Nanoscale surface modification of AISI 316L stainless steel by severe shot peening

Abstract

Surface nanocrystallization is gaining increased attention due to its high potential of enhancing mechanical functionality and modulating material's interaction with the surrounding environment. Among mechanical approaches, severe shot peening has recently shown to be a very promising technique for surface grain refinement, considering its efficiency, eco-friendliness, relative low cost and minimum geometrical restrictions. This study evaluates the effect of severe shot peening on microstructural and mechanical properties of 316L stainless steel, which is widely used in biomedical, food preparation, structural and marine applications. 316L samples, shot peened with different peening parameters, were studied in terms of morphological and structural features, defect density, grain size, phase transformation, surface topography, surface wettability, residual stresses and microhardness. The results indicated that severe shot peening induced near surface grain refinement to nano and sub-micron range and transformed the austenite phase into strain-induced α’- martensite in a layered deformation band structure. Severe shot peening also induced compressive residual stresses and work hardening in the top surface layer. Surface roughness and surface wettability, both of which favorably contribute to modulating the interaction of material with biological environment, were also notably enhanced by severe shot peening.