Irradiation-induced hardening mechanism of ion irradiated JLF-1 to high fluences

Reduced-activation ferritic/martensitic steels, RAFs, are leading candidates for blanket and first wall of fusion reactors, and effects of displacement damage and helium production on mechanical properties and microstructures are important subjects. The objective of this work is to clarify radiation hardening mechanism by means of ion irradiation and nano indentation. JLF-1 (9Cr-2W-V, Ta) steel was irradiated to 60 dpa at 693, 743 and 793 K. Single-ion irradiation was performed with 6.4 MeV Fe3+. The Fe3+ ions and the energy-degraded 1.0 MeV He+ ions were simultaneously irradiated for dual-ion irradiations. The displacement damage rate and helium injection rate were up to 1.0 x 10-3 dpa/s and 1.5 x 10-2 appm He/s, respectively. As the post-irradiation examination, transmission electron microscopy (TEM) observations and nano-indentation measurements were carried out. Small differences in micro-hardness between these irradiation temperatures were measured under single-ion irradiation. Radiation-induced precipitate (RIP) was formed at 743 K under single-ion irradiation, but the contribution of RIP to radiation hardening was estimated smaller than that of dislocation loops. Helium effect of microstructural evolution at 693 K under dual-ion irradiation was found to contain a finer defect clusters than that under single-ion irradiation, and a large increment of irradiation hardening was measured in the specimen irradiated at 693 K under dual-ion irradiations