Abstract: First principles plane wave pseudopotential method was executed to calculate the mechanical properties with respect to the uranium-0.95 mass fraction of titanium (U-0.95 mass fraction of Ti) alloy for quenching and aging, including the elastic modulus, the value of shear modulus to bulk modulus (G/B) and the ideal tensile strength. The further research has also been done about the crack mechanism through Griffith rupture energy. These results show that the elastic moduli are 195.1 GPa for quenching orthorhombic α phase and 201.8 GPa for aging formed Guinier-Preston (G.P) zones, while G/B values are 0.67 and 0.56, respectively. With the phase change of uranium-titanium (U-Ti) alloy via the quenching treatment, the ideal tensile strength is diverse and distinct with different crystal orientations of the anisotropic α phase. Comparison of quenching and short time aging treatment, both of the strength and toughness trend to improve slightly. Further analysis about electronic density of states (DOS) in the electronic scale indicates that the strength increases continuously while toughness decreases with the aging proceeding. The equilibrium structure appears in overaging process, as a result of decomposition of metastable quenching α phase. Thereby the strength and toughness trend to decrease slightly. Finally, the ideal fracture energies of G.P zones and overaging structure are obtained within the framework of Griffith fracture theory, which are 4.67 J/m² and 3.83 J/m², respectively. These results theoretically demonstrate strengthening effect of quenching and aging heat treatment on U-Ti alloy.

Key words: U-0.95 mass fraction of Ti alloy, First principles, Elastic modulus, Ideal tensile strength, Electronic structure, Griffith ruptures energy