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 AlTiNiCuCo_x (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 AlTiNiCuCo_x alloys and also indicate that AlTiNiCuCo_1.0 of BCC structure exhibits ductility unlike most HEAs. Besides, all the mechanical stable alloys show elastic anisotropy. The AlTiNiCuCo_1.0 of BCC exhibits the maximum anisotropy among all the AlTiNiCuCo_x alloys. Then various of thermodynamic properties including vibrational entropy S _vib, volumetric thermal expansion coefficient α, constant volume heat capacity C _v and Debye temperature ΘD are calculated by using quasi-harmonic Debye-Grüneisen model. The FCC AlTiNiCuCo_0.5 alloy exhibits outstanding thermodynamic properties compared with other HEAs of AlTiNiCuCo_x system. Finally, electronic structures are studied by density of states, partial density of states and Fermi energy.