U.S. patent application number 10/804297 was filed with the patent office on 2004-09-09 for semiconductive polycrystalline diamond, cutting elements incorporating the same and bit bodies incorporating such cutting elements.
Invention is credited to Middlemiss, Stewart.
Application Number | 20040172885 10/804297 |
Document ID | / |
Family ID | 27734770 |
Filed Date | 2004-09-09 |
United States Patent
Application |
20040172885 |
Kind Code |
A1 |
Middlemiss, Stewart |
September 9, 2004 |
Semiconductive polycrystalline diamond, cutting elements
incorporating the same and bit bodies incorporating such cutting
elements
Abstract
An ultra-hard semiconductive polycrystalline diamond (PCD)
material formed with semiconductive diamond particles doped with
and additive, as for example, Li, Be or Al and/or insulative
diamond particles having semiconductive surfaces, tools
incorporating the same, and methods for forming the same, are
provided. The ultra-hard PCD material may be formed using a layer
of insulative diamond grit feedstock that includes additives
therein, then sintering to convert a plurality of the diamond
crystals to include a semiconductive surface. In another
embodiment, the ultra-hard PCD material is formed by sintering
semiconductive diamond grit feedstock consisting of diamond
crystals doped with an additive as for example Li, Al or Be. The
ultra-hard semiconductive PCD cutting layer exhibits increased
cuttability, especially in EDM and EDG cutting operations. A
cutting element is provided having such a PCD layer. Furthermore, a
bit is provided having a cutting element having such a PCD
layer.
Inventors: |
Middlemiss, Stewart; (Salt
Lake City, UT) |
Correspondence
Address: |
CHRISTIE, PARKER & HALE, LLP
PO BOX 7068
PASADENA
CA
91109-7068
US
|
Family ID: |
27734770 |
Appl. No.: |
10/804297 |
Filed: |
March 19, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10804297 |
Mar 19, 2004 |
|
|
|
10374373 |
Feb 25, 2003 |
|
|
|
60359630 |
Feb 26, 2002 |
|
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Current U.S.
Class: |
51/293 ; 423/446;
501/99 |
Current CPC
Class: |
C04B 35/52 20130101;
C04B 2235/405 20130101; C04B 2235/96 20130101; C04B 2235/40
20130101; C04B 2235/427 20130101; B22F 7/06 20130101; C04B 2235/402
20130101; C23C 30/005 20130101; C23C 24/08 20130101; C04B 2235/404
20130101; B22F 2005/001 20130101; C04B 2235/421 20130101 |
Class at
Publication: |
051/293 ;
501/099; 423/446 |
International
Class: |
B01J 003/06; B24D
003/00 |
Claims
What is claimed is:
1. A polycrystalline diamond material formed by sintering diamond
crystals doped with an additive at sufficient temperature and
pressure for forming polycrystalline diamond.
2. The polycrystalline diamond material as in claim 1 wherein the
additive is selected from the group of additives consisting of Be,
Li and Al.
3. The polycrystalline diamond material as in claim 1, wherein said
polycrystalline diamond material is characterized as being a
semiconductive material.
4. The polycrystalline diamond material as in claim 1, wherein said
polycrystalline diamond material is characterized as being a P-type
semiconductive material.
5. The polycrystalline diamond material as in claim 1, in which
said polycrystalline diamond material has a resistance of no
greater than 10 ohms.
6. The polycrystalline diamond material as in claim 1, wherein said
polycrystalline diamond material has a resistance being less than
10% of a corresponding resistance of a substantially similar
polycrystalline diamond material formed substantially only of Type
I diamonds.
7. The polycrystalline diamond material as in claim 1, wherein said
polycrystalline diamond material has a thermal conductivity being
about 15 times greater than a corresponding thermal conductivity of
a substantially similar polycrystalline diamond material formed
substantially only of Type I diamond crystals, at 80.degree. K.
8. The polycrystalline diamond material as in claim 1, in which
said polycrystalline diamond material is substantially void of any
metal binder material and has a resistance no greater than 1000
ohms.
