Unraveling the Superior High-Temperature Oxidation Behavior of FeNiCuAl-Based High-Entropy Alloys: Roles of Cr, Co, and Mn Alloying Additions

This study proposes a novel synergistic design strategy to enhance the oxidation resistance of FeNiCuAl-based high-entropy alloys by integrating multi-element alloying (Cr-Co-Mn), trace Y modification, and laser-cladding-induced nanocrystallization. While the Base Alloy exhibited a mass gain of approximately 15 mg/cm2 after oxidation at 900 °C for 120 h, the addition of Cr2.5Co2.5Mn2.5 promoted the formation of a multilayered oxide scale (outer MnCr2O4/inner Al2O3), reducing the parabolic oxidation rate constant to 1.7 × 10−5 mg2·cm−4·s−1. The originality of this work lies in the coupling of compositional and microstructural engineering; further addition of 0.5 at.% Y decreased this constant to 1.7 × 10−6 mg2·cm−4·s−1—a three-order-of-magnitude reduction relative to the Base Alloy, while increasing the apparent oxidation activation energy to ~350 kJ/mol. After 100 thermal cycles at 1000 °C, the designed alloy showed a mass change of only 0.05 ± 0.02 mg/cm2, with its critical load and interfacial fracture energy reaching 78 N and 14.8 J/m2, respectively. Furthermore, the alloy retained a hardness of 310 HV, an elastic modulus of 135 GPa, and a tensile strength of 240 MPa at elevated temperature. These results demonstrate that the synergistic integration of chemical and structural optimization provides a new paradigm for designing low-cost, high-performance FeNiCuAl-based protective coatings.