Note: Descriptions are shown in the official language in which they were submitted.
1~ 4~
-- 1 --
This invention concerns novel refractory body composite
ceramics wherein the composite ceramics have improved toughness
and a process for producing said composite ceramics.
In comparison to noncomposite ceramics, composite
ceramics generally possess superior toughness, strength, wear
resistance and exhibit superior performance as cutting edges for
machining high strength alloys, drilling rocks, cutting or shaping
other hard materials, as high temperature fixtures or structural
materials and as wear-, abrasion- and chemical-resistant parts,
particularly at high temperatures, for example, in certain chemi-
cal reactors. Furthermore, such materials may be used in pump
seals, blast nozzles, as wear surfaces, and in impact materials.
Methods known for preparing refractory bodies have
involved hot pressing of powdered or compacted samples in a
close-fitting, rigid mold or isostatically hot pressing a sealed,
deformable container containing a
. ~ , ~
powdered or compacted sample utilizing a gas as the
pressure-transmitting medium. In both of these methods,
the sample, whether originally a powder or compact,
assumes the shape of the mold or deformed container.
Several problems are encountered when such methods are
used. The sizes and shapes of articles that can be
produced are limited. Finished articles having complex
shapes often contain undesirable density gradients because
of nonuniform pressure distribution during pressing. Also,
each sample must be compressed in a separate mold or con-
tainer and after hot pressing the sample often adheres
to the mold or container during separation.
Iso~tatic pressing of sel~-sustaining com-
pacts has been suggested as a possible method of over~
coming the above-mentioned ~roblems. For example,
Ballard and ~endrix, US~,279,917, teach the use of a
particulate material such as powdered glass or graphite
as a pressure~transmitting medium in the hot pressing
of refractory bodies. In this method, the particulate
pressure ~ransmitting medium does not conform completely
to the sample and as a consequence, pressure is still
not transmitted uniformly and truly isostatically.
Various shapes such as cubes, round rods and the like are
distorted when pressure is applied. It is virtually
impossible to form in-tricate contours by this method.
~n~
Barbaras, U~ 3,455,682, discloses an improved
method of isostatically hot pressing reractory bodies
which comprises the following steps: (A) surrounding the
body with a mixture consisting essentially of from about
5 percent to about 40 percent by weight of a first compo-
nent selected from alkali and alkaline earth metal chlo-
rides, fluorides and silicates and mixtures thereof and
from 60 to 95 percent by weight of a second component
C-33,262A -2-
-3~ 8~r
selected from silica, alumina, zirconia, magnesia,
calcium oxide,.spinels, mullite, anhydrous aluminosili-
cates and mixtures thereof; ~B) heating said mixture
to a temperature at which it is plastic; and (C) while
maintaining said temperature, applying to said mixture
sufficient pressure to increase the density of said
body. It is taught that in this manner, low porosity,
refractory bodies having a variety of shapes and sizes
: can be compressed to extremely low porosity and very
.0 high densi~y without substantially altering their origi-
nal shape.
~- Rozmus, USq~4,428,906, discloses a method for
consolidating material of metallic and nonmetallic com-
.~ positions and combinations thereof to form a densified
~5 compact of a predetermined density wherein a quantityof such material which is less dense than the predeter-
mined density, is encapsulated in a pressure-transmit-
ting medium to which external pressure is applied to
' the entire exterior of the medium to cause the predeter-
. 20 mined densification of the encapsulated material by
hydrostatic pressure applied by the medium in response
to the medium being substantially fully dense and incom-
pressible and capable of fluidic flow, at least just
prior to the predetermined densification. The invention
is characterized by utilizing a pressure-transmitting
medium of a rigid interconnected skeleton structure
which is collapsible in response to a predetermined
force and fluidizing means capable of fluidity and sup-
ported by and retained within the skeleton structure for
forming a composite of skeleton structure fragments dis-
persed in the fluidizing means in response to collapse
of the skeleton structure at the predetermined force
and for rendering the composite substantially fully
C-33,262A -3-
dense and incompressible and fluidic at the predetermined densi-
fication of the compact.
Also United States Patents 3,455,682 and 4,428,906
teach that in order to effect compaction hydrostatically through
a substantially fully dense and incompressible medium in a press,
the press must provide sufficient force to cause plastic flow of
the medium. It is desirable to heat the medium to a temperature
sufficient that the medium becomes very fluidic or viscous; how-
ever, the medium must retain its configuration during and after
being heated so it may be handled for placement in the press with-
out change in its configuration. The skeleton structure collapses
or crushes with minimal force and is dispersed into the fluidized
material which then offers relatively little xesistance to plastic
flow to thereby hydrostatically compact the powder. Thus, once
the skeleton structure has collapsed, the pressure applied by the
press is hydrostatically transferred to the powder to be compacted.
It is generally taught by United States Patents
3,455,682 and 4,428,906 that composite ceramics, such as those
prepared from tungsten carbide and cobalt, are prepared by contact-
ing the refractory material, such as tungsten carbide, with ametal, such as cobalt, under conditions wherein the metal is in
a liquid state. Under those conditions, the refractory material
partially dissolves in the metal and thereafter reprecipitates
from the metal as the metal cools. This forming method involves
a liquid-solid process wherein the metal serves as a wetting agent
and the refractory material undergoes significant agglomeration
~ 5~ 8~ 6 4 6 g 3 - 36 5 3
during reprecipitation. This agglomeration results in the pre-
paration of a composite ceramic which is quite brittle.
In general, the composite ceramics prepared by such
methods as described hereinbefore are extremely hard, but unfor-
tunately quite brittle (i.e. not tough). This brittleness results
in compositions which are sensitive to crack initiation and pro-
pagation and have very low impact strength.
In general, the composite ceramics prepared by such
methods as described hereinbefore are extremely hard, but unfor-
tunately quite brittle (i.e. not tough). This brittleness resultsin compositions which are sensitive to crack initiation and pro-
pagation and have very low impact strength.
Surprisingly, the present composite ceramics have the
desired property of toughness without sacrificing hardness.
According to the present invention, there is provided
a high density refractory body composite ceramic comprising:
densified (a) refractory material that is an oxide, carbide,
nitride, silicide, boride, sulfide or a mixture th~reof, and
(b) a binder material wherein the binder material is a material
capable of plastic deformation, wherein said binder material is
present in sufficient amount to at least partially fill the
interstices between the refractory material, wherein the refract-
ory body ceramic composite has a toughness to hardness ratio of
0.03 Rc/N-m/cm or greater.
According to another aspect of the present invention
there is also provided a process for the preparation of a high
density refractory body composite ceramic comprising subjecting
a mixture of: (a) a particulate refractory material selected
~ 6 ~2~4~ 64693-3653
from the group consisting of oxides, carbides, nitrides, borides,
silicides, sulfides and mixtures thereof, and (b) a metal binder
material present in sufficient amount to at least partially fill
interstices between the particles of the refractory material,
to a temperature of 60 to 95 percent of the liquidus temperature
of the binder material, under pressure of at least about 50,000
psi (345 MPa) for a period of time which is less than that time
sufficient for sintering to occur and less than about 10 minutes,
such that a density of at least about 85 percent is achieved.
Preferably such composite ceramics comprise between
(a) 50 and 97 percent by weight of the refractory material; and
(b) 3 and 50 percent by weight of the binder material. Particle
size is preferably 20 microns or less.
In the accompanying figures:
Eigure 1 is a scanning electron microscope picture of a
sample of Example 15A (backscatter image at 4000 times magnificat-
on);
Figure 2 is a scanning electron microscope picture of a
sample of Example 15B (backscatter image at 4000 times magnificat-
ion);
~2~
Figure 3 is a microseopy picture of Example l9B, pub-
lished in "Ameriean Society of Metals", Metals Handbook, 9th ed.,
Volume 3, page 454, (1980);
Figure 4 is a microseopy picture of Example 20B, pub-
lished in "American Society of Metals", Metals Handbook, 9th, ed.,
Volume 3, page 454, (1980); and
Figure 5 is a microscopy picture of Example 22B, pub-
lished in Science of Hard Materials, ed. R. K. Viswandhou,
.. . . .