9. A cutting element comprising the polycrystalline diamond
material as in claim 1, formed over a substrate.
10. A polycrystalline diamond material formed by sintering Type I
diamond crystals at sufficient temperature and pressure for forming
polycrystalline diamond, wherein after sintering a plurality of
said Type I diamond crystals comprising a semiconductive surface
layer.
11. The polycrystalline diamond material as in claim 10, in which
said polycrystalline diamond material further includes impurity
species therein, said impurity species selected from the group
consisting of Li, Be, B, and Al.
12. The polycrystalline diamond material as in claim 10, in which
said semiconductive surface layers include impurity species
therein, said impurity species selected from the group consisting
of Li, Be, B, and Al.
13. The polycrystalline diamond material as in claim 10, wherein
said polycrystalline diamond material is a P-type semiconductive
material.
14. The polycrystalline diamond material as in claim 10, wherein
said polycrystalline diamond material has a resistance no greater
than 50 ohms.
15. The polycrystalline diamond material as in claim 14, further
comprising a metal binder therein at a weight percentage no greater
than 10 percent.
16. The polycrystalline diamond material as in claim 10, wherein
said polycrystalline diamond material is substantially void of any
metal binder material and has a resistance of no greater than 1000
ohms.
17. A cutting element comprising the polycrystalline diamond
material as in claim 10, formed over a substrate.
18. A drill bit comprising a cutting element comprising a substrate
and a polycrystalline diamond layer over said substrate, said
polycrystalline diamond layer comprising Type I diamond crystals
therein, a plurality of said Type I diamond crystals comprising a
semiconductive surface layer.
19. A drill bit as in claim 18 wherein the polycrystalline diamond
is formed by sintering Type I diamond crystals at a sufficient
temperature and pressure for forming polycrystalline diamond.
20. A drill bit comprising a cutting element comprising a substrate
and a polycrystalline diamond layer over said substrate, said
polycrystalline diamond layer formed by converting diamond crystals
doped with a doping additive to polycrystalline diamond.
21. A drill bit as is claim 20 wherein the additive is selected
from the group of additives consisting of lithium, beryllium and
aluminum.
22. A drill bit as recited in claim 20 wherein the said diamond
crystals are converted to polycrystalline diamond by sintering.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional of U.S. application Ser.
No. 10/374,373 filed on Feb. 25, 2003, which is based upon and
claims priority of U.S. Provisional Patent Application No.
60/359,630, filed Feb. 26, 2002, the contents of which are herein
incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] This invention relates to polycrystalline diamond and more
specifically to semiconductive polycrystalline diamond that
exhibits enhanced cuttability, especially Electro-Discharage
Machining or Electro-Discharge Grinding cuttability. This invention
also relates to cutting elements incorporating such semiconductive
polycrystalline diamond and the bit bodies incorporating such
cutting elements.
[0003] Polycrystalline diamond (PCD) materials known in the art are
typically formed from diamond grains or crystals and a ductile
metal catalyst/binder, and are synthesized by high temperature/high
pressure ("HTHP") processes. Such PCD materials are ultra hard
materials well known for their mechanical property of high wear
resistance, making them a popular material choice for use in such
industrial applications as cutting tools for machining, and
subterranean mining and drilling, where the mechanical property of
wear resistance is highly desired. In such applications,
conventional PCD materials can be provided in the form of a surface
coating, e.g., on inserts used with cutting and drilling tools, to
improve wear resistance of the insert. Traditionally, PCD inserts
used in such applications are produced by forming one or more
layers of PCD-based material over a suitable substrate material.
Such inserts, also referred to as cutting elements, comprise a
substrate, a PCD surface layer, and optionally one or more
transition layers to improve the bonding between the exposed PCD
surface layer and the underlying substrate support layer.
Substrates used in such insert applications are commonly formed
from a carbide material such as tungsten carbide, WC, cemented with
cobalt, Co, and commonly referred to as a cemented tungsten
carbide, WC/Co system.
