Ion-Plasma Spraying and Electron-Beam Treatment of Composite Cr-Al-Co-ZrO 2 -Y 2 O 3 Coating on the Surface of Ni-Cr Alloy

: The blades of modern gas turbine engines are complex structures made of heat-resistant nickel alloys with a complex system of internal cavities. The article describes a method of strengthening samples of a heat-resistant Ni-Cr alloy by applying a composite coating (Cr-Al-Co + ZrO 2 -Y 2 O 3 ). The alloy prototypes were fabricated by vacuum melting. An ion-plasma technology of a two-layer coating with an inner metal and an outer ceramic layer on the prepared surface of the heat-resistant alloy matrix was developed. The morphology and structure of the alloy prototypes and the inves-tigated composite coating were studied by scanning electron spectroscopy. The total thickness of the two-layer wear-resistant coating was 17–18 µ m. The thickness of the inner layer (Cr/Al/Co) is 10–11 µ m and the thickness of the outer ceramic coating (ZrO 2 -Y 2 O 3 ) is 6–7 µ m. To improve the operational characteristics of the material, an electron-beam surface treatment was proposed. The research results showed a sevenfold increase in surface resistance compared with the initial state.


Introduction
Modern gas turbine engines operate at the temperatures of hot gases' expansion in a direction transverse to the rows of turbine blades. The blades of modern gas turbine engines are complex structures made of heat-resistant alloys with a complex system of internal cavities [1,2]. The efficiency and service life of blades of this design can be ensured by protecting them from high-temperature gas corrosion. Heat-resistant protective coatings are obtained by sequential application of layers by gas circulation and ion-plasma methods [3,4]. The use of protective coatings makes it possible to increase the service life by 3-5 times. The use of thermal barrier coatings on gas turbine blades has several advantages. Owing to the use of such coatings, a higher operating efficiency of the turbine blades can be achieved, as less cooling air is needed to maintain the temperature of the blade or shroud. In addition, the service life of the parts increases, because the rate of change in the metal temperature decreases as a result of the heat-insulating effect [5].
Nickel alloys are used as heat-resistant alloys for the manufacture of parts for gas turbine engines. During operation, the parts are subjected to significant alternating and "tensile" stresses; owing to heating and cooling, thermal stresses arise, leading to thermal fatigue and destruction of the metal [6,7].
To solve the problems of increasing the service life of critical units of power equipment, it is necessary to conduct comprehensive research. Therefore, when studying the features of the formation of composite coatings on the surface of a metal matrix, it is necessary to pay attention to the technology of obtaining the alloys themselves. Obtaining a stable heat-resistant Ni-Cr matrix is an important part of the overall process. It is essential to expect that the specificity of the substrate (primarily its crystal structure) be reflected in the structure of the coating. For example, the growth of an alumochromic layer can be, to some extent, associated with the orientation of the substrate.
The development of cast heat-resistant nickel-based alloys has gained wider application because a greater strengthening effect can be achieved in them owing to γ -phases and carbides, and higher structural stability compared with wrought alloys [6,7].
An increase in the oxidation-resistance at high temperatures in such alloys is achieved owing to the formation of Cr 2 О 3 compounds. In Ni-Cr alloys containing up to 10% of Cr, NiO oxide predominates on the surface; in the areas of the alloy-scale interface, Cr 2 O 3 precipitates surrounded by nickel are observed. As the Cr content increases, the mixed Ni-Cr 2 O 3 layer disappears, which leads to the formation of a continuous Cr 2 O 3 layer, above which the NiO layer with inclusions of NiCr 2 O 4 spinel is located. Alloys of Ni (20-25%)-Cr have a minimum oxidation rate owing to the optimal ratio of NiO and Cr 2 O 3 , which, during long exposure (1000-1050 • C), also turn into NiCr 2 O 4 spinel [8].