D. J. Rowcliffe and J. Garland, "Micro-structures of Cemen-ted
Carbides", M. EA Exner, page 245, (1983).
This invention generally concerns high density refrac-
tory body composite ceramics which are refractory ceramic materials
bound with binder materials, wherein the refractory body composi-te
ceramics have improved toughness. One component of the ceramic
composites of this invention is the refractory ceramic materials.
In general, any ceramic material which has refractory character-
istics is useful in this inven-tion. Useful refractory ceramic
materials include mixed crystals such as sialous. Preferred
refractory ceramic materials include refractory oxides, refractory
carbides, refractory nitrides, refractory silicides, refractory
borides, refractory sulfides or mixtures thereof. More preferred
refractory ceramic materials include refractory alumina, zirconia,
magnesia, mullite, zircon, thoria, beryllia, urania, spinels,
tungsten earbide, tantalum carbide, titanium carbide, niobium car-
bide, zirconium carbide, boron carbide, hafnium carbide, silicon
carbide, niobium boron carbide, aluminum nitride, titanium nitride,
zironium nitride, tantalum nitride, hafnium nitride, niobium
nltride, boron nitride, silicon nitride, titanium boride, chromium
boride, zirconium boride, tantalum boride, molybdenum boride,
tungsten boride, cerium sulfide, molybdenum sulfide, cadmium
sulfide, zinc sulfide, titanium sulfide, magnesium sulfide, zir-
conium sulfide or mixtures thereof. Even more preferred refractory
ceramic materials include tungsten carbide, niobium carbide,
titanium carbide, silicon carbide, niobium boron carbide, tantalum
carbide, boron carbide, alumina, silicon nitride, boron nitride,
titanium nitride, titanium boride or mixtures thereof. Even more
preferred refractory ceramic materials are tungsten carbide, nio-
bium carbide and titanium carbide. The most preferred refractory
ceramic material is tungsten carbide.
In general, binder materials useful in this invention are
defined as any metal, metalloids~ alloy or alloying elements
which are capable of plastic deformation. Preferred binder mate-
rials include cobalt, nickel, iron, tungsten, molybdenum, tantalum,
titanium, chromium, niobium, boron, zirconium, vanadium, silicon,
palladium, hafnium, aluminum, copper, alloys thereof or mixtures
thereof. More preferred binder materials are cobalt, nickel,
titanium, chromium, niobium, boron, palladium, hafnium, silicon,
tantalum, molybdenum, zirconium, vanadium, aluminum, copper, alloys
thereof or mixtures thereof. Even more preferred binder materials
include cobalt, chromium, nickel, titanium, niobium, palladium,
hafnium, tantalum, aluminum, copper, or mixtures thereof. Still
more preferred binder materials include cobalt, niobium, titanium
Il ~..
9~ -
or mixtures thereof. The most preferred binder material is cobalt.
The amount of binder material present is sufficient to
at least partially fill interstices between the particles of the
refractory ceramic material. Preferably, the binder material is
present in a sufficient amount to fill the interstices between the
particles of the refractory ceramic material. Preferably, the
refractory bodies of composite ceramics comprise betweenabout 0.5
and about 50 percent by volume of the binder material and between
about 50 and about 99.5 percent by volume of the refractory ceramic
material. More preferably, the refractory bodies of composite
ceramics of this invention comprise between about 0.5 and about
30 percent by volume of the binder material and between about 70
and about 99.5 percent by volume of the refractory ceramic mater-
ial. Even more preferably, the refractory bodies of composite
ceramics comprise between about 6 and about 20 percent by volume
of the binder material and between about 80 and about 94 percent
by volume of the refractory ceramic materials.
In a preferred refractory body composite ceramic, the
refractory ceramic material comprises at least about 85 percent
of a single refractory ceramic compound. In the most preferred
embodiment, the refractory ceramic material comprises at least
about 90 percent of a single refractory ceramic material.
In a preferred refractory body composite ceramic, said
composite ceramic consists of a refractory material of oxides,
carbides, nitrides, silicides, borides, sulfides or mixtures there-
of and a binder material capable of plastic deformation present in
.~ -9a~ 4~ 64693-3653
an amount sufficient to at least partially fill the interstices
between the refractory body particles.
One can now Eabricate a novel composite ceramic compos-
ition which comprises at least three phases:
(a) at least one phase of a particulate refractory material
of oxides, carbides, silicides, borides, nitrides or sulfides;
(b) at least one phase of binder material as defined herein-
before; and
(c) at least one phase comprising a compound which cor-
0 responds to the formula Xa bYbZC whereinX is the metal derived from the refractory material of
oxides, carbides, nitrides, silicides, borides or sulfides;
Y is a binder material capable of plastic deformation;
Z is carbon, oxygen, nitrogen, silicon, boron or sulfur;
a is an integer of about 1 to about 4;
b is a real number between about 0.001 and about 0.2;
and
c is an inte~er of between about 1 and 4.
A three-phase cobalt tungsten carbide composite ceramic
composition as hereinabove described has been observed and it is
theorized that three or more phase
composite ceramics composed of other materials as defined
herein may also be present.
It is believed phase (c) is a phase in which
a binder material atom is sub~tituted on the lattice of
the refractory material. It is further believed that in
the ceramic composites of this invention, these compounds
are found between the refractory ceramic material particles
and the binder material phase in the interstices between
the refractory ceramic material particles. The existence of
such a phase may be the reason for the siynificantly
enhanced toughness of the ceramic composites. In the abo~e
formula, b is preerably ~etween about 0.001 and about 0.1.
This three-phase ceramic composite preferably comprises
between about 50 and about 99 percent by ~olume of the
refractory ceramic material; between about 1 an~ about 50
percent by volume of the binder material, and be~ween about
O and about 0.2 percent by volume of the compound correN
sponding to the formula Xa bYbZC, wherein X, Y, Z, a, b
and c are as hereinbefore defined. More preferably, the
composite ceramics of ~his i~vention comprise between about
70 and abou~ 98 percent by volume of a refractory ceramic
material; about 2 and about 30 percent by volume of a binder
material; and between about 0 and about 0.2 percent by volume
of a compound corresponding to the formula Xa bYbZC. Most
preferably, the composite ceramics comprise between about
80 and about 94 percent by volume of a refractory ceramic
material; between about 6 and about 20 percent by volume of
a binder material; and between about 0.001 and about 0.1
percent by volume of a compound corresponding to the formula
Xa bYbZc. X is preferably aluminum, zirconium, magnesium,
~horium, beryllium, uranium, tungsten, tantalum, titanium,
niobi~m, boron, hafnium, silicon, chromium, mol~bdenum,
cerium, cadmium or zinc. X is more preferably tungsten,
niobium, titanium, silicon, tantalum, boron or aluminum.
C-33,262A -10-
~2'~
-- 11 --
Even more preferably, X is tungsten, niobium or titanium. Most
preferably X is tungsten. Y is preferably cobalt, nickel, iron,
tungsten, molybdenum, tantalum, titanium, chromium, niobium, zir-
conium, boron, vanadium, silicon or palladium. More pref`erably,
Y is cobalt, nickel, titanium, chromium~ niobium, palladium, boron,
silicon, tantalum, molybdenum, zirconium or vanadium. Even more
preferably, Y is cobalt, chromium, niobium, nickel, titanium,
palladium or tantalum. Even more preferably, Y is cobalt, niobium
or tantalum, with cobalt being most preferred. Z is preferably
carbon, nitrogen, boron or oxygen. Z is more preferably nitrogen,
carbon or oxygen; and most preferably carbon.
