Vickers hardness change of the Chinese low-activation ferritic/martensitic steel CLF-1 irradiated with high-energy heavy-ions

In the present work, irradiation hardening behavior of a Chinese low-activation ferritic/martensitic steel CLF-1 candidate to fusion reactor blankets is studied. Specimens were irradiated with high-energy 14N and 56Fe ions at a terminal of a cyclotron to three successively increasing damage levels of 0.05, 0.1 and 0.2 dpa at about -50 oC. Energy of the incident ions was dispersed to successively decreasing 11 grades by using an energy degrader, thereby generating an atomic displacement damage plateau in the specimens from the surface to a depth of 25 μm, which is sufficiently broad for the Vickers hardness test. Eight different loads (i.e. 98 mN, 196 mN, 490 mN, 980 mN, 1.96 N, 4.9 N, 9.8 N and 19.6 N) were performed on the specimens to obtain the depth profiles of the Vickers hardness by using a micro-hardness tester. Hardening was observable at the lowest damage level, and increases with the increase of irradiation dose. A power law correlation of the Vickers hardness with the damage level (HV0=1.49+0.76dpa0.31) is proposed. Test with nano-indentation technique was also performed, and a linear relationship between the Vickers micro-hardness and the nano-hardness (HV0=0.83H0) was observed. A comparison with other RAFM steels (CLAM, JLF-1, F82H, EUROFER97 etc.) under neutron or charged particle irradiation conditions show that most of the RAFM steels exhibit similar power-law exponents in the dose dependence of the irradiation hardening. The difference of the irradiation hardening may be attributed to difference in prior-irradiation microstructures.