Note: Descriptions are shown in the official language in which they were submitted.
POLYCRYSTALLINE DIAMOND BODY/
SILICON CARBIDE OR SILICON NITRIDE SUBSTRATE COMPOSITE
This invention relates to the production of a
polycrystalline diamond body/silicon carbide or silicon
nitride substrate composite comprised of a dense mass of
diamond crystals bonded to a silicon carbide or silicon
nitride substrate. The diamond crystals are bonded
together and to the silicon carbide or silicon nitride
substrate by a silicon atom-containing bonding medium.
loOne of the technical barriers to a high density ~high
volume o-f diamond in a body) diamond base compact made below
the diamond stable pressure region has been the development
of a suitable binder material which will infiltrate the
; capillaries of a densely packed fine particle size diamond
powder The binder must form a thermally stable strong bond
with diamond and should not graphitize or excessively react
with the diamond.
The present in~ention utilizes a eutectiferous
silicon-rich alloy which infiltrates well through the
~ocapillaries of a compressed mass of diamond crystals and
which wets the crystals to form a strong cemented diamond
body. In addition, the infiltrating alloy forms a strong
bond in a situ with a silicon carbide or silicon nitride
substrate. The present process also utilizes pressures
substantially below those required by the diamond stable
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RD-1033~/10335
region to produce a polycrystalline diamond body/silicon
carbide or silicon nitride substrate composite in a number of
` configurations and a wide range of sizes. It is useful as an
abrasive, cutting tool, nozzle or other wear resistant part.
Briefly stated, the present proeess for preparing a
polycrystalline diamond body/silicon carbide or silicon
nitride composite includes a hot-pressing step and comprises
placing within a protective container or cup a mass of solid
eutectiferous silicon-rich alloy, or solid components for
producing eutectiferous silicon-rich alloy, a mass of diamond
crystals and a silicon carbide or silicon nitride substrate,
said mass of diamond crystals being intermediate and in
contacts with said substrate and said mass of solid
eutectiferous silicon-rich alloy, or with at least one of
said components for providing eutectiferous silicon-rich
alloy, said eutectiferous silicon-rich alloy being composed
of silicon and a metal which forms a silicide with said
silicon, disposing said container and i~s contents wi-thin a
pressure transmitting powder medium that transmits applied
pressure substantially undiminished and remains substantially
unsintered during said hot-pressing applying sufficient
substantially isostatic pressure to said container and its
contents via said powder medium to substantially stabilize
the dimensions of said container and said contents
substantially uniformly producing a shaped substantially
isostatic system of powder-enveloped container wherein the
density of the resulting compressed mass of diamond crystals
is higher than 70/0 by volume of the volume of said compressed
diamond crystals, hot-pressing the resulting substantially
isostatic system producing fluid infiltrating eutectiferous
silicon-rich alloy and infiltrating said fluid eutectiferous
silicon-rich alloy through the interstices of said compressed
mass of diamond crystals and into contact with the contacting
surface of said substrate, said hot-pressing being carried
out at an hot-pressing temperature below 1600C under a hot-
pressing pressure sufficient to infiltrate said fluid
silicon-rich alloy through the interstices of said compressed
. RD-10334/10335
mass of diamond crystals, s~id solid eutectiferous silicon-
rich alloy, or solid components for eutectiferous silicon-
rich alloy being used in an amount sufficient to produce
suEficient fluid eutectiferous silicon-rich alloy at said
hot-pressing temperature to fill the interstices of said
compressed mass of diamond crystals and contact the
contacting surface of said substrate, said hot-pressing being
carried out at an atmosphere which has no significant
deleterious effect on said diamond crystals or on said
infiltratiug fluid silicon-rich alloy or on said silicon
carbide or silicon nitride substrate, said hot-pressing
converting less than 5% by volume of said diamond crystals to
non-diamond elemental carbon, said non-diamond carbon or the
surfaces of said diamond crystals reacting with said fluid
infiltrating silicon-rich alloy ~orming carbide, maintaining
sufficient pressure on the resulting hot-pressed
substantially isostatic system during cooling thereof to at
least substantially maintain the dimensions of said hot-
pressed system, and recovering the resulting polycrystalline
` 20 diamond body/silicon carbide or silicon nitride substrate
composite wherein the diamond crystals are present in an
amount of at least 70% by volume of the volume of the bonded
polycrystalline diamond body.
In an alternative embodiment of the present process no
protective container or cup is used, and in such embodiment
the mass of solid eutectiferous silicon-rich alloy, or solid
componènts for eutectiferous silicon-rich alloy, and mass of
diamonds and silicon carbide or silicon nitride substrate are
placed directly in a pre formed cavity of predetermined size
in the pressure transmitting powder medium. The cavity can be
formed in the powder by a number of techniques. For example,
the pressure transmitting powder medium can be placed in a
die, a solid mold of desired size can be inserted in the
- powder, and the resulting system pressed at ambient
temperature under pressure sufficient to ma~e the powder
~` stable in form, i.e. give the pressed powder sufficient
~`~ strength so that the mold can be withdrawn there~rom leaving
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RD-1033~/lQ335
the cavity it has depressed therein to function as a container
for the silicon carbide or silicon nitride substrate, mass of
diamonds and silicon-rich alloy. After ~he silicon carbide or
silicon nitride substrate, mass of diamonds and silicon-rich
alloy are placed within the cavity wi-th the mass of diamonds
intermediate said substrate and said alloy, additional
pressure transmitting powder is added to seal the cavity and
the entire system cold-pressed at ambient temperature to
dimensionally stabilize the cavity and its contents producing
a substantially isostatic system of powder-enveloped cavity
and contents.
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 iorming a part of the
speciication, in which:
Figure 1 is a portion of a silicon zirconium alloy phase
diagram showing the equilibrium diagram for eutectiferous
silicon-rich zirconiurn alloy useful in the present invention;
~o Figure 2 is a cross-sectional view of a cell, i.e.
container and contents, for carrying out infiltration of
silicon-rich alloy according to this invention;
` Figure 3 schematically represents apparatus for applyinglight pressure to the cell of Figure 2 whi]e the cell is bPing
vibrated to increase the density of the mass of diamond
crystals;
Eigure 4 is a sectional view through an apparatus for
applying at least substantially isostatic pressure to the
cell by means of a pressure trarlsmitting powder medium to
dimensionally stabilize the cell producing a substantially
isostatic system;
Figure 5 is a sectional view through a graphite mold or
the simultaneous application of heat and pressure9 i.e. hot-
pressing to the substantially isostatic system showing the
cell enclosed therein;
Figure 6 is an elevational view of a polycrystalline
diamond body/silicon carbide or silicon nitride substrate
composite prepared accordingly to this invention; and
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RD-lO334/~0335
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Figure 7 is a photomicrograph (magnified 690 X) of a
polished cross~sectional surface of the composite of the
present invention.
~ n carrying out the present process, the structure
comprised of the mass of diamond crystals intermedia-te and in
contact with a silicon carbide or silicon nitride subs-trate
and mass of the solid eutectiferous silicon-rich alloy is
subjected to a cold-pressing step at ambient or room
temperature to substantially stabilize their dinlensions
substantially uniformly and then to a ho-t-pressing step
whereby the silicon alloy produces fluid silicon-rich alloy
which is infiltrated throughout the mass of compressed
diamond crystals, and into contac~ with the silicon carbide
substrate.
Alternatively~ the mass of diamond crystals can be in
contact with at least one of the components used for forming
the eutectiferous silicon-rich alloy in situ, i.e. silicon or
alloying metal, and the silicon carbide or silicon nitride
substrate, mass of diamond crystals as well as the components
for forming the silicon-rich alloy, are subjected to a cold-
pressing step at ambient or room temperature to substantially
stabilize their dimensions and then to a hot-pressing step
whereby fluid eutectiferous silicon-rich alloy is produced
and infiltrated throughout the mass of compressed diamond
crystals and into contact with the silicon carbide or silicon
nitride substrate. The components for forming the silicon
alloy are positioned to form the silicon alloy before hot-
pressing is initiated, i.e. before the hot-pressing
temperature is reached.
The mass of diamond crystals~ mass of starting solid
silicon-rich alloy, or solid components for forming the
silicon-rich alloy, and silicon carbide or silicon nitride
substrate can be in a number of forms. For example, each mass
can be in the form of a layer with the layer of diamond
crystals intermediate the other layers. ~lternatively, the
starting silicon-rich alloy can be in the fo~m of a tube or
cylinder with a core extending through it, the alloy tobe
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RD-10334/10335
being ca~t so that it forms a close fit wi-th the inner wall of
the container, and the substrate can be in the form of a bar
which can be centrally positioned within-the core of the alloy
tube, and the encircling space between the silicon alloy tube
and substrate bar packed wi-th diamond crystals.
The diamond crystals used in the present process can be
natural or synthetic, i.e. man-made. They range in size in
largest dimension ~rom about 1 micron to about 1000 microns,
and the particular size or sizes used depends largely on the
particular packing or density of diamond crystals desired and
also on the particular use of the resulting body. ~or most
abrasive applications, for example, diamond crystals no
greater than about 60 microns are preferred. Preferably, to
maximize the packing of the diamond crystals in the present
process, they should be si~e-graded to contain a range oi
sizes, i.e. small, medium and large-si~ed crystals.
Preferably, the size-graded crystals range from about 1
micron to about 60 microns, and preferaly within this size
range, about 60~/o to about 80% by volume of the total mass of
crystals are of the larger sized portion of the range, about
5/0 to about 10% by volume are of medium size with the balance
. constitu~ing the small-sized crystals or particles.
Sizing of the diamond crystals is facilitated by the
jet-milling of larger diamond crystals. Preferably, the
diamond crystals are chemically cleaned to remove any oxides
or other impurities from the surface thereof before use in the
present process. This may be accomplished by heating the
diamond crystals in hydrogen at abou~ 900C for about one
hour.
In the present invention the starting solid
eutectiferous silicon-rich alloy, i.e. the term alloy herein
including intermetallic compound, is comprised of silicon and
a metal, i.e. alloying me-tal, which forms a silicide with the
silicon. Preierably, the present eutectiferous silicon-rich
alloy is comprised o~ silicon and a metal selected from the
group consisting of cobalt (Co), chromium (Cr), iron (Fe),
halnium (Hf), manganese (Mn), molybden~m (Mo), niobium (Nb),
.,
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RD-1033~/ 335
nickel (Ni), palladium (Pd), platium (Pt), rhenium (Re),
rhodium (Rh), ruthenium (Ru), tantalum (Ta)~ thorium (Th),
titanium (Ti), uranium (U), vanadium (V), tungsten (W) 9
yttrium (Y), zirconium (Zr) and mixtures thereof.
The present starting eutectiferous silicon-rich alloy is
a solid at room temperature and contains more than 50 atomic %
but less than 100 atomic % of silicon. Usually, it contains a
maximum of about 99.5 atomic % silicon depending largely on
the specific effect that the alloying metal has on the
resulting silicon-rich alloy. The present starting solid
silicon-rich alloy is eutectiferous in that it contains some
eutectic structure and can be of hypoeutectic, hypereutectic
or of eutectic composition. Using Figure 1 as an example, the
eutectic (2) is an alloy of specific composition which, under
equilibrium conditions, on cooling freezes at constant
temperature forming a solid of at least two phases, and which
on heating melts completely at the same constant temperature,
this constan~ temperature being referred to as the eutectic
temperature also given at (2). The eutectic (2) is the
composition at which two descending liquidus curves (3) and
(4), meet at eutectic point (2), and therefore, it has a lower
melting point than its neighboring hypoeutectic or
hypereutectic compositions. The liquidus is a curve or line
on a phase diagram representing under equilibrium conditions
the temperatures at which melting ends during heating of the
silicon alloy or freeæing begins during cooling thereof.