Toughness is defined herein as the energy absorbed in
fracture of a s-tandard sample. An approximate measure of toughness,
but a more convenient one, called the toughness index number is the
ultimate stress multiplied by the strain at rupture. This tough-
ness index number as used by Marin in "Strength of Materials",
page 16, equals the area below the stress strain curve and is
determined by the equation:
Toughness Index = ~(Stress to Fracture) x (Strain _ Fracture)]
for approximately straight stress, strain behavior (i.e., Elastic
Response). Since the modulus (i.e., slope) of a stress strain
(linear) plot passing through the origin e~uals the ordinate divid-
ed by the abscissa, the toughness index is also equal to:
(Stress to Fracture)
2 Modulus
in the elastic region. The standardized and convenient transverse
", . .
- 12 -
rupture strength values [e.g~ "Amerlcan Soc. of Metals", Metals
Handbook, 9th, Ed., Vol. 3 (1980)] may be substituted for the
stress to fracture term. Machining and testing of the transverse
rupture bars is done in accordance to methods known by those skill-
ed in the art as described in the 1976 Annual Book of ASTM
Standards, Part 9, pp. 193-194, in accordance with ASTM B 406-73.
In addition to exhibiting greater toughness, the com-
posite ceramics of this invention generally exhibit at least equal
hardness as compared to other composite ceramics of similar com-
positions and geometries. Since most of the materials of interest
in this invention are intended for applications using high hardness,
the multiplicative product of hardness and of the toughness index
may be used as a figure of merit. The composite ceramics of this
invention generally exhibit a greater hardness-toughness product
than exhibited by other composite ceramics of similar composition
and geometries; thereby exhibiting greater toughness without
sacrificing hardness.
The composite ceramics of this invention preferably have
an average grain size of about 10 micxons or less; more preferably
about 5 microns or less; still more preferably about 2 microns or
less; and most preferably about 1 micron or less. It is believed
that the configuration of the particles is responsible in part for
the enhanced properties of the composite ceramics of this invention.
The smaller rounded or elipsoidal-shaped particles appear to result
in the enhanced properties.
The high density refractory bodies of composite cexamics
~Lf~ t8;~
- 12a -
which comprise refractory ceramic materials bound together with
binder materials are prepared in a substantially solid state
process. A solid state process refers herein to a procedure where-
by the binder material and refractory ceramic materials are com-
bined while in a substantially solid state. It is believed that
the formation of the third phase or of other additional phases in
the composite ceramic of this invention is evidence of the solid
state process which takes place during the preparation of such
composite ceramics. In general, the binder material and refrac-
tory ceramic material
-13~ B~
are contacted in ~he powder form in a container capable of
performing as a pressure-transmit~ing medium at temperatures
high enough for ~he ceramic materials and binder materials to
form a composite ceramic bound together by binder materials
capable of plastic deformation. Such container is usually
filled with the powders to be contacted, evacuated to remove
all gases contained in the container and hermetically sealed.
Alternatively, the binder material and refractory ceramic
material can be preformed into a shape by a cold compressing
procedure, wherein such shaped ma~erial is not fully
densified. In general, it is preferable that the metal
powders and cer~mic powders have a particle size of about
10 microns or less, more preferably about 5 microns or lessi
still more preferably of about 2 microns ox less and most
preferably about 1 micron or less. The descrip~ion of
preferred particle sizes is given for a substantially mono-
-modal particle size distribution. It will be recognized
by ~hose skilled in the ar~ that small quantities of
particulate of considerably smaller sizP than the size of
the main proportion of particulate may be intermixed there-
with to achieve a hiyher packing density for a given degree
of consolidation.
Bound composite cexamics reers herein td
ceramic composites which are held together by binder
materials.
The conditions at which the binder material
and refractory ceramic material are bound are critical
in the preparation of a refractory body composite ceramic
with $urprisingly im~roved toughness. Three desirable
parameters are the temperature at which the binding proceeds,
the pressure used to achieve such binding, and the time
period over which such pressure is applied. It is further
desired that the pressure be applied in an isostatic manner.
C-33,262A -13-
~f~ B
-- 14 -
Isostatic pressure refers herein to pressure which is applied even-
ly to all portions of the material to be densified, regardless of
shape or size. The result of isostatic pressure on a less than
fully densified material is reduction of dimension equally along
all axes.
The particular pressure, temperature and time to give
the desired results are dependent upon the particular binder
material and refractory ceramic material chosen. Those skilled
in the art can choose the particular pressures, temperatures and
times based upon the teachings contained herein.
Temperatures useful in this invention are less than the
liquidus temperature, and preferably less than the solidus tempera-
ture, and more preferably less than the temperature at which a
cold compacted part will achieve about 99 percent of theoretical
density when held for about 8 hours with no applied pressure. For
the purposes of this invention, the liquidus temperature is that
temperature at which the binder material undergoes a phase change
from a solid to a liquid state (i.e., complete~y liquid). The
solidus temperature is that temperature at which the binder mater-
ial first begins to melt (i.e., plastic deformation occurs in the
mixed phase system without the application of pressure). The
solidus temperature may be presumed to have been exceeded if plas-
tic deformation occurs without the application of pressure. In
cases where the liquidus temperature is unknown, said temperature
may be estimated by standard methods known to those skilled in the
art. It has been discovered by the ~pplicants that the densifi-
~ ~,
- 15 -
cation of binder material and refractory ceramic materials at
temperatures at which the binder material is in a liquid state
generally results in refractory bodies with a much lower toughness
than those formed wherein tAe binder material is in a solid state.
Preferably the temperature is greater than that at which a pres~
sure of about 100,000 psi (6.89 x 102 MPa) will achieve 85
percent of theoretical density within one hour. Broadly, the
temperatures useful in this invention are between 400C and 2900 C.
It must be recognized that the temperatures which are useful for
a particular binder material are dependent upon the properties of
that binder material, and one skilled in the art would recognize
those temperatures which are useful based upon the functional
description provided. Generally, a preferred temperature will be
between about 60 percent and about 95 percent of the melting
temperature (C) of the binder material and more preferably between
about 75 percent and about 85 percent of the melting temperature
( C). Temperatures at which some preferred binder materials and
the temperatures at which these binder materials may be used in
this invention are included; for cobalt, between about 800C and
1500C; more preferably between about 1000C and about 1350C; for
nickel, between about 850C and 1455C; for chromium, between
about 720C and 1865C; for a chromium-nickel alloy, between about
700C and 1345C; for niobium, between about 800C and 2475C;
for silicon, between about 1275C and 1415C; for boron, between
1800C and 2105C; for tantalum, between about 1050C and 2850C;
for a tantalum-niobium alloy, between about 900C and 2550C; for a
cobalt-molybdenum alloy, between about 1015C and 1335C; for a
- -16- ~ 4693-3653
niobium-tantalum-titanium alloy, between about 400C and 1650C;
and for vanadium, between about 700C and 1855C.
The pressure is desirably provided in an isostatic
manner. The pressure may be provided in an amount sufficient such
that a permanent volume reduction (i.e., densification) in the
composite ceramic occurs. The pressure is between about 50,000
psi (3.45 x 10 MPa) and the fracture point of the refractory
body composite ceramic; more preferably between about 70,000 psi
(4.82 x l0 MPa) and said fracture point; and most preferably
between about 100,000 psi (6.89 x 102 MPa) and said fracture
point. The pressure must be sufficient to densify a cold compact
of the powder composite to at least 85 percent density in less
than one hour at a temperature below the liquidus temperature of
the phase mixture or of the binder material by itself. Preferably
the pressure is sufficient to accomplish the above-described den-
sification in less than one minute and even more preEerably in
less than ten seconds. A rate of pressure increase greater than
about 1,000 psi/sec (6.89 MPa/sec) is preferred and a rate of
pressure increase greater than 10,000 psi/sec is more preferred.
It is believed that if the pressure used is too high, the refract-
ory bodies prepared may fracture and if the pressure used is too
low, the refractory bodies prepared have a density too low for
desired uses.
