Abstract: Al₂O₃ scale-forming materials are highly desirable for high-temperature oxidation resistance, and the formation of α-Al₂O₃ scales with low-angle grain boundaries (LAGBs) will increase their service lifetime. However, the synthesis of LAGBs is a considerable challenge. Herein, a novel methodology for engineering in situ α-Al₂O₃ with LAGBs is designed, capitalizing on preferential nucleation. This approach employs a dual-stage preoxidation process, initiating with the selective nucleation of α-Al₂O₃ under extremely low oxygen partial pressures, followed by the growth of these nuclei into a dense, protective oxide layer under marginally higher oxygen partial pressures. Based on this method, an α-Al₂O₃ film with LAGBs is finally obtained, which significantly improves the oxidation resistance. This study not only paves the way for advanced materials to improve durability in high-temperature environments but also provides novel insight into the mechanisms of α-Al₂O₃ film formation and growth under controlled oxidative conditions.

Key words: High-temperature oxidation, Low-angle grain boundaries, α-Al₂O₃ scale, Preoxidation