First-Principles Study of the Influence of Lattice Misfit on the Behavior and the Ductility Effect of Hafnium in Ni–Ni3Al System

Two Ni/Ni3Al-interface-contained cluster models with/without lattice misfit are studied by first-principles method to clarify the debates about the segregation behaviors of Hafnium (Hf) and explore the influence of lattice misfit on the ductility effect of Hf. It is found that though Hf prefers to substitute Al rather than Ni in Ni3Al phase within most of the investigated misfit range, its stronger preferring to Ni phase than Ni3Al phase makes it impossible to go into Ni3Al phase to occupy Al site in Ni–Ni3Al alloys. Bond order analysis in Hf-free case shows that lattice misfit has different effects on the Griffith work of interfacial cleavage 2γ int/E and the maximum theoretical shear stress τ max of Ni and Ni3Al, contributing to the existence of anomalous strength-temperature phenomena in Ni3Al alloys. However, the addition of Hf will make the 2γ int/E (or τ max) of both Ni3Al and Ni decrease (or increase) with lattice misfit, indicating that the addition of Hf may make the anomalous strength-temperature relationship in Ni3Al region disappear locally.