Abstract
Helium bubble nucleation and growth processes were studied at elevated temperatures on type 304 stainless steel which had been neutron irradiated to 1.4 × 1026 n/ m 2 ( E > 1 MeV) and annealed at 400, 550, 650 and 900°C for 1 h. After annealing, specimens for microstructural observation were prepared and observed (by transmission electron microscope (TEM).) Radiation defects were present at high density in the as-irradiated specimens and annealed out with increasing annealing temperature. Helium bubbles became visible where defects were annealed out (above 650°C). The bubbles grew preferentially at dislocations and grain boundaries. At the grain boundaries, most of the helium bubbles formed on grain boundary dislocations. It was concluded that during post-irradiation annealing, the dislocations which remained after annealing played an important role in helium bubble growth, even in the grain boundaries.
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