Microstructure and high-temperature property of reaction hip-sintered sic-ain ceramic alloys

SiC and AIN are known to form an extensive solid solution, and preferable mechanical properties have been obtained particularly at room temperature for the SiC-AIN alloys than the end number materials. The present study was intended to investigate the high-temperature strength and deformation behavior of the SiC-AIN solid solution. For this purpose, dense SiC-AIN solid solution and its composite samples were prepared by HIP-sintering of Si, C and A1N powder premixtures as a handy process. The microstructures and solid solutioning compositions were investigated by STEM-EDX, and the fracture strength and deformation behavior of the alloys were evaluated up to 1773K by using a newly-developed Small Punch (SP) testing method. The HIP-sintered SiC-AIN alloys were found to be composed of SiC-rich and AIN-rich solid solutions with ultrafine grained-microstructure of 50 to 100 nm matrix grain size. High fracture strength was obtained in the SiC-AIN alloys up to 1473K, and below this temperature the load-deflection curve was linear, indicating typically brittle behavior. At 1773K, nonlinear deformation behavior was observed and it intensified with decreasing strain rate. No such fracture transition behavior was observed in the monolithic SiC and A1N with average grain size of up to 5 (im. The fractographic observation suggested that the grain boundary sliding enhanced by the ultrafine grained-microstructure was predominately responsible for the appearance of the non-linear deformation at high temperature.