The dependence of the width of a dissociated dislocation on dislocation velocity

Abstract

The motion of glide dislocations in f.c.c. alloy crystals subjected to a unixial stress is analyzed assuming that the steady-state velocity of each Shockley partial is a function of the total force acting on it per unit length. It is shown that the velocity of an a 2 〈110〉 glide dislocation is a function of the average Schmid factor of its Shockley partials. It follows that the usual interpretation of Schmid's Law where yield stress is correlated with the total Burgers vector of the glide dislocation is valid only when the magnitudes of the Burgers vectors of the partial dislocations are equal, as happens to be the case in the f.c.c. lattice. It is also shown that the degree of dissociation of a glide dislocation depends on its velocity and the direction and sense of the uniaxial stress. In tension near [111], glide dislocations are completely dissociated at moderately high velocities (∼10 cm/sec) in alloys with a high frictional drag and low stacking fault energies. In tension near [001], glide dislocations constrict at high velocities so that their cores may overlap in alloys with a high frictional drag and high stacking fault energies. These effects should exert an influence on the strain hardening characteristics of such alloys at high strain rates.