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• Coupled in-situ EBSD and CPFEM investigations of commercially pure Titanium. • Different strain evolution at notch tip of TD and RD orientations and related spatio-temporal evolution of slip/twinning and its validation with the simulations. • Localized complex stress/strain state and strain gradient causing high stress at grain boundary leading to activity of higher CRSS slip/twining systems at notch tip. • Anisotropic surface roughness with deformation for TD and RD orientations and its prediction with the simulations. This study investigates the impact of notch severity and initial texture on the micro-mechanisms during low strain deformation in commercially pure Titanium, exploiting in-situ electron back scatter diffraction (EBSD) experiments and crystal plasticity finite element model (CPFEM). In-situ tests were performed at different strain steps of un-notched and notched samples of transverse direction (TD) and rolling direction (RD) orientations. CPFEM, based on initial EBSD microstructures, predicted profuse prismatic slip traces and early activation of prismatic slip in notched sample, with RD orientation exhibiting higher activity. Further, CPFEM results revealed early activation of high CRSS slip systems as well as evidence of early twin activity at notch tip due to severely localized plastic deformation and steep strain gradient, as observed by GND maps causing higher stress at grain boundaries. At the notch tip, digital images correlation (DIC) at microscale indicated strain localization at 45 ∘ and 90 ∘ to the tensile axis for TD and RD orientations, respectively. Furthermore, 2.5D and 3D CPFEM confirmed distinct strain patterns at notch tip: TD orientation exhibited combined basal and prismatic slip influences, while RD orientation displayed dominant prismatic slip systems at localized strain. The model also successfully predicted anisotropic surface roughness, contributing to early necking in RD orientation. [Display omitted] [ABSTRACT FROM AUTHOR]

• Initial crystallographic texture notch severity controls deformation and damage micro-mechanisms in CP-Ti • Off-basal (BA) orientation shows higher apparent yield stress, greater plastic deformation, better notch strength ratio value than prismatic-pyramidal (PP) orientation • Extensive extension twinning in BA samples compared to PP samples which increases with notch severity from unnotched to U and V notch samples • Combination of dominant prismatic slip and crystallographic texture contributes to higher diffuse necking in BA sample and higher fraction of fluted voids in PP sample • Symbiotic role of texture and notch severity decides deformation and damage mechanisms in CP-Ti 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 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. [Display omitted] [ABSTRACT FROM AUTHOR]

Understanding of the deformation micro-mechanism as a function of grain orientation during cyclic loading is of significant importance to have failure safe design of structural components made of commercially pure titanium (CP-Ti). The evolution of deformation microstructure and texture of commercially pure titanium samples with prismatic-pyramidal (orientation A) and near basal (orientation B) as initial texture along the loading direction has been investigated during load reversal at ±8% and ± 12% strain using in-situ synchrotron X-ray diffraction. The synchrotron X-ray diffraction results have been further complemented with Elastic-Plastic Self-Consistent (EPSC) simulation of the texture data and ex-situ Electron backscatter diffraction (EBSD) scan taken at the same region. Orientation A showed partially reversible texture whereas orientation B showed non-reversible texture with mechanical reversibility. The partial textural reversibility has been attributed to the prism to basal slip transition which toggles the c-axis between the normal and transverse direction during the tension-compression cycle. With an increase in strain from 8 to 12%, microstrain and dislocation density in the basal plane of orientation A decreases sharply. On the other hand, for the same level of strain in orientation B, microstrain increases but the dislocation density of basal plane shows insignificant change. The crystal orientation map obtained from ex-situ EBSD of deformed microstructure complements to the fact indicating, with increase in strain, deformation of basal oriented grains show non-Schmid behaviour of contraction twin propagation due to local strain incompatibility in orientation A. On the other hand, the prism oriented grains of orientation B have mostly deformed by extension twinning, which reorients them towards basal orientation. The deformation proceeds by lateral thickening of twins due to the lower elastic stiffness of the twinned region compared to the grain matrix. The extension twin boundaries get converted to contraction twin boundaries at higher strain during load reversal. • Evolution of orientation specific deformation microstructure during load reversal • Role of prism to basal slip transition in partial textural reversibility • Non-Schmid behaviour of twin propagation during slip transition • Correlation of twin thickening and twin/matrix elastic stiffness difference [ABSTRACT FROM AUTHOR]