A study of the accommodation of coherency strain by interfacial defects at a grain boundary in gold

Abstract

The structure of a ⟨ 110 ⟩ 90° grain boundary in Au is investigated using high-resolution transmission electron microscopy (HRTEM) and atomistic simulation. It consists of coherent segments, exhibiting the extended 9R configuration described by Medlin et al. 10, with superimposed line defects to accommodate the coherency strain. Two types of defects are observed, crystal dislocations and disconnections, where the latter exhibit step nature in addition to dislocation character. Both types of defect are identified by HRTEM in combination with circuit mapping, and their parameters are shown to be consistent with the topological theory of interfacial defects 7. Moreover, the misfit-relieving function of observed defect arrays, their influence on interface orientation and the relative rotation of the adjacent crystals is elucidated. During observation, defect decomposition is observed in a manner which conserves Burgers vector and step height. One of the decomposition products is glissile, consistent with the ‘glide/climb’ rules for interfacial defects. This glissile motion is also found by atomistic simulation of the disconnection when an applied strain is imposed. The γ-surface for the interface is calculated and shows that no alternative boundary structure is stable, confirming, consistent with experimental observation, that defects separating different configurations are not feasible.