U.S. patent application number 10/928914 was filed with the patent office on 2005-10-20 for coated diamonds for use in impregnated diamond bits.
This patent application is currently assigned to Smith International, Inc.. Invention is credited to Beaton, Timothy P., Oldham, Thomas W..
Application Number | 20050230150 10/928914 |
Document ID | / |
Family ID | 34119177 |
Filed Date | 2005-10-20 |
United States Patent
Application |
20050230150 |
Kind Code |
A1 |
Oldham, Thomas W. ; et
al. |
October 20, 2005 |
Coated diamonds for use in impregnated diamond bits
Abstract
An insert for an impreg bit that includes coated diamond
particles disposed in a matrix material, wherein the coated diamond
particles include a boride, a nitride, and a carbide of a group
IVA, VA, VI transition metal or silicon disposed on synthetic,
natural, TSP diamonds, or combinations thereof is disclosed. A
method of forming a diamond-impregnated insert, including coating a
plurality of diamond particles with a coating formed from a boride,
a nitride, and a carbide of a group IVA, VA, VI transition metal or
silicon or mixtures thereof, and forming a diamond impregnated
insert body is also disclosed.
Inventors: |
Oldham, Thomas W.; (The
Woodlands, TX) ; Beaton, Timothy P.; (The Woodlands,
TX) |
Correspondence
Address: |
OSHA & MAY L.L.P.
Suite 2800
1221 McKinney
Houston
TX
77010
US
|
Assignee: |
Smith International, Inc.
Houston
TX
|
Family ID: |
34119177 |
Appl. No.: |
10/928914 |
Filed: |
August 26, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60498543 |
Aug 28, 2003 |
|
|
|
Current U.S.
Class: |
175/57 ;
175/434 |
Current CPC
Class: |
C22C 2001/1073 20130101;
E21B 10/56 20130101; B24D 18/0054 20130101; C22C 2026/005 20130101;
B22F 2005/001 20130101; C22C 1/1068 20130101; C22C 26/00
20130101 |
Class at
Publication: |
175/057 ;
175/434 |
International
Class: |
E21B 010/36 |
Claims
What is claimed is:
1. An insert for a impreg drill bit comprising: coated diamond
particles disposed in a matrix material, wherein the coated diamond
particles comprise at least one compound selected from a boride, a
nitride, and a carbide of a group IVA, VA, VI transition metal or
silicon disposed on synthetic, natural, TSP diamonds, or
combinations thereof.
2. The insert of claim 1, wherein the coated diamond particles are
coated prior to formation of the insert.
3. The insert of claim 1, wherein the matrix material comprises at
least one material selected from tungsten carbide, tungsten alloy,
tungsten carbide in combination with elemental tungsten, tungsten
alloy in combination with elemental tungsten, titanium-based
compounds, and nitrides.
4. The insert of claim 1, wherein the diamonds are coated with at
least one of titanium carbide and silicon carbide.
5. An impreg drill bit comprising: a bit body; and a plurality of
ribs formed in the bit body and at least in part from a matrix
material infiltrated with a binder alloy, the ribs being
infiltrated with a plurality of abrasive particles, at least a
portion of the abrasive particles being coated diamond particles,
wherein the coated diamond particles comprise at least one compound
selected from a boride, a nitride, and a carbide of a group IVA,
VA, VI transition metal or silicon disposed on synthetic, natural,
TSP diamonds, or combinations thereof.
6. The drill bit of claim 5, wherein the bit body comprises said
coated diamond particles.
7. An impreg drill bit, comprising: a bit body; and a plurality of
inserts affixed to said bit body, at least one of said plurality of
inserts comprising coated diamond particles disposed in a matrix
material, wherein the coated diamond particles comprise at least
one compound selected from a boride, a nitride, and a carbide of a
group IVA, VA, VI transition metal or silicon disposed on
synthetic, natural, TSP diamonds, or combinations thereof.
8. The drill bit of claim 7, wherein the bit body comprises said
coated diamond particles.
9. A method of forming a diamond-impregnated insert, comprising:
coating a plurality of diamond particles with a coating comprising
at least one compound selected from a boride, a nitride, and a
carbide of a group IVA, VA, VI transition metal or silicon; and
forming a diamond impregnated insert body using the coated diamond
particles and a matrix material.
10. The method of claim 9, wherein the forming the diamond
impregnated insert body uses a mold having at least one hole, and
at least one upper plunger.
