Microstructural evolution and corrosion properties of Ni-based alloy coatings fabricated by multi-layer laser cladding on cast iron

To solve the problem of brittleness at the bonding interface, the multi-layer laser cladding method was carried out to fabricate Ni-based alloy coating on the compacted graphite cast iron. The effect of dilution rate on the microstructure and corrosion behavior of the coatings were investigated. The results showed that the volume fraction and the secondary dendrite arm spacing of the dendrite increase significantly with the increasing number of the deposited layers. The dendritic phase in the coatings changed from gamma-Fe phase to gamma-(Fe, Ni) phase, and the interdendritic phase transformed from martensite phase to M7C3 (M = Fe, Cr) phase with the decrease of the dilution rate. The lattice parameter of the dendritic phase decreased gradually, as the increase of Ni content. The corrosion tests show that the coating with six deposited layers exhibited the best corrosion resistance at room temperature in 3.5% NaCl solution. The corrosion mechanism changed from severe intragranular corrosion to pitting corrosion and intergranular corrosion. According to the analysis results of electrochemical impedance spectroscopy curves, Mott-Schottky curves, and point defect model, the improvement of the corrosion resistance was attributed to the high compactness and resistance of the passive film, which provided fewer oxygen vacancies in the corrosion process due to the increase of Ni and Cr concentration of the coating. (C) 2020 Elsevier B.V. All rights reserved.