The time used is that which is sufficient to densify the
,:L,',~L~ B:~
- 17 -
refractory body to the desired density. The time which the refrac-
tory body is exposed to the desired pressure is between that time
sufficient for the ceramic composite to reach about 85 percent of
its theoretical density and that time sufficient for the material
densified to undergo sintering. It has been discovered that times
of between about 0.01 second and one hour are generally suitable
for achievement of the desired densification. The more preferred
time for achievement of the desired densification is less than one
hour; even more preferred is less than about ten minutes; still
more preferred is less than about one minute; and the most prefer-
red is less than about ten seconds.
It should be recognized that there are practical con-
siderations which will dominate the selection of the proper time,
temperature and pressure variables according to this invention.
Generally, the time variable may be minimized (in terms of utility
of this invention) to avoid getting into temperature ranges so high
that the grain structure begins to appreciably reshape and coarsen.
However, the temperature must be sufficiently high to minimize the
pressure requirements on the equipment. High pressure and high
temperature both accelerate flow; -therefore, both should be
maximized subject to the constraint that one doesn't want the
grains to grow too much. It will be evident to those skilled in
the art that grain growth inhibitors may be used to extend the
range of practice of this invention despite the fact that the
greatest utility and one of the most surprising results of this
invention is that composite ceramics with superior toughness can be
- 17a -
produced without resorting to expensive modifications of the com-
posite ceramics composition.
Isostatic pressure may be applied to the powdered binder
material and ceramic refractory material, or the prepressed pow-
dered binder material and refractory material~ Those methods of
isostatic pressing are known to those skilled in the art and all
such methods which allow for the use of the preferred parameters
of time, temperature and pressure as described hereinbefore are
useful.
One such preferred method of transmitting isostatic
pressure to a material to be bound and densified is described in
Rozmus, United States 4,428,906. The process described therein
involves first placing the powder of
-18~
the binder material and the ceramic material in the pro-
portion desired in a container which is capable of per-
forming as a pressure-~ransmitting medium at temperatures
and pressures used for densification of the powders, that
is, the container must be flexible or deformable yet
maintain structural integrity at elevated materials.
Prior to contacting the powdered binder material and
powdered refractory ceramic material in the container, the
container is evacuated as by a vacuum and then the powders
are placed into the material under vacuum condi~ions.
Such container with the less dense powder therein is then
placed in a casting mold wherein a pressure~transmitting
medium is cast about the container -to encapsulate the
entire container and the less dense powder material. The
pressure-transmitting medium is solidified so as to
retain its configuration and removed from the casting
mold. The pressure-transmitting medium includes a rigid
interconnected skeleton structure which is collapsible
when a predetenmined force is applied. The skeleton
structure may be of a ceramic-like material which is
rigid and retains its configuration, but which may be
broken up, crushed or fractionated at a predetermined
relatively minimal force. The skeleton structure is
defined by the ceramic material being interconnected to
form a framewor~, latticework or matrix. The pressure-
-transmitting medium is further characterized by including
a fluidizing means or material capable of fluidity and
supported by and retained within the skeleton structure.
The fluidizing material may, among other materials, be
glass or elastomeric material. In other words, glass
granules or particles are disposed in the openings or
interstices of the skeleton so as to be retained and
supported by the skeleton structure. A preferred transmit-
ting medium may be formed by mixing a slurry of structural
material in wetting fluid or activator with particles or
C-33,262A -18-
-19~
granules of a fluidizing material dispersed therein. The
encapsulated less than fully dense material is heated to
a compaction temperature prior to the densification.
This can be done by placing the encapsulated container
and powder in a furnace and raising it to a tempera~ure
at which compaction at the desired pressure or force will
take place. During such heating, the glass or other
fluidizing material supported by the skeleton structure
softens and becomes fluidic and capable of plastic flow
and incapable of retaining its configuration without the
s~eleton structure at the compac~ion temperature to which
the powder has been heated for densification. However,
the skeleton structure retains i~s configuration and
rigidity at the compaction temperature. The heated
pressure-transmitting medium may be handled without
losing its configuration after being heated to the
compaction t mperature so it may be placed within a pot
die. The pressure-transmitting medium which encapsulates
the container and less dense powder is then placed in a
press such as one having a cup-shaped pot die which has
interior walls extending upward from the upper extremity
of the pressure transmitting medium. Thereafter, a ram of
a press is moved downward in close-sliding engagement with
the interior walls to engage the pressure medium. The
ram therefore applies a force to a portion of the exterior
pressure-transmitting medium while the pot die restrains
the remainder of the pressure-transmitting medium so that
the desired external pressure is applied to the entire
exterior of the pressure-transmitting medium and the
pressure-transmitting medium acts as a fluid to apply
hydrostatic pressure to densify the powder to the desired
densification. When the ex-ternal pressure is applied on
the pressure transmitting medium, the skeletal structure
is crushed and becomes dispersed within the fluidizing
means such that the pressure applied is then directly
C-33,262~ -19-
~2~
- 20 -
transmitted by the fluidizing means to the container containing
the powder to be densified.
Thereafter, the densified material encapsulated within
the pressure-transmitting medium can be cooled. The pressure-
transmitting medium is then a rigid and frangible brick which may
be removed from the container by shattering it into fragments, as
by striking with a hammer or the like.
One preferred container useful for the densification of
powdered binder material and refractory ceramic material using iso-
static pressure is disclosed by Rozmus United States reissue Patent
31,355. This patent discloses a container for hot consolidating
powder which is made of substantially fully dense and incompres-
sible material wherein the material is capable of plastic flow at
pressing temperatures and that, if the container walls are thick
enough, the container material will act as a fluid upon the
application of heat and pressure to apply hydrostatic pressure to
the powder. Under such conditions, the exterior surface of the
container need not conform to the exterior shape of the desired
refractory body prepared.
Such containers can be made of any material which retains
its structural integrity but is capable of plastic flow at the
pressing temperatures. Included among acceptable materials would
be low carbon steel, other metals with the desired properties,
glass Or ceramics. The choice of the particular material would
depend upon the temperatures at which the particular binder mate-
rial and refractory ceramic material would be densified. Generally,
two pieces of -the material which would be used to make the con-
tainer are machined to prepare a mold
.~,.~
-21-
lB~
which has upper and lower die sections. These are thereafter
joined along their mating surfaces such that the upper
and lower die sections form a cavity having a predetermined
desired coniguration. The size and shape of the cavity
is determined in view of the final shape of the part to
be produced. Beore the upper and lower die sections are
assembled, a hole is drilled in one of the dle sections
and a fill tube is inserted. After the fill tube has
been attached, the two die sections are placed in a
mating relationship and welded together. Care is taken
during welding to ensure that a hermetic seal is produced
to permit evacuation. Thereaf~er, th~ container is
evacuated a~d filled with the powder to be densiied
through the fill tube. The ill tube i5 then hermetically
sealed by pinching it closed and welding it.
Thereafter, the container is e~posed to isostatic
pressure at the desired binding and densification temper-
atures. This can be done by the methods described herein-
before. Alternatively, the filled and sealed container can
be placed in an autoclave, such as an argon gas autoclave
and subjected to the temperatures and pressures desired
for the binding and densificatio~. The pressure in the
autoclave on the container is isostatic and because the
container is able to retain its configuration and has
plastic-like tendencies, the container will exert isostatic
pressure on the po~ders to be densified.
The size of the cavity in the container will
shrink until the powder therein reaches the desired density.
After consolidation, the container can be
removed from the autoclave and cooled. The container
is then removed from the densified refractory material
by pickling in a nitric acid solution. Alternatively,
C-33,262A -21
~2~4~3~
- 22 -
the container can be removed by machininy or a combination of
rough machining followed by pickling.
In an alternative method the thick-walled container can
be made of a material which melts at a combination of temperature
and time at that temperature which combination would not adversely
affect the desired properties of the densified article. Such
recyclable container materials are disclosed in Lizenby, United
States Patent 4,341,557. In the practice of the invention, the
container is prepared as described in United States reissue patent
31,355 described hereinbefore and the isostatic pressure can be
exerted on such container as described hereinbefore. The contain-
er, once the powdered binder metal and refractory ceramic material
are densified, is exposed to temperatures at which such container
will melt without affecting the properties of the refractory body
so prepared. Thereafter, the molten material or metal which has
been melted away from the refractory body can thereafter be re-
cycled to form a new container.
