A study of irradiated FeCr alloys: deviations from Matthiessen's rule and interstitial migration

Abstract

FeCr alloys with concentrations ranging from 50 p.p.m. to 3% Cr have been irradiated with electrons of 1.6 MeV at low temperature (30 K) and studied by resistivity measurements. Pre-irradiation measurements show important deviations from Matthiessen's rule in the annealed alloys: the resistivity increment per unit concentration of Cr in Fe depends strongly on the solute concentration. It increases from 180 mu Omega cm for a few per cent of chromium up to 400 or 600 mu Omega cm when the chromium concentration is lowered down to 50 p.p.m. This increase is explainable in the two-current model if one considers the dilute alloys with the residual impurities as ternary alloys. The radiation-induced resistivity, measured as 4 K, is also found to depend strongly on the Cr concentration. This can only be explained by assuming that the Frenkel pair specific resistivity, rho F, is an increasing function of the Cr concentration. This variation of rho F in the alloys can be interpreted, in the two-current model, as a deviation from Matthiessen's rule in the irradiated alloys considered as ternary alloys. Mixed Fe-Cr interstitials seem to be slightly more mobile than self-interstitials.