Experimental investigation and thermodynamic modeling of the Al–Dy and Ni–Al−Dy systems

The partial phase equilibria of the Ni–Al−Dy ternary system have been systematically investigated via experimental analyses and thermodynamic modeling. Using the equilibrated alloy method, the 1150 °C and partial 800 °C isothermal sections of the Ni–Al−Dy ternary system and related Al–Dy binary system were constructed based on scanning electron microscopy, energy-dispersive spectroscopy and X-ray diffraction. Twelve three-phase regions were confirmed and four three-phase equilibria regions were speculated at 1150 °C, eight three-phase regions were determined at 800 °C, and five kinds of primary solidification regions, DyAl₂, τ7, τ5, NiAl and Ni₂Al₃ were observed. A new ternary compound τ12 was discovered, which was stable at 800 °C and disappeared at 1150 °C, the τ1 phase was not stable at 800 and 1150 °C isothermal sections; the ternary compound τ11 was confirmed to be stable at 800 °C. In addition, the primary solidification phases were also identified, and five different primary solidification phases were found. Based on the experimental results available in this study and the literature, the thermodynamic modeling of the Ni–Al–Dy ternary system was obtained using the CALPHAD method. A set of self-consistent thermodynamic parameters for the Ni–Al–Dy ternary system was first obtained with a satisfactory agreement between the experimental and calculated results.