Ni3Altype

Ni3Al-type refers to a class of intermetallic compounds that crystallize in the ordered L12 (Cu3Au-type) structure and have the nominal composition A3B, with Ni3Al as the prototype (A = Ni, B = Al). These materials are isostructural with the gamma prime phase found in nickel-based superalloys and are characterized by long-range chemical order on a face-centered cubic lattice, with one sublattice preferentially occupied by Al and the other by Ni.

Crystal structure and ordering: The L12 structure is derived from the FCC lattice. In Ni3Al-type compounds, Al atoms occupy one sublattice in a regular, three-to-one arrangement, producing a well-ordered superlattice. This ordering leads to distinct diffraction signatures and a high degree of structural coherence that influences mechanical and thermal properties.

Properties: Ni3Al-type intermetallics typically exhibit high-temperature strength, stiffness, and creep resistance, along with good oxidation resistance. They tend to be brittle at room temperature, and their ductility can be sensitive to composition, ordering, grain size, and temperature. The degree of chemical order and substitutions on the Ni or Al sites can tune mechanical behavior and transformation temperatures.

Formation and phase behavior: In Ni-Al systems, the ordered Ni3Al phase forms from a disordered FCC solid solution through an ordering transition at elevated temperatures. Ordering enhances strength and leads to age-hardening behavior in alloys that contain Ni3Al-type precipitates, commonly referred to as gamma prime in Ni-based superalloys.

Related materials: The Ni3Al-type family encompasses other AB3 intermetallics that adopt the same L12 structure, including various substitutions on the Ni or Al sites. These materials are studied for high-temperature applications and fundamental ordering phenomena.