Influence of local heat flow variations on geometrical deflections, microstructure, and tensile properties of Ti-6Al-4 V products in powder bed fusion systems

This research investigated the geometry, microstructure and tensile properties of Ti-6Al-4 V samples produced by Selective Laser Melting (SLM) and Electron Beam Melting (EBM), which vary due to different heat transfer mechanisms occurring at different locations at the same time. The geometric variations were evaluated by comparing the cranial implants manufactured in this way with their Computer-Aided Designed files using a 3D scanner. The SLM samples were strongly deformed, while the EBM process affected the size but not the shape of the samples. The cooling rate varied from the core to the surface zones, so that the microstructural morphology varied between them. The size and orientation of the precipitated α phase varied significantly from the core to the surface zones in the EBM. Two new α colonies were identified; one was nucleated and grew from the prior β-grain boundary and the other formed parallelograms of equal size consisting of α lamellae. The tensile samples that were built up in the Z-direction in the EBM had the lowest yield strength and the highest elongation, due to the effect of the slowest cooling rate, which promoted continuous dynamic recrystallization, and α colonies precipitated from the α grain boundary. This can provide useful guidance to engineers in developing the functionally graded structure.