Crack-healing behavior of Al2O3/SiC composite

Al₂O₃/SiC composite was prepared at 1700°C by the hot-press sintering method, using Al₂O₃ and SiC powders as the raw materials. The composite was mechanically whittled with the different thicknesses for the bending strength test. The results exhibited that the bending strength decreased as the whittled thickness increasing. The SEM observations revealed more cracks appeared on the surface of the sample as the whittled thickness increasing. Then, the sample whittled with the thicknesses of 20μm was sintered at 1200°C for certain time to have a further insight into the effect of the sintering time on the microstructure and mechanical property in this study. It could be found that, after sintered at 1200°C for 60min, the maximum of the bending strength for Al₂O₃/SiC composite was obtained, reaching 343.88MPa. XRD and SEM results suggested that the crack-healing mechanism of Al₂O₃/SiC composite was mainly due to the oxidation of SiC when the composite was sintered in air. The oxidation reaction could be described as follows: SiC+2O₂→SiO₂+CO₂ (CO). The generated SiO₂ filled up the cracks, which made the cracks healed and the strength restored.