Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~13~ 4 2!~ RD-8615
- This invention relates to the production of a poly-
crystalline body comprised of a mass of diamond and/or
cubic boron nitride crystals bonded together by a medium
comprised of silicon carbide and elemental silicon.
The present process utilizes a partial vacuum, i.e.,
pressures substantially below the superpressures required
by the diamond or cubic boron nitride stable region.
The present polycrystalline body or product can be
produced in a variety of configurations and a wide range
of sizes of predetermined shape and dimensions. It is
useful as an abrasive, cutting tool, nozzle or other
wear-resistant part.
Briefly stated, the present process for producing
a polycrystalline body of predetermined shape and size
comprises providing at least a substantially uniform
mixture of diamond and/or cubic boron nitride crystals and
a carbonaceous material wherein none of the surfaces of
said crystals are exposed significantly and wherein at
least a substantial amount of said crystals are enveloped
and separated from each other by at least a coherent
continuous coating of said carbonaceous material on said ,
crystals, said carbonaceous material being selected from
the group consisting of elemental non-diamond carbon,
an organia material which completely deaomposes at a
temperature below 1400C to elemental non-diamond carbon
and gaseous product of decomposition, and mixtures thereof,
said o~ganic material being present in an amount suf-
ficient on decomposition to produce on the crystal surfaces
it coat8 a coherent continuous aoating of elemental non-
diamond carbon, providing a mold with a cavity of desired
size and shape and means for introducing fluid silicon into
said cavity and means for maintaining a partial vacuum in
:
,. : . :. ; .... :~.,. .:
~3S4~ RD-8615
saicl cavity, filling said cavity with said mixture of
crystals and carbonaceous material and confining said
mixture therein, associating said filled cavity with a ~
mass of silicon, providing the resulting associated :~ :
structure with a partial vacuum wherein the residual ~ :~
gases have no significant deleterious effect on said
associated structure, heating said associated structure
in said partial vacuum to a temperature about 1400C at
which said silicon is fluid and which does not have a
significant deleterious effect on said crystals and ~ :
in~iltrating said fluid silicon throughout said confined
mixture, said partial vacuum being at least sufficient~ ~
to remove gas from said confined mixture which blocks said : ~ .
infiltrating fluid silicon, said infiltrating silicon
reacting with non-diamond elemental carbon forming silicon
carbide, cooling the resulting infiltrated mass of
crystals in an atmosphere which has no significant de-
leterious effect on said infiltrated mass, and recovering
the resulting polycrystalline body of said predetermined
shape and size wherein the crystals are bonded together
by a bonding medium comprised of silicon carbide and
elemental silicon and wherein the bonded crystals range
from about 1% by volume up to about but less than 80~
by volume of the total volume of said body, said body
being pore free or containing pores up to less than 5%
by volume of said body.
The present shape polycrystalline body is the product
of a like-shaped compact wherein the crystals in the
product are not significantly different from the crystals
in the compact. Briefly stated, the present polycry-
stalline body is comprised of crystals selected from the
group consisting of diamond, cubic boron nitride, and
' ' ,
~ 1 36 4 2t7 RD-8615
mixtures or combinations thereof, adherently bonded to-
gether by a bonding medium comprised of silicon carbide
and elemental silicon, said crystals ranging in size
from submicron up to about 2000 microns, the density or
volume of said crystals ranging from about 1% by volume
to about but less than 80% by volume of said body, said
bonding medium being present in an amount ranging up to
about 99% by volume of said body, said bonding medium
being distributed at least substantially uniformly
throughout said body, the portion of said bonding medium
in contact with the surfaces of said crystals consisting
essentially of silicon carbide, said polycrystalline body
being at least substantially pore free.
Those skilled in the art will gain a further and
better understanding of the present invention from the
detailed description set forth below, considered in
conjunction with the figures accompanying and forming
a part of the specification, in which:
Figure 1 is a sectional view through an apparatus
showing a preferred embodiment for carrying out the present
process and
Figure 2 is a photomicrograph (magnified 200 X~ of a
polished section of a polycrystalline diamond body prepared
by the present process wherein the diamond content, i.e.
volume, was about 55% by volume of the body. Specifically,
Figure 2 shows almost all of the diamond crystals at least
enveloped with a continuous phase which is silicon carbide.
