Ab Initio Modeling of fcc Fe-Co-Cr-Ni High Entropy Alloys with Full Composition Range

Abstract

The Fe-Co-Cr-Ni quaternary system has been studied extensively in the past decade, not only because of the superior properties achieved like high tensile ductility and fracture toughness, but also it is the foundation for the development of FeCrCoNi-based HEAs. However, most of the investigations are mainly focusing on the equiatomic and semi-equiatomic compositions. The physical properties of non-equiatomic compositions are barely explored. In the current work, the ab initio approach is adopted to predict the lattice parameter, structure stabilities, elastic properties, and enthalpy of formations of fcc Fe-Cr-Co-Ni HEA single crystals with the special quasirandom structure (SQS) method. To expand the design of Fe-Co-Cr-Ni HEAs into a full composition range, the current simulations cover all the binaries, ternaries, and the whole quaternary system. The 2-D composition-property contour diagrams are created to show the physical properties in the ternary and quaternary systems. Our investigation shows that the fcc alloys' lattice parameter increases with the addition of Fe and Cr and decreases with Ni and Co. In addition to the enthalpy of formation at 0 K, the shape distortion rate is proposed to be another essential parameter to evaluate the crystal stability. The results show the addition of Cr would destabilize the fcc lattice and cause symmetry breaking. Finally, the result of Pugh's ratio shows that most of the fcc alloys show ductile behavior (P[ 1.75), especially for the alloys around Fe 3 Ni, FeCo, and Fe 2 NiCo (P[ 2.5). The brittle behavior (P\ 1.75) is located around Fe 3 Cr and Fe 2 CoCr. Meanwhile, Cr 2 NiCo and Cr 2 FeNiCo are considered promising compositions to be tried and verified experimentally because of the higher bulk modulus and moderate shear modulus.

High-entropy alloy screening for halide perovskites

“…The equimolar unit cell volume's mean, standard deviation, and coefficient of variation are:Here V̄ is equimolar unit cell volume, σ is equimolar alloy unit cell volume standard deviation, UCV is equimolar alloy unit cell volume coefficient of variation, and N is the number of end-members. Atomic radius differences, 62–64 lattice parameter differences, 65,66 and atomic position differences 67 have been previously parameterized to screen metal HEA. We instead parameterize unit cell volume to extend the approach to non-cubic crystals.…”

High-Entropy Materials Design by Integrating the First-Principles Calculations and Machine Learning: a Case Study in the Al-Co-Cr-Fe-Ni System

“…According to the rst-principles calculations, part of our results were adopted based on our previous work 39,49 , including structure stabilities, elastic stabilities, enthalpy of formations, and VEC-related properties.…”