Alloying effects on the phase equilibria among Ni(A1), Ni3Al(L12) and Ni3V(D022) phases

The effects of alloying elements (Ti, Nb, Ta, Cr, W, Re, Co and Si) on the phase equilibria among Ni (A1), Ni3Al (L12) and Ni3V (D022) phases were studied by means of microstructure observation and energy dispersive spectroscopy analysis on thin foils. It was found that the alloying elements can be classified into four categories: (a) Ti stabilizing the phases in the order: L12 > D022 > A1, (b) Nb and Ta stabilizing the phases: D022 > L12 > A1, (c) Cr, W, Re and Co stabilizing the phases: A1 > D022 > L12, (d) Si stabilizing the phases: Al > L12 > D022. The elements in the categories (a) and (b) raise the temperature of a eutectoid-type reaction (A1 → L12 + D022) while the elements in the category (c) reduce the temperature. The alloying effects were examined in terms of mixing enthalpy and electron concentration.