Electrochemical Impedance Spectroscopy Investigation of Alloy Inconel 718 in Molten Salts at High Temperature

Abstract

The corrosion behavior in molten salts of Inconel 718 (IN 718) superalloy was investigated by Electrochemical Impedance Spectroscopy (EIS). The corrosion test temperatures used were salt melting points of Na2SO4, 80V2O5-20Na2SO4, NaVO3 and natural ash (collected in a power plant). Different experimental runs were made attempting to establish the material behavior. The results showed that the corrosion process was controlled by activation and in some cases by diffusion. The aggressiveness of the salts increased with temperature, as indicated for the corrosion rates values derived. On the whole, the corrosion rates were somewhat similar at the lowest test temperatures. However at 588°C the 80V2O5-20Na2SO4 salt showed a much higher corrosion rate than that recorded for Na2SO4 or natural ash. The results obtained from electrochemical measurements correlated well with those corrosion degradation observed by SEM, and comments on the behavior found are made.