[0004] The layer or layers of PCD conventionally may include a
metal binder therein. The metal binder is used to facilitate
intercrystalline bonding between diamond grains, and acts to bond
the layers to each other and to the underlying substrate. The metal
binder material is generally included at a weight percentage of
about 10% by weight. Metals conventionally employed as the binder
are often selected from the group including cobalt, iron, or nickel
and/or mixtures or alloys thereof. The binder material may also
include metals such as manganese, tantalum, chromium and/or
mixtures or alloys thereof. The metal binder may be provided in
powder form as an ingredient for forming the PCD material, or can
be drawn into the PCD material from the substrate material during
the HTHP process also referred to as the "sintering" process.
[0005] The amount of binder material that is used to form PCD
materials represents a compromise between the desired material
properties of toughness and hardness/wear resistance. While a
higher metal binder content typically increases the toughness of
the resulting PCD material, higher metal content also decreases the
PCD material hardness, wear resistance and thermal stability. Thus,
these inversely affected desired properties ultimately limit the
flexibility of being able to provide PCD coatings having desired
levels of both wear resistance and toughness to meet the service
demands of particular applications. Additionally, when the PCD
composition is chosen to increase the wear resistance of the PCD
material, typically brittleness also increases, thereby reducing
the toughness of the PCD material.
[0006] In many instances, after the PCD is formed, it must be cut
to desired shapes for use in a cutting tool. Cutting is typically
accomplished using Electro-Discharge Machining (EDM) or
Electro-Discharge Grinding (EDG) operations which are well known in
the art. However, because of the insulating nature of the diamond
skeleton in conventional PCD it is essential to have a metallic
matrix material present at the cut to ensure some conductivity of
the PCD, essential to the aforementioned cutting operations. The
metal binder in the PCD forms a metallic matrix and provides
conductivity that supports EDM or EDG cutting. However, cooling
fluid or dielectric fluid used for cooling during EDM or EDG
cutting, may leach out the metal matrix from the PCD and
significantly increase the resistance of the PCD layer. Various
cooling/dielectric solutions such as Adcool.TM., and other
corrosion inhibiting solutions and/or de-ionized water may be used
during the EDM or EDG process. The electrical arcing produced
between the cutting surface and the wire in EDM operations, and the
grinding wheel in EDG operations, also causes leaching.
[0007] If the resistance of the PCD increases significantly due to
the metal matrix in the PCD leaching out, or if areas with
relatively little metal matrix are encountered, very slow or zero
cutting rates may result and breakage of the cutting wire
incorporated in the EDM process may occur. In some instances extra
metal is provided in the PCD material to overcome this problem.
Adding additional metal results in lower thermal stability of the
PCD as well as reduced material hardness and a correspondingly
reduced wear resistance.
[0008] Thus, a PCD material is desired that has enhanced EDM and
EDG cuttability without a reduction in material hardness, wear
resistance and thermal stability.
SUMMARY OF THE INVENTION
[0009] The present invention is directed to a polycrystalline
diamond (PCD) ultra hard material and a method for forming the
same, as well as to cutting elements incorporating such PCD
material and to bit bodies incorporating such cutting elements. In
one embodiment, the polycrystalline diamond ultra hard material
includes semiconductive diamond crystals therein. The
semiconductive diamond crystals may be diamond crystals doped with
lithium, beryllium or aluminum. In another exemplary embodiment,
the polycrystalline diamond ultra hard material is formed of
conventional diamond crystals, at least some of which include
semiconductive outer surface layers. According to either of the
aforementioned exemplary embodiments, the polycrystalline diamond
ultra hard material is a semiconductive material.
[0010] According to one exemplary method of the present invention,
a cutting element is formed by providing a substrate and forming a
polycrystalline diamond layer over the substrate. The
polycrystalline diamond layer is formed over the substrate by
providing a layer of diamond powder comprising non-conductive
diamond grit feedstock and an additive, and converting the layer of
diamond powder to polycrystalline diamond that is a solid
semiconductive material. The additive may be chosen from the group
consisting of lithium, beryllium, boron, and aluminum. Diamond grit
feedstock composed of conventional, insulative diamond crystals,
for example Type I diamond crystals, may be used.
