Effect of preheating on the thermal, microstructural and mechanical properties of selective electron beam melted Ti-6Al-4V components

Two-stage preheating is used in selective electron beam melting (SEBM) to prevent powder spreading during additive manufacturing (AM); however, its effects on part properties have not been widely investigated. Here, we employed three different preheat treatments (energy per unit area, E-A) to a Ti-6Al-4V powder bed, Each standalone build, we fabricated a large block sample and seven can-shaped samples containing sintered powder. X-ray computed tomography (XCT) was employed to quantify the porosity and build accuracy of the can-shaped samples. The effective thermal conductivity of the sintered powder bed was estimated by XCT image-based modelling. The microstructural and mechanical properties of the block sample were examined by scanning electron microscopy and microhardness testing, respectively. The results demonstrate that increasing E-A reduces the anisotropy of tortuosity and increases the thermal conductivity of the sintered powder bed, improving the heat transfer efficiency for subsequent beam-matter interaction. High preheat has a negligible effect on the porosity of large AM components; however, it decreases the microhardness from 330 +/- 7 to 315 +/- 11 HV0.5 and increases the maximum build error from 330 to 400 mu m. Our study shows that a medium E-A (411 kJ m(-2)) is sufficient to produce components with a high hardness whilst optimising build accuracy. (C) 2019 The Authors. Published by Elsevier Ltd.