Application of CALPHAD Based Tools to Welding and Joining and the Importance of Selecting Which Databases and Models to Use

CALPHAD based tools, such as Thermo-Calc and DICTRA, together with related thermodynamic and kinetic databases are increasingly being used to model phenomena of interest to the welding community such as phase transformations, solidification, microsegregation during solidification, microstructure evolution, prediction of phases formed and diffusion across the joins of dissimilar materials, post weld heat treatment and more. The success of these simulations relies on the capability to provide fundamental phase equilibrium and phase transformation information in materials of industrial relevance, which is possible due to the adopted methodology where free energy or atomic mobility of each phase in a multicomponent system can be modeled hierarchically from lower-order systems, and model parameters can be evaluated by considering both ab-initio and various experimental data for both stable and metastable phases.

In this talk we will give some background to this approach, and discuss some examples where Thermo-Calc and DICTRA have been applied to applications of interest to the welding community, while also stressing the potential pitfalls in running such simulations including for example the importance of selecting which thermodynamic and mobility databases to use, particularly in the cases where the materials involved vary widely in composition. We will also compare some of the different models available in DICTRA, where depending on the type of problem being modeled, simulations can be run as single-phase, moving interface, fixed interface or through a multi-phase mixture.