One-Dimensional Glide Motion of "Naked" Nanoscale 1/2<111> Prismatic Dislocation Loops in Iron

One-dimensional (1D) glide diffusion of interstitial-type prismatic dislocation loops is believed to play key roles in microstructural evolutions within nuclear-fusion and fission materials upon energetic particle irradiation. In the present study, using in-situ transmission electron microscopy, we have examined behaviors of nanoscale 1/2<111> loops in high-purity alpha-iron at "low temperatures" ranging from 15 to 290 K, under zero external stress. We observed 1D intermittent and fast motion of loops above approximately 100 K, which was significantly different from the 1D continuous and viscous motion observed at "high temperatures" above approximately 450 K. The estimated lower-limit values of diffusivities for "low temperatures" were considerably higher than the values obtained through the extrapolation of the temperature dependence of the diffusivities at "high temperatures." These results support the idea that strong obstacles for loop motion are formed by heating of the specimens to "high temperatures" after the introduction of loops.