Experimental Phase Diagram Investigations in the Ni-Rich Part of Al-Fe-Ni and Comparison with Calculated Phase Equilibria

The phase equilibria in the section Ni₃Fe-Ni₃Al and phase boundaries of γ′(Ni₃Al) at 1000 °C were studied by a combination of powder X-ray diffraction (XRD), differential thermal analysis (DTA), and electron probe microanalysis (EPMA). The existence of a continuous solid solution at 450 °C was confirmed by a linear decrease of the lattice parameter from Ni₃Al to Ni₃Fe. The phase boundaries of γ′ with γ and the B2-type phase were determined at 1000°C by EPMA. A vertical section of the phase diagram from Ni₃Al to Ni₃Fe above 450 °C, including the liquidus temperatures, is proposed based on the DTA investigations. The invariant four-phase equilibrium U: L + γ′ = γ + B2 is found to occur at 1366 ± 1 °C. The experimental data are compared with a calculated phase diagram obtained by extrapolation from the corresponding binary data sets.