Phase transformation via atomic-scale periodic interfacial energy

Displacive and diffusional transformations are the main processes during solid-state phase transformations, which have formed the basis of applied physics and materials technology for centuries. However, the relationship between diffusional and displacive transformations has remained elusive, which significantly hinders the fundamental understanding and control of the microstructures and properties of materials via phase transformations. Here, we introduce the concept of a periodic differential interfacial energy between atom layers. We develop the mechanism of an atomic-scale displacive process in the form of atoms groups (cells) based on the periodic differential interfacial energy and experimentally determine the displacive short-range order (SRO) cell size in an Mg–Li alloy using a neutron total scattering method. We proposed that the origins of both the displacive and diffusional transformations are displacive in nature governed by the driving force of transformations. Our work paves the way for building a bridge correlating the nature of various solid-state phase transformations. © 2022 Elsevier Ltd