{111} tilt grain boundaries as barriers for slip transfer in bcc Fe

Abstract

We have studied the interaction of an individual dislocation and a pile-up of dislocations with {111} tilt grain boundary in iron by means of atomistic simulations. The {111} tilt grain boundary, under externally applied stress, can change orientation by forming steps of three plane high thanks to shuffling of two atoms per Coincident Site Lattice (CSL) unit cell. When an individual crystal dislocation interacts with the GB, there is no transmission of the dislocation. Instead, we observe the formation of the same steps as found under the application of external stress. Depending on the orientation of the glide plane of the dislocation, two situations may occur. (i) If the glide plane perpendicular to the GB, the GB transforms into a stepped segment and a {112} twin boundary. (ii) For the other glide planes, the dislocation is absorbed by the GB and form a facet along the glide plane. Up on the interaction with a pile-up of dislocations, the stress concentration accumulated in the interaction region enhances the same reaction process, i.e. in (i) there is a penetration of one grain into the other with the dislocation in the tip of the intrusion bounded by the symmetric (112) and asymmetric stepped segment respectively. In (ii), the second dislocation is absorbed increasing the length of the facet. Based on the obtained results, one can conclude that {111} GB acts as a strong obstacle for gliding dislocations, does not allow a direct dislocation transmission, which makes a contrast with other types of {110} GBs (e.g. (112) and (332)).