Optimizing tribological property by inducing the gradient microstructure and surface topography in martensite stainless steel

In this study, ultrasonic surface rolling process (USRP) technology was used to prepare a diverse gradient microstructure in 17-4PH stainless steel. The treatment also induced various surface topographies and increased surface micro-hardness. Consequently, the tribological properties in 17-4PH stainless steel showed varying de-grees of improvement through different numbers of USRP passes. With an increase of USRP process passes, there was a gradual decrease followed by an increase in the friction coefficient. These results indicated that surface roughness played a dominant role in reducing the coefficient of friction (COF), with the sample subjected to five passes of USRP displaying the lowest COF. Furthermore, 17-4PH stainless steel exhibited superior wear resis-tance after fifteen USRP treatments, wherein the strong gradient nanocrystalline structure and lower surface roughness contributed to the reduction in the wear rate.