Oxidation behavior and failure mechanism of NiCoCrAl eutectic multi-principal element alloys co-doped with Y and Hf at 1100 °C and 1200 °C

This study investigates the oxidation behavior of Y/Hf co-doped NiCoCrAl-type EMPEAs with various Co and Cr concentrations (Ni_59.6Co₁₀Cr₁₀Al_20.4, Ni_50.7Co₁₅Cr₁₅Al_19.3 and Ni_33.4Co₂₅Cr₂₅Al_16.6 in at%) at 1100 °C and 1200 °C. After oxidation at 1100 °C, increasing Co and Cr contents enhances Y/Hf solubility in the β phase, which delays the θ- to α-Al₂O₃ phase transformation and promotes the formation of larger columnar grains of α-Al₂O₃ scale, thereby reducing the oxidation rate by up to 62 %. After oxidation at 1200 °C, the NiCoCrAl-type EMPEAs with higher Co and Cr content show significantly better spallation resistance due to the reduction of the coefficient of thermal expansion (CTE) and Y/Hf solubility in the γ phase. This reduction minimizes residual stress in the oxide scale and decreases the tendency for oxide intrusion at the scale/alloy interface, thereby enhancing the interfacial fracture energy. These findings provide scientific guidance for optimizing the composition of NiCoCrAl EMPEAs to enhance oxidation resistance in high-temperature applications. © 2025 Elsevier Ltd.