Ductilization of Ni₃Al by alloying with substitutional elements

This paper reviews recent research on ductility improvement of B-undoped Ni₃Al alloys. Ni₃Al binary alloys with hypostoichiometric compositions show appreciable ductility at room temperature when the samples are prepared by recrystallization annealing after cold pressing, although the alloys with stoichiometric and hyperstoichiometric compositions remain brittle. Melt-spun ribbons with hypostoichiometric compositions contain fine anti-phase domains (APDs), while no APD can be seen in melt-spun ribbons with a hyperstoichiometric composition. The ductility in hypostoichiometric Ni₃Al alloys is associated with low ordering energy of the alloys. The addition of ternary elements, which have been classified as γ formers such as Pd, Pt, Cu, Co and Ag, improves ductility of Ni₃Al alloys. Correspondingly, the microstructure of the melt-spun ribbons consists of fine APDs. The addition of γ′ formers such as Si, Ti, Zr, V, Nb and Ta leads to brittle intergranular fracture. No APD was observed in the melt-spun ribbons of these ternary alloys.