Machining Versus Heat Treatment in Additive Manufacturing of Ti6Al4V Alloy

Anisotropy in the mechanical properties of Laser Powder Bed Fusion (L-PBF)-fabricated titanium parts, which could be problematic in service, is dependent on the build directions and may be mitigated by post-fabrication treatments such as surface machining or heat treatment. However, investigation of the anisotropy in truly as-printed conditions, i.e., prior to any post-process, is always a challenge as the horizontally built parts are noticeably distorted compared to vertically built ones. In this study, by deploying a novel design, straight horizontal samples in the as-printed condition were fabricated. This allowed a comparison to be made possible in the mechanical properties of two built orientations of vertical and horizontal in the as-printed condition. This paper discusses how the surface machining or post-thermal treatment influences the anisotropy in the mechanical properties compared to as-printed conditions. It further highlights how annealing process at a temperature of 850 degrees C is more effective than stress relieving at a temperature of 670 degrees C to nearly diminish the anisotropy in mechanical properties even without any need for machining. Therefore, when machining becomes less feasible due to the geometrical complexity of L-PBF parts, a thermal treatment may be the solution for better service performance.