The binary Mo-Si system was thermodynamically modeled and optimized using the CALPHAD approach. Experimental thermodynamic data (heat capacities, enthalpies) and phase diagram information (solidus, liquidus) were used for modeling and calculation. Also, the well-documented silicon deficiency of the Mo3Si phase as well as newer data for the homogeneity ranges of intermetallic phases were taken into account. The application of the sublattice model, expressed in the compound energy formalism, enabled the development of analytical descriptions for the Gibbs energies of the solid system phases [1]. An existing ternary Mo-Si-Ti dataset from literature [2] was used to define key alloy compositions and explore the heterogeneous equilibria. 36 samples were prepared by arc melting and subsequent heat treating at 1300 °C. The thermally equilibrated and then water quenched samples were analyzed by scanning electron microscopy combined with EDX (SEM-EDX), electron probe micro analysis (EPMA), X-ray diffraction and inductively coupled plasma optical emission spectroscopy (ICP-OES). The homogeneity ranges of ternary solid solution phases and two- and three-phase equilibria, respectively, were studied in detail. Compared to earlier investigations [2], significantly different solid solution phase compositions were found. The experimental isothermal section at 1300 °C established a sound basis for further thermodynamic modeling. Additionally, literature data were incorporated. The ternary CALPHAD computer dataset was built up and used for a large variety of calculations: Thermodynamic functions (heat capacities, enthalpies, entropies), isothermal sections, isopleths, phase fraction diagrams and Scheil-Gulliver simulations were presented. Additionally, the Scheil reaction scheme was established. Such results are a valuable foundation for the development of new high temperature alloys for e.g. gas turbine components and power plant design, respectively.   
Acknowledgement: Funding by the German Research Foundation (DFG), Research Training Group 2561 is appreciated. We thank W. Ma, C. Hausner, J. Jung, C. Gebert, K. Erbes, T. Bergfeldt (all KIT, IAM-AWP) for helpful discussions and technical support.
References:         
[1] A. K. Czerny, W. Ma, C.S. Hausner, P. Franke, M. Rohde, H.J. Seifert, Adv. Eng. Mat. (2024), accepted for publication.  
[2] Y. Yang et al., Materials Science and Engineering A361 (2003), 281-293.