In situ enhancement of toughness of SiC-TiB2 composites

Abstract

A process based on liquid phase sintering and subsequent annealing for grain growth is presented to obtain the in situ enhancement of toughness of SiC-30 wt %, 50 wt %, and 70 wt % TiB2 composites. Its microstructures consist of uniformly distributed elongated alpha-SiC grains, relatively equiaxed TiB2 grains, and yttrium aluminium garnet (YAG) as a grain boundary phase. The composites were fabricated from beta-SiC and TiB2 powders with the liquid forming additives of Al2O3 and Y2O3 by hot-pressing at 1850 degrees C and subsequent annealing at 1950 degrees C. The annealing led to the in situ growth of elongated alpha-SiC grains, due to the beta-->alpha phase transformation of SiC, and the coarsening of TiB2 grains. The fracture toughness of the SiC-50 wt % TiB2 composites after 6 h annealing was 7.3 MPam(1/2), approximately 60% higher than that of as-hot-pressed composites (4.5 MPam(1/2)). Bridging and crack deflection by the elongated alpha-SiC grains and coarse TiB2 grains appear to account for the increased toughness of the composites.