This proposal describes a Phase II process and materials development effort focused on the use of Sinter/Hip to fabricate silicon nitride/silicon carbide whisker (Si(3)N(4)/SiC[w]) ceramic matrix composites. The target materials of the program will be generated from starting compositions of (Si(3)N(4) + < - 4 wt% Y(2)O(3) + 10-35 vol % SiC(w). The overall aim of the program will be to fabricate essentially fully dense products from these starting compositions. It is expected that such products will possess good high temperature strength and oxidation resistance, owing to the small amounts of sintering aid employed, while the SiC(w) will enhance the resultant fracture toughness. In addition, to improve the sinterability of the composites and to preclude or mitigate high temperature reactions between the SiC(w) and other species during processing, the SiC(w) will be CVD coated with boron nitride prior to their introduction into the starting powder mix. Further, by super-imposing Hip on Sintering, it should be possible to eliminate or markedly reduce residual porosity and homogenize the properties of the materials. If successful, the proposed program will result in commeralizable net or near-net shape process technology and ceramic matrix composites especially suited for high temperature structural uses.
