Influence of pre-oxidation on the hot corrosion of M38G superalloy in the mixture of Na2SO4–NaCl melts

Ni-based M38G superalloy suffered from serious hot corrosion attack in the mixture of 75 wt.%Na2SO4 + 25 wt.%NaCl melts at temperatures above 800 °C. In order to investigate the influence of pre-oxidation on the hot corrosion resistance of this superalloy, pre-oxidation treatment was conducted at 950 °C in air for 8 h. A compact scale composed of Cr2O3, NiCr2O4 and TiO2 formed on the alloy surface after the pre-oxidation. The pre-oxidized specimens exhibited good hot corrosion resistance during exposure to the mixture of 75 wt.%Na2SO4 + 25 wt.%NaCl melts at 800 °C for 102 h. With increasing the temperature, however, the degradation of the oxide scale was accelerated. For the corrosion at 850 °C, the pre-oxidized samples exhibited good hot corrosion resistance for 60 h, while at 875 °C, the pre-oxidation treatment could not improve the hot corrosion resistance of this superalloy with obvious mass loss. The degradation mechanism of pre-oxidation sample in the mixture of 75 wt.%Na2SO4 + 25 wt.%NaCl melts was discussed in this paper.