Oxidation-Sulfidation Behavior of Ni-Base Superalloys and MCrAl Coatings

摘要

The oxidation-sulfidation behavior of several nickel-base superalloys and a number of MCrAl coatings on an IN 738 substrate have been examined after exposure to ten different oxygen-sulfur mixed-gas environments. Selected alloys have been tested in a thermogravimetric system in which the weight change of the specimens was continuously monitored. Extensive metallurgical analyses of the exposed specimens were performed and the results were used to develop generalized maps that depict the corrosion product morphologies as a function of the exposure environment. The results, in general, showed that nickel-base superalloys are susceptible to sulfidation attack and undergo breakaway corrosion in low-oxygen environments that contained sulfur. Of several MCrAl coatings that were tested, CoCrAlY and NiCoCrAlY compositions showed superior sulfidation resistance over a wide range of sulfur partial pressures at the test temperatures of 1144 and 923 K. Other MCrAl coatings examined in this study showed promise at low to intermediate sulfur partial pressures. (ERA citation 12:004254)