Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to bonding of diamond to
diamond and more particularly to bonding of a plurality of - -
diamond particles together to form a rigid, hard, wear resistant
compact of use as a drill stone, gem stone, in various diamond
tools and in other applications normally employing diamond.
In several important respects, diamond is the ultimate
material. It is the hardest of all substances, the most rigid
material known and also has the highest known compressive
strength. Its wear resistance and ability to scratch, abrade,
indent, and cut are superb. In diamond compacts, the superior
- qualities possessed by diamond are diluted or diminished by
the presence of a bonding agent which is substantially inferior
to diamond with respect to these qualities. To preserve to a
greater extent the ultimate qualities of diamond in a diamond
compact it is desirable to utilize a bonding medium that
possesses more of the characteristics of diamond than do metallic
elements employed as bonding media in U.S. Patent No. 3,141,746
to DeLai.
It has been found that diamond compacts of superior
properties can be formed by using a non-diamond abrasive sub-
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stance as a bonding medium for diamond particles and an effect-
` ive method for preparing such compacts has been found.
Accordingly, it is an object of this invention to
provide an improved diamond compact.
-- It is another object of this invention to provide
-~ diamond compacts suitable for use as drill stones, saw stones,
burnishing stones, dressing stones, gem stones and so forth.
It is another object of this invention to provide
improved diamond tools including a unitary shaped diamond
compact suitable for use as cutters, indentors, stylii, abraders,
dies, anvils, and so forth.
It is another object of this invention to provide an
improved method of bonding diamond to diamond.
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The present invention relates to a rigid diamond
compact consisting essentially of discrete diamond particles
notsubstantially exceeding 325 mesh in particle size
sintered together so as to form diamond-diamond bonds and
a non-diamond abrasive substance in an amount grea-ter than
2~ by weight and sufEicient to substantially fill voids
between the diamond particles but not exceeding in volume
- the volume of the diamond par-ticles. The non-diamond
abrasive has a Knoop (100 gram) hardness of at least 1,000
and being selected from the group consisting of boron,
silicon carbide, titanium boride, aluminum boride, silicon
..... .
boride, zirconium boride, aluminum oxide, tungsten carbide,
boron nitride, hafnium carbide, niobium carbide, silicon,
, . . .
tantalum boride, vanadium boride, beryllium oxide, magnesium
~ oxide and boron phosphide.
'~ In its method aspect, the invention relates to a
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method of making rigid diamond compacts which comprises
subjecting a mixture of diamond particles and a non-diamond
abrasive substance having a Knoop (100 gram) hardness of at
least about 1000 or a progenitor of such substance under the
conditions of treatment to a temperature of at least 900 K
under pressure, not less than about 10 kilobars, at which
diamond is crystallographically stable at the temperature and
for the time of treatment; said non-diamond abrasive substance
being selected from the group consisting of boron, silicon
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carbide, titanium carbide, titanium boride, aluminum boride,
silicon boride, zirconium carbide, aluminum oxide, tun~sten
carbide, boron nitride, hafnium carbide, niobium carbide,
silicon nitride, beryllium carbide, vanadium carbide, silicon,
- 30 tantalum boride, vanadium boride, beryllium oxide, magnesium
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oxide, aluminum nitride and boron phosphide; and wherein the
mixture is subjected to a condition of pressure and temperature
specified later in this disclosure.
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Other ob~ects and ad~an~ages of the I~ention will
become apparen~ upon co~sideration of the method and produets
of the invention more ~ully described herein with reference
to the accompanying drawings whersin:
Figure 1 ls a graphical repre~entation of the critical
prcs~ure-temperature conditions utilized in the method o~ the
inventio~;
Fi~ure 2 is a schematic view o~ a suitable apparatu3
and cell for obtaining the critical pres~ure-temperature con-
ditions shown in Figure'l;
Figure 3 is a sectional Yiew of the cell shown ln
Figure 2; and
~ igure 4 i~ a representation of a unitary shaped
diamond compact tool made by the method of the i~ven~io~l,
The me~hod of this in~ention comprise~ in one of its
~orm~, the ~iKing together of diamond particles with the par_
ticles of a non-diamond hard abraqive and subje¢ting the ~xture
of the critical pre~sure-temperature ra~ge within area ~ o~
Figure 1 wherellpon bonding occur~ and a compact i5 formed~
In another form o~ the ~ention, diamond par~icles
and a ~ubstance tha~ i~ and of itself is not a hard abrasive
but w~ll become so when subjected to condi~ions within ar~a A
of Figuro 1 are tog~ther subjected to the erit~cal pr~ure-
temperature conditions of area A of Figure 1 whereupon the
hard abrasiv~ bonding agent ~s formed and bonding occur~.
