Microstructure and corrosion behavior of Fe-based amorphous composite coatings developed by atmospheric plasma spraying

Fe based metallic glass composite coatings with composition of Fe-2.5Cr-6.7Si-2.5B-0.7C (wt%) were deposited by atmospheric plasma spraying onto mild steel substrate under optimum spraying conditions with selected variation in heat input. The effect of spraying power on the microstructure, phase composition, hardness and corrosion behavior of the coatings were systematically investigated. The corrosion behavior of the coatings was studied by potentiodynamic polarization test in simulated sea water containing 3.5% NaCl solution. The corrosion resistance of the coating decreased with increasing plasma power, which is attributed to the decrease in amorphous content and formation of nanocrystalline phases at elevated plasma power. Nanoindentation was carried out for qualitative investigation of the effect of heat input on the transformation of relative fraction of different phases and subsequently on the nanohardness of the coatings. The values of nanohardness increased to similar to 12 GPa at higher plasma power as percentage of amorphous content decreased from 93% to 89% and amount of hard intermetallic nanoparticles increased. However, this resulted in increase in corrosion rate i.e. corrosion current density from 17.4 to 69 mu A/cm(2). The study revealed that low porosity, high hardness and superior corrosion resistance were observed for the plasma sprayed coatings. (C) 2019 Elsevier B.V. All rights reserved.