Abstract: An improved gunning composition for use in the steel industry includes between 60-75% by weight of a refractory base material, 10-20% by weight of silicon carbide, 7-15% by weight of ball clay, 4-8% by weight of a silica binder material, and, optionally, 5-10% by weight of a graphite material. The silica binder replaces binders composed of petroleum pitch or clay. The silica binder causes the composition to have (1) better adhesion, (2) less cracking, (3) improved strength, and (4) increased resistance to oxidation, corrosion and erosion.

Abstract: An improved casting composition utilizes an aqueous finely dispersed silica binder to provide reduced drying times and reduced cracking and explosion of troughs, runners and other containment equipment designed for use by the iron and steel industry. The composition is prepared by mixing 8-14% by weight of the aqueous silica binder with 55-90% by weight of a refractory base material and up to 35% by weight of silicon carbide. Preferably, the composition will also include 5-10% by weight of calcined alumina, 1-10% by weight of microsilica, and 0.02-1% by weight of a setting agent. Troughs and runners manufactured from the composition also exhibit increased strength and improved resistance to oxidation, corrosion and erosion.

Abstract: Substantially dense, void-free ceramic-metal composites are prepared from components characterized by chemical incompatibility and non-wetting behavior. The composites have a final chemistry similar to the starting chemistry and microstructures characterized by ceamic grains similar in size to the starting powder and the presence of metal phase. A method for producing the composites requires forming a homogeneous mixture of ceramic-metal, heating the mixture to a temperature that approximates but is below the temperature at which the metal begins to flow and pressing the mixture at such pressure that compaction and densification of the mixture occurs and an induced temperature spike occurs that exceeds the flowing temperature of the metal such that the mixture is further compacted and densified. The temperature spike and duration thereof remains below that at which significant reaction between metal and ceramic occurs. The method requires pressures of 60-250 kpsi employed at a rate of 5-250 kpsi/second.

Abstract: A ceramic cutting insert for high speed machining of materials is provided having an integral chip control surface thereon.

Abstract: Fiber-reinforced ceramic matrix composites incorporating a glass-ceramic matrix of lithium aluminosilicate composition in which is disposed a fiber reinforcement phase including at least one layer of unidirectionally oriented fibers (e.g. SiC), the matrix further comprising a whisker reinforcement phase selected from the group of SiC, alumina, HfC and Si.sub.3 N.sub.4, the whiskers imparting substantially improved transverse modulus of rupture strength and interlaminar shear strength to the composite.

Abstract: Ceramic matrix composite articles of improved high temperature oxidation resistance are provided, the articles comprising reinforcing fibers disposed within a ceramic matrix, the matrix further comprising a minor matrix addition consisting of a dispersion of fluormica crystallites in a proportion effective to improve the oxidation resistance of the article and ranging up to about 20% by weight of the matrix.

Abstract: In Al.sub.2 O.sub.3 composites used for machining tools for difficult-cutting steels, etc., strength and toughness are increased by dispersing a Ti compound with an average grain size of not greater than 0.1 .mu.m into Al.sub.2 O.sub.3 particles with the average grain size of not greater than 1 .mu.m, and SiC whiskers are uniformly dispersed between each of Al.sub.2 O.sub.3 particles to form a nanocomposite structure.For the above-mentioned purpose, SiC whiskers containing 0.3 to 1.5% by weight of oxygen, dissolved uniformly in a solvent, are mixed with a starting Al.sub.2 O.sub.3 series powder containing Ti compounds to form a uniform mixture, which is then molded and sintered.

Abstract: A composition containing MgAl.sub.2 O.sub.4, SiC, and B.sub.4 C is produced by the method comprising:(a) combining sources of magnesium silicate, B.sub.2 O.sub.3, Al and C to form a mixture, and(b) heating the mixture whereby the sources react to form MgAl.sub.2 O.sub.4, SiC, and B.sub.4 C.A sintered material containing MgAl.sub.2 O.sub.4, SiC, and B.sub.4 C, may be produced by the method comprising:(a) combining sources of magnesium silicate, B.sub.2 O.sub.3, Al and C to form a mixture,(b) compacting the mixture into a shape,(c) heating the shape, whereby the sources react to form MgAl.sub.2 O.sub.4, SiC, and B.sub.4 C, and(d) sintering the reacted shape.Possible sources of magnesium silicate are talc, vermiculite and mica.

