Aluminum nitride (AlN) films were synthesized onto Si(100) substrates by pulsed laser deposition (PLD) in vacuum or nitrogen, at 0.1, 1, 5, or 10 Pa, and substrate temperatures ranging from RT to 800 °C. The laser parameters were set at: incident laser fluence of 3–10 J/cm² and laser pulse repetition frequency of 3, 10, or 40 Hz, respectively. The films’ hardness was investigated by depth-sensing nanoindentation. The optical properties were studied by FTIR spectroscopy and UV-near IR ellipsometry. Hardness values within the range of 22–30 GPa and Young’s modulus values of 230–280 GPa have been inferred. These values were determined by the AlN film structure that consisted of nanocrystallite grains, strongly dependent on the deposition parameters. The values of optical constants, superior to amorphous AlN, support the presence of crystallites in the amorphous film matrix. They were visualized by TEM and evidenced by FTIR spectroscopy. The characteristic Reststrahlen band of the h-AlN lattice with component lines arising from IR active phonon vibrational modes in AlN nanocrystallites was well detectable within the spectral range of 950–500 cm⁻¹. Control X-ray diffraction and atomic force microscopy data were introduced and discussed. All measurements delivered congruent results and have clearly shown a correlation between the films’ structure and the mechanical and optical properties dependent on the experimental conditions.

A nanocomposite CrAlSiN–AlSiN coating with periodically modulated composition was developed and investigated regarding the effect of the composition and structure on the mechanical properties. The modulation was performed by variation of the pressure, cathode current and bias voltage during deposition. The structure and composition of the coating were investigated by X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS) analyses. The coating had a nanocomposite structure consisting of (CrAl)N and (AlSi)N nanograins embedded in a Si₃N₄ matrix. The EDS analysis of the cross-section revealed that the period composition had changed from Cr₀₅₁Al_0.41Si_0.08N to Al_0.82Cr_0.04Si_0.14N. It was shown that the elastic modulus could be adjusted by composition modulation. The coating hardness of 54 GPa was obtained by nanoindentation. The modulated CrAlSiN–AlSiN coating exhibited improved elastic strain to failure (H/E* = 0.11, H—nanohardness, E*—the effective elastic modulus), excellent resistance to plastic deformation (H³/E*² = 0.72), and elastic recovery of 70%, which suggested improved toughness.

This paper presents the results of the investigation of a multilayer TiAlSiN/AlSiN coating. A novel coating architecture with a period consisting of nanocomposite sublayers of TiAlSiN and AlSiN was developed. We discovered that the combination of a harder sublayer with a more elastic one allows for obtaining a suitable combination of superhardness and enhanced toughness. The coating was deposited by cathodic arc technology. The EDS, XRD, and XRS analyses revealed that the nanocomposite structure is composed of TiAlSiN and AlSiN nanocrystallites, with sizes of 12–13 nm and 4–5 nm, respectively. The nanograin phase is incorporated in an amorphous Si₃N₄ matrix. The achieved structure causes the presence of four factors contributing to the hardness increase: nanocomposition, solid solution, refinement hardening, and the formation of many interfaces. An instrumented indentation test was used to investigate the mechanical properties. The developed coating possesses a superhardness of 49.5 GPa and a low elastic modulus of 430 GPa, resulting in an improved elastic strain resistance of 0.11, a plastic deformation resistance of 0.58 GPa, and an elastic recovery of 68%. These results imply that the developed coating combines high stability with mechanical degradation under external influence and provides an improved ability to absorb energy at deformation before fracture, and high elastic recovery. The investigation of the effect of the period modulation on the structure, composition, and mechanical properties of the nanocomposite multilayer TiAlSiN/AlSiN coating showed that the superhardness was due to the nanocomposite and solid solution hardening rather than the increased number of interfaces. The demonstrated combination of superhardness with high elasticity and improved toughness determines the developed nanocomposite TiAlSiN/AlSiN coating as very suitable for industrial applications such as high speed and dry machining.

