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-1OTi, followed by irradiati on along with the nickel-free metals in HFIR to 2.3 x 10(26) n m(-2), E > 0.1 MeV (corresponding to 17.7 dpa) at 400 degrees C, has been use d to study the influence of helium on microstructural evolution and em brittlement. Approximately 15.3% of the vanadium transmuted to chromiu m in these alloys. The similar to 50 appm helium generated from the Ni -58(n, gamma)Ni-59(n, alpha)Fe-56 sequence was found to exert much les s influence than either the nickel directly or the chromium formed by transmutation. The V-1OTi and V-10Ti-1Ni alloys developed an extreme f ragility and broke into smaller pieces in response to minor physical i nsults during density measurements. A similar behavior was not observe d in pure V or V-1Ni. Helium's role in determination of mechanical pro perties and embrittlement of vanadium alloys in HFIR is overshadowed b y the influence of alloying elements such as titanium and chromium. Bo th elements have been shown to increase the DBTT rather rapidly in the region of 10% (Cr + Ti). Since Cr is produced by transmutation of V, this is a possible mechanism for the embrittlement. Large effects on t he DBTT may have also resulted from uncontrolled accumulation of inter stitial elements such as C, N, and O during irradiation.