Thermodynamic modeling of Al-Co-Cr, Al-Co-Ni, Co-Cr-Ni ternary systems towards a description for Al-Co-Cr-Ni

The phase relations and thermodynamic properties of the Al-Co-Cr, Al-Co-Ni, Co-Cr-Ni ternary alloys are investigated using first principles calculations based on DFT (density functional theory). Their thermodynamic descriptions are developed by means of the CALPHAD (calculations of phase diagrams) method using experimental and computational data from the present work and the literature. Emphasis is placed on modeling the A2, B2, fcc-γ, L12-γ′ and tetragonal-σ phases in the temperature range of 1173-1623 K. Liquid, A2 and fcc-γ phases are modeled using substitutional solution descriptions. A partitioning model is then used for the γ/γ′ and A2/B2 phases to effectively describe the order-disorder transitions. The critically assessed thermodynamic descriptions describe all experimentally determined phase equilibria data well. A2/B2 transitions are also shown to agree well with previous experimental findings in the Al-Co-Cr ternary system.