Microstructure and corrosion behavior of Co-free FeCrNiSi0.4 medium entropy alloy coating fabricated by laser cladding

To improve the performances of engineering components is a hot topic for materials science and engineering communities. In the present work, the Co-free FeCrNiSi0.4 medium entropy alloy (MEA) coating was manufactured onto a Q235 steel substrate using laser cladding. Then, the microstructure, hardness and corrosion resistance of the MEA coating were carefully examined. The results indicate that the MEA coating, without obvious cracks and pores, exhibits a duplex phase microstructure consisting of majority face-centered cubic (FCC) phase and minor hexagonal close-packed (HCP) phase. In 3.5 wt% NaCl solution, the MEA coating displays superior corrosion resistance with a pitting potential of 1.19 V (vs. SCE), which is much higher than that of 304 stainless steel. The remarkable anti-corrosion performance can be attributed to the multiple kinds of oxidation (NiO, Fe2O3, Cr2O3 and SiOx (x < 2)) formed on the passive film and the small difference of Volta potential (similar to 40 mV) between FCC phase and HCP phase. Moreover, the microhardness of the coating reaches 346 HV, which is 2.1 times higher than that of the Q235 steel. These findings offer an effective route to fabricate a MEA coating with superior corrosion resistance and mechanical property, which thus can improve the service stability of industrial components.