Fabrication and property of novel double-layer coating deposited on polyimide matrix composites by atmospheric plasma spraying

Thermal shock resistance of double-layer Al/Nd2Zr2O7 coating plasma-sprayed on the polymer substrate was optimized and its oxidation resistant property was evaluated. During thermal shock test at 723 K, thermal cycling lifetime of coating was prolonged by decreasing Al layer thickness or increasing Nd2Zr2O7 layer thickness. Relatively, the A45N225 coating with 45 µm Al layer and 225 µm Nd2Zr2O7 layer exhibited the best thermal shock resistance. Based on the microstructure evolution, coating failure was mainly attributed to the appearance of delamination at the substrate/Al interface or the formation of microcracks in the coating, resulted from stress accumulation and substrate oxidation during thermal cycling. After oxidation at 723 K for 22 h, with the protection of A45N225 double-layer coating, the weight loss of specimen reduced from 33.96 wt% to 5.31 wt%, and the corresponding weight loss per unit decreased from 90.58 mg cm−2 to 15.47 mg cm−2. However, at the later stage of oxidation, heat transfer and oxygen diffusion through the micro-defects of coating might lead to the oxidation of part resins.