Nuclear Materials and Energy (Dec 2023)
Radiation damage evolution in High Entropy Alloys (HEAs) caused by 3–5 MeV Au and 5 MeV Cu ions in a broad range of dpa in connection to mechanical properties and internal morphology
Abstract
High Entropy Alloys (HEAs) are prospective materials for nuclear fusion reactors and were irradiated in this study at a broad range of energetic ion fluences. Different ion masses (Cu and Au ions) and energies (3 and 5 MeV) were selected to investigate dpa (displacement per atom) development, radiation defect accumulation based on prevailing collision processes (Au ions) and ionization processes (Cu ions) in various HEAs. The studied HEAs differ in terms of elemental composition, internal morphology (grain structure) and other modifiers. Dpa values of 1 to ∼66 were achieved at Cu and Au ion fluences from 4 × 1014 to 1.3 × 1016 ions.cm−2 at room temperature, which generated varying levels of lattice damage. Theoretical simulations were performed to estimate the energy stopping and dpa depth distribution using SRIM code and compared with Au-concentration depth profiles determined by Rutherford backscattering spectrometry for Au-ions with 3 MeV ion energy. The prevailing energy losses of ions via ionization processes for Cu-5 MeV ions were found to increase the damage through lattice strain and probable lattice distortion, although the main defect introduction is expected to occur via collisions during nuclear stopping. Structural modification and defect accumulation were investigated by positron annihilation spectroscopy (PAS), which revealed a broader damaged layer with defects, where HEA-Nb (NbCrFeMnNi) exhibited the least damage accumulation from chosen alloys with no strong relation to the Au-5 MeV ion implantation fluence, whereas strong defect accumulation was recorded in the Au-ion implanted Eurofer97 used for comparison and HEA-Co (CoCrFeMnNi). PAS analysis also allowed defect sizes to be determined as an additional structural characteristic. The observed trends were also confirmed by thermal property analysis, with a worsening of thermal effusivity recorded after the irradiation in HEA-Co and Eurofer97. The worsening of the thermal properties was confirmed by the layer thickness, where the layer identified by PAS was found to be broader than the SRIM theoretical predictions. Nanoindentation measurements confirmed less pronounced radiation hardening of HEA-Nb relative to that observed in HEA-Co and Eurofer97. Transmission Electron Microscopy (TEM) analysis revealed layer thicknesses in reasonable agreement with the dpa depth profiles. The thermal effusivity decreased in the surface-irradiated layer in all investigated samples, the least influenced material was HEA-Nb.
