First-principles calculation on the thermodynamic and elastic properties of precipitations in Al-Cu alloys

First-principles calculations based on density functional theory was used to investigate the structural, thermodynamic and elastic properties of precipitations, θ″, θ′ and θ, in Al-Cu alloys. The values of lattice constants accord with experimental results well. The structural stability of θ is the best, followed by θ′ and θ″. In addition, due to the highest bulk modulus, shear modulus and Young's modulus, θ possesses the best reinforcement effect in precipitation hardening process considered only from mechanical properties of perfect crystal. According to the values of B/G, Poisson's ratio and C₁₁-C₁₂, θ′ has the worst ductility, while θ″ has the best ductility, the ductility of θ is in the middle. The ideal tensile strength of θ″, θ′ and θ calculated along [100] and [001] directions are 20.87 GPa, 23.11 GPa and 24.70 GPa respectively. The analysis of electronic structure suggests that three precipitations all exhibit metallic character, and number of bonding electrons and bonding strength are the nature of different thermodynamic and elastic properties for θ″, θ′ and θ.