Takeo Iwai

Role of nickel and manganese in recovery of resistivity in iron-based alloys after low-temperature proton irradiation

This study investigates the recovery of electric resistivity in pure iron, Fe–0.6Ni and Fe–1.5Mn as related to isochronal annealing following 1 MeV proton irradiation at lower temperature than 70 K, focusing on the relationship between solute atoms and irradiation defects. Both nickel and manganese prevent stage ID recovery, which corresponds to correlated recombination. Stage II recovery is also changed by the addition of a solute, which corresponds to the migration of small interstitial clusters. In both pure iron and Fe–0.6Ni, no evident difference was observed in the stage III region, which corresponds to the migration of vacancies. In contrast, two substages appeared in the Fe–1.5Mn at a higher temperature than stage IIIB appeared in pure iron. These substages are considered to represent the release of irradiation-induced defects, which was trapped by manganese.

Heterogeneity of ion irradiation-induced hardening in A533B reactor pressure vessel model alloys

Reactor pressure vessels comprise bainitic steel structures, and are heterogeneous on the mesoscale. Nanoindentation techniques were used to evaluate the hardness of these structures on the micrometer scale, and to evaluate the heterogeneity in a specimen using the distribution of the hardness. Three A533B model alloys were irradiated by 2.8 MeV Fe2+ ions at 563 K, and the effects of ion fluence, ion flux, and chemical composition on the change in the hardness distribution were examined. Heterogeneity of the hardening is observed in high-copper specimens irradiated up to (2–10) × 1014 ions/cm2, where the average hardness increases the most. In these specimens, the hardness distribution broadens, and demonstrates that the hardening in certain positions (possibly where the initial hardness is high) is greater than in other positions. Variation in initial chemical composition (especially copper and carbon) or sink strength may cause a difference in the curing behavior.