In situ SEM study of tensile deformation of a near-ß titanium alloy

In this study, the deformation behavior of a near-β Ti-17 titanium alloy under uniaxial tension was investigated using electron backscatter diffraction (EBSD) and tensile tests with in situ scanning electron microscope (SEM) observation. It is found slip mode is the main deformation mechanism in primary α grains of Ti-17 during the tensile test. Slip systems activated were identified by performing calculations on EBSD orientation data. The results show that all the three slip systems with a-type Burgers vector, i.e. basal, prism and 1st-order pyramidal slip, could be activated in the primary α grains of Ti-17, but no a+c-type slip (2nd-order pyramidal slip) activated is observed. Analysis reveals that basal and prism slips are the dominating slip mode, while 1st-order pyramidal slip acts as a subsidiary or deviated slipping mode. For the equivalent slip systems, Schmid factor dominates the slip behavior, while for the non-equivalent slip systems, critical resolved shear stress (CRSS) must be taken into account. It is proved that CRSS for a+c-type slip is much larger than that for a-type slips (basal and prism slips) in Ti-17 alloy (at least 2.5 times that for basal slip). a-type slip remains the easiest slip to be activated even in the condition favoring a+c-type slip and suppressing a-type slip (an angle of ~10° between the tensile axis and c-axis).