Effects of Chlorate on the Hot Corrosion Behaviors of Cr0.82Al0.18N Coating Deposited on a Ti3Al Based Alloy

Cr0.82Al0.18N coating was deposited on the surface of a Ti3Al base alloy by a reactive magnetron sputtering method and the hot corrosion behaviors of this coating in Na2SO4 +25 wt% K2SO4 and Na2SO4 +25 wt% NaCl molten salt were investigated. XRD and SEM were used to analyze the phase constituents and the morphologies of the corrosion products. The results show that the sample loses its mass when corroded in sulfate and chlorate mixture molten salts while the mass increases when corroded in sulfate molten salt and the corrosion products formed in both two kinds of molten salts are mainly composed of Cr2O3 and q-Al2O3. The mass loss of the sample tested in sulfate and chlorate mixture molten salts can be explained by the easy evaporation of the chlorate molten salt and the corrosion products. The accelerated dissolution of Cr2O3 oxide scale will occur in the chlorate containing molten salt owing to the increase of the oxygen ion activity by the reaction between water vapor in the air and gas chlorine formed during the hot corrosion process. The gas chlorine will also react with the coating to form volatility metal chlorides to increase the consumption of the coating.