The lighest colored phase of Figure 2 is elemental silicon
and appears to be substantially surrounded by the silicon
carbide phase, i.e., one side of the silicon carbide phase
enveLopes the diamond crystals whereas the opposite side
of the silicon carbide phase is in contact with the elemental
11364~ RD-8615
silicon phase.
The diamond crystals used in the present process can
be natural or synthetic. The diamond and/or cubic boron
nitride crystals of the present invention can range in
size in largest dimension from submicron up to about 2000
microns, and generally up to about 1000 microns. The
particular size or sizes used depends largely on the
particular packing or density of crystals desired and
also on the resulting body. For most abrasive applications,
crystals no greater than about 60 microns are preferred.
Preferably, to maximize the packing of the crystals, they
should be size-graded to contain a range of sizes, i.e.
small, medium and large-sized crystals. Preferably, the
size-graded crystals range from about 1 micron to about
60 microns, and preferably within this size range, about
60~ to about 80% by volume of the total mass of crystals
are of the larger sized portion of the range, about 5~ to
about 10~ by volume are of medium size with the balance
constituting the small-sized crystals or particles.
Sizing of the crystals is facilitated by the jet-
milling of larger crystals. Preferably, the crystals are
chemically cleaned to removed any oxides or other impurities
from the surface thereof before use in the present process.
This may be accomplished by heating the crystals in
hydrogen at about 900C for about one hour.
The present carbonaceous material is elemental non-
diamond carbon, an organic material, or mixtures thereof.
The present organic material decomposes completely at an
elevated temperature below 1400C, and ordinarily decomposes
completely at a temperature ranging from about 50C to
about 12Q0C, to produce elemental non-diamond carbon and
gaseous product of decomposition.
~13642~ RD-8615
Representative of the organic material useful in the
present process are polymers of aromatic hydrocarbons such
as polyphenylene and polymethylphenylene, derivatives of
polynuclear aromatic hydrocarbons contained in coal tar
such as dibenzanthracene and chrysene. Additional examples
of useful organic materials are the epoxy resins such as
the reaction product of epichIorohydrin and Bisphenol-A.
Still additional examples of useful organic materials are
phenolic resins obtained by the condensation of phenol -
or substituted phenols with aldehydes such as formaldehyde,
acetaldehyde, and furfural. Specific examples are the
condensation products of phenol-formaldehyde, resorcinol-
formaldehyde, aniline-formaldehyde, and cresol-formaldehyde.
In carrying out the present process, the mass of
crystals to be used to produce the present polycrystalline
body of predetermined size and shape is admixed with the
carbonaceous material to produce a uniform or at least a
substantially uniform mixture wherein none of the surfaces
of the crystals are exposed, or wherein at least none of
the surfaces of the crystals are exposed to any significant
extent. Also, at least a substantial amount, i.e., at
least about 90% by volume, of the crystals of the mixture
are enveloped and separated from each other by at least a
coherent coatin~ of the carbonaceous material. The surface
of the crystal that is not coated with carbonaceous material
is not exposed, but it is in direct contact with the surface
; of another crystal.
A number of techniques can be used to form the present
mixture of crystals and carbonaceous material and to shape
the resulting mixture to the form and dimensions desired
of the final product. For example, the elemental non-
diamond carbon can be deposited on the crystals by pyrolytic
, . . . ......... .
': , ' : . ' ` ~ ~ -
- ~
~36427 RD-8615
decomposition of a carbonaceous gas such as methane.
Specifically, the crystals can be placed in a furnace ~ ~
provided with a non-oxidizing atmosphere such as hydrogen, ~;
nitrogen or an inert gas such as argon. A source of
elemental non-diamond carbon such as natural gas or methane
is fed into the furnace ana the crystals are heated to a
temperature sufficient to decompose the methane, ordinarily
about 1200C whereby a pyrolytic carbon is deposited on
the crystals. As used herein the term, elemental non-
diamond carbon includes all forms of elemental non-diamond
carbon including graphite.
