Effect of Ion Irradiation on Surface Microstructure and Nano-Hardness of SA508-IV Reactor Pressure Vessel Steel.

A new type SA508-IV reactor pressure vessel steel was irradiated at 290 °C to 3 and 30 displacement per atom (dpa) with 3.5 MeV Fe²⁺ ions. The focused ion beam was used to cut the samples for the field emission transmission electron microscope (FE-TEM) after irradiation. The microstructure analysis under the scanning transmission electron microscope (STEM) mode of FE-TEM revealed that the heavy ion irradiation produced a large number of matrix defects and Cu-rich clusters. The high dosage of irradiation would also force Mo atoms to relocate to form Cr/Mn/Mo-rich precipitates. Dislocation loops were especially formed in samples irradiated by 30 dpa, which are one of the principal evolving defects in irradiated materials. The nanoindentation test results showed that the nano-hardness increases with the increase of irradiation doses. The semi-plateau stage in 3 dpa irradiation (I3 sample) curve of nano-hardness versus indentation depth corresponds to the saturation of Cu-rich clusters; while the plateau stage in the I30 sample curve should be attributed to the loop coalescence. [ABSTRACT FROM AUTHOR]