Abstract: A sialon based composite composite essentially consists of 5 wt % to 40 wt % of SiC fibers, 0.3 wt % to 10 wt % of an Hf component which is calculated in terms of Hf oxide, and the balance of sialon as a major constituent. In this case, the sialon is .alpha.-sialon or .beta.-sialon.

Abstract: This invention relates to a cutting tool material with improved toughness behavior using alumina or silicon nitride as the matrix material. The improved toughness is achieved by the addition of whiskers and optionally zirconia in a monoclinic or tetragonal phase, to the matrix. The whiskers are disc-shaped with a thickness of 0.5-8 .mu.m and an equivalent diameter (hypothetical diameter of a circle with the same area as the disc) of about 5-50 .mu.m.

Abstract: A ceramic matrix composite article having a varying thickness is fabricated by a process wherein multiple prepreg sheets comprising reinforcing fibers and powdered matrix material are stacked to provide a multi-layer prepreg stack wherein, through each cross-sectional dimension perpendicular to the plane of the sheets, the number of prepreg sheets contributing to the aggregate sheet thickness of the stack varies in proportion to the relative thickness desired in the layered article. The stack may consolidated to a composite article with a smoothly varying thickness profile without undue fiber breakage or ply wrinkling in the composite structure consolidated into a composite article having a smoothly varying thickness profile with reduced internal fiber bowing or breakage. Preferably, the exterior surfaces of the article comprise long, substantially continuous fibers and are free of ply drops.

Abstract: The flexural strength and fracture toughness of SiC whisker-reinforced ceramic composite are increased and the sintering temperature of the composite is lowered by the addition of chromia. The starting materials for the fabrication of the composite consist of SiC whiskers, chromia and alumina which during hot pressing will yield alumina-chromia solid solution, the matrix, and Cr.sub.3 C.sub.2 particles as individuals or coherently bonded to the ends of the whiskers, the reinforcements evenly distributed in the matrix.In the formation of the ceramic composites, the SiC whiskers are mixed with chromia and alumina. The mixture is hot pressed at pressures in a range of about 5 to 50 MPa for a duration about 0.2-2 hours and at temperatures of about 1350.degree. to 1650.degree. C. to provide a composite with a relative density greater than about 97% of theoretical density.

Abstract: A fiber-organic composition includes from about 5% to 50% by volume of uniformly dispersed, non-planar or three dimensionally random oriented inorganic fibers or whiskers, and a thermoplastic material such as paraffin wax. The composition also includes surfactants to promote wetting and dispersion of the inorganic fibers or whiskers. These materials are subjected to high shear mixing to form a uniform randomly oriented three-dimensional dispersion of the inorganic fibers or whiskers. After molding the mixture in such a manner so as not to disrupt the uniform, three-dimensional orientation of the fibers or whiskers, a majority of the thermoplastic material is removed leaving a shaped body or preform having sufficient strength for handling. The shaped body or preform can then be infiltrated with molten metal or the like to form a metal matrix composite.

Abstract: The invention relates to a method for producing ceramic composites obtained by oxidation of a parent metal to form a polycrystalline ceramic material by providing a filler having a coating of a silicon source on at least a portion of the filler different in composition from the primary composition of the filler, said silicon source possessing intrinsic doping properties. A body of molten parent metal, adjacent a mass of the filler material, reacts with an oxidant to form an oxidation reaction product which infiltrates the adjacent mass of filler, thereby forming the ceramic composite.

Abstract: Ceramic bodies are bonded together via a layer of an oxidation reaction product of a molten metal, which metal is present in one or both of the ceramic bodies prior to bonding. At least one of the ceramic bodies comprises a ceramic product formed by the oxidation reaction of molten parent metal (e.g., alumina from molten aluminum) and grown as molten metal is transported through, and oxidized on the surface of, its own oxidation product. One or both of the ceramic bodies used in the bonding process contains surface-accessible channels of residual metal, i.e., metal channels which have resulted from molten-metal transport during the ceramic growth process. When the suitably assembled ceramic bodies are heated in the presence of an oxidant at a temperature above the melting point of the residual metal, molten metal at the surface of at least one of the body ceramic bodies reacts with the oxidant to form a layer of oxidation reaction product, which may or may not incorporate at least one filler material.

