Comparative investigation on corrosion behavior of laser cladding C22 coating, Hastelloy C22 alloy and Ti–6Al–4V alloy in simulated desulfurized flue gas condensates

Corrosion behavior of laser cladding Ni–Cr–Mo alloy C22 coating, Hastelloy C22 alloy, and Ti–6Al–4V alloy in simulated desulfurized flue gas condensates (50wt.% H2SO4, 2wt.% HCl, 1.5wt.% HNO3, and 0.2wt.% HF) at 50–70 °C were investigated by combination of immersion testing, surface analyses, and electrochemical measurements. C22 coating exhibited similar excellent corrosion resistance but higher sensitivity to localized corrosion compared to C22 alloy. TC4 alloy exhibited poorer corrosion resistance but more stable passivation. The passive film of three materials possesses similar bilayer structure consisting of an outer porous layer and an inner barrier layer. The electrochemical behavior of C22 coating and C22 alloy is predominantly controlled by the charge transfer process through the solution in the defects of the outer porous layer, while that of TC4 alloy is controlled by the combination of charge transfer processes through outer porous layer and electrochemical process within the inner layer. The increase in temperature aggravates the corrosion of three materials by facilitating the degradation of passive film and changing the surface state. The effect of NO3- and halide ions at different temperature results in the different variation of passive film properties and/or surface state on each materials.