The present organic material is a solid or liquid
at room temperature and has no significant deleterious
effect on the crystals. If the organic material is a
solid-, it should be sufficiently softened, or preferably
dissolved in a suitabIe solvent to form a solution, before
being admixed with the crystals in order to produce a
uniform mixture. The organic materlal can be admixed with
the crystals by a number of techniques including, stirring ~ -
~ 20 the crystals with the organic material. If desired, the
; mixture then can be treated, for example subjected to a
vacuum or heat, to remove any solvent present and further
heated to decomposed the organic material producing elemental
non-diamond carbon in situ. Preferably, however, the wet,pliable
or plastic mixture is shaped or molded to the shape and
dimensions desired of the final product, and the resqlting
shaped mixture treated, if necessary, to retain its shaped
and dimensions and to impart sufficient mechanical strength i -
~ for handling. For example, a curing or cross-linkin~ agent
can be added to the organic material and the resulting
curable organic material admixed with the crystals, shaped
to the form and dimensions desired of the final product,
and cured sufficiently to retain its form. Shaping of the
- 6 ~
, . .', :': : , ' ~
. , , , . , ~ : . .
~1364Z7 RD-8615
wet, pliable or plastic mixture can be carried out by a
number of techniques, for example, in a temporary mold or
in the mold which is to receive the fluid silicon.
A mold with a cavity of desired shape and size is used.
The mold should be made of material which has no signi-
ficant deleterious effect on the present process or product.
Preferably, it is made of graphite and preferably it is
machinable to the size and shape desired of the final
product. Alternatively, the cavity of the mold can be
fitted, lined or pressed with a material which is sub-
stantially inert with respect to the present process and
product, such as hexagonal boron nitride powder, which can
be used to produce the final product of desired shape and
size. A parting agent, such as a film of hexagonal boron
nitride powder, preferably is sprayed on a material such
as graphite to enable a clean separation of the final
product from the mold.
The mold has means for introducing fluid silicon into
the cavity. For example, such means can be holes passing
through the mold wall and open to the cavity and to the
outside of the mold. Preferably, these infiltration holes
are located at the top or in the upper portion of the
mold so that the flow of fluid silicon into the aavity
is promoted by gravity. These holes can vary in number and
diameter depending largely on the extent desired for
introducing fluid silicon into contact with the confined
mixture.
The number of infiltration holes used is not critical
but with an increasing number of infiltration holes, the
faster the silicon is introduced into contact with the
confined mixture within the mold thereby reducing total
infiltration time. On the other hand, the infiltration
1136 427 RD-8615
holes should not be so great in number or diameter as to
allow the fluid silicon to be introduced into the cavity
to the extent that silicon surrounds the confined mixture
since that would entrap gas within the confined mixture
and prevent infiltration of the fluid silicon throughout
the confined mixture. Infiltration of the fluid silicon
should proceed through the confined mixture towards a
single external surface or external point of the confined
mixture which is sufficient in area to allow removal of
pockets of gas in the confined mixture by the partial
vacuum thereby allowing the silicon to infiltrate throughout
the confined mixture. Infiltration of the fluid silicon
through the confined mixture is by capillary action.
Generally, the infiltration holes range from about
10 mils to 125 mils in diameter and holes of large size
provide no significant advantage. Due to the surface
tension of elemental silicon which prevents it from passing
through such small holes,~these holes are provided with
a wick, preferably of elemental non-diamond carbon, which
passes, i.e., wicks, the fluid silicon through the holes
and into the cavity. The smaller the holes, the less
likely excess elemental Si/SiC material will be left on
the finished product. Ordinarily, any excess Si/SiC i
material on the surace of the finished product is in the ~ -
form of a nib or glob which can be ground, machined or
polished off in a conventional manner. `
The mixture of crystals and carbonaceous material
should fill the cavity of the mold in order to produce
the final product of desired shape and dimensions since
there is no change or no significant change between the
volume occupied by the mixture and the final product.
The mold, i.e., filled cavity, then is closed. Vents in
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~3~427 RD-8615
I
the mold preferably located in the bottom portion of the
mold, are used to evacuate the cavity and maintain the
desired partial vacuum therein. The filled mold is
associated with a mass of elemental silicon, which pre-
ferably is located above the mold.