Speci~ically, the present starting solid eutectiferous
silicon rich alloy is one of the series of alloys on a
eutectic horizontal (1), i.e. the horizontal passing through
the eutectic point (2), and which e~tends from any alloy whose
composition lies to the left of -the eutectic (2) on an
equilibrium diagram and which contains some eutectic
structure, i.e. hypoetectic, to any alloy whose composition
-; lies to the right of the eutectic (2) on the equilibrium
diagram and which contains some eutectic structure, i.e.
` hypereutectic alloy.
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8 RD-1033~/10335
The star~ing solid silicon-rich alloy may or not be of
the same composition as the infiltrating silicon-rich alloy.
If all of the starting solid silicon-rich alloy becomes fluid
at the hot-pressing temperature then it will have the same
composition as the infiltrating silicon-rich alloy. However,
if only a portion of the starting silicon-rich alloy, i.e.
hypoeutectic or hypereutectic~ becomes fluid at the hot-
pressing temperature, the s-tarting alloy does not have the
same composition as the fluid infiltrating silicon-rich
alloy, and in such instance the infiltrating silicon-rich
alloy will be more rich in silicon than the starting
hypoeutectic eutectic alloy bu~ less rich in silicon than the
starting hypereutectic silicon-rich alloy.
Using Figure 1 as an example, the composition oi the
present infiltrating eutectiferous silicon-rich alloy and its
melting temperature is found on liquidus curves (3~ and (4)
and includes eutectic point (2). The area (5) defined by (1),
(2) and (4) is comprised of a solid phase, (Si) and a liquid
phase, i.e. liquid infiltra~ing alloy phase, with the amount
of solid phase increasing and the amount of liquid phase
decreasing correspondingly as the distance to the right from
eutectic point (2) along horizontal (1) is increased, i.e. as
the amount of silicon in the alloy is raised from that
contained in the eutectic. Likewise, the area (6) defined by
tl), (2) and (3) is comprised of a solid phase ~rSi2 and a
liquid phase, i.e. liquid infiltrating alloy phase, with the
amount of solid phase increasing and the amount of liquid
~ phase decreasing correspondingly, as the distance to the left
`. from eutectic point (2) along horizontal (1) is increased,
i.e. as the amount of silicon in the alloy is lowered from
that contained in the eutectic.
In carrying out the present process, the desired
composition of the present infiltrating eutectiierous
silicon-rich alloy and its melting temperature are found as a
point on the liquidus curves including the eutectic poin~ of
the phase diagram for the present silicon-rich alloy, and the
hot-pressing temperature is the temperature at which such
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R~-10334/10335
desired infiltrating silicon-rich alloy composition is fluid,
i.e. sufficiently flowable to infiltrate through -the
compressed diamond mass. When a starting solid silicon-rich
alloy is used that has the same composi-tion as tha~ of the
desired infiltrating alloy, the hot-pressing temperature is
the temperature at which the alloy is fluid ~7hich ranges from
about 10C to preferably a maximum of about 100C higher than
the melting point of the alloy, bu~ if desired hot-pressing
temperatures higher than this preferred maximum are useful
depending largely upon the particular alloy used. However,
hot-pressing temperatures higher than 1600C are not useful
since they tend to graphiti~e the diamonds excessively.
However, when the starting alloy does not have the same
composition as that of the desired infiltrating alloy, but
when it is heated to the melting point of the desired
infiltrating alloy it produces such infiltrating alloy as a
liquid phase, then the hot-pressing temperature is a
temperature at which such infiltrating alloy phase is
produced in fluid form, i.e. about 10C higher than the
melting point of the infiltrating alloy phase.
Using Figure 1 as an example, for a specific
infiltrating alloy of hypereutectic composition, its melting
point is found on liquidus line 4. For example, if the
; desired infiltrating hypereutectic alloy contains 95 atomic/O
Si, its melting point is found on liquidus line 4 to be about
1400C as shown by line 7. When the starting silicon-rich
alloy is of the same composition as the desired infiltrating
alloy as shown by line 7, all of the starting alloy would melt
at the melting temperature of 1400C, and the fluid or hot-
pressing temperature would range from about 1410C to about
preferably 1510C, or if desired, up to but below 1600C.
However, when the starting silicon-rich alloy is any
hypereutectic alloy to the right of line 7, on horizontal line
1 in the equilibrium diagram in Figure 1, the hot-pressing
temperature is the temperature at which the desired
infiltrating 95 atomic % Si-5 atomic % Zr alloy is produced in
fluid form which would be ~bout 14L0C
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RD-10334/10335
.
Also, at the hot-pressing temperature the starting alloy
should produce the desired infiltrating alloy in fluid form
in an amount sufficient to fill the voids of the compressed
diamond mass herein having a density of crystals higher than
70% by volume and into contact with the contacting surface of
the silicon carbide substrate filling pores or voids in the
interface between the contacting polycrystalline body and
substrate so that the resulting composite has an inter~ace
which is pore-iree or at least substantially pore-free. As a
practical matter the fluid infiltrating alloy should be
` produced at hot-pressing temperature in an amount of at least
about 1% by volume of the starting silicon-rich alloy.
The present hot-pressing is carried out at a temperature
at which the infiltrating silicon-rich alloy is fluid under a
pressure which need only be sufficient at the ho-t-pressing
temperature to break up interfacial refractory layers in the
diamond mass which prevent penetration by the fluid alloy
through the voids thereof and usually this requires a minimum
pressure of about 500 psi. Specifically, the hot-pressing
pressure can range from about 500 p9i to about 20,000 psi, but
usually it ranges from about 1000 psi to about 10,000 psi.
Hot-pressing pressures in the present process higher ~han
.- 20,000 psi provide no significant advantage.
By a temperature at which the infiltrating alloy is
flui~ it is meant herein a temperature at which the
infiltrating alloy is readily flowable. Specifically, a-t its
melting point given on the liquidus line, or eutectic point in
the case of a eutectic alloy, the infiltrating alloy is a
liquid thick viscous substance, but as its tempera~ure is
raised from its melting point, the infiltrating alloy becomes
less viscous, and at a temperature about 10C higher than its
melting point, the liquid infiltrating alloy becomes readily
flowable, i.e fluid. The temperature at which the
infiltr~ting silicon-rich alloy i8 fluid is the temperature
at which it will infuse or infiltrate through -~he capillary-
size passages, interstices or voids of the present compressed
mass of diamond crystals having a crystal density higher than
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- RD-1033
70~ by volume. With still additional increase in temperature
the flowability of the fluid infiltrating silicon-rich alloy
increases resulting in a faster rate of penetration throughout
the mass of diamond crystals, and at a temperature of about 100C
higher than its melting point/ the infiltratlng alloy usually has its
highest flowability and temperatures higher than this maximum
ordinarily need not be used.
The present silicon-rich alloy of eutectic composition
melts at a temperature below about 1~30C. For the preferred
group of silicon-rich alloys herein, the eutectic melting point
ranges from 870C for siPd eutectic alloy, i.e~ about 56 atomic
% Si, to 1410C for SiMo eutectic alloy composition, i.e. about
; 97 atomic % Si. As shown in Figure 1, the SiZr eutectic alloy
(2) contains 90.4 atomic % Si and has a eutectic melting temperature
o 1360C. The major phase of the present solid silicon-rich
eutectic alloy is almost pure silicon.
The present infiltrating eutectiferous silicon-rich
alloy has a melting point below about 1500C, usually from about
850C to about 1450C, and the temperature at which it becomes
fluid is at least about 10C higher than its melting point.
~` The starting solid silicon-rich alloy or solid
components for producing the present silicon-rich alloy can
be in the form of a con-tinuous solid or in the form of a
powder. The particular amount or volume of starting solid
silicon-rich alloy used can vary depending on the amount of
fluid infiltrating silicon-rich alloy it produces and the
capacity of the equipment. Generally, the infiltrating silicon-
rich alloy ranges in amount from about 25~ by volume to about
80% by volume, but preferably for best results, it ranges from
about 30~ to about 60% by volume of the present compressed mass
~ of diamond crystals having a density of crystals higher than
`~ 70% by volume.
The present hot-pressing step is carried out in an
atmosphere which has no significant deleterious effect on the
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- 12 - RD-10334
diamond crystals, or infiltrating silicon-rich alloy, or silicon
carbide substrate. Specifically, the hot-pressing step can be
carried out in a substantial vacuum or in an inert gas such as
argon or helium, or it can be carried out in nitrogen or hydrogen.
The present hot-pressing is carried out sufficiently rapidly so
that there is no significant reaction between the infiltrating
silicon-rich alloy and nitrogen or hydrogen. The hot-pressing
step cannot be carried out in air because diamond graphiti~es
readily in air above 800C and the fluid infiltrating silicon-rich
alloy would oxidi~e to form solid silica before any significant
infusion by the fluid alloy of the diamond mass occurred.
The silicon carbide substrate is a polycrystalline body
having a density ranging from about 85% to about IOO~ of the
theoretical density of silicon carbide. Silicon carbide
density given herein is the fractional density based on the
theoretical density for silicon carbide of 3.21 gm/cc. A silicon
carbide polycrystalline body having density less than ~bout 85%
is not useful because it would not have the required mechanical
strength for most applications, for example for use as a tool
insert. Ordinarily, the higher the density of the silicon
carbide body, the higher is its mechanical strength.
The silicon nitride substrate is a polycrystalline body
having a density ranging from about 80% to about 100~ of the
theoretical density of silicon nitride. Silicon nitride densi-ty
given herein is the fractional densi~y based on the theoretical
density for silicon nitride of 3.18 gm/cc. A silicon nitride
polycrystalline body having a density less than about 80~ is not
useful because it would not have the required mechanical strength
for most applications, for example for use as a tool insert.
Ordinarily, the higher the density of the silicon nitride body,
the higher is its mechanical strength.
In the present invention the polycrystalline silicon
carbide or silicon nitride substrate is a hot-pressed or
sintered body comprised of silicon nitride, i.e. it contains
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RD-10334
- 13 -
silicon nitride in an amount of at Least 90% by weight and
usually at least 95% by weight, and generally from 96% to 99% or
higher by weight, of -the body. An constituent or component of the
present polycrystalline silicon nitride body other than silicon
nitride should have no significant deteriorating effect on the
mechanical properties of the resulting composite. SpeciEically,
it should have no slgnificant deteriorating effect on the properties
of the silicon nitride and all other materials used in the present
process in preparing the composite or on the properties of the
; 10 composite itself.
Preferably, the present silicon carbide body can be
;prepared by sintering processes disclosed in U.S. Patent 4,004,934
issued January 25, 1977 and U.S. Paten~ 4,209,A74 issued June 24,
m~ 1990, both in the name of Svante Prochazka and both assigned to the
. 15 assignee hereof.
