The effect of annealing on the microstructure and tensile properties of a β/γ′ Ni–Al–Fe alloy

The evolution of the microstructure of a (β/γ′) Ni–32 at.% Al–5 at.% Fe alloy during annealing has been studied by electron microscopy and X-ray diffraction. Annealing at 800°C and 1100°C causes a reverse martensitic transformation, L10→B2 (β), and a B2→L12 (γ′) phase transformation. The lower annealing temperature leads to a higher volume fraction of the γ′-phase but a smaller size of the γ′-particles. The kinetic laws of the coarsening and of the increase in the volume fraction of the γ′-phase are discussed. The orientation relationships between the β and γ′ phases appeared to be mainly of Nishiyama–Wassermann and Bain types after 800°C annealing, while Kurdjumov–Sachs and Bain orientation relationships were predominant in the alloys annealed at 1100°C. A strong correlation between the volume fraction of the γ′-phase and the tensile characteristics of the alloy has been established.