Hall-Petch relationship and corrosion behavior of cold-rolled CoNiFe medium entropy alloy

CoNiFe medium entropy alloy samples are synthesized by vacuum arc melting and subsequent thermo-mechanical processing. The fully-recrystallized face-centered-cubic (FCC) single phase microstructures with grain sizes ranging from 10 to 100 μm are obtained by annealing processes and the grain growth kinetics and Hall-Petch relationship are investigated. The activation energy for grain growth is 153.9 kJ mol−1 and the recrystallized sample processed at 700 °C possesses superior mechanical properties including high strength and ductility. The lattice friction stress is 168.4 MPa which is larger than that of the CoNiCrFeMn high entropy but less than that of the CoNiCr medium entropy alloy. In addition, in order to investigate the effect of solution temperature on corrosion behaviors of CoNiFe MEA, electrochemical tests in NaCl/H2SO4 solution with different temperature are carried out. The electrochemical experiments show corrosion current density increases and corrosion potential decreases, indicating the corrosion resistance of CoNiFe MEAs in NaCl and H2SO4 solution is weaken with increasing solution temperature.