INTERNAL-FRICTION IN FCC ALLOYS DUE TO SOLUTE DRAG ON DISLOCATIONS .1. A MODEL FOR THE EFFECT OF CORE DIFFUSION

The internal friction (mechanical loss) behavior of dislocations is st udied in a model which, for the first time, considers the substitution al solute mobility in the dislocation core to be higher than in the bu lk around it. The parameters investigated include the external stress sigma(xy), the solute concentration c0, the pinning length of the disl ocation and the temperature. It is shown that, at low c0 and high sigm a(xy), the kinetics of the dislocation motion is determined by the fas t diffusion of the solute atoms in the core, while for high c0 and low sigma(xy) the diffusion of the atoms far away from the dislocation is rate-limiting. The results are compared with the analytical model of Schoeck and are applied to the alloy system Al-Si. New experimental re sults supporting the model are described in a companion paper (Part II ).