Abstract: Disclosed is a method of forming an improved ceramic matrix composite wherein there is provided a slurry comprised of aluminum oxide, boron oxide and an organic binder suspended in a liquid, and combining the slurry with fibers. The aluminum oxide and boron oxide are capable of reacting to form aluminum borate. The improvement comprises providing the fibers with a coating which forms a stable interface between the fibers and the aluminum borate.

Abstract: A method of producing ceramic composites of Al.sub.2 O.sub.3 reinforced by shaped SiC particles preferably shaped as fine particles (random), platelets, whiskers or fibres by in situ production of SiC particles by heating a mixture of carbon particles of the desired shape with silicates of Al.sub.2 O.sub.3 to a temperature above 1500.degree. C., convert the silicates and carbon to Al.sub.2 O.sub.3 and SiC to produce in situ SiC particles of the desired shape and provide a ceramic powder that may be densified by techniques such as hot pressing, isostatic pressing or sintering.

Abstract: Disclosed herein is a sintered silicon carbide composite prepared by sintering a blend comprising from 25 to 85% by weight of silicon carbide, from 1 to 25% by weight of at least one of chromium and chromium compound, from 10 to 70% by weight of at least one of carbide, nitride and boride of elements belonging to the groups IVb and Vb of the periodical table, and from 3 to 25% by weight of aluminum oxide, in an inert gas atmosphere at a temperature from 1700.degree. to 2100.degree. C.

Abstract: Disclosed herein is a slider of which sliding performance, i.e., sealing performance is improved, without decline of combination strength of grain boundaries and abrasion resistance, by including 2-10%, more preferably 3-8% by weight of free carbon in a slider composed of a high density silicon carbide sintered compact of which relative density is not less than 95%.

Abstract: A conductive ceramic sintered body substantially free from large variation of electric resistivity, which consists essentially of: (a) a silicon nitride-base ceramic as a matrix; (b) 10-70 volume % of a first conductive material which consists of one or more conductive compounds selected from carbides, nitrides, oxides and their composite compounds of transition metals in Groups IVa, Va and VIa of the Periodic Table; and (c) 0.1-50 volume % of a second conductive material consisting of SiC; the first conductive material and the second conductive material serving to form paths for electric conduction.

Abstract: An improved ramming composition for use in the iron and steel industry includes between 65-80% by weight mullite, 5-15% by weight silicon carbide, 2-5% by weight graphite, 2-6% by weight ball clay, and 5-10% by weight of a binder formed from a dispersion of 15-70% by weight silica in water. The silica binder replaces binders composed of petroleum pitch, clay, or other organic materials. The silica binder causes the ramming composition to have a longer use life, increased strength, and reduced tendency to crack, oxidize or smoke.

Abstract: A ceramic composition is provided having a alumina based matrix with silicon carbide whiskers and titanium carbide phase dispersed therein. The composition includes about 1.0 to less than 30 volume percent silicon carbide whiskers, about 5 to about 40 volume percent titanium carbide phase. The sum of the volume percents of silicon carbide whiskers and titanium carbide phase is less than about 60 volume percent.

Abstract: Disclosed is a high strength aluminum borate ceramic matrix composite product and a method of making the same which comprises providing a slurry of aluminum oxide, boron oxide and organic or aqueous binder, the aluminum oxide and boron oxide capable of reacting to form aluminum borate. The slurry is introduced to a body, e.g., web of ceramic fibers, to provide an infiltrated web. After removing liquid and organic binder from the infiltrated web, it is sintered to react the aluminum oxide and boron oxide to form a ceramic matrix composite comprised of aluminum borate and said web of ceramic fibers. The reaction causes a volume expansion which aids in filling or removal of pores or voids resulting from the removal of organic binder.

Abstract: A method of producing a self-supporting ceramic composite body having therein at least one cavity which inversely replicates the geometry of a positive mold of parent metal. The method includes embedding the mold of parent metal within a conformable bed of filler to provide therein a cavity shaped and filled by the mold. The assembly is heated to melt the parent metal mold, e.g., an aluminum parent metal mold, and contacted with an oxidant to oxidize the molten parent metal to form a polycrystalline material which grows through the surrounding bed of filler, the molten metal being drawn through the growing polycrystalline material to be oxidized at the interface between the oxidant and previously formed oxidation reaction product whereby the cavity formerly filled by the mold of parent metal is eventually evacuated of the metal. There remains behind a cavity whose shape inversely replicates the original shape of the mold.

