Effect of Laser Peening on Surface Morphology and Deformation Level of Additively Manufactured 316L Stainless Steel

Laser peening (LSP) is a surface enhancement technology that utilizes a short-pulsed laser to improve the fatigue life of components. With the advent of additive manufacturing (AM), there has been an interest in studying LSP of AM parts. In this experimental work, we examine the effect of LSP on the microstructure and surface morphology of AM 316L stainless steel. LSP at moderate and extreme peak power densities of 7.86 and 17.68 GW/cm2 respectively, was performed on a 316L steel sample fabricated by directed energy deposition (DED). The samples were characterized for their surface morphology and near-surface microstructure using a range of analytical techniques. The results indicate that all LSP conditions had no significant effect on the surface topography or oxide level. When no ablative coating was used, the surface residual stress was tensile whilst with coating the surface residual stress state was compressive. The plastic strain (as measured by EBSD) was not significantly different for all LSP conditions. The use of extremely high peak power density (17.68 GW/cm2) showed no significant increment in plastic strain, hardness or surface residual stress compared to moderate peak power density (7.86 GW/cm2) possibly due to the dielectric breakdown of water. The findings indicate that a very high peak power density does not necessarily translate to larger peening effects and may not be required for material processing.