A general approach for stress anomalies and plastic instabilities in intermetallics

A general model for strength anomalies is proposed, based on an analysis of the relative kinetics of the different mechanisms (multiplication, annihilation, exhaustion, unlocking,…) controlling the evolution of the mobile dislocation density. A steady state in mobile dislocation density is reached when a balance is achieved between these mechanisms and can be described by simple rate equations. It is shown that a strain rate sensitivity (SRS) close to zero is the signature of a dominant exhaustion, whereas a positive SRS is expected from a locking–unlocking process. The SRS thus appears to be a key parameter in the selection of the relevant microscopic mechanisms responsible for stress anomalies. The stability of the steady state is also studied in terms of a linear stability analysis. It is shown that serrated flow is expected for strain rates lower than a critical value, which is particularly sensitive to the thermally activated exhaustion rate.