Abstract: The present invention is an electrical device made up of a mixture of silicon carbide and molybdenum disilicide, and may include silicon nitride or aluminum nitride or boron nitride. An electrical device is also disclosed which is particularly suited for use as an igniter in liquid and gas fuel burning systems. The device is made up of a sintered, preferably hot-pressed, mixture of fine powders of aluminum nitride or silicon nitride, silicon carbide and molybdenum disilicide where, when all three are present, they are present in substantial quantities.

Abstract: Fiber-reinforced ceramic matrix composite products are made by providing inorganic fiber reinforcement materials with pyrolytic carbon coatings, combining the carbon-coated fibers with a selected ceramic matrix material to make a composite preform, and consolidating the preform with heat and pressure to form the fiber-reinforced composite. Preferably, the peak consolidation temperature of the composite is moderated, with the retained pyrolytic carbon coating acting to preserve tough fracture behavior in the composite product notwithstanding the absence of the conventional graphitic fiber interface layer therefrom.

Abstract: A process for preparing a ceramic composite material containing alpha silicon carbide whiskers is disclosed.In the process, a slurry containing non-aqueous liquid and aluminum material, amorphous carbon, and silica is provided. This slurry is thereafter pelletized, the pellets are dried, the dried pellets are preheated, and the preheated pellets are then ignited. The ignited pellets undergo an exothermic reaction, forming the composite containing alpha silicon carbide whiskers.The composite material is heat-treated by first heating it to a temperature of 900-1100 degrees centigrade at a rate of 8-15 degrees per minute, and then heating it to a temperature of 1,250-1,350 degrees centigrade at a rate of 2-5 degrees per minute.

Abstract: The present invention relates to an unfired refractory brick for use in reducing conditions at temperatures above 1800.degree. F. The brick comprises a matrix of alumino-silicate clays, alumino-silicate-aggregates and high alumina aggregates. It also has 2 to 20% by weight of finally ground silicon carbide and 2 to 20% by weight of fine carbon particles distributed throughout the matrix. The matrix also includes a water soluble ammonium lignin sulphonate as a chemical binding agent. The brick of the present invention finds particular use in a furnace for kiln baking anodes used in the electrolytic production of aluminum metal.

Abstract: A metalcutting insert is provided with an alumina based ceramic composition composed of (in volume percent, v/o): about 1.5 to 37.5 silicon carbide whiskers; about 5 to 17.5 zirconia; residue of a magnesium oxide addition added in an amount effective to enhance the metalcutting lifetime of the cutting edge of the insert; and an alumina based matrix in which the silicon carbide whiskers, zirconia and residue of magnesium oxide are substantially homogeneously distributed. At least 2 v/o of the alumina based ceramic composition is tetragonal zirconia.

Abstract: Fibrous material is coated with boron nitride and a silicon-wettable material, the coated fibrous material is admixed with an infiltration-promoting material which is at least partly elemental carbon and the mixture is formed into a preform which is infiltrated with a molten solution of boron and silicon producing a composite containing boron nitride coated fibrous material.

Abstract: A method of producing self-supporting ceramic composite bodies of desired shape by infiltrating a permeable self supporting preform with polycrystalline matrix material comprising an oxidation reaction product obtained by oxidation of a parent metal precursor, such as aluminum, and optionally containing therein metallic constituents. The composite body is formed by contacting a zone of a permeable self supporting preform, having at least one defined surface boundary spaced from said contacting zone, with a body of molten metal which is reacted with a suitable vapor-phase oxidant to form an oxidation reaction product.

Abstract: A method is provided of producing a self-supporting ceramic composite structure having one or more encasement members, such as an encasing steel sleeve, joined to it by growth of the ceramic material to engagement surface(s) of the encasement member(s). A parent metal is contacted with a body of filler which is encased by the encasement member(s). The resulting assembly is heated to melt and oxidize the parent metal, e.g., aluminum, to form a polycrystalline material comprising an oxidation reaction product which grows through the body of filler and stops at the engagement surface(s) of the encasement member(s) which thereby determines the surface geometry of the grown ceramic matrix. Upon cooling, the encasement member(s) is shrink-fitted about the ceramic composite body. The invention also provides the resultant articles, for example, a ceramic composite body having a stainless steel member affixed thereto.

