Studies on Tensile Behaviour of Selective Laser Melted 316L Stainless Steel Using SEM Straining Stage

Abstract

Metallic components prepared by additive manufacturing are expected to exhibit microstructural anisotropy due to their layer-by-layer architecture. This in-homogeneity in microstructure can result in variations in the deformation behaviour of materials in different directions, which may lead to premature failure of a component loaded in a particular orientation. Therefore, in the present study, an attempt has been made to investigate the microstructural characteristics and ensuing mechanical properties, in three different orientations with respect to the build direction in a 316L stainless steel, printed using selective laser melting technique. Tensile tests were performed on micro-tensile specimens using a straining stage attached to scanning electron microscope (SEM) while observing crack initiation and propagation. The results were compared with that of conventionally processed AISI 316L stainless steel. Microstructural analysis of the SLM printed component revealed the presence of fine cellular structure within the clearly defined prior melt-pool boundaries. Furthermore, EBSD analysis revealed the presence of columnar grains, which were mostly oriented along the <001> to <101> direction in the build plane and along the <111> direction in the long transverse plane. The favourable grain orientation for twinning in the samples drawn along the build plane led to a better accommodation of plastic strain during tensile deformation. Hence, the sample drawn from build plane showed an improved combination of strength and ductility, in comparison to the transverse orientations. When compared with conventionally processed 316L stainless steel, the SLM printed samples showed a significant increase in the strength in all the three orientations with a concurrent decrease in the ductility.