Modeling of stoichiometric phases in off-eutectic compositions of directional solidifying NbSi-10Ti for phase-field simulations

To meet the requirements of modern technical and scientific applications, the development and investigation of high-performance materials with locally defined properties gets more and more into focus of actual research. These materials often contain phases with at least one stoichiometric component. To investigate such materials within grand potential-based phase-field simulations, a specialized method is needed, which allows to model the required Gibbs energy formulations for the stoichiometric phases. In this work, a modeling approach is introduced, based on the equilibrium conditions of the involved phases, to generate a Gibbs energy formulation for the stoichiometric (Nb, Ti)(3) Si phase in Nb-Si-Ti. With this formulation, the eutectic reaction in the ternary NbSi-10Ti system is investigated within two- and three-dimensional phase-field simulations, with eutectic and off-eutectic melt compositions. The solidified microstructures are qualitatively assessed by measuring the average front undercoolings, the adjusting phase fractions and the concentrations during the simulations. The validation of the results shows the ability of the generated material model to simulate the obtained system and proves the suitability of the presented approach to model stoichiometric phases.