Note: Descriptions are shown in the official language in which they were submitted.
WOg2~1~70 7 1 o ~ PCT/US92J01928
MET~ODS FOR ALLOYING A METAL-CONTAINING MATERIAL INTO A
DENSIFIED CERAMIC OR CERMET BODY AND ALLOYED BODIES
PRODUCED THEREBY
This in~e~tion relates to processes for
alloying metal, or an inorganic compound containing such
a metal, into a ceramic or ceramic-metal (cermet) body
that has a de~sity greater than or equal to 95% of the
body's theoretical de~sity.
It is well known that metal alloys often have
more desirable propertiec than pure metals. It would
follow that alloyed cermets and ceramics may have more
desirable properties than non-alloyed cermets and
ceramics. It would thereore be desirable to have
methods ~or making such alloyed cermets and ceramics. -
It would also be desirable to be able to alter the
properties of a ceramic or cermet body by alloying
without significa~tly changing the shape or density of
the body. It would further be desirable to be able to
make a cermet or ceramic body tha~ has different
properties such as improved oxidative resistance or wear
,' resistance at separate locations on the body.
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One aspect of the presen~ invention is a
process for alloying a ~etal or a metal-containing
material into a densified cermet body comprising:
(a) placing an alloying metal or an inorganic
compount containing an alloying metal in contact with at
least a portion of an exterior surface of a cermet body
that has a densi~y of at least 95% of the theoretical
full density and is formed of a ceramic that has a
~atrix metal di persed therein, the matrix ~etal
0 extending fro~ the exterior surface portion at least
partially into the cermet body; and
(b) heating ~he cermet body, while it is in
contact with the alloying metal or the inorganic
1~ compound containing the alloying metal~ to a temperature
that is greater than or equal to 50C belo~ the lesser
of the ~atrix metal's melting point and the temperature
at which the matrix metal and the alloying metal form an
eutectic, to diffuse the alloying metal into the cermet
body and form an alloy between the alloying metal and
the matrix metal.
A second aspect of the invention includes a
method for alloying a metal or a metal-containing
material into a densified ceramic body comprising:
(a) placing an alloying metal or an inorganic
compound containing an alloying metal in contact with at
least a portion of an exterior surface of a ceramic body
that has a density of at least 95% of the theoretical
full density and is formed of a glassy-phase component ~,
and a non-glassy-phase component, the glassy-phase
component extending from the exterior surface portion at
least partially into the ceramic body; and
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WO 92~T6670 2 1 a ~ 2 X ~ PCT/US92/01928
(b) heating the ceramic body to a temperature
~t least nea~ that at which the glassy-phase component
softens while the alloying me~al or the inorganic
compound containing an alloying metal is in contact with
the ceramic body to diffuse the alloying metal into the
ceramic body and form an alloy between the alloyi~g
metal and the glassy-phase component.
Bodies prepared by the methods described
immediately above are also disclosed.
The first aspect of the invention concerns a
method for alloying a metal, or a material containlng a
metal, into a densified cermet body. The term 'Imetal-
-containing maeerial" collectivel~ refers to alloying
metals and inorganic compounds co~taining an alloying
metal. The metal-containing material is ~uitably
selected fro~ pure metals, alloys of two or more metals,
and inorganic compounds containing at lea~t one metal.
A "metal" is an element from the Periodic Table of the
Elements that forms positive ions when its compounds are
in solution and whose oxides form hydroxides rather than
acids with water. De~irable metals include nickel,
chromium, copper, vanadium, titanium, silicon,
magnesium, hafnium, tungsten, molybdenum, manganese,
iron, copper or tantalum. Satisfactory inorganic
compounds relea~e or give up metal under conditions of
the present invention to form a metal alloy with the
matrix metal of the cermet. Inorganic compounds that
3 are stable, in that they do not release metal to form an
alloy under conditions of the present invention, are not
suitable. Illustrative inorganic compounds include
nitrides, oxides, carbides, borides or silicides of the
WO92/l~70 PCT/US~2/0192B
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metals. Carbides, nitrides and oxides are preferred
inorganic compound~.
