Geometrical Aspects of Dislocation-Obstacle Interaction in Iron

Experiments and atomic-scale computer simulations have shown that nano-scale voids and copper precipitates can be strong obstacles to the glide of dislocations in neutron-irradiated iron. Simulations have shown that voids are strong obstacles and that an edge dislocation climbs by absorbing vacancies at it breaks away from voids. The obstacle strength of copper precipitates is enhanced by a dislocation-induced structural transformation if they are large enough and the temperature is low enough. Most simulations have the centre of a spherical void or precipitate on the slip plane of an edge dislocation. The present work investigates how the strength of 2 and 4 nm voids and precipitates varies with the distance of their centre from the slip plane at temperatures across the range 0 to 450 K. The strength of voids is highest when their centre coincides with the slip plane, but this is not the case for small precipitates, which do not transform from the bcc structure. The strength of both type of obstacle, and the extent of climb at voids and transformation of large precipitates are not symmetric with respect to the position of their centre from the slip plane. The results are discussed in terms of the atomic mechanisms involved.