[0011] According to another exemplary method of the present
invention, a cutting element is formed by providing a layer of
diamond grit feedstock including diamond crystals doped with at
least one of beryllium, lithium and aluminum, then sintering to
convert the layer of diamond grit feedstock to a semiconductive,
solid polycrystalline diamond layer.
[0012] According to either of the exemplary methods of formation,
the ultra hard PCD layer is formed as a semiconductive material
with increased conductivity compared to PCD layers formed of
conventional insulative diamond crystals, such as Type I diamond
crystals. Even if all the metal binder materials that may be
included in the PCD layer are removed by leaching, the cuttability
of the semiconductive PCD material of the present invention is
enhanced, especially EDM and EDG cuttability.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The invention is best understood from the following detailed
description when read in conjunction with the accompanying
drawings. It is emphasized that, according to common practice, the
various features of the drawing are not to scale. On the contrary,
the dimensions of the various features may be arbitrarily expanded
or reduced for clarity. Like numerals denote like features
throughout the specification and drawings. Included are the
following figures:
[0014] FIG.1 is a perspective view of a cutting element according
to an exemplary embodiment of the present invention;
[0015] FIG. 2 is a perspective view of a bit body outfitted with
exemplary embodiment cutting elements of the present invention
shown in FIG. 1;
[0016] FIG. 3 is a graphical representation showing the effects of
diamond crystals having semiconductive surface layers, within PCD
material according to an exemplary embodiment of the invention
[0017] FIG. 4 is another graphical representation showing the
effects of diamond crystals having semiconductive surface layers,
within PCD material according to an exemplary embodiment of the
invention; and
[0018] FIG. 5 is a graphical representation showing a comparison
between conventional PCD material and exemplary semiconductive PCD
materials formed according to an exemplary embodiment of the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0019] A PCD material having enhanced cuttability, especially EDM
and EDG cuttability without comprising its hardness, wear
resistance, or thermal stability, cutting and other tools
incorporating such material, and a method of making such material
and tools, are provided. An exemplary embodiment PCD material of
the present invention has a substantial percentage of diamond
crystals that are semiconductive in nature or which include
semiconductive outer surface layers. Such diamond crystals contain
small quantities of interstitial impurities such as lithium (Li),
beryllium (Be), boron (B), and aluminum (Al) that are sufficient to
make them semiconductors.
[0020] Semiconductive diamonds are discussed in Wentorf, R. H. and
Bovenkirk, H. P., "Preparation of Semiconducting Diamonds," J.
Chem. Phys. 36, p. 1987 (1962); Field, J. E., "Properties of
Diamond," Academic Press, 1979; and, Wentorf, R. H., "Diamond
Formation at High Pressures", in Advances in High Pressure
Research, Academic Press, p.249-281 (1974), the contents of each of
which are hereby incorporated by reference. On the other hand, PCD
formed with conventional diamond crystals that are electrical
insulators, includes a much higher resistance than the PCD of the
present invention. This is true both for PCD materials which
include metal binder materials therein, and PCD materials void of
such metal binder materials.
[0021] An exemplary embodiment PCD of the present invention is
formed by using semiconductive diamond grit feedstock formed of
semiconductive diamond crystals doped with Li, Be or Al or
combinations thereof. In another exemplary embodiment of the
present invention, PCD may be formed by using a combination of
semiconductive and conventional, non-conductive diamond grit
feedstock such as Type I diamond grit feedstock. In yet another
exemplary embodiment of the present invention, the PCD is formed
using conventional undoped diamond grit feedstock (such as Type I
diamond grit feedstock) together with a suitable quantity of
additives such as B, Li, Be and Al. The additives diffuse
throughout the diamond lattice so as to cause the diamond crystals
to transform to diamond crystals that include semiconductive
surface layers. This diffusion phenomenon takes place during the
HTHP sintering process used to solidify the PCD material. The PCD
material formed according to each of the aforementioned methods, is
semiconductive in nature. Hereinafter, both the PCD material formed
using semiconductive diamond grit feedstock and the PCD material
formed using conventional diamond grit feedstock and an additive to
convert the diamond crystals to having semiconductive surface
layers, will be collectively referred to as semiconductive PCD.
