Phase-decomposition-related short-range ordering in an Fe-Cr alloy

A redistribution of Cr atoms related to a phase decomposition (PD) caused by an isothermal annealing at 415 °C in a 15.15 at.% Cr Fe-Cr alloy was studied in an ex situ way by the conversion electrons Mössbauer spectroscopy. Analysis of the spectra in terms of a two-shell model enabled the determination of probabilities of 17 different atomic configurations and average numbers of Cr atoms within the first (1NN) and the second (2NN) neighbor shells vs. annealing time, separately. The annealing-time evolution of these numbers, expressed in terms of the Cowley-Warren short-range order (SRO) parameters, was shown to follow the Johnson-Mehl-Avrami-Kolgomorov equation. The SRO parameter averaged over the 1NN-2NN shells was revealed to be linearly correlated with the average hyperfine field. Signatures in favor of the nucleation and growth mechanisms responsible for PD are also discussed.