To clarify the mechanisms of plastic deformation and ductile fracture, it is crucial to elucidate the defect-formation processes occurring during plastic deformation. In this study, we performed in situ transmission electron microscopy (TEM) observations of the formation of small prismatic dislocation loops via the double cross-slip of screw dislocations in high-purity iron during tensile deformation at elevated temperatures. Conventionally, the type of a dislocation loop (vacancy or interstitial) has been determined by exploiting the dependence of its image contrast on diffraction conditions, as well as the diffuse scattering patterns generated by the loop in electron diffraction. However, such “static” identification methods are inapplicable to small dislocation loops (approx. <30 nm in diameter) whose image contrast becomes indistinct due to the comparatively large thickness of specimens required for dynamic in situ observations. To overcome these limitations, we propose a new “dynamic” identification method that utilizes the dynamic behavior of a dislocation forming a loop, rather than the intrinsic image contrast or diffuse scattering patterns of the loop itself. Applying this method, we reveal that the dislocation loops formed during tensile deformation at elevated temperatures are of the vacancy type. This finding suggests that loop formation via double cross-slip at elevated temperatures is one of the vacancy-formation mechanisms during plastic deformation, providing important insight into the ductile fracture processes of iron-based materials.
Inoue et al. (Thu,) studied this question.