Effect of initial particle size on microstructure of liquid-phase sintered α-silicon carbide

Abstract

Three α-SiC powders of different particle sizes (∼0.42, ∼0.50 and ∼0.71 μm), containing 7.2 wt% Y 3Al 5O 12 (YAG) and 4.8 wt% SiO 2 as sintering aids, were hot-pressed at 1850°C and subsequently annealed at 1950°C to initiate grain growth. All the hot-pressed specimens consisted of equiaxed grains and showed unimodal grain size distribution. The smaller the starting powder the finer the microstructure was developed. After annealing, the fine (∼0.7 μm) and the medium (∼1.1 μm) grain-sized specimens showed self-reinforced microstructures whereas the large (∼1.5 μm) grain-sized specimen maintained an unimodal grain size distribution. These results suggest that the abnormal grain growth of α-SiC grains during annealing is critically dependent on the average grain size of sintered materials, which in turn depends on initial particle size. The fracture toughnesses (5.6 and 6.1 MPa m 1 2 ) of the annealed specimens with self-reinforced microstructures were higher than for the specimen with an unimodal grain size distribution (5.0 MPa m 1 2 ).