Barbaras, United States 3,455,682, discloses another
pressure-transmitting medium which consists essentially of from
about 5 to about 40 percent by weight of a first component selected
from alkali and alkaline earth metal chlorides, fluorides and
silicates and mixtures thereof and from about 60 percent to about
95 percent by weight of a second component selected from silica,
alumina, zirconia, magnesia, calcium oxide, spinels, mullite,
anhydrous aluminosilicates and mixtures thereof. This pressure-
transmitting medium can be used in the following manner. A mold or
- 23 -
combining cavity in which the densification is to be carried out
is preferably loaded by first cold pressing a portion of the
pressure-transmitting medium in the bottom of the mold to provide
a base on which a prepressed billet of the material to be densi-
fied is placed, thereafter the prepressed billet is placed on the
base and covered with further pressure-transmitting medium. The
mold is then heated to a temperatwre at which the densification
i~ to take place and its contents are allowed to equilibrate to
this temperature. Thereafter, the desired pressure for densifi-
cation is applied to the then plastic pressure-transmitting medium.
After the pressure is removed, it is preferable that the mold be
promptly ejected from the hot zone of the hot pressing apparatus
and allowed to cool rapidly to minimize grain growth within the
billet. The pressed mass, the fused pressure-transmitting medium
containing the densified refractory body, is then ejected from the
mold and the envelope of fused pressure-transmitting medium is
broken to recover the compressed refractory body. While the method
of said process is ordinarily most conveniently carried out utiliz-
ing rigid hot pressing molds, this method can be used by subjecting
a sealed, deformable container containing one or more billets
surrounded with one of the above-mentioned mixtures to elevated
temperatures and isostatic pressure.
Other methods of exposing the refractory ceramic material
and binding material to isostatic pressure are described in United
States Patent reissue 28,301; and United States Patents 4,142,888,
4,094,709, 4,255,103, 3,230,286, 3,824,097, 4,023,466,
r ~ ~
- 24 -
3,650,6~6, 3,841,870, 4,041,123, 4,077,109, 4,081,272 and
~,339,271.
In practice, the prepressed binder material and refrac-
tory ceramic material can be prepared by placing powders of the
binder material and the refractory ceramic material in a press and
partially densifying this material. The resulting partially
densified material can be referred to as a billet. Such pressing
is normally done under ambient temperatures. In one embodiment,
a rigid graphite mold can be used to apply the pressure. Suitable
pressures are generally between about 200 psi (1.38 MPa) and about
10,000 psi (6.89 x 101 MPa). Alternatively, the powder of binder
material and refractory ceramic material can be pressed directly
in a steel or tungsten carbide die in a powder metallurgy press.
Further, the powder can be charged into a thin-walled rubber mold
which is evacuated and sealed and subjected to isostatic pressure
in a liquid medium at ambient temperatures and pressures of from
about 1,000 psi (0.69 x 101 MPa) to about 100,000 psi (6.89 x 102
MPa). In one preferred embodiment, the partially densified binder
material and refractory ceramic material has a density of about 30
percent or greater, more preferably between about 50 and about 85
percent; and most preferably between about 55 and about 65 percent.
The high density refractory body ceramic composites of
this invention generally have a density of about 85 percent or
greater, preferably about 90 percent or greater and more preferably
about 95 percent or greater and most preferably about 100 percent.
High density refers herein to a density of about 90 percent or
',~"'~
~2'~
- 25 -
greater of theoretical. These products have a lower particle size
than refractory bodies prepared by heretofore known processes.
Furthermore, the refractory bodies of this invention have an in-
creased dispersion over those refractory bodies prepared by prior
art processes. A surprising feature of this invention is that
high toughness is achieved even in absence of full density. This
feature becomes more conspicuous as the density drops to abou-t 85
percent density. The compositions of this invention, even at
slightly low density, exhibit toughness equal to or greater than
the same compositions prepared by the standard liquid phase sinter-
ing operation. It is believed that there is less agglomeration of
the refractory materials and a product which has a greater tough-
ness at a desired hardness.
Said composite ceramics preferably possess at least about
10 percent greater toughness than exhibited by other composite
ceramics of similar compositions and geometries. More preferably,
the composite ceramics as taught by this invention possess 15 per-
cent greater toughness and most preferably they possess 25 percent
greater toughness. This increase in toughness is gained while
retaining at least equal hardness as compared to other composite
ceramics of similar compositions and geometries. In addition, the
composite ceramics of this invention generally possess higher trans-
verse rupture strength at about equivalent hardness of other com-
poslte ceramics. Known uses for the composite ceramics of this
invention include any use in which requires a material possessing
toughness at a desired hardness as exemplified by cutting tools and
- 26 -
drill bits.
It will be obvious to those skilled in the art that there
are additional ceragraphic distinctions which can be drawn between
solid phase formed product and liquid phased formed alloy composites
where the phase diagrams are known and available (e.g., such as
can be observed by scanning electron microscopy, light microscopy
or analytical transmission electron microscopy).
The microstructure of the composite ceramics of this
invention shows that said composite ceramics exhibit a smaller
grain size, a more well distributed binder material (e.g., cobalt
in the tungsten carbide-cobalt composite ceramic) and a more nearly
rounded grain shape or configuration. Depending upon the resolu-
tion required to resolve the characteristic grain particle size
and shape of the composite ceramics, light microscopy, scanning
electron microscopy, replica microscopy and analytical transmission
electron microscopy may be used. As long as the magnification of
the grain particles is known and sufficient resolution is obtained,
the processing of the generated data may be done in a substantially
similar manner independent of the microscopy technique employed.
The ceramic portion of the composite ceramics of this in-
vention generally has more nearly rounded or elipsoidal-shaped grains
(or grain clusters characterized by more nearly rounded protruber-
ances). Other composite ceramics generally exhibit ceramic phase
grains having a more angular shape (i.e., more polyhedral in form)
and the binder phase tends to be collected in angular-shaped
pockets where two or three of these angular-shaped ceramic phase
~.'`'',~
- 27 -
grains connect or lmpinge on one another.
Microscopy methods generally depend on examination of
planar sections cut through a sample. The grain structure of the
ceramic portion of the composite ceramics of this invention will
appear to be roughly circular or elipsoidal; whereas, the grain
structure of the ceramic portion of other composite ceramics will
appear as irregularly-shaped polygons generally possessing three
to eight or more sides.
The composite ceramics of this invention preferably have
an average grain particle size of the refractory material of about
10 microns or less, more preferably about 5 microns or less, still
more preferably about 2 microns or less and most preferably about
1 micron or less.
In addition, the composi-te ceramics of this invention
have a greater distributed binder material. If a straight line is
drawn on a microstructure picture, said lines will cross a grain
boundary (of the refractory material) more often in a finer grain-
ed material. In addition, if there is a greater dispersion of
binder particles in the picture, the straight line will also cross
binder particles more often in a material having more dispersed
binder particles. The average number of binder particles traversed
by a series of parallel lines (i.e., Binder Distribution) will be
greater for the composite ceramics of this invention as compared
with other composite ceramics of similar composition. The percent-
age increase in binder distribution for the composite ceramics of
this invention is preferably about 10 percent greater than for
- 28 -
other composite ceramlcs of similar composition. More preferably,
the binder distribution is at least about 50 percent greater -than
other composite ceramics of similar composition and most preferably
is at least about 100 percent greater than said composite ceramics.
It is believed that the composite ceramics of this invention have
greater binder distribution by virtue of the processing conditions,
comprising relatively high pressure, relatively high speed of
pressure application (i.e. small amount of time) and relatively
low temperature. Images of different magnification may be used
if the line length examined is converted to its absolute value by
dividing the line length on the image by the magnification.
