The Effect of Water Vapor on Oxidation Performance of Alloys Used in Recuperators

The use of a recuperator to recover waste heat from the exhaust gases is one method for improving a microturbine’s energy efficiency. This study looked at the effect of water vapor in the exhaust gas on the oxidation resistance of a current technology stainless steel and several high performance replacement alloys. Alloys of interest are high-Cr, Ni-base superalloys such as alloy 625 and aluminum-containing alloys such as Haynes alloy 214 and Plansee alloy PM2000, which is an oxide-dispersed FeCrAl. The latter two alloys form a protective external alumina scale which is more resistant to water vapor environments than chromia scales. Scanning and transmission electron microscopy characterization of the specimen surface oxides after laboratory exposures showed only minor effects of the addition of water vapor to the environment, which is consistent with the excellent corrosion resistance of these high performance alloys.