TiAlSiN/AlSiN coatings, with 3 and 30 periods, were successfully deposited by cathodic-arc evaporation technology. The composition, structure, mechanical, and tribological properties were studied at thermal treatment from 700 °C to 900 °C. The SEM observation and EDS analysis verified the dense structure and stable element composition in the coating depth at increased temperatures. A limited surface oxidation was identified at 800 °C, which increased moderately at a higher temperature of 900 °C. The coating period displays a nanocomposite structure of TiAl(Si)N and AlN nanograins incorporated in an amorphous Si₃N₄ matrix obtained by XRD and XPS analyses. The coatings exhibit high hardness of 41.1 GPa and 36.4 GPa for the 3- and 30-period coatings, respectively. The coatings with higher modulation periods demonstrate an excellent high temperature hardness and resistance to elastic and plastic deformations up to 900 °C. The hardness of the coatings with a smaller modulation period reduces to 29.7 GPa at the same temperature, causing a decrease in the H/E and H³/E^*2 ratios. The tribological tests found that the high-temperature wear resistance depends strongly on the coating composition and architecture. An oxidation wear mechanism dominates the coatings with a large modulation period, and the wear rate decreases with a temperature increase. Abrasive wear is predominant in coatings with a lower modulation period, leading to an increasing wear rate. Wear rate values of 7.27 × 10⁻⁶ mm³/N·m and 8.53 × 10⁻⁶ mm³/N·m were determined after annealing at 900 °C for the 3- and 30-period coatings, respectively.

A CrAlSiN-AlSiN coating with periodically modulated composition was investigated regarding dependence of the mechanical properties and toughness, morphology, composition, and structure on thermal treatment in the interval of 600–900 °C in argon ambience. The coating exhibited superhardness and high toughness up to 800 °C. A very slight decrease in the nanohardness, resistance to elastic strain to failure, and plastic deformation were observed. The coating had enhanced elastic recovery stable up to 700 °C. It was found that the coating morphology was not substantially influenced by the thermal treatment. X-ray diffraction (XRD) analysis revealed that the modulated coating had a nanocomposite structure, which did not change after annealing, even at 900 °C. The grains were composed mainly of fcc-CrN and h-AlN phases embedded into an amorphous Si₃N₄ matrix. A small amount of an h-Cr₂N phase appeared after heating at temperatures above 700 °C. The coating composition was examined by energy-dispersive X-ray spectroscopy (EDS). The coating was stoichiometric up to 800 °C. It became sub-stoichiometric with respect to nitrogen after annealing at 800 °C and 900 °C. It is thus concluded that the CrAlSiN-AlSiN coating with a periodically modulated structure keeps the combination of superhardness (45.3 GPa) and improved toughness (H³/E*² = 0.362 GPa, elastic recovery 57%) at temperatures up to 800 °C, and is suitable for high thermal applications.

A preliminary investigation of the optical properties of complex Cr-based hard coatings and their connection with the compound structure of the coatings is presented. Cr/CrN, Cr/CrN/CrAlN, Cr/CrN/CrTiAlN, and Cr/CrN/CrAlTiN coating structures were deposited through unbalanced magnetron sputtering. Their mechanical properties, especially nanohardness, coefficient of friction, and adhesion, were measured. The structure and composition of the coatings were characterised through SEM, FIB, XPS, and TEM. Their optical properties were investigated by UV-VIS ellipsometry. The optical parameters’ phase difference Δ, the amplitude ratio Ψ, the frequency-dependent real (ε₁(ω)) and imaginary (ε₂(ω)) part of the dielectric function, and the corresponding refractive and extinction indexes n(ω) and k(ω) were measured and modelled via regression analysis implemented using the WVASE© software version 3.686. Satisfactory coincidence was achieved between the measured optical data and the corresponding fitting models. The physical polycrystalline optical constants of the industrial samples were extracted from modelling data with roughness. The analysis of the data showed that ellipsometric characterisation can be used in order to determine the physical properties of Cr-based hard coatings with complex structure and composition, as well as for repeatability control of the deposition process. However, more detailed research is needed to predict the composition based on measured optical properties.