11. The method of claim 10, wherein the matrix material is selected
from tungsten carbide, tungsten alloy, tungsten carbide in
combination with elemental tungsten, tungsten alloy in combination
with elemental tungsten, titanium-based compounds, and
nitrides.
12. The method of claim 11, wherein the forming the diamond
impregnated insert body is performed at a temperature of at least
1500.degree. F. and at greatest 2200.degree. F.
13. The method of claim 12, wherein the forming the diamond
impregnated insert body is performed at a temperature of at least
1800.degree. F. and at greatest 2100.degree. F.
14. The method of claim 9, wherein the diamond impregnated insert
body is formed using a high pressure, high temperature process.
15. The method of claim 9, wherein the diamond impregnated insert
body is formed using hot isostatic pressing.
16. A method of forming a diamond-impregnated bit, comprising:
coating a plurality of diamond particles with a coating comprising
at least one compound selected from a boride, a nitride, and a
carbide of a group IVA, VA, VI transition metal or silicon; and
forming a diamond impregnated bit using the coated diamond
particles and a matrix material.
17. The method of claim 16, wherein at least one
diamond-impregnated insert is affixed to a bit body.
18. The method of claim 16, wherein the forming the diamond
impregnated insert uses a mold having at least one hole, and at
least one upper plunger.
19. The method of claim 16, wherein the matrix material is selected
from tungsten carbide, tungsten alloy, tungsten carbide in
combination with elemental tungsten, tungsten alloy in combination
with an elemental tungsten, titanium-based compounds, and
nitrides.
20. The method of claim 16, wherein the forming the diamond
impregnated insert bit is performed at a temperature of at least
1500.degree. F. and at greatest 2200.degree. F.
21. The method of claim 16, wherein the forming the diamond
impregnated insert bit is performed at a temperature of at least
1800.degree. F. and at greatest 2100.degree. F.
22. A method of drilling a formation comprising: contacting an
impreg bit with the formation, wherein the impreg bit comprises a
bit body; and a plurality of inserts affixed to said bit body, at
least one of said plurality of inserts comprising coated diamond
particles disposed in a matrix material, wherein the coated diamond
particles comprise at least one selected from a boride, a nitride,
and a carbide of a group IVA, VA, VI transition metal or silicon
disposed on synthetic, natural, TSP diamonds, or combinations
thereof.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority under 35 U.S.C. .sctn.119
to U.S. Provisional Application Ser. No. 60/498,543, filed Aug. 28,
2003. This provisional application is hereby incorporated by
reference in its entirety.
BACKGROUND OF INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to drill bits used
in the oil and gas industry and more particularly, to drill bits
having diamond-impregnated cutting surfaces. Still more
particularly, the present invention relates to drag bits in which
the diamond particles imbedded in the cutting surface have a
coating to improve diamond bonding and/or reduce diamond
degradation.
[0004] 2. Background Art
[0005] In the drilling industry, it is well known that different
types of bits work more efficiently with different formations.
Rotary drill bits with no moving elements on them, referred to as
"drag" bits, may be used to drill very hard or soft formations
depending on the type of drag bit. Drag bits include bits having
cutting elements attached to the bit body, such as polycrystalline
diamond compact insert bits, and those including abrasive material,
such as diamond, impregnated into the bit body material that
engages the formation. The latter bits are commonly referred to as
"impreg" bits.
[0006] An example of a prior art diamond impregnated drill bit is
shown in FIG. 1. The drill bit 10 includes a bit body 12 and a
plurality of ribs 14 that are formed in the bit body 12. The ribs
14 are separated by channels 16 that enable drilling fluid to flow
between and both clean and cool the ribs 14. The ribs 14 are
typically arranged in groups 20 where a gap 18 between groups 20 is
typically formed by removing or omitting at least a portion of a
rib 14. The gaps 18, which may be referred to as "fluid courses,"
are positioned to provide additional flow channels for drilling
fluid and to provide a passage for formation cuttings to travel
past the drill bit 10 toward the surface of a wellbore (not
shown).
[0007] Diamond impregnated drill bits are particularly well suited
for drilling very hard and abrasive formations. The presence of
abrasive particles both at and below the surface of the matrix body
material ensures that the bit will substantially maintain its
ability to drill a hole even after the surface particles are worn
down.
