Ni3Nb

Ni3Nb is a nickel-niobium intermetallic compound with a fixed stoichiometry of Ni3Nb. It forms in alloys containing nickel and niobium and can appear as a distinct phase when Nb is present in sufficient amounts or during aging of nickel-based materials.

Crystal structure and ordering: Ni3Nb is an ordered intermetallic. Reports describe it as adopting an ordered tetragonal structure related to the DO22 family; the precise lattice parameters and space group can vary with temperature and composition. The ordering produces a relatively high degree of chemical order and low atomic mobility, contributing to stability at elevated temperatures.

Properties: The phase exhibits a high melting point and good creep resistance at elevated temperatures, making it of interest for high-temperature applications. It is typically hard and brittle, with limited ductility at room temperature, and may fracture by cleavage under certain loading conditions. Oxidation resistance is generally good at high temperatures but depends on the surrounding matrix and environment.

Formation and role: In the Ni-Nb phase diagram, Ni3Nb is a line compound that forms upon cooling from Nb-rich regions or during aging of nickel alloys containing Nb. When present as precipitates in nickel-based matrices, Ni3Nb can strengthen the material by hindering dislocation motion, analogous in concept to gamma-prime strengthening but with different chemistry and mechanics.

Applications and occurrence: Ni3Nb has been studied primarily as a strengthening precipitate in high-temperature nickel alloys and as a model intermetallic for understanding Ni-Nb chemistry. See also Ni-Nb phase diagram and intermetallic compounds.