Thermodynamic modelling of bulk and surface properties of liquid Co-Cr-Ni alloys

The lack of experimental data and/or limited experimental information concerning both bulk and surface properties of liquid alloys often requires the prediction of these quantities. An attempt has been made to link surface properties of ternary Co-Cr-Ni system and its binary subsystems with bulk through the study of the concentration dependence of various thermodynamic, structural and surface properties in the framework of statistical mechanical theory in conjunction with the quasi-lattice theory (QLT). The description involve the input thermodynamic parameters of the ternary system, of its binary subsystems as well as thermophysical properties of pure components. The theoretical results on the thermophysical properties of binaries are compared with available literature data. Motivations and Objectives: The presence of sigma phase in complex transition metal systems is well known; its presence is critical since it tends to embrittle metallurgical systems such as NiCoCrAlY alloys used as bond coat in thermal barrier coatings. With appropriately selected composition, NiCoCrAlY alloys guarantee excellent performances even if long-term exposure at high temperature induces microstructural changes. In-depth examination of microstructural evolution is extremely interesting for life management of hot gas path components. This topic has been approached both theoretically and experimentally and this study deals with the first theoretical results regarding Co-Cr-Ni system in the liquid state. Bulk and surface properties of the liquid alloy are interesting because at least in the neighbourhood of the crystallization point there is a similarity in both structural arrangement and chemical interactions between liquid and solid state.