Microstructure evolution and corrosion mechanism of laser cladded Zr-Cu-Ni-Al in-situ metallic glass matrix composite coatings

Laser cladding provides a widely applicable method for the preparation of metallic glass matrix composite (MGMC) coatings, where the mechanical property and the corrosion resistance can be tailored by the in-suit precipitated crystalline phases. Thus, the investigation on the microstructure evolution and corrosion mechanism of MGMC coating to achieve superior performance is of great importance. In the presented work, Zr50.7Cu28Ni9Al12.3 MGMC coatings, which are constituted by Zr&Cu enriched dendrites and Ni&Al enriched metallic glass (MG) matrix, were prepared by laser cladding. The effect of the laser power on the microstructure and the corrosion property of the MGMC coatings was investigated. It has been found that the MG content increases and the size of the dendrites decreases with decreasing laser power. Increasing MG content in the coating can decrease the self-etching current density due to the rapid surface oxidation, and decrease the open-circuit-potential due to the higher chemical activity of MG. Besides that, a probable corrosion mechanism of the Zr-Cu-Ni-Al MGMC coating in the NaCl solution was proposed. The segregation of Cu could be the main inducement for pitting. The increasing MG phase content can suppress the segregation of Cu and therefore increase the pitting corrosion resistance of the coating.