Enhanced repeated frictional sliding properties in 304 stainless steel with a gradient nanostructured surface

Surface mechanical attrition treatment (SMAT) is a powerful and practical method to surface-harden metals and alloys through the generation of a gradient nanostructured surface. In this study 304 stainless steel was SMAT processed and the mechanical response upon repeated frictional sliding is studied as well as compared to the mechanical response of untreated as-received 304 stainless steel. The repeated frictional sliding experimental work is complemented by finite-element analysis in order to quantify the stress and strain distribution and to qualitatively determine the elastic-plastic deformation behavior. It is shown that repeated frictional sliding on the SMAT processed 304 stainless steel surface results in smaller residual depth, pile-up height and friction coefficient but higher maximum stresses compared to the as-received 304 stainless steel. After approximately 30 cycles the residual depth increases only minimally with each additional cycle because of strain hardening and increased contact area. At low cycle numbers the frictional sliding track of the as-received 304 stainless steel meanders and forms slip bands adjacent to the sliding track. Due to instability of the gradient structure of 304 SMAT processed stainless steel, asperities are formed in the inner zone of sliding tracks at increasing cycle numbers.