: Briefly stated, the sintered silicon carbide body can be
prepared by providing a submicron particulate mixture of B-silicon
. carbide, boron additive and a carbonaceous additive which is
free carbon or a carbonaceous organic material which is heat-
:20 decomposible to produce free carbon, and shaping the mixture into
a green body. In an alternative method a-SiC, submicron in size
but with an average particle size twice that of -SiC, is admixed
with the particulate mixture in an amount of 0.05% to 5% by weight
based on the -SiC. The green body is sinteredat a temperature
- 25 ranging from about 1900C to 2300C to the required density.
~ Specifically, the boron additive may be in the form of
-: elemental boron carbide or a boron compound which decomposes
at a temperature below sintering temperature to yield boron
or boron carbide and gaseous products of decomposition and is
used in an amount equivalent to 0.3% to 3.0% by weight of elemental
boron based on the amount of silicon carbide. During
sintering, the boron additive enters into solid solu~
tion with the silicon carbide, and when amounts of the
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14
RD10334/10335
:
additive in excess of that equivalent to about 1% by weight of
elemental boron are used, a boron carbide phase also precipitates.
The carbonaceous additive is used in an amount equivalent
to about 0.1% by weight to about 1.0% by weight of Eree carbon
based on the amount o~ silicon carbide. The additive can be
free carbon or a solid or li~uid carbonaceous organic ma-terial
which completely decomposes at a temperature of 50C to 1000C
to submicron size free carbon and gaseous products of decomposi-
tion. Examples of carbonaceous additives are polymers of aromatic
hydrocarbons such as polyphenylene or polymethlphenylene which
are soluble in aromatic hydrocarbons.
~he sintered body is comprisea of silicon carbide and
based on the amount of silicon carbide, from about 0.3% to
about 3~ by weight of boron and up to about 1% by weight o~
free carbon. The boron is in solid solution with the silicon
carbide or, alternatively, in solid solution with the silicon
carbide also present as a boron carbide phase. The free
carbon, when it is detectable, is in the form of submicron
par-ticles dispersed throughout the sintered body.
Preferably, hot-pressed silicon carbide bodies can be
prepared by processes disclosed in U. S. Patent 3,853,566
issued December 10, 1974 to Prochazka and U. S. Patent 4,108,929
issued August 22, 1978 in the names of Svante Prochazka and ~illiam
J. Dondalski, all assigned to the assignee hereof.
In one hot-pressing process, a dispersion of submicron
powder of silicon carbide and an amount of boron or boron
carbide equivalent to 0.5-3.0% by weight of boron, is hot-
pressed at lgO0-2000C under 5000-10,000 psi to produce a
boron-containing silicon carbide body. In another hot-
pressing process, 0.5-3.0% by weight of elemental carbon or
carbonaceous additive heat-decomposible to elemental carbon is
included in the dispersion.
Preferably, the polycrystalline silicon nitride body can be
prepared by sintering processes disclosed in Canadian Serial
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RD-10334/10335
Numbers 2~7,187 filed February 17, 1978 and 293,743 filed December
22, 1977 in the names of Svante Prochazka et al and assigned -to the
. assignee hereof.
Briefly stated, Serial No. 297,187 disclosed a sintered
`: silicon nitride body prepared by providing a homogeneous
dispersion of submicron size of silicon nitride and
a beryllium additive selected from the group consisting of
beryllium, beryllium carbide, beryllium fluoride, beryllium
nitride, beryllium silicon nitride and mixtures thereof, in
an amount wherein the beryllium component is equivalent to
from about 0.1% to about 2% by weight of elemental beryllium
based on the amount of silicon nitride, shaping the disper-
sion into a green body and sintering the green body from
about 1900C to about 2200C in a sin-tering atmosphere of
nitrogen at a superatmospheric pressure which at the sintering
temperature prevents significant thermal decomposition of the
silicon nitride and produces a sintered body with a density
of at least about 80% of the theoretical density of silicon
nitride, the minimum pressure of said nitrogen ranging from
about 20 atmospheres at a sintering temperature of 1900C to
a minimum pressure of about 130 atmospheres at a sintering
temperature of 2200C.
The process of Serial No. 293,743 is similar to that of
Serial No. 297,187 except that a magnesium additive is
included in the dispersion of silicon nitride and beryllium
additive, the green body is sintered from about 1800C to
about 2200C in a sintering atmosphere of nitrogen at superatmos-
pheric pressure which ranges from a minimum of about 10 atmospheres
at a sintering temperature 1800C to a minimum of about 130
atmospheres at a sintering temperature of 2200C. The magnesium
additive is selected from the group consisting of magnesium,
magnesium carbide, magnesium nitride, magnesium cyanide, magnesium
fluoride, magnesium silicide, magnesium silicon nitride and
: mixtures thereof. The magnesium additive is used in an amount
wherein the magnesium component is equivalent to from about
; 0.5~ by weight to about 4% by weight of elemental magnesium
based on the amount of silicon nitride.
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RD-1033~/10335
~ he polycrystalline body disclosed in Serial No. 297,187 has
a density ranging from about 80% to about 100% of the theoretical
density of silicon nitride and is comprised of silicon nitride
and beryllium ranging in amount from less than about 0~ eight to
less than about 2.0~ by weight of said silicon nitride. The poly-
crystalline body disclosed in Serial No. 293,743 is similar to that
disclosed in Serial No. 297,187 except that it also contains ma~nesium
ranging in amount from less than about 0.5% by weight to less that
about 4.0% by weight of the silicon ni-tride.
Preferably, hot-pressed polycrystalline silicon ni~ride bodies
can be prepared by processes disclosed in Canadian Serial No. 295,379
filed January 20, 1978 and 297,237 Ei.led February 17, 1978 in the
names of Greskovich et al and both assigned to the assignee hereof
Briefly stated, Serial No. 295,379 disclosed a hot-pressed
silicon nitrlde body prepared by providing ahomogeneous powder dis-
persion, submicron size, of silicon nitride and magnesium silicide
in an amount ranging from 0.5% to about 3% by weight based on the
amount of silicon nitride, and hot-pressing the dispersion in an
atmosphere of nitrogen from about 1600C to about 1850C under a
minimum pressure of about 2000 psi. The resulting polycrystalline
silicon nitride body has a density of about 80% to about 100% of the
theoretical density of silicon nitride and is comprised of silicon
nitride and magnesium ranging in amount from about 0.3% by weight
to about 1.9% by weight of the silicon nitride.
Briefly stated, Serial No. 297,237 discloses a hot-pressed
polycrystalline silicon nitride body prepared by providing
a powder disperson of submicron size of silicon nitride
and a beryllium additive selected from the group consisting
. of beryilium, beryllium nitride, beryllium fluoride,
30 beryllium silicon nitride and mixtures thereof, in an
amount wherein the beryllium component is equivalent to
about 0.1% by weight to about 2% by weight of elemental
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17
-10334/10335
beryllium based on the amount of silicon nitride, and hot-
pressing the dispersion in an atmosphere of nitrogen from
about 1600C to about 1850C under a minimum pressure of about
2000 psi. The resulting polycrystalline silicon nitride body
has a density of about 80% to about 100% of the theoretical
density of silicon nitride and is comprised o~ silicon
nitride and beryllium in an amount ranging from about 0.1% by
weight to about 2.0% by weight of said silicon nitride.
The thickness of the silicon nitride substrate can vary
depending on the final application of the resulting
composite, but it should be at least sufficiently thick to
provide adequate support for the polycrystalline diamond body
adhered thereto. For most applications9 to provide adequate
support for the adhered polycrystalline diamond body, the
silicon nitride substrate is preferably at least about twice
the thickness of the adhered polycrystalline diamond body.
In the arrangement shown in Figure 2, cell 10 consists of
cup 11 (right circular cylindrical wall with bottom). Within
cup 11 are disposed a disc 12 of eutectiferous silicon-rich
alloy, a mass 13 of diamond crystals in contact with silicon-
rich alloy 12, and a thick plug 14, e.g. a cylinder of
polycrystalline silicon nitride substrate fitting closely
into cup 11 and acting as a closure therefor.
Cup 11 is made of a material which is substantially inert
during the hot-pressing step, i.e. a material which has no
significant deleterious effect on the properties of the
present diamond body. Such a material can be a non-metal, such
as compressed hexagonal boron nitride, but preferably, it is
a metal, and preferably a metal selected from the group
consisting of tungsten, yttrium, vanadium, tantalum and
: molybdenum.
` No free space should be left within the plugged cup ~hich
would allow an intermixing or free movement of the contents
therein so that the contents, at least substantially as
; initially positioned, are subjected to the substantially
.~ isostatic prPssure of the cold-pressing step.
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RD-10334
- 18 -
The purpose of using size-graded diamond crystals is to
produce maximum packing of the diamond crystals. AlternatiVely,
or in addition thereto, the arrangement shown in Figure 3 is
useful for increasing the density or packing of the diamond
crystals. Specifically, cell 10 is placed on vibrating table
16 and held there under light pressure (about 50 psi) application
during the vibration of cell 10 to promote rearrangement of the
diamond crystals or particles to fill spaces and decreases void
content in order to increase the density of the diamond
mass to greater than 70% by volume of the diamond mass. The
requisite degree of consolidation is determinable by independent
testing on diamonds of the same size in a fixed dimension die.
Cell 10 is subjected to a cold-pressing step as shown
in Figure 4 which is carried out at room or ambient temperature
whereby only sufficient pressure need be applied to produce a
dimensionally stabilized substantially isostatic system.
Specifically, cell 10 is placed in the cylindrical core of pressure
mold 20 surrounded by mass 19 of very fine particles, preferably
-400 mesh, and more preferably ranging in size from about 2 microns
to about 20 microns of a pressure transmitting powder medium which
remains substantially unsintered under the pressure and temperature
conditions of the present process such as hexagonal boron nitride
and silicon nitride. This pressure transmitting particulate or
powder medium provides for the application of approximately
or substantially isostatic pressure to cell 10, whereby cell
10 and its contents are dimensionally stabilized, i.e. densified,
substantially unformly producing a shaped substantially
isostatic system of powder enveloped-cell wherein the density of the
resulting compressed layer of crystals is higher than 70% by volume of
` 30 the volume of compressed crystals. Pressure mold 20 (ring 22 and
pistons 23, 23a) may be made of tool steel and, if desired, ring 22
may be supplied within a sintered carbide sleeve 22a as shown
" to permit the application of pressure as high as 200,000 psi.
~,,.
Pressures higher that 200,000 psi provide no significant
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RD-10334
:, -- 19 --
advantage. Within the confines of piston 23, sleeve 22a and
piston 23a, pressure preferably in tl~e range of from about 20,000
psi up to about 100,000 psi, and usually up to about 50,000 psi,
is exerted on the pressure transmitting powder medium by the
pistons actuated in the conventional manner un-til the applied
- pressure becomes stabilized as is done in conventional powder
packing technology.
Specifically, the particular applied cold-pressing
pressure used in determinable empirically and a pressure higher
; lO than that pressure which produces a dimensionally stabilized
substantially isostatic system produces no signiflcant additional
densification or dimensional stabilization of cell 10 and its
contents.
The nature of present pressure transmitting power
medium, such as hexagonal boron nitride and silicon nitride, is
such that it results in an approximation of a hydrostatic action in
response to the uniaxially applied pressure to exert substantially
isostatic pressure over the entire surface of cell lO. It is
assumed that the applied pressure is transmitted substantially
undiminished to cell lO. The cold-pressing step diminishes the size
of the voids to maximize the pressure of capillary-size voids in
the diamond mass, and it also produces the required density of
; diamond crystals in excess of 70% by volume of the diamond mass.
