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.