U.S. patent application number 13/940346 was filed with the patent office on 2015-01-15 for use of surface modified diamond to manufacture polycrystalline diamond.
The applicant listed for this patent is Diamond Innovations, Inc.. Invention is credited to Neil Krishnan.
Application Number | 20150013234 13/940346 |
Document ID | / |
Family ID | 52275993 |
Filed Date | 2015-01-15 |
United States Patent
Application |
20150013234 |
Kind Code |
A1 |
Krishnan; Neil |
January 15, 2015 |
USE OF SURFACE MODIFIED DIAMOND TO MANUFACTURE POLYCRYSTALLINE
DIAMOND
Abstract
A superabrasive blank and a method of making the superabrasive
blank are disclosed. A superabrasive blank may comprise a plurality
of polycrystalline superabrasive particles made of surface modified
superabrasive particles. The surface modified superabrasive
particles may have sphericity less than about 0.70. The substrate
attached to a superabrasive volume formed by the polycrystalline
superabrasive particles.
Inventors: |
Krishnan; Neil; (Columbus,
OH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Diamond Innovations, Inc. |
Worthington |
OH |
US |
|
|
Family ID: |
52275993 |
Appl. No.: |
13/940346 |
Filed: |
July 12, 2013 |
Current U.S.
Class: |
51/309 ;
51/307 |
Current CPC
Class: |
B24D 99/005
20130101 |
Class at
Publication: |
51/309 ;
51/307 |
International
Class: |
B24D 3/10 20060101
B24D003/10; B24D 18/00 20060101 B24D018/00 |
Claims
1. A superabrasive blank, comprising: a plurality of
polycrystalline superabrasive particles made of surface modified
superabrasive particles, wherein the surface modified superabrasive
particles have sphericity less than about 0.70; and a substrate
attached to a superabrasive volume formed by the polycrystalline
superabrasive particles.
2. The superabrasive blank of the claim 1, wherein the
superabrasive particles are at least one of cubic boron nitride,
diamond, and diamond composite materials.
3. The superabrasive blank of the claim 1, wherein the surface
modified superabrasive particles have a plurality of pits on the
surface.
4. The superabrasive blank of the claim 1, wherein the surface
modified superabrasive particles have a plurality of spikes on the
surface.
5. The superabrasive blank of the claim 1, wherein the depth of the
pits ranges in size from about 5% to about 70% of the longest
length of the particle.
6. The superabrasive blank of the claim 1, wherein the
superabrasive particles have surface roughness less than about
0.89.
7. A method of making superabrasive material, comprising: providing
surface modified superabrasive particles, wherein the surface
modified superabrasive particles have surface roughness less than
about 0.89; providing a substrate attached to a superabrasive
volume formed by the plurality of superabrasive particles; and
subjecting the substrate and the superabrasive volume to conditions
of elevated temperature and pressure suitable for producing the
polycrystalline superabrasive material.
8. The method of the claim 7, wherein the substrate is cemented
tungsten carbide.
9. The method of the claim 7, wherein the surface modified
superabrasive particles have a plurality of pits on the
surface.
10. The method of the claim 9, wherein depth of the pits ranges in
size from about 5% to about 70% of the longest length of the
particle.
11. The method of the claim 7, wherein the surface modified
superabrasive particles have a plurality of spikes on the
surface.
12. The method of the claim 7, wherein the surface modified
superabrasive particles have sphericity less than about 0.70.
13. The method of the claim 7, wherein the superabrasive particles
are at least one of cubic boron nitride, diamond, and diamond
composite materials.
14. A superabrasive blank, comprising: a plurality of
polycrystalline superabrasive particles made of surface modified
superabrasive particles, wherein the surface modified superabrasive
particles have surface roughness less than about 0.89.
15. The superabrasive blank of the claim 14, wherein the
superabrasive particles are selected from a group of cubic boron
nitride, diamond, and diamond composite materials.
16. The superabrasive blank of the claim 14, wherein the surface
modified superabrasive particles have a plurality of pits on the
surface.
17. The superabrasive blank of the claim 14, wherein the surface
modified superabrasive particles have a plurality of spikes on the
surface.
18. The superabrasive blank of the claim 14, wherein the depth of
the pits ranges in size from about 5% to about 70% of the longest
length of the particle.
