Research on the corrosion resistance and the passive film growth of Ni-based superalloy surface treated by ultrasonic impact

Purpose- The purpose of this study is to investigate the corrosion resistance of superalloys subjected to ultrasonic impact treatment (UIT). The passive film growth on the superalloys' surface is analyzed to illustrate the corrosion mechanism.Design/methodology/approach- Electrochemical tests were used to investigated the corrosion resistance of GH4738 superalloys with different UIT densities. The microstructure was compared before and after the corrosion tests. The passive film characterization was described by electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS) tests.Findings- The compressive residual stress and corrosion resistance of the specimens significantly increased after UIT. The order of corrosion resistance is related to the UIT densities, i.e. 1.96 s/mm2 > 1.71 s/mm(2) > 0.98 s/mm(2) > as-cast. The predominant constituents of the passive films are TiO2, Cr2O3, MoO3 and NiO. The passive film on the specimen with 1.96 s/mm2 UIT density has the highest volume fraction of Cr2O3 and MoO3, which is the main reason for its superior corrosion resistance.Originality/value- This study provides quantitative corrosion data for GH4738 superalloys treated by ultrasonic impact. The corrosion mechanism is explained by the passive film's characterization.