In situ-toughened silicon carbide-titanium carbide composites

A process based on liquid-phase sintering and subsequent annealing for grain growth is presented to obtain in situ-toughened SiC-30 wt% TiC composites. Its microstructures consist of uniformly distributed elongated α-SiC grains, matrixlike TiC grains, and yttrium aluminum garnet (YAG) as a grain boundary phase. The composites were fabricated from β-SiC and TiC powders with the liquid forming additives of Al₂O₃ and Y₂O₃ by hot pressing. During the subsequent heat treatment, the β → α phase tansformation of SiC led to the in situ growth of elongated α-SiC grains. The fracture toughness of the SiC-30 wt% TiC composites after 6-h annealing was 6.9 MPa·m^1/2, approximately 60% higher than that of as-hot-pressed composites (4.4 MPa·m^1/2). Bridging and crack deflection by the elongated α-SiC grains appear to account for the increased toughness of this new class of composites.