Microstructure and corrosion behavior of different clad zones in multi-track Ni-based laser-clad coating

Abstract

In order to realize the application of large-area laser-clad coatings, the overlap of individual laser tracks is required. However, the feature of the overlap zone (C1) is different from non-overlap zone (C2) in multi-track laser-clad coating ascribed to the secondary thermal effect of the laser beam. Microstructural analysis showed that the coarse columnar structure and uniform cellular structure were found in C1 and C2, respectively. Meanwhile, the secondary thermal effect caused C1 a higher content of Fe diffused from the carbon steel substrate than C2. Electrochemical analysis displayed that C2 had a higher polarization resistance, a lower and more stable current density at under passive potential, and a lower donor density than C1. The corrosion morphology and elemental valence states analysis showed that C1 presented more serious inter-phase corrosion than C2 because of the higher elemental change between primary and eutectic phases. Meanwhile, C2 owned denser passive film than C1 considering higher contents of metallic oxidation states on the surface.