Characterization of dislocation loops in hydrogen ion-implanted Fe-Cr alloy annealed at different temperatures

Reduced-activation ferritic/martensitic (RAFM) steels, based on Fe-Cr alloys, have been considered to be one of the most promising candidate structural materials for future fusion reactors. Dislocation loops, as one of the most common microstructures induced by radiation, are the key factors in the deterioration of material properties. Dislocation loops with different Burgers vectors have different effects on material properties. Currently, a consensus exists suggesting that there are two kinds of dislocation loops with Burgers vectors of 1/2 〈111〉 and 〈100〉 in bcc iron-based alloys. In this study, the Burgers vectors of dislocation loops formed at the annealing temperatures of 400, 500, and 550℃ in hydrogen-ion implanted Fe-9%Cr model alloy were examined based on dislocation loop maps and dislocation loop invisibility criteria. Dislocation loop maps manifest such that under the 〈100〉 or 〈110〉 zone axes, it is easy to distinguish 1/2 〈111〉 and 〈100〉 edge dislocation loops, while under the 〈111〉 zone axis, the loops cannot be distinguished. By direct comparison between loop maps and loop images obtained through transmission electron microscope (TEM), the dislocation loops with Burgers vectors of 1/2 〈111〉 and 〈100〉, formed at different annealing temperatures, were characterized. The results of the characterization show that with increasing annealing temperature, the size of the dislocation loops increases while density decreases. Furthermore, the proportion of dislocation loops with a Burgers vector of 〈100〉 increases with rising temperature. After annealing at 400℃ and 500℃, the percentages of 〈100〉 type dislocation loops are 16.48% and 92.78% respectively, in hydrogen-ion implanted Fe-9%Cr alloy. While the temperature is raised to 550℃, all the dislocation loops are of 〈100〉 type loops. This indicates that the transition temperature range of dislocation loops in Fe-9%Cr is 400℃-500℃. Compared with pure iron, the presence of Cr element promotes the transition temperature of dislocation loops from 1/2 〈111〉 type to 〈100〉 type.