Another distinguishing feature of the composite ceramics
of this invention is their low circularity number. Circularity
may be defined as the square of the perimeter of a grain particle
divided by its area. If the grain particle is more circular (i.e.,
more nearly round) then the circularity number calculated will be
smaller. The dimensions of a circle generate the smallest circular-
ity number which is equal to 4~ or about 12.6. A regular octagon
may have a circularity number of about 13.25, but irregular poly-
gons generate circularity numbers of above about 20. An averagecircularity is calculated by determining the average of the circular-
ity of a representative sample of grain particles in a microscopy
picture. The ceramic portion of the composite ceramics of this
invention preferably have an average circularity number less than
about 17, more preferably less than about 15.5, still more prefer-
ably less than about 14 and most preferably less than about 13.5.
., c~
B;~
- 29 -
For comparison only, the average circularity number for
other composite ceramics of similar composition is above about 20.
The process of -this invention allows the preparation of
a refractory body of composite ceramic materials with a control-
lable toughness and hardness.
In one preferred embodiment, the binder material is co-
balt and the refractory ceramic material is tungsten carbide.
Preferably, the composite ceramic described above comprises between
about 0.5 and about 50 percent by volume of cobalt and between
about 50 and about 99.5 percent by volume of tungsten carbide.
More preferably, said composite ceramic comprises between about 0.5
and about 20 percent by volume of cobalt and between about 80 and
about 99.5 percent by volume of tungsten carbide, and most prefer-
ably said composite ceramic comprises about 6 percent by volume of
cobalt and about 94 percent by volume of tungsten carbide. The
-tungsten carbide cobalt composite ceramics hereinabove described
possess greater toughness than possessed by other tungsten carbide-
cobalt ceramics of similar composition and geometry. More prefer-
ably, the tungsten carbide-cobalt composite ceramics of this
invention possess at least about 10 percent greater toughness; even
more preferably they possess at least about 15 percent greater
toughness; still more preferably they possess at least about 25
percent greater toughness; and most preferably they possess at
least about 50 percent greater toughness.
The toughness of the tungsten carbide-cobalt composite
ceramics is preferably greater than about 2.1 MPa, more preferably
lZ~
- 30 -
about 3 MPa or greater, and most preferably about 4 MPa or greater.
The hardness of these ceramic composites is preferably about 1100
VHN (Vickers Hardness Number) or greater or more preferably about
1600 VHN or greater; or on a different hardness scale, said ceramic
composites preferably exhibit hardness of about 80 Rc (Rockwell
Hardness) or greater or more preferably about 95 Rc or greater.
The refractory bodies prepared from cobalt and tungsten carbide
may have a particle size of about 10 microns or less, more prefer-
ably about 5 microns or less, still more preferably about 2 microns
or less and most preferably 1 micron or less.
Specific Embodiments
The following examples are included for i]lustrative
purposes only, and are not intended to limit the scope of the in-
vention. Unless otherwise stated, all parts and percentages are
by volume.
In the following examples, the beginning refractory mate-
rial has a grain particle size less than about 2 microns and the
beginning binder material has a grain particle size less than about
10 microns. In the following comparative examples, the liquid
phase sintering process is performed substantially in accordance
with the procedures outlined in "American Society of Metals",
Metals Handbook, 9th ed., Volume 7, pp. 385-386 (1984).
Example 1
Fine tungsten carbide (23.5 g, particle size less than
0.5 microns) is weighed and proportioned with powdered cobalt (1.5
g)O The composition is 94 percent tungsten carbide (90 volume
- 31 -
percent) and 6 percent cobalt by weight (10 volume percent). The
powders are vibration milled for 8 hours to coat the tungsten
carbide with cobalt. About 0.5 (0.125 g) volume percent wax is
added to help form the cold compact. The cold compact is formed
using a uniaxial press or a silastic fluid die to form a preform
of about 55 percent density. Die pressure used is about 58.8 Ksi
(4 x 102 MPa). The preform is dewaxed at about 550F (287C) and
is subjected to vacuum dewaxing to improve removal. The preform
is placed in a fluid die of about a 3:1 ratio of ceramic to glass
and heated to about 2250F (1220C), the furnace is argon purged
and the time to reach 2250F (1220C) is about 2 hours. The heated
sample contained in the fluid die is thereafter placed in a press
and subjected to about 120 Ksi (8.2 x 102 MPa) pressure for about
2 seconds. The refractory body recovered has a density of about
100 percent (theoretical).
Example 2
The process of Example 1 is substantially repeated using
a composition of about 3 weight percent cobalt (5 volume percent)
and ahout 97 weight percent tungsten carbide (95 volume percent).
The preform contained in the fluid die is heated to about 2370F
(1240C) before exposing to the isostatic pressure. The refractory
body recovered has a density of about 99 percent (theoretical).
Examples 3-9
Several mixtures of about 6 weight percent cobalt and
about 94 percent tungsten carbide are prepared in suhstantially
the same manner as in Example 1. The mixtures are cold compacted
;;~
4~
- 32 -
under a pressure of about 41.2 MPa in a silastic fluid die using
about 0.5 volume percent of wax. The cold compacts are heated to
about 290C to remove the wax. The rod dimensions are about 0.563
inch long (1.4 cm), about 0.75 inch (1.9 cm) in diameter, and
have a mass of about 36.67 g.
The cold compact is thereafter placed in a glass/ceramic
transducer, heated in an argon atmosphere to the desired tempera-
ture, and held at such temperature for about 5 minutes. The cold
compact in the pressure-transducing medium (i.e., fluid die) is
pressed isostatically for the indicated dwell (i.e., time), with
a 2-second manual release of pressure. The results are compiled
in Table I.
ABLE I
Cold Hot iso- R
Compact static c
Exam- Press Press Temp Dwell Impact Hard- Density
ple (MPa) (MPa) (C) (sec) (Nm/cm2) ness (g/cc)
3 41.2 83.5 1100 2 225 85 13.05
4 41.2 83.5 1100 1/2 186 -- 13.07
41.2 83.5 1150 2 223 86 13.06
6 41.2 83.5 1220 1/2 117 90 14.99
7 41.2 83.5 1220 2 145 93 15.02
8 41.2 83.5 1300 2 225 87 15.00
9 41.2 ~3.5 1300 2 213 95 15.03
Example lOA
Fine tungsten carbide powder (4268 gm) is weighed and
proportioned with finely divided cobalt (272 gm) and 1000 ml of
acetone. The composition is about 94 percent by weight tungsten
"~.
f~4F~
- 33 -
carbide (90 volume percent) and about 6 percent cobalt (10 volume
percent). This slurry is added to a Union Process Model l-S
Attrition Mill along with about 120 lbs (55 kg) of 3/16" (1.2 cm)
diameter tungsten carbide grinding media. The powder is attrited
for 2 hours at 250 rpm. The acetone is removed by evaporating
and approximately 2.25 percent by volume of finely divided para-
ffin wax is added to 1000 ml of heptane and attrited for 15 minutes.
The resultant slurry is then evaporated to dryness.
The powder is then screened through -45 mesh screen
(American standard) to remove large lumps. A Trexlor ~ Isopress
bag is then filled and vibrated to reach thp density of about 30
percent to about 40 percent theoretical. The bag is evacuated,
sealed and then isopressed at about 30,000 psi (20.6 x 101 MPa) to
a green density of about 50 percent to about 65 percent theoretical.
The resulting bars are placed in a fluid die similar to
Rozmus (United States Patent No. 4,428,906) and packed with boro-
silicate glass cullet. This assembly is heated to about 2250F
(1232C) (about 1.5 hours) and held for 5 minuteC in a nitrogen
purged furnace. The assembly is placed in a supporting die and
subjected to about 120 Ksi, (8.2 x 102 MPa) said pressure being
maintained for 2 seconds. The pressure is released slowly (about
12 Ksi/sec or 80 MPa/sec). The refractory body recovered has a den-
sity of > 14.8 g/cm3, and has the properties listed in Table III.
Comparative Example lOB
Rods of substantially identical composition and cold
compact geometry to those prepared in Example lOA are prepared by
~.
