Microstructure and Corrosion Behavior of CoCr_xCuFeMnNi High‐Entropy Alloys Prepared by Vacuum Hot‐Pressing Sintering

Herein, CoCr_xCuFeMnNi (x = 0, 0.5, 1.0, 1.5, and 2.0, in molar ratio) high‐entropy alloys (HEAs) are prepared through vacuum hot‐pressing sintering. The influences of Cr content on the microstructure and the corrosion behavior in 3.5% NaCl solution are studied. The alloys are mainly composed of two face‐centered cubic (FCC) phases, namely, Cr–Co–Fe–Mn–Ni (or Co–Fe–Mn–Ni)‐rich FCC1 phase and Cu–Mn–Ni‐rich FCC2 phase. With the increase of Cr content, The FCC1‐phase area expands and the FCC2 phase area shrinks. In 3.5% NaCl solution, the corrosion current density (i_corr) and average corrosion rate (V_corr) of the HEAs decrease with the increase in Cr content. The i_corr and V_corr of Cr_2.0 alloy are lower at 1.87 × 10⁻⁶A cm⁻² and 0.02 mm year⁻¹, respectively. The increase of transfer resistance (R_p) and decrease of relative thickness (CPE₁⁻¹) of the passivation film indicate that the more difficult it is for ions in the corrosive medium to pass through the capacitor layer, the better the corrosion resistance of the alloy. Improvement of the corrosion resistance is mainly due to the formation of denser Cr₂O₃ passivation film and reduction of the segregation degree of Cu in the FCC2 phase.