Effect of substitutional Ni atoms on the Snoek relaxation in ferrite and martensite Fe-C alloys: An atomisitic investigation

Quantitative simulations of the carbon-induced internal friction in ferrite/martensite Fe-C and Fe-Ni-C alloys are performed by combining a mean-field elastic model and the atomistic kinetic Monte Carlo based on a pair interaction model to describe the composition-dependent carbon migration. The simulation is validated by experimental data and a thermo-kinetic theory. Our results predict that (i) additional peaks occur in the internal friction profiles of Fe-C and Fe-Ni-C due to C-C and Ni-C pair interactions; (ii) the Ni-alloying shifts the internal friction peak to lower temperature than in Fe-C alloys; (iii) the peak temperature is not simply related to the most frequent carbon jumps during the relaxation process; (iv) the internal friction behavior in martensite depends on the excitation direction with respect to the carbon ordering direction.