The structure of cast heat-resistant nickel alloys consists of a matrix (a complex alloyed solid solution based on nickel) and γ -phase (a solid solution based on Ni 3 Al). Ni 3 Al is precipitated in the axes of dendrites and in the interdendrite space, where carbides, borides, carboborides, and eutectics are also located [9].
Despite the fact that Ni-Cr-Al alloys have high heat resistance, to protect turbine blades, coatings are required that are capable of long-term operation under load at temperatures up to 1150-1200 • C. One of the ways to solve this problem is to create combined metal and metal-ceramic high-temperature coatings; for example, Al-Cr based coatings. The coatings' composition, along with aluminum, can include other alloying additives (for example, Ta, Si, Ti, Co, and Y), which reduce the oxidation rate and affect the processes of diffusion interaction of the coating with the base of heat-resistant alloys [10][11][12].
Currently, duplex and combined materials processing technologies are being developed and used, including plasma coating and subsequent surface treatment with a high-current electron beam (HCEB) [13,14]. Such treatments make it possible to optimize the physical and mechanical properties of the applied coatings. The use of combined processing allows not only to melt the near-surface layer (while healing the pores), but also to change the elemental composition, i.e., enhance the processes of mass transfer. Local damage determines the area of modification of the material. Energy transfer to the material and subsequent relaxation of the system causes this type of damage.
Tests of MiG and Su aircraft engines showed that powder aluminizing of the highpressure turbine blades does not provide their protection. The engine life was limited to 50 h, which was associated with an increase of~150 • C in the operating temperature of gases in the engines, as well as an increased level of thermal stress of the blades [15,16]. There is an urgent need to develop and create coatings capable of protecting turbine rotor blades from high-temperature (1100-1150 • C) gas corrosion, to provide the required level of resistance to the formation of thermal fatigue cracks on the blade surface and to increase their resource. Condensed multicomponent Me-Cr-Al-Y systems are used as such coatings [17][18][19].
The main goal of the research is to study the structure and properties of a composite coating (Cr-Al-Co-rare earth group) on the surface of a heat-resistant Ni-Cr alloy, as well as to study the structure of the alloy.
It is advisable to use ceramics based on zirconium stabilized with yttrium oxide (ZrO 2 ·Y 2 O 3 ) as the upper layer of the heat-protective coating, and it is recommended to use a heat-resistant material as the lower sublayer [20,21]. The application of a ceramic layer allows reducing the temperature on the surface of the metal, and the heat-resistant layer protects the surface from high-temperature corrosion and increases the adhesion of materials.
In diffusion coatings, the aluminum content is usually 15-25%. This aluminum content ensures the formation of α-Al 2 O 3 film during oxidation and sufficient plasticity of nickel (cobalt) aluminides. The thickness of the coatings on the blades does not exceed 0.06 mm and, for some aircraft engines, 0.04 mm. The second important component of the coatings is chromium, which ensures the formation of α-Al 2 O 3 film at the reduced aluminum content and is part of a protective film based on Ni(Cr,Al) 2 O 4 spinel. The chromium content in high-temperature coatings is usually 7-20%. The efficiency of aluminide coatings is limited by a temperature of 1100 • C, above which the flux of nickel atoms from nickel alloys into the coating increases sharplay, leading to the rapid disappearance of the main NiAl phase, which forms a protective film of α-Al 2 O 3 .