This reduction in void volume also reduces the ultimate content of
non-diamond material in the diamond mass and provides more juxtaposed
` crystal-to-crystal areas properly located for effective bonding
together.
After completion of the cold-pressing step, the density
of the compressed diamond crystals in cell lO should be in excess of
70~ by volume of the volume of crystals. Specifically, the density
of the compressed layer of mass of diamond crystals ranges from 71%
up to about but less than 95% by volume, and frequently from about
! 75% to about 90~ by volume of the volume of diamond crystals.
The higher the density of the crystals, the less will be the amount
of non-diamond material present between the crystals resulting in a
` proportionately harder diamond body.
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RD-1033
- 20 -
~ he substantially isostatic system 21 of powder en~eloped
container resulting from the cold-pressing step is then subjected to
a hot-pressing step whereby it is subjected to a hot-pressiny
temperature and pressure simultaneously.
Speci~ically, when the cold-pressing step is completed,
either one of pistons 23, 23a is withdrawn and the resulting
consolidated substantially isostatic shaped system 21 is forced
out of liner 22a and into a hole of identical diameter in graphite
mold 30, the transferred system 21 now being contained within the
wall of hole 31 between graphite pistons 32, 32a. Graphite mold 30
is provided with thermocouple 33 to provide an indication of the
temperature being applied to the dimensionally-stabilized
substantially-isostatic system 21. The mold 30, with the
substantially-isostatic system 21 so contained, is placed inside a
conventional hot-pressing furnace (not shown). The furnace chamber
is evacuated or at least substantially evacuated causing evacuation
of system 21 including cell 10, providing system 21 and cell 10
with a substantial vacuum in which the hot-pressing step can be
carried out. However, if desired, at this point, nitrogen, or
hydrogen, or an inert gas such as argon can be fed into the
furnace chamber to provide the furnace chamber as well as system
21 including the interior of cell 10 with a suitable hot-pressing
atmosphere. While piston 32, 32a apply a uniaxial pressure, i.e.
the hot-pressing pressure, to system 21, the temperature thereof
is raised to a temperature at which silicon-rich alloy disc 12
produces fluid infiltra-ting silicon-rich alloy.
In the hot-pressing step the hot-pressing temperature
should be reached ~uickly and held at such temperatuxe under
the hot-pressing pressure usually for at least about one minute to
insure satisfactory infiltration through the interstices of the diamond
crystal mass. Generally, a hot-pressing time period ranging from about
1 minute to about 5 minutes is satisfactory. Since conversion of
diamond to non-diamond elemental carbon depends largely on time and
temperature, i.e. the higher -the temperature and the longer
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RD-10334
- 21 -
the time at such temperature the more likely the conversion to
non-diamond elemental carbon, the hot-pressing step must be
carried out before 5% by volume of the diamond is converted to
non-diamond elemental carbon and this is determinable empirically.
Conversion of 5% or more by volume of diamond to non-diamond
elemental carbon is likely to result in elemental non-diamond
carbon phase being le~t in t~e final product which would have a
significantly deleterious effect on its mechanical propertles.
In the hot-pressing step the application of the hot-
pressing pressure to the fluid infiltrating silicon-rich alloy
breaks up interfacial refractory layer or slag, largely oxide
as well as carbide, which usually forms between the fluld
silicon-rich alloy and diamond surfaces exposing the capillary
void system to the silicon-rich alloy, after which infusion
by capillary action occurs. Tests have shown that unless
sufficient pressure is applied and maintained throughout
hot-pressing to system 21 when the silicon-rich alloy is fluid to
break up the slag, infusion of the diamond mass by the silicon-rich
alloy will not occur.
During hot-pressing, as the fluid silicon-rich alloy
infiltrates and flows through the diamond mass and into contact
with the substrate, it encapsulates the surfaces of the
compressed diamond crystals reacting wi-th the diamond surfaces,
or any non-diamond elemental carbon which may form to
produce a carbide which at least in major amount and usually
in substantial amount is silicon carbide. During hot-
pressing, the infiltrating alloy also fills the interface
` between the contacting surfaces of the polycrystalline diamond
`~ body and substrate resulting in the production of a strong
adherent bond in situ. The resulting product is an integral
well-bonded composite. The infiltrating alloy may also pentrate
or diffuse into the substrate.
It is during this hot-pressing step that it is
particularly important that substantially isostatic
conditions be maintained so that when the silicon-rich alloy
is converted to the fluid state, this fluid will not be able
~r
6~
- 22 - RD-10334
to pass between mass 13 and cup 11 and escape to any
significant extent, but will be forced to move throughout the
mass 13 of diamond crystals.
When the hot-pressing step is completed, at least
sufficient pressure should be maintained during cooling of the
hot-pressed system 21 so that hot-pressed cell 10 is subjected
to substantially isostatic pressure sufficient to preserve
its dimensional stability. Preferably, hot-pressed system
21 is allowed to cool to room temperature. Hot-pressed cell
10 is then removed from the system, and the present composite
36 is recovered comprised of polycrystalline diamond body
13a bonded in situ directly to substrate l~a. Adherent
metal, if any, from the protective container and any squeezed
out excess silicon alloy at the outside surfaces of the
composite can be removed by conventional techniques such as
grinding.
When the present process is carried out with the
components in the form of layers, coextensive with each other
the resulting composite can be in a number of forms such as a disc,
square or rectangle, rod or bar and can have a flat face of bonded
diamonds.
When the present process is carried out with the
- silicon-rich alloy in the form of a tube or a cylinder with a core or
hole extending through it and the substrate is in the form of a bar
centrally positioned within the core of the tube and the encircling
space between the silicon alloy tube and substrate bar packed with
diamond crystals, the resulting composite is in the form of a
~` circular bar.
The present composite is comprised of a polycrystalline
; 30 diamond body integrally bonded to a substrate of a polycrystalline
i silicon carbide or silicon nitride body by a bond formed in situ.
The adhered polycrystalline diamond body of the present
composite is comprised of diamond crystals adherently bonded
to each other by a silicon atom-containing bonding medium,
said diamond crystals ranging in size from about 1 micron to
about 1000 microns, the density of said diamond crystals
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RD-1033
- 23 -
ranging from at least about 70% by volume up to about but less
than 90% by volume and frequently about 89% by volume of said
polycrystalline diamond body, said silicon atom-containing
bonding medium being present in said diamond body in an amount
ranging up to about 30% by volume of said diamond body, said
bonding medium being distributed at least substantially uniformly
throughout the polycrystalline diamond body, the portion or
surface of said bonding medium in contact with the surfaces of
the bonded diamonds being at least in major amount silicon
carbide, i.e. m~re than 50~ by volume of the portion or surface
of the bonding medium in direct contact with the surfaces
of the diamond crystals in silicon carbide. Preferably, the
portion or surface of said bonding medium in contact with the
surfaces of the bonded diamonds is silicon carbide at least
in substantial amount, i.e. at least about 85% by volume and
preferably 100% by volume of the bonding medium in direct
contact with the surfaces of the bonded diamond crystals is
silicon carbide. The diamond body of the present composite
is pore-free or at least substantially pore-free.
In the composite, the polycrystalline silicon nitride
substrate ranges in density from about 80% to about 100% of
the theoretical density of silicon nitride and contains
silicon nitride in an amount of at least 90% by weight of said
body and is free of constituents which have a significantly
deleterious effect on the mechanical properties of said
` composite.
In the composite, the polycrystalline silicon carbide
substrate ranges in density from about 85% to about 100% of
the theoretical density of silicon carbide and contains
silicon carbide in an amount of at least 90% by weight of said
body and is free of constituents which have a significantly
deleterious effect on the mechanical properties of said
composite.
In the present composite, at the interface between the
polycrystalline diamond body and silicon carbide or s~ilicon
nitride substrate, the bonding medium extends Erom the
` 24
RD-1033~/10335
polycrystalline diamond body into contact with -the substrate
at least substantially -filling any pores throughout the
interface so that the interface is pore-free or at least
substantially pore-free, i.e. it may contain voids or pores
in an amount less than 1% by volume of the total volume of the
interface providing such voids or pores are small, less than
0.5 micron, and sufficiently uniformly distributed throughout
the interface so that they have no significant deleterious
effect on ~he adherent bond at such interface. The void or
pore content at the interface is determinable by standard
metallographic techniques such as for example, optically
examining a cross-section of the composite. Generally, the
distribution and thickness of the bonding medium throughout
the interface is substantially the same as the distribution
and thickness of the bonding medium throughout the
polycrystalline diamond body of the composite. Ordinarily,
on the basis of a polished cross-section of the composite, the
average ~hickness of the bonding medium at the interface
would be substantially the same as the a~erage thickness of
. 20 bonding medium between the contacting diamond crystals of the
polycrystalline diamond body of the composite. Also, on the
. basis of a polished cross-section of the composite, the
~, maximum thickness of bonding medium at the interface would be
substantially equivalent to the thickness of bonding medium
~ between the largest contacting diamond crystals of the
r polycrystalline diamond body of the composite. Alternatively,
the maximum thickness of bonding medium at the interface can
be defined as about 50% of the largest size diamond crystals
: in tlle polycrystalline diamond body measured along their
longest edge dimension. The silicon carbide substrate may
also contain bonding medium produced by the penetration or
diffusion therein by the infiltrating alloy during hot-
` pressing.
The present silicon atom-containing bonding medium
always contains silicon carbide. ~n one embodiment, the
- present bonding medium is comprised of silicon carbide and
metal silicide. In ano~her embodiment, the present bonding
R~-10334
~ 25 -
medium is comprised of silicon carbide, metal silicide and
elemental silicon. In yet another embodiment, the present
bonding medium is comprised of silicon carbide, metal silicide
and metal carbide. In yet another embodiment, the present
bonding medium is comprised of silicon carbide, metal silicide,
metal carbide and elemental silicon. In still another embodiment,
the present bonding medium is comprised of silicon carbide, metal
carbide and elemental silicon. The metal components of the metal
silicide and metal carbide in the present bonding medium are
produced by the alloying metals present in the infiltrating alloy.
The metal component of the metal silicide present in the
bonding medium is preferably selected from the group consisting
of cobalt, chromium, iron, hafnium, manganese, rhenium, rhodium,
ruthenium, tantalum, thorium, titanium, uranium, vanadium,
tangsten, yttrium, zirconium and alloys thereof.
The metal component oE the metal carbide present
in the bonding medium is a strong carbide former which forms
a stable carbide and is preferably selected from the group
consisting of chromium, hafnium, titanium, ~irconium, tantalum,
vanadium, tungsten, molybdenum and alloys thereof.
The amount of elemental silicon, if any, and silicon
carbide in the bonding medium of the adhered polycrystalline
diamond body can vary depending on the extent of the reaction
bet~een the surfaces of the diamond crystals and the
infiltrating silicon-rich alloy as well as the reaction
between non-diamond elemental carbon and infiltrating
silicon-rich alloy. Assuming all other factors are equal,
the particular amount of silicon carbide present in the
bonding medium in the adherent polycrystalline diamond body
depends largely on the particular hot-pressing temperature
used and the time period at such temperature. Specifically,
with increasing time and/or temperature, the amount of
silicon carbide increases while the amount of elemental
silicon decreases or is reduced to a non-detectable amount.
The production of the present body of bonded diamond crystals
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RD-1033
- 26 -
with a particular desired amount of sillcon carbide to attain
certain desirable properties, for example, is determinable
empirically.