[0008] During abrasive drilling with a diamond-impregnated cutting
structure, the diamond particles scour or abrade away the rock. As
the matrix material around the diamond crystals is worn away, the
diamonds at the surface eventually fall out and other diamond
particles are exposed.
[0009] Impreg bits are typically made from a solid body of matrix
material formed by any one of a number of powder metallurgy
processes known in the art. During the powder metallurgy process,
abrasive particles and a matrix powder are infiltrated with a
molten binder material. Upon cooling, the bit body includes the
binder material, matrix material, and the abrasive particles
suspended both near and on the surface of the drill bit. The
abrasive particles typically include small particles of natural or
synthetic diamond. Synthetic diamond used in diamond impregnated
drill bits is typically in the form of single crystals. However,
thermally stable polycrystalline diamond (TSP) particles may also
be used.
[0010] In a typical impreg bit forming process, the shank of the
bit is supported in its proper position in the mold cavity along
with any other necessary formers, e.g. those used to form holes to
receive fluid nozzles. The remainder of the cavity is filled with a
charge of tungsten carbide powder. Finally, a binder, and more
specifically an infiltrant, typically a nickel brass copper based
alloy, is placed on top of the charge of powder. The mold is then
heated sufficiently to melt the infiltrant and held at an elevated
temperature for a sufficient period to allow it to flow into and
bind the powder matrix or matrix and segments. For example, the bit
body may be held at an elevated temperature (>1800.degree. F.)
for a period on the order of 0.75 to 2.5 hours, depending on the
size of the bit body, during the infiltration process.
[0011] By this process, a monolithic bit body that incorporates the
desired components is formed. It has been found, however, that the
life of both natural and synthetic diamond is shortened by the
lifetime thermal exposure experienced in the furnace during the
infiltration process. Accordingly, it is desired to provide a
technique for manufacturing bits that includes imbedded diamonds
that have not suffered the thermal exposure normally associated
with the manufacture of such bits. Furthermore, it is desirable to
provide a bit that includes diamond particles in its primary or
leading cutting structures without subjecting the diamond particles
to undue thermal stress or thermal exposure. Such a bit structure
is disclosed in U.S. Pat. No. 6,394,202 (the '202 patent), which is
assigned to the assignee of the present invention and is hereby
incorporated by reference.
[0012] Referring now to FIG. 2, a drill bit 20 in accordance with
the '202 patent comprises a shank 24 and a crown 26. Shank 24 is
typically formed of steel and includes a threaded pin 28 for
attachment to a drill string. Crown 26 has a cutting face 22 and
outer side surface 30. According to one embodiment, crown 26 is
formed by infiltrating a mass of tungsten-carbide powder
impregnated with synthetic or natural diamond, as described
above.
[0013] Crown 26 may include various surface features, such as
raised ridges 27. Preferably, formers are included during the
manufacturing process so that the infiltrated, diamond-impregnated
crown includes a plurality of holes or sockets 29 that are sized
and shaped to receive a corresponding plurality of
diamond-impregnated inserts 10. Once crown 26 is formed, inserts 10
are mounted in the sockets 29 and affixed by any suitable method,
such as brazing, adhesive, mechanical means such as interference
fit, or the like. As shown in FIG. 2, the sockets can each be
substantially perpendicular to the surface of the crown.
Alternatively, and as shown in FIG. 2, holes 29 can be inclined
with respect to the surface of the crown 26. In this embodiment,
the sockets are inclined such that inserts 10 are oriented
substantially in the direction of rotation of the bit, so as to
enhance cutting.
[0014] As a result of the manufacturing technique of the '202
patent, each diamond-impregnated insert is subjected to a total
thermal exposure that is significantly reduced as compared to
previously known techniques for manufacturing infiltrated
diamond-impregnated bits. For example, diamonds imbedded according
to methods disclosed in the '202 patent have a total thermal
exposure of less than 40 minutes, and more typically less than 20
minutes (and more generally about 5 minutes), above 1500.degree. F.
This limited thermal exposure is due to the shortened hot pressing
period and the use of the brazing process.
[0015] The total thermal exposure of methods disclosed in the '202
patent compares very favorably with the total thermal exposure of
at least about 45 minutes, and more typically about 60-120 minutes,
at temperatures above 1500.degree. F., that occurs in conventional
manufacturing of furnace-infiltrated, diamond-impregnated bits. If
diamond-impregnated inserts are affixed to the bit body by adhesive
or by mechanical means such as interference fit, the total thermal
exposure of the diamonds is even less.
