EP0190346A4

EP0190346A4 - Novel composite ceramics with improved toughness.

Info

Publication number: EP0190346A4
Application number: EP19850905137
Authority: EP
Inventors: Patrick M Russell; Virgil B Kurfman; Robert R Mcdonald
Original assignee: Dow Chemical Co
Current assignee: Dow Chemical Co
Priority date: 1984-08-08
Filing date: 1985-08-05
Publication date: 1987-01-22
Also published as: JPS61502901A; WO1986001196A1; EP0190346A1; CA1244482A; BR8506869A

Abstract

A high density refractory body composite ceramic comprising a densified refractory body, possessing about 10 percent greater toughness than exhibited by other composite ceramics of similar composition and geometry, of a refractory material selected from the group consisting of oxides, carbides, nitrides, silicides, borides, sulfides and mixtures thereof, and a binder material capable of plastic deformation in a sufficient amount to at least partially fill the interstices between the particles of the refractory material and a method for producing said high density refractory body composite ceramics.

Description

NOVEL COMPOSITE CERAMICS WITH IMPROVED TOUGHNESS

Background of the Invention

This invention relates to novel refractory body composite ceramics wherein the composite ceramics have improved toughness and to a method 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 chemical 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 container and after hot pressing the sample often adheres to the mold or container during separation.

Isostatic pressing of self-sustaining compacts has been suggested as a possible method of overcoming the above-mentioned problems. For example,

Ballard and Hendrix, US 3,279,917, 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-transmitting 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 intricate contours by this method.

Barbaras, US 3,455,682, discloses an improved method of isostatically hot pressing refractory 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 component selected from alkali and alkaline earth metal chlorides, fluorides and silicates and mixtures thereof and from 60 to 95 percent by weight of a second component selected from silica, alumina, zirconia, magnesia, calcium oxide, spinels, mullite, anhydrous aluminosilicates 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 high density without substantially altering their original shape.

Rozmus, US 4,428,906, discloses a method for consolidating material of metallic and nonmetallic compositions and combinations thereof to form a densified compact of a predetermined density wherein a quantity of such material which is less dense than the predetermined density, is encapsulated in a pressure-transmitting medium to which external pressure is applied to the entire exterior of the medium to cause the predetermined densification of the encapsulated material by hydrostatic pressure applied by the medium in response to the medium being substantially fully dense and incompressible 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 supported by and retained within the skeleton structure for forming a composite of skeleton structure fragments dispersed in the fluidizing means in response to collapse of the skeleton structure at the predetermined force and for rendering the composite substantially fully dense and incompressible and fluidic at the predetermined densification of the compact.

It is taught 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; however, the medium must retain its configuration during and after being heated so it may be handled for placement in the press without 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 resistance 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 that composite ceramics, such as those prepared from tungsten carbide and cobalt, are prepared by contacting the refractory material, such as tungsten carbide, with a metal, 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 during reprecipitation. This agglomeration results in the preparation of a composite ceramic which is quite brittle. In general, the composite ceramics prepared by such methods as described hereinbefore are extremely hard, but unfortunately quite brittle (i.e. not tough). This brittleness results in compositions which are sensitive to crack initiation and propagation and have very low impact strength. What are needed are composite ceramics which have the desired property of toughness without sacrificing hardness.

Summary of the Invention The invention is a high density refractory body composite ceramic comprising a densified refractory body possessing about 10 percent greater toughness than exhibited by other composite ceramics of similar composition, of a refractory material selected form the group consisting of oxides, carbides, nitrides, suicides, borides, sulfides, and mixtures thereof and a binder material capable of plastic deformation present in an amount sufficient to at least partially fill the interstices between the refractory material particles.

Another aspect of this invention is a high density composite ceramic comprising

(a) at least one phase of a refractory material selected from the group consisting of oxides, carbides, nitrides, suicides, borides, sulfides, and mixtures thereof;

(b) at least one phase of a binder material capable of plastic deformation; and

(c) at least one phase in which the binder material atoms are substituted on the lattice of the refractory material; wherein the binder material and component (c) are present in sufficient amount to at least partially fill the interstices between the refractory material particles.

Another aspect of this invention is a process for the preparation of said high density refractory body composite ceramics comprising contacting a refractory material selected from the group consisting of oxides, carbides, nitrides, borides, suicides and sulfides, present in a sufficient amount to at least partially fill the interstices between the particles of the refractory material particles and a binder material capable of plastic deformation, present in a sufficient amount to at least partially fill the interstices between the particle of the refractory material particle, at a temperature less than the liquidus temperature of the binder material; under pressure, between about 10,000 psi (pounds/in ²)¬

(6.89 x 10¹ MPa) and about the fracture point of the refractory body, for a period of time of between that time sufficient for the composite ceramic to reach 85 percent of its theoretical density and less than that time sufficient for sintering to occur, under conditions such that a high density refractory body is prepared with a density of 85 percent or greater and possessing 10 percent greater toughness than exhibited by other composite ceramics of similar compositions.

