Al.sub.2 O.sub.3 composites, process for producing them and throw-away tip made of Al.sub.2 O.sub.3 composites

A method of producing Al.sub.2 O.sub.3 composites sintered product having high strength and high toughness comprising:

• 10 to 40% by weight of SiC whiskers containing 0.3 to 1.5% by weight of oxygen,
• 0.5 to 40% by weight of one or more of Ti compounds represented by the composition formula:
• TiC.sub.x N.sub.y O.sub.z in which x, y, z represent, respectively;
• 0.ltoreq.x.ltoreq.1, 0.ltoreq.y1, 0.8.ltoreq.x+y.ltoreq.1, 0.8 .ltoreq.x+y.ltoreq.1, 0.ltoreq.z.ltoreq.0.2 and
• 0.5 to 3% by weight of a sintering aid,
• remainder Al.sub.2 O.sub.3,
• wherein
• the average grain size of Al.sub.2 O.sub.3 particles in the sintered product is not greater than 1 .mu.m, and one or more of said Ti compounds with the average grain size of not greater than 0.1 .mu.m are dispersed in said Al.sub.2 O.sub.3 particles to form a nanocomposite structure, which comprises mixing the SiC whiskers uniformly dispersed in a solvent, with the other defined materials, removing said solvent to form a uniform mixture, subjecting said mixture to uniaxial press molding under a pressure of from 500 to 5000 Kg/cm.sup.2 and, further, applying sintering at an atmospheric pressure within a temperature range from 1700.degree. to 1950.degree. C.