Towards further understanding of stacking fault tetrahedron absorption and defect-free channels - A molecular dynamics study

The mechanisms leading to stacking fault tetrahedron (SFT) absorption via interactions with dislocations, and subsequent formation of plastic flow localization in defect-free channels, which were frequently observed in irradiated materials in transmission electron microscopy experiments, are still unclear. To address this, screw dislocation interactions with SFTs in copper were investigated using molecular dynamics (MD) simulations. The interaction details reveal that a screw dislocation can fully absorb an SFT through the thermally activated transformation of Lomer-Cottrell lock into Lomer dislocations. After absorption, almost all the vacancies in the SFT are transferred into Lomer dislocations, which are able to move transversely under complex loading conditions. As a result, SFTs can be removed from the material (for SFTs near surface) or from defect-free channels (for SFTs in the bulk) with the aid of Lomer dislocations. In addition, it was shown that this absorption process is favorable only at high temperature, low applied shear stress and/or high SFT density. These results are in good agreement with in situ TEM observations. The current simulations and analyses provide useful insights into the formation mechanisms of defect-free channels in irradiated materials.