Specifically, the bonding medium in the adhered
polycrystalline diamond will always contain at least a detectable
amount of silicon carbide and at least a detectable amount
of a silicide and/or carbide of the alloying me-tal present in the
infiltrating alloy. The metal silicide is usually in the
form of a disilicide depending upon the particular infiltratin~
- 10 alloy used. The bonding medium may also contain at contain at
least a detectable amount of elemental silicon. By a detectable
amount of silicon carbide, metal silicide, metal carbide or
elemental silicon it is meant herein an amount detectable by
selective area diffraction analysis of transmission electron
microscopy on a thin section of the present body. Generally,
however, the present bonding medium in the diamond body
contains silicon carbide in an amount ranging from about 1%
by volume to about 25~ by volume of the present polycrystalline
diamond body and usually metal silicide in at least a
detectable amount, and frequently in a minimum amount of about
0.1% by volume of the polycrystalline diamond body. The
particular amount of metal silicide present depends largely
on the composition of the infiltrating silicon-rich alloy.
The metal silicides are hard and also frequently have lower
linear thermal expansion coefficients than the metals, or
in some instances lower than diamond, as for example rhenium,
a desirable property for a phase in a polycrystalline diamond
body. The particular amount of silicon carbide and elemental
silicon present depends largely on the composition of the
infiltrating silicon-xich alloy as well as on the extent of
the reaction between the infiltrating silicon-rich alloy and a
diamond or non-diamond carbon. The particular arnount of metal
carbide present depends largely on the composition of the
infiltratin~ silicon-rich alloy.
Selective area diffraction analysis of tran.smission
electron microscopy on a thin section of the present
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~ D-10334
- 27 -
composite also will show that the portion of the bonding medium
in contact with the surfaces of ~he bonded diamonds is at least
in major amount silicon carbide.
The present adhered body of bonded diamond crystals is
void or pore-free or at least substantially pore-free, i.e. it
may contain voids or pores in an amount less than 1% by volume
of the body providing such voids or pores are small, less than
0.5 micron, and sufficiently uniformly distributed throughout
the body so that they have no significant deleterious eEfect on
its mechanical properties. The void or pore content of the present
body is determinable by standard metallographic technique such as,
for example, optically examining a polished cross-section of the
body.
The present adhered diamond body also is free of non-
di~mond carbon phase in that it does not contain non-diamond elemental
carbon phase in an amount detectable by X-ray diffraction analysis.
One particular advantage of the present invention is
that the polycrystalline diamond body of the present composite
can be produced in a wide range of sizes and shapes. For
example, the adhered diamond body can be as wide or as long as
one inch or longer. Polycrystalline diamond bodies one inch
in length or longer and having the present diamond density
are not producible as a practical matter, ox are not producible
at all, by techniques utiIizing the ultra high pressures and
temperatures of the diamond stable region due to the limitations
of the equipment necessary to sustain the severe pressure-
temperature requirements for the necessary period of time,
i.e. the equipment is so complex and massive that its capacity
is limited. On the other hand, the present adhered polycrystalline
diamond body can be as small or as thin as desired, however, it
will always be in excess of a monolaryer of diamond
crystals.
The present composite is highly useful as an abrasive,
cutting tool, nozzle or other wear-resistant part.
The invention is further illustrated by the
following examples where, unless otherwise stated, the procedure
was as follows:
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RD-10334
- - 28 -
SILICON CARBIDE SUBSTRATE
Hexagonal boron nitride powder of fine particle size,
e.g. ranging in size from about 2 microns to about 20 mi~rons, was
used as the pressure transmitting medium.
The polycrystalline silicon carbide substrate was in the
form of a disc with a thickness of about 120 mils.
The equipment used was substantially the same as that
shown in Figures 4 and 5.
Cold-pressing of the charge was carried out at room
temperature as shown in Figure 4 to about 80,000 psi.
The amount oE infiltrating alloy was sufficient to
completely infiltrate through the compressed diamond mass and
to contact the contacting surface of the substrate and fill the
pores of the interface.
The infiltrating alloy was a eutectiferous silicon-rich
alloy.
Density given herein of the polycrystalline silicon
carbide body used as a substrate is the fractional density based
on the theoretical density of the silicon carbide of 3.21 gm/cc.
All of the polycrystalline silicon carbide bodies,
sintered as well as hot-pressed, used as substrates had
substantially the same composition, which was comprised of
silicon carbide, about 1~ to 2% by weight of boron based on said
, silicon carbide and less than about 1% by weight of submicron
elemental carbon based on said silicon carbide. The carbon was in
particle form of submicron size.
The diamond powder used ranged in particle size from 1
micron -to about 60 microns with at least 40 weight % of the diamond
powder being smaller than 10 microns.
Where a particular diamond density is given as percent
by volume of the polycrystalline diamond body, it was
determined by the standard point count technique using a
photomicrograph of a polished surface magnified 690 times and
the surface area analyzed was sufficiently large to represent the
microstructure of the entire body.
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- 29 -
Where the ~iamond ~ensity is given as a range greater
than 70% by volume but less than gO% by volume oE the polycrystalline
diamond body, this range is based on experience, results with
similar runs, particularly runs where the polycrystalline
diamond body alone was prepared, and the appearance o~ the
adhered polycrystalline body as a whole, and also, the volume
oE the recovered cleaned polycrystalline diamond body portion of
the composite as compared to the volume o~ the starting diamond
powder on the assumption that less than 5% by volume of the
diamond powder had converted to non-diamond elemental carbon
phase.
In Table I, in Examples l to 5, a molybdenum cup with
zirconium liner was used and a cast alloy in the form o~ a
disc of the given composition and thickness and having essentially
the same diameter as the zirconium liner was placed within
the zirconium liner at the bottom of the cup. The diamond powder
in the given amount wàs packed on top of the disc. Finally, the
given polycrystalline silicon carbide disc was placed on top
of the diamond powder forming a plug in the cup as shown by 14 in
Figure 2.
The resulting plugged cup was then packed in hexagonal
boron nitride powder as shown in Figure 4 and the whole charge
was pressed at room temperature, i.e. cold-pressed, in a steel
die to about 80,000 psi subjecting the cup and contents to
substantially isostatic pressure until the pressure became
stabiliæed producing a dimensionally stabilized shaped substantially
isostatic system of powder-enveloped plugged cup. From
previous experiments it was known that in the resulting pressed
assembly, i.e. in the resulting shaped substantially isostatic
system of powder-enveloped plugged cup, the density of the
diamond crystals was higher than 75% by volume of the compressed
diamond mass.
The resulting pressed assembly 21 of powder-enveloped
plugged cup was then hot-pressed, i.e. it was pushed into a
graphite mold of the same diameter size as the steel die, as
shown in Figure 5, whicll was placed within an induction
heater. The interior Oe the plu~ed cup uas evacuated ~d
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RD-10334
- 30 -
nitrogen atmosphere introduced therein by evacuating the
heater to about 10 torr before back filling it with nitrogen.
A pressure of about 5000 psi was applied to the pressed
assembly 21 and maintained thereon by the graphite die which
was then heated by the induction heater at a rate which reached
the given maximum hot-pressing temperature in about 5 to 7
minutes. As the assembly was heated, the pressure increased
to the given maximum hot-pressure due to the expansion oE the
system.
At the given temperature at which infiltration begins
or proceeds, the piston and the pressure dropped to about 5000
psi indicating that the alloy had become fluid and had proceeded
to infiltrate through the compressed diamond mass. The pressure
was then raised bac~ to the given maximum hot-pressing pressure
where it was maintained at the given maximum hot-pressing
temperature for one minute to insure complete infiltration by
the alloy of the small capillaries of the compressed diamond
mass. The powder supply was then turned off but no additional
pressure was applied. This provided a firm pressure at high
temperature but reduced pressure at low temperature providing
adequate geometric stability, i.e. this maintained the dimensions
of the hot-pressed assembly until it was sufficiently cool for
handling.
The resulting composite was recovered by grinding and
grit blasting way can metal, i.e. molybdenum cup and zirconium
sleeve, and excess alloy at the outside surfaces of the
composite.
The resulting cleaned integral composite bodies had the
shape of a substantially uniform disc which in Examples 1 to 3
had a thickness of approximately .195 inch and in Example 4,
approximately .160 inch.
` In Examples 6 and 7 of Table I no metallic container,
liner or substrate was used but the equipment used was
substantially the same as that set forth in Figures 4 and 5.
Specifically, to carry out Examples 6 and 7, the hexagonal
boron nitride powder was packed into the die o~ Figure 4 and a
cylinder used as a mold was pressed into the power. The
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- RD-10334
- 31 -
cylinder was made of cemented metal carbide and was about 0.35
- inch in diameter and 0.25 inch in thickness. The axis of the
cylinder was approximately lined up with the central axis of the
die.
After the cylinder was inserted in the powder,
additional hexagonal boron nitride powder was placed in the
die covering the cylinder completely, and the resulting powder-
enveloped cylinder was pressed at room temperatures under a
pressure of 50,000 psi. Piston 23a was then withdrawn and piston
23 was used to push the resulting pressed powder-enveloped cylinder
partially out of the die.
me exposed portion of the pressed powder was removed
leaving the cylinder partially exposed. The cylinder was then
withdrawn leaving the cavity it had impressed therein. In
Examples 6 and 7, a cast alloy disc of the given composition
and thickness having a diameter essentially the same as the
inner diameter of the cavity was placed in the bottom of the
cavity. A layer of diamond powder of the given size, amount and
thickness was packed on top of the alloy.
A disc of hot-pressed hexagonal boron nitride powder of
about the same diameter as the inner diameter of the cavity was
placed within the cavity on top of the diamond powder as a plug
to insure that the surface of the resulting polycrystalline diamond
body would be flat.
The entire mass was then pushed into the center of the
die by piston 23a which was then withdrawn. An additional amount
of hexagonal boron nitride powder was added to the die to cover
the hot-pressed disc of hexagonal boron nitride resulting in the
cavity and contents being enveloped by hexagonal boron nitride as
illustrated by Figure 4. The resulting charge was then pressed at
room temperature, i.e. cold-pressed~ in the steel die under a pressure
of 80,000 psi as shown in Figure 4 subjecting the cavity and its
contents to substantially isostatic pressure until the pressure became
stabilized producing a dimensionally stabilized shaped
substantially isostatic system of powder-enveloped cavity and
contents. From previous experiments it was known that in the
~ X~
.
.
~- ~
., .
.
I
RD-10334
- 32 -
resulting pressed assembly, i.e. in the resulting shaped
substantially isostatic system of powder-enveloped cavity and
contents, the density oE tlle diamond crystals was higher than
75% by volume of the compressed diamond mass.
The resulting pressed assembly of powder-enveloped
cavity and contents, which was substantially the same as 21
except that no metal container was used, was then hot-pressed,
i.e. it was pushed into a graphite mold of the same diameter
size as the steel die, as shown in Figure 5, and placed within
10 an induction hea-ter. The interior of the cavity was evacuated
and a nitrogen atmosphere introduced therein by evacuating the
heater to about 10 torr before back filling it with flowing dry
nitrogen. A pressure of about 5000 psi was applied to the
pressed asse~bly and maintained thereon by the graphite die,
which was then heated by the induction heater at a rate which
reached the given maximum hot-pressing temperature in about 5
to 7 minutes. As the assembly was heated, the pressure increased
to the given maximum hot-pressure due to the expansion of the
entire system.
