Project 11: Thermodynamics, kinetics and constitution in the Mo-Ti-Si(-B) system
For an efficient development of high temperature materials in the ternary system Mo-Ti-Si as well as the quaternary system Mo-Ti-Si-B it is essential to elucidate the underlying thermodynamic facts by experiments as well as simulations. One approach is the CALPHAD method (CALculation of PHAse Diagrams). It allows the simulation of phase diagrams from the Gibbs free energies of all its phases and constituents. Based on this, microstructures can be derived and properties of materials can be predicted. Furthermore, it is possible to calculate thermodynamic data like enthalpies, heat capacities, chemical potentials and more.
In this subproject a thermodynamic data set will be created (or optimized), which will then be used for the CALPHAD method. For this purpose, a series of "key experiments" is planned, which aim to obtain the highest possible information density with the least possible expenditure of time and resources. Samples are to be prepared by vacuum arc melting and, as appropriate, heat-treated. Subsequently, the microstructure will be characterized by means of SEM and associated methods for elemental and phase analysis (e.g. EDX, WDX, and EBSD). Additionally, analyses using XRD are planned as well. Furthermore, thermodynamic data of the alloys will be obtained. This includes the determination of heat capacities and reaction enthalpies by differential scanning calorimetry, thermal expansion coefficients by dilatometry or thermal conductivities by laser flash analysis. The information thus obtained is used to perform thermodynamic modeling using crystallographic information in Compound Energy Formalism. The goal is to predict the properties of the system under different conditions (e.g. rapid solidification under Scheil conditions). This information will be, for example, directly relevant for subprojects 8 and 9.