Onset of plastic deformation and strain localization in relation to β phase in metastable β and dual phase Ti alloys

High strength metastable beta titanium alloys are widely used in the aerospace industry for their superior mechanical properties, including an outstanding strength-to-weight ratio. Although prior studies have suggested a major influence of the elastic anisotropies of alpha and beta phases on deformation, the under-standing of the onset and the development of plasticity at the beta grain scale is still limited. Strain localization was presently investigated in various Ti alloys with different microstructures. In-situ optical microscopy tensile tests were carried out in combination with digital image correlation and electron back -scattered diffraction in order to relate the local deformation behavior with the microstructure. The low directional modulus along the [001] direction of beta phase was observed to generate high incompatibility stresses, which governs the onset of slip activity and strain localization. However, it was found to emerge differently depending on the presence of alpha phase. In alpha phase free microstructures, high incompatibility stresses across beta grain boundaries triggers the onset of { 112 }( 111 ) slip on the side exhibiting the highest stiffness. In alpha+beta microstructures, beta grains with a [001] direction aligned with the loading direction were found to experience an early onset of plastic deformation and subsequent strain localization. A mechanistic understanding was obtained through the simulation of micromechanical fields in alpha and beta phases. The behavior of polycrystalline aggregates with explicit modeling of hierarchical dual phase microstructure inherent to beta grains was studied within an anisotropic elasticity framework using fast-Fourier transforms-based simulations. An early onset of plastic deformation was found to occur in alpha phase embedded in [001] oriented beta phase as compared to other beta orientations due to stress partitioning driven by the stiffness difference. The effects of the Burgers orientation relationships, the beta phase fraction and the selected set of single crystal elastic constants on stress heterogeneity were also examined and discussed. (c) 2022 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Automated summary

This study investigates strain localization behavior in high strength metastable beta titanium alloys and finds that the elastic anisotropy of the beta phase plays a crucial role in slip activity and strain localization, while the presence of the alpha phase also affects deformation behavior.