[0022] The semiconductive PCD of the present invention is a solid
structural body commonly referred to as an ultra-hard material or
ultra-hard layer and may be used as a cutting layer on cutting
tools and cutting elements, or a wear resistant layer for other
applications. For convenience, cutting elements and cutting tools
are referred to as "cutting elements" hereinafter. The
semiconductive PCD may be a layer formed over a substrate to
produce a cutting element. In an exemplary embodiment, the cutting
element may be inserted into a drill bit and used for earth boring.
The semiconductive PCD of the present invention may be used in
various other applications and industries, in other exemplary
embodiments.
[0023] An exemplary cutting element is shown in FIG. 1. FIG. 1
shows cutting element 10 formed of substrate 12 and ultra hard
layer 16 which is also referred to as a cutting table and includes
top surface 18. Ultra hard layer 16 is formed of semiconductive PCD
in the present invention. Interface 14 is formed between substrate
12 and ultra hard layer 16. According to another exemplary
embodiment, one or more transition layers (not shown) may be formed
between ultra hard layer 16 and substrate 12. The generally
cylindrically-shaped cutting element illustrated in FIG. 1 is
intended to be exemplary only and according to various other
exemplary embodiments, the cutting elements and ultra-hard layers
may take on any of various other shapes.
[0024] In an exemplary embodiment, the cutting element is mounted
on a bit such as the drag bit shown in FIG. 2, and contacts the
earthen formation along edge 28, during drilling. In the exemplary
embodiment shown in FIG. 2, the cutting elements 10 are joined to
pockets or other receiving shapes that extend into drag bit body 24
by brazing or other means well known in the art. The illustrated
arrangement is intended to be exemplary only and cutting elements
10 may be used in various other arrangements in other exemplary
embodiments.
[0025] The method for forming the semiconductive PCD material
includes providing a substrate and providing a layer of diamond
powder over the substrate, then using HTHP processing to sinter,
thereby solidifying the layer of diamond powder and converting the
same to an ultra-hard layer of PCD, and also bonding the PCD layer
to the substrate to form a cutting element. The substrate may be a
pre-formed solid substrate, or it may be provided in powder form
and also solidified during the sintering operation. The substrate
may be formed of various matrix materials. In an exemplary
embodiment, the substrate may be formed of cemented tungsten
carbide. Cemented tungsten carbide generally refers to tungsten
carbide particles disbursed in a substrate binder metal matrix such
as iron, nickel, or cobalt. Other substrate materials may be used
in other exemplary embodiments. Wear resistant materials suitable
for use as the substrate may be selected from compounds of carbide
and metals selected from Groups IVB, VB, VIB, and VIIB of the
Periodic Table of the Elements. Examples of other such carbides
include tantalum carbide and titanium carbide. Substrate binder
matrix materials suitable for use in embodiments of the invention
include the transition metals of Groups VI, VII, and VII of the
Periodic Table of the Elements. For example, iron and nickel are
good substrate binder matrix materials.
[0026] The layer of diamond powder used to form a semiconductive
PCD material in an exemplary embodiment of the present invention,
includes of a plurality of fine diamond crystals. The layer of
diamond powder may be provided directly on the substrate or one or
more optional transition layers may be provided between the layer
of diamond powder and the substrate.
[0027] According to one exemplary embodiment, the layer of diamond
powder includes at least some semiconductive diamond grit feedstock
consisting of diamond crystals doped with Li, Be, or Al. The
semiconductive diamond feedstock may be mixed with conventional,
undoped diamond feedstock to form the layer of diamond powder. In
another exemplary embodiment, the diamond crystals of the layer of
diamond powder may consist substantially only of semiconductive
diamond grit feedstock.
[0028] According to another exemplary embodiment, the layer of
diamond powder may consist of conventional diamond crystals that
are insulators such as, for example, Type I diamond crystals.
