Effect of thermal history on the short-range order in Fe-Cr alloys

TL;DR

This study investigates how thermal history affects the short-range atomic order in Fe-Cr alloys using Mössbauer spectroscopy, revealing that thermal treatments significantly influence Cr atom distribution in neighbor shells.

Contribution

It provides new insights into the impact of thermal treatment on short-range order parameters in Fe-Cr alloys, highlighting differences between quenched and annealed samples.

Findings

Quenched samples show positive <alpha1> for all x-values.

Inversion of <alpha2> occurs at x about 8 in quenched samples.

Annealed samples exhibit different ordering behavior, with inversion at x about 3 for x < 8.

Abstract

Effect of a thermal history of Fe(100-x)Cr(x) (x < 20) samples on a Cr atoms distribution within the first (1NN) and the second (2NN) neighbor-shells was studied with the M\"ossbauer spectroscopy. The distribution was expressed in terms of the Cowley-Warren short-range order (SRO) parameters: <alpha1> for 1NN, <alpha2> for 2NN and <alpha12> for 1NN-2NN. It was shown to be characteristic of the thermal treatment and of the neigbor shell. For quenched samples, <alpha1> is positive for all x-values, while <alpha2> shows inversion at x about 8 from positive to weakly negative. Similar character has <alpha12>, but the degree of ordering in 1NN-2NN is lower than that in 2NN. Isochronally annealed samples exhibit similar behvior for x > ~8, but significantly different for x < ~8 where the inversion both in <a1> and <a2> occurs at x about 3, yet in the opposite direction. The <alpha12> follows the trend predicted by Erhart et. al. [PRB 77, 134206 (2008)]. A clear-cut inversion induced by an isothermal annealing at 415 C was found for the Fe85Cr15 sample.