Development of Hybrid-Type Ceramic Matrix Composites Based on Fail-Safe Concept

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Fracture toughness of high-strength ceramics can be improved through the microstructure control and composite reinforcement. Nano-size-particle-dispersed composites are most promising among other candidate materials. The following three types of alumina based hybrid-type nano-composites were investigated through this study, in order to demonstrate the fundamental mechanism of nano-size intragranular dispersion and the contollability of the micructure by intergranular dispersion.(1) Al_2O_3/5vol% Nano-Size SiC Dispersed Composites : Although very small SiC particles tended to exist within alumina grains, larger ones are dispersed at grain boundaries. The dispersion process of nano-size particles was closely related with the degree of alumina matrix densification. The grain size of alumina could be contolled by carefully selecting the size of reinforcing particles.Both strength and toughness were improved through nano-size particle dispesion.(2) Al_2O_3/SiC/YAG Hybrid Composites : Micron-size YAG and nano-size SiC particles were successfully dispersed to fabricate Al_2O_3/SiC/YAG Hybrid Composites. Since the grain growth of alumina was controlled and homogeneous microstrucure was accomplished, the mechanical properties were much improved through hybritization.(2) Al_2O_3/LaAl_<11>O_<18> Composites : Alumina matrix composites with elongated fiber-like reinforcing phases were sucessfully fabricated. Both strength and fracture toughness increased as the volume fraction increased. In particular, the fracture toughness was much improved through the increase in the aspect ratio of reinforcement. Bridging and crack deflection contributed the toughness improvement to a large extent.