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

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 A. In this structure, nickel atoms preferentially segregate to the perimeter lattice sites of the 54-atom unit cell.