Effect of Dispersed Particle Size on Mechanical Properties of Alumina/Non-Oxides Composites

Abstract

Alumina with SiC or TiC particles was hot-pressed at 1500°C for 2h in N2 under a pressure of 40MPa, and the effect of the size and volume fraction of dispersed particles on mechanical properties of the composites was investigated. Compared with monolithic alumina, the flexural strength of both composites increased when the dispersed particle size was small. The fracture toughness of Al2O3/SiC composites increased with a decrease in particle size. However, a maximum fracture toughness was observed for Al2O3/TiC composites when the particle size was 4-6μm. These results are explained as follows. The increase in fracture toughness is caused by microcracks originated by thermal expansion mismatch between the matrix and the dispersed particle. In the case where the thermal expansion mismatch and the size of dispersion particles are both large, cracks develop spontaneously during cooling, releasing thermal stress, and thus hindering the operation of the microcracking mechanism that would increase the fracture toughness of the composites. It is concluded that each system has a suitable size of dispersed particles. On the other hand, the increase in strength is caused by the increase in fracture toughness and by the decrease in the length of pre-existing flaws due to suppression of abnormal grain growth of the matrix.