High Temperature Corrosion of 625 Supperalloy under Iron-Zinc-Lead Oxide / Sulfate / Chloride Salt Mixtures

摘要

The corrosion resistance and degradation mechanisms of 625 supperalloy at 800 °C under three molten salt compositions containing PbSO4, PbO, PbCl, ZnO, Fe2O3 and CdO in air atmosphere were studied. The concentrations of Fe2O3 and CdO were varied to evaluate the effect of these compounds on the corrosion reaction. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization technique were applied to evaluate the degradation mechanisms and corrosion properties of the alloy. Corrosion products and surface layer of the corroded specimens were studied by SEM/EDX and X-ray map analyses. Electrochemical evaluation confirmed that increasing the concentration of CdO in the molten phase could increase the corrosion rate of the alloy and in this condition the corrosion phenomena occurred under the control of charge transfer effect. The presence of a Cr-depleted layer on the surface of the alloy was the reason for the formation of an internally attacked area at the alloy/oxide interface.