Effect of He+ irradiation on Fe–Cr alloys: Mössbauer-effect study

Effect of He ions irradiation on three model Fe100−xCrx alloys (x = 5.8, 10.75 and 15.15) was investigated with the conversion electron Mössbauer spectroscopy. The study of the alloys irradiated with 25 keV ions revealed that the strongest effect occured in the Fe84.85Cr15.15 sample where an inversion of a short-range-order (SRO) parameter was found. Consequently, the investigation of the influence of the irradiation dose, D, was carried out on the chromium – most concentrated sample showing that the average hyperfine field, <B>, the average angle between the normal to the sample’s surface and the magnetization vector, < θ >, as well as the actual distribution of Fe/Cr atoms, as expressed by SRO parameters, strongly depend on D. In particular: (a) <B> increases with D, and its maximum increase corresponds to a decrease of Cr content within the two-shell volume around the probe 57Fe nuclei by ∼2.3 at%, < ⊝ > decreases by ∼13° at maximum, (c) SRO-parameter averaged over the two-shell volume increases with D from weakly negative value (indicative of Cr atoms ordering) to weakly positive value (indicative of Cr atoms clustering). The inversion takes place at D ≈ 7 dpa.