Oxidation behavior of rare earth silicide coatings fabricated by vacuum plasma spraying

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The Si bond coat in environmental barrier coatings (EBCs) exhibits a reliable temperature tolerance of approximately 1316°C, with its service life primarily constrained by cracking mechanisms caused by the phase transformation of SiO₂. In this study, two novel rare-earth silicide bond coat materials (Y-Si and Gd-Si coatings) for EBCs systems were designed. The coatings were fabricated on α-SiC substrates via vacuum plasma spraying (VPS). Cyclic oxidation tests were conducted at 1350°C for both coatings, while the temperature-bearing performance of the Y-Si coating was further evaluated at an elevated temperature of 1500°C. The oxidation kinetics and failure mechanisms of both coatings were systematically compared through comprehensive analyses of phase composition, microstructure evolution, and time-dependent mass change per unit area. The results indicate that at 1350°C, the primary phases of the two coatings undergo oxidation from GdSi 1.67 and YSi 2 to Gd 2 Si 2 O 7 and Y 2 Si 2 O 7 , respectively. The Y-Si coating demonstrates superior performance in spallation cycle life, crack propagation resistance, and thermal compatibility with the substrate compared to the Gd-Si coating, as well as a lower oxidation weight gain rate. After 4 h of oxidation at 1500°C, the Y-Si coating remains intact with the substrate, showing no cracks or spallation, indicating good high-temperature tolerance. • Gd-Si and Y-Si coatings were prepared using the VPS process. • Y-Si coating outperforms Gd-Si coating at 1350°C with lower oxidation, longer life, and better crack resistance. • Y-Si coating exhibits excellent temperature resistance at 1500°C.