In-situ nanocrystalline oxide formation in zirconium carbide ultra-high temperature ceramic under oxygen scarcity

Zirconium carbide exhibits remarkable thermal and mechanical resilience, making it a leading candidate for extreme applications. While its oxidation in oxygen-rich environments has been extensively studied, its behavior in oxygen-limited environments remains largely unexplored. To our knowledge, we present one of the first comprehensive in-situ study of ZrC under vacuum (5 × 10 –2 Pa) over 400–800 °C, systematically tracking phase evolution under different isothermal and cooling temperatures. A nanocrystalline zirconia–carbon composite layer forms, producing a single-layer scale distinct from double-layer structure observed in high oxygen pressures. We also observe phase transformation in vacuum-grown scale upon cooling at approximately 400 °C, far below the transformation temperature of undoped bulk zirconia. These results reveal that oxygen-deficient environments do not fully inhibit oxidation at high temperatures. This study advances the mechanistic understanding of ZrC oxidation under oxygen-scarce environments, offering new insights into ZrC surface chemistry and its thermally grown oxide behavior.