Thermodynamic modelling of the Co–Ti system

In the Co–Ti system many solid solutions are present: A1, L12, A2, B2, A3, and Laves C15 and C36 phases. Two of them exhibit order/disorder transitions: A1 and L12, A2 and B2. In this optimisation the sublattice model has been used to describe the thermodynamic functions of the above-mentioned phases. The order/disorder transformation A1↔L12 has been described by modelling the L12 phase with either two or four sublattices both descriptions being mathematically equivalent. The A2↔B2 relation was also modelled in a similar way. The cited solid solutions, together with the liquid (Redlich–Kister excess model) and the CoTi2, considered as stoichiometric, phases have been optimised by means of the Thermo-Calc software, on the basis of the literature data concerning both phase equilibria and thermodynamics.