According to this exemplary embodiment, an additive such as Li, Be,
B or Al is added to the layer of diamond powder. The additives may
be in powder or granular form and are mixed throughout the layer of
diamond powder. In an exemplary embodiment, the additives may be
mixed in uniformly throughout the diamond powder layer. The
additives are chosen to be small enough to diffuse into the diamond
lattice formed as the layer of diamond powder solidifies to form
the PCD layer. Because of the small size of the diamond lattice in
PCD, the lattice can only accommodate a limited number of impurity
species (i.e., additives) for transforming the conventional,
insulating diamond crystals to semiconductive diamond crystals. Li,
Be, B and Al are elements that are known to be small enough to
diffuse into the diamond lattice. Such are intended to be exemplary
only and other impurity atoms or compounds may be used in other
exemplary embodiments. Li, Be, B and Al make the PCD a P-Type
semiconductor.
[0029] The quantity of additive included in the layer of diamond
powder ranges from 0.1 wt % to 10.0 wt % in an exemplary
embodiment, but other weight percentages may be used in other
exemplary embodiments. The upper limit of additive weight
percentage is determined by the amount above which the sintering
process is adversely affected. An appropriate quantity of suitably
small elements or compounds of additives are chosen so that the
additives diffuse into and throughout the diamond lattice and cause
the insulating diamond crystals to transform to semiconductive
diamond crystals. It has been found that a very small amount of the
additives can convert the diamond crystals and achieve an
improvement of increased conductivity. During the transformation of
the insulating diamond material to a semiconductive material, some
or all of the diamond crystals are converted to diamond crystals
having a semiconductive surface due to diffusion of the additive.
This diffusion phenomenon takes place during the HTHP sintering
process used to solidify the PCD, during which the additive species
are free to diffuse throughout the PCD. It is not necessary to
obtain full conversion of the entire diamond crystal to a
semiconductive diamond crystal in order to realize a significant
conductivity improvement. Rather, the transformation of the surface
layer of the diamond crystals to semiconductive surface layers,
improves the conductivity and, hence, cuttability of the formed
PCD. According to this embodiment, undoped diamond crystals, such
as Type I diamond crystals, are converted to diamond crystals that
include semiconductive surface layers.
[0030] According to either of the aforementioned exemplary methods
of formation, an ultra-hard material of semiconductive PCD is
produced. According to either of the exemplary embodiments,
sufficient metal binder material may be included in the layer of
diamond powder to produce a metal binder material within the PCD
material at a volume percentage of up to about 30%, but other
volume percentages of binder material may be used in other
exemplary embodiments. According to another exemplary embodiment,
the metal binder material may diffuse into the PCD layer from the
substrate, during the HTHP sintering operation. In an exemplary
embodiment, the weight percentage for metal binders may range from
8-12% by weight and it is common for a weight percentage of no
greater than 15% to be used. Metals such as cobalt, iron, nickel,
manganese, tantalum, chromium and/or mixtures or alloys thereof may
be used as a metal binder material. The metal binder material
facilitates intercrystalline bonding between the diamond grains of
the PCD layer, acts to bond the PCD layer to other layers or the
substrate, and increases the conductivity of the PCD layer. An
aspect of the present invention, however, is that because of the
conductive nature of the diamond skeleton in the semiconductive PCD
formed with semiconductive diamond crystals or diamond crystals
having a semiconductive surface layer, it is not necessary to have
a metal matrix present to ensure cuttability.
[0031] According to the various embodiments of the present
invention, the PCD material has a conductivity sufficiently high to
enable cutting using EDM and EDG, even when the PCD was formed
without a metal binder or after the metal matrix material has
essentially been completely removed by leaching. In one exemplary
embodiment, PCD of the present invention that is substantially free
of metal binders, was formed to have a resistance of less than 1000
ohms. In another embodiment, the PCD layer formed with a metal
binder therein at a weight percentage no greater than 10%, had a
resistance of less than 50 ohms.
[0032] The resistance values recited herein, are conventional
resistance measurements made using probes spaced about 1 cm apart
on the sample surface.
