In Situ Self‐Assembled “Brick‐and‐Mortar” Ceramic Coating with Exceptional Thermal Shock Resistance: Coupling Plastic Deformation Toughening and Biomimetic Self‐Healing

ABSTRACT Ultrahigh‐temperature ceramics (UHTCs) commonly act as non‐ablative coatings for advanced thermal structural materials exceeding 2000°C, while balancing their thermal‐resistant and oxygen‐barrier performance has been a long‐standing dilemma in extreme thermal protection. Herein, we designed a novel dual‐layer UHTC coating that addressed this dilemma through in situ self‐assembled “brick‐and‐mortar” oxide scales during ablation. The outer layer ((Hf 6/19 Zr 12/19 Ti 1/19 )C‐La 2 O 3 ) leveraged the plastic deformation toughening strategy to mitigate thermal shock‐induced strain, facilitated by twin and anti‐phase boundary within Ti‐doped m‐(Hf, Zr)O 2 oxide skeleton (“thermal‐resistant brick”). The inner layer ((Hf 2/7 Zr 4/7 Ti 1/7 )C‐La 2 O 3 ) not only retained a brick‐like structure, but also contained a higher Ti content, which facilitated the formation of low‐melting liquid phases (Hf, Zr)TiO 4 and La 5 Ti 5 O 17 . These phases enhanced the oxide scales’ densification and blocked the oxygen transport through ablative defects into C/C substrates (biomimetic self‐healing strategy), thus acting as the “oxygen‐barrier mortar”. Additionally, the “mortar” bound and sealed the fractured “brick”, and the “brick” pinned the “mortar”, improving the oxide scales’ thermal‐resistant and oxygen‐barrier performance. Thereby, the in situ self‐assembled “brick‐and‐mortar” oxide scales achieved the exceptional thermal shock resistance after nine 120‐s ablation cycles (totaling 1080 s), exhibiting net‐zero ablation recession with the 0.02 mg/s and 0.07 µm/s under the maximum temperature beyond 2200°C, which surpassed the few‐hundred‐second durability limit for current non‐ablative UHTC coatings. The bioinspired design concept provided significant inspiration for advanced ultrahigh‐temperature materials with excellent thermal shock resistance in extreme thermal environments.