Glide and cross-slip of a-dislocations in Zr and Ti

Slip systems involving dislocations with Burgers vectors have been studied in hexagonal close packed Zr and Ti, by means of in situ straining experiments in a transmission electron microscope, at various temperatures and as a function of resolved shear stress. The results show that Zr and Ti are very similar in many respects. Prismatic slip is activated at rather low resolved shear stresses, and is controlled by the interaction between mobile dislocations and solute atoms (presumably oxygen). Pyramidal slip requires substantially higher resolved shear stresses and is characterized by straight screw dislocations moving by a kink-pair mechanism. Basal slip is activated at and above room temperature, for resolved shear stresses equal or higher than those in the prismatic planes. The slip traces are always wavy, presumably due to intensive cross slip from basal to prismatic planes. It also involves straight screw dislocations moving by a kink-pair mechanism. These microscopic observations are discussed in the light of some aspects of the mechanical behavior, in particular the increase of yield-stress at decreasing temperature and the discontinuity of activation area close to room temperature. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.