Effect of energy density and scanning strategy on densification, microstructure and mechanical properties of 316L stainless steel processed via selective laser melting

Abstract

Laser-based additive manufacturing opens up a new horizon in terms of processing novel alloys that are difficult to process using conventional techniques. Selective laser melting (SLM) is a powder bed fusion type additive manufacturing (AM) process, for fabricating metallic parts where powder particles are fused using a high energy laser beam as a thermal source. Although SLM is widely used for manufacturing end-use metal tools and components, it requires careful tailoring of a range of parameters (e.g. layer thickness, laser spot size, laser power, hatch spacing, scanning strategy, etc.) to achieve the required densification, microstructures, and mechanical properties. Therefore, there is a critical need to systematically investigate the effect of these processing parameters on densification, microstructures and mechanical properties of materials. In this research work, 16 samples fabricated by SLM process with varying processing parameters have been investigated. We have studied the effect of scanning speed, scanning strategy, and energy density on microstructure and mechanical properties of these samples by performing microhardness tests, tensile tests, and a scanning electron microscopy (SEM) analysis. We have concluded that samples fabricated with alternate hatches and single pass of a laser beam exhibited highest densification and most refined microstructure. Furthermore, samples processed at higher scanning speeds had better densification, as well as excellent mechanical properties. We have also observed an increase in the width of dendrites as a result of decreasing the scanning speed primarily due to decrease in cooling rate.