The high density composite ceramic of this invention exhibits greater toughness without sacrificing hardness than exhibited by other composite ceramics of similar compositions and geometries. Furthermore, the process of this invention involves shorter formation times at less severe conditions than the heretofore known processes. Detailed Description of the Invention

This invention generally relates to high density refractory body composite ceramics which are refractory ceramic materials bound with binder materials, wherein the fractory body composite 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 characteristics is useful in this invention. Preferred refractory ceramic materials include refractory oxides, refractory carbides, refractory nitrides, refractory suicides, refractory borides, refractory sulfides or mixtures thereof. More preferred refractory ceramic materials include refractory alumina, zirconia, magnesia, mullite, zircon, thoria, beryllia, urania, spinels, tungsten carbide, tantalum carbide, titanium carbide, niobium carbide, zirconium carbide, boron carbide, hafnium carbide, silicon carbide, niobium boron carbide, aluminum nitride, titanium nitride, zirconium nitride, tantalum nitride, hafnium nitride, niobium nitride, 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, zirconium 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, niobium 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 materials 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 or mixtures thereof. The most preferred binder material is cobalt.

In general, the binder material is present in sufficient amount to at least partially fill the 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 between about 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 material. 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.

This invention may further involve a novel composite ceramic composition which comprises at least three phases:

(a) at least one phase of a refractory material selected from the group consisting of oxides, carbides, suicides, borides, nitrides and sulfides;

(b) at least one phase of binder material as defined hereinbefore; and (c) at least one phase comprising a compound which corresponds to the formula X_a-bY_bZ_c wherein

X is the metal derived from the refractory material selected from the group consisting of oxides, carbides, nitrides, suicides, borides and 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 integer 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 substituted 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 significantly enhanced toughness of the ceramic composites. In the above formula, b is preferably between about 0.001 and about 0.1. This three-phase ceramic composite preferably comprises between about 50 and about 99 percent by volume of the refractory ceramic material; between about 1 and about 50 percent by volume of the binder material, and between about 0 and about 0.2 percent by volume of the compound corresponding to the formula X_a-bY_bZ_c, wherein X, Y, Z, a, b and c are as hereinbefore defined. More preferably, the composite ceramics of this invention comprise between about 70 and about 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 X_a-bY_bZ_c . 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 X_a-bY_bZ_c. X is Preferably aluminum, zirconium, magnesium, thorium, beryllium, uranium, tungsten, tantalum, titanium, niobium, boron, hafnium, silicon, chromium, molybdenum, cerium, cadmium or zinc. X is more preferably tungsten, niobium, titanium, silicon, tantalum, boron or aluminum. 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, zirconium, boron, vanadium, silicon or palladium. More preferably, 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 standard sample. Toughness as herein used can be quantified by a toughness index which is substantially the same as used by Marin in "Strength of Materials", page 16, said toughness index equals the area below the stress strain curve and is determined by the equation:

Toughness Index = [(Stress to Fracture) x (Strain to Fracture

2

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 equals the ordinate divided by the abscissa, the toughness index is also equal to:

(Stress to Fracture)²

2 Modulus

in the elastic region. The standardized and convenient transverse rupture strength value may be substituted for the stress to fracture term. In addition to exhibiting greater toughness, the composite ceramics of this invention generally exhibit at least equal hardness as compared to other composite ceramics of similar compositions and geometries. Since most of the materials of interest in this invention are intended for applications using high hardness (and usually correspondingly limited ductility), 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 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. 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 ceramics 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 whereby the binder material and refractory ceramic materials are combined while in a 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 refractory ceramic material are contacted in the powder form in a container capable of performing as a pressure-transmitting medium at temperatures high enough for the 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 material is not fully densified. In general, it is preferable that the metal powders and ceramic powders have a particle size of about 10 microns or less, more preferably about 5 microns or less; still more preferably of about 2 microns or less and most preferably about 1 micron or less. The description of preferred particle sizes is given for a substantially mono-modal particle size distribution. It will be recognized by those skilled in the art that small quantities of particulate of considerably smaller size than the size of the main proportion of particulate may be intermixed therewith to achieve a higher packing density for a given degree of consolidation.

Bound composite ceramics refers herein to 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 surprisingly improved 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. Isostatic pressure refers herein to pressure which is applied evenly 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 temperature, 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., completely liquid). The solidus temperature is that temperature at which plastic deformation occurs in the mixed phase system without the application of pressure (i.e., first begins to melt). The solidus temperature may be presumed to have been exceeded if plastic 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 Applicants that the densification of binder material and refractory ceramic materials at temperatures at which the binder material is substantially in a liquid state generally results in refractory bodies with a much lower toughness than those formed wherein the binder material is in a solid state. Preferably the temperature is greater than that at which a pressure of about 100,000 psi (6.89 x 10 ² MPa) will achieve 85 percent of theoretical density within one hour. Broadly, the temperatures useful in this invention are between 400°C 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 800°C and 1500°C; more preferably between about 1000°C and about 1350°C; for nickel, between about 850°C and 1455°C; .for chromium, between about 720°C and 1865°C; for a chromium-nickel alloy, between about 700°C and 1345°C; for niobium, between about 800°C and 2475°C; for silicon, between about 1275°C and 1415°C; for boron, between 1800°C and 2105°C; for tantalum, between about 1050°C and 2850°C; for a tantalum-niobium alloy, between about 900°C and 2550°C; for a cobalt-molybdenum alloy, between about 1015°C and 1335°C; for a niobium-tantalum-titanium alloy, between about 400°C and 1650°C; and for vanadium, between about 700°C and 1855°C.