Figure 1 shows a cross-section of an associated
structure or apparatus 10 illustrating a preferred
embodiment for carrying out the present process. Supporting
frame 11 is non-metal, preferably is made of graphite and
can be machined to the configuration desired. Mold 12
and cavity 13 are provided with a non-metallic connector
19, preferably of graphite, which passes through cavity
13 and which has a threaded end to keep mold 12 closed
during silicon infiltration. The mixture of carbonaceous
material and crystals 14 fills cavity 13 surrounding
connector 19. Holes 15 and 16 are provided with wicks 17
and 18 which pass silicon 20 in fluid into cavity 13 to
infiltrate through mixture 14. Vent holes 21 and 22 allow
for the escape of gas from cavity 13 which exit out of
vent 23. Vent holes 21, 22 and 23 are used to maintain
the required partial vacuum in cavity 13. Connector 19
leaves a hole of like diameter passing through the
finished product which has the form of a wheel with a
sharp edge and which is useful as a grinding wheel.
The associated structure or apparatus 10 is placed
within a furnace and provided with a partial vacuum wherein
the residual gases have no significant deleterious effect
on said associated structure. Specifically, the furnace
chamber is maintained under the partial vacuum which also
maintains the associated structure, i.e. the confined
mixture within the cavity of the mold and the associated
mass of elemental silicon, under partial vacuum. The
- ` 11364Z~ RD-8615
partial vacuum should be at least sufficient to remove
pockets of gas which may be trapped within the confined
mixture and which would block the infiltrating fluid silicon
thereby leaving pores in the finished product. Generally,
such a partial vacuum ranges from about 0.01 torr to about
200 torr, and usually from about 0.01 torr to about 100
torr to insure removal of entrapped gas in the confined
mixture.
Ordinarily and as a practical matter, the furnace
used is a carbon furnace, i.e. a furance fabricated from
elemental non-diamond carbon. Such a furnace acts as an
oxygen getter for the atmosphere within the furnace re-
acting with oxygen to produce CO or CO2 and thereby provides
a non-oxidizing atmosphere, i.e. the residual gases have
no significant deleterious effect on the crystals or in-
filtration cannot be carried out in air because diamond
graphitizes rapidly in air above 800C and the liquid
silicon would oxidize to form solid silica before any
significant infusion by silicon of the confined mixture
occurred. In such instance where a carbon furnace is not ` ~ `-
used, it is preferably to have an oxygen getter present `
in the furnace chamber, such as elemental non-diamond ;
carbon, in order to insure the maintenance of a non- `i
oxidizing atmosphere. Alternatively, such non-oxidiæing ~
atmosphere, or atmosphere which has no significant ~ -
deleterious effect on the associated structure within
the furnace, can be provided by a sufficiently high
partial vacuum, i.e. about 10 2 torr to 20 torr.
The confined mixture and silicon are heated to in-
filtration temperature which is above 1400C. When the
carbonaceous material is an organic material, such organic
material decomposes compLetely at a temperature below
- 10 -
~13~4Z7 RD-8615
1400C producing elemental non-diamond carbon and gaseous
product of decomposition. The mold-confined mass or
mixture that is infiltrated by the silicon consists
essentially of crystals, i.e. diamond, cubic boron nitride
or combinations thereof, and elemental non-diamond carbon.
The elemental non-diamond carbon in the mold-confined
mixture must be at least slightly porous to allow the
silicon to infiltrate therethrough. Specifically, the
elemental non-diamond carbon may range in porosity but
its density should not exceed 0.96 g/cc. If the elemental
non-diamond carbon is more dense than 0.96 g/cc, fluid
elemental silicon may not penetrate it, or if it should
penetrate such a dense elemental non-diamond carbon, the
resulting body will puff up and be distorted. The maximum
porosity of the elemental non-diamond carbon is that
which maintains the shape of the mold-confined mixture ~ ~ -
with none of the surfaces of the crystals being exposed
significantly, Generally, the maximum porosity for the
elemental non-diamond carbon is about 50% by volume of
the total volume of the elemental non-diamond carbon
present in the mold-confined shaped mixture.
The pores in the mold-confined mixture consisting
essentially of the crystals and elemental non-diamond
sarbon should be distxibuted uniformly or at least
significantly uniformly throughout the mixture to prevent
formation of excessively large pockets of elemental silicon
which may lower the mechanical properties of the re-
sulting polycrystalline product thereby limiting its
applications. The pores can range in size, and generally -
can range up to about 2000 microns, but preferably are not
larger than the size of the crystals used. For best
results, the pores are submicron in size.
