Effects of lamellar α orientation on the mechanical behavior of Ti–6Al–4V alloy manufactured by electron beam directed energy deposition

Abstract

Crystallographic texture of alloy can trigger anisotropic properties, which have been studied extensively. However, the effect of spatial orientation of grains on the mechanical properties, especially for additive manufactured metals with lamellar morphology has remained elusive. Herein, this work theoretically calculated the spatial and crystallographic orientations of α lath from the <100>β//Z-axis (build direction) fiber texture, and investigate the relationship between the orientations of α lath and the deformation behaviors and mechanical properties of the Ti–6Al–4V alloy built via electron beam directed energy deposition (EB DED). Deformation features display the prismatic slip system of α lath that exists a smaller angle to the broad face of α lath showing a lower effective critical resolved shear stress (CRSS). This is because this prismatic slip system has a greater slip range when compares with other slip systems. Such deformation features, combined with the spatial orientation distribution characteristic of α lath that is induced by the <100>β//Z-axis fiber texture, lead to strongly tensile anisotropy, specifically, the samples oriented 45° and 67.5° angles to z-axis present greater strengths but lower ductility, whereas the sample in the z-axis direction generally displays a minimum strength but a superb ductility. This finding is vital for providing an important theoretical basis for optimizing the consistency of mechanical properties of the additive manufactured α+β dual phase titanium alloy.