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. Preferably, the pressure is between about 10,000 psi (6.89 x 10¹ MPa) and the fracture point of the refractory body composite ceramic. More preferably, said pressure is between about 50,000 psi

(3.45 x 10² MPa) and the fracture point of the refractory body composite ceramic; still more preferably between about 70,000 psi (4.82 x 10² MPa) and said fracture; 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 densification in less than one minute and even more preferably in less than ten seconds. A rate of pressure increase greater than about 1,000 psi/sec (6.89 x 10¹ 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 refractory 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 refractory body to the desired density. The time which the refractory body is exposed to the desired pressure is between that time sufficient for the ceramic composite to reach 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 ten minutes; still more preferred is less than one minute; and the most preferred is less than ten seconds. It should be recognized that there are practical considerations 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 produced without resorting to expensive modifications of the composite ceramics composition.

Isostatic pressure may be applied to the powdered binder material and ceramic refractory material, or the prepressed powdered 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 critical 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, US 4,428,906 (relevant portions incorporated herein by reference). The process described therein involves first placing the powder of the binder material and the ceramic material in the proportion desired in a container which is capable of performing as a pressure-transmitting 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 conditions.

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 predetermined 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 framework, 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 transmitting medium may be formed by mixing a slurry of structural material in wetting fluid or activator with particles or 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 temperature 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 skeleton structure at the compaction temperature to which the powder has been heated for densification. However, the skeleton structure retains its 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 temperature 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 external 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 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 isostatic pressure is disclosed by Rozmus US reissue 31,355 (relevant portions incorporated herein by reference). This patent discloses a container for hot consolidating powder which is made of substantially fully dense and incompressible 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 material and refractory ceramic material would be densified.

Generally, two pieces of the material which would be used to make the container are machined to prepare a mold 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 configuration. The size and shape of the cavity is determined in view of the final shape of the part to be produced. Before the upper and lower die sections are assembled, a hole is drilled in one of the die 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. Thereafter, the container is evacuated and filled with the powder to be densified through the fill tube. The fill tube is then hermetically sealed by pinching it closed and welding it.

Thereafter, the container is exposed to isostatic pressure at the desired binding and densification temperatures. This can be done by the methods described hereinbefore. 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 densification. 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 powders 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, the container can be removed by machining 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, US 4,341,557 (relevant portions incorporated herein by reference). In the practice of the invention, the container is prepared as described in US reissue 31,355 described hereinbefore and the isostatic pressure can be exerted on such container as described hereinbefore. The container, 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 recycled to form a new container.

Barbaras, US 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 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 densified 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 temperature at which the densification is to take place and its contents are allowed to equilibrate to this temperature. Thereafter, the desired pressure for densification 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 utilizing 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.

Another method of exposing the refractory ceramic material and binding material to isostatic pressure is described in Havel, US reissue 28,301 (relevant portions incorporated herein by reference); Rozmus, US 4,142,888

(relevant portions incorporated herein by reference); Rozmus, US 4,094,709 (relevant portions incorporated herein by reference); Rozmus, US 4,255,103 (relevant portions incorporated herein by reference); Bobrowski, US 3,230,286 (relevant portions incorporated herein by reference); Smythe et al., US 3,824,097 (relevant portions incorporated herein by reference); Loersch et al., US 4,023,466 (relevant portions incorporated herein by reference); Kirkpatrick, US 3,650,646 (relevant portions incorporated herein by reference); Hamjion, US 3,841,870 (relevant portions incorporated herein by reference); Lange et al., US 4,041,123 (relevant portions incorporated herein by reference); Larson, US 4,077,109 (relevant portions incorporated herein by reference); Adlerborn, US 4,081,272 (relevant portions incorporated herein by reference); and Isaksson et al., US 4,339,271 (relevant portions incorporated herein by reference).

In practice, the prepressed binder material and refractory 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 (6.89 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 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 increased 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 about 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 sintering operation. It is believed that there is less agglomeration of the refractory materials and a product which has a greater toughness at a desired hardness.

Said composite ceramics preferably possess 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 percent 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 transverse rupture strength at about equivalent hardness of other composite 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 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 resolution 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 composite ceramics of this invention generally have more nearly rounded or elipsoidal-shaped grains (or grain clusters characterized by more nearly rounded protruber ances). Other composite ceramics generally exhibit grains having a more angular shape (i.e., more polyhedral in form) and the binder phase tends to collected in angular-shaped pockets where two or three of these angular-shaped grains connect or impinge on one another.

