molten binder. Among the types of tungsten carbide particles
used in the fabrication of the bit body, those generally used
include, for example, macrocrystalline tungsten carbide, cast
tungsten carbide, carburized tungsten carbide, and cemented or
sintered tungsten carbide.
[0023] In an infiltrated bit body, the metallic binder surrounding
the tungsten carbide particles may be formed from a metallic binder
powder and an infiltration binder. The metallic binder powder may
be pre-blended with the matrix powder hard carbide particles, which
is then 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. Suitable metals include all transition
metals, main group metals and alloys thereof. 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 embodiment,
the infiltration binder is selected from at least one of nickel,
copper, and alloys thereof. In another embodiment, the infiltration
binder includes a Cu--Mn--Ni--Zn alloy. Such matrix bit bodies may
have, for example, a hardness ranging from 38-45 HRc, a fracture
toughness of at least 20 ksi(in.sup.0.5), and a transverse rupture
strength of at least 120 ksi in one embodiment and ranging from
about 130 to 180 in another embodiment.
[0024] In one embodiment, the matrix powder comprises a mixture of
tungsten carbides and a metallic binder powder. In a particular
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
15% may yield higher matrix strength and toughness, as well as
higher braze strength.
[0025] The matrix powder mixture may include 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.
[0026] The amount of the metallic binder and carbide hard particles
in forming the matrix body may range, in one embodiment, in a ratio
of from 30:70 to 40:60 by volume (binder:carbide). In other
embodiments, the total carbide may be used in an amount less than
60% by volume or greater than 70% by volume of the matrix body,
such matrix bodies may also not possess the desired physical
properties to yield optimal performance.
[0027] While reference has been made to forming the matrix bit
bodies disclosed herein by an infiltration process, no limitation
is intended by such description. Rather, it is specifically within
the scope of the present invention that a matrix bit body formed by
any technique, including for example hot pressing or casting, as
described in U.S. Patent Publication No. 2005/0247491, which is
herein incorporated by reference in its entirety, may be used in
conjunction with the reinforcing overlays disclosed herein.
[0028] Reinforcing Overlay
[0029] The reinforcing overlay that may be disposed on the matrix
bit body according to various embodiments disclosed herein may
include particles of tungsten carbide or other wear resistant
particles (e.g., borides, nitrides, carbides or mixtures thereof)
bonded to the matrix bit body by a metal alloy, which is also
generally referred to as a binder alloy. In effect, the carbide
particles are suspended in a matrix of metal forming a layer on the
surface. The wear resistant particles give the reinforcing overlay
hardness and wear resistance, while the matrix metal (or alloy)
provides fracture toughness to the reinforcing overlay and
contributes to the bonding between the reinforcing overlay and the
matrix bit body.
[0030] Various types of tungsten carbide may be used in the
reinforcing overlay, including cast tungsten carbide,
macro-crystalline tungsten carbide, cemented tungsten carbide, and
carburized tungsten carbide. One of ordinary skill in the art would
recognize that the types, sizes, percentages of the various carbide
particles may be varied depending on the properties desired in the
reinforcing overlay for a particular application. In various
embodiments, carbide combinations suitable for use in the
reinforcing overlay disclosed herein may include those combinations
described in U.S. Pat. Nos. 4,836,307, 5,791,422, 5,921,330, and
6,659,206, which are herein incorporated by reference in their
entirety.
[0031] In one embodiment, the carbide content in the reinforcing
overlay may vary from about 40 to 80 weight percent, with a binder
alloy constituting the balance of the reinforcing overlay. Binder
alloys that may be used in various embodiments disclosed herein may
include Ni and Co. In other embodiments, the binder alloy may
include Group VIII metals such as Co, Ni, Fe, alloys thereof, or
mixtures thereof. By applying a reinforcing overlay comprised of a
binder alloy, such as Ni- or Co-based alloys, to a matrix bit body
having a composition as disclosed herein, with the present
inventors have advantageously discovered that the combination of
the particular binder and matrix body composition provides adequate
adhesion/bonding of the reinforcing overlay to the matrix
substrate. As shown in Table 1 below, various examples of
reinforcing overlays suitable for use in the present disclosure are
listed.
