PROCESS FOR PRODUCING A SINTERED SILICON CARBIDE/CARBON COMPOSITE CERAMIC BODY HAVING ULTRAFINE GRAIN MICROSTRUCTURE

Sintered silicon carbide/carbon composite ceramic body having a homogeneous very fine grain microstructure with at least 50 percent of its silicon carbide grains having a size not exceeding about 5 microns and an aspect ratio less than about 3, with graphite grains having an average size not exceeding that of the silicon carbide grains uniformly dispersed throughout the matrix of silicon carbide and having a density of at least 75 percent of theoretical can be made by firing of an infiltrated, microporous shaped green body having prior to infiltration a density of at least about 45 percent of theoretical, the shaped green body being infiltrated with an organic material which can be coked at elevated temperatures to form carbon, a sintering aid selected from the group consisting of aluminum, beryllium or boron or compounds containing any one or more of these or a mixture of any of the foregoing elements or compounds, silicon carbide having a surface area of from about 5 to about 100 square meters/gram and, optionally, a temporary binder at a sintering temperature of from about 1900 DEG C to about 2300 DEG C in an inert atmosphere or vacuum. The process for making such pressureless-sintered composite bodies is relatively undemanding of exact temperature/time control during sintering. Certain embodiments of such composite sintered bodies may be electrical-discharge machined. Fully dense composite bodies exhibiting no open porosity may be formed.