Positron annihilation studies on 9Cr reduced activation ferritic/martensitic steels

Abstract

Positron annihilation, microstructural and hardness studies were carried out in a 9Cr reduced activation ferrtic - martensitic steel (9%Cr-1%W-0.1%C) subjected to isochronal annealing in the temperature range of 300 to 1273 K. The measured lifetime in the 'as-received' (normalized and tempered) condition was 147 ps, which exhibited considerable reduction around 670 K, indicating the annealing out of small vacancy-defects in the matrix or matrix-precipitate interfaces. The observed positron lifetime exhibited a broad maximum between 670 K and 1070 K, indicating the existence of second annealing stage. Between 1070 K and 1270 K, a sharp maxium is exhibited in lifetime as third annealing stage. Doppler S-parameter has also exhibited similar annealing stages. Ab-intio positron lifetime calculations for various defect-impurity cluster configurations in ferritic-matrix based Fe system are reported to understand the experimental results.