In situ monitoring of the deformation mechanisms in titanium with different oxygen contents

The deformation mechanisms of two titanium batches with different oxygen contents were monitored during tensile tests performed along the rolling and transverse directions under an optical or scanning electron microscope, after EBSD mappings of grain orientations. Whereas the contribution of mechanical twinning was very limited, grain boundary sliding, sometimes leading to intergranular decohesion, as well as kink bands formation were observed. Based on the identification of the primary slip traces in a significant number of grains, the critical resolved shear stresses (CRSSs) for prismatic, basal and π1〈a〉 were estimated. Transmission electron microscopy was used to identify unambiguously dislocations of π1〈c+a〉 systems and to estimate the corresponding CRSS. The difference in oxygen content between T40 and T60 was found to modify the magnitude of the CRSSs, but to leave their relative values nearly unchanged. The evolutions in the work hardening rate were correlated with the active deformation mechanisms.