Thermodynamic modeling and experimental investigation of the phase stability at the Ni-rich region of the Ni-Al-Cr-Ir system

The effect of adding 3 at.% Cr on the phase stability of the Ni-Al-Ir system was studied experimentally at 1250 °C. A thermodynamic description of the Ni-Al-Cr-Ir quaternary system in the Ni-rich region was then developed based on the microstructures, the crystal structures and the phase compositions determined by experiment for eight alloys in both as-cast and 1250 °C annealed states. The calculated isothermal section at 1250 °C using the obtained description was consistent with the phase-equilibrium data obtained in this study. The calculated two-dimensional section of liquidus projection was also in accordance with the primary phases of solidification observed from alloys in the as-cast state. The effects of Cr additions to the Ni-Al-Ir alloys on the as-cast and annealed microstructures were elucidated through Scheil simulation and phase-equilibrium calculation using Pandat.