The Anisotropic Dislocation Activities of a Near-α Ti6321 Titanium Alloy During Cryogenic Tensile Creep Tests

Near-α Ti6321 titanium alloy serves as a critical load-bearing material for deep-sea pressure hulls and polar equipment. These structural components, however, are prone to suffer from creep deformation during long-term service even in cryogenic cases. While the dislocation dependency of such anomalous creep is documented, the specific dislocation activity remains less clarified, especially at low temperatures. Therefore, in situ tensile creep tests at −120 °C were carried out on a rolled Ti6321 plate along the rolling direction (RD) and the 45° direction. The characteristics of dislocation activity were illustrated by the joint EBSD-assisted slip-trace analysis, Schmid factor calculation, and statistical analysis of the local misorientation of deformed samples. Significantly distinct dislocation activities are detected in the RD and 45° specimens, respectively. The results demonstrate that the creep behavior of the RD specimen is dominated by basal and prismatic slip, accounting for 55.5% and 25.8%, respectively. In contrast, basal slip is severely suppressed in the 45° specimen—only 3.1%—accompanied by the extensive activation of pyramidal {101¯1} <a> and pyramidal {112¯2} <c + a> slips, which account for 29.8% and 41.9%, respectively. Compared with RD specimens exhibiting a relatively uniform microstrain distribution, the severe local stress concentration in the 45° specimen is attributed to the pile-ups of dislocations as α/β phase interfaces. This study unveils the anisotropic activities of dislocations in Ti6321 alloy during cryogenic creep.