Thermal stability assessment of mixed phase AlCoCrFeNi high entropy alloy: In silico studies

Abstract

Thermal stability assessment is crucial for materials used in high temperature applications. Present study uses atomistic simulations to demonstrate the changes in microstructural, mechanical and thermodynamic properties of mixed phase stabilized AlCoCrFeNi high entropy alloy (HEA) subjected to thermal treatment in the range of 298–2500K. Results infer that the alloy undergoes accelerated phase transition at 1700K as confirmed from a sudden increase in lattice parameters, cell volume, coefficient of thermal expansion, local lattice distortion and a sudden decrease in density, and number of nearest neighbors. The elastic moduli such as bulk modulus, shear modulus, Young's modulus, hardness, and fracture toughness, also showed a significant drop at 1700K followed by a rapid reduction till 2200K. The specific heat capacity, lattice thermal conductivity and Gruneisen parameter also showed abrupt changes at 1700 K confirming the onset of phase transition which was also confirmed from radial distribution function and centrosymmetry parameter at 298K and 1700K. The mixed phase AlCoCrFeNi has maintained good fracture toughness (4.8 MPa m^0.5) and hardness (2.8 GPa) at 1700K. The HEA exhibited a very low lattice thermal conductivity of 0.71–3.5 W/m K. Analysis of mean square displacements of atoms indicates the displacement of atoms initiated at 1500 K and accelerated from 1800K which was also confirmed from microstructural changes depicting liquid phase through common neighbor analysis. Therefore, present study demonstrates the thermal stability and phase transition of mixed phase AlCoCrFeNi in the range of 1500–2200 K with a peak activity at 1700K.