Contents lists available at ScienceDirect Materials Characterization journal homepage: www.elsevier.com/locate/matchar Microstructural and texture evolution during thermo-hydrogen processing of Ti6Al4V alloys produced by electron beam melting Merve Nur Doğu a,c , Ziya Esen b , Kemal Davut c,d , Evren Tan e , Berkay Gümüş e , Arcan F. Dericioglu a, ⁎ a Middle East Technical University, Metallurgical and Materials Engineering Department, Ankara, Turkey b Çankaya University, Materials Science and Engineering Department, Ankara, Turkey c Atılım University, Metallurgical and Materials Engineering Department, Ankara, Turkey d Metal Forming Center of Excellence, Atılım University, Ankara, Turkey e ASELSAN Inc. Defense Systems Technologies Business Sector, Ankara, Turkey ARTICLE INFO Keywords: Titanium alloys Additive manufacturing Electron beam melting Thermo-hydrogen processing Microstructure Crystallographic texture ABSTRACT The present study was conducted to reveal the effects of building angles and post heat-treatments (2-step Thermo-Hydrogen Processing (THP) and conventional annealing treatment) on the density, microstructure and texture of Ti6Al4V alloy parts produced by Electron Beam Melting (EBM). The results showed that regardless of the building angle; the density, microstructure and crystallographic texture (defined with respect to building angle) of the as-produced samples were identical; having Widmanstätten α structure and columnar β-grains which are parallel to building direction. The main texture component for the α phase was (10 10)//building direction, and for β phase (001)//building or heat flow direction. The first step of THP, namely, the hydro- genation step, produced a needle-like microstructure and increased the local misorientations due to lattice distortion. On the other hand, after application of the second step of THP, dehydrogenation step, microstructure was refined, particularly α-grains that were larger than 10 μm and located at grain boundaries. Moreover, THP randomized the crystallographic texture since it involves β to α phase transformation, at which one β-grain can produce 12 distinct α-variants. The grain boundary misorientation distributions also changed in accordance with the microstructural changes during the 2-step THP. On the other hand, annealing coarsened the grain boundary and Widmanstätten α phases; moreover, it changed the texture so that the basal planes (0001) rotated 30° around the building direction. 1. Introduction Ti and its alloys with their outstanding properties such as high strength-to-weight ratio and toughness, good corrosion resistance, ex- cellent mechanical properties, and biocompatibility have been used extensively in aerospace, automobile, biomedical and chemical in- dustries [1–9]. Today, Ti6Al4V alloy is the most widely used titanium alloy due to its heat treatability and a good balance between mechan- ical properties and workability in addition to the aforementioned properties [1,2,9,10]. In order to manufacture a single Ti6Al4V alloy part, generally, more than one conventional fabrication technique (casting, machining, welding/joining, powder metallurgy, forging, etc.) is required. Although conventional techniques are suitable for the production of large numbers of parts, the complexity of the part geo- metry produced by conventional techniques is limited and the techniques generate scrap, thus, they are not cost-effective [11,12]. In recent years, there have been growing interest in additive man- ufacturing (AM) techniques [13] due to their notable advantages such as freedom to manufacture complex geometries at a single manu- facturing step along with cost-saving by optimized material usage and minimum waste [14–17]. Among all AM techniques, selective laser melting (SLM) and EBM are the two most widely used ones for the production of Ti6Al4V alloy parts with intricate geometry and cellular structures for industries such as defense, aerospace, automotive and biomedical industries [18–27] where special part design is needed. Due to the faster cooling rates appearing during the SLM process, larger residual stresses are formed, and non-equilibrium martensitic phase formation is observed. Thus, the ductility of the part is decreased sig- nificantly [28–30]. On the other hand, ductility problem could be al- leviated by the incorporation of preheating step in the EBM process. https://doi.org/10.1016/j.matchar.2020.110549 Received 25 March 2020; Received in revised form 23 July 2020; Accepted 3 August 2020 ⁎ Corresponding author. E-mail address: arcan@metu.edu.tr (A.F. Dericioglu). Materials Characterization 168 (2020) 110549 Available online 07 August 2020 1044-5803/ © 2020 Elsevier Inc. All rights reserved. T