It is well understood that one-dimensional (1D) high-speed motion of self-interstitial atom (SIA) clusters play important roles in radiation-induced microstructural evolution in metals and alloys. Recently, extensive classical molecular dynamics calculations have suggested an anomalous structure of small interstitial-type dislocation loops–agglomerations of self-interstitial atoms (SIAs) on a habit plane–comprising several to several tens of SIAs. According to these studies, these small loops comprise bundles of crowdions and their Burgers vector is oriented along the axis of the crowdions; moreover, these loops can move one-dimensionally along the Burgers vector by the almost independent motion of all the crowdions along their axis in the loop. In contrast, the motion of nanometer-sized loops has been experimentally examined by transmission electron microscopy (TEM) for a few pure metals and alloys. These experimental studies showed that loops can make 1D back-and–forth motion along the directions of their Burgers vectors (prismatic glide); however, important problems still remains unresolved. In this seminar, I will present recent results of our study, which have not been clarified so far, on the dynamic behavior of loops in high-purity bcc iron upon high-energy electron irradiation and simple heating following the induction of loops by irradiation, by using in situ TEM. The main topics are as follows: (1) processes of motion (prismatic glide and self-climb) of both types of loops (those with the Burgers vectors of 1/2 and ), (2) change in the Burgers vector of loops, and (3) quantification of mobility of loops, and so on.
Research Center for UHVolt. Electron Microscopy, Osaka University, Japan