Abstract
The orientation relationship (OR) between phases related by a phase transformation is often reproducible. This study interprets and predicts the reproducible ORs with a two-stage approach. The initial OR formed at the nucleation stage tends to allow a periodic structure of a preferred state to form in the interface. A matching correspondence of either a one-to-one or n-to-m nature can be specified in the periodic structure. An initial OR will become the final reproducible OR if there is no misfit. Otherwise, a reproducible OR developed at the growth stage tends to permit a singular dislocation structure to form in an interface where the preferred state must be sustained locally. The actual change in the OR is subject to the given material system and the phase-transformation condition. Various singular dislocation structures and their constraints on the ORs are analyzed, with thermodynamics and kinetics applied conceptually. The resulting ORs can be specified by following one or more Δg parallelism rules. A set of workable steps is provided to facilitate the interpretation of observed reproducible ORs. Some unsolved problems are identified, which call for further studies that can quantitatively combine the thermodynamics, kinetics and crystallography of phase transformations.
Highlights
The crystallography of a structural phase transformation in a crystalline material concerns the orientation relationship (OR) between the product and matrix phases and the morphology of the product phase expressed on the crystal basis of both phases
Our approach specifies the ORs initiated at the nucleation stage in a number of small regions, and it further confines the ORs developed at the growth stage to discrete descriptions
While this study mainly concerns two phases related by a phase transformation, the two-stage approach can be applied, in principle, to other cases in which reproducible ORs are observed, including eutectic reactions, eutectoid reactions, surface reactions and the growth of thin films
Summary
The crystallography of a structural phase transformation in a crystalline material concerns the orientation relationship (OR) between the product and matrix phases and the morphology of the product phase expressed on the crystal basis of both phases. The present study provides a general approach to separately analyzing the development of the OR at the nucleation and growth stages of a phase transformation, in which the product phase can be either an equilibrium or a metastable phase. This two-stage approach facilitates the examination of the effects of thermodynamics and kinetics, with sophisticated theories for these stages, on phase-transformation crystallography. It is believed that with the progress in consolidation, the simulation of microstructural evolution, which is mainly based on thermodynamics and kinetic models, will become more realistic and predictive
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