Microscopy methods generally depend on examination of planar sections cut thorugh a sample. The composite ceramics of this invention will appear to be roughly circular or elipsoidal; whereas, 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 composite 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 grained material. In addition, if there is a greater disperson 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 to other composite ceramics of similar composition. The percentage increase in binder distribution for the composite ceramics of this invention is preferably about 10 percent greater than for other composite ceramics of similar composition. More preferably, the binder distribution is about 50 percent greater than other composite ceramics of similar composition and most preferably is 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., time) and relatively low temperature. Images of different magnificaτ:ion 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 circularity number which is equal to 4π or about 12.6. A regular octagon may have a circularity number of about 13.25, but irregular polygons generate circularity numbers of above about 20. An average circularity is calculated by determining the average of the circularity of a representative sample of grain particles in a microscopy picture. 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 preferably less than about 14 and most preferably less than about 13.5.

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 controllable toughness and hardness.

In one preferred embodiment, the binder material is cobalt 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 prefe 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 preferably, the tungsten carbide-cobalt composite ceramics of this invention possess 10 percent greater toughness; even more preferably they possess 15 percent greater toughness; still more preferably they possess about 25 percent greater toughness; and most preferably they possess about 50 percent greater toughness.

The toughness of the tungsten carbide-cobalt composite ceramics is preferably greater than about 2.1 MPa, more preferably about 3 MPa or greater, and most preferably about 4 MPa or greater. The hardness of these ceramic composites is preferably about 1100 VHN 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 R_C or greater or more preferably about 95 R_C or greater. The refractory bodies prepared from cobalt and tungsten carbide may have a particle size of about 10 microns or less, more preferably 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 illustrative purposes only, and are not intended to limit the scope of the invention or claims. Unless otherwise stated, all parts and percentages are by volume. 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). The composition is 94 percent tungsten carbide (90 volume 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 550°F (287°C) 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 2250°F

(1220°C) as quickly as possible, the furnace is argon purged and the time to reach 2250°F (1220°C) 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 with a slow release. 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 about 97 weight percent tungsten carbide (95 volume percent). The preform contained in the fluid die is heated to about 2370°F (1240°C) before exposingto 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 substantially the same manner as in Example 1. The mixtures are cold compacted 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 290°C 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 temperature, and held at such temperature for about 5 minutes. The cold compact in the pressure-transducing medium is pressed isostatically for the indicated dwell, with a 2-second manual release of pressure. The results are compiled in Table I.

Example 10

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 carbide (90 volume percent) and about 6 percent cobalt (10 volume percent). This slurry is added to a Union Process Model 1-S attrition along with about 120 lbs (55 kg) of 3/16" (1.2 cm) diameter Wc 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 paraffin 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 to remove large lumps. A Trexlor® Isopress bag is then filled and vibrated to reach tap 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 Rosmos (U.S. Patent No. 4,428,906) and packed with borosilicate glass cullet. This assembly is heated to about

2250°F (1232°C) (about 1.5 hours) and held for 5 minutes in a nitrogen purged furnace. The assembly is placed in a supporting die and subjected to about 120 Ks, (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 density of > 14.8 g/cm³.

Example 11

Niobium carbide powder is weighed (4086 gm) and placed under acetone (1000 ml) immediately to prevent oxidation or fire. Cobalt 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 10 yielding a refractory body of about 7.60, g/cm³.

Example 12 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 10. The composition of the powder is about 95 percent by weight tungsten carbide (91 volume percent) and 5 percent by weight nickel (9 volume percent). The greenware is then placed in a ceramic vessel, surrounded with pyrex and heated to about 2150°F for about 2 hours.

A pressure of about 120 Ksi (8.2 x 10¹ MPa) is then applied for 2 seconds duration, and slowly released (about -12 Ksi/sec or 80 MPa/sec). The resultant part has a density of about 99.7 percent of theoretical.

Example 13

A sample of nickel ferrite (250 gm) and nickel powders (25 gm) are physically blended with no attempt at attrician yielding 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 (8.2 mPa) in a uniaxial double acting die. No wax is used. The resulting pellet is about 68 percent of theoretical density.

The part is placed in a glass die similar to

Example 10 and heated to about 2000°C for 2 hours. The pressure (about 120 Ksi) is then applied for 2 seconds dwell and slowly released. The resultant ceramic is about 97.8 percent of theorectical density.

Example 14

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 percent Wc (90 volume percent)/5 percent Co (8.5 volume percent)/1 percent Ni by weight (1.5 volume percent). The powder is attrited, green processed and consolidated in substantially the same manner as Example 10. The resultant ceramic has a density of about 14.66 gm/cc.

Example 15A

Tungsten carbide powder (4268 gm) is blended, attrited with cobalt powder (272 gm) and is cold compacted in a substantially similar manner as in Example 10 to produce rods having a composition 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 10, to finished rods of about 0.5 inches (1.25 cm) diameter 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 results are give in Table II.

Comparative Example 15B

Rods of substantially identical composition and cold compact 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.

Comparative Example 15C

Rods of substantially identical composite and cold compact 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.

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 sintering or the rods prepared by sintering and then pressure densification. Impact Energy equals the energy required to fracture a rigidly supported sample by impacting with a pendulum.

