Formation and morphology of Kurnakov type D022compound in disordered face-centered cubic γ–(Ni, Fe) matrix alloys

Abstract

Formation and morphology of D0₂₂compound Ni₃V in γ face-centered cubic (fcc) matrix phase were investigated to understand fundamentals for controlling microstructure of alloys strengthened by Kurnakov-type geometrically close-packed (GCP) intermetallics. The D0₂₂phase with plate-shaped morphology coherently precipitates in the γ + D0₂₂two-phase region above theT₀line in Ni–V binary alloys. Due to the negative and positive lattice misfits along thea-axis and thec-axis of D0₂₂(δ_a< 0 < δ_c), an invariant line exists between the two phases, and the morphology of D0₂₂phase is changeable by controlling the two factors; the misfit strain ratio δ_c/δ_ais a decisive factor to determine the habit plane defined by the invariant line and one of thea-axes of D0₂₂, whereas the magnitude of |δ_a| is responsible for the shape of D0₂₂phase with either prism or plate. These findings were extended to Ni–Fe–Nb–V system by partial replacement of Ni and V with Fe and Nb, respectively.