The metal component of the metal-containing -;
material is preferably different from the matrix metal
of the cermet body~ The metal-containing material may
be either solid or molten when it is initially placed in
contact with the cermet body. When the metal-containing
material is solid, it may be in any form including
powder or foil. When the metal-containi~g material is
in the form of a foil, the foil is desirably less than
0.75 mm thick, more desirably~ less than 0.5 mm thick,
and, preferably, less than 0.1 mm thick.
Examples of cermet/alloying metal combinations
suitable for this invention include those provided in
Table 1.
Table 1
Cermet Possible AlloYinq Metals
B4C/Al Ni, Cr, Cu, V, Ti, Si, Mg, ~f, W
SiC/Al Ni, Cr, Cu, Mn, V, Ti, Mg, Si, Hf, W
Tis2/Al Ni, Cr, Cu, Mn, Ti
TiB2/Cu Al, Ti, Si, Ta, Fe, Co
Si3N4/Al Cr, Mn, Ti
Si3N4/Ni Ti, Fe, Co, Mn
SiB6/Al Ni, Cr, Cu, Mn, Tl, Si
The cermet body, prior to contact with the
metal-contai?ning material, has a ceramic component and a
matrix metal component. The cermet body desirably
cont~ins from 15 to 99 weight percent ceramic component ?
and from 85 to 1 weight percent matrix metal component.
The cermet body preferably contains from 60 to 80 weight
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WO92/1~70 ~1 a i 2 .~ ~ PCT/U~92/0i928
percent ceramic component and from 40 to 20 weight
percent matrix metal component. The weight percen~ages
total lO0 percent. The ceramic component is desirably
boron carbide, silicon carbide, titanium boride,
alumina, or silicon nitride. The matrix me~al component
is desirably aluminumt titanium, copper or nickel. In
order for the metal-containing material to d;ffuse into
the cermet body, two conditions must exist. First, the
matrix metal must be in physical contact with the metal-
-containing material at least at an exterior surface
portion of the cermet body. Second, the matrix metal
must extend at least partially i~to the cermet body from
that surface portion. The matrix ~etal may be
continuous throughout the bulk of the cermet body with
the ceramic being the discontinuous phase.
The non-alloyed cermet body may be prepared by
any conventional method. For example, the cer~et body
may be prepared by densifying a mixture of ceramic and
matrix metal powders into a desired shape. The
densification may be accomplished by conventional
processes such as cold pressing or slip casting. If
desired, these processes may be follo~ed by sintering to
further densify the cermet body.
Another method of preparing a non-alloyed
cermet body includes a first step of forming a porous
ceramic body. Conventional procedures, such as slip
casting a ceramic dispers~on or cold pressing ceramic
pcwder, produce porous bodies with a desired shape.
Molten matrix metal is then placed in contact ~ith the
porous ceramic body. The molten metal infiltrates into
the porous ceramic body by capillary actisn. Such
WO92~l~7~ PCT/US92/0!928
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methods are di~closed in U.S. Patent Nos. 4,702,770,
4,718,941, and 4,834,938.
U.S~-A 4,702,770 describes, at column 6, lines
5-25, a four ~tep method for producing low density boron
carbide-aluminum ~omposites. The first three ~teps
yield a satisfactory cermet body. In step one, a
colloidal consolidation technique is u~ed to form a
porous boron carbide compact from a homogeneous
dispersion of boron carbide. In step two, the compact
in enriched with carbon by heat treating or sintering
the boron carbide in the pre~ence of graphite. In step
three, aluminum is infiltrated into the enriched
compact.
U.S.-A 4,718,941 discloses the infiltration of
molten reactive metals into chemically pretreated boron
carbide, boron or boride starting material~. The
chemical pretreatment procedure is described in detail
at column 7, line 8 through column 8, line 12. The
starting materials are immersed in a chemical substance
that reacts with B203, BH303, or both, for as long as
necessary to change the surface chemistry by forming
boron-carbon-hydrogen-oxygen complexes that pyrolyze
upon heating, either prior to, or during, infiltration.
Suitable chemical substances include various alcohols,
such as methanol, isopropyl alcohol and denatured
ethanol.
U.S.-A 4~834,938 outlines a process for making
a composite article having an internal surface or
cavity. A porous compact is formed about an insert body
that has an external surface corresponding to the
internal surface of the composite. The article is
heated to the wetting temperature of the insert body to
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wos2/l667o PCT/US92/0192~
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melt the insert and cause it to infiltrate into the
porous compact.
