Influence of transmutation on microstructure, density change, and embrittlement of vanadium and vanadium alloys irradiated in HFIR

Addition of 1 at% nickel to vanadium and V-10Ti, followed by irradiation along with the nickel-free metals in HFIR to 2.3x1026 n m−2, E > 0.1 MeV (corresponding to 17.7 doa) at 400°C, has been used to study the influence of helium on microstructural evolution and embrittlement. Approximately 15.3% of the vanadium transmuted to chromium in these alloys. The ∼50 appm helium generated from the 58Ni(n, γ)59Ni(n, α56 Fesequence was found to exert much less influence than either the nickel directly or the chromium formed by transmutation. The V-10Ti and V-10Ti-1Ni alloys developed an extreme fragility and broke into smaller pieces in response to minor physical insults during density measurements. A similar behavior was not observed in pure V or V-1Ni. Helium's role in determination of mechanical properties and embrittlement of vanadium alloys in HFIR is overshadowed by the influence of alloying elements such as titanium and chromium. Both elements have been shown to increase the DBTT rather rapidly in the region of 10% (Cr + Ti). Since Ci is produced by transmutation of V, this is a possible mechanism for the embrittlement. Large effects on the DBTT may have also resulted from uncontrolled accumulation of interstitial elements such as C, N, and O during irradiation.