Synthesis of SiC-AlN Powder and Characterization of Its HIP-Sintered Compacts.

Abstract

SiC-AlN powder was synthesized from a powder mixture of Si, Al and C through direct reaction between the constituent elements, i.e., (1-x)Si+(1-x)C+xAl+(x/2)N2=(SiC)1-x(AlN)x. A green compact of the mixed elemental powders was fired in nitrogen, and a porous compact composed of SiC and AlN and their solid solutions was obtained. This porous compact could be easily pulverized to fine SiC-AlN powder by ball-milling. Ultrafine microstructure with fine grains smaller than 100nm was obtained by hot-isostatic pressing (HIP) of the synthesized powders without external additives. Most grains therein were SiC-AlN solid solutions with compositions close to the nominal mixed ratio. The obtained SiC-AlN ceramic alloys, here referred to as homogeneous solid solutions and their mixture, showed better mechanical properties than SiC and AlN. In particular, high strength, more than twice that of the conventional monolithic SiC, was obtained in the SiC-50 mol% AlN composition mainly because of its ultrafine-grained microstructure. This was also the main reason for the present SiC-AlN ceramic alloys to exhibit ductile deformation at relatively low temperatures.