Abstract
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/m 2 for {111} ({100}) IPBs as T is lowered from the critical temperature (calculated to be 760 K) to 450 K. Monte-Carlo simulations, based on the same set of ECIs used in the CVM work, have been performed to compute GP-zone morphologies at 450 K. 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.
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