Oxidation Behavior at 1000 °C of Low-Mn High-Cr Cantor’s HEA-Based Alloys Strengthened or Not by MC Carbides

A conventionally cast CoNiFeMn0.5Cr1.5 alloy and two versions with 0.25 C & 3.7 Ta or 0.25 C & 3.7 Hf were tested in oxidation at 1000 °C for 50 h with thermogravimetric recording of the oxidation kinetic. In all cases, the obtained mass gain curve is parabolic. The parabolic constants are much lower than the Kp previously determined for the original alloys with an equimolar base (CoNiFeMnCr). However, the post-mortem exploitation of the oxidized samples revealed analogous oxidation features on the surface and the subsurface, also with external oxide strata on the surface with different Mn and Cr contents, and rather great Mn depletion, in addition to a moderate Cr depletion, in the subsurface. Globally, the oxidation behavior is significantly better than was earlier observed for the equimolar version of these alloys.