On the atomic nature of complex dislocation locks in C15 Laves phases

The practical applications of Laves alloys are hindered by their intrinsic brittleness at ambient temperature. Dislocation lock structures are expected to play a critical role in governing the plasticity of these alloys; however, their atomic-scale nature remains poorly understood. Here, combining conventional transmission electron microscopy analyses, atomic-resolution scanning transmission electron microscopy images, and atomistic simulations, we unveiled the types, configurations, and formation mechanisms of dislocation locks in a Nb-rich (35 at.% Nb) C15 NbCr 2 Laves phase alloy. Moreover, complex defect structures within the cores of dislocation locks, including antisite-like columns of Nb and vacancy-like columns of Cr, were experimentally identified at the atomic scale and rationalized by atomistic simulations. The dislocation locks may serve as preferential sites for crack initiation due to the localized stress concentration. Such stress concentration–induced cracking was experimentally confirmed by the observed intersection of slip planes. Furthermore, the formation mechanisms of four types of dislocation locks and their potentially distinct influences on crack initiation were discussed. The discovery of these lock structures and their influence on crack formation may offer new insights into defect engineering in Laves phases, paving the way for improved strategies to mitigate their intrinsic brittleness.