The quaternary Al–Fe–Ni–Si phase equilibria in Al-rich corner: experimental measurement and thermodynamic modeling

Two ternary alloys (Al94Fe1Si5 and Al91Fe1Si8, at.%) and four quaternary alloys with the Ni contents of 1 and 2 at.% along two vertical sections (5 at.% Si, 1 at.% Fe; 8 at.% Si, 1 at.% Fe) in Al-rich corner of the quaternary Al–Fe–Ni–Si system were prepared. The annealed alloys were examined by a variety of analysis techniques to provide accurate phase relations at 500 °C and phase transition temperatures. The previously reported ternary compounds, i.e., Al9Fe2Si2 and Al9FeNi, were confirmed, and no quaternary compound was found at 500 °C. The measured average solubility of Si in Al9FeNi is 4 at.% at 500 °C. The as-cast alloys were carefully analyzed for characterizing the solidified microstructure. Particularly, transmission electron microscopy was employed to identify the nanosized precipitates. Moreover, the volume fractions for each solidified phase were also determined. Based on the experimental information from the present work and the literature, a self-consistent thermodynamic description of the quaternary Al–Fe–Ni–Si system in Al-rich corner was then obtained via the CALPHAD (CALculation of PHAse Diagrams) method. Most of the experimental data can be well reproduced. The liquidus projection for the quaternary Al–Fe–Ni–Si system in the Al-rich corner was also constructed. Furthermore, the Gulliver–Scheil simulation was performed for each alloy, and the simulated microstructure constituents are consistent with the experimental observation in as-cast alloys. The present approach to study the phase equilibria in quaternary system is also applicable in other multicomponent alloys.