Preparation of Alloy Samples
To develop a comprehensive technology for increasing the service life of turbine blades, a number of model samples of the heat-resistant Ni-Cr alloy were made. This alloy was obtained by vacuum induction melting of an ingot into a cylindrical mold. The heating of the measured charge billet of the finished alloy was carried out in a UPPF-4 vacuum melting unit (Elektromekhanika, Rzhev, Russia). The components of the charge were 3-5 mm thick trimming of sheet heat-resistant 20Kh23N18 steel (Ni-Cr alloy) after guillotine shears. The charge components were obtained from "Elektrostal" Metallurgical Plant JSC, Elektrostal, Russia.
Manufacturing of the experimental castings from 20Kh23N18 alloy included the following operations:

•
Heating of the measured charge blank of the finished alloy. The metal was placed in a melting quick-change rammed crucible made of Al 2 O 3 , which had undergone preliminary sintering with a graphite template; • The metal was melted and heated to a temperature of 1600 • C in 10 −2 -10 −4 Pa. Exposure at maximum heating temperature was no more than 5 minutes; • The sample was poured into the mold at a metal temperature of 1480-1530 • C, while the mold temperature was 950-1000 • C. With a decrease in the casting temperature to 900 • C, the mold was removed from the device for directional solidification.
In the process of forming the ingot, the principle of superposition was used: (1) pouring out the melt from the crucible; (2) as a consequence, a drop in the temperature of the melt in the pouring funnel, as part of the heat is spent on heating the ceramics; (3) the temperature in the melt jet decreases in proportion to the drop height; (4) a decrease in temperature associated with heating the mold; and (5) crystallization of the melt, in separately taken small volumes, due to the temperature difference.
Thus, using the method of vacuum induction melting of an ingot into a cylindrical mold, a cylindrical ingot with a diameter of 120 mm and a length of 400 mm was obtained. Next, the ingot was machined. The chemical composition of the heat-resistant alloy samples was as follows: Fe-96-97%; C-0.14-0.15%; Si-0.89-0.90%; Mn-1.93-1.95%; Cr-23.52-23.55%; Ni-18.63-18.65%; and S-0.013-0.015%. The chemical composition of the obtained alloy was determined using SPECTROMAXx optical emission spectrometer (Spectro Analytical Instruments GmbH, Kleve, Germany). The digital spark generator made it possible to create a spark of increased energy (HEPS method) while preparing the sample for analysis to eliminate the influence of the structure. The frequency of the current in the spark was 500 Hz.
After analyzing the chemical composition of the alloy, the ingot was subjected to the removal of the bottom parts and machining. According to the calculated allowance rate, turning along the diameter of the ingot, until the actual removal of surface defects was 4% or 3 mm per diameter. After machining, the cast billet was subjected to plane cutting into rectangular plates 50 × 50 × 3 mm in size.
The samples were prepared for coating by surface treatment using a DBS-100 pressuretype sandblaster (Contracor, CompragGroup, Wuppertal, Germany). Silicate sand was used as an abrasive material. The size of the abrasive particles was 0.8-1.1 mm, the compressed air pressure was 0.5 MPa, the processing distance was 0.1 m, the angle of the counter flow with the surface was 70 • , the consumption of abrasive particles was 320 kg/h, and the degree of purification was SA-3.0.

Ion Plasma Spraying
The method of applying the wear-resistant coating on the heat-resistant alloy included plasma spraying of a cermet system by layer-by-layer application of Cr/Al/Co powder (alternate deposition of layers) + ZrO 2 -Y 2 O 3 . Before applying the wear-resistant coating, the surface of the heat-resistant alloy was subjected to vacuum treatment at a temperature of 290-310 • C for 40-50 minutes. Then, hydroabrasive treatment was carried out in a mixture of sand and water, followed by washing in distilled water with simultaneous exposure to ultrasonic treatment and drying. Ultrasonic treatment was carried out using an IL 10-0.63 generator (TekhultraSnab, Saint Petersburg, Russia). The generator power was 630 W, the ultrasonic vibration frequency was 20 kHz, and the ultrasonic vibration amplitude was 10 µm.
Ionic cleaning of the heat-resistant alloy with argon was carried out using vacuum universal post VUP-5 (SELMI JSC, Sumy, Russia).
The powder (Cr, Al, Co-separately, ZrO 2 -Y 2 O 3 -in one composition) was ground in Pulverisette 6 ball mill (Fritsch, Idar-Oberstein, Germany) for 2.5 h at 420-520 rpm and stirred with a mechanical stirrer for 1.5 h. The targets were in the form of disks with a diameter of 240 mm and a thickness of 7.5-8 mm. Molding was carried out in PLG-25 laboratory mold (Sibir-komplekt, Novosibirsk, Russia) by uniaxial pressing at 60 MPa. A day later, the target was annealed in PM-8 (Elektropribor, Cheboksary, Russia) in air at 1050 • C for 1.2 h.
The ion-plasma installation (KVO, Tomsk Polytechnic University, Tomsk, Russia) for coating is a vacuum chamber with two magnetron-sputtering systems of an unbalanced type and an ion source with a closed electron drift. The vacuum chamber of the installation is a sealed volume with a diameter of 500 mm and a height of 300 mm, equipped with flanges of various diameters for connecting vacuum fittings, vacuum sensors, and other necessary devices (Figures 1 and 2).
The gas supply and regulation system is represented by BronkhorstELFLOW precision mass flow controllers (Bronkhorst, AK Ruurlo, Netherlands) with an adjustment accuracy of 0.01 mL/min. The temperature of the samples was controlled by chromel-alumel thermocouple (the range of measured temperatures is 200-1100 • C).
Before spraying the coatings, the working volume of the vacuum chamber was pumped out to a pressure of 10 −4 Pa. Then, the working gas (argon) was supplied and, after reaching the working pressure (0.4 Pa), the discharge was ignited. The following temperature regime of deposition was used: the temperature rate at the initial stage of deposition was 3.0 • C/min, and the substrate temperature after 1.7 h was 240-260 • C. The target-substrate distance was 37-40 mm.  The total thickness of the double-layer coating was 17-18 µm. The thickness of the inner layer (Cr/Al/Co) was 10-11 µm (Al-20-25%, Cr-17-20%, Co-30-34%). The thickness of the outer ceramic coating (ZrO 2 -Y 2 O 3 ) was 6-7 µm. The concentration of yttrium oxide and zirconium oxide in the heat-resistant layer was 40-43% and 60-63%, respectively.