The non-alloyed cermet body required for
purposes of the present invention has a density o at
least 95% of theoretical density. The density is more
preferably at least 99% of theoretical de~sity.
Alloying, or the diffu~ion of an alloying metal
into a matrix metal, is desirably initiated by heating
the cermet body to a temperature greater than or equal
to that at which the matrix metal melt~. If an eutectic
alloy is formed between the matrix metal and the
alloying metal, the eutectic alloy typically ha~ a
melting point lower than that of the matrix metal. If
an eutectic alloy i9 formed, the temperature may be
decreased to equal or exceed the melting point of the
eutectic alloy. If no eutectic alloy is formed, the
temperature is preferably maintained at or above the
melting temperaturc of the matrix metal until alloying
reaches a desired level.
Temperature plays an important role in
determining the rate at which alloys between the matrix
metal and the alloying metal form. Diffusion occurs so
slowly at room temperature that it is not readily
detected over a period of several days. As the
temperature approaches the melting temperature of the
matrix metal, diffusion becomes more discernible. At
the melting temperature, diffusion is rapid enough to
yield a readily detectable amount of alloy. At
temperatures in excess of the melting temperature,
diffusion occurs very rapidly. The temperature must
not, however, be 30 high that the ceramic portion of the
cermet begin~ to decompose or dissociate. The term "at
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W092/1~70 PC~/~JS92/01928
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least near" means greater than or equal to a temperature
that is 50C below the melting temperature of the matrix
metal. The temperature preferably equals or exceed~ the
melting temperature of the matrix metal, but is less
than the di~sociation temperature of the ceramic portion
5 of the cermet.
During the alloying process, the metal-
-containing material ~ay or may not become molten,
depending on its melting po;nt. A satisfactory degree
0 of alloying is attainable if only the matrix metal
becomes liquefied. When foils are used and the metal-
-containing material is to become molten during the
alloying process, thin foils are preferred as they melt
15 faster and result in more uniform diffusion across the
contacted susface of the cermet body. The matrix metal
preferably has a melting point that is less than or
equal to the melting point of the metal-containing
material.
The second aspect of the invention is a method
for alloying a metal-containing material into a
densified ceramic body. The ceramic body contains a
glassy-phase compone~t and a ~on-glassy-phase component.
25 The ceramic body desirably contains from 70 to 99 weight
percent of non-glassy phase and from 30 to 1 weight ?
percent glassy phase. The ceramic body preferably
contains from 85 to 97 weight percent non-glassy phase
and from 15 to 3 weight percent glassy phase.
The non-glassy-phase component of the ceramic
body is desirably silicon nitride. The glassy-phase
component of the ceramic body is desirably formed of a
metallic oxide such as yttria, magnesia, alumina,
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Wo92JI~7~ 2 i ~ i, PC~ S~2tO192
silisa, zirco~ia, tantalum oxide, calcium oxide or a
mixture of two or more o such oxides.
In order for the metal-containing material to
diffuse into the ceramic body, t~o conditions must be
met. First, the glassy-phase component must be in
physical contact with the ~etal-containing material at
least at an exterior surface portion of the ceramic
body. Second, the glassy-phase component must extend at
least partially into the ceramic body from that surface
portion. The glassy-phase component may be continuous
throughout the bulk of the ceramic body while the non-
-glassy phase component may be discontinuous throughout
the remainder of the bulk of the ceramic body.
The ceramic body may be prepared by densifying
a mixture of powders that will constitute the ~lassy-
phase and non-glassy-phase components. For instance,
silicon nitride, yttria, magnesia, and zirconia powders
may be densified into a desired shape by cold pressing,
or slip casting, the powders into a body and then
sintering the body. The ceramic bodies desirably have a
density of at least 95% of theoretical density. The
density is preferably at least 98Z of theoretical
density.
Metal-containing materiaLs suitable for
purposes of the second aspect of the present invention,
like those of the first aspect~ are metals, inorganic
compounds containing a ~etal or having a metallic
constituent, a metal alloy, or a metal o~ide. Metal
oxides are commonly available me~al-con~aining
materials. The metal or metallic constituent is
suitably yttrium, magnesium, chromium, zirconium,
molybdenum, vanadium, titanium or a rare earth metal
WO 92/16670 PCr/US92/01928
(elements 57-71 of the Periodic Table). The ~etal or
metallic constituent must differ from that contained in
the glassy-phase component if alloying is to occur.
