Vacancy induced brittle-to-ductile transition of Nb5Si3 alloy from first-principles

Highlights: • Nb vacancies are more stable than that of Si vacancies. • Nb₅Si₃ prefers to form the Nb_-va2 vacancy. • Vacancies weaken the deformation resistances and reduce elastic stiffness. • Vacancies result in brittle-to-ductile transition. • The removed atom changes the localized hybridization between Nb–Si and Nb–Nb atoms. - Abstract: The effect of vacancy on mechanical properties of α-Nb₅Si₃ is systematically investigated by first-principles calculations. Four different mono vacancies in this alloy are considered in detail. The vacancy formation energy, formation enthalpy, elastic modulus, hardness, B/G ratio, thermodynamic properties and electronic structure of α-Nb₅Si₃ with different vacancies are discussed. The calculated vacancy formation energies show that Nb vacancies are more stable than that of Si vacancies, and α-Nb₅Si₃ prefers to form the Nb_-va2 vacancy. Those vacancies weaken the volume, shear deformation resistances and reduce the elastic stiffness. However, those vacancies result in brittle-to-ductile transition and α-Nb₅Si₃ with Si_-va1 mono vacancy exhibits ductile behavior. The calculations of electronic structure reveal that these vacancies change the localized hybridization between Nb–Si and Nb–Nb atoms, which are the origin of brittle-to-ductile transition. Finally, we conclude that vacancy is beneficial for improving the ductility of Nb₅Si₃.