Microstructural Impacts on the Oxidation of Multi-Principal Element Alloys

The impacts of thermal treatment on the precipitate morphology and oxidation behavior of a dual-phase (FCC + L1₂) multi-principal element alloy (MPEA), Ni₄₅Co₁₇Cr₁₄Fe₁₂Al₇Ti₅, was studied at 1000 °C via isothermal and cyclic testing. Thermogravimetric analysis and subsequent characterization revealed that smaller precipitates had an increased capacity to form protective sub-surface oxide layers which mitigated total mass gain. The smaller-precipitate-containing samples exhibited a decrease in thickness of the primary Cr₂O₃ scale and parabolic growth rate. Mechanistically this behavior is believed to stem from the increased growth rate of initial Al₂O₃ nuclei and decreased inter-precipitate spacing which results in faster lateral diffusion and agglomeration.