Study of point defect behaviors in vanadium and its alloys by using HVEM

Microstructural evolution and point defect behavior in vanadium and V-xFe (x=0.1, 0.2, 0.3, 3, 5 at.%) have been examined by using high voltage electron microscopy. During irradiation, interstitial-type dislocation loops are formed and grow in all materials. In V-xFe, measured saturated loop number density is much higher than that in pure vanadium, indicating iron atoms in the matrix strongly interact and trap self-interstitial atoms (SIAs). The shapes of loops formed in V-xFe are complicated, i.e., loops grown to >100 nm show stacking fault-like shapes. Those complicated shapes become more significant with increasing iron concentration. This means iron atoms segregate to loops through the strong interaction with SIAs. The apparent migration energies of 0.21 eV and 0.81 eV have been determined from the temperature dependence of loop number density for pure vanadium and V-xFe, respectively. Various observed phenomena are discussed in terms of the obtained binding energy