Correlation between CALPHAD data and the Cahn–Hilliard gradient energy coefficient and exploration into its composition dependence

Expressions for the Cahn–Hilliard gradient energy coefficient κ for a binary, face-centered cubic crystal are derived by consideration of pair-wise, three-body, and four-body nearest-neighbor interactions. The resulting equations are expressed in terms of the interaction energies of clusters of atoms, and are related to bulk thermodynamic data available in CALPHAD databases. The three- and four-body interactions introduce a composition dependence into the expressions for κ . Values of κ calculated for the Al–Zn system are in good agreement with those reported elsewhere. Equilibrium composition profiles and interfacial energies are calculated using each approximation.