Thermodynamic Estimation of the Formation of a High-Entropy Al–Nb–Ti–V–Zr Alloy

Abstract

High-entropy alloys (HEAs) are the subject of attention of many scientific researchers. More than 200 thousand publications are known for HEAs and their number is growing every day. Particular interest in HEAs is caused by the peculiarities of their formation and structure, as well as the properties that such alloys have. In the material science classification, HEAs make up a special group, since the processes of structure and phase formation in them, the diffusion mobility of atoms, the mechanism of formation of mechanical properties, and thermal stability are significantly different from analogous processes in traditional alloys. The main feature of HEAs is the formation of a single-phase thermodynamically stable substitutional solid solution, mainly with an fcc or bcc lattice. To predict the formation of the structure of HEAs is a challenging problem to obtain information about new systems without using a complex and expensive experiment. Currently, there are two basic approaches to predicting the possible phase composition of HEAs in the world. The first approach implies the use of phenomenological parameters based on the Hume-Rothery criteria and thermodynamic parameters, and the second, the use of thermodynamic simulation. In this work, the probability of existence of the Al–Nb–Ti–V–Zr system as a HEA is considered for the following compositions: AlNbTiVZr_0.25, AlNbTiVZr_0.5, AlNbTiVZr, and AlNbTiVZr_1.25. The phenomenological parameters are calculated, and the boundary conditions determining the stability and type of phases are revealed. CALPHAD is used to construct binary phase diagrams, which point to the possibility of formation of single-phase structures and intermetallic compounds during the formation of the alloy compositions under study. The results obtained demonstrate that the AlNbTiVZr-based are most likely to be disordered single-phase bcc solid solutions.