Gradient ultrafine-grained titanium: Computational study of mechanical and damage behavior

A computational model of ultrafine-grained (UFG) titanium with random and gradient distribution based on Voronoi tessellation and the composite model of nanomaterials is developed. The effect of grain size, non-equilibrium state of the grain boundary phase (characterized by the initial dislocation density and diffusion coefficient) and gradient of grain sizes on the mechanical behavior and damage initiation of the UFG titanium are studied in numerical experiments. Using computational experiments, the authors determined the likely damage criterion (dislocation-based model) and found several effects that can positively influence the mechanical response and strength of UFG titanium (homogeneity of grain sizes, dispersoids/precipitates in grain boundaries and initial dislocation density in grain boundaries). It is shown that the homogeneous structures of UFG titanium ensure higher yield stress and lower likelihood of damage than gradient structures. The availability of dispersoids or precipitates in UFG titanium changes its damage mechanisms and delays the evolution of damage.