Effect of retained beta layer on slip transmission in Ti–6Al–2Zr–1Mo–1V near alpha titanium alloy during tensile deformation at room temperature Dong He a,⇑ , Jingchuan Zhu b , S. Zaefferer c , D. Raabe c a State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China b National Key Laboratory for Precision Hot Processing of Metals, Harbin Institute of Technology, Harbin 150001, China c Max-Planck-Institut für Eisenforschung, Abteilung Mikrostrukturphysik und Umformtechnik, Max-Planck-Strasse 1, 40237 Düsseldorf, Germany article info Article history: Received 2 September 2013 Accepted 6 December 2013 Available online 15 December 2013 Keywords: Retained beta Slip transmission Burgers orientation relationship Tensile deformation Titanium alloys abstract Slip is the main plastic deformation mechanism in titanium alloys at room temperature. This is especially so for near alpha titanium alloy like Ti–6Al–2Zr–1Mo–1V, which contains low beta stabilizing and high aluminum (alpha stabilizing) element additions. The effects of retained beta layers on slip transmission across a/b interfaces in Ti–6Al–2Zr–1Mo–1V during tensile deformation have been studied in the current work. High resolution scanning electron microscopy (HR-SEM) and electron backscatter diffraction (EBSD) techniques were used to study the deformation microstructure. The results indicate that the full Burgers crystal orientation relationship (OR) between the a and the thin retained b phase layers facilitates slip transition but is not the necessary requirement/restriction. Some novel slip trace morphologies that are characterized by deflection and bifurcation (fork-like morphology) are revealed in the retained b layers between two abutting a grains. The possible reasons for these different slip transmission patterns are analyzed by EBSD results and a schematic model is proposed. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction As a typical near a titanium alloy, Ti–6Al–2Zr–1Mo–1V (TA15) is widely used for aerospace applications due to its high specific strength, excellent thermal stability, low growth rate of fatigue crack and strong corrosion resistance [1–3]. Because of its high aluminum content, slip is the dominant deformation mechanism for TA15 titanium alloy even at room temperature [4–5]. The mechanical properties of a and near a titanium alloys are mainly determined by their microstructures, especially by the size, the morphology and the crystallographic orientations distribution of the a phase [4,6–9]. In addition, slip nature and distribution dur- ing deformation processes are also very important [10–12]. The slip system activation and slip transmission phenomena across grain and phase boundaries were reported in the publications [10–11,13–16]. The slip transmission across low-angle a/a grain boundaries of deformed Ti occurs at room temperature with two verified criteria: (I) the angles between slip planes/directions at boundaries should be minimized and (II) the Burgers vector of the residual dislocation should be minimized [14]. In a/b titanium alloy, the mechanism of slip transmission in oriented single-colony crystals has been studied by transmission electron microscopy (TEM) and analyzed with a simple model based on the accumula- tion of residual dislocations at the a/b interface [13]. However, this research was limited to a single colony and a very local area imposed by the thinning process of TEM foils. The micro gliding and deformation mechanisms in a a/b titanium alloy with polycrystals were described by Bridier et al. [10], who observed slip transmission between the two parallel a lamellae. However, the details of the slip transition have not been revealed. In another study, parallel a lamellae with similar orientation were treated as a single a grain to simplify the analysis; however, due to this simpli- fication the b layers between the a lamellae were completely neglected [17]. To our knowledge, the effects of the retained b layers on slip mode in the b forged [18] (forging deformation of the alloy is done above the beta transus) TA15 titanium alloy, which do not have a perfect Burgers OR between the a and retained b layers, have not been investigated. Furthermore, the details of slip line morphology during transfer across the retained b layers are also not clear. The current work will focus on these problems. The effects of the crys- tal orientations of a and retained b phase on the slip transmission across a/b interface will be studied and discussed. Some novel slip trace morphology during the slip transmission will be revealed. Finally, a schematic model based on EBSD observations and the identification of activated slip systems will be proposed to account for those various slip trace patterns. 0261-3069/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.matdes.2013.12.018 ⇑ Corresponding author. Tel./fax: +86 10 82543962. E-mail address: hedong@imech.ac.cn (D. He). Materials and Design 56 (2014) 937–942 Contents lists available at ScienceDirect Materials and Design journal homepage: www.elsevier.com/locate/matdes