Unraveling the friction and wear mechanisms of surface nanostructured stainless-steel

In an effort to improve the friction and wear resistance of coarse grain (CG) 316L stainless steel (SS), the influence of surface nanostructuring formed by a novel surface mechanical rolling treatment (SMRT) technology was investigated. The tribological tests performed in this work consisted of dry reciprocating ball-on-flat tests using Al2O3 as the counter substrate. Results indicate that the SMRT process improved the abrasion resistance of the CG specimen at 15 N, 30 N, and 45 N loads. This finding was due to the combination of surface strengthening, surface smoothening, and the martensite phase transformation induced by SMRT treatment. Aside from the observed change in abrasion resistance, the frictional response of the SMRT specimen was lower than the CG specimen across all loads. Interestingly, the coefficient of friction (COF) for both the CG and SMRT specimens was observed to decrease as the load increased. The formation of surface oxidation contributed to this decrease, as a protective oxide layer was formed. As the load increased, a greater amount of frictional energy was converted into surface oxidation, which reduced the frictional response. Scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS) investigations of the worn surfaces confirmed these findings, indicating that a combination of oxidative and abrasive wear took place. Collectively, these findings indicate that SMRT treatment is a viable technique to improve the tribological resistance of CG 316L SS.