Effect of initial alpha-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 alph a -phase content of SiC on microstructure and mechanical properties of the hot-pressed and subsequently annealed SiC-30 wt.% TiC composites were inves tigated. The microstructures developed were analyzed by image analysis. The ir microstructures consist of uniformly distributed elongated alpha -SiC gr ains, equiaxed TiC grains and an amorphous grain boundary phase. During ann ealing, the beta-->alpha phase transformation of SiC leads to the in-situ g rowth of elongated alpha -SiC grains. The average diameter of SiC increases with increasing alpha -SiC content in the starting powder and the aspect r atio shows a maximum at 1% alpha -SiC and decreases with increasing alpha - SiC content in the starting powder. Such results suggest that microstructur e of SiC-TiC composites can be controlled by changing alpha -SiC content in the starting powder. The strength increased with increasing alpha -SiC con tent when alpha -SiC content is higher than 10% while the fracture toughnes s decreased with increasing alpha -SiC content, i.e. the same trend with th e variation of aspect ratio of SIC in the composites. (C) 2000 Elsevier Sci ence Ltd. All rights reserved.