OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 1 2022 was introduced through the plasma source to a working pressure of 0.3 Pa. By triggering a gas discharge with a current of about 40 A and applying a bias voltage of 700 V to the substrate holder with the hard alloy samples, the substrates were heated to a temperature of 400 ºC. After ion bombardment cleaning of the sample surfaces and its chemical activation, a nitrogen-argon mixture in a percentage ratio of 90/10 (N2:Ar) was injected to a pressure of 0.5 Pa and arc discharges with currents of 80 A were triggered in the evaporators. Along with multilayer ZrCrN coatings, ZrN and CrN coatings deposited under similar conditions, but using only one of the cathodes, were examined for a comparative analysis of the coating properties. The phase composition and properties of multilayer coatings were changed by varying the rotation speed of the sample holder. Four holder rotation speeds were used: 0.5 rpm (designation for ZrCrN-1 sample), 3.5 rpm (ZrCrN-2), 5 rpm (ZrCrN-3), and 8 rpm (ZrCrN-4). The holder rotation speed during the deposition of ZrN and CrN coatings was 0.5 rpm. Nanoindentation was performed on a NHT-TTX S nanoindentation tester (CSEM, Switzerland) with a linearly increasing load from 0 to 25 mN and a loading rate of 1.5 μm/min. The nanoindentation data were analyzed by the Oliver–Pharr method. Scratch indentation was performed on a Revetest RST macro scratch tester (CSM Instruments, USA) with a Rockwell diamond indenter, a scratching speed of 3 mm/min, a scratch length of 3 mm, and a linearly increasing load from 0 to 50 N. X-ray diffraction analysis was performed using a DRON-7 X-ray diffractometer (Burevestnik, Russia) in the angle range 2Θ = (20–90)° and with the X-ray wavelength λ = 1.54 A. The surface morphology of the samples was examined using an Apreo 2 S high-resolution scanning electron microscope (FEG SEM) (Thermo Fisher Scientifi c, USA). The cross section of the coatings was examined on fracture surfaces. The surface roughness was examined using an Olympus OLS LEXT 4100 confocal laser scanning microscope (Olympus, Japan). Results and discussion The surface images of the studied coatings are presented in Figure 1. One can see small black dots on the surface of all samples. Surface examination by confocal laser scanning microscopy revealed that these points are both droplet inclusions on the surface and pores. It appears visually similar and has comparable diameters of the order of 0.5–5 μm. The number and size of these dots are larger on the surface of multilayer ZrCrN coatings (Figs. 1c–1f) compared with ZrN (Fig. 1a) and CrN (Fig. 1b) coatings. Surface roughness analysis was performed with the Olympus LEXT software to quantify differences in the surface morphology of the coatings. The evaluation was carried out using two parameters Sa and Sz, which are the arithmetic mean and the maximum height of surface microroughness, respectively. The analysis data (Fig. 2) indicate that the roughness of multilayer ZrCrN coatings in terms of the Sa parameter is by a factor of 1.8–2.9 higher compared to CrN coating, and a factor of 1.1–1.8 than for ZrN coating. Amuch less increase in the roughness of multilayer ZrCrN coatings is observed in terms of the Sz parameter, which is by a factor of 1.5–1.8 higher compared to CrN and only 3–15 % higher compared to ZrN. It follows from the data obtained that surface roughness in terms of the Sa parameter increases monotonically from the sample with CrN coating to the sample with multilayer ZrCrN-4 coating. Increasing the substrate holder rotation speed from 0.5 to 8 rpm leads to an ~38% increase in surface roughness in terms of the Sa parameter. The surface roughness change due to variation in the deposition conditions for samples with multilayer ZrCrN-1…ZrCrN-4 coatings in terms of the Sz parameter is less signifi cant and does not exceed 12 %. Surface roughness measurements of the coatings by confocal laser scanning microscopy allow evaluating such parameters as the roughness amplitude and the number of roughness elements per unit area. This is done according to GOST R ISO 25178-2-2014 that involves the determination of the void volume, peak volume, and core material volume.
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