Effect of impurities on mechanical properties of vanadium alloys under liquid-lithium environment during neutron irradiation at HFIR

Vanadium alloys, including the highly purified V-4Cr-4Ti alloy, were irradiated in liquid lithium up to a damage level of 3.7 dpa in the HFIR at 425 deg. C and 598 deg. C. Neutron irradiation caused an increase of the ductile-brittle transition temperature (DBTT) and irradiation hardening was observed. Adding titanium to the V-Cr alloys was effective for increasing irradiation hardening at 425 deg. C. For highly purified (Zr-treated) V-4Cr-4Ti alloys the irradiation hardening was significantly reduced at both 425 deg. C and 598 deg. C. However, microstructural observations after the irradiation experiments showed that there was no significant difference in microstructure between the original and the highly purified specimens. It is suggested that the reduction of irradiation hardening in the highly purified V-4Cr-4Ti alloys was caused by the configuration and distribution of interstitial impurities in the neutron-irradiated specimen matrix. Controlling the impurities in V-4Cr-4Ti alloys has a very important effect for improving their mechanical properties that take place under neutron irradiation at around 400 deg. C.