Thermodynamic properties of coherent interfaces in f.c.c.-based Ag–Al alloys: a first-principles study

The thermodynamic properties of coherent interphase boundaries (IPBs) between the Al-rich-matrix and Guinier–Preston-zone (GP-zone) precipitate phases in Ag–Al are studied from first principles. The cluster-variation-method (CVM), with effective-cluster-interaction (ECI) parameters derived from the results of ab initio total energy calculations, is used to compute the interfacial free energies (γ) and composition profiles of flat {111} and {100} IPBs as a function of temperature (T). The calculated values of γ increase monotonically from zero to 35 (37) mJ/m2 for {111} ({100}) IPBs as T is lowered from the critical temperature (calculated to be 760K) to 450K. Monte-Carlo simulations, based on the same set of ECIs used in the CVM work, have been performed to compute GP-zone morphologies at 450K. Simulated precipitate shapes are found to be anisotropic, consistent with experimental observations. The CVM is used also to compute the gradient coefficient (κ) in the Cahn–Hilliard coarse-grained free energy. Calculated values of κ are found to display non-negligible concentration and temperature dependencies, in contrast to the predictions of regular-solution theory.