Study of PRIMAVERA steel samples by positron annihilation spectroscopy technique II – Lifetime measurements

In the present article, a positron annihilation lifetime technique was used for the study of VVER-440/230 weld materials, manufactured in the frame of the international PRIMAVERA project on microstructural investigation of the irradiated WWER-440 reactor pressure vessel steel. The present results complement our previous report of positron angular correlation experiments and provide in-depth characterization of vacancy type defects behavior under irradiation and thermal treatment. The results give new insight into the previously published atom probe tomography and angular correlation of annihilation radiation studies. The measurements do not show any association of phosphorus or its segregation to the open volume defects investigated by positron annihilation spectroscopy. The embrittlement effects related to the phosphorus seem to be effectively annealed-out during 475 °C thermal treatment and the post annealing microstructure and mechanical properties of the material are consequently affected mostly by agglomerations of vacancy clusters coarsened during thermal treatment.