Effect of build orientation on the surface quality, microstructure and mechanical properties of selective laser melting 316L stainless steel

Abstract

Selective laser Melting (SLM) is an additive manufacturing technique for three dimensional parts. The process parameters are known to affect the properties of the eventual part. In this study, process parameters were investigated in the building of 316L structures at a variety of building orientations and for which the fracture toughness was measured. The relationship between the process parameters, microstructure, surface quality and toughness has not previously been reported. Hardness and tensile tests were carried out to evaluate the effect of consolidation on the mechanical performance of specimens. Optical and electron microscopy were used to characterise the microstructure of the SLM specimens and their effects on properties relating to fracture and the mechanics. It was found that the density of built samples is 96% and the hardness is similar in comparison to conventional material. The highest fracture toughness value was found to be 176 MPa m12⁄ in the xz building direction, and the lowest value was 145 MPa m12⁄ in the z building direction. This was due to pores and some cracks at the edge, which are slightly lower in comparison to a conventional product. The build direction does have an effect on the microstructure of parts, which subsequently has an effect upon their mechanical properties and surface quality. Dendritic grain structures were found in xz samples due to the high temperature gradient, fast cooling rate and reduced porosity. The tensile properties of such parts were found to be better than those made from conventional material. Keywords