Effect of annealing on mechanical properties of self-reinforced alpha-silicon carbide

Abstract

Alpha-SIC powder containing 7.2 wt % Y3Al5O12 (YAG, yttrium aluminum garnet) and 4.8 wt % SiO2 as sintering aids were hot-pressed (SC0) at 1820°C for 1 h and subsequently annealed at 1920°C for 2 h (SC2), 4 h (SC4) and 8 h (SC8). When the annealing time was increased, the microstructure changed from equiaxed to elongated grains and resulted in self-reinforced microstructure consisted of large elongated grains and small equiaxed grains. Development of self-reinforced microstructure, consisted of mostly 6H phase, resulted in significant improvements in toughness. However, the improved toughness was offset by a significant reduction in strength as in the materials consisted of 4H originated from β-SiC. The fracture toughness and strength of the 8-h annealed materials were 5.5MPa · m1/2 and 490 MPa, respectively.