Fracture Toughness of TiC-SiC Composites Fabricated by CVD and the Mechanism of Toughening

Abstract

Fracture toughness (KIC) of CVD⋅TiC-SiC composites with columnar structure was measured by the indentation microfracture method. In order to explain the resulting high fracture toughness, residual stress in the composites was measured by the X-ray diffraction method (2θ-sin2Ψ method). Crack deflection was observed in both surfaces perpendicular and parallel to columnar structure of TiC-SiC composites, more pronounced with the latter. The KIC values were about three to four times as large as that of monolithic SiC or TiC, and were about twice as large as sinterd TiC-SiC composites with TiC-dispersed type of structure. It was presumed that the residual stress in the CVD⋅TiC-SiC composites was much larger than that in monolithic SiC or TiC, and the values parallel to the columnar structure of the composites was larger than that perpendicular. From above result, it was considerd that the high fracture toughness of CVD⋅TiC-SiC composites was achieved by crack deflection, the effect of which depended on the residual stress in the composites.