RU2120494C1 - Method of applying protective coatings with chemical composition and structure gradient along its thickness with outside ceramic layer (version) - Google Patents

Abstract

FIELD: protective coatings. SUBSTANCE: invention relates to manufacturing high-temperature materials used to protect from oxidation and gas corrosion and as protective coatings for parts of gas turbines and internal combustion engines. Method involves electron-beam heating of ceramic ingot from stabilized zirconium dioxide installed in water-cooled crucible, its evaporation, and subsequent condensation of vapor stream on heated substrate in vacuum. As condensable material, mixture of metals (alloys) and oxides with different vapor pressure at evaporation temperature is used. Metal and oxide mixture represents compacted and vacuum- annealed rod and gradient coating itself is formed via consecutive evaporation and condensation of rod and ceramic ingot bearing the rod on its end from the same crucible. The following systems are advantageously used as mixtures for evaporation. EFFECT: improved protective characteristics. 10 cl, 5 dwg, 2 tbl, 4 ex

Description

Technical field
The invention relates to the field of high-temperature materials used to protect against oxidation and gas corrosion and as protective coatings for thermally loaded parts of gas turbines and internal combustion engines. In particular, the invention relates to the field of electron beam technology for producing protective coatings with a gradient of chemical composition and thickness structure (functionally gradient coatings - FG Coats) with an external ceramic layer on a substrate by evaporation and condensation of metals / alloys and chemical compounds (oxides) having different melting points and vapor pressure in a vacuum.

State of the art
Functionally gradient coatings are characterized by continuous (smooth) or intermittent (layered) changes in the chemical composition and structure along the thickness of the protective layer. The gradient of changes in chemical composition and structure can be obtained by various technological processes.

 A well-known example of a method for producing a protective coating (with a gradient of chemical and phase composition over the thickness of the protective layer) is a diffusion method for producing coatings using chemical-thermal treatment methods [Tamarin Yu.A., Heat-resistant diffusion coatings of GTE blades. - M., Mechanical Engineering, 1978, 134 pp.]. The main disadvantage of such protective coatings in view of the method of their preparation is the low thermal stability of the protective layer at high temperatures. These coatings also cannot provide thermal protection for gas turbine blades.

 Other methods for producing protective coatings are plasma spraying in air (APS), vacuum plasma spraying (VPS, LPPS), and electron beam deposition (EB-PVD) of coatings on the protected substrate. These coatings are classified as overlay or independent coatings.

 It is known [application PCT / US93 / 95005 dated 05/26/93 (WO 093/24676 dated 12/09/93)] the use of several plasmatrons in the application of heat-protective and wear-resistant coatings, when their formation is carried out by programmatically changing the operating modes of the plasmatrons controlled by a computer. As a result, a variable concentration of the hardening phase MeX (where X is oxygen) is achieved over the thickness of the applied layer from 0% at the substrate to an optimal value of 60-80-100% on the outer surface of the coating. This method requires large energy costs, it is very time-consuming, but the main disadvantage is the difficulty of stabilizing the plasma torch operating modes to accurately reproduce the required gradient of composition and structure along the thickness of the protective coating.

A method for producing a thick (δ ≤ 2 mm) gradient coating consisting of separate microlayers (δ ≈ 70 μm) of variable composition with a flat interface between the layers using a single plasma torch having two separate feeders is described in [S. Sampalh et al. Thermal spray processing of FGMs / MRS Bulletin. - 1995, 20, 1, p. 27-29]. It also provides an example of computer support for the operation of the plasma torch when applying gradient coatings of NiCr- (ZrO ₂ -8% Y ₂ O ₃ ) with 100% ceramic on the surface of the protective layer. The total coating thickness reaches 800 microns. However, such coatings are not durable, since the presence of flat boundaries between individual microlayers creates favorable conditions for the initiation of microcracks at these boundaries, their growth and, as a result, the delamination and destruction of the coating material during thermal cycling.

To increase the durability of heat-resistant coatings with a thickness of δ ≤ 250 μm obtained by plasma spraying in air (APS), the surface of the bonding layer, for example Ni-10Co-18Cr-6,5Al-0,3Y, is subjected to additional aluminization in order to obtain in the outer layer the structure of β- (Mi, Co) Al type intermetallic compound with an aluminum thickness gradient when the aluminum content on the surface reaches 26-30%. The specified technological technique increased the durability of the outer ceramic layer of the heat-shielding coating with a cyclic temperature change of 1135 ← → 50 ^o C (cycle time 1 hour) from 70 to 210-170 thermal cycles (hours) [Wortman DH et al. Bond coat development for thermal barrier coating. - Trans. ASME, J. Eng. for Gas Turbines & Power, - 1990, 12, 10, p. 527-530].