At the given temperature at which infiltration begins
or proceeds the piston and the pressure dropped to about 5000 psi
indicating that the given alloy had melted and become fluid and
had infiltrated through the diamond mass. The pressure was then
raised back to the given maximum hot-pressing pressure where it
was maintained at the given maximum hot-pressing temperature for
one minute to insure complete infiltration by the alloy of the
smaller capillaries of the compressed diamond mass. The power
supply was then turned off but no additional pressure was applied.
This provided a firm pressure at high temperature but reduced pressure
30 at lower temperature providing adequate geometric stability. At
room temperature, the resulting polycrystalline diamond body was
recovered. me plug did not bond to the diamond body. After
removing surface scales of hexagonal boron nitride powder and
excess alloy by grinding and grit blasting the resulting integral
polycrystalline diamond body had the shape of a disc with the given
` thickness.
.~.
.``. ~9
`~ : ' ` '
,
'~;
RD-10334/10335
In Table I the hot-pressing temperature at which
infiltration begins is that temperature at which the alloy
is fluid and proceeds to infiltrate through the compressed
diamond mass. The given maximum hot-pressing temperature
and maximum hot-pressing pressure were maintained
simultaneously for one minute to insure complete infiltra-
tion of the smaller capillaries of the compressed idamona
crystal mass.
X-ray diffraction analysis given in Table I of
10 Examples 6 and 7 was made on the polycrystalline diamond
body in crushed form.
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- RD-10334
- 36 -
In Examples l to 5, the interface of each composite
disc between the adhered polycrystalline diamond body and silicon
carbide substrate could not be detected. Each composite appeared
to be a continuous structure through its thickness and the grain
size of the diamond portion distinguished it from the substrate.
The external surface of each adhered polycrystalline diamond body
appeared to be well-infil-trated with bonding medium which appeared
to be uniformly distributed. The diamonds appeared to be well-
bonded to each other~
~he adhered polycrystalline diamond body of the
composites of Examples 1 to 4 had a diamond density higher than
70~ by volume but ~ess than 90% by volume of the volume of
the polycrystalline boby.
The diamond face of the composite of Example 5 was
polished on a cast iron scaife. Examination of the polished
surface, showed no strings of holes formed from diamond fragment
pullout illustrating the strong bonding therein. The density of the
diamond crystals was about 73% by volume of the adhered polycrystalline
diamond body.
In Examples 6 and 7/ the polycrystalline diamond bodies
were well-infiltrated and well-bonded. Using a hammer and wedge, each
disc, i.e. polycrystalline diamond body, was fractured substantially
in half and the fractured cross-sectional sur~aces were examined
~" optically under a microscope magnified about lO0 times. Examination
of their fractured surfaces showed them to be pore-free, that the
bonding medium was uniformly distributed throughout the body, and
that the fractures were transgranular rather than intergranular,
` i.e. each had fractured through the diamond grains rather than along
the grain boundaries. This indicates that the bonding medium was
highly adherent and was as strong as the diamond grains or crystals
themselves.
The diamond density of the disc of Example 6 was greater
than 70% but less than 90% by volume of the body.
. A fractured surface of the disc of Example 7 was pol-
;~ ished on a cast iron scaife and examination of the polished
:`:
, ~
: .
RD-1033
- 37 -
sur~ace showed no strings of holes formed from diamond fragment
pullout illustrating the strong bonding therein. The density
of -the diamond crystals was about 80% by volume of the polycrystalline
diamond body.
EXAMPLE 8
The composite produced in Example 1 was evaluated as a
cutting tool. The exposed surface of the polycrystalline diamond
body of the composite was ground with a diamond grinding wheel
to smooth it out and produce a sharp cutting edge. The substrate
10 of the composite was then clamped in a tool holder.
A portion of the cutting edge was evaluated on a lathe
turning of Jackfork Sandstone with a feed per revolution of .005
inch and a depth of cut of .020 inch.
At a cutting speed of 98 surface feet per minute, the
wear rate was determined to be .077 cubic inch per minute X
10 . Another portion of the cutting edge was evaluated at
a cutting speed of 276 surface feet per minute and was found
to have a wear rate of .53 cubic inch per minute X 10 6.
Still another portion of the cutting edge was evaluated at a
20 cutting speed of 290 surface feet per minute and was found to have
a wear rate of 1.46 cubic inch per minute X 10
The composite was removed from the tool holder and
examination of the interface between the diamond body and
'~ substrate showed that it had not been affected by these machining
tests.
EXAM2LE 9
The procedure used in this example was -the same as that
set forth in Example 8 except that the composite produced in
Example 2 was used.
A portion of the cutting edge at a cutting speed of 110
surface feet per minute showed a wear rate of .203 cubic inch
per minute X 10 . Another portion of the cutting edge at a
cutting speed of 320 surface feet per minute showed a wear rate
of 1.48 cubic inch per minute X 10
Examination of the composite after machining showed
that the interface between the polycrystalline diamond body
-
,'' , ' ' ' ~
,
$.~
RD-10334
- 38 -
and silicon carbide substrate was not affected by these machining
tests.
- ExAMæLE 10
The procedure used in this example was the same as that
set forth in Example 8 except that the composite of Example 3 was
used.
A portion of the cutting edge at a cutting speed of 110
surface feet per minute showed a wear rate of .234 cubic inch
per minute X 10 6. ~nother portion of the cutting edge at a
cutting speed of 320 surface feet per minute showed a wear rate
of 1.85 cubic inch per minute X 10
Examination of the composite after machining showed
that the interface between the polycrystalline diamond body and
silicon carbide substrate was not affected by these machining
tests
EXAMPLE 11
The procedure used in this example was the same as that
set forth in Example 8 except that the composite of Example 4 was
used.
; 20 After 4 minutes of successful cutting at a cutting
speed of 98 surface feet per minute, small pieces of the cutting
edge broke. Using another portion of the cutting edge, after
6 minutes of successful cutting at a cutting speed of 280 surface
feet per minute, small pieces of cutting edge broke. It is
believed that the cutting edge breakage was due to the hot-pressing
temperatures not being sufficiently high to completely infiltrate
the small capillaries of the polycrystalline diamond mass during
hot-pressing. A comparison with Example 7 of Table I shows that
the higher hot-pressing temperatures produced a well-infiltrated
and well-bonded polycrystalline diamond body.
EXAMPLE 12
; The procedure for preparing a composite was substan-
tially the same as that set forth in Example 2 except that
260 mg of the silicon chromium alloy were used, and the alloy
disc was .050 inch thick.
f3(~
:
39
RD-10334/10335
Also, 250 mg of diamond powder were used wherein 60 w/o
(weight /0) ranged in size from 53 to 62 microns, 30 w/o
ranged from 8 to~ 22 microns, and 10 w/o ranged from 1 to
about 5 microns. The diamond powder was packed to an ap-
proximate thickness o about .055 inch. Also a zirconium
cup with a zirconium liner were used.
The maximum hot-pressing pressure was abou-t 13,000 psi
and the hot pressing temperature ranged from about 1250C
when infiltration be~an to a maximum hot-pressing tempera-
ture of about 1500C. The composite was recovered in the
same manner as Example 2 and was in the form of a substan-
tially uniform disc having a thickness of about .060 inch.
The silicon carbide substrate was ground o~f the compo-
site and the resulting polycrystalline diamond body was
subjected to a thermal stability test. Speciically, it was
heated in air to a temperature of 900C, which was the
limiting temperature of the furnace. As it was heated9 its
linear thermal expansion coefficient was determined for
; temperatures ranging from 100C to 900C. At 900C, the
power was cut off.
The test data and inspec~ion of the sample, i.e. the
polycrystalline diamond body, after the test indicated that
there was no sudden change in length in the sample during
the entire range of the heating cycle and there was no
evidence of any permanent damage caused to the sample by
this heating cycle.
EXAMPLE 13
The procedure used in the example was substantially the
same as that set forth in Example 2 except that a disc of
silicon was used in a zirconium cup with a zirconium liner
to form a silicon-rich zirconium alloy in situ.
Six composites were prepared. To p~epare three of the
composites, a diamond powder was used wherein 60 w/o ranged
in size from 53 to 62 microns, 30 w/o ranged from 8 to 22
microns and 10 w/o ranged from 1 to about 5 microns. The
three other composites were prepared using a diamond powder
which ranged from 1 to 60 microns in si~e wherein at least
40 w/o was smaller than 10 microns in size.
6~;~
.
~o
RD-10334/103~5
The maximum hot-pressing pressure was abou-t 13,000 psi,
and the hot-pressing temperature ranged from about 1340C
which is the temperature at which infiltration proceeded,
indicating that the silicon-rich zirconium alloy had formed
in situ and had become fluid, to a maximum hot-pressing
temperature of about 1500C.
Each composite was recovered in substantially the same
manner as Example 2 and each was in the form of a disc.
The top and cylindrical faces of the adhered poly-
crystalline diamond body of all six composites were surface
ground. The difficulty of grinding these composites with a
diamond grindin8 wheel indicated that the abrasion resis-
tance of these adhered diamond bodies was comparable to
commercially available polycrystalline diamond products.
~`~ The three composites prepared with the diamond powder
which ranged from 1 to 60 microns in size had improperly
mixed aggregates of diamond powder of less than 2 microns in
size and inspection of the ground edges of the adhered
polycrystalline body showed incomplete infiltration of these
aggregates by the alloy but the remainder of the ground
diamond area was well-bonded.
Optical examination of the composites showed no detect-
able defects or distinctively different interlayer between
the silicon carbide subs-trate and the diamond layer. Four of
the composites were broken to see the in-ternal structure.
Optical examination of the fractured surfaces showed no
visible interlayer or defects at the intexface between the
silicon carbide substrate and the adhered polycrystalline
diamond layer.
The continuity of structure at the substrate-diamond
layer interface was excellent and only the grain size dif-
ference in diamonds and silicon carbide enabled recognition
of the boundary between the substrate and diamond layers.
Two of the composites were evaluated as cutting tools
by lathe turning of a very abrasive sand-filled rubber bar.
The cutting parameters were 30 mil depth of cut, S mil feed
per revolution, and 600 surface feet per minute of cutti.ng
-
~1
RD-10334/10335
- speed. After 16 minutes, 22 seconds of cutting, both tools
showed about 5 mil size uniform flank wear indicating that
the wea~ resistance of cutting edge was excellent.
EXAMPLE 14
The composite produced in Example 1 was fractured
substantially in half by means of a hammer and wedge, and
the fractured cross-sectional surfaces were examined opti-
cally under a microscope magnified about 100 X. Examination
of the fractured surfaces showed that the polycrystalline
diamond body as well as the interface of the composite were
pore-free, that the bonding medium was distributed uniformly
throughout the diamond body and that the fracture was trans-
granular rather than intergranular, i.e. that the fracture
occurred through the diamond grains rather than along the
grain boundaries. This indicates that the bonding medium
was highly adherent and was as strong as the diamond grains
or crystals themselves. Also, no visible interlayer or
defects at the interface between the silicon carbide sub-
strate and the adhered polycrystalline diamond layer could
be detected. The fractured surface of the composite appear-
ed to have a continuous structure and only the difference in
grain size between the diamond and strongly adhered sub-
strate enabled recognition of the boundary between the
substrate and adhered polycrystalline diamond body.
