Interplay Between Inclusion Evolution, Tensile Properties, and Volumetric Energy Density During Additive Manufacturing of 316L Stainless Steel

The present work focuses on understanding the evolution of volume defect, i.e., non-metallic inclusion during the selective laser melting (SLM) process of additive manufacturing (AM) of 316L stainless steel. AM samples were prepared by systematically varying different SLM process parameters such as laser power (300 to 380 W), scan speed (800 to 1200 mm/s), hatch spacing (0.08 and 0.12 mm), and powder layer thickness (0.03 to 0.07 mm). For the chosen set of process parameters, the relative density of the samples increased with increasing volumetric energy density (VED). Mechanical properties like UTS, yield strength, and elongation increased with increasing VED to maxima and then decreased with a further increase in VED. However, a reverse trend has been observed for the number density of inclusions which reduced from 107 to 8.6/mm² with increasing VED from 29.76 to 105.5 J/mm³ followed by a slight increase to 16.7/mm² as the VED was further increased to 156.25 J/mm³. The efficiency of VED as a criterion to evaluate inclusion evolution was studied. It is concluded that the absolute values of VED cannot account for the dynamics of inclusion evolution in the AM process. Alternatively, a new modified VED is proposed, which accurately considers the process's physics and, hence, emerges as a better criterion for assessing inclusion evolution during the AM process.