Self-ordered defect structures in two model F/M steels under in situ ion irradiation

Two model F/M steels, 9Cr-model and 12Cr-model, were irradiated with 1 MeV Kr ions in situ in a TEM at temperatures between 20 K and 573 K to doses as high as 15 dpa. During the early stages of irradiation of the two F/M steels, defect clusters were rather uniformly distributed within grains, and a saturation density was quickly reached. However, at higher doses, self-ordering alignments of defect clusters were found in some grains. The regularly ordered arrays of small loops were observed in the two F/M steels along 〈1 1 0〉 directions with spacing about 30-50 nm. Once the aligned structure was created, it was stable under further irradiation. The possible mechanisms for the “self-organization”/“ordering” of the clusters were investigated. This paper describes the process and its temperature dependence, and the possible mechanisms are discussed.