Temperature and stain rate effect on the deformation of nanostructured pure titanium

Abstract

The behavior of nanostructured pure Ti has been studied experimentally and theoretically using a crystal plasticity (CP) finite element polycrystalline model. The actual polycrystalline microstructure (grain shape and orientation distributions) was accounted in voxel-based representative volume elements. The crystal behavior was described by a standard CP model with a physically-based description of the plastic slip rate based on the theory of thermally activated dislocation motion. Prismatic, basal and pyramidal <c+a> slip systems were considered. The parameters of the CP model were obtained by combining experimental measurements (i.e. dislocation densities) and an inverse analysis of the macroscopic experimental results. The resulting polycrystalline model was validated by an accurate reproduction of independent experimental tests performed at different temperatures and strain rates. The critical resolved shear stresses (CRSS), predicted by the model for the different slip systems, show the expected increase with respect to those for coarse grained pure Ti. The nanostructured Ti shows lower strain rate sensitivity and activation volumes than coarse grained pure Ti. The ratios between the CRSSs of the different slip systems at room temperature were almost independent of grain size. The model was used to predict the evolution of the CRSSs as a function of temperature and a faster decay of pyramidal CRSS was found compared to prismatic and basal ones.