Similar, thickness-gradient coatings of MeCrALHf and MeCrALHfPt obtained by combining electron beam evaporation of standard MeCrAl alloys and subsequent ion deposition or cathodic sputtering of hafnium and platinum are described in US Pat. No. 4,123,595 of 10.31.78. U.S. Patent No. 4,101,715 of July 18, 78, proposes platinum plating on a CoCrAlY condensed coating followed by heat treatment in vacuum, which significantly increased the corrosion resistance of heat-resistant alloys having a gradient of platinum thickness distribution in the outer layer of CoCrAlYPt coating. Corrosion resistance of coatings containing platinum is improved due to the deterioration of wetting of the Al ₂ O ₃ film by molten salts. The disadvantage of the above methods for producing gradient corrosion-resistant coatings is the high thermal conductivity and insufficient heat resistance of the protective layer with multiple heat exchanges.

In a three-layer metal-ceramic coating of the MeCrAlY / ZrO ₂ -8% Y ₂ O _{3 type, in} order to increase the thermocyclic durability of the outer ceramic layer, an intermediate single-phase plastic layer 30–40 μm thick is introduced between the substrate to be protected and the main heat-resistant layer, providing an aluminum concentration gradient over the layer thickness from 3.5-5% at the surface of the protected alloy to 11-13% on the surface of the heat-resistant binder layer. This technical solution is implemented by sequential electron beam evaporation of alloys of different chemical composition from two independent sources in one vacuum chamber [UK patent N 2252567 from 09/11/91, German patent N 4103994 from 02/09/91, Italian patent N 1247155 from 02/07/91].

There is a method of producing a ceramic coating having high adhesion to a substrate (intermediate binder coating) using electron beam evaporation technology in vacuum [US patent N 4321311 from 03/23/82]. This patent describes the use of annealing parts with a Ni-Co-Cr-Al-Y bonding layer obtained by plasma spraying in air or vacuum-plasma spraying (APS, VPS) in wet hydrogen or low vacuum and the possible introduction of dispersed particles of oxide phases to increase its thermal stability during heat exchange. US Pat. Nos. 4,405,660 of 09/20/83 and Nos. 4,414,249 of 11/08/83 propose polishing the surface of a NiCoCrAlY binder layer obtained by vacuum-plasma spraying and treating it in an oxidizing atmosphere with a metered oxygen inlet to form a fine-grained, strongly bonded Al film substrate ₂ O ₃ with a thickness of 0.5 - 2.5 μm as a metal-ceramic transition zone before electron beam deposition of a ceramic thermal barrier layer ZrO ₂ -7% Y ₂ O ₃ with a thickness of 125 to 1250 μm.

The authors of US patents N 4880614 from 11/14/89 and N 5015502 from 05/14/91 to increase the durability of the thermal insulation coating with an external ceramic layer of partially stabilized zirconia obtained by electron beam deposition in vacuum, it is proposed to form an intermediate homogeneous non-porous interlayer of high-purity oxide Al ₂ O ₃ (1 μm thick) by chemical deposition methods (the method is not disclosed), while it is recommended to use laser fusion of the surface to obtain a gradient of the structure of the external heat-protective layer ty ceramic coating.

The above solutions are quite cumbersome in terms of technology and require the use of additional equipment and, most importantly, a long (4-8 hours) time to obtain the corresponding barrier layers in the form of α-Al ₂ O ₃ on the coating surface.

 In the publication [K. J. Schmilt-Thomas et al. Thermal barrier coatings with improved oxidation resistance / Suiface & Cont. Technology - 1994, 68/69, p. 113-115] the possibility of obtaining a barrier layer of aluminum oxide with a thickness of 2-5 microns by reactive spraying in vacuum from a separate source is considered. An oxide film is formed on the surface of heat-resistant coatings of the type Ni-Cr, Ni-Cr-Al, MeCrAlY (Co-31Ni-21Cr-8Al-0.3Y) obtained by LPPS methods. The specified technical solution provided an increase in the scale resistance of the binder layer and resistance to peeling of plasma-sprayed ceramic coatings of stabilized zirconia.

The closest in combination of features and therefore taken as a prototype method is described in US patent N 4676994 from 06.30.87, cl. B 05 D 3/06, C 23 C 11/00. MeCrAlY metal heat-resistant coating is applied to the surface to be protected in a certain way, which subsequently acts as an intermediate bonding layer. After thermomechanical processing of the specified MeCrAlY layer on the substrate, final cleaning and drying, the parts are placed in a coating unit and subjected to radiation heating. The heat source is the end face of a fully stabilized zirconia ZrO ₂ ingot (containing 20% yttrium oxide Y ₂ O ₃ ) installed in a water-cooled crucible heated by an electron beam before melting (excluding evaporation). The protected part is heated for 10 minutes with a metered oxygen injection so that an adaptive layer based on Al ₂ O ₃ oxide with a thickness of 0.5 - 2.5 μm is formed on its surface (the modification is indicated, but judging by the stated temperature of the condensation surface in in the range of 900 - 1200 ^o C, it can correspond to γ- and α-modifications of Al ₂ O ₃ ).

After performing the indicated technological operations, by varying the specific power deposited in the molten ceramic bath, by evaporation and subsequent condensation of the vapor stream, a gradient coating of stabilized zirconia with a different grain size and ceramic density in the protective layer is obtained. The density of the ceramic layer (δ = 2–3 μm) adjacent to the binder layer is 96% of the theoretical one and is achieved at a vapor deposition rate of 0.5 μm / min stoichiometric zirconia. The pressure of the injected gas (air or oxygen) should be in the range (0.1 - 10 • 10 ^-3 mm Hg).

