Structural, Electronic, Mechanical and Thermal Properties of AlxCoCrFeNi (0 ≤ x ≤ 2) High Entropy Alloy Using Density Functional Theory

Abstract

High Entropy Alloys (HEA) are new class of materials exhibiting remarkable properties owing to multiple alloying elements to form solid solution phase and high configurational entropy. The properties of HEA are greatly influenced by the composition of each metallic element. Therefore, the focus of present study is to evaluate the effect of aluminum (Al) molar ratio ‘x’ on the structural, electronic, mechanical, and thermal properties of Al_xCoCrFeNi (x = 0.0, 0.1, 0.3, 0.5, 0.9, 1.0, 1.5 and 2.0) HEA using Density Functional Theory (DFT). Based on the reported literature, Face Centered Cubic (FCC) crystal form of Al_xCoCrFeNi was chosen for x = 0.0, 0.1, 0.3, 0.5,1.0 and Body Centered Cubic (BCC) form was chosen for x = 0.9, 1.0, 1.5, 2.0. The Special Quasi Random Structure (SQS) models of Al_xCoCrFeNi were used for the property evaluation. The phase stability of Al_xCoCrFeNi HEA for all molar ratios of Al was confirmed based on thermodynamic stability criteria and atomic size difference parameter. The thermodynamic stability of Al_xCoCrFeNi increased with Al molar ratio. Mechanical properties were computed for a microscopic level strain rate of ± 0.7% and were evaluated based on elastic moduli, Vickers hardness, fracture toughness, Debye temperature and acoustic wave velocity. The properties computed based on phase change from FCC to BCC at x > 1.3 of Al_xCoCrFeNi match well with available experimental and theoretical literature values. Positive Cauchy pressure, B/G > 1.75 and ν > 0.26 indicate that as Al concentration increases, ductility of the alloy increases. Further, the elastic moduli, hardness, and fracture toughness decrease with increase in Al concentration. The lattice thermal conductivity of the HEAs studied using DFT match well with molecular simulation-based literature values and suggest that Al_1.5CoCrFeNi has lowest thermal conductivity.

Graphical Abstract