A scanning electron microscope 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 Figure 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 photograph, appears relatively rounded in shape and there are many small lines on the photograph suggesting cobalt containing but very thin boundaries between tungsten carbide particles. In marked contrast, the liquid phase sintered material in Figure 2 (Example 15B) 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 response] to the development of the highly facetted and crystallographic 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.

We 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 we find 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 15B). The Example 15C case is intermediate and requires precision analytical 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 10. 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 10 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. 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. Machining and testing of the transverse rupture bars is done in accordance to methods known by those skilled 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. The results are compiled in Table III.

Example 17 A cold compacted rod was prepared as in Example 14 and was likewise hot pressed as in Example 14 except that the pressing temperature was about 2150°F (1176°C) instead of 2250°F (1232°C). The bar was prepared and impacted as in

Example 14, 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/cm

(about 90 percent of theoretical) and the Vickers 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 10 is substantially repeated using tungsten carbide (4472 g) and cobalt (68 g) to produce a composition 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 2250°F (1232°C) before exposing to the isostatic pressure. The refractory body recovered has the properties listed in Table III.

Comparative Example 18B

Rods of substantially similar composition 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 19A

The process of Example 10 is substantially repeated using tungsten carbide (4403 g) and cobalt (237 g) to produce a composition of 97 weight percent tungsten carbide (98.8 volume percent) and of 3 weight percent cobalt (5.2 volume percent). The preform is heated to about 2250°F (1232°C) before exposing to the isostatic pressure. The refractory body recovered has the properties listed in Table III.

Comparative Example 19B

Rods of substantially similar composition and cold compact geometry to those prepared in Example 19A 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.)

Example 20A

The process of Example 10 is substantially repeated using 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 2250°F (1232°C) before exposing to the isostatic pressure. The refractory body recovered has the properties listed in Table III.

Comparative Example 20B Rods of substantially similar composition and cold compact geometry to those prepared in Example 20A 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 sample is shown in Figure 4. (Published in "American Society of Metals", Metals Handbook, 9th ed., Vol. 3, p. 454, 1980.)

Example 21A

The process of Example 10 is substantially repeated using titanium boride (4449 g) and nickel (91 g) to produce a composition of 98 weight percent titanium diboride (99 volume percent) and of 2 weight percent nickel (1 volume percent). The preform is heated to about 2550°F (1400°C) 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 compact 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 10 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 weigh percent molybdenium carbide (11.2 volume percent) and of 12 weight percent nickel (7.7 volume percent). The preform is heated to about 2250°F (1232°C) before exposing to the isostatic pressure. The refractory body recovered has the properties listed in Table III. Comparative Example 22B

Rods of substantially similar composition and cold compact 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.)

Example 23A

The process of Example 10 is substantially repeated using alumina (3178 g) and chromium (1362 g) to produce a composition 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 2876°F (1580°C) before exposing to the isostatic pressure. The refractory body recovered has the properties listed in Table III.

Comparative Example 23B

Rods of substantially similar composition. and cold compact 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 comparison in Table III.

Example 24A

The process of Example 10 is substantially repeated using boron carbide (4813 g), molybdenum (204 g), nickel (14 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 2372°F (1300°C) 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 10 is substantially repeated using zirconium nitride (4267 g), nickel (227 g) and molybdenum (45 g) to produce a composition of about 94 weight percent zirconium 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 2498°F (1370°C) before exposing to the isostatic pressure. The refractory body recovered has the properties listed in Table III.

Comparative Example 25B

Rods of substantially similar composition and cold compact 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.

Example 26A

The process of Example 10 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 is heated to about 2876°F (1580°C) before exposing to the isostatic pressure. The refractory body recovered has the properties listed in Table III.

Comparative Example 26B

Rods of substantially similar composition and cold compact 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 in Table III.

Example 27A

The process of Example 10 is substantially repeated using 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) 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 compact geometry to those prepared in Example 27A 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.

Claims

WHAT IS CLAIMED IS:

1. A high density refractory body composite ceramic comprising a densified refractory body, possessing about 10 percent greater toughness than exhibited by other composite ceramics of similar composition and geometry, of a refractory material selected from the group consisting of oxides, carbides, nitrides, suicides, borides, sulfides and mixtures thereof, and a binder material capable of plastic deformation present in sufficient amount to at least partially fill the interstices between the refractory material particles.

2. The composite ceramic of Claim 1 wherein said ceramic possesses 10 percent greater toughness than exhibited by other composite ceramics which have been substantially presintered prior to final densification.

3. The composite ceramics of Claim 2 wherein said ceramic possesses 15 percent greater toughness.

4. The composite ceramic of Claim 2 wherein said ceramic possesses 25 percent greater toughness.

5. The composite ceramic of Claim 2 wherein said composite ceramic possesses binder material distribution 10 percent greater than other composite ceramics of similar composition.

6. The composite ceramic of Claim 2 wherein said composite ceramic possesses binder material distribution 50 percent greater than other composite ceramics of similar composition.

7. The composite ceramic of Claim 2 wherein said composite ceramic possesses binder material distribution 100 percent greater than other composite ceramics of similar composition.

8. The composite ceramic of Claim 2 wherein said composite ceramic possesses an average grain particle size less than about 10 microns.

