Nanoscale multilayer coating (NMC) based on Zr/Nb layers (100/100 nm) before and after H+ irradiation was investigated by combining experimental techniques with first-principles calculations. Detailed studies of structural and phase state and defect structure of Zr/Nb NMC were performed using methods of transmission electron microscopy, X-ray structural analysis, glow discharge optical emission spectrometry, and the Doppler broadening spectroscopy using variable energy positron beam. The first-principles calculations of binding energies for hydrogen in metal Zr/Nb layers was carried out by the pseudopotential method within the density functional theory framework. First-principles calculations and experimental data indicate the presence of macro- and microstrains predominantly in the zirconium layers of Zr/Nb NMC. The main feature of the studied Zr/Nb NMC is the predominant hydrogen localization in Zr layers near the interfaces. The annihilation of positrons is shown to occur mainly in the Zr layers in the vicinity of the interface.

Radiation damage is one of the significant factors limiting the operating time of many structural materials working under extreme conditions. One of the promising directions in the development of materials that are resistant to radiation damage and have improved physical and mechanical properties is the creation of nanoscale multilayer coatings (NMCs). The paper is devoted to the experimental comprehension of changes in the defect structure and mechanical properties of nanoscale multilayer coatings (NMCs) with alternating layers of Zr and Nb under irradiation. Series of Zr/Nb NMCs with different thicknesses of individual layers were fabricated by magnetron sputtering and subjected to H+ irradiation. The evolution of structure and phase states, as well as the defect state under proton irradiation, was studied using the methods of high-resolution transmission electron microscopy (HRTEM), X-ray diffraction analysis (XRD), glow discharge optical emission spectroscopy (GDOES), and positron annihilation spectroscopy (PAS). The layer-by-layer analysis of structural defects was carried out by Doppler broadening spectroscopy (DBS) using a variable-energy positron beam. To estimate the binding energy and the energy paths for the hydrogen diffusion in Zr/Nb NMCs, calculations from the first principles were used. When the thickness of individual layers is less than 25 nm, irradiation causes destruction of the interfaces, but there is no significant increase in the defect level, the S parameter (open volume defects amount) before and after irradiation is practically unchanged. After irradiation of NMC Zr/Nb with a thickness of layers 50 and 100 nm, the initial microstructure is retained, and the S parameter is significantly reduced. The GDOES data reveal the irregular H accumulation at the interface caused by significant differences in H diffusion barriers in the bulk of Zr and Nb multilayers as well as near the interface’s region.

Nanoscale multilayer coatings (NMCs) with different crystal structures are considered as capable of self-healing after radiation damage due to the recombination of vacancies and interstitials. This work is focused on a defect distribution study of NMCs based on Zr/Nb layers (25/25 nm and 100/100 nm) after proton irradiation. Coatings with a total thickness of 1.05 ± 0.05 µm were irradiated by 900-keV protons using a pelletron-type electrostatic accelerator with an ion current of 2 µA for durations of 60 min to 120 min. The influence of the irradiation effect was studied by X-ray diffraction analysis (XRD), glow discharge optical emission spectrometry (GD–OES), and Doppler broadening spectroscopy using a variable energy positron beam. The results obtained by these methods are compatible and indicate that defect concentration of Zr/Nb NMCs remains unchanged or slightly decreases with increasing irradiation time.

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The effect of helium ion irradiation on the microstructure and properties of composites based on Zr/Nb nanoscale multilayer coatings (NMCs) was studied. X-ray diffraction (XRD), transmission electron microscopy (TEM), and variable-energy Doppler broadening spectroscopy (DBS) were used for the in-depth analysis of defects in the irradiated NMCs. After irradiation of the Zr/Nb NMCs with helium ions at a 1017 ion/cm2 dose, the layered structure was generally retained, but the internal stresses in the layers were increased, which caused wave-like distortion in the ion deposition zone. The Zr/Nb NMCs with an individual layer thickness of 25 nm were characterized by the smallest microstress changes, but single blisters were formed in the near-surface region. The microstructure of the Zr/Nb NMCs with a layer thickness of 100 nm exhibited relatively smaller changes upon helium ion irradiation. The prevailing positron-trapping center was the reduced-electron-density area at the interfaces before and after irradiation of the Zr/Nb NMCs regardless of the layer thickness. However, the layer thickness affected the DBS parameter profiles depending on the positron energy, which was probably due to the different localization of implanted ions within the layers or at the interfaces.