The fractured cross-section of the composite was polish-
: ed on a cast iron scaife. Optial examination of the polish-
ed cross-sectional surface, which is shown in Figure 7,
showed no strings of holes formed from diamond fragment
pullout illustrating the strong bonding therein. The poly-
crystalline diamond body is shown in the upper portion and
the substrate in the lower portion of Figure 7, and the
interface therebetween can be distinguished by the di-ffer-
ence in crystal structure between the diamond body and the
substrate. The density of the diamond crystals was about
71% by volume of the polycrystalline diamond body in
Figure 7.
.
~2
RD- 10334/1033g
- SILICON NITRIDE SUBSTRATE
.
Hexagonal boron nitride powder of fine particle size,
e.g. ranging in size from about 2 microns to about 20 mi-
crons, was used as the pressure transmitting medium.
The polycrystalline silicon nitride substrate was in
` the form of a disc which in Examples 2 and 3 had a thicknessof about 125 mils and in Examples 5 and 6 had a thickness of
about 100 mils. It was a commercially available hot-pressed
material with a density higher than 99~, i.e. it was almost
100~ dense, and was comprised, by weight of the silicon
nitride hot-pressed body, of 1/2% MgO, about 1/2/~ Fe, about
1/200% metallic impurities such as Ca, A1 and Cr, 2% free
.- Si, 1~ SiC with the remainder being silicon nitride.
The equipment used was substantially the same as that
shown in Figures 4 and 5.
Cold-pressing of the charge was carried out at room
temperature as shown in Figure 4 to about 80,000 psi, and in
the resulting pressed assembly, the density of the diamond
crystals was higher than 75% by volume of the compressed
diamond mass.
The amount of infiltrating allow was sufficient to
` completely infiltrate through the compressed diamond mass
and to contact the contacting surface of the substrate and
fill the pores of the interface.
- The infiltrating alloy was a eutectiferous silicon-rich
alloy.
Density given herein of the polycrystalline silicon
nitride body used as a substrate is the fractional density
based on the theoretical density of the silicon nitride of
3.18 gm/cc.
Fracturing of a composite or a polycrystalline diamond
body was carried out with a hammer and wedge.
Optical eXaminatiOt1 was under a microscope magnified
about 100 X.
Polishing was carried out on a cast iron scaife.
Where a particular diamond density is given as percent
.; by volume of the polycrystalline diamond body, it was
``'', '
` ,. ,
..
. :` .
~3
~D-10334/103~5
determined by the standard point count technique using a
photomicrograph of ~ polished surface magnified 690 times
and the surface area analy~ed was sufficiently large to
represent the microstructure of the entire body.
Where the diamond density is given as a range greater
than 70% by volume but less than 90/O by volume of the poly-
crystalline diamond body, this range is based on experience,
results with similar runs, particularly runs where the
polycrystalline diamond body alone was prepared, and the
appearance of the adhered polycrystalline body as a whole,
and also, the volume of the recoverd cleaned polycrystalline
diamond body portion of the composite as compared to the
volume of the starting diamond powder on ~he assumption that
less than 5% by volume of the diamond powder had converted
to non-diamond elemental carbon phase.
In Examples 15 and 16, the infiltrating silicon-rich
alloy was an alloy of silicon and zirconium formed in situ.
EXAMPLE 15
In this example a polycrystalline diamond body was
prepared witout a substrate.
- A cast silicon disc weighing 330 mg was placed within a
zirconium sleeve in a molybdenum cup. About 500 mg of fine
diamond powder, particle size ranging from 1 micron to about
60 microns with at least 40 weight /O of the diamond powder
being smaller than 10 microns was packed on top of the
silicon disc. A molybdenum cup slightly larger in diameter
than the original cup, i.e. the cup containing silicon and
diamonds, was placed over the opening of the original cup as
a cover.
~he resulting container was then packed in hexagonal
- boron nitride powder as shown in Figure 4 and the whole
charge was pressed at room temperature, i.e. cold-pressed,
` in a steel die to about 80,000 psi subjecting the container
and its contents to substantially isostatic pressure until
the pressure became stabilized producing a dimensionally
stabilized shaped substantially isostatic system oi powder-
enveloped container. From previous experiments i-t was known
~` `
. .
~ . .
,;.` . :
4~ 1
RD-1033~/10335
that in the resulting pressed assembly, i.e. in the result-
ing shaped substantially isostatic system of powder-envel-
` oped container, the density of diamond crystals was higherthan 75% by volume of the compresscd diamond mass. Also, the
; amount of silicon present was about 80% by volume of the
compressed diamond mass.
; The resulting pressed assembly 21 of powder-envelopedcontainer was then hot-pressed, i.e. it was pushed into a
graphite mold of the same diameter size as the steel die, as
shown in Figure 5, which was placed within an induction
heater. The interior of the container was evacuated and a
nitrogen atmosphere introduced therein by evacuating the
heater to about 10 torr before back filling it with nitro-
gen. A pressure of about 5000 psi was applied to the pressed
assembly 21 and maintained thereon by the graphite die which
was then heated to a temperature of 1500C in about 7 min-
utes by the induction heater. As the assembly was heated,
the pressure also went up to about 10,000 psi due to the
expansion of the system. When the temperature reached about
1350C the piston 23a dropped and the pressure dropped to
about 5000 psi indicating that silicon-rich zirconium alloy
had formed, become fluid and had proceeded to infiltrate
through the compressed diamond mass. The pressure was
raised to the maximum hot-pressing pressure o~ 10,000 psi
and when the tempe-rature reached 15~0C, the assembly was
maintained at the maximum hot-pressing ternperature ~f 1500C
under 10,000 psi for 1 minute to insure complet infiltration
by the alloy of the smaller capillaries of the compressed
diamond mass. The power supply was then turned off but no
additional pressure was applied. This provided a firm pres-
sure at high temperature but reduced pressure at low temper-
ature providing adequate geometric stability, i.e. this
maintained the dimensions of the hot-pressed assembly until
~-- it was sufficiently cool ior handling.
The resulting polycrystalline diamond body was recov-
ered by grinding and grit blasting away can metal, i.e.
~ molybdenum cup and zirconium sleeve, and e~cess silicon at
` the outside surface and faces of the body.
.
. .
:
.
RD-10334/10335
The resulting integral polycrystalline diamond body had
the shape of a disc about 0.115 inch thick. It appeared to
. be well-infiltrat~d and bonded.
X-ray dif~raction analysis of the cleaned face through
which the alloy entered showed it to be comprised of dia-
mond, silicon carbide and elemental silicon, indicating that
the silicon carbide and elemental silicon were present in an
amount of at least 2% by volume o~ the body. ~owever, the
X-ray difraction analysis did not detect non-diamond
elemental carbon phase.
Examination of the fractured cross-sectional surfaces
of the disc showed that the fracture was transgranular
rather than intergranular, i.e., it had fractured through
the diamond grains rather than along grain boundaries. This
indicates that the bonding medium was highly adherent and
was as strong as the diamond grains or cr~stals themselves.
Examination of the fractured surfaces showed them to be
pore-free and the bonding medium was uniformly distributed
throughout the body.
Examination of the polished cross-sectional surfaces
showed no strings of holes formed from diamond ragment
pullout illustrating the strong bonding therein and its
usefulness as an abrasive.
The density of the diamond crystals was about 81% by
volume of the polycrystalline diamond body.
A photomicrograph of the polished surface, magniiied
; 690 times, showed a white phase. X-ray spectral analysis of
this phase showed that it consisted of zironium and silicon
indicating that this phase was zirconi~m silicide.
EXAMPLE 16
In this example, the eomposite was prepared using
` hot-pressed polycrystalline silicon nitride as a substrate.
A cast silicon disc weighing 142 mg was placed within a
` zirconium sleeve in a zirconium cup. 270 mg of diamond
powder wherein 85 weight % of the diamond ranged in size
rom 53 mi~rons to 62 microns and 15 weight % was about 5
microns in size was packed on the silicon disc producing an
. `
.:
~ . :- . - :
t "`
~ ~ ' ` `!
.` ~ .
46
RD-1033li/10335
approximate powder thickness of .06~ inch. Instead of the
: metal can cover used in Example 1, hot-pressed polycrystal-: line silicon nitride was used as a plug~ i.e. plug 14, as
shown in Figure 2.
The resulting plugged cup was then pac~ed in hexogonal
boron nitride powder as shown in Figure 4 and the whole
charge was cold-pressed at room temperature in the same
manner disclosed in Example 1 subjecting the plugged cup and
its contents to substantially isostatic pressure until the
pressure became stabilized producing a dimensionally stabi-
lized shaped substant:ially isostatic system of powder-envel-
oped plugged cup. From previous experiments it was known
that in the resulting pressed assembly, i.e. in the result-
- ing shaped substantially isostatic system of powder-envel
oped plugged cup, the density of diamond crystals was higher
than 75% by volume of the compressed diamond mass. The
resulting pressed assembly 21 of powder-enveloped plugged
cup was then hot-pressed in the same manner disclosed in
Example 15 except as given in Table II.
~o The resulting composite was recovered by grinding and
grit blasting away can metal and excess silicon at the
outside surface and faces of the composite.
Examples 15 and 16 are shown in Table II. Also, in
Table II, in Examples 17, 19 and 20 a cast alloy in the form
of a disc of the given composition and thickness and having
essentially the same diameter as the given liner was placed
within the liner at the bottom of the given cup. The dia
mond powder in the given amount was packed on top of the
disc. Finally, the given pol~crystalline silicon nitride
substrate was placed on top of the diamond powder forming a
plug in the cup as shown by 14 in Figure 2. The resulting
plugged cup was then cold-pressed and hot-pressed in the
same manner disclosed in Example 2 e~cept as given in Table
I~. The resulting composite was recovered substantially in
the same manner disclosed in Example 16.
.
:
~ L6~L
~7
. RD-10334/1033~
The resulting cleaned integral composite bodies of
Examples 1~, 17, 19 and 20 had the shape o~ a substantially
uniform disc which in Examples 16 and 17 had a thickness of
approximately .185 inch, and in Examples 19 and 20 of ap-
proximately .150 inch.
In Example ~8, a polycrystalline diamond body was
produced and no metallic container, liner or substrate was
used but the equipment used was substantially the same as
that set forth in Figures 4 and 5. Specifically, to carry
out ~xample 18, the hexagonal boron nitride powder was
packed into the die of Figure 4 and a cylinder used as a
mold was pressed into the powder. The cylinder was made of
cemented metal carbide and was about 0.35 inch in diameter
and 0.25 inch in thickness. The axis o the cylinder was
approximately lined up with the central axis of the die.
After the cylinder was inserted in the powder, addi-
tional hexagonal boron nitride powder was placed in the die
covering the cylinder completely, and the resulting powder-
enveloped cylinder was pressed at room temperatures under a
pressure of 50,000 psi. Piston 23a was then withdrawn and
piston 23 was used to push the resul-ting pressed powder
enveloped cylinder partially out of the die.
The exposed portion of the pressed powder was removed
leaving the cylinder partially exposed. The cylinder was
then withdrawn leaving the cavity it had impressed therein.
In Example 4, a cast alloy disc of the given composition and
thickness having a diameter essentially the same as the
inner diameter of the cavity was placed in the bottom of the
cavity. A layer of diamond powder of the given size, amount
and thickness was packed on top of the alloy disc.
A disc of hot-pressed hexagonal boron nitride powder of
about the same diameter as the inner diameter of the cavit~
. ~ .
. ~
.'` ' ~
'
' ~ .
