Computer Calculation of Intermetallic Phase Diagrams

The computer calculation of phase diagrams has been developed in the last two decades starting with the pioneering work of Kaufman et al.. His approach was applied and extended by a number of research groups known under the logo of CALPHAD. Most of their work can be found in the CALPHAD journal and at the occasion of their annual CALPHAD meetings. The purpose of these activities was and still is to provide a tool for estimating the phase equilibria in multicomponent systems. Usually the amount of experimental data is meagre and comes from different areas, e.g. phase diagram data, calorimetric and general thermophysical measurements, structural data. The computer programs are constructed in such a way that they can bundle all these different kinds of informations in an optimizer module to arrive at numerical values for adjustable parameters which define the thermodynamic functions. These functions have been developed in the past and this activity goes on. We may distinguish three types of approaches: (I) the pure formal mathematical approach consisting in a polynomial representation of the thermodynamic functions (CALPHAD approach), (II) the modeling of thermodynamic functions, (III) statistical thermodynamics treatments.The presented paper tried to give an overview of these techniques with emphasis on the special aspects of materials development based on intermetallic phases. Special aspects were: How good is the description of intermetallic phases? What about the homogeneity range of intermetallic phases? What about the predictive power of the techniques, e.g. what can be predicted in a ternary system from existing knowledge in the binary subsystems? These aspects were discussed and illustrated with particular examples out of the huge amount of existing data in the literature as well as unpublished new results.The interested reader is refered to the references listed below. This list cannot be complete. A selection has been made such that the main strategies can be found and that typical aspects of phase diagrams of intermetallic systems are treated.