Characterization and Analysis of Strain Heterogeneity at Grain-Scale of Titanium Alloy with Tri-Modal Microstructure during Tensile Deformation

Grain-scale strain heterogeneity characteristics play a critical role in the ductile damage behavior and mechanical properties of two-phase titanium alloys. In this work, the grain-scale strain distribution, strain heterogeneity, and strain localization of titanium alloy with tri-modal microstructure (consisting of equiaxed α (α(p)), lamellar α (α(l)), and β transformed matrix (β(t))) during tensile deformation were experimentally investigated. The results show that the strain probability distribution of the whole microstructure obeys normal distribution during deformation. Significant strain heterogeneities exist in each constituent (α(p), α(l), and β(t)) and the whole microstructure. At lower macro-strain, α(p) and α(l) exhibit higher average strain than those of β(t) and the whole of the microstructure. Meanwhile, strain heterogeneity of each constituent is small and has a negligible change. The strain heterogeneity of the whole microstructure is mainly determined by α(p). At larger macro-strain, some highly deformed regions produce and their positions do not change during further deformation. As a result, the strain heterogeneity of each constituent increases fast, and the strain heterogeneity of whole microstructure is mainly related to α(l) in this deformation stage. On the other hand, two types of strain localization may be generated within α(p) and α(l) and at the α(p)/β(t) and α(l)/β(t) boundaries, respectively. The former type is caused by transgranular intense slip deformation and presents crystal orientation dependence. The latter type is related to the boundary sliding and presents spatial distribution dependence for α(l). These strain localizations greatly determine the micro-damages, thus forming the corresponding micro-voids within α(p) and α(l) and the micro-cracks at α(p)/β(t) and α(l)/β(t) boundaries in tri-modal microstructure at larger deformation.