FIRST-PRINCIPLES CALCULATIONS OF BULK AND INTERFACIAL THERMODYNAMIC PROPERTIES FOR FCC-BASED AL-SC ALLOYS

The configurational thermodynamic properties of fee-based AI-Se alloys and coherent Al/Al3Se interphase-boundary interfaces have been calcul ated from first principles. The computational approach used in this st udy combines the results of pseudopotential total-energy calculations with a cluster-expansion description of the alloy energetics. Bulk and interface configurational-thermodynamic properties are computed using a low-temperature-expansion technique. Calculated values of the {100} and {111} Al/Al3Se interfacial energies at zero temperature are, resp ectively, 192 and 226 mJ/m(2). The temperature dependence of the calcu lated interfacial free energies is found to be very weak for {100} and more appreciable for {111} orientations; the primary effect of config urational disordering at finite temperature is to reduce the degree of crystallographic anisotropy associated with calculated interfacial fr ee energies. The first-principles-computed solid-solubility limits for Sc in bulk fee Al are found to be underestimated significantly in com parison with experimental measurements. It is argued that this discrep ancy can be largely attributed to nonconfigurational contributions to the entropy which have been neglected in the present thermodynamic cal culations.