Surface characteristics and tribological performance of severely surface deformed AISI 304L stainless steel

Abstract

Surface Mechanical Attrition Treatment (SMAT) is a severe surface plastic deformation (SSPD) technique employed to induce grain refinement and improve the near-surface mechanical and tribological properties of metallic materials. This study systematically investigates the effect of varying SMAT parameters namely, ball diameter, impact velocity, and treatment duration on the microstructural evolution and performance of metastable austenitic 304L stainless steel. Microstructural characterization via X-ray diffraction (XRD) revealed progressive transformation of the y-austenite phase into strain-induced o'-martensite with increasing SMAT severity. Electron Backscatter Diffraction (EBSD) imaging further confirmed the development of a nanocrystalline gradient structure and a significant increase in geometrically necessary dislocations (GNDs) near the treated surface. Optimal treatment conditions (5 mm ball diameter, 10 m/s velocity, 20 minutes duration denoted as S10,5) achieved a 48% increase in surface hardness (up to 410 HVo.i) and a high martensite volume fraction, indicating effective strain-induced phase transformation.