Oxidation behavior and cracking evolution of atmospheric plasma spraying Si and 60Si-40HfO₂ bond coats at 1400 °C

The pure Si and 60Si-40HfO₂ bond coats were prepared by atmospheric plasma spraying (APS) on the SiC substrate, and the oxidation resistance and cracking evolution were researched at 1400 °C. The thickness of part of the Si bond coat reduces to 10–30 μm after oxidation at 1400 °C for 100 h due to the softening of Si and the exfoliation caused by the CTE mismatch. On the 60Si-40HfO₂ bond coat, the oxidation product SiO₂ reacted with HfO₂ to form a dense HfO₂/HfSiO₄ mixtures layer. The Hf-rich phases aggregate and connects to form the HfO₂ framework, increasing the diffusion channel of oxygen, and the thickness of thermally grown oxide reaches ∼50 μm after oxidation for 100 h. Despite not achieving the expected oxidation resistance, the formation of dispersed Hf-rich phases substantially improves the toughness of the 60Si-40HfO₂ bond coat and effectively prevents the bond coat from exfoliation.