19. The superabrasive blank of the claim 14, wherein the
superabrasive particles have sphericity less than about 0.70.
20. The superabrasive blank of the claim 14, further comprises a
substrate attached to a superabrasive volume formed by the
polycrystalline superabrasive particles.
Description
TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY
[0001] The present invention relates generally to superabrasive
materials and a method of making superabrasive materials; and more
particularly, to polycrystalline diamond (PCD) by using surface
modified diamond.
SUMMARY
[0002] In one embodiment, superabrasive blank may comprise a
plurality of polycrystalline superabrasive particles made of
surface modified superabrasive particles, wherein the surface
modified superabrasive particles have sphericity less than about
0.70; and a substrate attached to a superabrasive volume formed by
the polycrystalline superabrasive particles.
[0003] In another embodiment, a method may comprise steps of
providing surface modified superabrasive particles, wherein the
surface modified superabrasive particles have surface roughness
less than about 0.89; providing a substrate attached to a
superabrasive volume formed by the plurality of superabrasive
particles; and subjecting the substrate and the superabrasive
volume to conditions of elevated temperature and pressure suitable
for producing the polycrystalline superabrasive material.
[0004] In yet another embodiment, a superabrasive blank may
comprise a plurality of polycrystalline superabrasive particles
made of surface modified superabrasive particles, wherein the
surface modified superabrasive particles have surface roughness
less than about 0.89.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] The foregoing summary, as well as the following detailed
description of the embodiments, will be better understood when read
in conjunction with the appended drawings. It should be understood
that the embodiments depicted are not limited to the precise
arrangements and instrumentalities shown.
[0006] FIG. 1 is schematic perspective view of a cylindrical shape
polycrystalline blank produced in a high pressure high temperature
(HPHT) process according to an exemplary embodiment;
[0007] FIG. 2a is a scanning electron microscope (SEM) image of
surface modified diamond using a nickel coating process or diamond
modified using an iron powder process;
[0008] FIG. 2b is an enlarged scanning electron microscope (SEM)
image of surface modified diamond according to FIG. 2a;
[0009] FIG. 3 is a flow chart illustrating a method of
manufacturing polycrystalline blank according to an embodiment;
[0010] FIG. 4 is illustrating a concept of ferret tangent and
ferret diameter according to an embodiment;
[0011] FIG. 5 is illustrating a concept of convex perimeter which
is formed from the intersection of many Feret tangent lines
according to an embodiment;
[0012] FIG. 6 is illustrating concepts of perimeter and convex
perimeter according to an embodiment;
[0013] FIG. 7a is illustrating microstructure of polycrystalline
diamond blank using surface modified diamond feed; and
[0014] FIG. 7b is illustrating microstructure of polycrystalline
diamond blank using conventional diamond feed.
DETAILED DESCRIPTION
[0015] Before the present methods, systems and materials are
described, it is to be understood that this disclosure is not
limited to the particular methodologies, systems and materials
described, as these may vary. It is also to be understood that the
terminology used in the description is for the purpose of
describing the particular versions or embodiments only, and is not
intended to limit the scope. For example, as used herein, the
singular forms "a," "an," and "the" include plural references
unless the context clearly dictates otherwise. In addition, the
word "comprising" as used herein is intended to mean "including but
not limited to." Unless defined otherwise, all technical and
scientific terms used herein have the same meanings as commonly
understood by one of ordinary skill in the art.
[0016] Unless otherwise indicated, all numbers expressing
quantities of ingredients, properties such as size, weight,
reaction conditions and so forth used in the specification and
claims are to the understood as being modified in all instances by
the term "about". Accordingly, unless indicated to the contrary,
the numerical parameters set forth in the following specification
and attached claims are approximations that may vary depending upon
the desired properties sought to be obtained by the invention. At
the very least, and not as an attempt to limit the application of
the doctrine of equivalents to the scope of the claims, each
numerical parameter should at least be construed in light of the
number of reported significant digits and by applying ordinary
rounding techniques.
[0017] As used herein, the term "about" means plus or minus 10% of
the numerical value of the number with which it is being used.
Therefore, about 50 means in the range of 45-55.
