CORE STRUCTURE OF A DISSOCIATED EASY-GLIDE DISLOCATION IN COPPER INVESTIGATED BY MOLECULAR-DYNAMICS

The atomic structure in the core of two Schockley partial dislocations in copper, resulting from the dissociation of a perfect easy-glide dislocation, and its influence on the fault ribbon, have been investigated for the first time as a function of temperature using molecular dynamics. We employed a resonant model pseudopotential adapted to copper. Our results show that at increasing temperature, the core of the partial dislocations becomes increasingly extended and invades entirely the fault ribbon, but the separation distance between the partial dislocation pairs is not altered. It follows that the structure of the fault ribbon differs significantly from that of an infinitely extended stacking fault and for this reason experimental determinations of the stacking-fault energy, based on the measure of the separation distance between partial dislocation pairs, should be considered with caution. We found that the temperature dependence of the fault ribbon energy in our model is mainly due to the elastic-modulus variation. Moreover, at high temperatures vibrational amplitudes of atoms are much larger in the core of the partial dislocations than in the bulk of the perfect crystal and the local atomic structure becomes highly disordered. Although disordered, the core structure remains solidlike up to the melting point Tm. Above Tm the liquid nucleates always in the core region, thus qualitatively indicating that the nucleation barrier therein is lower than in the bulk. © 1990 The American Physical Society.