*Article* **Irradiation Hardening Behavior of He-Irradiated V–Cr–Ti Alloys with Low Ti Addition**

**Ken-ichi Fukumoto 1,\* , Yoshiki Kitamura <sup>1</sup> , Shuichiro Miura <sup>1</sup> , Kouji Fujita <sup>1</sup> , Ryoya Ishigami <sup>2</sup> and Takuya Nagasaka <sup>3</sup>**


**Abstract:** A set of V–(4–8)Cr–(0–4)Ti alloys was fabricated to survey an optimum composition to reduce the radioactivity of V–Cr–Ti alloys. These alloys were subjected to nano-indenter tests before and after 2-MeV He-ion irradiation at 500 ◦C and 700 ◦C with 0.5 dpa at peak damage to investigate the effect of Cr and Ti addition and gas impurities for irradiation hardening behavior in V–Cr–Ti alloys. Cr and Ti addition to V–Cr–Ti alloys for solid–solution hardening remains small in the unirradiated V–(4–8)Cr–(0–4)Ti alloys. Irradiation hardening occurred for all V–Cr–Ti alloys. The V–4Cr–1Ti alloy shows the highest irradiation hardening among all V–Cr–Ti alloys and the gas impurity was enhanced to increase the irradiation hardening. These results may arise from the formation of Ti(CON) precipitate that was produced by He-ion irradiation. Irradiation hardening of V–Cr–1Ti did not depend significantly on Cr addition. Consequently, for irradiation hardening and void-swelling suppression, the optimum composition of V–Cr–Ti alloys for structural materials of fusion reactor engineering is proposed to be a highly purified V–(6–8)Cr–2Ti alloy.

**Keywords:** vanadium alloy; ion irradiation; irradiation hardening; radiation damage
