Initial damage behavior of Al 2 O 3 ‐modified SiC f /SiC–B 4 C composites after oxidation under wet atmosphere at 1200°C

Abstract Al 2 O 3 was incorporated into SiCf/SiC–B4C composites to improve their mechanical properties after oxidation. The results showed that Al 2 O 3 reduced the weight gain of these composites, and the oxidized layer became smooth and dense. The fibers pull‐out lengths of the Al 2 O 3 ‐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 Al 2 O 3 ‐modified composites was improved by 7.3% and 8.4% after oxidation times of 50 and 100 h, respectively. But Al 2 O 3 modification led to 20.6% and 44.3% improvements in σ onset (acoustic emission, AE onset stress) as well as 76.5% and 95.5% the improvements in σ min (first AE stress), respectively. Further investigation indicated that a higher proportion of high‐energy level events occurred in the Al 2 O 3 ‐modified composites when the load just reached the damage thresholds stress compared with the virgin composites.