Helium trapping in carbide precipitates in a tempered F82H ferritic–martensitic steel

• F82H steel irradiated with multi‐energy He to ~ 1016 He·cm− 2 at 50 and 600 °C
• Material was characterised using TEM and APT.
• He bubbles observed to nucleate preferentially within carbides due to trapping of diffusing He.

The microstructural changes of a tempered F82H ferritic–martensitic steel following He implantation at 60 and 500 °C have been examined by transmission electron microscopy (TEM) and atom probe tomography (APT). After irradiation at 500 °C, numerous He bubbles were formed throughout the matrix, whereas after irradiation at 60 °C, no bubbles were seen to form in the matrix. In both irradiations, He bubbles were observed to have formed within large carbide precipitates, determined by APT compositional analysis to be M23C6. The observed preferential He bubble formation in carbides during low temperature He irradiation occurs as a result of the diffusing He being trapped in the carbide due to the strong He–C bond. As the He concentration increases in the carbide due to trapping, He bubbles are formed.