RD-1033~/10335
was placed within the cavity on top o~ the diamond powder as
a plug to insure that the surface o~ the resulting polycrys-
talline diamond body would be flat.
The entire mass was then pushed into the center of the
die by piston 23a which was then withdrawn. An additional
amount of hexagonal boron nitride powder was added to the
die to cover the hot-pressed disc of hexagonal boron nitride
resulting in the cavity and contents b~ing enveloped by
hexagonal boron nitride as illustrated by Fi~ure 4. The
rèsulting charge was then pressed at room temperature, i.e.
cold-pressed, in the steel die under a pressure of 80,000
psi as shown in Figure 4 subjecting the cavity and its
contents ~o substantially isostatic pressure until the
pressure became stab~ ed producing a dimensionally stabi-
lized shaped substantially isostatlc system of powder-
enveloped cavity and contents. From previous experiments it
was known that in the resulting shaped substantially iso-
static system of powder-enveloped cavity and contents, the
density of the diamond crystals was higher than 75% by
volume of the compressed dismond mass.
The resulting pressed assembly of powder-enveloped
cavity and contents, which was substantially the same as 21
except that no metal container was used, was then hot-
pressed, i.e. it was pushed into a graphite mold of the same
diameter size as the steel die, as shown in Figure 5, and
placed within an induction heater. The interior of the
cavity was evacuated and a nitrogen atmosphere introduced
therein by evacuating the heater to about 10 torr before
back filling it with flowing dry nitrogen. A pressure of
` 30 about 5000 psi was applied to the pressed assembly and
maintained thereon by the graphite die, which was then
heated by the induction heater at a rate which reached the
given maximum hot-pressing temperature in sbout 5 to 7
.~
49
RD-1033~/103315
minutes. As the assembly was heated3 the pressure increased
to the given maximum hot-pressure due to the expansion of
the entire system.
At the given temperature at which infiltration begins
or proceeds the piston and the pressure dropped to about
5000 psi indicating that the given alloy had melted and
become fluid and had infiltrated through the diamond mass.
The pressure was then raised back to the given maximum
hot-pressing pressure where it was maintained at the given
maximum hot-pressing temperature for one minute to insure
complete infiltration by the alloy o~ the smaller capillar-
ies of the compressed diamond mass. The power supply was
then turned off but no additional pressure was applied.
This provided a firm pressure at high -temperature but
reduced pressure at lower temperature providing ade~uate
geometric stability. At room temperature, the resulting
polycrystalline diamond body was recovered. The plug did
not bond to the diamond body. After removing surface scales
of hexagonal boron nitride powder and excess alloy by
grinding and grit blasting the resulting integral poly-
crystalline diamond body had the shape of a disc with the
given thickness.
In Table II the hot-pressing temperature at which
infiltration begins is that temperature at which the alloy
is fluid and proceeds to infiltrate through the compressed
diamond mass. The given maximum hot-pressing temperature
and maximum hot-pressing pressure were maintained simulta-
neously for one minute to insure complete infiltration of
the smaller capillaries of the compressed diamond crystal
mass.
RI3-to334/lû335
-50-
TABLE II
g ¦ Atol~ic 11 . ~=51 ~prox.(ln) Dl=nd od~r ¦~ ¦ r Plu~
silicou ~ I iJ~ bout j I Ho cup /lth Hun;dP-
I I ~allcr than I I co~er
_ . I l l
16 Csi;icon 1 142 1 .03D S3~-62,q, ~ l 2r li~nr nltrid~
l I ~ '~ __
17 as A/o 51 1 260 1 .040 S~o a 1290 1 .063 Zr-lLnor pro~aod
15 A/o Cr ~ ~ Ex. ~ I nit~ido
. _ I I I _~ , _
18 ô6 A/o 51 1 210 1 .040 l l llono 1
__ ~ I ~
19 06 A/o Si 1 133 ! ~tO30 S~o ao ! 227 ! ?lo cup wlth pro ord
l l l l nltrido
_ I I l l
5 A/o Re 1 121 ¦ 60u. wh r~ Mo cu~p ~llth h~POil8ic d
I and 30~1/o ! ! nitrid~
Ip,-~5,~ 1 1
~ ~ - _
! ! " ,
RD-10334/10~35
-51 -
TABLE II (Continued)
~1 lltlo8 YolDt
Pre~Rlng ~t Pr~ ln& T~ rlltln3 Alloy Yolycry~t~llln- Dl~d ~1~
Pr~ uro Inflltrlltlonl~ls~ In Lltora- Ap ro~ r~ Ancl~ of
~y~l (C~ Tc IP.& turo C ool ~cb~ I Dla oDd 3Ody
15 ,0.OOO 1350 1 1500 ~Sl-9c6~ o ~r ! di~, 81C ~nd
_ I _ T
1613 000 "~300 11525 1360 .060
. l ~51-9.6A/o Zr
t~ctlc)
_ _ I
17Il,ooo 1260 11450 1335 .055
l (SlCr blm~ry~
I _ _ __ __
1813,000 1345 11540 1330 .060 1 <of cruo~ ody)
l ~ T1512
l 1~
_ _ r
-- 19 13.000 1322 1 1525 1330 050 1
~ I_ _ ~
20 13.000 1340 !1540 ~prl2i5ctod~ .045 1
l ll ll
_ l I __~
52
R~-10 34/10335
Examples 16, 17, 19 and 20 illustrate the produc-
tion of the present composite. ~n these examples, on
optical examination, each composite appeared ~o be a
continuous structure, bu~ the boundary between the diamond
body and substrate could be detected by the difference in
grain size as well as the difference in color between the
diamond body and substrate, i.e. the silicon ni-tride
substrate being darker in color than the grey diamond body.
The external surface of each adhered polycrystalline diamond
body appeared to be well-infiltrated with ~onding medium
which appeared to be uniformly distributed. The diamonds
appeared to be well-bonded to each other.
The adhe~ed polycrystalline diamond body o the compos-
ites of Examples 17 and 18 had a diamond densit~ higher than
7Q/O by volume but less than 90~ by volume of the volume of
the polycrystalline body.
The diamond face of the composite of Example 16 was
polished and optical examination of the polished face showed
no strings of holes formed from diamond fragment pullout
illustrating the strong bonding therein. The density of the
diamond crystals was about 71% by Yolume of the adhered
polycrystalline diamond body of Example 16.
In ~xample 18, the polycrystalline diamond body was a
well-infiltrated~ well-bonded hard disc. The diamond body
was fractured substantially in hal-f. Optical examination of
the fractured cross-sectional surfaces showed them to be
pore-free, that the bonding medium was uniformly distributed
throughout the body, and that the fracture was transgranular
rather than intergranular, i.e. it had fractured through the
diamond grains rather than along the grain boundaries. This
indicates that the bonding medium was highly adherent and
was as strong as the diamond grains or crystals themselves.
A fractured surface of the disc of Example 18 was
polished and examination of the polished surface showed no
53
RD-1033l~/1033~
strings of holes formed from diamond fragment pullout
illustrating the strong bonding therein. In Example 18 the
density of the diamond crystals was about 80% by volume of
the polycrystalline diamond body.
EXAMP~E 21
The composite produced in Example l7 was evaluated as a
cutting tool. The exposed surface of the polycrystalline
diamond body of the composite was ground with a diamond
grinding wheel to smooth it out and produce a sharp cutting
edge. The substrate of the composite was then clamped in a
tool holder.
A portion of the cutting edge was evaluated on a lathe
turning of Jackfork Sandstone with a feed per revolution of
.005 inch and a depth of cut of .020 inch.
At a cutting speed of 9~ surface feet per minute, the
wear rate was determined to be .22 cubic inch per minute
X 10 6. Another portion of the cutting edge was evaluated
at a cutting speed of 260 surface feet per minute and was
found to have a wear of .501 cubic inch per minute X 10 6.
The composite was removed from the tool holder and
examination of the interface between the diamond body and
substrate showed that it had not been affected by these
machining tests.
EXAMPLE 22
The procedure used in this example was the same as that
set forth in Example 21 except that the composite produced
in Example 19 was used.
A portion of the cutting edge at a cutting speed of 100
surface feet per minute after two minutes of cutting time
generated very small wear scar indicating excellent wear
resistance, but the Jackfork Sandstone had a deep recess and
since the composite was brittle, a small piece of the cutt-
ing edge broke.
54
RD-10034/10335
Examination of the composite after the cutting showed
that the interface between the polycrystalline diamond body
and silicon nitride substrate was not affected by these cutting
tests.
EXAMPLE 23
The composite produced in Example 20 was fractured sub-
stantially in half, and the fractured cross-sectional surfaces
were exa~ined optically. Examination of the fractured surfaces
showed that the polycrystalline diamond body as well as the
interface of the composite were pore-free, that the bonding
medium was distributed uniformly throughout the diamond body -
and that the fracture was transgranular rather than intergranular,
i.e. that the fracture occurred through the diamond grains
rather than along the grain boundaries. This indicates that
the bonding medium was highly adherent and was as strong as the
diamond grains or crystals themselves. Also, no ~isible inter-
layer or defects at the interface between the silicon nitride
substrate and the adhered polycrystalline diamond layer could
be detected. The fractured surface of the composite appeared
to have a continuous structure. However, the difference in
grain size between the diamonds and the strongly adhered substrate
as well as the darker color of the substrate, enabled recogni-
tion of the boundary between the substrate and adhered polycrystal-
line diamond body.
The fractured cross-section of the composite was polished.
Optical examination of the polished cross-sectional surface, as
in Example 14, showed no strings of holes formed from diamond
fragment pullout illustrating the strong bonding therein. A micro-
pho-tograph of the surface revealed this to be almost identical
to that illustrated in Figure 7, and the body-substrate interface was
distinguished by the difference in crystal structure and
RD-1033~/10335
color between the diamond body and the substrate. The
density of the diamond crystals was about 75% by volume of
the polycrystalline diamond body.
EXAMPLE 24
The composite produced in Examples 16, 17 and 19 were
fractured substantially in half, and the fractured cross-
sectional surfaces were examined optically. Examination of
the fractured surfaces showed that the polycrystalline diamond
body as well as the interface of each compositè were
pore-free, that the bonding medium was distributed uniformly
throughout the diamond body and that the fractures were
transgranular rather than intergranular, i.e. the fractures
occurred through the diamond grains rather than along grain
boundaries. This indicated that the bonding medium was
highly adherent and was as strong as the diamond grains or
crystals themselves. Also, no visible interlayer or defects
at the interface between the silicon nitride substrate and
the adhered polycrystalline diamond layer could be detected.
The fractured surface of each composite appeared to have a
continuous structure. However, the difference in grain si~e
between the diamonds and the strongly adhered substrate as
well as the darker color of the substrate enabled recogni-
tion of the boundary between the substrate and adhered poly-
crystalline diamond body.
The fracture cross-section of the composite of Example
l9 was polished. Examination of the polished cross-sectional
surface showed no strings of holes formed from diamond
fragment pullout illustrating the strong bonding therein.
A photomicrograph taken of the polished surface magnified
690 X indicated an interlayer of bonding medium through the
interface. A scanning of electron micrograph of the polished
surface magnified 1000 X showed an interlayer of bonding
medium through the interface which had a maximum thickness of
about 3 microns.
.
`\
5 6
RD-10334/10335
X-ray spectral analysis of the bonding medium in the
interlayer and in the polycrystalline diamond body sho~ed
that the components in each were the same.
