Neutron/proton irradiation and He effects on the microstructure and mechanical properties of ferritic/martensitic steels T91 and EM10

In the European EUROTRANS/DEMETRA program, the synergistic effect of radiation damage and helium on microstructure and mechanical properties of two 9Cr 1Mo ferritic/martensitic (FM) steels T91 and EM10 was evaluated after irradiation in SINQ targets. In addition, the helium induced effect was investigated using helium implanted specimens. The results demonstrate that helium can induce significant embrittlement effect in FM steels as shown by the tremendous increase in ductile-to-brittle transition temperature, the great reduction in ductility and fracture toughness at >∼15 dpa and 1000 appm He and the occurrence of intergranular fracture mode. Further, high-density helium bubbles can produce pronounced hardening effect.