MODELING OF STRENGTHENING MECHANISMS IN IRRADIATED FUSION-REACTOR 1ST WALL ALLOYS

Tensile property evaluations of austenitic stainless steels irradiated at 60 to 400-degrees-C in the ORR have been conducted. The neutron spectrum was tailored to achieve the appropriate helium/dpa ratio for austenitic stainless steels in a fusion reactor. The components of the alloy microstructure considered to contribute to strengthening are black dot defect clusters, Frank loops, network dislocations, voids, bubbles, and precipitates. Accepted expressions for hardening by defect interactions were employed in the calculation. It was found that the strengthening could be accounted for by the observed defects at temperatures below 330-degrees-C. However, strength was underpredicted at the higher temperatures. Since the voids and precipitates were observed to nearly always occur in coupled pairs, they were considered to be one large defect contributing to hardening through the Orowan bowing mechanism. This mechanism alone could not account for the strengthening observed. However, radiation-induced segregation of alloy components to the bubbles could account for the observed hardening, although defects below the limit of detectability are also believed to make a contribution.