TABLE-US-00001 Method of Melting or Fusion Coating Composition
Application Hardness (HRc) Point Deloro Stellite 50 WC/NiCrFeSiBC
Spray fused/laser 49 52 M: ~1063.degree. C. cladded D-Gun 2040
WC/CoC Super D-Gun 64 69 -- Colmonoy 750 WC/NiWCrCoSiFeB Flame
sprayed/laser 58 63 F: ~1060.degree. C. cladded GHF5 WC/CoCrNiBSi
Flame sprayed/oxy- 63 70 -- acetylene welded Praxair LW-1N30 WC/Co
D-Gun 70 72 --
[0032] Many factors affect the durability of the reinforcing
overlay in a particular application. These factors include the
chemical composition and physical structure (size, shape, and
particle size distribution) 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. While higher proportions of the
wear-resistant particles will increase the wear resistance of the
reinforcing overlay, unfortunately it decreases the fracture
toughness of the hardfacing overlay and weakens the bonding between
the reinforcing overlay and the underlying matrix body.
[0033] In one embodiment, the reinforcing overlay may have a
hardness greater than that of the matrix bit body on which it is
disposed. In other embodiments, the reinforcing overlay has a
hardness of greater than about 50 HRc; from about 50 to 75 HRc in
another embodiment; and greater than about 60, 65, and 70 HRc in
various other embodiments. In another embodiment, the reinforcing
overlay may have a strength greater than the strength of the matrix
bit body on which the reinforcing overlay is disposed.
[0034] In some embodiments, the melting point of the reinforcing
overlay may be selected in accordance with a particular process of
manufacturing the matrix bit body having a reinforcing overlay
thereon. That is, the melting point of the reinforcing overlay may
be selected to be greater than that of the braze material used to
secure the PDC cutting element to the matrix bit body if the
reinforcing overlay is applied prior to brazing the cutting
elements to the bit body, and conversely, less than the melting
point of braze material if the reinforcing overlay is applied
subsequent to the brazing of the cutting elements to the bit body.
In a particular embodiment, the reinforcing overlay has a melting
point greater than that of the braze material used to secure the
PDC cutters to the matrix bit body. In another particular
embodiment, the reinforcing overlay has a melting point greater
than about 1000.degree. C. In yet another particular embodiment,
the reinforcing overlay has a melting point ranging from about 1050
to 1400.degree. C.
[0035] The reinforcing overlay may be disposed on substantially all
surfaces of the matrix bit body. The thickness of the reinforcing
overlay may range from about 0.01 to 0.125 inches in one
embodiment. One of skill in the art would recognize the thickness
need not be uniform across all surfaces of the matrix bit body;
rather, it is within the scope of the present invention that the
thickness may be varied to optimize performance.
[0036] Additionally, while the described embodiments make reference
to a single reinforcing overlay, no limitation is intended on the
scope of the invention by such a description. In fact, during
application of the reinforcing overlay, multiple layers of a
reinforcing overlay may be applied to the bit body. If multiple
layers of a reinforcing overlay are provided, one of ordinary skill
in the art would recognize that compositions and resulting
properties may be varied across the multiple layers to promote
bonding and adhesion of the reinforcing overlay to the matrix body
substrate.
[0037] Application of Reinforcing Overlay
[0038] The reinforcing overlay disclosed herein may be applied to
the matrix bit body by using one of several various spraying
techniques. In various particular embodiments, the reinforcing
overlay may be applied by one of a d-gun, spray-and-fuse, or high
velocity cold spray technique.