[0016] Thermal degradation is only one mechanism for bit failure in
drag bits. The diamonds are also subjected to a number of different
forces that may cause the diamonds to be lost from the bit.
Typically, diamonds are retained merely by mechanical locking in
the matrix, because the diamonds cannot be wetted by the matrix
material. As such, the diamonds can be forcibly dislodged from the
matrix, through the action of the various forces and/or fluids
flowing around the bit. One solution, therefore, to increasing bit
life is to increase the amount of force required to dislodge the
impregnated diamonds from the bit.
SUMMARY OF INVENTION
[0017] In one aspect, the present invention relates to an insert
for a drill that includes coated diamond particles disposed in a
matrix material, wherein the coated diamond particles comprise a
boride, nitride, or carbide of a group IVA, VA, or VI transition
metal disposed on synthetic, natural, TSP diamonds, or combinations
thereof.
[0018] In one aspect, the present invention relates to a drill bit
that includes a bit body, and a plurality of ribs formed in the bit
body and at least in part from a matrix material infiltrated with a
binder alloy, the ribs being infiltrated with a plurality of
abrasive particles, at least a portion of the abrasive particles
being coated diamond particles, wherein the coated diamond
particles comprise a boride, nitride, or carbide of a group IVA,
VA, or VI transition metal disposed on synthetic, natural, TSP
diamonds, or combinations thereof.
[0019] In one aspect, the present invention relates to a method of
forming a diamond-impregnated insert, including coating a plurality
of diamond particles with a coating comprising a boride, nitride,
or carbide of a group IVA, VA, VI transition metal, or mixtures
thereof, and forming a diamond impregnated insert body.
[0020] Other aspects and advantages of the invention will be
apparent from the following description and the appended
claims.
BRIEF DESCRIPTION OF DRAWINGS
[0021] FIG. 1 shows a prior art impreg bit;
[0022] FIG. 2 is a prior art perspective view of a second type of
impreg bit;
[0023] FIG. 3 shows a process for coating diamonds in accordance
with an embodiment of the present invention;
[0024] FIG. 4 shows a process for forming an insert in accordance
with an embodiment of the present invention.
DETAILED DESCRIPTION
[0025] In one aspect, the present invention relates to diamonds
that have a specialized coating for use in diamond impregnated
bits. In selected embodiments, the coating is a boride, nitride, or
carbide of a group IVA, VA, or VI transition metal (Ti, Zr, Hf, V,
Nb, Ta, Cr, Mo, W, or mixtures thereof). In particular embodiments,
the coating is a silicon carbide. Other silicon coatings may be
used as well. Further, those having ordinary skill in the art will
recognize that other coatings may be used. The present inventors
have discovered that by providing a strongly bonded wettable
coating for the diamonds, enhanced diamond bonding and/or retention
strength results, improving the performance of the impreg bit.
[0026] In one embodiment of the invention, coated diamonds 100 are
manufactured prior to the formation of the impregnated bit, as
shown for example in FIG. 3. In this embodiment, uncoated diamond
particles 90 are placed on a work surface 92. The diamond particles
can be natural, synthetic, or TSP diamonds, or a combination of
some or all of these types.
[0027] The manufacture of TSP is known in the art, but a brief
description of the process is provided herein. When formed, diamond
tables comprise individual diamond "crystals" that are
interconnected by diamond to diamond bonds. The bonded diamond
crystals thus form a lattice structure. Metal catalysts such as
cobalt are often found within the interstitial spaces in the
diamond lattice structure. Cobalt has a significantly different
coefficient of thermal expansion as compared to diamond, so upon
heating of the diamond table, the cobalt will expand, causing
cracks to form in the lattice structure, resulting in deterioration
of the diamond table. In order to obviate this problem, strong
acids are used to "leach" the cobalt from the diamond lattice
structure.
[0028] After being placed on a work surface 92, the uncoated
diamond particles 90 are treated with a coating 94. Those having
ordinary skill in the art will recognize that no limitation on the
scope of the present invention is intended by the description of
any one process. In one embodiment, chemical vapor deposition (CVD)
may be used to apply a TiC coating to diamonds. Those having
ordinary skill in the art will recognize that CVD processes are
known in the art, and the particular process used is not intended
to limit the scope of the present invention. In CVD, the coating
chemically bonds to the diamond crystals, resulting in a strong
bond between the coating and the diamond crystals. In addition, the
coating may be applied to synthetic, natural, and/or TSP diamonds,
depending on the particular application.
