Radiation-induced Precipitates in Ferritic-Martensitic Steels and Their Radiation Resistance Effects

Designing high-performance radiation-tolerant materials and understanding the atomistic mechanism of radiation resistance are important topics in nuclear energy structural materials research. In this study, we investigated the atomistic mechanism of the formation of rod-like precipitates in helium-irradiated ferritic-martensitic steels (F-M steels) by positron annihilation spectroscopy (PAS) and transmission electron microscopy with energy dispersive X-ray spectroscopy (TEM/EDX). The results indicated that vacancies tended to accumulate near dislocation lines to form complexes in the reduced activation ferritic-martensitic (RAFM) steel. Moreover, Fe and Cr atoms diffused toward these complexes and eventually depleted therein, which was not conducive to the formation of rod-like precipitates. Conversely, impurity atoms such as C atoms were found to segregate near dislocations in the Y-bearing oxide dispersion strengthened (Y-ODS) steel. When Fe and Cr diffused toward dislocations, they exchanged positions with C atoms until Fe and Cr exceeded their saturation solubilities and precipitated on the glide plane. We also analyzed the distribution of vacancy defects and bubbles/voids in the four irradiated materials and discussed the radiation resistance mechanism of the precipitates. The results of this study are significant in demonstrating a microscopic mechanism of radiation-induced precipitates to swelling resistance in materials.