| Popis: |
To examine influence of helium on irradiation-induced embrittlement, helium gas release on brittle fracture has been investigated for high-nickel precipitation-strengthened alloys D21, D25 and a ferritic steel HT-9, irradiated in EBR-II to the fluence of 3 × 1026n/m2 (E > 0.1 MeV), using a quadrupole massfilter in the ultra-high-vacuum fracture system. The irradiated alloys, D21 and D25, fractured intergranularly (Ttest = RT) and released considerable amounts of helium on fracture. From the observed helium release, the helium population segregated on the grain boundary was estimated to be a few percent of the metallic atoms there (1000–2000 times the average helium density ~15 ppm). The HT-9 (Ttest = 77 K) showed a similar concentration ratio in spite of the small helium content in average ( ~ 1 ppm). The result suggests that the segregated helium may contribute to the embrittlement, as well as the brittle phase formation along the grain boundaries bubble formation. |
