Corrosion and electrochemical behavior of CoСrFeNiMo high-entropy alloy in acidic oxidizing and neutral chloride solutions

Corrosion and electrochemical behavior of equimolar CoCrFeNiMo high-entropy alloy in various chloride-containing solutions with different pH were investigated by electrochemical and long-term immersion tests. The microstructure and surface characterization of the HEAs were studied by X-ray diffraction and scanning electron microscopy. Based on the accelerated electrochemical tests, it is difficult to assess the effect of hydrogen peroxide on the decrease in the corrosion resistance of the HEAs. The results of immersion tests for more than 3000 h showed that the CoCrFeNiMo HEAs have excellent long-term corrosion resistance in the neutral and acidic NaCl solutions (corrosion rates – not higher than 1 μm/year). The long-term corrosion resistance decreased with the addition of 0.01 M H2O2 in the acidic solution of NaCl (corrosion rates – about 21 μm/year). The corrosion resistance significantly decreased in the presence of the strong oxidizing reagent FeCl3 (corrosion rates – about 0.26 mm/year). The SEM results showed that the (Cr, Mo)-depleted regions were mainly corroded. The phases enriched in Cr and Mo became susceptible to active corrosion in the presence of FeCl3 or under high anodic polarization in the acidic NaCl solution containing 0.01 M H2O2.