Abstract: A method of producing ceramic composites of Al.sub.2 O.sub.3 reinforced by shaped SiC particles preferably shaped as fine particles (random), platelets, whiskers or fibres by in situ production of SiC particles by heating a mixture of carbon particles of the desired shape with silicates of Al.sub.2 O.sub.3 to a temperature above 1500.degree. C., convert the silicates and carbon to Al.sub.2 O.sub.3 and SiC to produce in situ SiC particles of the desired shape and provide a ceramic powder that may be densified by techniques such as hot pressing, isostatic pressing or sintering.

Abstract: A SiC whisker-reinforced ceramic article produced by subjecting the SiC whiskers to acid- and/or base-washing; subjecting ceramic particles and SiC whiskers to fluid classification; forming a suspension of the powdered ceramic and SiC whiskers; consolidating the suspension to form a green compact; optionally infiltrating the green compact with an aluminum compound which is a precursor to Al.sub.2 O.sub.3, and pressureless sintering the green compact to produce an SiC whisker-reinforced composite having high relative density at high SiC whisker loading.

Abstract: A process for preparing a ceramic composite material containing alpha silicon carbide whiskers is disclosed.In the process, a slurry containing non-aqueous liquid and aluminum material, amorphous carbon, and silica is provided. This slurry is thereafter pelletized, the pellets are dried, the dried pellets are preheated, and the preheated pellets are then ignited. The ignited pellets undergo an exothermic reaction, forming the alpha silicon carbide whiskers.

Abstract: A porous form body is produced of sinterable SiC-powder by forming a suitable suspension of said SiC-powder and then treating the suspension to convert it into droplets and the droplets into a granular material in which the granules are substantially larger than the particles of SiC-powder. The granular material is then formed into a green body, e.g. by spraying the granules onto a negative mold of the form body or slip-casting or the like. The green body is then sintered whereby the resulting porosity in the final form body provides the form body with low drag.

Abstract: The semi-conductive ceramic composition is obtained according to the invention from (a) a basic composition containing 40 to 80% by weight of a semi-conductor which is a silicon or boron carbide, 5 to 40% by weight of a binder or of a mixture of binders chosen from aluminum oxide, beryllium oxide, zirconium oxide, magnesium oxide, silica and silicon nitride, and 0 to 40% of a flux of a mixture of fluxes chosen from alkaline-earth carbonates and oxides, rare earth oxides and metal silicates, and (b) 5 to 40% by weight, relative to the basic composition (a), of a heat-emitting dope chosen from titanium, barium titanate, tungsten and lanthanum boride.

Abstract: Silicon carbide whisker-reinforced ceramic composites are fabricated in a highly reproducible manner by beneficating the surfaces of the silicon carbide whiskers prior to their usage in the ceramic composites. The silicon carbide whiskers which contain considerable concentrations of surface oxides and other impurities which interact with the ceramic composite material to form a chemical bond are significantly reduced so that only a relatively weak chemical bond is formed between the whisker and the ceramic material. Thus, when the whiskers interact with a crack propagating into the composite the crack is diverted or deflected along the whisker-matrix interface due to the weak chemical bonding so as to deter the crack propagation through the composite. The depletion of the oxygen-containing compounds and other impurities on the whisker surfaces and near surface region is effected by heat treating the whiskers in a suitable oxygen sparaging atmosphere at elevated temperatures.

Abstract: The present invention relates to a refractory material which consists of 63 to 82 weight percent of SiC, 15 to 27 weight percent of Si.sub.3 N.sub.4 and 3 to 10 weight percent of inorganic oxides.

Abstract: A process for preparing a ceramic composite which is comprised of alpha silicon carbide whiskers and alpha aluminum oxide powder is disclosed. In the first step of this process, there is provided a slurry comprised of from about 80 to about 92 volume percent of solid material and from about 20 to about 8 volume percent of a non-aqueous liquid. In this slurry, the solid material comprises from about 30 to about 38 weight percent of aluminum material, from about 10 to about 14 weight percent of amorphous carbon, and from about 52 to about 62 weight percent of silica.The slurry provided in the first step of this process is thereafter passed through a twin-deck sieve to pelletize it.The pellets are then dried to a moisture content of from about 0.1 to about 1.

