WEB Phase-field simulations of niobium-silicide-based eutectic microstructuresWednesday (23.09.2020) 10:40 - 10:55 M: Modelling and Simulation 2 Part of:
Due to their high melting point and relatively low density, niobium-silicide-based alloys are promising candidates to replace nickel-base superalloys in high temperature applications such as in aircraft turbines or stationary gas turbines. In order to control the arising microstructure during directional solidification, it is important to identify the key parameters and to understand the mechanisms controlling the pattern evolution processes. As the phase-field method allows to investigate the morphology changes in their complex three-dimensional spatial arrangement, three-dimensional phase-field simulations based on a Grand potential formalism are performed to study the microstructure evolution of eutectic niobium-silicide-based systems.
To ensure a thermodynamically consistent modeling of these systems for the application in phase-field simulations, thermodynamic calphad databases are used for the modeling of the phases. As several of the involved phases in these systems have a stoichiometric character, the modeling via calphad data is challenging. For a stoichiometric phase the calphad databases only provide the Gibbs energies at the exact stoichiometric composition. Therefore a modeling based on the concentrations of the phases, as it is commonly made, is not suitable.
In this work a modeling approach based on the temperature dependence of the Gibbs energies is introduced to model the binary Nb-Si and the ternary Nb-Si-Ti system. To validate the approach, the stability of the stoichiometric composition of the phases during the solidification process is investigated depending on different temperatures and melt concentrations in two- and three-dimensional simulations. Due to the variation of the melt composition, the phase fractions of the evolved phases are changing and hence a transition from lamellar to fibrous structures and vis-versa can be observed in the three-dimensional large-scale microstructures.