[0018] As used herein, the term "superabrasive particles" may refer
to ultra-hard particles or superabrasive particles having a Knoop
hardness of 5000 KHN or greater. The superabrasive particles may
include diamond, and cubic boron nitride, for example. The term
"abrasive", as used herein, refers to any material used to wear
away softer material.
[0019] The term "material removal", as used herein, refers to the
weight of a workpiece removed in a given period of time reported in
milligrams, grams, etc.
[0020] The term, "material removal rate", as used herein, refers to
material removed divided by the time interval reported as
milligrams per minute, grams per hour, etc.
[0021] The term "monocrystalline diamond", as used herein, refers
to a diamond that is formed either by
high-pressure/high-temperature synthesis or a diamond that is
naturally formed. Fracture of monocrystalline diamond proceeds
along atomic cleavage planes. A monocrystalline diamond particle
breaks relatively easily at the cleavage planes.
[0022] The term "particle" or "particles", as used herein, refers
to a discrete body or bodies. A particle is also considered a
crystal or a grain.
[0023] The term "pit", as used herein, refers to an indentation or
crevice in the particle, either an indentation or crevice in the
two-dimensional image or an indentation or crevice in an
object.
[0024] The term "polycrystalline diamond", as used herein, refers
to diamond formed by explosion synthesis or high pressure high
temperature resulting in a polycrystalline particle structure. Each
polycrystalline diamond particle consists of large numbers of
monocrystalline particles of any sizes. Polycrystalline diamond
particles do not have cleavage planes.
[0025] The term "spike", as used herein, refers to a sharp
projection pointing outward from the centroid of a particle, a
sharp projection pointing outward from the centroid of a
two-dimensional image or a sharp projection pointing outward from
an object.
[0026] The term "superabrasive", as used herein, refers to an
abrasive possessing superior hardness and abrasion resistance.
Diamond and cubic boron nitride are examples of superabrasives and
have Knoop indentation hardness values of over 3500.
[0027] The term "weight loss", as used herein, refers to the
difference in weight of a group of particles before being subject
to the modification treatment and the weight of the same mass of
diamond particles or abrasive particles after being subjected to
the modification treatment.
[0028] The term "workpiece", as used herein, refers to parts or
objects from which material is removed by grinding, polishing,
lapping or other material removal methods.
[0029] The term "perimeter", as used herein, refers to the boundary
of a closed plane figure or the sum of all borders of a
two-dimensional image.
[0030] The term "convex perimeter", as used herein, refers to a
line joining Feret tangent points, where Feret is the distance
between two parallel tangents touching the boundary on each side of
a two dimensional image or object. FIGS. 4-6 provide illustrations
of these concepts. Feret diameter is defined as the distance
between two parallel lines touching the boundary of a 2-dimensional
image or particle profile. The convex perimeter is formed from the
intersection of many Feret tangent lines.
[0031] The term "surface roughness", as used herein, refers to the
measurement of a two-dimensional image that quantifies the extent
or degree of pits and spikes of an object's edges or boundaries as
stated in the CLEMEX image analyzer, Clemex Vision User's Guide PE
3.5 .COPYRGT.2001. Surface roughness is determined by the ratio of
the convex perimeter divided by the perimeter.
Surface Roughness = ConvexPerimeter Perimeter ##EQU00001##
[0032] Note that as the degree of pits and spikes increases, the
surface roughness factor decreases.
[0033] The term "sphericity", as used herein, refers to the
estimate of the enclosed area of a two dimensional image or object
(4.pi.A) divided by the square of perimeter (p.sup.2).
Sphericity = 4 .pi. A p 2 ##EQU00002##
[0034] The term "surface area" as used herein, refers to the
external surface of a particle. When used with a plurality of
particles, i.e., powder, the term specific surface area is used and
is reported as surface area per gram of powder.
[0035] The terms diamond particle or particles and diamond powder
or powders are used synonymously in the instant application and
have the same meaning as "particle" defined above.
[0036] It is important to note that although the terms defined
above refer to measuring two-dimensional particle profiles using
microscopic measuring techniques, it is understood that the
features extend to the three-dimensional form. Automated image
analysis of particle size and shape is recognized by one skilled in
the art as a reliable, reproducible method of measuring particle
characteristics. Although the CLEMEX image analyzer was used,
similar devices are available that may reproduce the data.
