Thermally activated motion of a screw dislocation overcoming the Peierls potential for prismatic slip in an hcp lattice

The prismatic slip in hcp metals has been studied by calculating the thermally activated motion of a 1/3[11 (2) over bar 0] screw dislocation in a two-dimensional Peierls potential assumed in the (11 (2) over bar 0) plane. The kink pair formation process for the transition of the dislocation from a stable position to another under applied stress has been investigated and the activation energies for the two types of transitions constituting the prismatic slip have been calculated. Using the activation energies, the critical Bow stress tau(c) has been deduced as a function of the direction of the applied stress chi and temperature. The calculated tau(c)-chi relations deviate significantly from the Schmid law and well reproduce the deviation relation observed in the experimental data of Ti. The deviation from the Schmid law originates in a structural feature of the hcp lattice itself, i.e., a zigzag arrangement along the prismatic plane of atomic rows.