The influence of nickel on the structure and properties of Ti-Cr-N ion-plasma coatings obtained by arc-PVD method has been studied. With a nickel content of up to 11.9 at. %, the coating consists of Cr₂N, _{Ti1 – x}Cr_xN, and metallic Ni. Upon further increase in Ni concentration in the coating, intermetallic compound Ni3Ti is formed. The structure of the coatings was studied using the transmission electron microscopy. The coatings of Ti-Cr-N system are characterized by a columnar structure, in the columns of which _{Ti1 - x}Cr_xN and Ti_{1 - y}Cr_yN (x > y) sublayers, being several nanometers thick and containing variable concentration of titanium and chromium, as well as Cr₂N sublayers of about 25 nm are formed due to the complete solubility of TiN and Cr₂N and the planetary rotation of the substrates, resulting in layer-by-layer stacking of the components of the evaporated cathodes. This structure remains intact in coatings of Ti-Cr-N-Ni system with a low nickel concentration (on the order of tenths of at. %). However, upon that, the column size refinement and an increase in biaxial compressive stresses from 6.7 to 9.7 GPa are observed, which results in an increase in hardness from 30 to 42 GPa. The coatings with a high nickel content are characterized by a multilayer architecture with an equiaxed polycrystalline structure of nanograins in layers. As Ni concentration increases, the hardness of the coating decreases to 16.7 GPa, which is associated with an increase in the fraction of relatively soft nickel in the coating and a decrease in macrostresses to -0.6 GPa. Upon that, the wear intensity increases from 3·10^-15 to 5·10^-15 m³/(N·m). The studied coatings of Ti–Cr–N and Ti–Cr–N–Ni systems are resistant to adhesive and cohesive destruction. With an increase in the nickel content upon measuring scratching, the destruction of the coatings occurs exclusively due to the plastic deformation.

The electrochemical properties of Ti–Al–Mo–Ni–N coatings with a molybdenum content of 20 and 25 at % fabricated by cathodic arc deposition (Arc-PVD) are studied. Series 2 coatings are characterized by the presence of Mo in both a chemically bound (Mo₂N, as with series 1 coatings) and free states (i.e., metallic phase). Considering the multilayer architecture of coatings based on the mixed nitride (TiAl)N and molybdenum-containing phases, their corrosion destruction proceeds layer by layer due to different corrosion resistance of these phases in acidic and alkaline environments. Annealing the coatings at 600°C in vacuum gives rise to diffusional processes in them that lead to a growth of crystallites of the (TiAl)N nitride phase and a decrease in the microstrain. This phenomenon is considerably more conspicuous in series 2 coatings, which can be explained by the higher diffusivity of Mo atoms in the metallic phase than in the case of their counterparts in the nitride phase.

We have studied photoelectrochemical and photocatalytic properties of porous materials based on hollow α-Fe₂O₃ microspheres, characterized by the presence of dangling magnetic Fe–O–Fe bonds due to an increased oxygen vacancy concentration on the wall/closed pore interface. Using such powder and firing slips at an isothermal holding temperature of 400°C, we obtained two series of thin-film samples on glass with a conductive layer from suspensions of two compositions: aqueous Fe(NO₃)₃ solution + hollow α-Fe₂O₃ microspheres (series 1) and aqueous Fe(NO₃)₃ solution + polyethylene glycol + hollow α-Fe₂O₃ microspheres (series 2). The films of series 2 were shown to have a structure with spatially separated particles differing in size: α-Fe₂O₃ nanoparticles and hollow α-Fe₂O₃ microspheres. The films of series 1 consisted predominantly of hollow microspheres connected by “necks” formed during heat treatment. The thickness of the films of series 2 was of order 2 μm and that of the films of series 1 was of order 4 μm. The structural distinctions between the films of the two series had a significant effect on the optical properties of the material. In the wavelength range 350–1500 nm, the absorption coefficient of the films of series 2 (3.50 × 10⁵ m^–1) was about twice that of the films of series 1 (1.75 × 10⁵ m^–1). Photoelectrochemical characterization in an aqueous 0.1 M KOH solution showed that the onset potential for the anodic reaction was 0.87 V vs. Ag/AgCl in the case of the films of series 2 and 0.97 V vs. Ag/AgCl in the case of series 1. The films of both series showed an unusual increase in current density during prolonged illumination at a potential of 1 V vs. Ag/AgCl, due to Fe(IV) formation on the photoanode surface. Photocatalytic properties of the materials were assessed from the rate of methylene blue degradation. The reaction rate constant (k) was determined to be 0.015 and 0.018 min^–1 for the films of series 1 and 2, respectively, whereas the k of the photocatalyst-free reaction was 2.8 × 10^–4 min^–1.

—Comparative durability tests of carbide cutting tools with (Ti, Al)N–Cu and (Ti, Al)N–Ni coatings applied to its working surfaces were carried out under conditions of continuous and interrupted cutting of steels 09G2S and EP302-Sh, respectively. Under milling conditions of EP302-Sh steel, using VK6NST inserts with (Ti, Al)N–Cu and (Ti,Al)N–Ni coatings, the tool life increases by 3.1 and 1.7 times, respectively. When turning the 09G2S steel using VK6NST inserts coated with (Ti, Al)N–Cu and (Ti, Al)N–Ni, the tool life increases by 7.6 and 10.8 times, respectively, and the cutting forces F_z, F_x, and F_y are reduced by ~20%. It is shown that this effect is determined by the presence of a nanostructure in the formed coatings and the presence of a highly consistent ceramic component and ductile metal, which determine their hardness (more than 35 GPa) and fracture toughness (relative work of plastic deformation during indentation over ~60%) and increased tribological characteristics (friction coefficient of ~0.5 compared to uncoated carbide of ~0.7).

The arc-PVD Ti–Cr–Mo–Ni–N coatings on HG20, HS123, HV420 carbide alloys and C80W1 tool steel, while having approximately the same elemental and phase compositions, differ in morphology, macrostructure, and level of macrostresses. When deposited on steel, the coating exhibits macrolayering, a more extended coating–substrate transition zone, and develops tensile macrostresses, in contrast to the coatings on carbide alloys, which develop compressive macrostresses. The behaviour can be explained by the overheating of the coating during deposition, which results from ion bombardment and is more pronounced on steel due to its poorer thermal diffusivity relative to carbide alloys. The CLTE difference between steel and the coating is significantly larger than that between the carbides and the coating, further contributing to the effect. It was found that, considering these features, the Ti–Cr–Mo–Ni–N coating on steel exhibits lower hardness (~20.3GPa), lower adhesion strength to the substrate (Lc3≈30N, the indenter load at scratch testing corresponding to the onset of coating wear), and a higher wear intensity at room temperature and 500°C (49.80 and 74.20·10−6 mm3·N−1·m−1, respectively), as compared with the hardness values of 25.1–21.7GPa, Lc3≈100N, and wear intensity (corresponding to the absence of a visible wear crater) for the Ti–Cr–Mo–Ni–N coatings on the aforementioned carbide alloys.