Thermodynamic reassessment of the Al-V system

An optimized set of thermodynamic functions to describe the AI-V system has been obtained by a computer-operated least squares method applied to the experimental phase diagram and thermodynamic data available from the literature. Special attention is paid to the modeling of the intermediate phase Al8V5. Based on the crystal structure data, Al8V5 is described by a sublattice model Al-6/13(Al, V)(2/13) (Al, V)(3/13)V-2/13 in a final treatment. The boldface Al and V mean the normal atoms (i.e., major species) in the sublattices. In order to provide reasonable starting values for the final modeling, three treatments are performed. In the first treatment, Al8V5 is assumed to be a stoichiometric compound; in the second and third ones, it is described by sublattice models Al-6/13(Al, V)(2/13)V-5/13 and Al-8/13(Al, V)(3/13)V-2/13, respectively. This step-by-step modeling procedure provides reliable estimates and useful starting values for the parameters at each of the higher levels. The other phases (liquid, fcc (Al), and bcc (V)) are modeled with the Redlich-Kister formula or as stoichiometric phases (Al21V2, Al45V7, Al23V4, and Al3V). Comparisons between the calculated and measured phase diagrams as well as thermodynamic quantities indicate that almost all of the reliable experimental information is satisfactorily accounted for by the thermodynamic description of the final treatment. The consistent thermodynamic functions from the first, second, and third treatments are useful for a simplified description of the Al-V system if less accuracy for the Al8V5 phase is required.