The effect of surface gradient nanostructure and compressive residual stress on fretting fatigue of A100 ultra-high strength steel by ultrasonic surface rolling process

The critical challenge in enhancing the fretting fatigue performance of A100 ultra-high strength steel (A100 steel) involved reconciling the conflicting attributes of strength and toughness. In our study, the ultrasonic surface rolling process (USRP) was harnessed to induce gradient nanostructures and a compressive residual stress field on the surface of A100 steel, with the goal of strengthening its wear and fatigue resistance. Through meticulous optimization of USRP parameters over 30 passes, a gradient nanostructure with a substantial depth of approximately 400 mu m was successfully formed, while minimizing the martensite lath width on the surface to a mere 44.5 nm. The nanocrystalline mechanism of USRP treatment of A100 steel was the interaction of dislocation proliferation and nailing of nanoscale carbides to form high density low angle grain boundaries and smaller martensitic laths. The introduction of these gradient nanostructures resulted in a notable increase in the depth of the hardened layer and the compressive residual stress field, doubling the original state. Additionally, the fretting fatigue threshold was found to be enhanced by 14.3 %. A factor separation approach revealed that the combined influence of the gradient nanostructure and compressive stress field considerably improved resistance to fretting wear and extended fatigue life. This synergy effectively curbed the nucleation and growth of fretting fatigue cracks, with the compressive residual stress playing a pivotal role in bolstering fretting fatigue resilience.