Hot corrosion of four superalloys: HA-188, S-57, IN-617, and TD-NiCrAl

Abstract

Four superalloys were subjected to cyclic oxidation and hot corrosion attack in a Mach 0.3 burner rig. Two of the alloys, HA-188 and S-57, were cobalt-base and the other two, IN-617 and TD-NiCrAl, were nickel-base. The alloys were exposed to maximum temperatures of 900 and 1000°C. For hot corrosion tests the burner rig flame was doped with various concentrations of sea salt and one concentration of sodium sulfate. Samples were evaluated based on maximum depth of attack. These data were subjected to a regression analysis for the development of model equations relating corrosion to temperature and for determining how significantly changes in salt concentration and composition affected the corrosion. The ranking of the alloys with respect to their corrosion resistance was found to vary with temperature, sea salt concentration, and salt composition. Some of the variation was attributed to changes in the mode of attack from straight oxidation to hot corrosion. Under those test conditions where the mode of attack was readily discernible S-57 was found to be the most hot corrosion-resistant alloy and TD-NiCrAl was the least resistant. This order was reversed when the attack was straight oxidation, TD-NiCrAl being the most resistant alloy and S-57 the least.