Twin Toughening‐Driven Martensitic Transformation Strategy Synergistic Improvement for Plasticity‐Thermal Shock Resistance of (Hf─Zr─Ti)C Ceramic Coating in Severe Thermal Environments

The inherent brittleness and insufficient thermal shock resistance of ultra-high temperature ceramic (UHTC) in severe thermal environments (above 2000 °C) remain significant challenges. This characteristic notably shortens their operational lifespan as thermal protective coatings on structural composites in reusable aerospace applications. To address these challenges, a "ceramic self-toughening strategy" is introduced, aimed at enhancing the plasticity and thermal shock resistance of (Hf─Zr─Ti)C coatings through twin toughening-driven martensitic transformations in the oxide scale. In this work, the oxidation of (Hf_1/2Zr_1/4Ti_1/4)C and (Hf_1/4Zr_1/2Ti_1/4)C coatings produced Ti-doped (Hf_2/3Zr_1/3)O₂ and Ti-doped (Hf_1/3Zr_2/3)O₂, with martensitic transformations initiated by "slip band-twin transfer" and "stacking fault-twin transfer", respectively. The mechanism facilitated the formation of stable, dense, and high-toughness oxide scales after repeat ablation, and then endowed the prepared coatings with superior repeat ablation resistance than current thermal protective coatings. The findings elucidated the role of martensitic transformation mechanisms of Ti-doped (Hf, Zr)O₂ during repeat ablation, and provided general design guidelines for synergistically controlling the component, microstructure, toughness, and thermal shock resistance of UHTC blocks and UHTC-modified composites in severe thermal environments.