Oxidation Behavior of CoCrFeMnNi High-Entropy Alloy Fabricated by Selective Laser Melting

The present study investigated the microstructure and oxidation behavior of the CoCrFeMnNi high-entropy alloy (HEA) prepared by selective laser melting (SLM). The microstructure of the as-built sample comprised layer-by-layer overlapping melt pools, columnar grains, and cellular structures. The melt pool boundaries (MPBs) and cellular structures disappeared, and the dislocation density decreased after annealing at 900 °C. The high-temperature oxidation behavior of the CoCrFeMnNi HEA was investigated via oxidation kinetics, morphology observation, and oxidation product analysis. The oxidation kinetics followed the parabolic law at 800 to 1000 ℃. There were three layers of oxide scale at all temperatures. At 800 to 1000 °C, the inner oxide layer was Cr2O3; the intermediate layer consisted of Cr-oxides and Mn-oxides. The outer oxide layer mainly consisted of Mn2O3 at 800 to 900 °C and Mn3O4 at 1000 °C. At 1000 °C, the fast diffusion channels provided by MPBs led to preferential oxidation in the as-built HEA. And the preferential oxidation behavior in the annealed HEA was inhibited due to the removal of MPBs by annealing. At each temperature, the annealed HEA showed relatively better oxidation resistance than the as-built sample.