Toughening mechanisms in SiC-TiC composites

Three different microstructures in SiC-TiC composites containing Al2O3 and Y2O3 as sintering additives were prepared by hot-pressing and subsequent annealing. To investigate the dominant toughening mechanism operating in toughened SiC-TiC composites, the microstructure-crack interaction was examined by image analysis. Crack deflection by elongated alpha-SiC grains was most frequently observed (61% of the observed sites) as the dominant toughening mechanism in the SiC-TiC composites. Crack deflection was generally observed for elongated alpha-SiC grains with aspect ratio (AR) > 2.5 and grain thickness (t) < 2.5 mu m. Crack bridging (21% of the observed sites) was also observed as one of the operating toughening mechanisms. The rest (18%) of the observed grains fractured transgranularly. The crack bridging mechanism was mostly related to thinner grains with thickness t < 2 mum, while transgranularly fractured elongated-grains were mostly related to thicker grains with thickness 2 < t < 4 mum.