Rossi Kaschel, FredericoFredericoRossi KaschelVijayaraghavan, R. K.R. K.VijayaraghavanShmeliov, A.A.ShmeliovDowling, Denis P.Denis P.DowlingCelikin, MertMertCelikinet al.2021-02-152021-02-152020 Acta2020-04-15Acta Materialiahttp://hdl.handle.net/10197/11945Additive manufacturing is being increasingly used in the fabrication of Ti-6Al-4V parts to combine excellentmechanical properties and biocompatibility with high precision. Unfortunately, due to the build-up of ther-mal residual stresses and the formation of martensitic structure across a wide range of typical processingconditions, it is generally necessary to use a post-thermal treatment to achieve superior mechanical perfor-mance. This investigation aims to obtain a deeper understanding of the micro/nanostructural evolution(a0martensite phase decomposition), accounting for the kinetics of phase transformation during the heattreatment of 3D-printed Ti-6Al-4V alloy. As the mechanism of phase transformation and stress relaxation isstill ambiguous, in this study the changes in crystal lattice, phase, composition and lattice strain were investi-gated up to 1000°C using bothin situhigh temperature X-ray diffraction (XRD) and transmission electronmicroscopy (TEM). Based on the result a mechanism of phase transformation is proposed, via the accommo-dation/substitution of Al, V and Ti atoms in the crystal lattice. The proposed mechanism is supported basedon elemental concentration changes during heat treatment, in combination with changes in crystal structureobserved using the high temperature XRD and TEM measurements. This study provides a deeper under-standing on the mechanism of phase transformation through martensitic decomposition, as well as a deeperunderstanding of the influence of post-thermal treatment conditions on the alloy’s crystal structure.enThis is the author’s version of a work that was accepted for publication in Acta Materialia. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Acta Materialia (188, pp. 720-732. (2020)) https://doi.org/10.1016/j.actamat.2020.02.056Additive manufacturingTi-AI-4VIn situHigh temperature transmission electron microscopyHigh temperature X-ray diffractionPhase transformationStress relaxationJournal Article188720732https://doi.org/10.1016/j.actamat.2020.02.05616/RC/3872CoG 3D2D Printhttps://creativecommons.org/licenses/by-nc-nd/3.0/ie/