Ti6A14V anisolropy and texture evolution predictions using multisite and self consistent crystal plasticity models

The goal of this study is to assess whether the MULTISITE and the Viscoplastic Self Consistent (VPSC) models can predict the mechanical behaviour and the texture evolution of plastically deformed hexagonal metals. Two types of Ti6Al4V,a sheet and a bar,are considered in the application. Plastic anisotropy of this type of titanium alloy is known to depend predominantly on texture due to their hexagonal closed packed structure (hep) ,but other microstructural parameters,such as the average grain shape,also have a potential influence. Hexagonal close-packed crystals usually demonstrate larger anisotropy than cubic crystals. In this respect,the interaction between adjacent grains should be taken into consideration. The MULTISITE model is based on polycrystalline plasticity and the underlying hypotheses of the model are (i) that the deformation of each grain is significantly influenced by the interaction with a limited number of adjacent grains,and (ii) that local strains deviate from their macroscopic average according to specific "relaxation modes". A quantification criterion of the Ti6Al4V texture is also done to improve texture prediction. The models are used to simulate different tension and compression tests performed on rolled sheet and on a bar,made of Ti6Al4V,in different directions. The Lankford coefficients (r) and the yield limit calculated in various directions in the plane of the sheet are analysed and compared to experiments. Based on experimental r-values and X-Ray Diffraction (XRD) measured texture of a Ti6Al4V,an identification of the critical resolved shear stresses (CRSS) of the different slip system families of the HCP.the hardening parameters and the strain rate sensitivity parameter was made for the two models and discussed after comparisons with experiments. Texture prediction is discussed with comparison to measured deformed textures by XRD and Electron BackScattered Diffraction (EBSD).