In this study, the deposition, annealing process, and oxidation properties of HfNbTaTiZr high-entropy alloy thin films were thoroughly investigated. The films, approximately 250 nm thick, were deposited on MgO substrates by DC magnetron sputtering using a single target. The preparation temperature was identified as a key factor influencing the resulting structure. Amorphous films formed at room temperature, whereas nanocrystalline films, characterized by multiple intermetallic phases, were obtained either by deposition at elevated temperatures (600 °C – 750 °C) or through in situ annealing of amorphous films (600 °C – 700 °C). Positron annihilation spectroscopy revealed that nanocrystalline films predominantly contain vacancy-like misfit defects, with concentration decreasing as the preparation temperature increases. Additionally, amorphous films exhibited a high concentration of large vacancy clusters. X-ray photoelectron spectroscopy showed greater oxygen absorption in amorphous films due to their defective structure, with preferential oxidation of Zr and Hf. Further annealing of naturally oxidized films in a vacuum at temperatures up to 1400 °C led to films' recrystallization and eventually the formation of complex oxides, including ZrO2, HfO2, and various Mg-containing oxides, indicating a reaction with the MgO substrate. This work demonstrates the ability to fine-tune the microstructure and defect characteristics of high-entropy alloy films and highlights their direct correlation with oxidation properties.@en

Self healing of early stage radiation damage by site selective solute segregation is a promising approach to extend the lifetime of nuclear reactor components. In the present study, the creation and autonomous healing of irradiation-induced damage is investigated in pure Fe and high purity Fe–Au and Fe–Cu model alloys. To create radiation damage samples are irradiated at 550 °C by 120 keV He⁺ ions with fluences of 5.0 × 10¹⁵, 1.0 × 10¹⁶ and 5.0 × 10¹⁶ ions/cm². The observed increase in the S and W parameters determined in the variable energy positron annihilation spectroscopy measurements indicates the formation of vacancy-like defects, precipitates and vacancy-solute complexes. The presence of substitutionally dissolved Au is found to reduce the formation of radiation defects more efficiently than solute Cu. Site-specific Au precipitation at defect sites is indicated, which results in damage healing with a reduced swelling, whereas Cu precipitates and radiation damage only show weak interaction. Ab initio calculations show that the binding energies of Au solutes to vacancy clusters (Au-V_n) are significantly larger than those of Cu solutes (Cu-V_n) whereas the binding energies of helium filled vacancy clusters Au-He_nV_n and Cu-He_nV_n are comparable.

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In order to characterize the free volume of a homologous series all-aromatic poly(ether imide) (PEI) membranes, two positron annihilation techniques were utilized: positron annihilation lifetime spectroscopy (PALS) and Doppler broadening (DB) of annihilation radiation. First, DB, which is a fast and convenient method, indicated differences in free volume of all PEIs investigated, whereas PALS experiments gave more quantitative information, with respect to the size and distribution of the voids. DB results show that S, W pairs for this PEI-series tend to group according to their dianhydride moiety, meaning that, in this series, dianhydrides govern the differences in the S parameter, indicating more free volume with increasing S value. The semicrystalline PEI samples exhibit the lowest S parameter, while the amorphous samples based on 3,3′,4,4′-oxydiphthalic dianhydride (ODPA) all lie on the higher S side of the S-W plot. With the 1,4-bis(4-aminophenoxy)benzene (P1)-based PEI (ODPA-P1) standing out with the highest S parameter. The same could be confirmed and quantified by PALS, where ODPA-P1 is the only membrane in this series with its free volume described by both smaller and larger free-volume elements. The larger voids in ODPA-P1 can be characterized as having a radius (R) of 3.3 Å, which is 5 times larger than the lowest measured free-volume content in this series observed for 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) and 1,3-bis(4-aminophenoxy)benzene (M1)-based PEI (BPDA-M1), which has voids with a radius of R ≈ 0.7 Å. When comparing results obtained by DB and PALS, a very good correlation is observed between the S parameter (determined by DB) and the free-volume content (quantified by PALS).@en