Partition of alloying elements between γ (A1), γ′ (L1₂), and β (B2) phases in Ni-Al base systems

Abstract

Phase equilibria between γ (Al), γ′ (Ll₂), and β (B2) phases in the Ni-rich portions of the Ni-Al-X ternary systems were investigated over a temperature range of 800 °C to 1300 °C. The tie lines and phase boundaries were accurately determined by the diffusion couple technique. It was established that Co, Cu, Mn, Fe, and Cr concentrated more into the γ phase than into the γ′ phase, while Ta, Nb, Ti, V, and Si mostly partitioned to the γ′ phase. The partition coefficients for alloying elements between γ and γ′ phases varied as a function of temperature for most of the elements and also as a function of concentration for some of the elements, such as Mo, W, and V. In the equilibrium between γ′ and β phases, Mn, Fe, Co, and Cu partitioned to the β phase rather than to the γ′ phase, whereas Nb, Mo, Ta, Ti, W, V, Cu, and Si concentrated into the γ′ phase. The partition of alloying elements in the metastable equilibrium between γ and β phases, in the Ni-Al binary system, was estimated from the data on γ/γ′ and γ′/β equilibria. Based on these data, the relative stabilizing effects of alloying elements on γ, γ′, and β phases are also discussed.