Specificity of stage III in electron-irradiated Fe-Cr alloys

Abstract

It has been found that no typical features of stage III are traced in the resistivity recovery (RR) and positron lifetime (PL) data of electron-irradiated Fe-Cr alloys (4-10 at.%). None of the observed RR stages has shifted its temperature position with changing concentration of defects, which is characteristic of stage III. A new quantity was considered -the difference between RRs (DRR) of samples having different defect concentrations. The onset of free migration is indicated in the DRR plot by a peak, which corresponds in physical meaning to a partial (separated) RR peak of the free migration stage. Such a single peak was found in Fe-9Cr at 205-210 K and identified as the sign of stage III, however, the peak amplitude turned out inverted, i.e. it corresponded to a resistivity rise instead of the usual resistivity drop. In Fe-4Cr the peak amplitude is about zero. Such anomalous RR behaviour is related to a very high resistivity contribution of immobile di-vacancies formed in stage III. This contribution masks the resistivity reduction and makes stage III invisible in conventional RR spectra. Close PLs in mono-and di-vacancies make stage III poorly detectable by PL spectroscopy as well. The RR stage and PL increase at 220 K, considered earlier as the signs of stage III, are actually connected with the onset of long-range migration of interstitial atoms. Recombination and a release of mobile mono-vacancies resulted from this onset give rise, correspondingly, to a conventional RR stage and clearly detectable enlargement of the small vacancy aggregates formed in stage III.

Effects of solute atoms on evolution of vacancy defects in electron-irradiated Fe–Cr-based alloys

“…This is an indication that the clusters and the complexes are dominant sinks for SIAs and vacancies, which are mobile at RT [5,20].…”

“…The maximum electron fluence was 2 Â 10 23 m À2 . According to the resistivity increments of the Fe-16Cr alloy after low-temperature irradiation [15] and the specific resistivity of the Frenkel pairs equal to 75 lX Â cm/at.% [5], a fluence of 1 Â 10 22 m À2 corresponds to a damaging dose of $1.5 Â 10 À4 dpa.…”

“…The recent studies [5] on resistivity recovery have pictured the evolution of radiation-induced defects in Fe-Cr model alloys upon annealing after low-temperature electron irradiation as follows. At temperatures of stage I (below 130 K), self-interstitial atoms (SIAs) in the form of mixed dumbbells are captured in configuration traps; that is, configurations consist of two chromium atoms, and the long-range migration of SIAs is suppressed up to 220 K. Stage III occurs near 205-210 K, and its position at the same concentration of vacancies almost coincides with that in pure iron [6].…”

Interaction of carbon with vacancy and self-interstitial atom clusters in α-iron studied using metallic–covalent interatomic potential

“…Above 500 K, only vacancy clusters remain and they anneal at 700 K. Resistivity recovery (RR) measurements followed by annealing done by Takaki et al [19] suggested that in Fe-C doped specimens (i) vacancies (so called stage III defects) are trapped and immobilized by carbon atoms; (ii) v-C pairs act as saturable sinks for freely migrating carbon (presumably forming v-C N complexes with N = 4-10); (iii) the dissociation of v-C N complexes occurs at 580 K, with the activation energy of 1.55 eV. The latter is deduced by taking into account the heating rate and position of the stage following the expression suggested in [40]. We see that the results and their interpretations are consistent in the two above mentioned independent experimental works.…”

The EU programme for modelling radiation effects in fusion reactor materials: An overview of recent advances and future goals

“…In FeCr alloys migration of vacancies is influenced by Cr atoms, with the maximum of the interdiffusion coefficient occurring at $13% Cr [23]. Analysis of resistivity recovery curves [24] suggests that the presence of Cr atoms has a significant effect on the transport of SIA defects to sinks, which may be interpreted in terms of trapping and de-trapping of SIAs [25] as well as in terms of Cr-assisted diffusion of SIAs at low temperatures, or in terms of the Fig. 1.…”