V. S. Sergevnin

Phase composition, structure, and mechanical properties of arc PVD Mo–Si–Al and Mo–Si–Al–N coatings

Using an arc physical vapor deposition process, we have produced nanostructured Mo–Si–Al coatings with a uniform distribution of equiaxed grains 8–12 nm in size and Mo–Si–Al–N coatings with a multilayer structure and a modulation period from 22 to 25 nm. The former coatings consist of MoSi2 and Mo and the latter consist of Mo2N and amorphous Si3N4 and AlN. The hardness of the Mo–Si–Al–N and Mo–Si–Al coatings is 41 and 18 GPa, respectively; they are similar in resistance to elastic deformation; and the Mo–Si–Al–N coating has a considerably higher resistance to plastic deformation. The coatings have roughly identical coefficients of friction (~0.67–0.69 at 20°C and ~0.52–0.56 at 550°C), but the wear resistance of the Mo–Si–Al–N coating is higher by three and two orders of magnitude at 20 and 550°C, respectively. The coatings of the two systems exhibit good adhesion to the substrate and cohesive fracture. Partial wear of the Mo–Si–Al and Mo–Si–Al–N coatings in the course of scratch testing occurs at indentation loads of 80 and 63 N, respectively.

Phase formation in the Ti–Al–Mo–N system during the growth of adaptive wear-resistant coatings by arc PVD

Ti–Al–Mo–N coatings have been grown by arc PVD at different bias voltages, Vb, applied to the substrate and partial pressures of nitrogen reaction gas, p(N2), in the working chamber. The coatings have a nanocrystalline structure, with an average grain size on the order of 30–40 nm and a layered architecture made up of alternating layers based on a (Ti,Al)N nitride and Mo-containing phases of thickness comparable to the grain size. It has been shown that the phase composition of the coatings depends on Vb and p(N2): raising the energy of deposited ions by increasing Vb from–120 to–140 V, as well as raising p(N2) from 0.3 to 0.5 Pa, leads to a more complete molybdenum nitride formation during coating growth, which causes a transition from (Ti,Al)N–Mo–Mo2N compositions to (Ti,Al)N–Mo2N. Measurements of the binding energy of Mo 3d photoelectrons in metallic Mo and the Mo2N nitride by X-ray photoelectron spectroscopy have shown that the transition from the former phase to the latter is accompanied by a negligible energy shift.

(Ti,Al)N–Ni nanostructured coatings: Thermal stability, heat resistance, electrochemical behavior, and adhesive strength with a substrate

In this work, thermal stability and oxidation resistance at temperatures up to 800°C are studied for (Ti,Al)N–(8–10 at %)Ni coatings with a thickness on the order of 4 µm and a crystallite size below 20 nm, which have been prepared via ion–plasma vacuum arc deposition. The composition and structural characteristics of coatings remain stable during 1-h heating in vacuum of 10–4 Pa at temperatures of 600 and 700°C. Heating at a temperature of 800°C leads to an increase in the crystallite size and a decrease in microstrains of a ceramic phase, which is accompanied by a reduction in the hardness of the coating from 51–53 to 31–33 GPa. The coatings are heat resistant up to 800°C and characterized by cohesive failure in scribing. The adhesive strength of coatings with a substrate exceeds 85 N. Studying electrochemical behavior reveals the high efficiency of (Ti,Al)N0.87–Ni coatings in corrosion protection of cutting tools in acid and alkaline environments.

Superhard Nanostructured Ceramic–Metal Coatings with a Low Macrostress Level

The macrostressed state of (Ti,Al)N–Cu and (Ti,Al)N–Ni ceramic–metal coatings obtained by the arc-PVD method has been studied using X-ray diffraction and by measuring the radius of curvature of a coating–base composite sample (Stoney’s method). It is established that the presence of a tough metal phase favors significant reduction in the level of macrostresses in these structures as compared to those in (Ti,Al)N ceramic coatings, the absolute values of which decrease from 4.7–4.3 to 0.17–0.32 GPa. At the same time, both Ti–Al–Cu–N and Ti–Al–Ni–N coatings retain high hardness of 43 and 51 GPa, respectively, versus 29 GPa for Ti–Al–N coatings. The obtained results give grounds to suppose that the high hardness of the ceramic–metal coatings studied is determined by their nanocrystalline structure rather than by compressive macrostresses.

