Generalized interfacial fault energies

Disconnections in' metals have been shown to be the driving mechanism behind a variety of orientation and phase transformation changes. Thus, they have a profound effect on the microstructure, plastic deformation, and mechanical properties of interest to the engineer. Disconnections glide along interfaces, procedurally moving the interface by a characteristic step by causing the parent crystal to change its structure and/or Orientation. The intrinsic deformation caused by this process depends on the character of the active disconnection among other possible disconnection candidates. While for phase transfohnadons admissible defects depend on the extent of long-range diffusion, in general, the selection process of active disconnections is highly affected by their mobility. In deformation twinning, the magnitude of the characteristic shear, the complexity of local atomic rearrangements, and step height have been all shown to determine the disconnection's possible activation and typical growth rate and thereby the morphology of the associated twin. However, despite these seminal refinements, no formal criterion exists yet which predicts the most active disconnection in comparison to other possible deformation modes. There is still confusion, for example, about the dependence of twinning on the c/a ratio, i.e. why a certain twin mode would appear in a given hexagonal metal and not in another one. This paper fills these gaps by introducing a new quantitative metric for disconnection mobility, and an example application is extended for the case of deformation twinning in hexagonal-close packed metals. This metric draws inspiration from the generalized stacking fault concept which is only relevant for bulk defects. (C) 2017 Elsevier Ltd. All rights reserved.