  Citation: Tevet, O.; Svetlizky, D.; Harel, D.; Barkay, Z.; Geva, D.; Eliaz, N. Measurement of the Anisotropic Dynamic Elastic Constants of Additive Manufactured and Wrought Ti6Al4V Alloys. Materials 2022, 15, 638. https://doi.org/10.3390/ ma15020638 Academic Editor: Federica Bondioli Received: 20 December 2021 Accepted: 11 January 2022 Published: 15 January 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). materials Article Measurement of the Anisotropic Dynamic Elastic Constants of Additive Manufactured and Wrought Ti6Al4V Alloys Ofer Tevet 1,2,† , David Svetlizky 1,† , David Harel 1 , Zahava Barkay 3 , Dolev Geva 4 and Noam Eliaz 1, * 1 Department of Materials Science and Engineering, Tel Aviv University, Ramat Aviv, Tel Aviv 69978, Israel; tevet.ofer@gmail.com (O.T.); dsvetlizky@gmail.com (D.S.); dharel@tauex.tau.ac.il (D.H.) 2 Materials Department, Nuclear Research Center Negev (NRCN), Beer Sheva 84190, Israel 3 The Wolfson Applied Materials Research Centre, Tel Aviv University, Ramat Aviv, Tel Aviv 69978, Israel; barkay@tauex.tau.ac.il 4 Israel Ministry of Defense, Hakirya, Tel Aviv 61909, Israel; dolev24@yahoo.com * Correspondence: neliaz@tau.ac.il; Tel.: +972-3-640-7384 † These authors contributed equally to this work. Abstract: Additively manufactured (AM) materials and hot rolled materials are typically orthotropic, and exhibit anisotropic elastic properties. This paper elucidates the anisotropic elastic properties (Young’s modulus, shear modulus, and Poisson’s ratio) of Ti6Al4V alloy in four different conditions: three AM (by selective laser melting, SLM, electron beam melting, EBM, and directed energy de- position, DED, processes) and one wrought alloy (for comparison). A specially designed polygon sample allowed measurement of 12 sound wave velocities (SWVs), employing the dynamic pulse-echo ultrasonic technique. In conjunction with the measured density values, these SWVs enabled deriving of the tensor of elastic constants (C ij ) and the three-dimensional (3D) Young’s moduli maps. Electron backscatter diffraction (EBSD) and micro-computed tomography (μCT) were employed to characterize the grain size and orientation as well as porosity and other defects which could explain the difference in the measured elastic constants of the four materials. All three types of AM materials showed only minor anisotropy. The wrought (hot rolled) alloy exhibited the highest density, virtually pore-free μCT images, and the highest ultrasonic anisotropy and polarity behavior. EBSD analysis revealed that a thin β-phase layer that formed along the elongated grain boundaries caused the ultrasonic polarity behavior. The finding that the elastic properties depend on the manufacturing process and on the angle relative to either the rolling direction or the AM build direction should be taken into account in the design of products. The data reported herein is valuable for materials selection and finite element analyses in mechanical design. The pulse-echo measurement procedure employed in this study may be further adapted and used for quality control of AM materials and parts. Keywords: Ti6Al4V; additive manufacturing (AM); directed energy deposition (DED); electron beam melting (EBM); selective laser melting (SLM); wrought alloy; pulse-echo ultrasonic technique; dynamic elastic constants; Young’s modulus; shear modulus; Poisson’s ratio 1. Introduction Ti6Al4V alloy was developed in the 1950s for the aerospace industry, which is still its largest consumer [1,2]. However, thanks to its unique combination of properties, such as high strength, high fracture toughness, excellent corrosion resistance, superior biocom- patibility, and low density, Ti6Al4V has also become common in the energy, chemical, marine, automobile, and biomedical industries [1,3]. Due to the significant advantages of additive manufacturing (AM) over traditional Ti6Al4V manufacturing processes, for example, the ability to form near-net-shape parts and complex geometries, a relatively short lead time, design flexibility, and minimal material waste, the interest in AM of Ti6Al4V has rapidly increased [1,4–8]. Despite the abovementioned advantages of metal AM in general, and AM of Ti6Al4V specifically, the ability to fabricate fully dense, defect-free parts with Materials 2022, 15, 638. https://doi.org/10.3390/ma15020638 https://www.mdpi.com/journal/materials