Effect of notch severity and crystallographic texture on local deformation and damage in commercially pure titanium

The evolution of local deformation and damage in commercially pure titanium was studied for flat un-notched, U-notch and V-notch tensile specimens with two distinct initial textures namely off-basal (BA) and prismatic-pyramidal (PP) orientations to establish the micro-mechanisms of anisotropic deformation and damage in titanium for different notch severity. BA orientation showed higher apparent yield stress, greater plastic deformation, better notch strength ratio (NSR) value than PP orientation for all the cases. Electron backscatter diffraction investigation showed an increase in the number of twins per grain and the thickness of twins with notch severity irrespective of orientation with BA samples showing higher twin activity than corresponding PP samples. In addition, extensive slip activity was observed within twins and parent grains in BA orientation unlike PP orientation that showed slip activity near grain boundaries. These microstructural observations correlated well with strain measurement from digital image correlation which also showed that the local maximum longitudinal strain for BA orientation increased with notch severity unlike PP orientation. Viscoplastic self-consistent crystal plasticity simulations at the mesoscale indicated that the activity of basal, pyramidal slip < c+a > systems and twinning increased at the expense of prismatic slip with an increase in notch severity for both the orientations. The experimental observations show extensive diffuse necking in BA orientation, while higher fraction of fluted voids with c-axis aligned along the major axis of the void are observed in the PP orientation. Prismatic slip promotes nucleation and growth of voids in the prism plane which is perpendicular to the tensile axis for PP orientation contributing to void growth along c-axis forming fluted voids, while higher twinning in BA orientation leads to fewer fluted voids, thus highlighting the significant role of crystallographic texture in controlling anisotropic deformation and damage mechanisms in titanium.

Automated summary

The local deformation and damage in commercially pure titanium were studied, and different anisotropic deformation and damage mechanisms were found for different initial textures and notch severity. The microstructural observations and strain measurements showed that crystallographic texture had a significant influence on slip activity, twin activity, and void growth.