Cognition on oxidation behavior of Ni-based superalloy GH4742 when exposed to water vapor

Abstract

The oxidation behavior of Ni-based superalloy GH4742 exposed to water vapor was investigated at 900–1100 °C for 50 h in Ar+20%H2O, with Ar+20%O2 included for comparison. The presence of H2O is adverse to formation of continuous Cr2O3 oxide layer but contributes to generation of big voids. Based on this, Ni2+ and Co2+ are more easily to diffuse towards the outermost oxide layer (OOL), forming non-protective Ni- and Co-rich oxides with high proportion. This leads to a higher weight gain in Ar+20%H2O than that in Ar+20%O2. At elevated temperatures, the spallation of oxide scale occurs while the consumption of Cr is reduced in Ar+20%H2O, and the contents of Ni- and Co-rich oxides at this moment are reduced in the OOL. The oxidation mechanism was also discussed.