-- 11 --
:, ;
113642 7 RD-8615
The ~orosity of the shaped mixture of crystals and
elemental non-diamond carbon is determinable by a number
of conventional techniques.
The present infiltration is carried out at a temperature
above 1400C at which silicon becomes fluid and which has no
significant deleterious effect on the crystals. For cubic
boron crystals infiltration temperatures significantly
higher than about 1450C are not useful since they are
likely to cause conversion to hexagonal boron nitride. On
the other hand, for diamond crystals, temperatures higher
than 1550C provide no significant advantage. By a
temperature at which silicon becomes fluid it is meant
herein a temperature at which the silicon is readily
flowable. The fluid silicon is highly mobile and highly
reactive with elemental non-diamond carbon, i.e. it hac an
affinity for elemental nondiamond carbon, wetting it and
reacting with it to form silicon carbide. Specifically, ~ -~
when silicon is at its melting temperature, which has been :~
~ . .
~; given in the art to range from about 1412C to about ;
1430C, it has a high`viscosity, but as its temperature is ~-
~: :
raised, it becomes less viscous and at a temperature about
ten degrees higher than itu melting point, it becomes fluid.
The temperature at which the silicon is fluid is the
temperature at whiah it will infuse or in~iltrate throu~h
the capillary-size passages, interstices or voids of the
present mold-confined mixture of crystals and elemental
non-diamond carbon. With increase in temperature, the
flowability of the fluid silicon increases resulting in a
faster rate of reaction.
Sufficient sllicon is infiltrated throughout the
mold-confined mass or mixture, infusing or infiltrating
11364Z7 RD-8615
through the voids or pores of the mixture by capillary
action to react with the total amount of elemental non-
diamond carbon present in the confined mixture forming
silicon carbide, and also to fill any pores or voids
which may remain after formation of the silicon carbide
producing an integral, strongly bonded and at least
substantially pore-free body. Specifically, silicon
carbide occupies more volume than elemental non-diamond
carbon thereby reducing porosity, and and p~ores remaining
after formation of silicon carbide are filled during
infiltration with elemental silicon. Also, during in-
filtration the silicon reacts with the elemental non-
diamond carbon coating on the surfaces of the crystals
forming a protective adherent coating of silicon carbide
on the diamond surfaces and causing no loss or no signi-
ficant loss of crystal and no change or no significant
change in the shape and dimensions of the crystals. The
resulting infiltrated mass is cooled in an atmosphere
which has no significant deleterious effect on said in-
filtrated mass, preferably it is furnace cooled in the
partial vacuum to about room temperature, and the
resulting polycrystalline body is recovered.
The period of time for full infiltration by the
silicon is determinable empirically and depends largely
on the size of the shaoed mixture, and frequently,
infiltration by the fluid silicon through the mold-
confined shaped mixture is completed within about 15
minutes.
A number of techniques can be used to determine the
extent to which silicon has infiltrated the mold-confined
shaped mixture of crystals and elemental non-diamond carbon.
- 13 -
11364Z~ RD-8615
For example, the mold can be cooled to room temperature,
opened and the extent of silicon infiltration observed.
In another technique the composition and weight of
the final polycrystalline body can be determined from the
porosity, amount of elemental non-diamond carbon and
amount of crystals present in a shaped mixture comprised
of the crystals and elemental non-diamond carbon~ Specifically,
the content of silicon carbide in the polycrystalline product
can be calculated from the amount of elemental non-diamond
carbon in the mixture. The porosity remaining after silicon
carbide reaction is completed will be the volume occupied ;
by elemental silicon. The weight of the final poly-
crystalline body is the total or approximately the total, - -~
of the weights of its crystal content, its silicon carbide
content and its elemental silicon content. As a result,
during infiltration, any gain in weight by the silicon~
infiltrated mixture can be used to determined the extent
of infiltration.
- The present polycrystalline body is comprised of
crystals selected from the group conisting of diamond,
cubic boron nitride and combinations thereof adherently
bonded together by a bonding medium comprised of silicon
carbide and elemental silicon, said crystals ranging in
size from submicron to about 2000 microns, the density
of said crystals ranging from about 1% by volume of said
body, frequently up to about 75% by volume of said body,
said bonding medium being present in an amount ranging up
to about 99~ by volume of said body, said bonding medium
being distributed at least substantially uniformly through-
out said polycrystalline body, the portion or surface ofsaid bonding medium in direct contact with the surfaces of
the bonded crystals being silicon carb~de. The present
- 14 -
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. .
