Micromechanism of stress state effect on plasticity of Ti-6Al-4 V alloy

To better understand the underlying mechanism of stress state effect (SSE) in the deformation of Ti-6Al-4 V alloy under different loading conditions, an interrupted test scheme is adopted to correlate the macroscopic plasticity characteristics to microphysical mechanisms. Complemented by the electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) techniques, it's confirmed that dislocation motion and grain boundary (GB) migration, both exhibiting a strong dependence on the stress states, play a dominant role in the plastic deformation of the material, and the evolution of them are quantified for compression, tension, and shear loading conditions. Specifically, the migration behavior of V2GB under compression loading is clearly observed for the first time through a post-deformation EBSD analysis. A novel plastic model is proposed by incorporating different deformation mechanisms with stress state parameters. This model comprehensively considers the effects of dislocation motion and GB migration on the plasticity of the material under different deformation and stress states. The results show that this model not only reasonably predicts the SSE of Ti-6Al-4 V, but also effectively captures the work-hardening behavior of the material. This work offers an in-depth understanding of the SSE in materials, thereby facilitating the modeling between macroscopic mechanical behavior and microscopic physical mechanisms in metallic materials.