Effects of defects and microstructures on tensile properties of selective laser melted Ti6Al4V alloys fabricated in the optimal process zone

The aim of selective laser melting (SLM) technology is to obtain high quality workpieces through optimization of processing parameters. However, the defects and microstructures are simultaneously changed with the change of process parameters, so their effects are hard to discuss separately. To meet this challenge, 24 combinations of laser power and scanning speed were designed to fabricate the SLM manufactured Ti6Al4V alloy, and the volumetric energy density (VED) of them ranges from 30 J/mm(3) to 100 J/mm(3). It is found that with the increase of VED the prior beta boundary tended to be straighter and wider, while the morphology of alpha lamella did no change distinctively. The porosity varies from nearly 0% to 4% in this process zone, which has significant effects on the tensile properties. For samples with high porosity (0.25%-4%), the influence of defects covered the influence of microstructure, leading to stochastic ultimate tensile strength and stably low elongation. For samples with low porosity (0.01%-0.25%) and extra-low porosity (<0.01%), the stably high ultimate tensile strength revealed the slight difference between microstructures. The poor productivity of elongation for samples with low and extra low porosity was also discussed.