Y/Sc Co-Doping Enhances Cyclic Oxidation Resistance of AlCoCrFeNi High-Entropy Alloy via Improved Scale Adhesion and Spallation Resistance

This study details the developmenty of a Y and Sc co-doped AlCoCrFeNi HEA with 0.05 at.% of each dopant (designated YSc-0.05), which exhibits exceptional oxidation and spallation resistance during 100 h of cyclic oxidation at 1100 °C (20 cycles, each consisting of 5 h isothermal heating followed by forced air cooling to room temperature within 10 min). Y and Sc co-doping significantly decreases the specific weight change, reducing it from approximately 3.39 mg/cm² for the unmodified AlCoCrFeNi (YSc-0) to 0.56 mg/cm² for YSc-0.05, a reduction of over 80%. This improvement is attributed to the enhanced spallation resistance of YSc-0.05 during cyclic oxidation, which is driven by a lower driving force for oxide scale spallation and improved scale adhesion (as evidenced by greater resistance to indentation‑induced delamination) compared to YSc-0. These findings highlight a promising strategy for designing advanced HEAs with superior oxidation and spallation resistance, although the specific doping level of 0.05 at.% Y and 0.05 at.% Sc serves as a proof-of-concept demonstration rather than an optimized composition.