Initial damage behavior of Al2O3-modified SiCf/SiC-B4C composites after oxidation under wet atmosphere at 1200°C

Al2O3 was incorporated into SiCf/SiC-B4C composites to improve their mechanical properties after oxidation. The results showed that Al2O3 reduced the weight gain of these composites, and the oxidized layer became smooth and dense. The fibers pull-out lengths of the Al2O3-modified composites were longer than that of virgin composites oxidized for the same amount of time. Compared with the virgin composites, the tensile strength retention rate of Al2O3-modified composites was improved by 7.3% and 8.4% after oxidation times of 50 and 100 h, respectively. But Al2O3 modification led to 20.6% and 44.3% improvements in sigma(onset) (acoustic emission, AE onset stress) as well as 76.5% and 95.5% the improvements in sigma(min) (first AE stress), respectively. Further investigation indicated that a higher proportion of high-energy level events occurred in the Al2O3-modified composites when the load just reached the damage thresholds stress compared with the virgin composites.