Contributions to the theory of jogged screw dislocation glide

Abstract

The velocity of screw dislocations limited by the nonconservative motion of jogs is investigated. The vacancy concentration profile near a moving screw dislocation containing alternately signed jogs separated by a distance λb, whereb is the magnitude of the Burgers vector, has been calculated. It is shown that for λ > 20 the vacancy profile is essentially the same as that found previously for the case of a moving screw dislocation containing isolated jogs. It is shown that the jog-jog diffusion interaction does not change the stress dependence of the glide velocity as has been suggested. The steady state velocity of a gliding jogged screw dislocation responding to an effective stress τe is calculated using the quasiequilibrium approach to dislocation climb and the steady state vacancy concentration profile. It is shown that the glide velocity exhibits hyperbolic tangent stress dependence if the average vacancy concentration in the crystal equals the equilibrium vacancy concentration, Co. If, however, the average vacancy concentration in the crystal follows the relation Co cosh (λb3 τekT) during deformation, the glide velocity can be expressed as υ = πDυb2C0 sinh (λb3 τe/kT whereDυ is the diffusion coefficient for vacancies in the crystal. A model which suggests that the equilibrium vacancy concentration follows a relation similar to the hyperbolic cosine dependence is presented.