| Formation and growth of precipitates in thermally aged Fe-Cu-Ni-Mn alloys at temperatures above 300° C is studied by kinetic Monte Carlo simulations. By means of a thermal activated vacancy diffusion mechanism on a rigid bcc lattice, it is possible to characterize the processes of nucleation, growth, and Ostwald ripening of the Cu-rich clusters for a wide range of temperatures and temporal scales. In addition, the role of the Ni and Mn solute atoms - which have the tendency to form shells around the precipitates - is thoroughly investigated for relevant concentration ranges. Due to the fact that the kinetic Monte Carlo method can be used only for early stages of the system evolution, phase-field modeling provides the proper framework to complement the atomistic simulations and extend them to larger spatial and temporal scales. Here we present how interfacial energies between a Cu-rich cluster and the surrounding Fe-rich matrix as well as the spatial distribution of precipitates obtained in the Monte Carlo simulations are transfered as input for the phase-field simulations, which use other thermodynamic data from Calphad database. We show that our phase-field model can be validated quantitatively for Gibbs-Thomson effect and it also predicts the coarsening kinetics (Ostwald ripening) correctly. While Monte Carlo method captures the nucleation of small precipitate clusters, phase-field model is able to capture the coarsening regime and coalescence events at high volume fraction of precipitates, and thereby both models complement each other. Finally validation of the results with available experimental data is discussed. (Coauthors: D. Molnar, S. Hocker,P. Binkele, A. Choudhury, R. Mukherjee, B. Nestler and S. Schmauder) |
|