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

Abstract

Powder mixtures of beta-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 degrees C for 1 h by hot-pressing and subsequently annealed at 1950 degrees C for 2, 6, and 12 h. These materials had a microstructure of 'in situ toughened composites' as a result of the beta --> alpha phase transformation of SiC during annealing. The introduction of larger amount of additives accelerated the grain growth of elongated alpha-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. (C) 1998 Elsevier Science Limited and Techna S.r.l. All rights reserved.