Helium and hydrogen induced hardening in 316LN stainless steel

In certain radiation environments, such as the spallation neutron source (S NS) presently in design and construction, the high transmutation production rate for helium and hydrogen, concomitant with displacement damage, may af fect the mechanical properties of structural materials. To better understan d this effect, we have studied type 316LN stainless steel specimens implant ed with medium energy Fe-, He-, and H-ions, alone and in combination. In th is report, we present nanoindentation measurements of the incremental incre ase in hardness caused by 360 keV He-ions implanted at 200 degreesC to conc entrations from 2 to 200 000 appm. The He-induced hardening was found to sa turate at twice the level measured for Fe-induced displacement damage alone . The additional hardening at high helium concentrations was associated wit h the presence of helium filled cavities (bubbles), observed by transmissio n electron microscopy (TEM). We also found that co-injection of helium and hydrogen resulted in more hardening than was observed for He-implantation a lone. (C) 2000 Elsevier Science B.V. All rights reserved.