Formation and migration of helium bubbles in Fe–16Cr–17Ni austenitic alloy at high temperature

Abstract

The formation and migration of helium bubbles in Fe–16Cr–17Ni austenitic model alloy at temperatures 400–1250°C have been studied by in situ electron microscopy, energy dispersive spectrometry (EDS) and EELS analysis. The nucleation of bubbles under 10 keV He+ ion irradiation was dominant at 400°C, while the growth was dominant above 600°C. It was revealed that the mean square of the migration distance was proportional to time, which is quantitative evidence of Brownian type motion and yielded diffusivities from 10−18 to 10−20 m2/s at 1185°C, depending on the diameter from 1 to 3 nm. These facts suggest that the mobility of helium–vacancy complexes or bubbles is an important factor governing the formation process of helium bubbles. The analysis by scanning transmission electron microscope-electron energy loss spectrometry (STEM-EELS) elucidated Ni precipitation even around small helium bubbles.