The Surface Cracking Resistance of Al2O3-Modified SiCf/SiC-B4C Composites after Cyclic Oxidation in Wet Environment

Aluminum oxide is introduced into SiC f /(SiC + B 4 C) composites to improve the surface cracking resistance after oxidizing at 1100 °C in O 2 /H 2 O (40/60) atmosphere. Research on morphology observation of oxidized composites reveals that Al 2 O 3 can lead to the formation of a dense and smooth oxidation layer, resulting in a relatively shallow oxygen penetration depth. In-depth studies on acoustic emission reveal that composites with Al 2 O 3 can improve the surface cracking resistance after oxidizing at 1100 °C in O 2 /H 2 O (40/60) atmosphere since the retention rates of σ min (first acoustic emission [AE] stress) and σ onset (AE onset stress) are significantly increased compared with virgin composites. Moreover, a small number of cumulative events and steep slope of strength–time curves at the initial stage further confirm the improvement of surface cracking resistance after oxidation.