Effect of alumina coatings on corrosion behavior of X10CrAlSi7 steel in sulfuric acid

Abstract

The results of experimental studies of the effect of the plasma sprayed alumina coating on the improved corrosion resistance of the heat-resistant ferritic stainless steel (W.Nr. 1.4713, EN X10CrAlSi7) in the sulfuric acid are presented in this research. In this investigation, the plasma spray process was employed on the substrate of ferritic stainless steel with deposition of Al2O3 ceramic coatings with Ni5%Al as a bond layer. Two different coating thicknesses of 0.3 mm and 0.5 mm were tested. The investigation was performed by electrochemical characterization and weight loss method. Electrochemical characterization of corrosion behavior of steel with and without ceramic coating was performed by: the open circuit potential measurement (OCP), the linear polarization resistance (LRP) method, and the Tafel extrapolation method. All electrochemical measurements were performed in the sulfuric acid with a concentration of 0.25 mol/dm3 (pH  1.00). Weight loss method was performed with a duration of 240 h in the 38 wt.% sulfuric acid. Corrosion current densities obtained by electrochemical methods with the coatings were between 3 and 4 % of the values of the samples without coatings. Nearly the same results were obtained with the weight loss method. In both cases, these values are similar to the porosity of the coatings.