TCNI5: A New Thermodynamic Database for Ni Based Superalloys

Thermodynamic databases developed using the CALPHAD method have been successfully applied to the modeling and simulation of Ni based superalloys for more than fifteen years. Such databases when combined with suitable software can be used for accelerating alloy design as well as improving understanding of existing alloys in terms of their processing and in-service behavior. Additionally, such databases are also essential to the modeling of microstructural evolution using methods such as phase field codes and steady state approaches.

 A new thermodynamic database has been developed for Ni-base superalloys based on the critical evaluation, using the CALPHAD method, of all the constituent binary systems across their full range of composition and most of the ternary systems containing Ni as well as a number of other key ternary systems. This new database contains all the important Ni-based superalloy phases within a 20-element framework [Ni Al B C Co Cr Fe Hf Mo N Nb Pd Pt Re Si Ta Ti V W Zr] + Ar, H and O for the gas phase only and in total 292 solution and intermetallic phases are included in this database.  Also of note is that the ordered and disordered bcc (A2 and B2) and fcc (A1 and L12/γ´) phase have been modeled with a two sub-lattice model using a single Gibbs energy curve, and this type of description is of particular importance to be able to predict second order transformations between A2 and B2.

 All necessary volume data, including molar volume and thermal expansivity, for various phases have been implemented in TCNI5. Together with the new MOBNI2 database, which includes mobilities for ordered B2 and L12 as well as for the disordered bcc and fcc, TCNI5 can be used with DICTRA to predict different kinetic aspects taken all relevant phases into account, e.g. simulate interdiffusion across Ni based coatings.

 This presentation will describe the motivations for developing this database, as well as the basis for some of the modeling and also give some examples of predictions compared with real alloy data and potential applications.