An investigation of fretting fatigue behavior and mechanism in 17-4PH stainless steel with gradient structure produced by an ultrasonic surface rolling process

•A gradient structure layer was produced on 17-4PH specimens via USRP.•Element redistributions and texture appeared in the USRP treated samples.•Residual compressive stress played a main function in terms of improving FF life.•Nano-grains and “fish scale-like” topography had important influences. A gradient structure layer was fabricated on 17-4PH specimens using an ultrasonic surface rolling process. The separation-factor methods confirmed that residual compressive stress played a critical role in improving fretting fatigue (FF) life, while gradient nano-crystalline structure and “fish scale-like” surface topography also had a beneficial influence. Residual compressive stress could enhance crack closures and reduce effective tensile stress. Nano-grains grew, and dislocation density reduced after FF experiment, which could accommodate an externally applied strain and neutralize any stress concentration. Additionally, the “fish scale-like” topography reduced total contact area between the specimen surface and fretting pad, which alleviated surface damage.