Multiphase phase field theory for temperature-induced phase transformations: Formulation and application to interfacial phases

The main conditions for the thermodynamic potential for multiphase Ginzburg Landau theory are formulated for temperature-induced phase transformations (PTs). Theory, which satisfies all these conditions for n-phase material, is developed. The key point is a new penalizing term in the local energy that allows controlling absence or presence and the extent of the presence of the third phase within the interface between two other phases. A finite-element method is applied for studying PT between beta and delta phases of HMX energetic crystal via intermediate melting more than 100 degrees C below melting temperature. Depending on material parameters (ratio of the width and energy of the solid solid (SS) to solid melt interface and the magnitude of the penalizing term), there are either two (meta)stable stationary interfacial nanostructures, corresponding to slightly and strongly disordered interfaces (in the limits, pure SS interface or complete melt within SS interface), or these nanostructures coincide. A parametric study of these nanostructures is presented. The developed requirements and approach are applicable to various PTs between multiple solid and liquid phases and can be elaborated for PTs induced by mechanical and electromagnetic fields, diffusive PTs, and the evolution of multi-grain and multi-twin microstructures. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.