Phase decomposition and bubble evolution in Xe implanted U3Si2 at 450∘C

Abstract The microstructure investigations of a U3Si2 specimen implanted by 84 MeV Xe ions at 450∘C are reported here. In the region that corresponds to the highest irradiation dose, U3Si2 was found to decompose into a Si-enriched nanocrystalline USi matrix phase and a U-enriched amorphous inclusion phase. Density functional theory (DFT) calculations were used to help understand the decomposition mechanism. Xe bubbles of different morphologies were observed in USi nano-grains, on USi grain boundaries, and phase boundaries. Original U3Si2 micro-grains were preserved on both sides of the irradiation damage peak region within the sample, implying a radiation dose threshold for decomposition of approximately 150 dpa at 450∘C. In the preserved U3Si2 region beneath the irradiation damage peak, where significant amount of Xe ions were deposited, a monomodal size distribution of intragranular Xe bubbles with an average size of 2.68 nm formed. In both decomposed and preserved U3Si2, the size of Xe bubbles was found to be lower than 50 nm. Based on this observation, the fission gas behavior of U3Si2 is controllable and free of run-away swelling despite the occurrence of decomposition at this irradiation temperature.