[0039] D-gun (detonation gun) coatings, such as, for example, those
described in U.S. Pat. No. 5,535,838, which is herein incorporated
by reference in its entirety, include those coatings applied by the
use of a d-gun. The d-gun process includes gases, usually
consisting of oxygen and a fuel gas mixture, that are fed into a
barrel of the gun along with a charge of fine tungsten
carbide-based powder. The gases and the resulting detonation wave
heat and accelerate the powder as it moves down the barrel. The
powder is entrained for a sufficient distance for it to be
accelerated to a high velocity and for virtually all of the powder
to become molten. A pulse of inert nitrogen gas is used to purge
the barrel after each detonation. The process may be repeated many
times per second. Each detonation results in the deposition of a
coating material, a few microns thick on the surface of the matrix
bit body. Additionally, although most coating materials are heated
to temperatures well beyond their melting points, substrate
temperatures generally remain very low. Thus, in various
embodiments, a reinforcing overlay applied by a d-gun process may
be applied either prior to or subsequent to brazing of the cutting
elements to the bit body.
[0040] The high velocity cold spray, such as that described in U.S.
Pat. No. 6,780,458, which is herein incorporated by reference in
its entirety, involves a kinetic spray process that uses supersonic
jets of compressed gas to accelerate near-room temperature powder
particles at ultra high velocities. The unmelted particles,
traveling at speeds between 500 to 1,500 m/sec plastically deform
and consolidate on impact with their substrate to create a coating.
The basis of the cold spray process is the gas-dynamic acceleration
of particulates to supersonic velocities (500-1500 m/sec), and
hence high kinetic energies, so that solid-state plastic
deformation and fusion occur on impact to produce dense coatings
without the feedstock material being significantly heated.
[0041] The spray-and-fuse process is a two-step process in which a
powdered coating material is deposited by using either a combustion
gun or plasma spray gun, and subsequently fused to the matrix body
substrate using either a heating torch or a furnace, for example,
to temperatures ranging from 700-1200.degree. C. depending on the
melting point of the overlay material. The coatings are usually
made of nickel or cobalt self-fluxing alloys to which hard
particles, such as tungsten carbide, may be added for increased
wear resistance. A reinforcing overlay having the desired thickness
may be formed by building up several layers at a rate of 0.005 to
0.030 inches per pass. Deposit thickness is controlled by the
traverse speed of rotation (when done between centers on
cylindrical parts), powder flow, and the number of layers
applied.
[0042] Among other typical thermal spray process that may be used
are high velocity oxy-fuel spraying (HVOF), high velocity air fuel
spraying (HVAF), flame spray, plasma spray or other applicable
process as known by one of ordinary skill in the art.
[0043] Among the welding techniques that may be used are an
oxyacetylene welding process (OXY), plasma transferred arc (PTA),
an atomic hydrogen welding (ATW), welding via tungsten inert gas
(TIG), gas tungsten arc welding (GTAW) or other applicable
processes as known by one of ordinary skill in the art.
[0044] While above embodiments make reference to tungsten carbide
particles, no limitation is intended on the scope of the invention
by such a description. It is specifically within the scope of the
present invention that other "hard materials" such as metal oxides,
metal nitrides, metal borides, other metal carbides, and alloys
thereof may be used.
[0045] Advantageously, embodiments disclosed herein provides for a
fixed cutter drill bit that may simultaneously achieve the
inversely related properties of toughness and wear/erosion
resistance. A matrix bit body that includes a reinforcing overlay
disclosed herein may possess the benefits of a tough core,
providing resistance to cracking, and a superior wear resistant
surface. Furthermore, it is generally necessitated that
conventional matrix body bits are designed by balancing toughness
and wear/erosion resistance; however, the bits disclosed herein may
allow for a matrix bit body having improved transverse strength and
toughness with aggressive blade design, without the concern of
blade failure by erosion or wear. The combination of the tough core
and superior wear/erosion resistant exterior may allow faster rate
of penetration, superior cutting element retention strength and
durability due to the protected cutter surface by preventing
erosion of the braze alloy and other areas surrounding the cutters,
improved bit life due to minimal erosion of the bit body, and
rebuildability of the bit.
[0046] While the invention has been described with respect to a
limited number of embodiments, those skilled in the art, having
benefit of this disclosure, will appreciate that other embodiments
can be devised which do not depart from the scope of the invention
as disclosed herein. Accordingly, the scope of the invention should
be limited only by the attached claims.
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