Electron-Beam Treatment
The coatings were formed using the technologies combining ion-plasma spraying and electron-beam treatment of coatings.
Irradiation was carried out on an TEU-500 electron accelerator (Institute of High Technology Physics, Tomsk Polytechnic University, Tomsk, Russia). The pulsed electron irradiation parameters were as follows: accelerating voltage up to 500 kV, current pulse duration of 100 ns, extracted electron beam current of 4 kA, beam current density on the target of 50 A/cm 2 , and beam energy of 100 J. The absorbed dose in the samples was about 12 kGy per pulse. The samples were processed in an air atmosphere. The pulse repetition rate is 0.3 imp/s. The maximum number of pulses was determined by the change in the strength properties of the matrices at a given pulse repetition rate; at more than 20 pulses, the samples became brittle.

Study of the Structure of Samples
Heat treatment of the coating samples was carried out in a SUOL 0.4.2.5/15 muffle furnace (Soltek, Moscow, Russia) at a temperature of 1250 • C. The furnace with samples loaded into corundum crucibles was heated for 2.5 h at a rate of~15 • C/min. Samples were held for 6 h at a given temperature, followed by cooling. The heating and cooling cycle was repeated three times.
Heat-treated coated samples were cut on an Isomet 4000 precision cutting machine (Buehler, Lake Bluff, IL, USA). Next, the samples were poured into the EpoMet resin (Buehler, Lake Bluff, IL, USA). For this, a SimpliMet 1000 automatic hot press (Buehler, Lake Bluff, IL, USA) was used. Pressing conditions: pressure of 29 MPa and temperature of 250 • C.
The preparation of thin sections of samples for structural studies was carried out in several stages: grinding on abrasive paper with a transition to smaller sizes of abrasive particles. Before each transition to a finer surface treatment, the section was turned 90 • and washed under a stream of cold water using a brush to remove crumbs, dust, and abrasive particles (washing time 5-10 min). Further, the thinning of the section was carried out on a cloth-covered disc of JSSG-8-M grinding and polishing machine (JET, Fällanden, Switzerland) using an aqueous suspension of chromium oxide.
Metallographic studies were carried out on a Neophot-21 optical microscope (Car-lZeissJena, Jena, Germany) at a magnification of 100-700 times in cross section.
Structural analysis was performed on a JSM-6390LV scanning electron microscope (JEOL, Tokyo, Japan) with energy-dispersive analysis at 20 kV of an accelerating voltage. The resolution of the electron microscope is 3.0 nm; the sample diameter is 120 mm; and, for the automation of the movement of the sample stage in three directions, X Y Z, the inclination of the sample stage is up to 10 • .

Sample Testing
Erosion tests of samples and the study of erosive wear processes under the influence of a liquid (drop-impact erosion) were carried out at "Erosion-M" stand developed by the Moscow Power Engineering Institute at 20 • C. The studies were carried out at the collision velocities of liquid particles with a size of 800 µm and υ sp = 300 m/s. Condensate of an operating coal-fired power plant was used as a working liquid (total hardness of 70 µg-eq/kg; iron content of 160 µg/kg; copper of 30 µg/kg; zinc of 32 µg/kg; nickel of 29 µg/kg; silicic acid of 160 µg/kg; petroleum products such as oil and fuel oil of 0.8 mg/kg; dry residue of 2.8 mg/kg; chromate oxidizability of 28 mg/kg). The criteria were the average depth of erosion (E), which is equal to the ratio of the decrease in the volume of the material to the area of the eroded surface and the volume of liquid (G/Se) falling out per unit surface area.
CA/2 unit (Eltech, Tver, Russia) was used to carry out fretting corrosion wear tests. The tests were carried out on samples of the obtained heat-resistant Ni-Cr alloy, processed according to the following options:
The tests were carried out on the basis of 2·10 5 cycles on VEDS-500 electrodynamic stand (Ukrspetskomplekt, Kharkiv, Ukraine) in a mode simulating the operating conditions of the rotor blades of a gas turbine engine low pressure compressor: pressure at the contact point of 10 MPa; amplitude of mutual displacement of samples of (100 ± 25) µm; and frequency of relative vibrations of 100-130 Hz.

