Thermodynamic Properties of Coherent Interphase Boundaries in Substitutional Fcc Alloys

ABSTRACTThermodynamic and structural properties of coherent interphase boundaries (IPBs) in the Al-Li and Ag-Al alloy systems are studied using the cluster variation method (CVM) and low-temperature expansion (LTE) techniques. The energy parameters required as input for the CVM and LTE calculations were obtained by fitting to phase diagram data in the case of Al-Li alloys and from a fit to the results of first-principles total energy calculations for Ag-Al. Interphase energies are calculated as a function of temperature and composition profiles across coherent IPBs are computed for high-symmetry crystallographic orientations. It is demonstrated that the calculated temperature dependence of interphase energies and the “widths” associated with compositionally diffuse IPBs can be appreciable even at temperatures well away from critical points.