Plastic deformation kinetics of polycrystalline FCC metals at low homologous temperatures (T<0.4TM)

The flow stress, its strain rate dependence and the athermal component were determined at 77-300K for polycrystalline Ag, Cu and Al. The data were analyzed employing the concept of thermally-activated plastic now. The derived stacking fault energy for the three metals is approximately 20, 50 and 180 x 10(-3) J/m(2), respectively; the Helmholtz free energy for overcoming the obstacles to dislocation motion is 1.6, 1.0 and 0.7 mu b(3), respectively. The obstacle to dislocation motion is overcome when the separation of the partials is reduced by the applied stress to similar to 1.5 b. The magnitude of the pre-exponential factor at small strains (gamma less-than 0.01) is in accord with that for the intersection of dislocations, but decreases orders of magnitude at large strains (gamma = 0.10), suggesting that the rate-controlling mechanism may change with strain. The present results suggest that forest dislocations provide both the long-range and short-range internal stresses opposing dislocation glide.