Evaluating stability, elastic and thermodynamic properties of AlTiNiCuCox (x = 0.5,0.75,1,1.25,1.5) high entropy alloys

Alloying effect of Cobalt on structural stability, elastic and thermodynamic properties of AlTiNiCuCox (x = 0.5,0.75,1,1.25,1.5) high entropy alloys are investigated via performing ab-initio calculations combined with quasi-harmonic Debye-Grüneisen model. The equilibrium lattice constants and density are evaluated by ab-initio calculations, third-order Birch-Murnaghan equation of state and Vegard's law. The results of cohesive energy and obtained elastic constants screen out the mechanical stable AlTiNiCuCox alloys and also indicate that AlTiNiCuCo1.0 of BCC structure exhibits ductility unlike most HEAs. Besides, all the mechanical stable alloys show elastic anisotropy. The AlTiNiCuCo1.0 of BCC exhibits the maximum anisotropy among all the AlTiNiCuCox alloys. Then various of thermodynamic properties including vibrational entropy Svib, volumetric thermal expansion coefficient α, constant volume heat capacity Cv and Debye temperature ΘD are calculated by using quasi-harmonic Debye-Grüneisen model. The FCC AlTiNiCuCo0.5 alloy exhibits outstanding thermodynamic properties compared with other HEAs of AlTiNiCuCox system. Finally, electronic structures are studied by density of states, partial density of states and Fermi energy.