[0029] Those having ordinary skill in the art will recognize that a
number of other techniques may be used to apply the coating to the
diamonds, and that no limitation on the scope of the present
invention is intended by the above description. Moreover, while
this embodiment discloses using a titanium carbide coating, it is
expressly within the scope of the present invention that the
coating may be a boride, nitride, or carbide of a group IVA, VA, or
VI transition metal (Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, or mixtures
thereof). In addition, the coating may be a silicon carbide. Other
silicon coatings may be used as well. Further, those having
ordinary skill in the art will recognize that other coatings may be
used.
[0030] Next, the coated diamond particles 100 and powdered matrix
material are placed in a mold. The contents are then hot-pressed or
sintered at an appropriate temperature, preferably between about
1500 and 2200.degree. F., more preferably between about
1800.degree. F. to about 2100.degree. F., to form an insert or
coated bit body. While embodiments of the invention may be used to
manufacture an insert or an impreg bit, for clarity, the following
description is focused on the formation of an insert. One of
ordinary skill in the art would appreciate that the coated diamond
of the invention may also be used to form bit bodies using any
suitable method known in the art. Heating of the material can be by
furnace or by electric induction heating, such that the heating and
cooling rates are rapid and controlled in order to prevent damage
to the diamonds. The inserts may be heated by resistance heating in
a graphite mold. The dimensions and shapes of the inserts and of
their positioning on the bit can be varied, depending on the nature
of the formation to be drilled.
[0031] The matrix in which the coated diamonds are embedded to form
the coated diamond impregnated inserts preferably satisfies several
requirements. The matrix preferably has sufficient hardness so that
the diamonds exposed at the cutting face are not pushed into the
matrix material under the very high pressures encountered in
drilling.
[0032] In addition, the matrix preferably has sufficient abrasion
resistance so that the diamond particles are not prematurely
released. Lastly, the heating and cooling time during sintering or
hot-pressing, as well as the maximum temperature of the thermal
cycle, preferably are sufficiently low that the diamonds embedded
therein are not thermally damaged during sintering or
hot-pressing.
[0033] To satisfy these requirements, as an exemplary list, the
following materials may be used for the matrix in which the coated
diamonds are embedded: tungsten carbide (WC), tungsten alloys such
as tungsten/cobalt alloys (W--Co), and tungsten carbide or
tungsten/cobalt alloys in combination with elemental tungsten (all
with an appropriate binder phase to facilitate bonding of particles
and diamonds), and the like. Those of ordinary skill in the art
will recognize that other materials may also be used for the
matrix, including titanium-based compounds, nitrides (in particular
cubic boron nitride), etc.
[0034] It will further be understood that the concentration of
diamond in the inserts can differ from the concentration of diamond
in the bit body. It should be noted that combinations of coated and
uncoated diamonds may be used, depending on the particular
application. According to one embodiment, the concentrations of
diamond in the inserts and in the bit body are in the range of 50
to 150 (100=4.4 carat/cc). Those having ordinary skill in the art
will recognize that other concentrations of diamonds may also be
used depending on particular applications.
[0035] Initial tests of bits manufactured according to the above
process have indicated that bit performance is significantly
enhanced by the use of the coated diamonds. The reasoning behind
the improved performance is believed to result from the bonding
that occurs between the matrix material and the coating. Uncoated
diamonds do not significantly bond to the matrix material.
Application of the coating provides a surface layer on the diamonds
that is wettable and bondable to the tungsten carbide matrix and
GHI bond materials. This allows the diamonds to bond to the matrix
instead of just being held by mechanical locking. In addition, some
of the coatings are believed to retard diamond degradation that
would otherwise occur during the processing of the bit.
[0036] It will be understood that the materials commonly used for
construction of bit bodies can be used in the present invention.
Hence, in one embodiment, the bit body may itself be
diamond-impregnated. In an alternative embodiment, the bit body
comprises infiltrated tungsten carbide matrix that does not include
diamond.
[0037] In an alternative embodiment, the bit body can be made of
steel, according to techniques that are known in the art. Again,
the final bit body includes a plurality of holes having a desired
orientation, which are sized to receive and support the inserts.
The inserts, which include coated diamond particles, may be affixed
to the steel body by brazing, mechanical means, adhesive or the
like.
[0038] One suitable method of forming an insert in accordance with
the present invention is now described with reference to FIG. 4.
