Impact of the oxide layer and subsurface micromechanical properties of laser peened 31L stainless steel on biocorrosion resistance in simulated body fluid

Biomedical grade 316 L stainless steel alloy subjected to laser shock peening (LSP) without sacrificial coating was appraised for the electrochemical stability by investigating the corrosion resistance of the treated surface in simulated body fluid (SBF) environment. The specimen surface was modified by different laser power densities (3 (3LP), 6 (6LP) and 9 GW/cm 2 (9LP)) and subsequent surface oxidation , microstructural and morphological changes were evaluated. Preliminary results showed that the porous oxide layer comprised of Fe 2 O 3 , FeO, Cr 2 O 3 , and hydroxides (of Fe, Cr and Ni), and their stability in the physiological environment depends on oxidation states and percentage composition of oxides. Roughness and wettability character of surface altered with the power density and among peened alloys 3LP sample recorded the least value. Compressive residual stress of ∼ 357 MPa up to a depth of 100 µm and severe plastic deformation hardened (234 HV) surface beneath (∼25 µm) the oxide layer containing induced defects (including twins) strengthened the 3LP sample subsurface. Corrosion current density of 3LP sample was very low (0.052 µA/cm 2 ) compared to other samples showing better passivation against decomposition. The EIS spectrum with smaller radius and improved polarisation resistance aided by perfect oxide layer composition (mostly Cr 2 O 3 ) with increased high angle grain boundary (HAGB) fractions, refined grains and increased dislocation density in 3LP sample resulted in better biocorrosion resilient characteristics.