Microstructures in many engineering alloys are predominantly influenced by solid-state phase transformations that occur during industrial processing; these transformations almost always proceed by nucleation and growth. Quantitative modelling of the process often requires detailed knowledge of the interfaces, notably the interfacial energies that determine nucleation barriers and the interfacial mobilities that control growth kinetics—both of which depend sensitively on the the interfacial structures. Beyond their role in transformation kinetics, interfacial structures and the accompanying orientation relationships (ORs) and interface orientations (IOs) are microstructural features in their own right and directly influence bulk properties. Based on extensive studies of diverse alloy systems, we have formulated a unified framework that rationalises the preferred interfaces and their reproducible ORs produced by phase transformations, by employing preferred interfacial structures of two hierarchical levels. At the fine (atomic) level, the interface adopts a low-energy, periodically matched configuration that minimises the nucleation barrier. Such matching is possible only for specific intrinsic ORs and IOs, thereby imposing the geometric constraints. The structures of the coarse level are characterized by singular interfacial defects. Their development, preferred under given phase transformation conditions, allows the OR and IO to deviate within certain limits from the intrinsic values. This talk will present general methods for correlating ORs and IOs with interfacial structures at both levels and will illustrate the approach with examples from several material systems
[more]