Heat Resistance, High-Temperature Tribological Characteristics, and Electrochemical Behavior of Arc-PVD Nanostructural Multilayer Ti–Al–Si–N Coatings

The present paper has aimed at studying heat resistance, electrochemical behavior, and tribological characteristics at high temperatures of superhard (~48 ± 2 GPa), multilayered with a modulation period of 17–18 nm, and nanostructured (nc)AlN-(am)Si3N4/(nc)TiN coatings obtained with an ion-plasma vacuum arc. The heat resistance of the coatings studied in the temperature range of up to 800°C inclusive was mainly determined by the oxidation of their surface layers without the substrate intrusion. Having a high coefficient of friction from 0.6 at 20°C to 0.8–0.85 at elevated temperatures, the coatings are characterized by virtually no wear, which was confirmed by profilometry measurements of friction zones. The obtained results concerning electrochemical behavior indicate that the Ti–Al–Si–N coatings are highly efficient in the protection of a cutting tool from corrosion in both acidic and alkaline media.

Structure, Composition, and Properties of Arc PVD Mo–Si–Al–Ti–Ni–N Coatings

Using an arc physical vapor deposition process, we have produced nanostructured Mo–Si–Al–Ti–Ni–N coatings with a multilayer architecture formed by Mo2N, AlN–Si3N4, and TiN–Ni and a crystallite size on the order of 6–10 nm. We have studied the physicomechanical properties of the coatings and their functional characteristics: wear resistance, adhesion to their substrates, and heat resistance. According to high-temperature (550°C) wear testing and air oxidation (600°C) results, the coatings studied here are wearand heat-resistant under appropriate temperature conditions. Their properties are compared to those of Mo–Si–Al–N coatings.

Influence of ion energies on the structure, composition, and properties of multilayer Ti–Al–Si–N ion-plasma-deposited coatings

It is established that the energy of deposited particles influences the structure, composition, and properties of multilayer nitride coatings consisting of alternating layers of nanocrystalline TiN and amorphous Si3N4 phases with inclusions of nanocrystalline hexagonal AlN formed at energies of titanium, aluminum, and silicon ions exceeding ~317 × 10–19, 267 × 10–19, and 230 × 10–19 J, respectively. As the energy of titanium ions bombarding the substrate increases above ~512 × 10–19 J, the phase transition from disordered TiNx to Ti3N2 and the appearance of 2- to 3-nm-thick sublayers in 15-nm-thick nanocrystalline TiNx layers take place in the coating. The maximum hardness of such coatings reaches a level of ~54 GPa.

Hardness, adhesion strength, and tribological properties of adaptive nanostructured ion-plasma vacuum-arc coatings (Ti,Al)N–Mo2N

The properties of nanostructured multilayered coatings of the composition (Ti,Al)N–Mo2N, which were fabricated by the ion-plasma vacuum-arc deposition (arc-PVD), are investigated. The thickness of coating layers is comparable with the grain size, which is about 30–50 nm. The coating hardness reaches 40 GPa with relative plastic deformation work of about 60%. It is established by measuring scratching that the cohesion destruction character of the coating occurs exclusively according to the plastic deformation mechanism, which evidences its high fracture toughness. The local coating attrition to the substrate takes place under a load on the order of 75 N. The coating friction coefficient in testing conditions according to the “pin-on-disc” layout using the Al2O3 counterbody under a load of 5 N is 0.35 and 0.50 at temperatures of 20 and 500°C, respectively. The coating is almost unworn because of the formation of MoO3 oxide (the Magneli phase) operating as the solid lubricant in the friction zone. An increase in the friction coefficient and noticeable wear are observed with the further increase in the testing temperature, which is associated with the sublimation intensification of MoO3 from the working surfaces and lowering its operational efficiency as the lubricant.

Hardening the hard-alloy edge tool used for cutting the tough-to-machine titanium alloys and chromium–nickel steels with multilayered nanostructured coatings

Complex investigations into physicomechanical properties and adhesion strength in the coating–carbide cutting insert system of monolayered coatings (Ti–Al–N) and multilayered coatings (Ti–Al–N/Cr–N, Ti–Al–N/Zr–N/Cr–N) are performed. The advantage of using the latter, which is associated with the passage from the adhesion mechanism of coating destruction to the cohesion mechanism with an increase in parameters H3/E2 and H/E that characterize the material resistance to plastic and elastic deformation, respectively, is shown. The introduction of chromium into the composition of Ti–Al–N coatings decreases the friction coefficient (from 0.52 to 0.45) and decreases the probability of adhesion interaction with the treated material. Comparative operational tests of carbide cutting inserts (CCIs) with coatings under study in the course of continuous cutting steel #12Kh18N10T# showed that the largest wear resistance is characteristic of Ti–Al–N/Zr–N/Cr–N coatings. Wear tests of CCIs made of VK6NST and TT10K8B alloys with Ti?Al–N/Zr–N/Cr–N coatings in the course of longitudinal turning steel 12Kh18N10T and VT20 alloy evidence an increase in their resistance up to a factor of 3.0–3.5 both at low and high cutting rates. These coatings provide an increase in resistance of cutting tool and in milling operations of VT20 titanium alloy at a cutting velocity up to 40 m/min.