Microstructural evolution of the 21Cr32Ni model alloy under irradiation

The microstructural evolution of the 21Cr32Ni model alloy under ion irradiation is investigated. A set of bulk materials were irradiated at the Michigan Ion Beam Laboratory using single beam (5 MeV Fe⁺⁺) to 1, 10 and 20 dpa at 440 °C and dual beam (5 MeV Fe⁺⁺ plus energy degraded 1.95 MeV He⁺⁺ ions) to 16.6 dpa at 446 °C. The average diameter and number density of the faulted loops and cavities formed under irradiation were characterized using Transmission Electron Microscopy (TEM). The behavior of faulted loop in the model alloy was also investigated in-situ using the Intermediate Voltage Electron Microscope (IVEM) at Argonne National Laboratory (ANL). Results show that the average faulted loop diameter decreases, but the faulted loop number density increases with increasing dose. In-situ experiments showed that the faulted loops become unfaulted during ion irradiation by interacting with network dislocations. Although the average faulted loop diameter after 16.6 dpa dual beam irradiation at 446 °C was found to be similar to those seen in samples irradiated with single beams to 10 and 20 dpa, the faulted loop number density was significantly higher in the dual beam irradiated sample. Moreover, the dual beam irradiated model alloy exhibits a significantly higher density of smaller cavities. It is also found that the size and density of the faulted loops and voids calculated for the dual beam irradiation of 21Cr32Ni model alloy at 446 °C are in better agreement with those measured in a sample neutron irradiated at 375 °C. Further discussion is presented in this study.