Coupling of the phase-field and CALPHAD methods for predicting multicomponent, solid-state phase transformations

Abstract

The development of an effective microstructure design method for multicomponent alloys is of considerable importance for improving both the design of alloys and the design of processes for producing alloys with unique properties. The coupling of the phase-field method and the calculation of phase diagrams (CALPHAD) method can be used for predicting the evolution of microstructures in multicomponent alloys. Such predictions make use of CALPHAD thermodynamic information with the chemical free energy function in the phase-field method. This article reviews several of these coupling methods, focusing on solid-state phase transformations in multicomponent systems, such as phase separation and disordered or ordered phase precipitation from a matrix. When calculating disordered phase transformations, the Gibbs energy function derived from the CALPHAD database can be used directly in the phase-field method. On the other hand, when dealing with an order/disorder transition, the degrees of freedom of the element site fraction for an ordered phase in the CALPHAD method can be reduced using the Gibbs energy single formalism for constituent phases, by using a database that stores the Gibbs energy and chemical equilibrium conditions, or by obtaining the driving force calculated using the Thermo-Calc software. The current status and future directions for further development of these coupled methods are discussed.

Keywords:

• computer simulation
• phase-equilibria
• solid-state transformation

Acknowledgements

The author acknowledges Dr. Hiroshi Harada for valuable comments, and Dr. Machiko Ode for providing her unpublished paper. I express my sincere thanks to Dr. Jincheng Wang at the State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, P.R. China, for criticizing the draft of this paper.