Momentum transfer and damage energy gradient effects on helium distributions in type 304 stainless steel

The elastic scattering of 18 MeV α particles and transmission electron microscopy were used to study the effects of atomic displacement damage on preinjected helium distributions in type 304 stainless steel at 500°C. Helium implantation was conducted at 25°C or 500°C. The target foils were bombarded in either the solution annealed or 60% cold worked condition. Damage energy profiles were varied by changing the bombarding ion species (oxygen or hydrogen) or incident ion energy. Theoretical calculations of helium transport by atomic collisions were made for comparison with the experiment. For all of the experimental conditions, helium was shown to be very effectively trapped. No significant changes in helium concentration profiles or long-range migration (&> 100 nm) were induced by the superposition of highly nonuniform atomic displacement profiles at damage levels up to ~20 dpa. Most of the helium could be accounted for by the appearance of small near-equilibrium bubbles.