**3. Materials and methods**

Multicomponent coatings of Ti-(Ti,Al)N-(Zr,Nb,Ti,Al)N with three-layer architecture, including adhesion, transition, and wear-resistant layers [43–50] were studied. The Ti-(Ti,Al)N coating widely used as a coating for metal-cutting tools was assumed as an object of comparison. The coating was chosen with the multilayer architecture, including an (Cr,Al,Si)N adhesive-smoothing layer, a DLC-Si transition layer, and a DLC wear-resistant layer, in order to secure high adhesion to the ceramic substrate and release the smoothing effect of the coating. Following some studies [51–53], it was found that the adhesion of the coating to the substrate was enhanced due to a DLC-Si layer included in the coating. Furthermore, in [51], the studies found that the DLC-Si demonstrated lower hardness and wear resistance compared to those of the DLC coating, and that fact contributed to the selection of DLC-Si as a transition layer ensuring high adhesion and a smooth transition of properties.

The adhesion layer of (Cr,Al,Si)N can demonstrate the extremely high hardness (up to 55 GPa [54]) in a combination with significant toughness [55]. High thermal stability is another important feature of the above compound [55, 56]. Therefore, there is a possibility of a transition from a ceramic substrate (with the hardness of 15 to 20 GPa) through the (Cr,Al,Si)N layer to DLC-Si layers and a DLC coating (with the hardness from 30 to 80 GPa). Furthermore, due to its greater toughness compared to the DLC coating, the (Cr,Al,Si)N layer is able to "heal" microcracks and micropores by penetrating them on the surface of a ceramic substrate. In [57–59], the studies found that due to its nanocomposite structure, the (Cr,Al,Si)N layer improved the crack resistance while retaining high hardness.

The filtered cathodic vacuum arc deposition (FCVAD) was used to deposit the coatings of Ti-(Ti,Al)N-(Zr,Nb,Ti,Al)N and Ti-(Ti,Al)N in the VIT-2 unit [43, 60–66].

The lateral rotating cathode technology (LARC; developed by PLATIT – BCI Group, Switzerland) was applied to deposit DLC coatings on a PLATIT π-311 unit.

A nitride coating was deposited using cathodes containing Cr, Al, or Al–Si (88:12 at%). Argon (Ar) ions were subjected to purification using a beam of Ar ions at an anode voltage of 800/200 V and a current of 0.5 A for 20 min. A coating of Si-DLC was deposited using a mixture of gases, including 90% acetylene (C2H2), 8% Ar, and 2% tetramethylsilane (Si(CH3)4). A similar mixture of gases, except for Si(CH3)4, was used to deposit a pure DLC coating.

The microstructural investigation of samples involved a scanning electron microscope (SEM; Field Electron and Ion Company) Quanta 600 FEG.

The micro- and nanostructures of the samples were analyzed with a JEM 2100 high-resolution transmission electron microscope (HR-TEM), at the accelerating voltage of 200 kV. The energy-dispersive X-ray spectroscopy (INCA Energy) was applied to study the chemical composition of the samples.

The nanoindentation technique on an Instron Wilson Hardness Group Tukon device at the load of 0.01 N was applied to find the microhardness of the coatings. A CU 500 MRD lathe (Sliven) with a ZMM CU500MRD variable speed drive was used during the turning of workpieces made of AISI 52100 (HRC 56–58) hardened steel to study the cutting properties of the coated tool and the dynamics of its wear, at f = 0.1 mm/rev, ap = 0.5 mm, and vc = 320 m/min (for the tool with the DLC coatings) and ASTM T31507 hardened steel (DIN 1.2419, HRC 58–60) and ASTM X153CrMoV12 (DIN 1.2379, HRC 60–61) hardened steel vc = 80–350 m/min; f = 0.1–0.25 mm/rev; ap = 0.5–1.0 mm for the tool with the Ti-(Ti,Al) N-(Zr,Nb,Ti,Al)N and Ti-(Ti,Al)N coatings.
