Microstructure development and helium behavior in nickel and vanadium base alloys

Transmission electron microscopy and thermal helium desorption spectrometry (TDS) have been used to investigate the influence of alloying elements on helium behavior and bubble microstructure evolution in FCC (Ni+1…7.5 wt%Al) and BCC (V+10…40 wt%Ti) metals. The samples were irradiated by 40-keV He+ ions at room temperature up to a fluence of 5×1020 m−2. Post-irradiation annealings were performed at 1023 K (Ni–Al) and 1075 K (V–Ti) for 1 h. It was shown that alloying elements reduced the bubble size (d̄b) and increased their density (ρb) in both types of alloys. In the Ni–Al alloys the TDS peaks are displaced to higher temperatures with increasing Al concentration in contrast to V–Ti alloys where the TDS peaks are displaced to lower temperatures with increasing Ti content. However in both systems of alloys the effective activation energy for helium desorption grows with alloying element concentration. The results are discussed in terms of alloying element influence on the mechanisms of bubble growth and migration.