The oxidation of MAR M247 superalloy with Na2SO4 coating

Tungsten-bearing and Al2O3-forming superalloy, MAR M247, with and without Na2SO4 coatings were oxidized in still air at 1000, 1100 and 1200 K for 4–120 h to investigate the oxidation and hot corrosion behaviors. The results showed that the deposition of Na2SO4 accelerated the oxidation of alloy at all temperatures tested. The weight losses of specimens with and without Na2SO4 coating take place due to the evaporation of tungsten oxide from alloy in the absence of protective Al2O3, Cr2O3, or other compact oxide layers. Moreover, the molten Na2SO4 causes the internal grain boundary attacks in the specimen oxidized at 1200 K by comparing the results of the tests at 1000 and 1100 K. The large content of tungsten in alloy enhance the acidic fluxing in Na2SO4 even at a temperature lower than the melting point of Na2SO4.