9. The composite ceramic of Claim 2 wherein said composite ceramic possesses an average grain particle size less than about 5 microns.

10. The composite ceramic of Claim 2 wherein said composite ceramic possesses an average grain particle size less than about 2 microns.

11. The composite ceramic of Claim 2 wherein said composite ceramic possesses an average grain particle size less than about 1 micron.

12. The composite ceramic of Claim 5 wherein said composite ceramic possesses an average grain particle size less than about 10 microns.

13. The composite ceramic of Claim 2 wherein said composite ceramic possesses an average circularity number less than about 17.

14. The composite ceramic of Claim 2 wherein said composite ceramic possesses an average circularity number less than about 15.5.

15. The composite ceramic of Claim 2 wherein said composite ceramic possesses an average circularity number less than about 14.

16. The composite ceramic of Claim 2 wherein said composite ceramic possesses an average circularity number less than about 13.2.

17. The composite ceramic of Claim 13 wherein said composite ceramic possesses binder material distribution 10 percent greater than other composite ceramics of similar composition.

18. The composite ceramic of Claim 17 wherein said composite ceramic possesses an average grain particle size less than about 10 microns.

19. The composite ceramic of Claim 2 wherein said composite ceramic possesses 10 percent greater toughness and at least about equal hardness as compared to other composite ceramics of similar composition and geometry.

20. The composite ceramics of Claim 2 wherein the binder material is selected from the group consisting of cobalt, nickel, iron, tungsten, molybdenum, tantalum, titanium, chromium, niobium, boron, zirconium, vanadium, silicon, palladium, hafnium, aluminum, copper, alloys thereof, and mixtures thereof.

21. The composite ceramic of Claim 20 comprising between about 50 and about 99.5 percent by volume of the refractory material and between about 0.5 and about 50 percent by volume of the binder material.

22. The composite ceramic of Claim 20 comprising between about 70 and about 99.5 percent by volume of the refractory material and between about 0.5 and about 30 percent by volume of the binder material.

23. The composite ceramic of Claim 20 comprising between about 80 and about 94 percent by volume of a refractory material and between about 6 and about 20 percent by volume of the binder material.

24. The composite ceramic of Claim 2 comprising refractory material selected from the group consisitng of alumina, zirconia,. magnesia, mullite, zircon, thoria, beryllia, urania, spinels, tungsten carbide, tantalum carbide, titanium carbide, niobium carbide,, zirconium carbide, boron carbide, hafnium carbide, silicon carbide, niobium boron carbide, aluminum nitride, titanium nitride, zirconium nitride, tantalum nitride, hafnium nitride, niobium nitride, 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, zirconium sulfide and mixtures thereof; and (b) a binder material selected from the group consisting of cobalt, nickel, titanium, chromium, niobium, boron, palladium, hafnium, silicon, tantalum, molybdenum, zirconium, vanadium, aluminum, copper, alloys thereof and mixtures thereof.

25. The composite ceramic of Claim 2 comprising

(a) a refractory material selected from the group consisting of tungsten carbide, niobium carbide, titanium carbide, silicon carbide, niobium boron carbide, tantalum carbide, boron carbide, alumina, silicon nitride, boron nitride, titanium nitride, titanium boride and mixtures thereof; and

(b) a binder material selected from the group consisting of cobalt, nickel, titanium, chromium, niobium, palladium, hafnium, tantalum and mixtures thereof.

26. The composite ceramic of Claim 2 comprising (a) a refractory material selected from the group consisting of tungsten carbide, niobium carbide, titanium carbide and mixtures thereof; and (b) a binder material selected from the group consisting of cobalt, niobium, titanium and mixtures thereof.

27. The composite ceramic of Claim 2 comprising tungsten carbide and cobalt.

28. The composite ceramic of Claim 27 comprising between about 50 and about 99.5 percent by volume of tungsten carbide and between about 0.5 and about 50 percent by volume of cobalt.

29. The composite ceramic of Claim 27 comprising between about 80 and about 99.5 percent by volume of tungsten carbide and between about 0.5 and about 20 percent by volume of cobalt.

30. The composite ceramic of Claim 27 comprising about 94 percent by volume of tungsten carbide and about 6 percent by volume of cobalt.

31. A process for the preparation of a high density refractory body composite ceramic comprising contacting a refractory material selected from the group consisting of oxides, carbides, nitrides, borides, sulfides and mixtures thereof, and a binder material capable of plastic deformation, present in sufficient amount to at least partially fill the interstices between the particles of the refractory material, at a temperature less than the liquidus temperature of the binder material under pressure of between about 10,000 psi (6.89 x 10¹ MPa) and the fracture point of the refractory body, for a period of time between that time sufficient for the ceramic composite to reach 85 percent of its theoretical density and less than that time sufficient for sintering to occur, under conditions such that a high density refractory body is prepared with a density of 85 percent or greater possessing 10 percent greater toughness than exhibited by other composite ceramics of similar composition and geometry.

32. The process of Claim 31 wherein the pressure is applied isostatically.

33. The process of Claim 32 wherein the refractory body possesses 10 percent greater toughness than exhibited by other refractory bodies which have been substantially presintered prior to final densification.

