Synergistic effect of ablative resistance of Zr <i> _x </i> Hf <i> _y </i> (YCeTi) _1‒ <i> _x </i> _‒ <i> _y </i> O _2‒ <i> _δ </i> spiral‐fiber‐toughened ZrB <sub>2</sub

Abstract Although ZrB 2 ‒SiC (ZS) ceramics have been extensively researched for reusable space vehicles, the gaseous Si‐bearing oxides are actively yielded, which limits their service for ultra‐high‐temperature applications (&gt;2000°C). In this work, medium‐entropy oxide spiral fibers (MEO sf ) with a composition of Zr 0.68 Y 0.07 Ce 0.2 Ti 0.05 O 2‒ δ (Zr 0.68 ) were developed to promote the generation of oxide scale. The MEO sf ‐ZS composites demonstrated a low ablation rate of 0.27 µm/s when exposed to ten 60 s cycles of oxyacetylene flame at 2150°C. The first‐principle calculations revealed that the MEO‐Zr 0.68 exhibited minimum lattice distortion in the ferroelastic tetragonal ( t ) phase and a highly integrated crystal orbital overlap of the Ti–O bond, which contributed the good phase stability at high temperature. The enhanced ablation resistance of MEO sf ‐ZS was ascribed to the outstanding t ‐phase stability and structural integrity of the oxide scale. The intact MEO‐glassy SiO 2 oxide scale formed by capillary resistance effect of spiral geometry finally retarded the active oxidation of SiC grains.