Microstructural design and 1100 °C oxidation resistance of a multiphase high entropy alloy

This study addresses the dual requirements of lightweight and high-temperature oxidation resistance for aircraft engine hot-end components. A multi phase, multi scale high-entropy alloy (HEA) in the NiCoFeCrAlMo system was designed by benchmarking GH4169, achieving a density of only 7.55 g/cm 3 . Its microstructure is based on an interdendritic(ID) FCC/intradendritic(DR) B2 dual-matrix skeleton combined with multi scale precipitates of Laves phase and MC type carbides. It shows excellent oxidation resistance at 1100 °C, with steady-state oxidation kinetics following a sub-parabolic law. The primary oxidation-resistance mechanisms involve the formation of an Al 2 O 3 -based composite protective scale, together with element redistribution and interfacial reconstruction induced by the B2 → FCC phase transformation. MC decomposition, Laves-phase evolution, and the formation of nanoscale (Ti,Nb)O 2 serve as secondary synergistic factors, promoting local oxide-scale densification and increasing the tortuosity of oxygen diffusion paths. In addition, the refinement of B2 grains to 17.3 ± 3.3 μm and the reconstruction of FCC grain boundaries reflect the adjustment of grain-boundary networks during high-temperature oxidation. Together with the Al 2 O 3 -dominated protective scale and the auxiliary densification effect of nanoscale (Ti,Nb)O 2 , these microstructural responses contribute to improved interfacial stability between the oxide scale and the alloy matrix.