This work studied the effect of sequential irradiation by krypton and helium ions at room temperature on the composition and structure of CoCrFeNi and CoCrFeMnNi high-entropy alloys (HEAs). Irradiation of the HEAs by 280 keV Kr¹⁴⁺ ions up to a fluence of 5 × 10¹⁵ cm^–2 and 40 keV He²⁺ ions up to a fluence of 2 × 10¹⁷ cm^–2 did not alter their elemental distribution and constituent phases. Blisters formed on the nickel surface after sequential irradiation, where large blisters had an average diameter of 3.8 μm. The lattice parameter of the (Co, Cr, Fe and Ni) and (Co, Cr, Fe, Mn and Ni) solid solutions increased by 0.17% and 0.37% after sequential irradiation, respectively. Irradiation by Kr ions led to a decrease in tensile macrostresses in the HEAs in the region of krypton ion implantation (Region I) and the formation of compressive macrostresses in the region behind the peak of implanted krypton (Region II). Sequential irradiation formed large compressive stresses in Ni and HEAs equal to −131.5 MPa, −300 MPa and −613.5 MPa in Ni, CoCrFeNi and CoCrFeMnNi, respectively, in the Region II. Irradiation by krypton ions decreased the dislocation density by 1.6–2.3 times, and irradiation with helium ions increased it by 11–15 times relative to unirradiated samples for CoCrFeNi and CoCrFeMnNi, respectively. Sequentially irradiated CoCrFeMnNi HEA had higher macrostresses and dislocation density than CoCrFeNi.

High-entropy alloys (HEAs) have prospects for use as nuclear structural materials. Helium irradiation can form bubbles deteriorating the structure of structural materials. The structure and composition of NiCoFeCr and NiCoFeCrMn HEAs formed by arc melting and irradiated with low-energy 40 keV He²⁺ ions and a fluence of 2 × 10¹⁷ cm⁻² have been studied. Helium irradiation of two HEAs does not change the elemental and phase composition, and does not erode the surface. Irradiation of NiCoFeCr and NiCoFeCrMn with a fluence of 5 × 10¹⁶ cm⁻² forms compressive stresses (−90 … −160 MPa) and the stresses grow over −650 MPa as fluence increases to 2 × 10¹⁷ cm⁻². Compressive microstresses grow up to 2.7 GPa at a fluence of 5 × 10¹⁶ cm⁻², and up to 6.8 GPa at 2 × 10¹⁷ cm⁻². The dislocation density rises by a factor of 5–12 for a fluence of 5 × 10¹⁶ cm⁻², and by 30–60 for a fluence of 2 × 10¹⁷ cm⁻². Stresses and dislocation density in the HEAs change the most in the region of the maximal damage dose. NiCoFeCrMn has higher macro- and microstresses, dislocation density, and a larger increase in their values, with an increasing helium ion fluence compared to NiCoFeCr. NiCoFeCrMn a showed higher radiation resistance compared to NiCoFeCr.

This work is devoted to studying blistering in ZrN, AlN, and CrN films formed by reactive magnetron sputtering. The surface morphology and cross-sectional microstructure of mononitride films after irradiation with He ions (energy 40 keV and doses of 3 × 10¹⁷−1.1 × 10¹⁸ cm^–2) at room temperature are analyzed by scanning, atomic force, and transmission electron microscopy. The critical doses of blistering are determined for ZrN (6 × 10¹⁷ cm^–2), AlN (5 × 10¹⁷ cm^–2), and CrN (6 × 10¹⁷ cm^–2) films. The high density of blisters in ZrN films leads to the merging of neighboring blisters (average size 0.75 μm) and the formation of large blisters (average size 1.35 μm). The blisters in the AlN films have a regular round shape (average size 1.7 μm). The СrN films are characterized by the presence of open blisters having a two-level structure: an upper blister with a diameter of 2−10 μm and a lower one with a diameter of 1.2 μm. As follows from the TEM results, 40‑keV He-ion irradiation of the films and their subsequent vacuum annealing leads to the formation of chains of radiation-induced pores filled with helium in the region of the projective ion range R_p. The formation of extended cracks is found to occur in the R_p region of ZrN, which is caused by interbubble fracturing due to high excess pressure in pores located at a depth close to R_p.

In the present work, the structure, stress state and phase composition of MeN/SiN_x (Me = Zr, Cr, Al) multilayered films with the thickness of elementary layers in nanoscale range, as well as their stability to high temperature oxidation, were studied. Monolithic (reference) and multilayered films were deposited on Si substrates at the temperatures of 300 °C (ZrN/SiN_x and AlN/SiN_x systems) or 450 °C (CrN/SiN_x) by reactive magnetron sputtering. The thickness ratios of MeN to SiN_x were 5 nm/2 nm, 5 nm/5 nm, 5 nm/10 nm and 2 nm/5 nm. Transmission electron microscopy (TEM), X-ray Reflectivity (XRR) and X-ray Diffraction (XRD) testified to the uniform alternation of MeN and SiN_x layers with sharp interlayer boundaries. It was observed that MeN sublayers have a nanocrystalline structure with (001) preferred orientation at 5 nm, but are X-ray amorphous at 2 nm, while SiN_x sublayers are always X-ray amorphous. The stability of the coatings to oxidation was investigated by in situ XRD analysis (at the temperature range of 400–950 °C) along with the methods of wavelength-dispersive X-ray spectroscopy (WDS) and scanning electron microscopy (SEM) after air annealing procedure. Reference ZrN and CrN films started to oxidize at the temperatures of 550 and 700 °C, respectively, while the AlN reference film was thermally stable up to 950 °C. Compared to reference monolithic films, MeN/SiN_x multilayers have an improved oxidation resistance (onset of oxidation is shifted by more than 200 °C), and the performance is enhanced with increasing fraction of SiN_x layer thickness. Overall, CrN/SiN_x and AlN/SiN_x multilayered films are characterized by noticeably higher resistance to oxidation as compared to ZrN/SiN_x multilayers, the best performance being obtained for CrN/SiN_x and AlN/SiN_x with 5 nm/5 nm and 5 nm/10 nm periods, which remain stable at least up to 950 °C.

High-entropy alloys (HEA) are promising structural materials that will successfully resist high-temperature irradiation with helium ions and radiation-induced swelling in new generations of nuclear reactors. In this paper, changes in the elemental and phase composition, surface morphology, and structure of CoCrFeNi and CoCrFeMnNi HEAs irradiated with He²⁺ ions at a temperature of 700 °C were studied. Structural studies were mainly conducted using the X-ray diffraction method. The formation of a porous surface structure with many microchannels (open blisters) was observed. The average diameter of the blisters in CoCrFeMnNi is around 1.3 times smaller than in CoCrFeNi. It was shown that HEAs’ elemental and phase compositions are stable under high-temperature irradiation. It was revealed that, in the region of the peak of implanted helium, high-temperature irradiation leads to the growth of tensile macrostresses in CoCrFeNi by 3.6 times and the formation of compressive macrostresses (−143 MPa) in CoCrFeMnNi; microstresses in the HEAs increase by 2.4 times; and the dislocation density value increases by 4.3 and 7.5 times for CoCrFeNi and CoCrFeMnNi, respectively. The formation of compressive macrostresses and a higher value of dislocation density indicate that the CoCrFeMnNi HEA tends to have greater radiation resistance compared to CoCrFeNi.