Microstructural evolution of P92 ferritic/martensitic steel under Ar+ ion irradiation at elevated temperature

Irradiation damage in P92 ferritic/martensitic steel irradiated by Ar+ ion beams to 7 and 12 dpa at elevated temperatures of 290 °C, 390 °C and 550 °C has been investigated by transmission electron microscopy, scanning electron microscopy and atomic force microscopy. The precipitate periphery (the matrix/carbide interface) was amorphized only at 290 °C, while higher irradiation temperature could prevent the amorphization. The formation of the small re-precipitates occurred at 290 °C after irradiation to 12 dpa. With the increase of irradiation temperature and dose, the phenomenon of re-precipitation became more severe. The voids induced by irradiation were observed after irradiation to 7 dpa at 550 °C, showing that high irradiation temperature (≥ 550 °C) was a crucial factor which promoted the irradiation swelling. Energy dispersive X-ray analysis revealed that segregation of Cr and W in the voids occurred under irradiation, which may influence mechanical properties of P92 F/M steel. - Graphical Abstract: High density of small voids, about 2.5 nm in diameter, was observed after irradiation to 12 dpa at 550 °C, which was shown in panel a (TEM micrograph). As shown in panel b (SEM image), a large number of nanometer-sized hillocks were formed in the surface irradiated at 550 °C, and the mean size was ∼ 30 nm. The formation of the nanometer-sized hillocks might be due to the voids that appeared as shown in TEM images (panel a). High irradiation temperature (≥ 550 °C) was a crucial factor for the formation of void swelling. Highlights: ► Small carbides re-precipitated in P92 matrix irradiated to 12 dpa at 290 °C. ► High density of voids was observed at 550 °C. ► Segregation of Cr and W in voids occurred under irradiation.