ISOTOPIC TAILORING WITH NI-59 TO STUDY THE INFLUENCE OF HELIUM DPA RATIO ON TENSILE PROPERTY CHANGES

Irradiation of miniature tensile specimens of simple model Fe-Cr-Ni alloys is proceeding in the Fast Flux Test Facility to study the interactive effects of alloy composition, cold work level, helium/dpa ratio and irradiation temperature on the evolution of microstructure and associated changes in mechanical properties. The addition of Ni-59 to these alloys allows side-by-side irradiation of otherwise identical specimens, differing only in helium/dpa ratio. In the absence of differences in displacement rate and temperature history, it is shown that helium in this experiment exerts a rather small influence on tensile properties at 365 and 600-degrees-C. While the saturation level of yield stress in Fe-25Ni-15Cr is strongly dependent on irradiation temperature, it is relatively insensitive to cold work level and helium/dpa ratio. The yield strength of Fe-25Ni-15Cr, both unirradiated and irradiated at 365-degrees-C, is increased slightly by addition of 0.04 wt% phosphorus.