Structure of the Heat-Resistant Alloy
Ni-based dendrites, MC carbides, MB borides, and eutectic (γ + γ ) can be distinguished at the magnifications of 50×-400× in the structures of the alloy (Figure 3). Carbides, borides, and eutectics in the studied alloy are located mainly in the interdendrite space (Figure 4). In turn, carbides have either type or globular morphology. In the photographs, at magnifications of 10,000×, the main strengthening γ -phase of cuboid morphology of two types is visible-finely dispersed in the axes of dendrites and coarsely dispersed in the interdendritic space ( Figure 5).
The intermetallic phase Ni 3 Al or γ -phase is the main hardener in the studied alloys. Its main part is formed in the solid state during the decomposition of a supersaturated solid solution. The presence of the γ matrix and γ -phases of conjugated crystallographic lattices and the proximity of their periods lead to the fact that, because of the low surface energy of the phase boundary, the formation of the γ -phase during the decoµmposition of the solid solution can occur at very small radii of nuclei.

Plasma Spraying of Composite Coating
To prevent or reduce the formation of the secondary reaction zone, we proposed the following: alternate deposition of pure metals (Cr, Al, and Co) on the alloy surface; vacuum heat treatment; and formation of a barrier layer to prevent the development of diffusion processes of exchange of alloying elements of the coating with the base. To isolate the metal matrix from the hot gas flow, ZrO 2 -Y 2 O 3 -based thermal barrier coatings with low thermal conductivity were applied to its surface.
With the ion-plasma coating method, many different deformed bumps are observed ( Figure 6). This is because the modification of the alloy surface by deposition of powder coatings based on the Cr-Al-Co-rare earth group is accompanied by the formation of an alloyed structure. The surface structure of the coatings has a layered flaky character. The coatings have high relief without sharp protrusions. During the flight, small particles were completely melted while the large particles only partially melted and, deforming upon impact, formed the coating matrix. The mechanism of powder coatings' formation was as follows: moving at a high speed, developed in the process of plasma-forming gases, the powder particles are melted in a high-temperature plasma flow. Once on the substrate, they deform and fill various micro-cavities on the substrate surface. Figure 7 shows images of thin sections obtained on coated samples. The structure of the coating formed by the dynamic introduction of the powder material into the nearsurface regions of the substrate and the structure of the transition region are rather complex. Etching revealed non-etched white stripes along the "coating-substrate" interface ( Figure 7, section h 1 ). Multiple deposition of layers during the formation of the coating in several passes led to the partial or complete destruction of such contact strips with advancement into the depth of the substrate surface (section h 2 ). Analysis of the surface structure of the coatings showed that it consists of areas of a continuous coating with fused powder particles and areas of voids small in diameter. During the formation of coatings, most of the powder, moving at a high speed and strongly melting in the plasma flow, fell on the surface of the substrate and, upon impact, was strongly deformed and spread out. The powder material filled various cavities on the substrate and powder coating surfaces after each successive pass. The larger the particle diameter, the less it heated up in the plasma flow and, falling on the substrate surface, created local areas of the stressed state on the surface, which is a good prerequisite for the formation of a strong adhesive and cohesive bond. The very structure of the coating is such that those layers of the powder that are closer to the surface of the substrate have a porosity much lower than the near-surface regions. Most likely, with an increase in the number of passes during spraying of coatings, the underlying layers were hardened under the influence of thermal effects and mechanical loads. It is also likely that, after each subsequent pass during spraying, the surface had time to cool down a little and the next layer of powder partially destroyed the surface of the previous sublayer, introducing powder particles there.
Metallographic studies (Figure 8) of the structure of ion-plasma coatings showed that the process of deposition of powders based on the Cr-Al-Co-rare-earth group under the selected modes is accompanied by the formation of a developed interface between the coating and the substrate. Because of this interaction, deformation (or the process of "macrochanneling" of powder particles) occurs in some places of the surface layer of the substrate. At the interface, there are areas where, at the initial stage of formation, powder particles are embedded in the melted surface of the substrate. Beyond the interface, approximately to the depth of the coating, the region of the transition layer extends, which was subjected to high-temperature action and mechanical hardening during the spraying process.
In the process of deposition, the coating with high-relief character was formed ( Figure 9). The surface of such coating consists of a large number of incompletely melted powder particles. We assume that, in the photographs, the round areas (about 50 µm in diameter) are the centers of the solid matrix of the powder.