[0033] After the solid semiconductive PCD is formed, an
Electro-Discharge Machining or Electro-Discharge Grinding cutting
operation may be required to cut the PCD to a desired shape.
Increased cutting rates can be achieved on such semiconductive PCD
materials using EDM and EDG due to the semiconductive nature of the
PCD. This is true even though the cooling and dielectric fluids
used throughout the EDM and EDG processes, and the electrical arcs
produced by the EDM and EDG processes themselves, leach any metal
binder material from the semiconductive PCD during the cutting
operation. Even if the metal binder is lost due to leaching, or if
metal binder materials are not included at all, applicant has
discovered that the PCD of the present invention is sufficiently
conductive to ensure cuttability in Electro-Discharge Machining and
Electro-Discharge Grinding cutting operations. The semiconductive
PCD further includes a very high abrasion resistance while still
retaining its cuttability. Since the addition of metal binder
material can be reduced or even eliminated, the hardness, wear
resistance and thermal stability of the formed PCD layer is not
compromised and may be improved.
[0034] After the solid semiconductive PCD is cut to form a cutting
element, the cutting element may be joined to a drill bit body by
brazing or other means well known in the art.
[0035] FIGS. 3-5 are graphical representations showing the
advantages of exemplary semiconductive PCD formed according to
embodiments of the present invention. FIGS. 3-5 collectively show
that the semiconductive PCD formed according to the present
invention includes a significantly lower resistance, i.e., a
significantly higher conductivity, than standard PCD material. The
figures also show that, after acid leaching of the metal matrix
material during the cutting process, the semiconductive PCD of the
present invention also exhibits a significantly reduced resistance
(i.e., increased conductivity) with respect to standard PCD formed
of conventional, insulative diamonds. FIGS. 3-5 also show that the
effect of acid leaching during the cutting process, is suppressed
in semiconductive PCD formed according to the present invention, in
comparison to standard PCD. "Standard PCD" consists of conventional
insulative diamonds, such as Type I diamonds.
[0036] FIG. 3 is a Weibull plot commonly used for displaying a
non-normal distribution of data samples and shows the measured
resistance after HTHP processing of a semiconductive PCD layer, as
compared to standard PCD, as above. Conventional resistance
measurements were made using probes spaced about 1 cm apart on the
sample surface, in all cases. In FIG. 3, Sample 1 is PCD formed by
adding 2.0 weight percent of boron to a layer of diamond powder
including conventional Type I (insulating) diamond grit feedstock,
then sintering to convert at least some of the insulative diamond
crystals to include a semiconductive surface layer. FIG. 3 also
shows Sample 2 which is PCD formed by adding 0.5 weight percent of
boron to a layer of conventional diamond powder including
conventional Type I diamond grit feedstock, then sintering to
convert at least some of the insulative diamond crystals to include
a semiconductive surface layer. Each of Sample 1 and Sample 2 are
PCD materials that include a cobalt matrix material at about 10% by
weight. The standard PCD sample is a conventional PCD material that
is substantially similar to Samples 1 and 2, except that the
standard PCD material is formed only with conventional, insulative
diamonds. As illustrated in FIG. 3, the two PCD samples of present
invention exhibit a reduced resistance.
[0037] FIG. 4 is another Weibull plot of measured electrical
resistance of the PCD material samples used in FIG. 1, after
removal of substantially all of the cobalt matrix phase of such
samples by acid leaching. In the examples used to provide the data
shown in FIG. 4, acid leaching was intentionally caused for data
gathering purposes, by boiling in hydrofluoric acid and nitric
acid, but other exemplary techniques may be used alternatively.
Similar acid leaching of the cobalt matrix phase from the PCD also
occurs as a result of the cooling and dielectric fluids used in
conventional EDM and EDG cutting operations which can leach out any
metal binder material present in the PCD material. As such, FIG. 4
is representative of PCD material during EDM and EDG cutting
operations. FIG. 4 shows a difference of several orders of
magnitude in resistance between each of Sample 1 and Sample 2 of
the present invention, and standard PCD. Each of the standard PCD
and Samples 1 and 2 were substantially free of metal binder
materials when the measurements plotted in FIG. 4 were made.
