Designing a gradient structure in a Ni-based superalloy to improve fretting fatigue resistance at elevated temperatures through an ultrasonic surface rolling process

In this study, a gradient nanostructured GH4169 superalloy was prepared by ultrasonic surface rolling process (USRP), and the fretting fatigue resistance was investigated at elevated temperatures. After USRP, a high density of deformation twins, stacking faults and dislocations as well as precipitates were observed in the surface of the gradient nanostructured GH4169 superalloy when examined using transmission electron microscopy. Factor separation analysis was carried out to determine the leading factor for the improvement of the fretting fatigue properties of GH4169 at elevated temperatures, and the compressive residual stress was found to be the leading factor. The mechanism was determined to be dislocation movement that can be pinned by deformation twins, stacking faults and precipitates and, thus, is able to stabilize the compressive residual stress at elevated tem-peratures. As a result, the USRP-treated GH4169 with gradient nanostructure was found to have the highest fretting fatigue resistance at elevated temperatures.