**2. Experimental**

Coatings are being developed with a nanolayer architecture, characterized by a

number of significant advantages compared to traditional monolithic coatings [3, 6–8]. In particular, the studies detect improved crack and impact resistance of the coatings with a nanolayer architecture [9–13]. The influence of a nanolayer structure of the coating on its tribological properties is of great importance. The studies have found that the coatings with a nanolayer structure are characterized by a reduced COF, high hardness, and a low level of residual stresses [6], while with a decrease in a thickness of the binary nanolayer λ, the COF decreases and the wear resistance increases [8]. The investigation has also demonstrated that a decrease in the nanolayer period λ leads to an increase in hardness, a decrease in the

*Tribology in Materials and Manufacturing - Wear, Friction and Lubrication*

COF, and an improvement in the resistance to the failure of cohesive bonds between nanolayers [14–17]. In particular, in [15], the studies of the TiAlCN/VCN nanostructured coating with λ = 2.2 nm have found that for this coating, the COF grows with an increase in temperature up to 200°C, but begins to decrease at temperatures above 650°C. The experiments found a decrease in the COF for the CrAlYN/CrN nanolayer coating with λ = 4.2 nm with an increase in temperature up to 650°C [16]. The study of the Ti/TiAlN/TiAlCN nanolayer coating detected its low COF and high wear resistance [17]. The tribological properties of the TiAlN/CNx nanostructured coating with λ = 7 nm were considered in [18]. The tests have found that the TiAlN/CNx nanostructured coating is characterized by small grain sizes and lower surface roughness in comparison with a monolithic coating of a similar

composition and also by a lower COF and higher wear resistance.

temperature and 0.6–0.7 – at a temperature of 550°C.

decrease with a further increase in temperature;

• for coated products, the COF varies significantly with an increasing

• in general, the above variation of the COF is initially characterized by its

• the parameters of the nanolayer structure (in particular, the value of the nanolayer period λ) have a noticeable influence on the COF variation.

gradual increase with a growth of temperature and then by its more significant

Thus, it can be asserted that:

temperature;

**152**

The influence of the elemental composition of the coatings on their tribological properties was also investigated. The experiments revealed the COF value at room temperature for the coatings of TiN (0.55), TiCN (0.40), TiAlN (0.50), AlTiN (0.7), as well as AlTiN/Si3N4 consisting of AlTiN nanoparticles embedded into amorphous Si3N4 matrix (0.45) [19]. During the studies focused on the TiAlCrN/ TiAlYN and TiAlN/VN coatings, Hovsepian et al. [20] found that the introduction of Y in the coating composition led to a decrease in the COF from 0.9 up to 0.65 during the tests conducted at temperatures ranging from 850 to 950°C. For the TiAlCrN coating, the COF was 1.1–1.6 (at temperatures of 600–900°C), while for the TiAlN/VN coating, the COF was 0.5 (at 700°C). Mo et al. [21] found that the COF of the AlCrN and TiAlN coatings was 0.75 and 0.85, respectively. With an increase in the Cr content in the CrAlN coating, a slight increase in the COF was detected [22]. Nohava et al. [23] studied the properties of the AlCrN, AlCrON, and α-(Al,Cr)2O3 coatings in comparison with the properties of the TiN-AlTiN reference coating at temperatures of 24, 600, and 800°C. The maximum value of the COF was detected at a temperature of 600°C for all the studied samples, while at a temperature of 800°C, there was a significant decrease in the COF (to 0.6–0.8) to the values lower than those detected at a room temperature (0.3–0.5). Bao et al. [24] found that for the TiCN/TiC/TiN coating, the COF was 0.4–0.5 at a room