~2~8'~
- 34 -
liquid phase sintering, as practiced by those skilled in the art
and are similarly machined and impacted. The results are given
in Table III.
Example llA
Niobium carbide powder is weighed (4086 gm) and placed
under acetone (1000 ml) immediately to prevent oxidation or fire.
Cobalt powder is proportioned (454 gm) to yield a composition of
about 90 percent by weight niobium carbide (91 volume percent) and
about 10 percent cobalt (9 volume percent). The slurry is attrited
and processed under substantially the same conditions as Example
lOA yielding a refractory body with a density of about 7.60,
g/cm3. The refractory body recovered has the properties listed in
Table III.
Comparative Example llB
Rods of substantially identical composition and cold
compact geometry to those prepared in Example llA are prepared by
liquid phase sintering, as practiced by those skilled in the ar-t
and are similarly machined and impacted. The results are given in
Table III.
Example 12A
.
Fine tungsten carbide powder is weighed (4268 gm) and
proportioned with fine nickel powder (272 gm). This powder is
slurried with 1000 ml of acetone, attrited and processed to green
state substantially similar to Example lOA. The composition of
the powder is about 95 percent by weight tungsten carbide (91 vol-
ume percent) and 5 percent by weight nickel (9 volume percent).
~ ``t .
B'~
- 35 -
The greenware is then placed in a ceramic vessel, surrounded with
Pyrex* ylass powder (greater than about Tyler 100 mesh screen) and
heated to about 2150F for about 2 hours.
A pressure of about 120 Ksi (8.2 x 101 MPa) is then ap-
plied for 2 seconds duration, and slowly released (about 12 Ksi/
sec or 80 MPa/sec). The resultant refractory body part has a
density of about 99.7 percent of theoretical. The refractory body
recovered has the properties listed in Table III.
Comparative Example 12B
Rods of substantially identical composition and cold com-
pact geometry to those prepared in Example 12A are prepared by
liquid phase sintering, as practiced by those skilled in the art
and are similarly machined and impacted. The results are given in
Table III.
Example 13
A sample of nickel ferrite (250 gm) and nickel powders
(25 gm) are physically blended with no attempt at attrician yield-
ing a composition of about 90 percent by weight of nickel ferrite
and 10 percent by weight of nickel. The powder is then compacted
at about 58.8 Ksi (802 MPa) in a uniaxial double acting die. No
wax is used. The resulting pellet is about 68 percent of theoreti-
cal density~
The part is placed in a glass die similar to Example 10
and heated to about 2000C for 2 hours. The pressure (about 120
Ksi) is then applied for 2 seconds dwell and slowly released. The
resultant refractory body is about 97.8 percent of theoreticaldensity.
*Trade mark
- 36 -
Example 14A
A mixture of about 4268 gm of tungsten carbide, about
227 gm of cobalt, and about 45 gm of nickel is added to 1000 ml of
acetone. The composition of the attrited powder is about 94 per-
cent tungsten carbide (90 volume percent)/5 percent Co (8.5 volume
percen-t)tlpercent Ni by weight (1.5 volume percent). The powder
is attrited, green processed and consolidated in substantially
the same manner as Example lOA. The resultant ceramic has a den-
sity of about 14.66 gm/cc and other properties as listed in Table
III.
Comparative Example 14B
Rods of substantially identical composition and cold
compact geometry to those prepared in Example 14A are prepared by
liquid phase sintering, as practiced by those skilled in the art
and are similarly machined and impacted. The results are given in
Table III.
Example 15A
Tungsten carbide powder (4268 gm) is blended, attrited
with cobalt powder (272 gm) and is cold compacted in a substantial-
ly similar manner as in Example lOA to produce rods having a com-
position of about 94 percent by weight tungsten carbide (90 volume
percent) and about 6 percent cobalt (10 volume percent). The rods
are further hot pressed, in a substantially similar manner as in
Example lOA, to finished rods of about 0.5 inches (1.25 cm) dia
meter by about 2.5 inches long (6.35 cm). The ends of the rods
are machined -to fit into the grips of a standard pendulum impact
machine and are broken in impact. The resulting refractory body
- 37 -
has the properties given in Table II.
Comparative Example 15B
Rods of substantially identical composition and cold com-
pact geometry to those prepared in Example 15A are prepared by
liquid phase sintering, as practiced by those skilled in the art
and are similarly machined and impacted. The results are given in
Table II.
Comparatlve Example 15C
Rods of substantially identical composite and cold com-
pact geometry to those prepared in Example 15A are prepared and
densified by a short sinter cycle to about 90 percent theoretical
density and are then pressurized to full density. These rods are
also end machined and impacted as hereinabove described. The
results are given in Table II.
TABLE II
Example Impact Energy Hardness VHn
15A (Rods per the 2.33 GN/m 1680
Invention)
15B (Rods Liquid 1.16 GN/m2 1590
Phase Sintered)
15C (Rods Sintered then 1.22 GN/m 1670
Pressure Densified)
The rods prepared substantially in accordance with the
teaching of this invention (Example 15A) exhibit greater Impact
Energy and Hardness than the rods prepared by liquid phase sinter-
ing or the rods prepared by sintering and then pressure densifica-
' ' !; `~
~2~
- 3~
tion. Impact Energy equals the energy required to fracture a rigid-
ly supported sample by impacting with a pendulum.
~ scanning electron mlcroscope picture (backscatter image
at 4000 times magnification) of a sample of Example 15A is shown
in Figure 1 and a similar picture of Example 15B is shown in Fig-
ure 2. As may be seen in Figure 1 (Example 15A) the boundary
material (predominantly cobalt) is well distributed in the hot
pressed sample. The tungsten carbide phase, light in this photo-
graph, appears relatively rounded in shape and there are many small
lines on the photograph suggesting cobalt containing thin boun-
daries between tungsten carbide particles. In marked contrast, the
liquid phase sintered material in Figure 2 (Example 15s) is typical
of the microstructure seen in medium to coarse grained liquid
phase sintered of this composition. The tungsten carbide granules
are well defined, angular, blocky with a characteristic linear
edging between the light tungsten carbide and the dark shade of the
cobalt. In particular, if one notes in Figure 2 the nearly black
regions of the cobalt material, it can be seen that they often
assume triangular or trapezoidal shapes which seem to be in res-
ponse to the de~elopment of the highly facetted and crystallo-
graphic tungsten carbide grains. There is a tendency for samples
of the type described in Example 15C to be intermediate in
character between the cases shown here and it tends to be necessary
-to utilize analytical transmission microscopy to demonstrate that
such samples indeed partake of the character of the sintered
samples.
- 39 -
One can also superimpose on the Figures a grid of
straight lines and count the frequency of intersection of the lines
with material which can be identified as CO rich boundary phase,
and one finds that the frequency of such intersection is at least
twice as high for the hot pressed material Figure 1 (Example 15A)
as for the liquid phase sintered material Figure 2 (Example 15~).
The Example 15C case is intermediate and requires precision ana-
lytical transmission electron microscopy to characterize it.
Example 16A
An attrited blend of about 94 percent tungsten carbide
and about 6 percent cobalt is prepared substantially in accordance
with the procedure in Example 10A. Samples of the powder are cold
compacted into a disk configuration in a uniaxial press. The
disks are further hot pressed in a substantially similar manner as
in Example 10A to finished disks.
Comparative Example 16B
Additional disks of substantially identical composition
and cold compact geometry to those prepared in Example 16A are
prepared by liquid phase sintering as practiced by those skilled in
the art. The refractory body recovered has the properties listed
in Table III.
' Comparative Example 16C
Transverse rupture bars are machined from both sets of
disks as well as from one of the rods sintered and then pressure
densified in substantial accordance with Example 15A. The results
are compiled in Table III.
. .
- 40 -
Example 17
A cold compacted rod was prepared as in Example 14A and
was likewise hot pressed as in Example 14A except that the pressing
temperature was about 2150F (1176 C) instead of 2250F (1232 C).
