Microstructure and flexure creep behaviour of SiC-particle reinforced Al2O3 matrix composites

The flexure creep behaviour of monolithic Al2O3 and 10 vol% SiC-particle reinforced Al2O3 matrix composites was investigated in air atmosphere at 1160 to 1400 degrees C and under a stress of 40 to 125 MPa. Two kinds of SiC particles with different particle sizes and oxygen contents were used in the composites, one having an average size of 0.6 mu m with 1.7 vol% SiO2 impurities and the other of average size 2.7 mu m with 3.4 vol% SiO2 impurities. Compared with the creep behaviour of monolithic Al2O3 the strain rate of the composites with 0.6 mu m SiC particles did not decrease; however, the composites with 2.7 mu m SiC particles exhibited excellent creep resistance. Microstructure analysis showed that the Al2O3 grains in the composites with 0.6 mu m particles were mainly equiaxed with most of the SiC particles lying at the grain boundaries or triple-grain junctions, whereas the grain features of the composites with 2.7 mu m SiC particles were irregular and elongated into Al2O3 matrix grains. It was revealed that the entrapment of 2.7 mu m SiC particles into Al2O3 matrix grains was related to the high SiO2 impurity content on SiC particle surfaces, and the change of grain morphology and the good high-temperature oxidation resistance were responsible for the creep resistance increase of the composites with 2.7 mu m SiC particles. (C) 1996 Elsevier Science Limited