[0037] In one embodiment, monocrystalline diamond particles may be
used. Monocrystalline diamond particles in sizes of less than about
100 microns are useful. However, diamond particles in sizes over
about 100 microns may be used as well. The sizes of the diamond
particles range from about 0.1 to about 1000 microns. One example
of diamond particles that may be used is SJK-5 4-8 micron,
synthetic industrial diamond particles manufactured by Diamond
Innovations, Inc. (Worthington, Ohio, U.S.A).
[0038] In another embodiment, natural diamond particles, sintered
polycrystalline diamond or shock synthesized polycrystalline
diamond particles may be subjected to the modification treatment
discussed below.
[0039] In an embodiment, other abrasives may be subjected to a
modification treatment. Examples of abrasives include any material,
such as minerals, that are used for shaping or finishing a
workpiece. Superabrasive materials such as natural and synthetic
diamond and boron, carbon and nitrogen compounds may be used.
Suitable diamond materials may be crystalline or polycrystalline.
Other examples of abrasive grains may include calcium carbonate,
emery, novaculite, pumice dust, rouge, sand, ceramics, alumina,
glass, silica, silicon carbide, and zirconia alumina.
[0040] In another embodiment, a reactive coating is used to modify
the abrasive or superabrasive particles. Such reactive coatings
include but are not limited to alkali metal hydroxides, such as
lithium hydroxide, sodium hydroxide, potassium hydroxide, potassium
carbonate, sodium peroxide, potassium dichromate and potassium
nitrate, etc. The reactive coatings may also include a combination
of alkali metal hydroxides.
[0041] Still other examples of metals that may be utilized as the
reactive coating are those included in Group VIII of the Periodic
table, their metal compounds and combinations thereof. Other
examples of material that may be used as reactive coatings include
the catalyst metals taught in U.S. Pat. No. 2,947,609 and the
catalyst metals taught in U.S. Pat. No. 2,947,610.
[0042] Polycrystalline diamond composite (or "PCD", as used
hereafter) may represent a volume of crystalline diamond grains
with embedded foreign material filling the inter-grain space. In
one particular case, composite comprises crystalline diamond
grains, bound to each other by strong diamond-to-diamond bonds and
forming a rigid polycrystalline diamond body, and the inter-grain
regions, disposed between the bound grains and filled with a
catalyst material (e.g. cobalt or its alloys), which was used to
promote diamond bonding during fabrication. Suitable metal solvent
catalysts may include the metal in Group VIII of the Periodic
table. In another particular case, polycrystalline diamond
composite comprises a plurality of crystalline diamond grains,
which are not bound to each other, but instead are bound together
by foreign bonding materials such as borides, nitrides, carbides,
e.g. SiC.
[0043] Polycrystalline diamond blanks and PCD cutters may be
fabricated in different ways and the following examples do not
limit a variety of different types of diamond composites and PCD
cutters which may be coated according to an embodiment. In one
example, polycrystalline blank are formed by placing a mixture of
diamond polycrystalline powder with a suitable solvent catalyst
material (e.g. cobalt) on the top of WC--Co substrate, which
assembly is subjected to processing conditions of extremely high
pressure and high temperature (HPHT), where the solvent catalyst
promotes desired inter-crystalline diamond-to-diamond bonding and,
also, provides a binding between polycrystalline diamond body and
substrate support. In another example, polycrystalline blank is
formed by placing diamond powder without a catalyst material on the
top of substrate containing a catalyst material (e.g. WC--Co
substrate). In this example, necessary cobalt catalyst material is
supplied from the substrate and melted cobalt is swept through the
diamond powder during the HPHT process. In still another example, a
hard polycrystalline diamond composite is fabricated by forming a
mixture of diamond powder with silicon powder and mixture is
subjected to HPHT process, thus forming a dense polycrystalline
cutter where diamond particles are bound together by newly formed
SiC material.
[0044] Abrasion resistance of polycrystalline diamond composites
and PCD cutters may be determined mainly by the strength of bonding
between diamond particles (e.g. cobalt catalyst), or, in the case
when diamond-to-diamond bonding is absent, by foreign material
working as a binder (e.g. SiC binder), or in still another case, by
both diamond-to-diamond bonding and foreign binder.
