Dislocation dynamics in strain aging alloys

The problem of dynamic strain aging is treated using a new approach to the aging kinetics. The moving dislocations are considered as an ensemble of double loops which overcome the forest dislocations by thermal activation. This implies an exponential distribution of waiting times in front of the obstacles during which additional pinning agents arrive at the dislocation. The temporal development of the mean number of pinning points per loop can be calculated from an appropriate master equation which is based on the dynamic transition rates for pinning and depinning of the dislocation segments. It is shown that the two pinning mechanisms, lineal pinning and forest strengthening discussed in the literature, can be treated in a unified way. This leads to the definition of a single parameter, the mobility factor, which completely describes the effect of dynamic aging on dislocation velocity and plastic strain rate. The role of local instabilities and the problem of strain rate sensitivity are discussed.