Corrosion of Al2O3 Scale Forming Haynes Alloy 214 in a Molten Chloride Salt Mixture

Abstract

The effect of pre-oxidation on corrosion of Haynes Alloy 214 (Ni-Cr-Al-Fe-Y) in a binary molten KCl-MgCl₂ salt mixture was investigated. Pre-oxidation was evaluated in isolation and in combination with chemical purification of salt mixture by adding Mg metal to determine the corrosion performance relative to the "unprotected" case. Test samples were immersed in a molten chloride salt (62.5 wt.% KCl + 37.5 wt.% MgCl₂·6H₂O) at 100 h at 700°C using a horizontal tube furnace with an inert Ar carrier gas. An in-situ dehydration (thermal purification) procedure was incorporated into the heating stage. Post-exposure SEM-EDS characterization of cross-sections and surfaces was performed to elucidate the mechanism through which corrosion mitigation was achieved in each case. Pre-oxidation was found to significantly reduce corrosion, primarily through retention of a continuous physical barrier layer, originally present as Al₂O₃. Additional chemical purification reduced corrosion further, but the extent was not as dramatic.