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 $\text{R(T)≡}\text{d}\text{d}\text{t}\text{α}{}_{\mathrm{<mtext>Mo|Fe</mtext>}}\text{d}\text{d}\text{t}\text{α}{}_{\mathrm{<mtext>Co|</mtext>}}$ 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.