RD-8615
~1364Z7
polycrystalline body is pore free or at least substantially
pore free.
The amount of silicon carbide in the present poly-
crystalline body depends on the amount of elemental non-
diamond carbon in the mold-confined mixture, and this is
illustrated by the following equation:
si + c > sic.
On the other hand, the amount of elemental silicon in the
polycrystalline body depends on the porosity or pores
remaining after the total amount of elemental non-diamond
carbon is reacted to form silicon carbide. However, the
present polycrystalline body always contains silicon carbide
in an amount of at least about 1% by volume of the body
and elemental silicon in an amount of at least about 1
by volume of the body.
The present polycrystalline body usually is free of
elemental non-diamond carbon phase. However, it may contain
non-diamond elemental carbon phase in an amount ranging -
up to about 5~ by volume of the body provided such non-
diamond elemental carbon phase is sufficiently distributed
throughout the body so as not to have any significant
deleterious effect on its mechanical properties. The
presence of the elemental non-diamond carbon phase is
detectable by standard metallographic techniques such as,
for example, by optically examinin~ a polished cross-
section of the body, or by transmission electron micros-
copy on a thin section of the body.
The present polycrystalline body is void or pore-free
or at least substantially pore-free, i.e. it may contain
voids or pores in an amount less than about 5% by volume of
the body dedending on its particular application application
providing such voids or pores are small, preferably less
- 15 -
` . ' ' . ': , , ' ,
113~427 RD--8 615
than 1 micron, and sufficiently uniformly distributed
throughout the body so that they have no significant
deteriorating effect on its mechanical properties. The
void or pores content of the present body is determinable
by standard metallographic technique such as, for example,
optically examining a polished cross-section of the body.
One particular advantage of this invention is that
the present polycrystalline body can be produced directly ~;
in a wide range of sizes and shapes which heretofore could ~ '
not be manufactured or required expensive and tedious
machining because of the very nature of the material. For
example, the present body can be as long as several inches,
or as long as desired, and be of very complex geometry,
and specifically, it can be produced in the form of a tube
or a hollow cylinder, a ring, a sphere or a bar having a
sharp point at one end. Also, since the present poly- ~
crystalline body is produced in a predetermined con- ~ -
figuration of predetermined dimensions, it requires
little or no machining. ~-
~20 A portion of the polycrystalline body produced by
the present invention can be soldered, brazed or other-
wise adhered to a suitable support material such as
sintered or hot-pressed silicon carbide, sintered or hot-
pressed silicon nitride, or a aemented carbide, or a metal
such as molybdenum forming a tool insert which, for
example, can be held by a tool shank adapted to be held
in a machine tool whereby the exposed surface of the poly-
crystalline body can be used for direct machining.
Alternatively, the present polycrystalline body can be
mechanically clamped to a lathe tool for direct machining
by the exposed surface of the polycrystalline body.
The invention is further illustrated by the following
- 16 -
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~13~7 RD-8615
examples tabulated in Table I where, unless otherwise
stated, the procedure was as follows:
Commercially pure silicon was used for infiltration.
The "Epon 828~' used is a resin formed from the
reaction of epichlorohydrin and Bisphenol A, which is a
liquid at room temperature and which has an epoxide
equivalent of 185-192. Epon 828 decomposes completely
below 1300 C.
The curing agent used was diethylenetriamine, a
liquid commonly called DTA which cures Epon 828 at room
temperature thereby solidifying it.
In each Example of Table I, the given crystals were
coated with a very thin coating of pyrolitic carbon ~;
deposited by the decomposition of natural gas. Specific- ~-
ally, for this coating procedure, the crystals were spread
out in a graphite crucible and placed in a graphite
furance which was a vacuum bell jar. The furnace was
evacuated down to 0.003 torr and heated to 1200C.
Methane from a natural gas line was admitted into the -
furance maintained at 4 pressure of 50 torr for about
five minutes. The furnace was then shut off and the
crystals were furnace-cooled to room temperature in the
0.003 torr vacuum. The crystals were then re-spread in
the crucible, returned to the furnace and the coating
procedure was repeated to insure a complete coating of
the crystals.
