Microstructure and Tribological Response of Selective Laser Melted AISI 316L Stainless Steel: The Role of Severe Surface Deformation

Abstract

This study investigates the effect of surface mechanical attrition treatment (SMAT) (a severe surface-deformation process) on microstructure and tribological behavior of AISI 316L steel samples manufactured using the selective laser melting (SLM) technique. The specimens are built in different directions (0°, 45°, and 90°). The microstructure of annealed SLM samples shows the non-uniform distribution and random orientation of grains. It contains high-angle grain boundaries and a high density of dislocations. The average grain size is about 63, 51, and 41 μm for 0°, 45°, and 90° build direction, respectively. SMAT is beneficial for SLM steel to reduce surface roughness (by ~ 87%) and eliminate internal porosity. The deformed layer of SLM steel shows a highly dense network of slip bands, distortion of grains, and hardness gradient (up to the depth of about 600 μm). Increase in surface hardness due to SMAT is maximum (~ 54%) for the sample having 90° build direction. Typical observation of deformation-induced martensite is absent for the SMAT-processed SLM steel. Under the higher load (especially, 20 N), the tribological response of sample manufactured in the 90° direction is superior amongst the non-treated samples. Severe surface deformation enhances the wear resistance and reduces the COF of SLM steel.