In-situ investigation of the evolution of microstructure and texture during load reversal of commercially pure titanium using synchrotron X-ray diffraction

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.