Identification of a Ni 16Ti 11 Precipitate Phase within Nickel-Rich, Nickel-Titanium-Based Alloys

Abstract

A "cubic Ni₃Ti₂" precipitate phase recently reported to exist within NiTi and NiTiNb alloys is documented to also form within a Ni₅₆Ti₃₆Hf₈ alloy upon aging. Using transmission electron microscopy and ab intio density functional theory techniques, the phase is more precisely identified to be Ni₁₆Ti₁₁ with symmetry of the pm3m space group and a lattice parameter a = 8.816 Å. In this structure, nickel atoms preferentially segregate to the perimeter lattice sites of the 54-atom unit cell.