Use of Anodic Polarization in Fused Na₂SO₄ for Estimating Hot Corrosion Rates

A technique based on potentiokinetic anodic polarization in fused Na₂SO₄ has been developed for the purpose of estimating the hot corrosion resistance of Ni- and Co-base superalloys. Because it is relatively fast, this technique has been used to preliminarily identify promising candidate alloys, which may then be further evaluated in a conventional burner rig apparatus. An empirical correlation has been established between values of log i_corr from the electrochemical test and penetration rates from the burner rig test. In a further use of the electrochemical test, corrosion rates of IN-738 were determined in several Na₂SO₄ melts which encompassed a range of acidities. Both basic and acidic melts produced considerably higher corrosion rates than were found in neutral (reagent grade) salt.