Formation and migration of helium bubbles in Fe-16Cr-17Ni austenitic alloyat high temperature

The formation and migration of helium bubbles in Fe-16Cr-17Ni austenitic mo del alloy at temperatures 400-1250 degreesC have been studied by in situ el ectron microscopy, energy dispersive spectrometry (EDS) and EELS analysis. The nucleation of bubbles under 10 keV He+ ion irradiation was dominant at 400 degreesC, while the growth was dominant above 600 degreesC. It was reve aled that the mean square of the migration distance was proportional to tim e, which is quantitative evidence of Brownian type motion and yielded diffu sivities from 10(-18) to 10(-20) m(2)/s at 1185 degreesC, depending on the diameter from I to 3 nm. These facts suggest that the mobility of helium-va cancy complexes or bubbles is an important factor governing the formation p rocess of helium bubbles. The analysis by scanning transmission electron mi croscope-electron energy loss spectrometry (STEM-EELS) elucidated Ni precip itation even around small helium bubbles. (C) 2000 Elsevier Science B.V. Al l rights reserved.