[0045] The presence of some catalysts inside the polycrystalline
diamond body promotes the degradation of the cutting edge of the
cutter during the cutting process, especially if the edge
temperature reaches a high enough critical value. Probably, the
cobalt driven degradation may be caused by the large difference in
thermal expansion between diamond and catalyst (e.g. cobalt metal),
and also by catalytic effect of cobalt on diamond graphitization.
Removal of catalyst from the polycrystalline diamond body of PCD
cutter, for example, by chemical etching in acids, leaves an
interconnected network of pores and a residual catalyst (up to 10
vol %) trapped inside the polycrystalline diamond body. It has been
demonstrated that a chemically etched polycrystalline diamond
cutter by removal of a substantial amount of cobalt from the PCD
cutter significantly improves its abrasion resistance. Also it
follows that a thicker cobalt depleted layer near the cutting edge
provides better abrasion resistance of the PCD cutter than a
thinner cobalt depleted layer.
[0046] As shown in FIG. 1, a superabrasive cutter 10 which is
insertable within a downhole tool, such as a drill bit (not shown)
in according to an embodiment. One example of the superabrasive
cutter 10 may include a superabrasive volume 12 having a top
surface 21. The superabrasive blank may comprise a plurality of
polycrystalline superabrasive particles made of surface modified
superabrasive particles shown in FIG. 2a. The surface modified
superabrasive particles have sphericity less than about 0.70.
[0047] In one embodiment, the superabrasive blank may be a
standalone blank without a substrate. In another embodiment, the
superabrasive cutter 10 may include a substrate 20 attached to the
superabrasive volume 12 formed by the polycrystalline superabrasive
particles. The substrate may be metal carbide, attached to the
superabrasive volume 12 via an interface 22 between the
superabrasive volume 12 and the metal carbide. The metal carbide
may be generally made from cemented cobalt tungsten carbide, or
tungsten carbide, while the superabrasive volume 12 may be formed
using a polycrystalline ultra-hard material, such as
polycrystalline diamond, polycrystalline cubic boron nitride
("PCBN"), or tungsten carbide mixed with diamond crystals
(impregnated segments). The superabrasive particles may be selected
from a group of cubic boron nitride, diamond, and diamond composite
materials.
[0048] One embodiment pertains to monocrystalline diamond particles
having very rough, irregular surfaces as shown in FIG. 2a. The
particles have been modified using the method described below. In
addition to the roughened appearance, the modified diamond
particles have unique characteristics as compared to conventional
monocrystalline diamond particles.
[0049] FIG. 2b shows an enlargement of a surface modified diamond
particle from FIG. 2a. The surface modified diamond particles 24
contain one or more pits and/or spikes. An example of a diamond
particle exhibiting these features is shown in FIG. 2b. Diamond
particle 1, having a weight loss of about 45%, includes pits 26, 28
that form spike 29. The lengths of the spikes and depths of the
pits vary according to the modification treatment parameters. The
average depth of the pits on a particle ranges in size from about
5% to about 70% of the longest length of the particle.
[0050] As shown in FIG. 1b, the modified diamond particles 24
include significantly more spikes and pits than conventional
monocrystalline diamond. The spikes 29 act as cutting edges when
used in free-abrasive slurry applications. It has been discovered
that the performance of the diamond particles of the instant
application significantly improves when used in free abrasive
lapping applications within a liquid slurry or suspension. When the
modified diamond particles are used in a fixed bond system, the
pits and the spikes help secure the particle within the bond
system.
[0051] The superabrasive cutter 10 may be fabricated according to
processes known to persons having ordinary skill in the art. The
cutting element 10 may be referred to as a polycrystalline diamond
compact ("PCD") cutter when polycrystalline diamond is used to form
the polycrystalline volume 12. PCD cutters are known for their
toughness and durability, which allow them to be an effective
cutting insert in demanding applications. Although one type of
superabrasive cutter 10 has been described, other types of
superabrasive cutter 10 may be utilized. For example, in some
embodiment, superabrasive cutter 10 may have a chamfer (not shown)
around an outer peripheral of the top surface 21. The chamfer may
have a vertical height of 0.5 mm and an angle of 45.degree.
degrees, for example, which may provide a particularly strong and
fracture resistant tool component.
