Irradiation data of vanadium alloys have been accumulated by intensive irra
diation experiments in fission reactors. In evaluating irradiation performa
nce of the alloys in fusion environments, we should consider the effects of
high energy cascade damage and transmutation reactions under 14 MeV neutro
n irradiation. Effects of high generation rate of helium on microstructural
evolution and mechanical properties in vanadium alloys have been studied b
y several techniques including dynamic helium charging experiments (DHCE) a
nd boron doping. However, fundamental understanding on defect cluster forma
tion under cascade damage in vanadium has not yet been clarified in detail.
In this study, the effect of cascade damage on vacancy cluster formation w
as investigated as a function of energy transfer by cascades using several
kinds of heavy ion irradiations to thin foils specimens. No defect clusters
were observed by transmission electron microscope (TEM) in thin foils of 9
9.8% pure vanadium irradiated with 200 and 400 keV self-ions (V+) up to 1 x
10(16) ion/m(2) at room temperature. Thin foil specimens were also irradia
ted with Au+ and Xe+ ions to 1 x 10(16) ion/m(2). Energies of irradiating i
ons were 50, 100, 200, 300 and 400 keV. In the specimens irradiated with Au
+ ions, defect clusters of about 2-2.5 nm were detected by TEM. The areal d
ensity of the observed defect clusters increased with ion energy and was al
so found to be dependent on the thickness of the specimens. In the thin reg
ion of the specimens, density of the defect clusters per damage energy depo
sition increased with ion energy. These indicate that vacancy clusters are
produced by high density of displacements in cascade damage. In the thicker
region of the specimens, interstitials can easily annihilate vacancy clust
ers and form interstitial clusters. At the foil thickness of 20 nm, the min
imum energy of gold ions to produce vacancy clusters was estimated to be 12
0 keV. This corresponds to the damage energy transfer density of 4.5 keV/nm
/ion. (C) 1999 Elsevier Science B.V. All rights reserved.