Thermodynamic Assessment of the Co-Ti System

A new thermodynamic assessment of the Co–Ti system is presented on the basis of the literature data concerning phase equilibria and thermodynamics. A set of parameters of Gibbs-energy expressions for phases is obtained by means of CALPHAD approach. Excess Gibbs energy of fcc, bcc, and hcp disordered solutions is modeled using Redlich-Kister polynomials. The thermodynamic properties of liquid alloys are described using the associate solution model. Compound Energy Formalism is used to describe the thermodynamic properties of Laves C15 and C36 phases and order-disorder transformations L1₂-A1 and B2-A2 by applying of the corresponding two-sublattice models. The CoTi₂ compound is treated as stoichiometric. The phase diagram, coordinates of invariant equilibria, and thermodynamic properties of liquid and solid phases are calculated. Metastable phase transformations with the participation of supercooled liquid alloys and boundary solid solutions are analyzed.