Release of helium from irradiation damage in Fe–9Cr ferritic alloy

Thermal desorption of helium from Fe–9Cr and pure Fe which were irradiated with 5 keV He+ ions at 85 or 473 K have been studied by thermal desorption spectrometry (TDS) at temperatures from room temperature to 1270 K and related microstructure changes by TEM. It is found that five TDS peaks appear in Fe–9Cr specimen and these peaks are well correlated with microstructure changes. From these results, the five peaks ICr, IICr, IIICr, IVCr and VCr may be attributed to release of trapped helium atoms by the break-up of vacancy–helium–self-interstitial atom complexes or very tiny loops, glide to the specimen surface or coalescence of interstitial type dislocation loops, shrinkage of dislocation loops, bubble migration to the specimen surface and α–γ phase transformation, respectively. Precipitation of Cr around the loops and bubbles in Fe–9Cr is revealed by STEM-EELS and this could shift the related TDS peaks to higher temperatures.