Dislocation glide velocity in creep of Mg alloys derived from dip tests

摘要

Creep generally results from a certain density of dislocations gliding at a certain velocity. In order to decouple the two quantities one needs information beyond the creep rate-stress-temperature relationship. Stress dip tests have been proposed to yield information on the athermal and the thermal components of creep stress. The athermal stress component is connected to the density of dislocations, the thermal stress component is effective in driving glide. Assuming simple relations between the stress components and the density it is possible to derive the relation between dislocation velocity and effective stress which is needed to model the creep behavior on a microstructural basis. Results in the range of 473-673 K are presented for Mg of technical purity and the Mg-alloy AS21. The dislocation velocities obtained are compared with theoretical expressions modeling either solute drag, forest cutting, or prismatic glide. The observed magnitude and small temperature dependence of the dislocation velocity cannot be consistently explained by any of the three models.