Positron annihilation spectroscopy of ferritic/martensitic steels F82H and T91 irradiated with protons and neutrons at PSI

Abstract

Reduced activation ferritic/martensitic steels F82H and T91 irradiated with high-energy protons and spallation neutrons were investigated using positron annihilation spectroscopy. Subnanometer-sized He-filled vacancy clusters, which cannot be observed by transmission electron microscopy, were detected. In the low dose region, positrons were trapped at relatively large He-filled vacancy clusters, small He-filled vacancy clusters and other defects (dislocations, precipitates and interfaces). In the high dose region, almost all positrons were trapped at vacancy clusters containing a lot of He atoms and at other defects. Large He-filled vacancy clusters absorb He atoms produced by the irradiation, and the long and mean lifetimes decreased. Conspicuous peaks related to He atoms could not be obtained in CDB ratio curves, and it was also difficult to detect the effect of He atoms in S–W plots. However, almost all data for irradiated samples lay on one line in the S–W plots, indicating that the change in the S- and W-parameter was caused by growth process of one type of defects. This may be caused by absorption of He atoms leading to the lifetime change. To prove this, further experiments and analysis are necessary.