Simulation of precipitate evolution in Fe-25 Co- 15 Mo with Si addition based on computational thermodynamics

摘要

Multi-component nucleation theory is applied to decipher the precipitate evolution of solution-treated and quenched Fe-25Co-15Mo (mass%) with Si addition during continuous heating and isothermal aging. For computer simulation of the nucleation and growth kinetics of precipitates, we optimize thermody-namic model parameters of the Fe-Co-Mo system with experimental data and enthalpies of formation of ternary ferrite phase determined by density functional theory analysis. Si-solubility in the precipitation-hardening μ-phase is considered in the thermodynamic modeling. The body-centered cubic (bcc) ferrite phase reveals a metastable miS_cibility gap between Fe- and Mo-rich phase below 1033 K. Based on thermodynamic modeling of the Fe-Co-Mo system, it is shown that the alloy Fe-25Co-15Mo is located outside the spinodal region, which is in contrast to some previous work on this system. Thermo-kinetic simulations, which are validated on experimental data from atom probe tomography, propose that during aging, the first microstructures form by means of nucleation and growth of metastable bcc-precipitates before the formation of rhombohedral u-phase. For the thermokinetic analysis, we evaluate and utilize theoretically predicted nucleus compositions of bcc-precipitates from the minimum nucleation barrier concept.