Behavior of helium bubbles in cold worked aluminium-lithium alloys

Various kinds of cold worked Al-Li alloys were irradiated JRR-2 and the change in microstructure with post-irradiation annealing was examined in an electron microscope. in 30% cold worked specimen, bubbles are preferentially distributed on sub-boundaries. The grain interior contains only a small amount of bubbles. On the contrary, in 2% cold worked specimen, in which distinct sub-boundaries are rarely formed, most of bubbles are distributed within the grains. Bubbles aligned on a dislocation are frequently observed These experimental results are explained as follows. In heavily cold worked specimen, moving dislocations collect most of He atoms or their clusters in the course of subboundary formation after irradiation. In slightly cold worked specimen, dislocation density is insufficient to perform this process and He atoms or their clusters precipitate either upon dislocations or within the grains. (auth.)