Thermodynamic modelling of a six component (C-Co-Cr-Ni-Ta-W) system for the simulation of Cobalt based alloys

Co-based alloys are key materials for several high temperature applications where high corrosion and wear resistance are required. Main alloying elements, in addition to Co, are Cr, Ni, Ta, Mo, W, Ti, Al, etc. and C. In order to simulate these materials a new thermodynamic database has been implemented which includes the six most important alloying elements: Co, Cr, Ni,Ta, W and C. The liquid and 30 solid phases have been modelled by means of the Compound Energy Formalism (CEF) with particular attention to the consistency between thermodynamic and crystallographic sublattices. Interaction parameters for all the binary and ternary sub-systems are included. When possible they have been taken from the literature but, for several systems, partial or complete reassessment was needed, due to inconsistency of the phase models or incompatibility between assessments of different authors. As a result phase equilibria in selected commercial alloys are calculated. - Highlights: • A new Calphad thermodynamic database for Co-based alloys has been implemented. • The database includes six alloying elements: Co, Cr, Ni,Ta, W and C. • Phase fractions vs T are calculated for selected commercial alloys.