Modeling grain fragmentation and deformation textures for titanium using a combined approach of the viscoplastic self-consistent model and a shear fluctuation model

A new grain fragmentation model is proposed for the formation of grain substructures in polycrystalline materials during plastic deformation. Micro-shear bands and twins are assumed to originate from grain boundaries due to the local stress concentrations caused by the interaction of grain boundaries and slip bands. These stress concentrations will impose shear fluctuations on the neighboring grains, which can be relaxed by the formation of corresponding substructures, i.e., micro-shear bands and twins, in these neighboring grains. Texture simulations for cold rolling and equal channel angular pressing (ECAP) of commercially pure titanium are performed using a combined approach of the viscoplastic self-consistent (VPSC) model and the shear fluctuation model. The texture update scheme in the combined approach is presented. Experimental textures at different thickness reductions of cold rolling at room temperature (300 K) and after the first pass of ECAP at 473 K are measured and compared with simulated textures obtained by the standard VPSC approach and the combined approach. In comparison with the standard VPSC approach, the combined approach gives better texture predictions for the two cases: The missing components at low to intermediate rolling reductions in the standard VPSC approach are reproduced; at high rolling reductions and after ECAP, the dominating fibers are also essentially smoothened in the combined approach, in better agreements with the experimental textures.