Effect of Compositional Trade-off Between Cr and Mo on the Corrosion Resistance of Additively Manufactured Co-Cr-Fe-Ni-Mo High-Entropy Alloys

In this study, the corrosion behavior of Co-Cr-Fe-Ni-Mo high-entropy alloys additively manufactured via direct energy deposition was investigated according to the compositional trade-off between Cr and Mo elements. Two distinct alloy compositions were fabricated by adjusting the feeding rate of two powders with different chemical compositions through a dual nozzle. Electrochemical testing in a 3.5 wt% NaCl solution revealed that the Cr-rich and Mo-lean alloy exhibited inferior corrosion resistance compared to the Cr-lean and Mo-rich alloy. Specifically, the corrosion potential of the Cr-rich and Mo-lean alloy shifted negatively by approximately 200 mV compared to the Cr-lean and Mo-rich alloy, accompanied by an increase in corrosion current density and the pronounced initiation of localized pitting. This deterioration is attributed to a lack of passivation caused by the small amount of Mo in the Cr-rich and Mo-lean alloy. The passive film of the Cr-lean and Mo-rich alloy was more robust, characterized by a higher concentration of Mo, which effectively inhibited pit propagation through repassivation. These findings demonstrate that maintaining a critical Cr-Mo balance is more vital for the electrochemical stability of additively manufactured high-entropy alloys than unilateral Cr enrichment.