Effect of periodic temperature variations on the microstructure of neutron-irradiated metals

Specimens of pure copper, a high purity austenitic stainless steel, and V-4Cr-4Ti were exposed to eight cycles of either constant temperature or periodic temperature variations during neutron irradiation in the High Flux Isotopes Reactor to a cumulative damage level of 4-5 displacements per atom. Specimens exposed to periodic temperature variations experienced a low temperature (360 °C) during the initial 10% of accrued dose in each of the eight cycles, and a higher temperature (520 °C) during the remaining 90% of accrued dose in each cycle. The microstructures of the irradiated stainless steel and V-4Cr-4Ti were qualitatively similar to companion specimens that were continuously maintained at 520 °C during the entire irradiation. The microstructural observations on pure copper irradiated at a constant temperature of 340 °C in this experiment are also summarized. The main radiation-induced microstructural features consisted of dislocation loops, stacking fault tetrahedra and voids in the stainless steel, Ti-rich precipitates in the V alloy, and voids (along with a low density of stacking fault tetrahedra) in copper.