Creep and creep-recovery behavior in silicon-carbide-particle-reinforced alumina

Flexure creep and creep-recovery behavior were investigated for monolithic Al₂O₃ and 10-vol%-SiC-particle-reinforced Al₂O₃-matrix composites in an air atmosphere at temperatures of 1160°-1400 °C. Two types of SiC particles were used: one has an average size of 2.7 μm and has an amount of SiO₂ impurities per unit surface area that is one order of magnitude higher than the other, which has an average size of 0.6 μm. Compared to the creep behavior of monolithic Al₂O₃, the strain rate of the composites with the 0.6 μm SiC particles (denoted here as S-10) did not decrease; the composites with the 2.7 μm SiC particles (denoted here as L-10) exhibited excellent creep resistance. This difference was related to the microstructural features and the oxidation behavior of the composites: the Al₂O₃ grains in S-10 were mainly equiaxed, only approximately 10% of the Al₂O₃ grains were elongated, and most of the SiC particles that resided at the grain boundaries or at triple-grain junctions were oxidized during creep, whereas the Al₂O₃ grains in L-10 were mostly irregularly shaped and elongated and most of the SiC particles were entrapped in the Al₂O₃ matrix grains, which prevented the oxidation of the SiC particles. These different microstructural features were associated with different amounts of SiO₂ impurity content per unit surface area on the SiC particle surfaces. In addition, the monolithic Al₂O₃ showed no anelastic recovery when the load was removed; however, the composites exhibited significant anelastic recovery, especially for L-10. This phenomenon was attributed to the elongated grain morphology.