In certain instance~, this type of bonding age~t may react or
illteract ~ith the diamond powder to form the hard abrasive
bo~di~g agent~ the ultimate result of this mathod (wh~ch might
be called the indirect method) i9 that the compact f~nally
~ormad undsr the critical pressure-t~mperature co~dition~
co~is~s e~e~tially o~ diamond particl~ bonded together by
a non~diamond hard abrasive ~ub~tanc~.
TYPiGa1 of the abra~ive sub~tarlce~ wh~ch may be
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utili%ed as bonding age~ts for diamond p~rtlcles in producing
the diamo~d compacts of the invention are boron, Qilicon
carbide, ti~anium carbide, titanium boride, aluminum boride,
Rilicon boride, zirconlum carbide, aluminum oxide, tungsten
carbide, boron nitr~de, hafnium carbide9 niobium carbide9
~ilicon nitride, beryllium carbide, vanadium carbide, silicon,
kantalum boride? vanadium boride beryllium oxide, magnesium
o~ide~ aluminum nitride and boron phosphide and in ganeral non-
diamond abra~ive substances having a Knoop (100 gram) hardnes~
of at least about 1000.
In the method of my copending Ca~adian patent
application 5erial No. 61,157 filed September 4, 1969, diamond
powder may be H~elf bonded'l. That is to Aay, no extran~ous bond-
ing agent is added to the diamond powder. IR self bonding, the
ultimate intrinsic properties of diamond can be preserved in
their en~irety in ~he compositeO However, when it is required
to maka a nearly fully dense composite (a composite of nearly
zero porosity)? the pressure a~d temperature required are very
~ear the upper practical produc~ion limits than can be achieved
in known high pres~re, high t~mperature devices. ~t ~hese
upper limi~s o~ pressure and temperature, the sample size i8
relatiYely small and the breakage of expe~siYa, vital device
compo~ents ~uch as anvils i~ relatively high~ Tharefore,
while self bonding ~f diamond powder can produce a composite
prod~ct most clo3ely re~embling ma~sive diamond, the composit~
thus obtained is rolatlvely small in si3e a~d the production
cost is relatively higho
In ~o~trast to these limlting co~sideratio~g diamo~d
powder may be bonded with a non~diamond hard abrasive ~ubstance
to give a compact of ~early zero porosi~y a~ a ~igni~icantly
lower te~perature a~d pressure. ~n~eq~en~ly largar compacts
ca~ be produced and a cost reduction can also be obta~ned~
In or~er to produce a diamond compact by the me~hod o~
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~- the present invention, it is essential to carry out the bonding
in a critical pressure-temperature region shown as A in Figure
1. Region A i9 bounded on the left by an approximate minimum
practical bonding temperature of about 900K and on the right
by a temperature dependent minimum stabilization pressure line.
The minimum stabilization pressure at any given temperature
may vary somewhat from that given by the graph since it depends
to a certain extent on the size, purity, and surface character-
istics of the diamond particles present in the powder and also
on the nature of the bonding agent.
The approximate minimum practical bonding temperature
also depends somewhat on the characteristics of the diamond
particles and on the bonding agent. Region A is also bounded
by a minimum practical bonding pressure of about 10 kilobars
as is shown by the horizontal line at this pressure in Figure 1.
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The minimum practical bonding pressure is also influenced some-
; what by the purity, size, surface characteristics and other
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properties of the diamond and also by the nature of the bonding
agent.
