Enhanced atomic short-range ordering of the alloy Fe–15 at. % Cr caused by ion irradiation at elevated temperature and thermal effects only

A solid solution of 15 at. % Cr in α-Fe was prepared by rapid quenching from 1200 °C and cold plastic deformation (foils 30-μm thick). Under ion irradiation at a temperature of 450 °C with the use of 20-keV Ar+ and 40-keV Fe+ ions, this metastable alloy undergoes partial decomposition. The corresponding short-range-order parameter was determined by transmission Mossbauer spectroscopy. It ranges between 0.07 and 0.14 depending on the irradiation conditions. By comparison with an annealing treatment using the same temperature of 450 °C, it was proved that the effect of short-range-order formation is mainly caused by the irradiation and not by the elevated temperature. The time dependence of the decomposition shows a saturation effect after the first minutes of ion irradiation. Conversion electron Mossbauer spectroscopy (CEMS) data have shown that transformation of the initially disordered homogeneous solid solution is not limited to the penetration depths of the ions but extends over the whole sample thickness. This effect is explained by the radiation-dynamic action of the accelerated ions: probably propagation of after-cascade microshock waves, becoming non-attenuating in metastable media and driving phase transformations or correlated atom regrouping at their front.