Experimental and computational studies of ultrasound wave propagation in hexagonal close-packed polycrystals for texture detection B. Lan a,⇑ , M. Lowe b , F.P.E. Dunne b a Department of Engineering Science, Oxford University, Parks Road, Oxford OX1 3PJ, UK b Imperial College, London SW7 2AZ, UK Received 23 August 2013; received in revised form 8 October 2013; accepted 8 October 2013 Abstract Texture in hexagonal close-packed (hcp) polycrystalline metals, often developed during thermomechanical processing, affects ultra- sonic wave velocity. In this study, the relationship between bulk texture and ultrasonic wave velocity in aggregates of (predominantly) hcp grains is investigated using theoretical, numerical and experimental methods. A representative volume element methodology is presented, enabling the effects of texture on ultrasonic wave speed to be investigated in two-phase polycrystals, and is employed to examine the ultrasonic response of random polycrystals, textured polycrystals and macro-zones often observed in titanium alloys. Numerical results show that ultrasonic wave speed varies progressively with changing texture, over a range of 200 m s 1 , within bounds set by the two extreme single-crystal orientations. Experimental ultrasound studies and full electron backscatter diffraction (EBSD) characterization are conducted on unidirectionally rolled and cross-rolled Ti–6Al–4V samples in three orthogonal directions. In addition, the EBSD-determined textures are incorporated within the polycrystal model and predicted ultrasonic velocities compared directly with ultrasonic experiments. Good quantitative agreement is obtained and both the experimental and computed results dem- onstrate that ultrasonic velocity profiles exist for random, unidirectionally rolled and cross-rolled textures. The combined results indi- cate the possibility of the development of a methodology for bulk texture determination within Ti polycrystal components using ultrasound. Ó 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Hcp polycrystal; Ultrasound; Texture; Macro-zones; EBSD 1. Introduction Hexagonal close-packed (hcp) metals, particularly tita- nium, zirconium and magnesium, are key materials in the aero, nuclear and auto industries. For example, Ti–6Al– 4V is employed extensively in aero-engine components and Zircaloy has been selected as the key material for clad- ding nuclear reactor fuels [1,2]. Often, the commercially useful metals are two-phase alloys (for example Ti–6Al– 4V), comprising both hcp (alpha) and body-centred cubic (bcc) (beta) phases, which have differing elastic (and hence ultrasonic) responses [3]. At the single crystal level, both hcp and bcc materials are anisotropic elastically [4], which often results in properties at the macro- or component level, which are also highly anisotropic, depending upon the nature of the distribution of crystallographic orienta- tions. The latter, known as texture, is highly relevant in determining component properties and performance. The texture of an hcp polycrystal may be described in terms of at least three well-established techniques: pole fig- ures, which are stereographic projections of relevant plane normals to show the distribution of orientations through- out the polycrystal; orientation distribution functions (ODFs), which are probabilistic distribution functions to depict the occurrence possibilities of orientations on 1359-6454/$36.00 Ó 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.actamat.2013.10.012 ⇑ Corresponding author. Tel.: +44 07741 738648. E-mail address: bo.lan@eng.ox.ac.uk (B. Lan). www.elsevier.com/locate/actamat Available online at www.sciencedirect.com ScienceDirect Acta Materialia xxx (2013) xxx–xxx Please cite this article in press as: Lan B et al. Experimental and computational studies of ultrasound wave propagation in hexagonal close-packed polycrystals for texture detection. Acta Mater (2013), http://dx.doi.org/10.1016/j.actamat.2013.10.012