Residual stress measurements using synchrotron X-ray on nickel-based superalloy at cryogenic temperatures

Akita, Koichi*; Ono, Yoshinori*; Shobu, Takahisa  ; Miyashita, Daisuke*; Yuri, Tetsumi*; Ogata, Toshio*; Oya, Shinichi*

In this study, residual stress distributions beneath the surface of a shot-peened Ni-based superalloy INCONEL718 were measured at cryogenic temperatures from 5K to room temperature using monochromatic high energy synchrotron X-rays in SPring-8. The compressive residual stress was introduced into the surface to a depth about 0.12 mm by shot-peening. The changes in residual stress distributions with temperature were observed within about 0.05 mm depth from the surface. The maximum residual stress just beneath the surface increased with decreasing temperature. The residual stress distribution deeper than 0.05 mm was not changed in spite of the temperature changes. The changes in the fatigue crack initiation sites from the surface at room temperature to inside at cryogenic temperatures can be explained by the results obtained in this study; namely, the temperature dependence of the residual stress just beneath the surface.