Oxidation Performance of CoCrCuFeMnNix High-Entropy Alloys Prepared via Vacuum Hot Pressing Sintering

CoCrCuFeMnNix (x = 0 mol, 0.5 mol, 1.0 mol, 1.5 mol, and 2.0 mol, named Ni-0, Ni-0.5, Ni-1.0, Ni-1.5, and Ni-2.0, respectively) high-entropy alloys (HEAs) were prepared using vacuum hot pressing sintering. The atmospheric oxidation behavior of the alloys was studied using a constant-temperature oxidation discontinuous weighing method. The kinetic curve of the alloys after oxidation at 800 degrees C for 50 h follows a parabolic law. A high Ni content corresponds to a small oxidation weight gain of the alloy. After 50 h of oxidation, the oxidation weight gain and oxidation rate constant K-p value of Ni-2.0 alloy are the smallest at 3.03 mg/cm(2) and 6.59 x 10(-12) g(2) cm(-4) s(-1), respectively. The outer oxide layer of the alloys is composed of loose and porous Mn-containing oxides (Mn4O3 or Mn3O2), and the dense layer is composed of continuous and dense Cr2O3. The increase in Ni content promotes the formation of NiCr2O4 oxides with a spinel structure, inhibits the formation of porous MnO, improves the thermal stability of FCC phase, and weakens the volatilization of Cr2O3, thereby improving the oxidation resistance of HEAs. The oxidation mechanism of the alloys is mainly selective oxidation, which involves the outward diffusion of metal cations and the inward permeation of oxygen ions.