The time required to produce a satisfactory compac-t
is rather long near the minimum practical bonding temperature
line hut decreases as the temperature is increased. Also,
the density of the compact increases and the porosity corres-
pondingly decreases with increasing temperature.
- Increased pressure also increases the density and
decreases the porosity of the diamond compact.
Any type of pressure-temperature apparatus or means
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` (as, for example, explosive means) capable of generating the
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: ; pressures and temperatures falling within the scope of this
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` 3~ invention may be utilized to make the compact. The following
description relates to one type of apparatus that may be
`~ employed and is intended only to be exemplary and to be non-
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~ limiting. Shown schematically in Figure 2 is a high pressure-
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: temperature apparatus representative of the apparatus of my
- U.S. Patent 3,159,876. The apparatus includes a pair 10 of
identical anvils wi~h square faces whose edges are 0.500 inch
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in length mounted for rectilinear movement along a common axis.
Two additional pairs of identical anvils 10' and 10" also mounted
Eor rectilinear movement are positioned in the common plane normal
to the common axis of the first pair of anvils 10. The three pairs
- of anvils converge to a common intersection and the six faces of
the anvils would define the faces of a cube at their position of
contact if cell 12 were absent.
The main body of the cell 12 is 0.625 inch on edge and is
fabricated of pyrophyllite. As illustrated in Figure 3, within
the body of the cell are steel current rings 15 and 15' 0.437 inch
-` O.D. by 0.374 inch I.D. by 0.150 inch long contacting molybdenum
current discs 14 and 14' each 0.437 inch in diameter by 0.003
inch thick. Contacting the molybdenum discs is a graphite tube
16 0.250 inch O.D. by 0.21 inch I.D. by 0~283 inch long via
identical graphite and discs 17 and 17'. The sample 13 to be
bonded is contained within the graphite tube.
In beginning a run a mixture of diamond particles and
bonding substance or its progenitor are placed inside the graphite
tube 16. The cell is assembled, its exterior painted with a water
suspension of rouge and dried for 10 minutes a-t about 150C. The
cell is then positioned in the press and the three pairs of anvils
` advanced until their faces inpinge squarely on the six cubic faces
of the cell. The anvil faces are smaller than the cell faces and
a further increase in pressure squeezes out pyrophyllite from the
edges of the cell to form a gasket with the sloping shoulders of the
anvils. The oil pressure -to the press is then rapidly increased
to the desired value to give a ram thrust of the required amount to
generate the appropriate pressure within the sample.
` A 60 cycle, single phase alternating current is then passed
; from one anvil face successively through the steel current ring 15,
molybdenum current disc 14, graphite end disc 17,
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graphite tube 16, graphite end disc 17', molybdenum current
disc 14' and steel current ring 15' to the opposite anvil face.
The relatively high electrical resistance of the graphite and
molybdenum components of the cell causes them to heat up quickly
and within seconds transfer their heat to the sample 13. In
some instances, the sample 13 may in and of itself be electrica-
lly conducting and current passing through it may also contribute
to the heating. The electrical power for heating is supplied by
a high current low voltage transformer. The voltage to the
primary of this transformer is controlled by a variable auto-
transformer which is connected to the electrical mains. The
temperature attained in the sample is controlled by ad]usting
; the variable auto-transformer. Temperature within the sample
may be measured by a thermocouple placed therein or may be
estimated by measuring the powerinput to the sample by calli-
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bration procedures known to those skilled in the art.
After heating the sample for the n~cessary time,
heating power is discontinued after which the sample returns
to room temperature within a few seconds. After the sample
has cooled, the pressure is rapidly reduced to atmospheric.
; The cell is then removed from the press, broken open and the
-- diamond compact that has been produced is removed. Pressure
within the sample cell may be estimated by means of fixed point
; electrical resistance transitions occurring in certain metals,
for example bismuth, barium and thallium by procedures familiar
to those skilled in the art.