Electron-Beam Treatment of Coatings to Protect Blade Surfaces
The main problem of the coatings applied by the ion-plasma method is the insufficient adhesion to the substrate in some cases, which reduces the anticorrosive and tribological properties of the coatings. To eliminate these disadvantages, the method of combined treatment was used, which made it possible to melt the surface layer (while healing the pores). Figure 10 shows the surface structure after electron-beam treatment, where the change in the microstructure of the substrate to depth is seen. Mutual mixing of materials occurs in the boundary layer. Superdeep penetration of the jet substance occurs as a result of the introduction of micro-cumulative jets. Confirmation of this mechanism follows from the analysis of the micrograph in Figure 10a, in which the under-collapsed microcumulative notches 2 with preserved pestles 1 and the beginnings of superdeep penetration channels 3 can be seen.
The micrographs shown in Figure 10 clearly show long ultra-deep penetration channels (Figure 10b), which end at a depth of 110-200 µm (Figure 10c).

Sample Test Results
The results of the erosion tests showed that the incubation period of the kinetics of erosion wear for coated samples increased by 1.01 times compared with the same characteristic for uncoated samples (in the initial state) ( Figure 11). The erosion resistance of the samples during the period of maximum wear with the coating is 1.20 times higher than that for the samples without hardening. The erosion rate during the steady-state wear rate was found to be the same for coated samples and samples without hardening. Kinetic curves of erosional wear are shown in Figure 11. Wear tests (fretting and fretting corrosion) resulted in the formation of a typical fretting spot of contact with secondary wear products on the surface: an oxide film ( Figure 12a); traces of abrasive action-particles of the material of the destroyed surface ( Figure 12b); an oxide film and traces of abrasive action (Figure 12c); pitting and microcracks uniting them (Figure 12d).
To assess the surface defectiveness and calculate the fretting resistance coefficient for the contact spot, profilograms were taken and the main roughness parameters-Ra and R max -were determined (Table 1).  The results of calculating the coefficient of defectiveness k, its change dk, as well as the coefficient of fretting resistance D are shown in Table 2. To compare the hardening options and select the most preferable one, the fretting resistance coefficient D was calculated (Table 2), reflecting the change in the resistance of the sample after hardening in comparison with the initial state (polishing without hardening).
Analyzing the results obtained, it can be concluded that all the studied treatment methods prevent the development of surface defects during fretting wear and can be used to increase the resistance to this type of wear. In this case, the combined method of applying a multilayer coating is more preferable (treatment option 4), which increases the surface resistance by more than seven times compared with the initial state.

Conclusions
The following conclusions were drawn: • Ni-based dendrites, MC carbides, MB borides, and eutectic (γ + γ ) were found in the structure of the Ni-based heat-resistant alloy-substrate. The intermetallic phase Ni 3 Al (γ -phase) is the main hardener in the studied alloy; • To reduce the formation of the secondary reaction zone, a number of technical solutions have been proposed: alternate deposition of pure metals (Cr, Al, and Co) on the surface of the alloy, vacuum heat treatment, and the formation of a barrier layer at the boundary of the alloy with the coating to prevent the alloying elements exchange processes between the coating and the base; • To isolate the metal matrix from the hot gas flow, ZrO 2 -based thermal barrier coating was applied to the surface. The developed coatings with the proposed thickness provide improved performance; • The proposed surface treatment methods prevent the development of surface defects during fretting wear and can be used to increase the resistance to this type of wear. In this case, the combined method of applying a multilayer coating is more preferable, increasing the resistance of the surface by more than seven times compared with the initial state; • The data obtained will make it possible to apply coatings of variable thickness in accordance with the most loaded zones of turbine blades.
Aircraft engine manufacturers who use heat-resistant coatings to improve the reliability and durability of turbine blades can use the results of this study.
In the future, it is proposed to carry out thermophysical calculations of the temperature distribution on the surface of the rotor blades, both with and without heat-resistant coatings. It is also planned to approbate comparative laboratory tests of various options for coatings made from rear earth metals components, a detailed study of the variable thickness of the ceramic layer of the heat-resistant coatings, and permissible defect rates.