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

By using alpha- and beta -SiC starting powders, the effects of initial alpha -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 alpha -SiC grains, equiaxed TiC grains and an amorphous grain boundary phase. During annealing, the beta-->alpha phase transformation of SiC leads to the in-situ growth of elongated alpha -SiC grains. The average diameter of SiC increases with increasing alpha -SiC content in the starting powder and the aspect ratio shows a maximum at 1% alpha -SiC and decreases with increasing alpha -SiC content in the starting powder. Such results suggest that microstructure of SiC-TiC composites can be controlled by changing alpha -SiC content in the starting powder. The strength increased with increasing alpha -SiC content when alpha -SiC content is higher than 10% while the fracture toughness decreased with increasing alpha -SiC content, i.e. the same trend with the variation of aspect ratio of SIC in the composites. (C) 2000 Elsevier Science Ltd. All rights reserved.