Dislocation pairing transition

The structure of grain boundaries can depend on the temperature and other environmental conditions. In this project we investigate this structural transition in delta iron using Ginzburg-Landau models, which are derived from phase field crystal or classical density functional theory. In partiuclar, we can identify that the temperature dependent dislocation core volume is the decisive factor for the dislocation pairing transition.

Overview

A transition between different grain boundary structures in delta-iron has been reported recently: At high temperatures close to the melting point the dislocations at a low angle grain boundary of a [100] symmetric tilt have pure edge character, whereas at low temperatures they split into partials with a mixed edge and screw character. The predictions are based on molecular dynamics and phase field crystal simulations. Different reasons for this transition have been found. We observe the same phenomon using amplitude equations desciptions. This underlines the relevance of the previous findings and further supports the newly developed model.

This transition is visualized in our 3D virtual materials laboratory.

Fig. 1: 3D visualization of the dislocation pairing transition. At high temperatures, the dislocations have pure edge character (left), whereas at low temperatures they split into dislocations with a mixed edge and screw character (right). This leads to a bending of the lattice planes (bottom right).
© Robert Spatschek, Max-Planck-Institut für Eisenforschung GmbH
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