The metal-containing material may be solid or
liquid when it is initially placed in contact with the
ceramic bodyO As in the first aspect, it may be in the
form of a powder or a foil when it is a solid. As the
ceramic body is heated to soften the glassy-phase
component, the metal-containing material may retain its
0 initial form or be converted to a liquidO
If d2sired, two or more differ~nt metal-
-containing materials may be placed in contact with
exterior surface portions of either the cer~et of ~he
first aspect of the invention or the ceramic of the
seco~d aspect. If, for example, two different materials
are placed in contact with exterior surface portions of
a cermet or ceramic body, they are preferably not
applied to the same surface portion.
During the heating step of the invention, the
metal-containing material gradually diffuses into the
cermet or ceramic body from the exterior surface portion
2~ in contact with said material. Before alloying i~
complete, alloying occurs in a gradient manner. The
term "gradie~t manner" means that alloying occurs to a
greater exten~ at or near the exterior surface portion
and to a progressively lesser extent as distance from
that portion increases as one travels in a direction
perpendicular to the surface portion into the ceramic or
cermet body~ Alloying may change only the chemistry of
the matrix metal or glassy-phase component. It may also
change the chemistry of the ceramic or non-glassy phase
component thereby forming new phases. The alloying
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WO 92/16670 2 1 () ~ PC~/lJS92/01928
process may be conti~ued uutil the body is substantially
free of chemical composition gradients. M~re typically,
alloying is terminated while gradients are still
present. Termination occurs by conventional means, such
as cooling the cermet body or the ceramic body to a
temperature ~ell below the respective matrix metal
liquidus temperature or the glassy-phase component
softening temperature.
After termination of alloying, any excess
0 metal-containing material on the surface of the cermet
or the ceramic body may be removed by conventional
processes. These processes include peeling or grinding.
The alloyed bodies of this iuvention are
especially useful for making abrasion-resistant parts,
such as cutting tools and drilling tools, and wear
parts, such as automobile brakes.
The following examples are illustrative only
and should not be construed as limiting the invention
which is properly delineated in the appended claims.
Example _l
A block-shaped porous body of boron carbide,
measuring about 1 cm thick, was prepared by slip casting
a dispersion of boron carbide powder. The slip-cast
body had a de~sity of about 64% of the theoretical
density of boron carbide. The porous body was
3 impregnated with aluminum by contacting the boron
carbide body with aluminum and heated to 1180C to form
a cermet body. At that temperature, sintering was
effected and the cermet body comprised about 64 weight %
boron carbide, about 25 weight % aluminum and about 11
weight % reaction products containing aluminum. The
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WO92/16670 PCT/US92/0l928
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body had a den~ity of greater than 99% of the
theoretical density. Table 2 shows typical reaction
products.
Copper foil measuring about 0.75 mm thick was
placed on one side of the cermet body, while a foil of
nickel measuring about 0.75 mm thick was placed on the
opposite side. The ~espective melting points of the
matrix metal (aluminum), the copper, and the nickel are
660C, 1085C, and 1445C. The cermet body and the
0 associated copper and nickel foils were placed in a
graphite crucible. The crucible ~as placed in an oven
with a flo~ing argon atmosphere. The temperature of the
oven was increased from room temperature to 1100 in
about two hours and held at 1100C for one hour. The
cermet body was then removed from the furnace and
allowed to cool naturally to ambient temperature.
Cooling occurred over a period of about 1 1/2 hours.
Chemical analysis of the alloyed cermet body
was completed using an MBX-CAMECA microprobe~ available
from Cameca Co., France. The results are provided in
Table 2 which shows the volume percent amounts of the
various phases listed on the side of the table at three
locations in the alloyed cermet body~ The first
location was in copper side, the second location was in
the bulk of the boron carbide cermet body, and the third
location was in the nickel side.
