Macro-micro behaviors of Ti–22Al–26Nb alloy during warm tension

In this paper, the plastic flow rules and fracture evolution mechanisms of the nearly O + B2 Ti–22Al–26Nb alloy during warm tension have been studied within a wide temperature range of 20–800 °C. The macro-micro deformation behaviors of the material have been investigated by means of SEM, EBSD and TEM. It is found that the stress-strain curve at 400 °C exhibits serrated patterns, indicating the occurrence of dynamic strain aging at mild temperature. The overall yield strength decreases and the uniform elongation increases with the temperature in general. However, an unexpected peak of yield strength and also an unexpected valley of uniform elongation are exhibited at 600 °C. Additionally, the uniform elongation shows a positive correlation with strain rate at 600 °C. With the comprehensive analyses of fracture surface characteristics, the morphological variation of the constituent phases and the dislocation structure evolution, the causations of the above phenomena are further explained as follows. The B2 phase is mainly responsible for deformation coordination between O laths with the original {110} B2 ∥(001) O orientation barely changed, and act as a media for propagating localized slip deformation to O grains. The abnormal mechanical responses at 600 °C are mainly attributed to the change of fracture mode caused by the precipitation of fine acicular O grains, while the softening mechanism at 800 °C is mainly dominated by the dynamic globularization of the O phase. • Serrated yielding and high elongation of 22.73% at 400 °C relates to dynamic strain aging. • Unexpected yield peak at 600 °C rises from the additional strengthening by nanoscale secondary O. • Unexpected elongation valley at 600 °C is due to quasi-cleavage fracture of B2–O lath interface. • B2 and O phase keeps {110} B2 ∥(001) O relation during warm tension via deformation coordination. • Enhanced globularization and coarsening of O laths causes flow softening at 800 °C.