High temperature oxidation behavior of low-density AlCuFeNiTi-based high entropy alloy

This study explores the high-temperature oxidation behavior of compositionally tailored non-equiatomic high-entropy alloys (HEAs): Al 30 Ni 20 Cu 15 Fe 25 Ti 10 , Al 25 Ni 25 Cu 20 Fe 25 Ti 05 , and Al 15 Ni 30 Cu 20 Fe 25 Ti 10 , subjected to isothermal oxidation at 800, 900, and 1000°C in ambient air for 100 h. This work reveals how non-equiatomic design and strategic use of Al, Ni, and Ti enhance oxidation resistance and structural stability in HEAs, an area with limited prior exploration. Detailed analysis using oxidation kinetics, SEM-EDS, EBSD, and XRD revealed that higher Al content promoted the formation of BCC structures and coarser grains. In contrast, reduced Al content promoted FCC phase formation. The average grain size decreased from 125 μm (Al 30 Ni 20 ) to 40 μm (Al 15 Ni 30 ). The oxidation kinetics followed an initial linear regime transitioning to parabolic behavior, indicating the development of protective oxide layers over time. Al 30 Ni 20 exhibited the lowest oxidation mass gain (0.04–0.36 mg/cm²) and the most stable oxide scale, attributed to the formation of a dense Al 2 O 3 layer, synergistically supported by Ti- and Ni-containing spinels. Conversely, Al 15 Ni 30 showed the highest weight gain (0.65 mg/cm² at 1000 °C), due to its less protective scale. Notably, Ni and Ti contributed to oxidation resistance by forming complex spinels, while Fe and Cu played secondary roles, affecting oxidation kinetics. • Oxidation behavior of HEAs was evaluated at 800–1000 °C for 100 h in air. • Higher Al content led to BCC/B2 structure, and superior oxidation resistance. • Grain size decreased from ~125 µm (Al30Ni20) to ~40 µm (Al 15 Ni 30 ). • Oxidation followed a two-stage (linear to parabolic) mechanism. • Dense Al 2 O 3 -rich layers formed in Al 30 Ni 20 , while mixed oxide scales in others.