Effect of Iron Content on the Pitting Corrosion Behavior of Laser-Cladded Ni-Cr-Mo Alloy Coating in a Simulated Seawater Environment

Abstract

In order to study the effect of iron content on the pitting corrosion behavior of a Ni-Cr-Mo alloy coating in a simulated seawater environment, a Ni-Cr-Mo-xFe (x = 0, 5, 10, 15, 20, 25) alloy coating was prepared through laser cladding technology. These coatings primarily consist of a γ-Ni solid solution phase, with observable iron segregation in the interdendritic regions when the iron content reaches 25 wt%. After 42 days of salt spray corrosion, it was found that pitting began to appear on the surface when the iron content in the coating increased to 10 wt%. The results of electrochemical behavior revealed that the coatings with iron contents in a range of 10–25 wt% exhibited metastable pitting characteristics, and the impedance modulus decreased with the increase in iron content. Pitting corrosion occurs due to selective corrosion of the dendritic regions. When the iron content exceeds 10 wt%, the accumulation of iron in the outer layer of the passivation film would lead to an excess of cationic vacancies, and the stability of the passive film is then reduced. This study provides a reference for the control of the iron content in a Ni-Cr-Mo alloy coating when applied in marine environments.