High-entropy alloys: Interrelations between electron concentration, phase composition, lattice parameter, and properties

• Published in: Physics of metals and metallography Vol. 118; no. 10; pp. 970 - 981
• Main Authors: Gorban’, V. F., Krapivka, N. A., Firstov, S. A.
• Format: Journal Article
• Language: English
• Published: Moscow Pleiades Publishing 01.10.2017; Springer Nature B.V
• Subjects: Alloying elements; Chemical compounds; Chemistry and Materials Science; Crystal lattices; Diffusion; Electrons; Enthalpy; Entropy; Entropy of formation; High entropy alloys; Lattice parameters; Laves phase; Materials Science; Metallic Materials; Modulus of elasticity; Phase composition; Phase Transformations; Sigma phase; Solid solutions; Structure; Temperature; modulus of elasticity; high-entropy alloys; lattice parameter; phase-formation
• ISSN: 0031-918X; 1555-6190
• DOI: 10.1134/S0031918X17080051

An analysis of more than 200 high-entropy alloys (HEA) allowed us to find interrelations between the electron concentration, phase composition, lattice parameter, and properties of solid solutions with bcc and fcc crystal lattices. Main conditions for the appearance of high-entropy chemical compounds, such as Laves, σ, and μ phases were determined. The necessary condition for the formation of 100% high-entropy σ phase is the formation of σ phase in two-component alloys for different combinations of elements, which are components of the HEA, and the electron concentration should be 6.7–7.3 electrons per atom. To form a 100% high-entropy Laves phase, the following conditions should be fulfilled: the total negative enthalpy of mixing of alloy is about –7 kJ/mol and less; the difference between the atom sizes in a pair is more than 12%; the enthalpy of the mixing of two present elements is less than –30 kJ/mol; and the average electron concentration is 6–7 electrons per atom. It was shown that the ratios of lattice parameters of solid-solution HEA, which were experimentally determined, to the lattice parameter of the most refractory metal in the HEA determine the value of the modulus of elasticity.