The bar was prepared and impacted as in Example 14A, and the
impact energy was measured to be 760 ft lb/in2 (4.23 GN/m2). The
density was measured to be 13.6 g/cm3 (about 90 pexcent of theoret-
ical) and the ~ickers hardness number was found to be 1,100,
appreciably below the number of about 1,700 typical of fully dense
samples of this composition.
Example 18A
The process of Example lOA is substantially repeated us-
ing tungsten carbide (4472 g) and cobalt (68 g) to produce a com-
position of 98.5 weight percent tungsten carbide (97.4 volume
percent) and of 1.5 weight percent cobalt (2.6 volume percent).
The preform is heated to about 2250F (1232C) before exposing to
the isostatic pressure. The refractory body recovered has the
properties listed in Table III.
Comparative Example 18B
Rods of substantially similar compositions and cold
compact geometry to those prepared in Example 18A are prepared by
liquid phase sintering, as practiced by those skilled in the art
and are similarly evaluated. The results are listed for comparison
in Table III.
Example l9A
The process of Example lOA is substantially repeated
..h, ~ , -i
- 41 -
using tlmgsten carbide (4403 g) and cobalt (237 g) to produce a
composition of 97 weight percent tungsten carbide (98.8 volume per-
cent) and of 3 weight percent cobalt (5.2 volume percent). The
preform is heated to about 2250F (1232C) before exposing to the
isostatic pressure. The refractory body recovered has the proper-
ties listed in Table III.
C arative Example 19B
Rods of subs-tantially similar composition and cold com-
pact geometry to those prepared in Example l9A are prepared by
liquid phase sintering, as practiced by those skilled in the art
and are similarly evaluated. The results are listed for comparison
in Table III. A representative microscopy picture of this example
is shown in Figure 3. (Published in "American Society of Metals",
Metals Handbook, 9th ed., Vol. 3, p. 454, 1980.)
~xample 2OA
The process of Example lOA is substantially repeated us-
ing tungsten carbide (3814 g) and cobalt (726 g) to produce a
composition of 84 weight percent tungsten carbide (74.6 volume
percent) and of 16 weight percent cobalt (25.4 volume percent).
The preform is heated to about 2250F (1232C) before exposing to
the isostatic pressure. The refractory body recovered has the
properties listed in Table III.
Comparative Example 2OB
Rods of substantially similar composition and cold com-
pact geometry to those prepared in Example 2OA are prepared by
liquid phase sintering, as practiced by those skilled in the art
~,,
;
- 42 -
and are similarly evaluated. The results are listed for comparison
in Table III. A representative microscopy picture of this sample
is shown in Figure 4. (Publ'shed in "American Society of Metals",
Metals Handbook~ 9th ed., Vol. 3, p. 454, 1980.) The refractory
body recovered has the properties listed in Table III.
Example 21A
The process of Example lOA is substantially repeated
using titanium boride (4449 g) and nickel (91 g) -to produce a com-
position of 98 weight percent titanium diboride (99 volume percent)
and of 2 weight percent nickel (1 volume percent). The preform
is heated to about 2550F (1400C) before exposing to the isostatic
pressure. The refractory body recovered has the properties listed
in Table III.
Comparative Example 21B
Rods of substantially similar composition and cold com
pact geometry to those prepared in Example 21A are prepared by
liquid phase sintering, as practiced by those skilled in the art
and are similarly evaluated. The results are listed for comparison
in Table III.
Example 22A
The process of Example lOA is substantially repeated
using titanium carbide (3178 g) and molybdenum carbide (817 g) and
nickel (545 g) to produce a composition of 70 weight percent
titanium carbide (81.1 volume percent) and of 18 weight percent
molybdenum carbide (11.2 volume percent) and of 12 weight percent
nickel (7.7 volume percent)O The preform is hea-ted to about 2250 F
~2'~
- ~3 -
(1232C) before exposing to the isostatic pressure. The refractory
body recovered has the properties listed in Table III.
Comparative Example 22B
Rods of substantia]ly similar composition and cold com-
pact geometry to those prepared in Example 22A are prepared by
liquid phase sintering, as practiced by those skilled in the art
and are similarly evaluated. The results are listed for comparison
also in Table III. A representative microscopy picture of this
sample is shown in Figure 5. (Published in Science of Hard
Materials, ed. R. K. Viswandhou, D. J. Rowcliffe and J. Garland,
"Microstructures of Cemented Carbides", M. E. Exner, p. 245, 1983).
The refractory body recovered has the properties listed in Table
III.
Example 23A
The process of Example lOA is substantially repeated
using alumina (3178 g) and chromium (1362 g) to produce a composi-
tion of about 70 weight percent alumina (about 80.6 volume percent)
and about 30 weight percent chromium (about 19.4 volume percent).
The preform is heated to about 2876F (1580C) before exposing to
the i50static pressure. The refractory body recovered has the
properties listed in Table III.
Comparative Example 23B
,
Rods of substantially similar composition and cold com-
pact geometry to those prepared in Example 23A are prepared by
liquid phase sintering, as practiced by those skilled in the art
and are similarly evaluated. The results are listed for compari-
son in Table III.
~'Z~ B'~
- 44 -
Example 24A
The process of Example lOA is substantially repeated
using boron carbide (4813 g), molybdenum (204 g), nickel (14 g)
and iron (9 g) to produce a composition of about 95 weight percent
boron carbide (about 98.7 volume percent) and about 4.5 weight
percent molybdenum (about 1.15 volume percent) and about 0.3 weight
percent nickel (about .08 volume percent) and about 0.2 weight
percent iron (about .06 volume percent). The preform is heated to
about 2372F (1300C) before exposing to the isostatic pressure.
The refractory body recovered has the properties listed in Table
III.
Comparative Example 24B
Rods of substantially similar composition and cold
compact geometry to those prepared in Example 24A are prepared by
liquid phase sintering, as practiced by those skilled in the art
and are similarly evaluated. The results are listed for comparison
in Table III.
Example 25A
The process of Example lOA is substantially repeated
using zirconium nitride (4267 g), nickel (227 g) and molybdenum
(45 g) to produce a composition of about 94 weight percent zircon-
ium nitride (about 95.1 volume percent) and about 5 weight percent
nickel (about 4.1 volume percent) and about 1 weight percent
molybdenum (about 0.7 volume percent). The preform is heated to
about 2498F (1370C) before exposing to the isostatic pressure.
The re~ractory body recovered has the properties listed in Table
III.
j! `. `
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- 45 -
Comparative Ex mple 25B
Rods of substantially similar composition and cold com-
pact geometry to those prepared in Example 25A are prepared by
liquid phase sintering, as practiced by those skilled in the art
and are similarly evaluated. The results are listed for comparison
in Table III.
xample 26A
The process of Example lOA iS substantially repeated
using lanthanum chromate (4403 g) and chromium (136 g) to produce
a composition of about 97 weight percent lanthanum chromate (about
97.5 volume percent) and about 3 weight percent chromium (about
2.5 volume percent). The preform ls heated -to about 2876F (1580 C)
before exposing to the isostatic pressure. The refractory body
recovered has the proper-ties listed in Table III.
Comparative Example 26B
Rods of substantially similar composition and cold com-
pact geometry to those prepared in Example 26A are prepared by
liquid phase sintering, as practiced by those skilled in the art
and are similarly evaluated. The results are listed for comparison
~0 in Table III.
Example ;.27A
The process of Example lOA is substantially repeated us-
ing silicon nitride (4313 g) and aluminum (227 g) to produce a
composition of about 95 weight percent silicon nitride (about 94.2
volume percent) and about 5 weight percent aluminum (about 5.8
volume percent). The preform is heated to about 1220 F (660 C)
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- 46 -
before exposing to the isostatic pressure. The refractory body
recovered has the properties listed in Table III.
Comparative Example 27B
Rods of substantially similar composition and cold com-
pact geometry to those prepared in Example 27A are prepared by
liquid phase sintering, as practiced by those s~illed in the art
and are similarly evalua-ted. The results are listed for comparison
in Table III.
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