Influence of SiC whisker and AlPO₄ particle on the resistance for bi-layer mullite/SiC coating in burner rig tests

To increase the oxidation resistance of the mullite coating in high-temperature and high-speed gas scour environments in burner rig tests, bi-layer mullite/SiC, (SiC_w-mullite)/SiC, and (SiC_w-AlPO₄-mullite)/SiC coatings were prepared on the surface of carbon fiber-reinforced SiC (C_f/SiC) ceramic matrix composites. The results revealed that the weight loss of the bi-layer mullite/SiC coating-coated sample reached 38.49×10⁻³ g/cm² after 16 cycles (240 min). After adding SiC whiskers to the mullite outer coating, the weight loss of the bilayer (SiC_w-mullite)/SiC coating-coated samples decreased to 14.09×10⁻³ g/cm² owing to the toughening effect of the SiC whiskers. After further addition of the AlPO₄ particles to the SiC_w-mullite outer coating, the weight loss of the bilayer (SiC_w-AlPO₄-mullite)/SiC coating-coated samples was only 5.59×10⁻³ g/cm², which was much lower than the weight loss of the bilayer (SiC_w-mullite)/SiC coating-coated samples, indicating that the AlPO₄ particles can further prevent the formation of cracks and reduce the weight loss of the coating sample owing to its adhesive performance in high-temperature environments.