Abstract: A process of forming a coherent refractory mass on a surface comprises projecting against that surface, together with oxygen, a mixture of refractory particles and fuel which reacts in an exothermic manner with the projected oxygen to release sufficient heat to melt at least the surfaces of the refractory particles and thus form the refractory mass. The projected mixture contains, as fuel, finely divided particles of at least one element which is oxidizable to form a refractory oxide and it also contains carbonaceous particles which are of such a size or composition that carbon particles become occluded in the formed refractory mass. The mixture may contain, as said fuel, finely divided particles having a mean grain size of less than 50 .mu.m of silicon, aluminum and/or magnesium. The carbonaceous particles may comprise a carbonaceous core which is covered by a mantle inhibiting oxidation of the core.

Abstract: A slider, the sliding performance, i.e., sealing performance of which is improved, without a decline in the combination strength of the grain boundaries and the abrasion resistance, by including 2-10%, more preferably 3-8%, by weight of free carbon in a slider composed of a high density silicon carbide sintered compact the relative density of which is not less than 95%.

Abstract: A method for producing shaped heat-insulating bodies based on water-insoluble oxidic metal compounds particularly of the elements silicon and aluminum, clouding agents and other additives, whereby the bodies are thermally hardened and have a heat conductivity of 0.02 to 0.1 W/K.m at temperatures of approximately 300.degree. to 500.degree. C. and are comprised of (a) 100 parts by weight of water-insoluble oxidic metal compounds having a BET-surface of 10 to 700 m.sup.2 /g, with the provision that at least 5% by weight of these compounds have a BET-surface of at least 50m.sup.2 /g; (b) 0 to 100 parts by weight of mineral clouding agents having at least one absorption maximum in the wave length range of 1.5 to 10 .mu.m; and (c) 0.1 to 30 parts by weight of elements capable of forming a solid oxide having a standard formation enthalpy of less than minus 900 kJ/Mol. In addition, 0-100 parts by weight of mineral fibers can be added.

Abstract: A carbon-containing refractory is formed by mixing 1-10 weight % of silicon nitride, 1-35 weight % of carbon, and a remainder of a refractory raw material, molding the mixture into a molded body, and burning the molded body such that fine whiskers of silicon carbide are uniformly distributed within the matrix.

Abstract: An improved ceramic foam filter for use in filtering molten metal prepared from a ceramic slurry containing silicon carbide and a colloidal silica binder. The filter has a solids content of at least 50% silicon carbide and at least 3% of silica.

Abstract: An alumina based ceramic composition is provided containing (in volume percent, v/o): about 1.5 to 17.5 silicon carbide whiskers; about 5 to 17.5 zirconia; residue of a magnesium oxide addition added in an amount of about 0.03 to 3; and an alumina based matrix in which the silicon carbide whiskers, zirconia and residue of magnesium oxide are substantially homogeneously distributed. At least 4 v/o of the alumina based ceramic composition is tetragonal zirconia.

Abstract: Cutting tools are disclosed which are comprised of composite bodies comprising a ceramic matrix reinforced by ceramic whiskers. The ceramic matrix may be alumina or silicon nitride, and may contain toughening components. The whiskers are preferably silicon carbide, but may be other known ceramic whiskers. Whisker content in the composite is 2-40%, with higher contents generally used for tools when the expected service involves interrupted cutting and lower contents generally used for continuous cutting tools.

Abstract: An alumina based ceramic composition is provided containing (in volume percent, v/o): about 1.5 to 37.5 whiskers; about 5 to 17.5 zirconia; residue of a magnesium oxide addition added in an amount of about 0.03 to 3 v/o; and an alumina based matrix in which the silicon carbide whiskers, zirconia and residue of magnesium oxide are substantially homogeneously distributed. At least 2 v/o of the alumina based ceramic composition is tetragonal zirconia.

Abstract: A metalcutting insert is provided with an alumina based ceramic composition composed of (in volume percent, v/o): about 1.5 to 17.5 silicon carbide whiskers; about 5 to 17.5 zirconia; residue of a magnesium oxide addition added in an amount effective to enhance the metalcutting lifetime of the cutting edge of the insert; and an alumina based matrix in which the silicon carbide whiskers, zirconia and residue of magnesium oxide are substantially homogeneously distributed. At least 4 v/o of the alumina based ceramic composition is tetragonal zirconia.

Abstract: A metalcutting insert is provided with an alumina based ceramic composition composed of (in volume percent, v/o): about 1.5 to 12.5 silicon carbide whiskers and about 7.5 to 17.5 v/o zirconia. The silicon carbide whiskers and zirconia are substantially homogeneously distributed in an alumina base matrix. Preferably, at least about 7 v/o of the alumina based ceramic composition is tetragonal zirconia.