34. The process of Claim 33 wherein said refractory body possess 15 percent greater toughness.

35. The process of Claim 33 wherein said refractory body possess 25 percent greater toughness.

36. The process of Claim 33 wherein the composite ceramic possesses binder material distribution 10 percent greater than other composite ceramics of similar composition.

37. The process of Claim 33 wherein the composite ceramic possesses an average grain particle size less than about 10 microns.

38. The process of Claim 33 wherein the composite ceramic possesses binder material distribution 10 percent greater than other composite ceramics of similar composition.

39. The process of Claim 33 wherein the composite ceramic possesses an average circularity number less than about 17.

40. The process of Claim 33 wherein the composite ceramic possesses 10 percent greater toughness and at least about equal hardness as compared to other composite ceramics of similar composition and geometry.

41. The process of Claim 33 wherein the binder material is selected from the group consisting of cobalt, nickel, iron, tungsten, molybdenum, tantalum, titanium, chromium, niobium, boron, zirconium, vanadium, silicon, hafnium, palladium, aluminum, copper, an alloy thereof, and mixtures thereof.

42. The process of Claim 41 wherein between about 50 and about 99.5 percent by volume of (a) a refractory material selected from the group consisting of oxides, carbides, nitrides, silicides, borides, sulfides and mixtures thereof, is contacted with (b) between about 0.5 and about

50 percent by weight of a binder material.

43. The process of Claim 33 wherein the pressure is between about 50,000 psi (3.4 x 10 ² MPa) and about the fracture point of the refractory body.

44. The process of Claim 33 wherein the pressure is between about 70,000 psi (4.8 x 10 ² MPa) and about the fracture point of the refractory body.

45. The process of Claim 33 wherein the pressure is between about 100,000 psi (6.89 x 10² MPa) and about the fracture point of the refractory body.

46. The process of Claim 33 wherein the temperature is between about 400°C and about 2900°C.

47. The process of Claim 33 wherein the contact time is less than about 1 hour.

48. The process of Claim 33 wherein the contact time is less than about 1 minute.

49. The process of Claim 33 wherein the contact time is less than about 10 seconds.

50. The process of Claim 33 wherein (a) a refractory material selected from the group consisting of alumina, zirconia, magnesia, mullite, zircon, thoria, beryllia, urania, spinels, tungsten carbide, tantalum carbide, titanium carbide, niobium carbide, zirconium carbide, boron carbide, hafnium carbide, silicon carbide, niobium boron carbide, aluminum nitride, titanium nitride, zirconium nitride, tantalum nitride, hafnium nitride, niobium nitride, 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, zirconium sulfide and mixtures thereof; is contacted with (b) a binder material selected from the group consisting of cobalt, nickel, titanium, chromium, niobium, boron, palladium, hafnium, silicon, tantalum, molybdenum, zirconium, vanadium, aluminum, copper, alloys thereof and mixtures thereof.

51. The process of Claim 33 wherein (a) the refractory material is selected from the group consisting of tungsten carbide, niobium carbide, titanium carbide, silicon carbide, niobium boron carbide, tantalum carbide, boron carbide, alumina, silicon nitride, boron nitride, titanium nitride, titanium boride and mixtures thereof; is contacted with (b) a binder material selected from the group consisting of cobalt, nickel, titanium, chromium, niobium, palladium, hafnium, tantalum or mixtures thereof.

52. The process of Claim 33 wherein (a) the refractory material is selected from the group consisting of tungsten carbide, niobium carbide, titanium carbide and mixtures thereof; is contacted with (b) a binder material selected from the group consisting of cobalt, niobium, titanium and mixtures thereof.

53. The process of Claim 33 wherein tungsten carbide is contacted with cobalt.

54. The process of Claim 53 wherein the temperature is between about 800°C and about 1500°C.

55. The process of Claim 53 wherein the contact time is less than 1 hour.

56. The process of Claim 53 wherein the contact time is less than 1 minute.

57. The process of Claim 53 wherein the contact time is less than 10 seconds.

58. A high density refractory body ceramic composite prepared by the process comprising contacting a refractory material selected from the group consisting of oxides, carbides, nitrides, borides, sulfides and mixtures thereof, and a binder material capable of plastic deformation, present in sufficient amount to at least partially fill the interstices between the particles of the refractory material at a temperature less than the liquidus temperature of the binder material, under pressure, of between about 10,000 psi (6.89 x 10¹ MPa) and the fracture point of the refractory body for a period of time between that time sufficient for the composite ceramic to react 85 percent of its theoretical density and less than that time sufficient for sintering to occur, under conditions such that a high density refractory body is prepared with a density of 85 percent or greater possessing 10 percent greater toughness than exhibited by other composite ceramics.

59. The ceramic composite of Claim 58 wherein the pressure is applied isostatically.

60. The ceramic composite of Claim 59 wherein said composites possess toughness greater than exhibited by other ceramic composites which have been substantially presintered prior to final densification.

