The effect of Cr composition on the local atomic and magnetic structure of pristine and ion-irradiated FeCr alloys

High Cr (9-14% Cr) ferritic/martensitic steels are considered as one of the most promising candidates for structural materials for advanced nuclear power plants. Therefore, the understanding of the evolution of properties under operation conditions is of primary importance. This work focuses on the effect of Cr composition on the local atomic and magnetic structure of pristine and ion-irradiated FeCr alloys. The materials considered for this study are commercial purity FeCr binary alloys with varying Cr content up to 16% at.Cr, which were also implanted with heavy ions (Fe+) under different conditions. Using a combination of spatially resolved and element specific techniques the following results were obtained: - The dependence of the total (bulk) magnetic moments is linearly decreasing as the Cr-content is increasing - The Fe magnetic moments at the surface reduced by the presence of impurities and defects. The dependence on Cr-content is non-linear, with a tendency of increasing the spin moments above 10% Cr. - The Cr spin moments exhibit a reorientation transition around 9% Cr from ferromagnetically to anti-ferromagnetically aligned with respect to the Fe spin moments. - The effects of ion irradiation are fairly complex, with an overall higher spin magnetic moment after exposure to the heavy ions. The ion dose has a reduced effect on the spin moments while the target temperature shows a more significant, but scattered influence on the Fe spin moments. - All specimens show a decrease of the Cr nearest neighbor distance for Cr contents between 6 – 10% Cr. Also, the atomic disorder around the Cr atoms is enhanced compared to the Fe atoms. - For the Fe9% Cr irradiated alloy the effect of elevated temperatures and dose is clearly seen as a reduction of atomic coordination numbers around the Cr atoms, which can be associated with formation of vacancies. - For the Fe5% Cr and Fe12% Cr alloys, the number of nearest neighbors around the Cr atoms is not sensitive to irradiation.