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Abstract-Structures and mechanical properties of thin films of the Nb-Al-N system produced by mag netron sputtering of targets from niobium and aluminum in the Ar-N 2 atmosphere have been studied. It has been shown that as the aluminum concentration increases, the structure of a thin film transforms from the nanocrystalline into the nanocomposite one, which consists of nanocrystallites of solid solutions in a matrix of amorphous aluminum nitride. Hardness, elastic modulus, and yield strength of Nb-Al-N thin films have been studied by nanoindentation in the mode of continuous control of the contact stiffness. It has been found that the transition of the structures of Nb-Al-N thin films from the nanocrystalline to the nanocomposite structures results in an increase of hardness and decrease of elastic modulus due to the for mation of a thin amorphous interlayer between grains of nanocrystallites. A high hardness to elastic mod ulus ratio of Nb-Al-N nanocomposite thin films indicates that the films are a promising material for wear resistant coatings.

Abstract-This review summarizes the present-day achievements in the study of the structure and properties of protective nanocomposite coatings based on NbN, NbAlN, and NbSiN prepared by a variety of modern deposition techniques. It is shown that a change in deposition parameters has a significant effect on the phase composition of the coatings. Depending on the magnitude of negative potential on the substrate, the pressure of nitrogen or a nitrogen-argon mixture in the chamber, and the substrate temperature, it is possible to obtain coatings containing different phases, such as NbN and SiN x (Si 3 N 4 ), AlN, and NbAl 2 N. It is found that, in the case of formation of the ε-NbN phase, the coatings become very hard; their hardness achieves values on the order of 53 GPa. At the same time, they remain thermally stable at temperatures of up to 600°C, chemically inert, and resistant to wear. The effect of the nanograin size, the volume fraction of boundaries and interfaces, and the point defect concentration on the physicomechanical properties of these coatings is described. Niobium nitride-based coatings can be used in superconducting systems and single-photon detectors; they are capable of operating under the action of strong magnetic fields of up to 20 T; they can be used in integrated logic circuits and applied as protective coatings of machine parts, edges of cutting tools, etc.

Aerospace is an actively developing industry that continuously requires the implementation of modern technologies. The rapid growth in new vehicle production demands much support. Hence, the problem of resources with complicated supply and distribution is always of current interest. These critical raw materials (CRMs) are involved in almost all areas of aerospace manufacturing and service. An efficient and profitable solution to the problem of critical materials can be found in protective coatings, especially in such advanced concepts as multilayer and high-entropy alloy (HEA)-based coatings. In this paper, we study both ways of manufacturing effective coatings. We have shown that multilayer CrN/MoN coatings with exceptional toughness and hardness could find promising applications in the aerospace industry. The developed strategy for the novel materials screening based on the prediction of their properties has been demonstrated on the example of the refractory HEA-based coatings. A brief state of the art of the EU critical raw materials and their place in the aerospace/defence industry has been given.

The first results of studying the phase-structural state, properties, sizes of nanograins, hardness, and microstresses in nanocomposite NbN and Nb-SiN films are given. The investigated films were obtained by the method of the magnetron sputtering of Nb and Si targets onto silicon substrates at different negative potentials at the substrate (from 0 to-70 V), nitrogen pressures P N , and discharge powers at the tar gets. To determine the thermal stability of the films, they were annealed at 600, 800, and 1000°C in a vacuum. It was revealed for the first time that the NbN films have a two phase nanocomposite structure, which consists of δ NbN (NaCl structure type) and α' NbN. The δ NbN phase is also formed in Nb-SiN films, where it is enveloped by an amorphous Si 3 N 4 phase The hardness of the Nb-SiN films reaches 46 GPa, which cor responds to the level of superhardness, while the hardness of the NbN nanocomposites is somewhat lower, but also very high (34 GPa). The experimental results for the Nb-SiN films were explained based on the data obtained from the first principles calculations of the NbN/Si x N y heterostructures by the molecular dynamics method.

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