High entropy allows have received significant research attention in the last decade. To date, a good number of single phase high-entropy alloys have been collected and reviewed. Apart from hexagonal closed-packed high-entropy alloys made of early rare Earth elements, majority of the single phase face centered cubic high-entropy alloys are made of near-equal-molar late 3d transition metals while refractory counterparts lead to single phase body centered cubic high-entropy alloys. When aluminum is added, the phase of 3d-high-entropy alloys change from face centered cubic to body centered cubic. A small amount of refractory elements added to the 3d high-entropy alloys retains the single face centered cubic phase.
Counting of collected experimental information, the Hume-Rothery rules have been applied to analyze the production of single-phase high-entropy alloys. Most researchers have considered the mixing entropy, effects of atomic size, valence electron concentration, mixing enthalpy and electronegativity as key physical parameters. Valence electron concentration has been implemented to distinguish the body centered cubic phase and face centered cubic phase high-entropy alloys. In addition, the formation enthalpy of binary alloys from ab initio calculations has been applied successfully to reproduce single-phase high-entropy alloys.
Valence electron concentration as well as atomic radius difference can be used implemented to approximate the hardness of the single-phase high-entropy alloys. Researchers led by Dr. Fuyang Tian at the University of Science and Technology Beijing made an attempt to design new refractory high-entropy alloys including late transition metals through the Hume-Rothery rules as well as ab initio formation enthalpy computations. Their work is published in Intermetallics.
The authors used the effect of atomic size, valence electron concentration, elastic strain energy, mixing enthalpy, mixing entropy, and Pauling electronegative difference to analyze the single phase high-entropy alloys. The atomic size effects included the average atomic radius, atomic radius difference, maximum atomic radius difference, and atomic packing misfit ratio.
The coherent potential approximation was a powerful tool to treat the substitutional disorder with magnetic as well as chemical degrees of freedom. For paramagnetic high-entropy alloys, which include chromium, manganese, iron, and nickel magnetic materials, the authors used the disordered local magnetic moment picture was implemented to account for magnetization loss.
The authors successfully predicted high entropy alloys composed of late 3d transition metals, which included manganese, iron, copper, nickel, and cobalt, by implementing the Hume-Rothery rules. Their evaluations alluded that CrMoW, CrMoWNi, CrMoWCo, and CrMoWMn adopt single-phase body centered cubic structure. If dual phase high entropy alloys was desired, the authors considered increasing cobalt and nickel amounts slightly.
The research team used the ab initio alloy method to compute the phase stability, ideal tensile strength, and elastic moduli of the present high-entropy alloys. The results showed that the body centered cubic phase was more stable as compare to face centered cubic structure. The elastic constants indicated that the body centered cubic phase was thermodynamically stable and the late 3d transitional metals decreased the mechanical integrity of the body centered cubic phase. Nickel increased the intrinsic ductility and decreased the intrinsic strength of CrMoW.
Fuyang Tian, Lajos Karoly Varga, and Levente Vitos. Predicting single phase CrMoWX high entropy alloys from empirical relations in combination with first-principles calculations. Intermetallics, volume 83 (2017), pages 9-16.Go To Intermetallics