The proportion of bonding substance relative to the
. amount of diamond is not particularly ~riticaI ~owever, better
~` bonding is effected when the amount of bonding substance present
- 30 in the final compact does not exceed 50% by volume. The
amount of bonding substance is preferably such that the final
compact is firmly bonded and t~e voids between the diamond particles
filled without an excess of binding substance being present since
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excess bonding substance will unnecessarily dilute or diminish
- the intrinsic properties of diamond that it is desirable to
preserve in the compact.
The following non-limiting examples are given to illustrate
the present invention. The pressure-temperature apparatus of
Figure 1 is employed in each example.
EXAMPLE 1
An intimate mixture of about 1 micron average particle
diameter boron powder and of about 3 micron average particle
diameter diamond powder was prepared in the weight ratio of
1 part boron to 3 parts diamond. This sample was tamped into
the sample space within graphite heater tube 16 and subjected
to a pressure-temperature cycle as follows:
(a) Pressure was increased to about 65 kilobars in
about 60 seconds time,
(b) heating power was abruptly switched on whereupon
temperature in the sample increased to a steady state value
of about 2000K in about 4 seconds~
.~
(c) heating power was abruptly disconnected 10
seconds after it had been applied, the sample thereupon cooling
to room temperature in about 6 seconds,
(d) the pressure was then released to atmospheric
` over a period of about 10 seconds,
(e) the cell was removed from the press, broken
open and the compact that had been formed retrieved.
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The compact thus produces was in the form of a
cylinder about 0.153 inch in diameter by about 0.228 inch
long and weighed 0.220 gram or l.l carat. Its pycnometric
measured density was 3.11 grams per cubic centimeter. This
compact was mounted on the end of a l/2 inch diameter steel
rod and used as a single point dressing tool on a 14 inch
diameter by 3 inch face heavy duty grinding wheel in comparison
with a one carat natural diamond dressing stone similarly
mounted. The compact was almost as effective as the natural
diamond in dressing the grinding wheel and its wear was only
slightly greater. The compact was very tough, standing up to
repeated hammer blows without fracturing. When polished, the
compact revealed a beautiful black gem-like lustre.
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EXAMPLE 2
An intimate mixture of 28.5 wt% 1000 grit green
silicon carbide powder and 71.5 wt% 3 micron average particle
size diamond powder was subjected to a pressure of about 65
. . .
kilobars and while being sustained at this pressure temperature
was increased to about 2000K in about ~ seconds time said
temperature then being maintained for about 25 seconds follow-
ing which the temperature was reduced to room temperature in
; about 7 seconds after which the pressure was reduced to
' atmospheric in about 10 seconds whereupon the unitary cylindri-
~` cal diamond compact formed was recovered from the high pressure
apparatus. The compact weighe~d 1.28 caract and had a
pycnometric measured density of 3.26 grams per cubic centimeter
which is 95.0~ of the theoretical density of a pore-free com-
` pact containing silicon carbide and diamond in the porportions
of the original mixture of powders. This compact is hard and
tough and is very wear resistant to the action of the rotating
~` cast iron lap charged with diamond powder.
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EXAMPLE 3
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A mixture of 28.5 wt% soft non-adamantine boron
nitride and 71.5 wt~ of 3 micron diamond powders was subjected
to a pressure of about 65 kilobars simultaneously with a
temperakure of about 1~00K for about 180 seconds after which
the temperature was reduced to room temperature and then the
presssure was reduced to atmospheric. The cylindrical boron
nitride-diamond compact retrieved was hard, strong, and tough.
Its resistance to wear on the diamond charged cast iron lap
was very good. The pycnometric density was 3.41 grams per
- 10 cubic centimeter which is 97.5% of theoretical assuming that
all of the boron nitride was converted to dense hard
adamantine boron nitride.
- EXAMPLE 4
A mixture of 33.3 wt% titanium carbide powder and
66.7 wt% diamond powder both of -325 mesh size was subjected
to a pressure of about 65 kilobars and a temperature of about
1800K for about 10 seconds to yield a hard dense strong
electrically conducting black colored compact in the shape ~-
: of a cylinder about 0.165 inch diameter by 0.200 inch long
~: 2Q with a pycnometric density of 3.67 gram per cubic centimeter
which is 95.0% of the theoretical density of a pore-free com-
pact. This compact was very resistant to the action of the
cast iron lap and scratches silicon carbide with ease.