61. The ceramic composite of Claim 60 wherein said ceramic possesses 15 percent greater toughness.

62. The ceramic composite of Claim 60 wherein said ceramic possesses 25 percent greater toughness.

63. The composite ceramic of Claim 60 wherein the binder material is selected from the group consisting of cobalt, nickel, iron, tungsten, molybdenum, tantalum, titanium, chromium, niobium, boron, zirconium, vanadium, silicon, palladium, hafnium, aluminum, copper, alloys thereof and mixtures thereof.

64. The composite ceramic of Claim 63 wherein between about 50 and about 99.5 percent by volume of (a) a refractory material selected from the group consisting of oxides, carbides, nitrides, silicides, borides, sulfides and mixtures thereof, is contacted with (b) between about 0.5 and about 50 percent by volume of a binder material.

65. The composite ceramic of Claim 60 wherein the pressure is between about 50,000 psi (3.4 x 10 ² MPa) and the fracture point of the refractory body.

66. The process of Claim 60 wherein the pressure is between about 70,000 (4.8 x 10² MPa) and about the fracture point of the refractory body.

67. The composite ceramic of Claim 60 wherein the pressure is between about 100,000 psi (6.89 x 10¹ MPa) and the fracture point of the refractory body.

68. The composite ceramic of Claim 60 wherein the temperature is between about 400°C and about 2900°C.

69. The composite ceramic of Claim 60 wherein the contact time is less than about 1 hour.

70. The composite ceramic of Claim 60 wherein the contact time is less than about 1 minute.

71. The composite ceramic of Claim 60 wherein the contact time is less than about 10 seconds.

72. The composite ceramic of Claim 60 wherein (a) a refractory material is selected from the group consisting of alumina, zirconia, magnesia, mullite, zircon, thoria, beryllia, urania, spinels, tungsten carbide, tantalum carbide, titanium carbide, niobium carbide, zirconium carbide, boron carbide, hafnium carbide, silicon carbide, niobium boron carbide, aluminum nitride, titanium nitride, zirconium nitride, tantalum nitride, hafnium nitride, niobium nitride, 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, zirconium sulfide and mixtures thereof; is contacted with (b) a binder material selected from the group consisting of cobalt, nickel, titanium, chromium, niobium, boron, palladium, hafnium, silico tantalum, molybdenum, zirconium, vanadium, aluminum, copper, alloys thereof and mixtures thereof.

73. The composite ceramic of Claim 60 wherein (a) the refractory material is selected from the group consisting of tungsten carbide, niobium carbide, titanium carbide, silicon carbide, niobium boron carbide, tantalum carbide, boron carbide, alumina, silicon nitride, boron nitride, titanium nitride, titanium boride and mixtures thereof; is contacted with (b) a binder material selected from the group consisting of cobalt, nickel, titanium, chromium, niobium, palladium, hafnium, tantalum and mixtures thereof.

74. The composite ceramic of Claim 60 wherein (a) the refractory material is selected from the group consisting of tungsten carbide, niobium carbide, titanium carbide and mixtures thereof; is contacted with (b) a binder material selected from the group consisting of cobalt, niobium, titanium and mixtures thereof.

75. The composite ceramic of Claim 60 wherein tungsten carbide is contacted with cobalt.

76. The composite ceramic of Claim 75 wherein the temperature is between about 800°C and about 1500°C.

77. The composite ceramic of Claim 75 wherein the temperature is between about 1000°C and about 1350°C.

78. The composite ceramic of Claim 76 wherein the contact time is less than 1 hour.

79. The composite ceramic of Claim 76 wherein the contact time is less than 1 minute.

80. The composite ceramic of Claim 76 wherein the contact time is less than 10 seconds.

81. A high density refractory body ceramic composite comprising

(a) a refractory material selected from the group consisting of oxides, carbides, nitrides, silicides, borides, and mixtures thereof;

(b) a binder material capable of plastic deformation; and

(c) a phase in which binder material atoms are substituted on the lattice of the refractory material.

wherein the binder material and component (c) are present in a sufficient amount to at least partially fill the interstices between the particles of the refractory material.

82. The composite ceramic of Claim 81 wherein the binder material is selected from the group consisting of cobalt, iron, nickel, tungsten, molybdenum, tantalum, titanium, chromium, niobium, boron, zirconium, vanadium, silicon, hafnium, palladium, aluminum, copper, an alloy thereof, and mixtures thereof, and component (c) corresponds to the formula X_a-bY_bZ_c wherein X is the metal derived from the refractory material; 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 integer of between about 1 and 4.

83. The composite ceramic of Claim 81 comprising between about 50 and about 99 percent by weight of the refractory material; between about 1 and about 50 percent of the binder metal and between about 0.001 and about 2 percent by weight of component (c).

84. A high density refractory body composite ceramic comprising a densified refractory body, possessing a binder material distribution 10 percent greater than exhibited by other composite ceramics of similar composition and geometry and an average circularity number less than about 17, of a refractory material selected from the group consisting of oxides, carbides, nitrides, silicides, borides, sulfides, and mixtures thereof, and a binder material capable of plastic deformation present in sufficient amount to at least partially fill the interstices between the refractory material particles.