First principles calculations of the influence of nitrogen content on the mechanical properties of α-Ti

Abstract

Interstitial N atoms have pronounced influence on deformation behaviors and mechanical properties of Ti alloys. In this work, by first-principles approach we systematically explored the impact of N content on the tensile and shear responses of α-Ti. Firstly, the formation energy calculations demonstrate that α-Ti solution with N atom in octahedral position is more stable. Then five solid solutions with 0 at.%, 6 at.%, 11 at.%, 16 at.% and 20 at.% nitrogen concentrations have been considered. Moreover, elastic constants and phonon spectrum are analyzed for checking mechanical and dynamical stabilities of all considered Ti–N systems. Additionally, ideal tensile and shear strengths across different crystallographic orientations are calculated by stress-strain relationship under loading. The results prove that nitrogen addition effectively increases the ideal shear strength compared with pure α-Ti, which fully demonstrates the strengthening behavior of N solute atom on Ti. Particularly, the minimum shear resistance and tensile strength appear in (101¯0)[1¯21¯0] and [1¯21¯0] direction, respectively. Furthermore, the mechanical features underlying loading are explained by the evolution of the Ti–N bonds and electronic structures.