Kinetic paths in two order parameters: A Mössbauer spectrometry experiment with FeCoMo

Abstract

Mössbauer spectrometry was used to measure short range correlations between 57Fe and Mo atoms, and between 57Fe and Co atoms in crystalline Fe-49 at.%Co-2 at.%Mo alloys. After a rapid quench from the melt, both types of correlations were characteristic of those of a nearly disordered alloy. After annealing, we found FeCo correlations characteristic of B2 order, and a Co-rich environment around Mo atoms. We found that the Warren-Cowley SRO parameters, α Mo|Fe and α Co|Fe, do not change at the same relative rates when rapidly quenched specimens are annealed at different low temperatures. At lower temperatures we observe a smaller ratio, R(T), where R(T)≡ d dt α Mo|Fe d dt α Co| Because the critical temperature for B2 ordering in FeCoMo is only weakly dependent on Mo concentration, we attribute the temperature-dependence of R(T) to a high activation barrier for the diffusive jumps of Mo atoms.