In-situ TEM observation of migration behavior of helium bubbles in F82H

Formation and migration behaviors of helium (He) bubbles in reduced activation ferritic/martensitic steel F82H have been investigated by in-situ electron microscope observation, where the investigation of bubble formation was done under 5 keV He+ ions irradiation at three different temperatures, and then the investigation of bubble migration was done in thermal annealing process at temperatures in a range from 573 to 1073 K for samples after the He+ ions irradiation. The formation of He bubbles much depends on temperature and fluence; many He bubbles with small size are observed at below 773 K, while a few He bubbles with large size are observed at 1073 K. At relatively high temperatures above 873 K, the Brownian type motions of He bubbles were clearly detected, in which the diffusion coefficient of bubbles strongly depends on temperature and bubble size. A relation between the bubble diffusion coefficient and the bubble diameter indicates that the observed bubbles in this study migrate by the surface diffusion mechanism. In construction of an approximate expression for the bubble diffusion coefficient, the obtained fitting curves based on an empirical equation under assumption of the surface diffusion nicely reproduce the experimental data. [GRAPHICS] .