Control of microstructure of alumina ceramics by dispersion of nano SiC particulates

Al₂O₃/SiC composites were prepared by hot-pressing in order to investigate the microstructural characteristics and nano-disperse behavior of alumina matrix composites. The grain size of the monolithic alumina ceramics increased with increasing hot-pressing temperature, and the exaggerated grain growth occurred above 1800 °C. However, the addition of SiC particulates effectively suppressed the growth of the alumina matrix in the composites. The average matrix grain size was smaller and the grain size distribution was narrower than those of the monolithic alumina ceramics. Very fine SiC particulates were well dispersed in composites as nano-sized intragranular grains in the alumina matrix, on the other hand, coarse SiC particulates were found to exist at grain boundaries of the alumina matrix. The intragranular SiC seems to be trapped like a pores in the matrix grains during the densification by hot-pressing. It is concluded that nano-sized SiC particulates are grain growth inhibitors and microstructural stabilizers thus giving a uniform microstructures with fine grains.