Hardness and defect structures in EC316LN austenitic alloy irradiated under a simulated spallation neutron source environment using triple ion-beams

For an assessment of the future US spallation neutron source (SNS) target performance, radiation induced hardening and microstructural evolution were investigated as a function of ion dose for EC316LN stainless steel. Irradiation was carried out using 3.5 MeV Fe+, 360 keV He+, and 180 keV H+ simultaneous ion-beams at 200 degrees C to simulate the damage, He and H production in the SNS target vessel wall, At low dose (< dpa), the predominant defects were black dots whose number density saturated rapidly within a few dpa. This was followed by the evolution of interstitial loops whose number density saturated below 15 dpa. Although He-bubbles were not visible, severely scalloped loops suggested that the implanted He/H atoms existed in the form of small clusters. Comparison with reported neutron irradiation data showed that hardening and ductility loss occurred mostly in the black dot regime (<1 dpa), but that good ductility (>20% elongation) was maintained up to a dose level of similar or equal to 10 dpa. (C) 2000 Elsevier Science B.V. All rights reserved.