First-principles study of the influence of lattice misfit on the segregation behaviors of hydrogen and boron in the Ni–Ni 3Al system

Abstract

A first-principles method is employed to investigate the segregation behaviors of hydrogen and boron in Ni-based and Ni 3Al-based alloys using two models. Chemical binding energy analysis shows that both boron and hydrogen are able to segregate to the interstices in the Ni phase, Ni 3Al phase and Ni/Ni 3Al interface. Boron, however, is bound to its neighbor atoms more tightly than hydrogen in both models and its stable state exists over a broader lattice misfit range compared with hydrogen. The bond order analysis we have proposed reveals the origin of the boron-induced ductility and hydrogen-induced embrittlment at the Ni/Ni 3Al interface with different lattice misfit. The calculations indicate that hydrogen causes more severe embrittlement at the Ni/Ni 3Al interface in Ni 3Al-based than in Ni-based alloys. Furthermore, it is found that the boron-induced ductility and hydrogen-induced embrittlement are changed, and thus controllable, by the lattice misfit. Our results provide a quantitative explanation of many experimental phenomena caused by the addition of boron and hydrogen to Ni-based and Ni 3Al-based alloys.