Grain-scale micromechanical behaviors of hexagonal titanium utilizing in-situ high-energy diffraction microscopy and crystal plasticity finite element simulations

Abstract

Coupling crystal plasticity finite element (CPFE) simulations with in-situ characterization techniques offers a robust framework for exploring the micromechanical behavior of polycrystalline metals. In this study, we tracked the evolution of the complete elastic strain tensor and orientation rotation of hundreds of grains in a hexagonal titanium (Ti) sample under uniaxial tension using in-situ high-energy diffraction microscopy (HEDM). These experimental observations were systematically compared to CPFE simulations instantiated with experimentally characterized results. It was found that CPFE simulations successfully replicate the macroscopic stress-strain response and texture evolution of polycrystalline Ti, however, only partially capture grain-scale micromechanical behaviors, particularly regarding grain-resolved elastic strains and orientation rotations. Detailed grain-to-grain comparison metrics reveal that incorporating residual stresses into CPFE models significantly improves the predictive accuracy of micromechanical behaviors. Moreover, simulations involving pyramidal <a> slip systems with high critical resolved shear stress, show slightly enhanced predictive performance. Further analyses of individual grains showcase how residual stresses and slip systems selections influence the micromechanical behaviors, highlighting the importance of the grain-scale stress state in determining deformation mechanisms. To understand the role of strain gradient effects in grain-scale stress heterogeneity, a non-local dislocation-based CPFE model was further compared to the phenomenological model discussed above. Although pronounced localized stresses and altered deformation mechanisms were observed near grain boundaries, the dislocation-based CPFE model still cannot significantly improve the predictions of grain-scale micromechanical behaviors. This work deepens the fundamental understanding of deformation mechanisms in hexagonal metals, and offers valuable insights into micromechanical modeling of polycrystalline materials.