Ni3Ti

Ni3Ti is an intermetallic compound in the nickel-titanium system with a nominal composition of three nickel atoms to one titanium atom. It can form as a stoichiometric phase in Ni-rich Ni-Ti alloys and may appear as a precipitate during aging treatments.

Crystal structure and phase behavior: Ni3Ti is commonly described as adopting an ordered L12-type crystal structure, a cubic arrangement related to the face-centered cubic lattice. Depending on temperature, composition, and thermal history, it may also exist in a high-temperature disordered phase or show slight distortions from perfect cubic symmetry. The stability of Ni3Ti is sensitive to processing conditions and can be limited to specific temperature ranges in the Ni-Ti phase diagram.

Properties: The intermetallic is hard and has good high-temperature stability and oxidation resistance relative to pure nickel, along with a high modulus. However, it tends to be relatively brittle and can exhibit limited ductility, which influences processing, fabrication, and weldability. As a precipitate phase, Ni3Ti can strengthen Ni-based alloys through precipitation hardening while potentially altering fracture behavior.

Formation and relevance: Ni3Ti forms by diffusion-controlled reaction from nickel-rich solid solutions in the Ni-Ti system during appropriate heat treatments. It can be retained as a secondary phase in aged alloys and contributes to high-temperature performance and mechanical strength in certain nickel-based materials.

Relation to other Ni-Ti intermetallics: Ni3Ti is one of several intermetallics in the Ni-Ti system. It is distinct from NiTi (the shape-memory alloy) and from other Ni-containing intermetallics such as Ni3(Al,Ti) found in related alloy systems.