Mechanism of adding rhenium to improve hot corrosion resistance of nickel-based single-crystal superalloys

Hot corrosion behavior in sulfate salt at 950℃ of Rene N5 single-crystal superalloys with 3 wt%rhenium(NSR)was investigated compared with that of nickel-based single-crystal superalloys without rhenium(NS).After 30-h corrosion,the surface of the NS superalloy is seriously corroded.Many holes and exfoliation appear on the surface.The NSR superalloys exhibit better hot corrosion resistance than the NS superalloys.After 30-h corrosion,a continuous and compact Al_(2)O_(3) film is observed on its surface.The Al_(2)O_(3) film with dense structure formed on the surface provides protection for the matrix.The characterization results show that A1 is aggregated in theγ’phase,while Re is aggregated in the y phase during the formation of oxide scale.Considering that Re can inhibit the diffusion of A1 in the nickel matrix,it is inferred that Re can inhibit the outward diffusion of A1 and prevent the decrease of Al concentration in theγ’phase.High concentration of Al hinders the decomposition of Al_(2)O_(3) due to the reaction of acid and basic dissolution.Al_(2)O_(3) keeps its structure intact and provides protection for the matrix.