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.

Key words: GH4742, Superalloy, H₂O, Diffusion, Oxidation, Mechanism