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EXAMPLE 5
A mi~ture consisting of 23.5~wt% aluminum oxide
powder of about 5 micron size and of 71.5 wt% diamond powder
of about 3 micron size was sub~ected to a pressure of about
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65 kilobars at a temperature of about 2000K for about 7
seconds and yielded a cylindrical compact about 0.155 inch
diameter by 0.245 inch long weighing 0.267 gram with a density
of 98~ of theoretical. This compact is white in color and has
a very high electrical resistance. It is hard and strong and
scratches tungsten carbide with ease.
EXAMPLE 6
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The experimental set up for this run was similar
to the foregoing examples with the exception that a graphite
10 insert of 0.210 inch diameter was 0.105 inch length with
a re-entrant conical void of 90 included angle and base
of 0.210 inch diameter with the cone axis coincident with
the cylindrical axis was placed adjacent to the graphite
- disc 17 with the re-entrant cone facing the opposite graphite
` disc 17'.
:
This served to modify the shape of the mixture from that
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``~ of a right circular cylinder when it was tamped into the sample
space surrounded by the graphite tube 16. The starting mixture
in this example consisted of 33.3 wt~ titanium boride and 66.7 wt~
diamond powders both of 325 mesh particle size. This mixture was
~;~ subjected to a pressure of about 65 kilobars at a temperature
' of about 2000K for about 7 seconds. The retrieved diamond-
titanium boride compact was a strong cohere~t cylinder with a
90 point formed on one end. This unitary shaped diamond compact
;- was mounted on the end of a steel shank as illustrated in Figure 4
` to provide a single point wheel dressing tool.
The particle size of the diamond and the hard abrasive
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~`.` bonding substance used in the practice of this invention are
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`~ : not critical. ~owever, better results are obtained when the
bonding substance particle size is equal to or smaller than
~- the diamond particle size. Relatively large diamond particles
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may be imbedded in a matrix consisting of smaller particles
of diamond and bonding substance to give a kind of concrete
analogous to the portland cement-sand-gravel mixtures used
in making construction concrete. Best results are obtained
when the finer particles of diamond (analogous to the sand) and
o~ bonding substance agent (analogous to the portland cement)
are of 325 mesh and smaller with even smaller sizes of 10
microns and less preferred. The diamond particle may be natural
or synthetic.
One of the advantages of operating in region A of
Figure 1 in the formation of a diamond compact is to prevent
the transformation of the diamond to graphite or other non-
diamond forms of carbon that are soft and weak. 'It is apparent
that, starting with a sample containing diamond particles at
normal room temperature and pressure, it is necessary to pass
through other pressure-temperature conditions in order to
bring the sample to the desired pressure-temperature area A
of Figure 1. In general any route through areas B or D to
area A is acceptable and the time taken to pass through area
B or D is not critical. On the other hand, passage through
area C, a region in which diamond particles transform into
non-diamond carbon, should be aYoided or else the region should
be traversed at an extremely rapid rate. In practice, region
C may be conveniently avoided by cooling prior to pressure
reductinn as was done in the examples cited.
The products of the present invention have particular
utility as drilli~g stones, gem stones, cutting tools, abrading
tools, burnishing tools, tool bits, indentors, stylii, anvils,
wear-resistant parts, bearings, heat sinks, dies, abrasives,
and, in fine, have uses in the same applications where diamond
is normally employed.
While specific compositions, methods, and devices in
accordance with this invention have been illustrated and
described, it is not intended that the invention be limited
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to the particular compositions, descriptions, or configurations
illustrated and it is intended by the appended claims to
cover all modifications within the spirit and scope of this
invention. The term "compact" as employed in the claims is
intended to be generic to masses of bonded, cemented, or
joined particles. The work "particle" includes crystalline
or non-crystalline solids or solid fragments of any shape.
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