Dislocation Motion in Crystals With a High Peierls Relief: A Unified Model Incorporating the Lattice Friction and Localized Obstacles

Abstract

The combined effect of the lattice friction and localized obstacles on the individual dislocation velocity is considered. First the two effects are considered separately. The velocity of an individual dislocation is described by the Hirth-Lothe equation for the case of lattice friction and by a power law for the case of localized obstacles. The power law is modified to introduce a static waiting time: the time a dislocation has to wait in its equilibrium configuration at an obstacle until it breaks away by virtue of thermal activation. As a next step, a combination of the two mechanisms is described. A dynamic waiting time is introduced: it corresponds to a situation when a dislocation overcomes the obstacle before it reaches the equilibrium configuration. The model provides a good description of the effects when they are independent, and also gives an interpolation of the two regimes. A simulation for a model material is proposed to illustrate the transition between the two regimes. This unified model is tested against experimental data for in-situ deformation of monocrystalline germanium in a transmission electron microscope. The purpose is to determine an equivalent power law exponent in a regime of plastic flow that does not follow a proper power law. The resolution is not complete because the strength of the localized obstacles is not known. However, the results are promising and allow a discussion relating to the strength of localized obstacles.