Zirconium carbide (ZrC) is an ultra-high-temperature ceramic valued for its excellent thermomechanical properties, yet its vulnerability to oxidation and its thermal shock behavior upon oxidation remain insufficiently understood. This study examines how prior oxidation history, defined by cyclic exposure temperature and duration, affects the thermal shock response of monolithic ZrC. Near-stoichiometric specimens were oxidized in atmospheric air across a temperature range of 600°C–800°C, then water-quenched from those temperatures. Increasing oxidation severity produced thicker oxide scales, higher monoclinic ZrO₂ content, and greater crack density. A transition to failure-prone behavior occurred between 700°C and 800°C, when monoclinic ZrO₂ and crack density both exceeded approximately 10%, leading to critical degradation. Given the oxidation parameters explored, the temperature threshold for thermal shock occurrence was identified as 700°C–800°C. The combined oxidation–quench approach establishes oxidation-dependent thresholds for thermal shock resistance and provides a framework for evaluating the stability of oxidized structures in harsh thermal environments. ... Read more

Zirconium carbide (ZrC) is a promising ultra-high-temperature ceramic (UHTC) for thermal protection systems (TPS) due to its high melting point, thermal stability, and mechanical strength. However, its susceptibility to oxidative degradation and limited thermal shock resistance poses challenges for aerospace applications. This thesis investigates how prior oxidation history (defined by exposure temperature and duration) influences the thermal shock response of the zirconia oxide scale on monolithic ZrC. Samples were oxidized at 600°C, 700°C, and 800°C for varying durations, followed by thermal shock via water quenching. Post-exposure analysis using X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), and mass change measurements showed that increasing oxidation severity leads to thicker, brittle oxide scales with higher monoclinic ZrO2 content and elevated crack densities. A transition to failure-prone behavior occurs between 700°C and 800°C, with failure thresholds defined by a ≥10% surface crack density and monoclinic ZrO2 content exceeding 10%. These results establish oxidation-dependent limits for ZrC’s thermal shock resistance.
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