[0052] As shown in FIG. 2, a method 30 of making superabrasive
material may comprise steps of providing surface modified
superabrasive particles, wherein the surface modified superabrasive
particles have surface roughness less than about 0.89 in a step 32;
providing a substrate attached to a superabrasive volume formed by
the plurality of superabrasive particles in a step 34; and
subjecting the substrate and the superabrasive volume to conditions
of elevated temperature and pressure suitable for producing the
polycrystalline superabrasive material in a step 36.
[0053] In the method 30, the substrate may be cemented tungsten
carbide. The surface modified superabrasive particles may have a
plurality of pits on the surface. The depth of the pits may range
in size from about 5% to about 70% of the longest length of the
particle. The superabrasive particles may be at least one of cubic
boron nitride, diamond, and diamond composite materials.
[0054] One or more steps may be inserted in between or substituted
for each of the foregoing steps 32-36 without departing from the
scope of this disclosure.
EXAMPLE I
[0055] A 4-8 um monocrystalline diamond particles, e.g., diamond
powder, with a nominal mean size of 6 um was coated with a
nickel/phosphorous coating (90% Ni/10% P). The nickel coated
diamond powder contained 30 weight percent NiP and 70 weight
percent diamond. Each diamond particle was uniformly covered with
the NiP coating. Two 25 gram samples of the Ni coated powder were
heated in a furnace. One 25 gram sample was heated at 825.degree.
C. for 1 hour and the other at 900.degree. C. in a hydrogen
atmosphere for 2 hours. After the heating cycle was completed and
the coated diamond powder was cooled to room temperature, the
modified diamond particles were recovered by dissolving the nickel
coated diamond in two liters of nitric acid. The mixture was then
heated to 120.degree. C. for a period of five hours. The solution
was then cooled to room temperature, the liberated diamond settled
and the solution was decanted. The acid cleaning and heating steps
were repeated one additional time until substantially all of the
nickel had been digested.
[0056] After the nickel was removed from the diamond, the converted
graphite (carbon from diamond that has been converted to graphite
during the reaction with nickel) was then removed from the
particles using 2 liters of sulfuric acid heated to 150.degree. C.
for seven hours. The solution was then cooled to room temperature,
the diamond allowed to settle and the solution was decanted. The
sulfuric acid cleaning and heating steps were repeated one
additional time until substantially all of the graphite had been
digested.
[0057] The surface roughness and sphericity were obtained from
images of the base material and modified diamond particles taken
with a Hitachi model S-2600N Scanning Electron Microscope (SEM) at
a 2500.times. magnification. The SEM images were saved as TIFF
image files which were then uploaded into a Clemex image analyzer
Vision PE 3.5 that was calibrated to the same magnification
(2500.times.). In this example and for this magnification, the
calibration resulted in 0.0446 .mu.m/pixel resolution. The image
analysis system measured particle size and shape parameters on a
particle by particle basis. Measurements for a population of at
least 50 particles from each set of experiments were generated
automatically by the Clemex image analyzer. Mathematical formulas
used by the image analyzer device to derive the measurements are
found in the "Definitions" section above and can also be found in
the Clemex Vision User's Guide PE 3.5 .COPYRGT.2001. Surface
characteristics of the diamond particles of the five powder samples
are shown in the following Table 1.
TABLE-US-00001 Physical and Performance Data for 4-8 um Diamond
Powder Weight Powder Mean Specific Surface Material Re- Clemex,
Clemex, Sample Loss, % Size, um Area m.sup.2/gram moval, mg/hr
Roughness Sphericity 825C 30% Nickel (DOE #40) 35 5.6 1.29 279 0.77
0.47 900C 30% Nickel (DOE #9) 56 5.0 1.55 304 0.78 0.46 Iron-etched
SJK-5 4-8 um 52 5.7 1.55 276 0.68 0.34 SJK-5 4-8 um Baseline -- 5.7
0.88 126 0.89 0.64 4-8 um Polycrystalline -- 4.7 2.9 168 0.84
0.60
[0058] As can be seen from FIG. 2a, the surface texture of the
modified diamond particles produced using the nickel coating method
is significantly different than the surface texture of the starting
material. It is apparent that, at temperatures above 800.degree.