[0038] FIG. 5 is a bar graph summarizing the electrical resistance
measurements shown in FIGS. 3 and 4. FIG. 5 shows that, after
sintering and prior to leaching, each of PCD Samples 1 and 2 have a
measured resistance of about 10 ohms, while the standard PCD sample
has a measured resistance of about 400-500 ohms. In particular,
after HTHP processing, Sample 1 has a measured resistance of about
8 ohms and Sample 2 has a measured resistance of about 20 ohms,
i.e. both samples have a resistance less than 50 ohms. As formed,
then, it can be seen that each of the semiconductive PCD samples
exhibit a resistance of less than 10%, and more specifically less
than about 5%, of the corresponding resistance of a substantially
similar PCD layer formed only of Type I or other conventional
insulative diamonds. After leaching substantially all metal binder
material from Samples 1 and 2 of the present invention, Samples 1
and 2 both exhibit a measured resistance of about 1000 ohms,
whereas the standard PCD has a resistance of about 2-3.times.108
ohms. The increase in resistance due to acid leaching is much more
significant in the standard PCD as compared to Samples 1 and2.
[0039] It is believed that semiconductive PCD material of the
present invention formed using diamond grit feedstock consisting of
Li--, Be-- or Al-doped diamond crystals and without the addition of
metal binder materials, will exhibit an even greater improvement in
resistance/conductivity characteristics, than the PCD layers formed
to initially include metal binder materials and from which the
metal binder materials are subsequently removed by leaching (as
illustrated in FIGS. 4 and 5), when compared to PCD material
consisting only of conventional diamonds. Applicant believes that
the absence of the additive impurity species used to convert
conventional PCD to semiconductive PCD, provides superior diamond
crystal-to-diamond crystal bonding.
[0040] FIGS. 3-5 and Samples 1 and 2 are provided to be
illustrative of the advantages of the present invention. Samples 1
and 2 are exemplary only and the reduced resistance advantage of
the semiconductive PCD materials of the present invention is
similarly achievable for samples formed having different metal
binder materials and samples having binder materials present in
different percentages.
[0041] The semiconductive PCD material of the present invention
(i.e., a PCD layer with at least some Al-doped, Be-doped or
Li-doped diamond crystals, or at least some diamond crystals having
semiconductive surfaces), also has a much greater thermal
conductivity than conventional PCD. Applicants believe that the
thermal conductivity of the semiconductive PCD material of the
present invention may be 15 times greater than the conductivity of
conventional PCD material at 80 .quadrature.K and 4-5 times greater
than the conductivity of conventional PCD material at room
temperature. When used as a cutting layer in a cutting tool, a
semiconductive PCD material is better able to conduct the heat
generated by the abrasion of the PCD cutting layer against the
object being cut, and thus maintain a lower temperature on the
cutting layer. Increased temperatures on the cutting layer and the
tool are known to decrease the life of the cutting tool.
Consequently, the use of the semiconductive PCD of the present
invention as a cutting layer, will provide an increased operating
life of the cutting element.
[0042] The preceding merely illustrates the principles of the
invention. It will thus be appreciated that those skilled in the
art will be able to devise various arrangements which, although not
explicitly described or shown herein, embody the principles of the
invention and are included within the scope and spirit.
Furthermore, all examples and conditional language recited herein
are principally intended expressly to be only for pedagogical
purposes and to aid in understanding the principles of the
invention and the concepts contributed by the inventors to
furthering the art, and are to be construed as being without
limitation to such specifically recited examples and conditions.
Moreover, all statements herein reciting principles, aspects, and
embodiments of the invention, as well as specific examples thereof,
are intended to encompass both structural and the functional
equivalents thereof. Additionally, it is intended that such
equivalents include both currently known equivalents and
equivalents developed in the future, i.e., any elements developed
that perform the same function, regardless of structure. The scope
of the present invention, therefore, is not intended to be limited
to the exemplary embodiments shown and described herein. Rather,
the scope and spirit of the present invention is embodied by the
appended claims.
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