The equiatomic CoCrFeMnNi alloy and the equiatomic quaternary alloys with no addition of one element of the CoCrFeMnNi alloy were fabricated, and the roles of the alloying elements in corrosion resistance were clarified. In 1M H2SO4, the passivity of the CoCrFeMnNi alloy was mainly due to Cr. The Co and Fe additions also contributed the decrease in the passivity current density. While Ni addition was found to suppress active dissolution, Mn addition increased the active dissolution rate. The quaternary alloy without Mn indicated superior pitting corrosion resistance in 0.1M NaCl. To improve the corrosion resistance of the CoCrFeMnNi alloy, Mn was replaced with Mo, and the effect of the Mo content on the pitting corrosion resistance and the role of Co addition were assessed in 1M HCl.
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