Examination of the coated crystals showed them to
have a continuous, coherent, very adherent coating of
elemental non-diamond carbon, i.e. over 99% by volume
of the crystals were separated from each other by the
carbon coating, and none of the surfaces of the crystals
were exposed. Since the deposited coating of elemental
non-diamond carbon on the crystals was very thin, i.e.
17
113~427 RD-8615
it ranged in thickness from about 500 Angstroms to about
1000 Angstroms, it did not add to the weight of the
crystals significantly, and therefore, the given crystal
weight in Table I is that of these carbon-coated crystals.
The given amounts of elemental non-diamond carbon,
Epon 828 and crystals, i.e. carbon-coated crystals, were
stirred at room temperature along with 0.1 gram curing
agent and sufficient methylethylketone, i.e. about 0.1 g
to 0.2 g, to form a substantially uniform mixture. Methyl-
ethylketone is a solvent for the Epon 828 resin anddistributes it through the mixture.
The resulting mixture was manually shapable and
was then shaped in a Teflon mold and heated in air to
about 80C for about 1 hour to evaporate methylethylketone
therefrom and accelerate curing of the resin. The cured
shaped mixture was removed from the mold without sticking,
in one piece, being held together by the cured resin. It
has the dimensions given in Table I, i.e. that of a uniform
bar in Example 1 and that of a uniform disc in Examples
2-6.
In each of the Examples the shaped mixture was fitted
into a graphite mold, wherein all of the surfaces had been
sprayed with hexagnol boron nitride.
The associated structure or apparatus for carrying
out the silicon infiltration was similar to that shawn in
Figure 1. Specifically, a solid graphite cylinder was used
with a cavity drilled into its upper end portion for
holding silicon and a cavity drilled in its lower end
portion for use as a mold cavity. The mold cavity was
drilled to correspond to the shape and dimensions of the
shaped mixture so that there was no significant free
space within the mold cavity when it was closed. An
- 18 -
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~13~2'7 RD-8615
infiltration hole, about 60 mils in diameter was drilled
substantially perpendicularly between the two cavities
connecting them. A wick of elemental non-diamond carbon
fiber, about 500 mils long and about 50 milsin diameter,
was positioned within the infiltration hole to extend
into the upper cavity, but to be just in contact with the
shaped mixture in the mold cavity. The shaped mixture was
placed within the mold cavity which was then closed with a
graphite plate forming a mold which was not air tight and
therefore could be ventilated without a vent hole. The
graphite plate was held in place by carbon filament or
graphite bars. A mass of granular elemental silicon was
placed in the upper cavity.
The resulting associated structure was placed in a
graphite vacuum furnace which was evacuated to about
0.1 torr and maintained at about 0.1 torr during silicon
infiltration and subsequent furnace-cooling to room
temperature. The residual gases in the furnace were
non-oxidizing. -
The furnace was heated to the given infiltration
temperature and maintained at such temperature for the
given period of time. The power was then cut off and the
structure was furnace-cooled to room temperature.
The amount of infiltrating silicon was sufficient
to completely infiltrate throughout the mold-confined
mixture of crystals and elemental non-diamond carbon, and
completion of the silicon infiltration in the given time
was based on experience and results with similar runs.
In each example, the polycrystalline body was
recovered from the mold without sticking. The remains of
the infiltration wick were machined off. The resulting
polycrystalline body was in the form of a uniform bar or
113~427 RD-8615
disc as given in Table I.
Density of the Polycrystalline Body was determined
by means of water displacement.
A portion of a surface of each polycrystalline body
was polished on a cast iron scaife.
In each example the polished surface of the poly-
crystalline body was examined optically magnified about
500 times under a microscope to determine its micro-
structure.
Since the amount of crystals remained the same or
dld not change significantly from that in the shaped
mixture the volume fraction of crystals in the poly-
crystalline body was calculated and also was based on the
appe?rance of the polycrystalline body.
The volume fraction of silicon carbide in the poly-
crystalline body was calculated based only on the amount
of elemental non-diamond carbon added to the shaped
mixture, since in all of these examples the amount of --
elemental nondiamond carbon deposited as coating on the
crystals and that produce from "Epon 828" was not
significant.