The results summarized in Table 2 demonstrate
that diffusion of the metal-containing materials
occurred. The nickel co~ponent ranged from a high of 20
volume percent at the "nickel end" through an
intermediate value of 12 volume percent in the middle of
the cermet body to a low of not being detectable in the
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wos2/t~70 2 1 9 ~ 2 ~ ~ PCT/US~2/01928
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"copper end". The copper component (CuAl2) sho~ed a
similar gradient. Furthermore, the boron carbide volume
percent remained fairly consistent throughout the cermet
body.
Table 2
Vol 96
Vol% of of phase in Vol ~ of
phase in Middle of phase in
Phase CoPPer end cermet body Niokel end
o (NiCu)2Al3 nda 12 20
Al with about lO l5 20
2 wt% Cu
CuAl2 with 20 8 nda
about 0~4 wt%
AlE324C4 10 9 9
s4c 58 54 49
Al4BC <lb cl <l
Al4C3
a = not detected
b = present, but in an amount less than l vol
Example 2
A boron carbide-aluminum cermet body was
prepared by the method described in Example l. A copper
foil, measuring about l mm thick, was placed on ~he
cermet body. The cermet body was then heated to l100C,
and the te~perature was maintained for l hour. After
cooling the cermet body, the copper foil was removed.
It was fou~d that the copper content of the foil was
reduced by 3.5 wt%.
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Example 3
This example illustrates the use of a powder
form of a metal-containing material. A densified
ceramic body having a composition of 86.3 wtX Si3N4, 8.5
wt% Y203, 4.7 wt% MgO and 0.5 wt.% GaO was prepared by
hot-pressing a mixture of the Si3N4 and oxide powders at
1825C for 1 hour. The ceramic body had a density of
about 99.5% of the maximum theoretically possible
density. The ceramic body was buried in a HfO2 powder
0 bed in a quartz container. The ceramic body and HfO2
bed were heated to 1400C and held at this temperature
for 1 hour while in a flowing nitrogen atmosphere~ The
ceramic body a~d the HfO2 bed were then allowed to cool.
After cooling, the ceramic body was separated from the
HfO2 po~der, sectioned, and analyzed. 0~ the surface of
the ceramic body, an alloyed layer rich in HfO2
measuring approximately 50 micrometers deep was
observed. The diffusion of HfO2 altered the ceramic
body's composition, but did not alter the chemistry or
shape of the Si3N4 grains. Analysis indicated that the
alloyed layer contained Si3N4 grains in two glassy
phases: a phase relatively high in Mg, relatively low
in Y, and having no Hf; and a phase havi~g a relatively
intermediate levels of Mg and Y and a relatively high
level of Hf.
Example 4
A densified ceramic body was prepared as in
Example 3 and placed in a bed of Cr203 powder. After
heating the ceramic body and Cr203 powder to 1400C,
maintaining this temperature for 1 hour, then cooling,
three alloyed layers near the surface of the ceramic
body were observed. The first, or outside layer,
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WO92/16670 2 ~ PC~/USg2tO1928
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consisted of Cr3Si, Cr2N, a relatively high level of
yttria silicate crystals, and a mixture of two glassy
phases. The glassy phases were: a phase having Y and
Mg in a weight ratio of about 1:1; and a phase
contai~ing a relatively low level of Y, and relatively
high levels of Mg and Ca. The second, or middle layer,
consisted of Si3N4, Cr3Si and a relatively low level of
CaO glass. The third, or innermost, layer consisted of
Si3N4 and glass containing a relatively intermediate
amount of Y, a relatively intermediate amount of Mg, and
no Ca. The weight ratio of Y to Mg in this inner~ost
layer was about 0.6:1. The total thickness of all three
layers was about 200 micrometers. This example
illustrates that eve~ though diffusion occurred through
the glassy phase, the majority of the Cr formed new
cry5talli~e phases and the gla.q~ chemistry remained
uncha~ged. Therefore, the properties of the Si3N4 body
were changed without cha~ging the che~istry of the
glassy phase.
The examples show that the processes of the
present invention produce alloyed cermet or ceramic
bodies. So~e of the resultant bodies optionally have
chemical composition gradients. The main ad~antage is
that the processes can alter the chemistry of a cermet
or ceramic body without significantly altering the
density or shape of the original body.
While our invention has been described in terms
of a few specific embodiments, it will be appreciated
that other embodiments could readily be adapted by one
skilled in the art. Accordingly, the scope of our
invention is to be considered limited only by the
foLlowing claims.
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