First, a mold, which defines dimensions of an insert, is formed
(400). The mold may be made of any suitable material known in the
art, such as graphite. In one embodiment, the mold comprises a
block having one or more holes and at least an upper and a lower
plunger for each hole (not shown). Alternatively, a series of upper
and lower plungers may be used. The upper and lower plunger are
used to define the height of the insert. Alternatively, the hole
may have a fixed bottom and only an upper plunger is required for
defining the height of the insert.
[0039] After forming the mold, powder of a suitable material, as
noted above, that includes the coated diamonds and the matrix
powder, is loaded into the holes, with the lower plungers in place
(404). Then, the upper plunger is placed into the hole, "capping"
the hole shut (408). The mold assembly may then be pre-pressed in a
press (410). Finally, the mold assembly is placed in the hot press
furnace (412) for the production of a diamond-impregnated insert
body.
[0040] Alternate methods of forming an insert may be used. For
example, a high pressure, high temperature (IPHT) process for
sintering diamond or cubic boron nitride may be used. Such a
process has been described in U.S. Pat. Nos. 5,676,496 and No.
5,598,621 and their teachings are incorporated by reference herein.
Another suitable method for hot-compacting pre-pressed
diamond/metal powder mixtures is hot isostatic pressing, which is
known in the art. See Peter E. Price and Steven P. Kohler, "Hot
Isostatic Pressing of Metal Powders", Metals Handbook, Vol. 7, pp.
419-443 (9th ed. 1984).
[0041] In another embodiment, the present invention relates to
coated diamonds for use as abrasive particles that are impregnated
into a drill bit. Typically, impreg bits are manufactured from a
base matrix material that is infiltrated with binder materials.
Examples of these infiltrated materials may be found in, for
example, U.S. Pat. No. 4,630,692 issued to Ecer and U.S. Pat. No.
5,733,664 issued to Kelley et al. These materials are advantageous
because they are highly resistant to erosive and abrasive wear, yet
are tough enough to withstand shock and stresses associated harsh
drilling conditions.
[0042] During the metallurgy process, coated diamonds, which
comprise a coating, as described above, deposited over synthetic
diamond, natural diamond, and/or TSP diamond, are added to the base
matrix material, generally along the exterior surface portion of
the ribs to form an impregnated drill bit. In certain embodiments,
the coating comprises a boride, nitride, or carbide of a group IVA,
VA, or VI transition metal, or combinations thereof. In one
specific embodiment a titanium carbide coating is used. In addition
the coating may be a silicon carbide. Other silicon coatings may be
used as well. Further, those having ordinary skill in the art will
recognize that other coatings may also be used.
[0043] In some embodiments, the coated diamond particles may be
located in limited regions proximate the bit surface. In other
embodiments, the coated diamond particles may be dispersed
throughout the bit body proximate the bit surface. In some
embodiments, the coated diamond particles may be dispersed
throughout the entire bit body.
[0044] As described above, with reference to FIG. 2, impreg bits
may include a plurality of gage protection elements disposed on the
ribs and/or the bit body. In some embodiments of the present
invention, the gage protection elements may be modified to include
coated diamonds.
[0045] By positioning coated diamond particles at and/or beneath
the surface of the ribs, the impreg bits exhibit increased
durability and are less likely to exhibit premature wear than
typical prior art impreg bits. It has been discovered that the
coated diamond particles are less likely to be sheared off or
"popped out" of the impreg bit than are uncoated diamond
particles.
[0046] Advantageously, embodiments of the present invention provide
coated diamonds that are useful in drill bit inserts or impreg
bits. In particular, embodiments of the present invention improve
the durability of impreg bits by increasing the amount of force
required to eject diamonds from the matrix. The mechanism for this
improvement is believed to result from bonding between the coating
and the surrounding matrix. In addition, the coating provides
additional thermal protection.
[0047] Further, embodiments of the present invention, by using a
coating, reduces diamond degradation. Most of the harmful
degradation occurs at the diamond surfaces, where graphitization
can occur. Surface graphitization of the diamond is what hurts
bonding. Internal degradation weakens diamond making it more
susceptible to fracture. Generally speaking, surface graphitization
is more problematic than the internal degradation. Embodiments of
the present invention are particularly suited to reduce surface
graphitization. No restriction on the scope of the invention is
intended by the above specific examples and description.
[0048] 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.
* * * * *