Application of the thermodynamic extremal principle to diffusion-controlled phase-transformations in multi-component substitutional alloys: Modeling and applications

The thermodynamic extremal principle was applied to model of diffusion-controlled phase-transformations in multi-component substitutional alloys, in which dissipations by interface migration and trans-interface diffusion were integrated for a sharp interface. In the modeling, a new concept of trans interface diffusion in two-steps, i.e. from the product phase to the interface and from the interface to the parent phase, was introduced, ascribing to which the model follows the Onsager's reciprocal relation. In contrast to the work of Svoboda et al. (2004) that considers only the interfacial dissipation by interface migration, non-equal jumps of chemical potentials across the interface are herein allowed. Applications to the Fe-Cr-Ni and Fe-Ni alloys showed that the model is able to describe accurately not only the kinetic processes of massive transformation and diffusive transformation but also the critical limit between them. Since the transformation direction is not a priori condition for model calculations, the model is of potential value in applications to the cases in which the migrating direction changes, e.g. cycle phase-transformations etc. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.