Using a multiscale quantum-mechanics/molecular-mechanics approach, the interactions between impurities (H, He) and dislocations (edge, screw) in α-Fe were examined. The impurity trapping at the dislocation core was examined by calculating the impurity-dislocation binding energy and the impurity solution energy. It was found that in general both H and He prefer the tetrahedral sites at the dislocation core, as well as in the bulk; the exceptions were due to deformed structures at the dislocation cores. Both H and He have a greater solution energy and binding energy to the edge dislocation than to the screw dislocation. The impurity pipe diffusion along the dislocation core was investigated using the quantum-mechanics/molecular-mechanics nudged-elastic-band method. It was found that the diffusion barrier along the screw dislocation was lower than the bulk value for both H and He impurities. For the edge dislocation, although H had similar diffusion barriers as in the bulk, He had much higher diffusion energy barriers compared with the bulk. Finally the impurity effect on the dislocation mobility was examined. It was found that both H and He could lower the Peierls energy barrier for the screw dislocation significantly. The H-enhanced dislocation mobility was consistent with experimental observations.

QM/MM Study of Dislocation-Hydrogen/Helium Interactions in α-Fe. Y.Zhao, G.Lu: Modelling and Simulation in Materials Science and Engineering, 2011, 19[6], 065004