C., the nickel reacts with the diamond and creates a unique texture
that can be described by roughness and sphericity factors using the
image analysis method. Based on the data obtained in this example,
the roughness values changed from 0.89 to 0.77 for the 35 percent
weight loss sample and from 0.89 to 0.78 for the 56 percent weight
loss diamond. The sphericity values changed from 0.64 to 0.47 for
the 35 percent weight loss sample and from 0.64 to 0.46 for the 56
percent weight loss diamond after the modification process.
[0059] Note that, as can be seen in Table 1, although the
modification process at 900.degree. C. resulted in a higher weight
loss of diamond, and a slightly finer size and slightly higher
specific surface area compared to the process performed at
825.degree. C., there was essentially no difference in the
roughness and sphericity of these two samples. The surface texture
produced of the diamond particles could be qualitatively described
as having many small "teeth" or cutting points. Although these
features were most apparent when looking at the boundary of
particle profiles, they also exist across the entire surface of
each particle. It was thought that the increase in the number of
cutting points, or teeth, was responsible for the improved
performance of the modified diamond particles.
EXAMPLE II
[0060] A MBG-620 70/80 mesh monocrystalline diamond particles were
coated with a nickel/phosphorous coating (90% Ni/10% P). The nickel
coated diamond powder contained 56 weight percent NiP and 44 weight
percent diamond. Each diamond particle was uniformly covered with
the NiP coating. 5 grams sample of the Ni coated powder were heated
in a furnace at 1000.degree. C. for one and half hour under
hydrogen environment. After the heating cycle was completed and the
coated diamond powder was cooled to room temperature, the modified
diamond particles were recovered by dissolving the nickel coated
diamond in 500 ml of nitric acid. The mixture was then heated to
120.degree. C. for a period of five hours. The solution was then
cooled to room temperature, the liberated diamond settled and the
solution was decanted. The acid cleaning and heating steps were
repeated one additional time until substantially all of the nickel
had been digested.
[0061] After the nickel was removed from the diamond, the converted
graphite was then removed from the particles using 500 ml of
sulfuric acid and 100 ml nitric acid and heated to 150.degree. C.
for seven hours. The solution was then cooled to room temperature,
the diamond allowed to settle and the solution was decanted. The
sulfuric acid cleaning and heating steps were repeated one
additional time until substantially all of the graphite had been
digested.
EXAMPLE III
[0062] Surface modified diamond was made according to Examples I or
II by etching conventional diamond feed with a metal catalyst at
high temperature. The presence of metal catalyst back-converted
diamond to graphite and causes surface irregularities at localized
spots. The resultant product was treated with acid at high
temperature to remove any graphite and residual metal to give
diamond micron powder with a surface topology starkly different
than conventional product. The surface was rough due to large scale
pitting and these sites could act as locations of fracture
initiation when the diamond micron powder was subjected to HPHT
conditions. Therefore, for the same applied pressure conditions,
surface-modified diamond powder was crushed to a larger extent than
conventional diamond micron feed.
[0063] The method of fabrication was similar to conventional PCD
process. The micron feed was added to a cup of refractory metal
like tantalum, niobium etc. and encased in the cup with a source of
metal catalyst like cobalt, nickel etc. The cup was then surrounded
by gasket material and subjected to high pressure-high temperature
conditions (50 to 80 kbar, 1200 to 1800.degree. C.) in a hydraulic
press. At these HPHT conditions, the metal catalyst melted and
infiltrated the pack bed of diamond. Diamond went into solution in
the metal catalyst and re-precipitates out at contact points
between diamond crystals eventually forming an interlinked solid
structure of polycrystalline diamond as shown in FIG. 7a. FIG. 7b
shows polycrystalline diamond by using conventional diamond feed.
By using surface modified diamond, the PCD cutter showed more
fractured crystals in the diamond table and a novel
microstructure.
[0064] Cobalt counts for conventional diamond feed made PCD and
surface modified diamond feed made PCD are 1208 and 1298
respectively. Tungsten counts for conventional diamond feed made
PCD and surface modified diamond feed made PCD are 161 and 132
respectively. Compared to conventional diamond feed with surface
modified diamond feed, surface modified diamond made PCD cutter has
7.4% increase of cobalt and 18% decrease of tungsten by portable
XRF measurements.
[0065] While reference has been made to specific embodiments, it is
apparent that other embodiments and variations can be devised by
others skilled in the art without departing from their spirit and
scope. The appended claims are intended to be construed to include
all such embodiments and equivalent variations.
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