Caution regarding ambiguities in similar expressions of orientation relationships

Reproducible Orientation Relationships Developed from Phase Transformations—Role of Interfaces

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.

PTCLab: free and open-source software for calculating phase transformation crystallography

PTCLab(Phase Transformation Crystallography Lab) is free and open-source software to calculate the crystallographic features formed during a phase transformation, such as orientation relationship, interface orientation, interfacial structureetc. This program covers the crystallographic theories for both martensitic and diffusional transformation and allows users to represent the results in stereographic projection. The crystallographic models treated inPTCLabinclude the classical phenomenological theory of martensite crystallography (PTMC), the double shear version of PTMC, the invariant line model, O-lattice theory, the O-line model, the recently developed three-dimensional near coincidence site method, the edge-to-edge matching model and variant selection analysis. In addition, a number of basic crystallographic calculations for single or multiple crystal structures can be performed with the calculation pad. High-quality composite stereographic projection and electron diffraction patterns can be also obtained by the present application.PTCLabis written in Python, runnable cross platform, and is distributed at https://sourceforge.net/projects/tclab/.