Faceted interfaces: a key feature to quantitative understanding of transformation morphology

Faceted interfaces are a typical key feature of the morphology of many microstructures generated from solid-state phase transformations.Interpretation,prediction and simulation of this faceted morphology remain a challenge,especially for systems where irrational orientation relationships(ORs)between two phases and irrational interface orientations(IOs)are preferred.In terms of structural singularities,this work suggests an integrated framework,which possibly encompasses all candidates of faceted interfaces.The structural singularities are identified from a matching pattern,a dislocation structure and/or a ledge structure.The resultant singular interfaces have discrete IOs,described with low-index g’s(rational orientations)and/orΔg’s(either rational or irrational orientations).Various existing models are grouped according to their determined results regarding the OR and IO,and the links between the models are clarified in the integrated framework.Elimination of defect types as far as possible in a dominant singular interface often exerts a central restriction on the OR.An irrational IO is usually due to the elimination of dislocations in one direction,i.e.,an O-line interface.Analytical methods using both three-dimensional and two-dimensional models for quantitative determinations of O-line interfaces are reviewed,and a detailed example showing the calculation for an irrational interface is given.The association between structural singularities and local energy minima is verified by atomistic calculations of interfacial energies in fcc/bcc alloys where it is found that the calculated equilibrium cross-sections are in a good agreement with observations from selected alloys.