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

Aluminum oxide is introduced into SiCf/(SiC + B4C) composites to improve the surface cracking resistance after oxidizing at 1100 degrees C in O-2/H2O (40/60) atmosphere. Research on morphology observation of oxidized composites reveals that Al2O3 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 Al2O3 can improve the surface cracking resistance after oxidizing at 1100 degrees C in O-2/H2O (40/60) atmosphere since the retention rates of sigma(min) (first acoustic emission [AE] stress) and sigma(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.