Effects of additive amount on microstructure and fracture toughness of SiC-TiB₂ Composites

Powder mixtures of β-SiC-30 wt% TiB₂ containing 5 wt% (ST1), 10 wt% (ST2), and 20 wt% (ST3) Al₂O₃-Y₂O₃ as sintering additives were liquid-phase sintered at 1850°C for 1 h by hot-pressing and subsequently annealed at 1950°C for 2, 6, and 12 h. These materials had a microstructure of 'in situ-toughened composites' as a result of the β→α phase transformation of SiC during annealing. The introduction of larger amount of additives accelerated the grain growth of elongated α-SiC grains with higher aspect ratio, resulting in the improved fracture toughness. The fracture toughnesses of 12-h annealed materials with 5, 10, and 20 wt% additives were 5.7, 5.9, and 7.1 MPam^1/2, respectively.