Evolution, migration and clustering of helium-vacancy complexes in RAFM steel- depth resolved positron annihilation Doppler broadening study

Abstract

Indian Reduced Activation Ferritic Martensitic steel is implanted with 130 keV helium ions to a fluence of 5 × 10¹⁴ and 1 × 10¹⁶ ions/cm² and investigated using positron annihilation spectroscopy. The samples were characterised by defect sensitive S and W-parameters using depth resolved slow positron beam. A dose dependency is observed in the nucleation and growth of helium bubbles with annealing temperature. An experimental evidence for the migration of smaller helium-vacancy complexes is observed via the variation in thickness/width of irradiated layer with temperature. The S–W plot clearly shows the regions corresponding to defect annealing, bubble nucleation and growth.

Keywords:

• Positron annihilation
• helium implantation
• RAFM steel
• irradiation damage

Acknowledgements

The authors acknowledge Dr. K. Laha, Materials and Metallurgy Group, IGCAR for providing the samples. The authors also thank P. Magudapathy, Materials Science Group, IGCAR for helium irradiation. We also thank Dr. Govindaraj, Head, MPS/MPD for his constant support and Dr. S. Abhaya for fruitful discussions.