Ti-6Al-4V is a widely adopted alloy for components produced by Laser Powder Bed Fusion (LPBF). Due to its high strength-to-weight ratio, its excellent corrosion resistance, and biocompatibility, it is used in a wide range of applications in the aerospace, chemical and process engineering, energy, and biomedical sector. While conventionally produced Ti-6Al-4V typically features an \(\alpha +\beta \) microstructure, additively manufactured Ti-6Al-4V is well known to develop an acicular martensitic \(\alpha^{\prime}\) structure with often pronounced anisotropic properties resulting from the hexagonally closest packed (hcp) structure of \(\alpha^{\prime}\) . This study investigates the effect of the build direction of an LPBF printed Ti-6Al-4V (Grade 23) alloy on the resulting thermal expansion behaviour up to 1100 °C. Vertically built samples show a distinctly positive step in the apparent thermal expansion between approximately 850 °C and 1000 °C, while that of horizontally built specimen exhibit a dip. This is shown to be associated with (1) the alignment of prior \(\beta \) grains growing epitaxially with \({\langle 001\rangle }_{\beta }\) along the direction of the thermal gradient that is related (but not parallel) to the build direction, (2) the Burgers orientation relationship and crystallographic variant selection causing acicular \(\alpha^{\prime}\) laths to grow at approximately 40 deg to the primary axis of prior \(\beta \) grains, and (3) the strain occurring during the \(\alpha^{\prime}\to\, \beta \) transformation. The apparent anisotropy of the thermal expansion of the as-printed Ti-6Al-4V is expected to have a relevant impact on the residual stress state after heat-treatment of LPBF components.
