Effect of initial α-phase content of SiC on microstructure and mechanical properties of SiC–TiC composites

By using α- and β-SiC starting powders, the effects of initial α-phase content of SiC on microstructure and mechanical properties of the hot-pressed and subsequently annealed SiC–30 wt.% TiC composites were investigated. The microstructures developed were analyzed by image analysis. Their microstructures consist of uniformly distributed elongated α-SiC grains, equiaxed TiC grains and an amorphous grain boundary phase. During annealing, the β→α phase transformation of SiC leads to the in-situ growth of elongated α-SiC grains. The average diameter of SiC increases with increasing α-SiC content in the starting powder and the aspect ratio shows a maximum at 1% α-SiC and decreases with increasing α-SiC content in the starting powder. Such results suggest that microstructure of SiC–TiC composites can be controlled by changing α-SiC content in the starting powder. The strength increased with increasing α-SiC content when α-SiC content is higher than 10% while the fracture toughness decreased with increasing α-SiC content, i.e. the same trend with the variation of aspect ratio of SiC in the composites.