Molecular statics and molecular dynamics simulations of the critical stress for motion of a/3 image screw dislocations in α-Ti at low temperatures using a modified embedded atom method potential Original Research Article

Molecular statics and molecular dynamics, and constant temperature, constant volume (NVT) simulations, were performed to determine the core structure and critical stress for motion of a/3image screw dislocations in α-Ti at temperatures ranging from 0 to 50 K using a modified embedded atom method (MEAM) potential. Five different core structures were obtained for the a/3image screw dislocations in α-Ti, one completely spread on the prism plane, three others partially spread on the prism plane and partially spread on the pyramidal and basal planes, and one with predominantly Shockley partial splitting on the basal plane. The core completely spread on the prism plane is found to be the lowest energy structure. The Peierls stress for the minimum energy structure completely spread on the prism plane at 0 K is found to be a high value of 6.875 × 10−3 μ, where μ is the shear modulus and is independent of the orientation of the applied stress. It is shown that this high Peierls stress at 0 K is a consequence of the angular interactions in the MEAM potential. The kink-pair formation energy at zero applied stress is found to be low and equal to 0.16 eV. NVT molecular dynamics simulations show that the minimum stress required to move the screw dislocations by kink-pair formation at temperatures ranging from 5 to 50 K is significantly lower than the 0 K Peierls stress value. A classical phenomenological kink-pair model is fitted to the molecular dynamics data and used to correct for the significantly lower strain rate of deformation present in experiments as compared to molecular dynamics simulations. The corrected simulation data are in reasonable agreement with low-temperature experimental observations of yield stress in single-crystal α-Ti oriented for a/3image prism slip. The developed kink-pair model for prism slip in α-Ti will be useful in higher length scale crystal plasticity models for the deformation behavior of α-Ti.