atom

micro

macro

A

B

C
Calphad

Calphad: CALculation of PHAse Diagrams
Definition:Computer coupling of phase diagrams and thermochemistry.
Explanation:Phase diagrams are a very powerful tool for predicting the state of a system under different conditions. The Calphad approach is based on the fact that a phase diagram is manifested by the equilibrium thermodynamic properties of the system. Hence, it is possible to calculate a phase diagram by modeling the thermodynamic properties of all the phases in a system. By combining the models for several low order systems, it is possible to construct multi-component databases, which can be used to predict the state of multi-component alloys.

Obvious applications include the direct calculation of phase diagrams, phase equilibria and thermodynamic properties such as Gibbs energies, chemical potentials, activities, enthalpies and heat capacities using software such as Thermo-Calc. The Calphad method also forms the basis for simulation of phase transformations using phase field modeling or diffusion simulation methods (→DICTRA) and for process simulation, which makes it to be one of the key tools for ICME (Integrated Computational Materials Engineering).
Picture /
Figure /
Diagram:

(a) Overview of the Calphad method,
(b) Calculated isothermal section of the Fe-Mn-C phase diagram.
SFB-Link:Within the SFB the Calphad method is used for the calculation of stacking fault energy (→SFE), T0, Ms for ε-martensite as well as more conventional phase equilibria and phase diagrams which are used to predict solidification ranges, microsegregation, formation of carbides (cementite and kappa carbide) and other phases. It is also used for the calculation of solubilities of gaseous elements such as nitrogen and hydrogen.
References:HL Lukas, SG Fries, B Sundman, Computational Thermodynamics – The Calphad Method, Cambridge University Press, Cambridge, UK, 2007.
D Djurovic, B Hallstedt, J von Appen, R Dronskowski, Calphad, 35, 479-491(2011).