The volume fraction of elemental silicon in the
polycrystalline body was calculated and also was based
on the pore-free or substantially pore-free appearance
of the polycrystalline body of each example.
- 20 -
.
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~3~42q
RD-8615
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-- 21 --
~13~`42~ RD-8615
A11 of the examples of Table I illustrate the present
invention.
In each example the recovered polycrystalline body
was integral and had dimensions which were not different
or not significantly different from the given dimensions
of the shaped mixture.
In each example, optical examination of the external
polished surface of the polycrystalline body showed it
to be uniformly and completely infiltrated and the bonding
medium appeared to be uniformly distributed. These appeared
to be no loss or no significant loss of diamond or cubic
boron nitride crystals, and no change or no significant
change in the shape and dimensions of the diamond or
cubic boron nitride crystals. Elemental silicon was seen
as a shiny phase, submicron in size, and substantially
uniformly distributed. In addition, the polished surfaces
of the polycrystalline bodies appeared to be free or
substantially free of elemental non-diamond carbon phase.
A polished section of the polycrystalline body of
Example 3 is shown in Figure 2. Specifically, Figure 2
shows almost all of the diamond crystals at least
surrounded with a continuous phase which is silicon
carbide. The lightest coloxed phase of Figure 2 is
elemental silicon and appears to be substantially
surrounded by the silicon carbide phase, i.e. one side
of the silicon carbide phase envelope the diamond crystals
whereas the opposite side of the silicon carbide phase
is in contact with the elemental silicon phase.
Because of their particular volume fraction of
crystals, the polycrystalline body produced in Example 1
would be useful as a saw blade segment, whereas the poly- ~
crystalline bodies of Examples 2-6 would be useful as a
- 22 -
,
` 1136427 RD-8615
wear surface or cutting tool.
A polycrystalline diamond body was prepared in
substantially the same manner as disclosed for Example 3
and had substantially the same composition.
Its abrasion resistance was tested by means of a
lathe turning test. Specifically, the cylindrical poly-
crystalline dia~ond body was ground on the outside diameter
to 0.5065 inches o.d. and surface ground to a thickness
of 0.178 inches. The finished tool, i.e. the ground
polycrystalline diamond body, was mounted in a clamping
tool holder at a slightly negative rake angle. A work-
piece consisting of a cylinder of "Black Diamond"
(Ebonite filled with silicon sand), 5.6 inches in diameter
and 24 inches long was used for testing. The workpiece
was rotated at 293 rpm. The depth of cut was set to
0.030 inches and the tranverse rate to 0.005 inches per
revolution. After 16.2 minutes of machining by the
polycrystalline diamond tool, a wear land, 0.010 incbes
- long formed on the edge of the diamond tool. Its
abrasion resistance factor, calculated by dividing the
machining time in minutes by the length of the wear land,
was 16.2. The polycrystalline diamond tool was rotated
to expose a fresh cutting edge and the lathe turning test was
repeated with identical results.
The tool was then rotated again to expose fresh
diamond cutting edge and *he lathe turning test was
repeated again. After 32.4 minutes of machining, an
abrasion resistance factor of lB.0 was produced~ The tool
was then rotated again to expose a fresh diamond cutting
edge, and the lathe turning test was repeated. After 64.8
minutes of machining, an abrasion resistance factor of
36.0 was produced.
1~ 3~ ~ 2 ~ RD-8615
A polycrystalline diamond body was prepared in
substantially the same manner as set forth for Example 1
and it had substantially the same composition.
The polycrystalline body was abraded manually against
a piece of sandstone to expose the diamond. Its use-
fulness as a saw blade segment was determined by attaching
the polycrystalline diamond body in a clamping device to
the blade of a laboratory scale frame saw. The saw was
then set in motion reciprocating a distance of 2 5/8 inches,
60 times per minute. The workpiece, a block of Somerset
(Ohio) Marble, was fed up through the blade at an initial
rate of 0.005 inches per minute and gradually increased to
0.25 inches per minute. Free cutting of the workpiece
by the diamond body was observed throughout until the
diamond body fractured due to stress from the clamping
device. Similar results were obtained in sawing Tarn
granite (0.005 inches/minute only~.
- 24 -