 The method of forming protective coatings described above with a gradient of chemical composition and structure over thickness allows one to obtain two-, three-, or multilayer coatings, usually with flat metal / metal + oxide or oxide / oxide interfaces. The difference in the physicochemical properties of the layers, primarily thermal linear expansion coefficients (LTEC), Young's modulus, as well as irreversible oxidation reactions (gas corrosion) on the interface during operation cause premature destruction of coatings, mainly of the ceramic layer.

 Elimination or limitation of undesirable physical and chemical processes at the metal - ceramic interface can be achieved by creating protective coatings with a gradual (smooth) change in composition and structure during the transition from one layer to another. Such coatings can be obtained by condensation from the vapor phase by electron beam evaporation of multicomponent mixtures from a single source containing substances with different vapor elasticities at an evaporation temperature. In [G. Zinsmeister. The direct evaporation of alloys / Vakuum - Technik. - 1964, N 8, p. 233 - 237] it is shown that the evaporation of two-component melts always begins with the evaporation of a component having a higher vapor pressure. Then, as the amount of evaporated melt increases, evaporation of the component with a low vapor pressure begins. These differences are manifested the stronger, the higher the concentration of the element with high vapor pressure in the vaporized mixture. As a result of this sequence of changes in the composition of the vapor phase during evaporation and condensation on the substrate (coated part), a concentration gradient of the component is formed over the thickness of the coating. Thus, the layer adjacent to the substrate contains the maximum amount of a component with high vapor pressure.

 This phenomenon is used in the proposed method for producing protective coatings with a gradient of chemical composition and structure in thickness.

SUMMARY OF THE INVENTION
The task: to improve the known method of obtaining a protective coating with a gradient of chemical composition and structure by thickness by using a mixture of metals (alloys) and oxides having different vapor elasticity at an evaporation temperature as vaporized by electron beam heating from one crucible and condensed on a protected substrate .

 The problem can be solved using two variants of the method.

 According to the first embodiment, in a method for producing a protective coating on a substrate with a gradient of chemical composition and thickness structure with an external ceramic layer, comprising placing a stabilized zirconia ceramic ingot in a water-cooled crucible, electron beam evaporation and subsequent condensation of the vapor stream on a heated substrate, according to the invention preliminarily pressed the head from a mixture of metals (alloys) and oxides having different vapor pressure at the evaporation temperature, anneal it in vacuum and placed on the end face of the ceramic ingot, followed by sequential electron beam evaporation of the staff and the ceramic ingot.

 According to a second embodiment, in a method for producing a protective coating on a substrate with a gradient of chemical composition and thickness structure with an external ceramic layer comprising electron beam evaporation of a material placed in a water-cooled crucible and condensation of a vapor stream on a heated substrate in vacuum, according to the invention, as vaporized The material used is a beam pre-compressed from a mixture of metals and oxides having different vapor pressure at an evaporation temperature and annealed in vacuum.

To effect condensation at a lower temperature of the substrate without deterioration of adhesion, the Al-A ₂ O ₃ -ZrO ₂ system is preferably used as the vaporized mixture, in the following ratio, wt.%:
Al - 5-4
Al ₂ O ₃ - 1-60
ZrO ₂ - Else
To improve the wettability of the substrate with a condensable material, it is preferable to use the Al-Si-Y-Al ₂ O ₃ -ZrO ₂ system as the vaporized mixture, in the following ratio, wt.%:
Al - 5-40
Si - 0.3-3
Al ₂ O ₃ - 3-84
Y - 0-1.5
ZrO ₂ - Else
To increase the reliability of the adhesive coating as an evaporated mixture, it is preferable to use the system Al-Cr-Ni-Al ₂ O ₃ Y-ZrO ₂ , in the following ratio, wt.%:
Al - 2 - 18,
Cr - 5 - 40,
Ni - 0 - 40,
Al ₂ O ₃ - 2 - 58,
Y - 0 - 1.5,
ZrO ₂ - Else
To increase the corrosion resistance of the gradient coating, it is preferable to use the Al-Cr- (Ni, Co) -Al ₂ O ₃ Y-Pt-ZrO ₂ system as the vaporized mixture, with the following ratio of components wt.%:
Al - 4 - 12,
Cr - 10 - 25,
Ni - 25 - 45
Co - 25 - 45,
Al ₂ O ₃ - 1 - 60,
Y - 0.5 - 2.5,
Pt - 0.5 - 2.5,
ZrO ₂ - Else
The coating systems proposed above are canonical in the corrosion protection of products operating at high temperatures in aggressive gas flows.

In the Al-Al ₂ O ₃ ZrO _{2 system, the} predominant evaporation of aluminum at the first moment of exposure of the electron beam to the beam made it possible to carry out condensation at a temperature of 30 - 50 ^o C below normal without deterioration of adhesion. The presence of aluminum in the inner layer of the gradient coating compensated for the partial dissociation of Al ₂ O ₃ at the initial moment during electron-beam heating, which improved the sintering ability of a thin oxide layer of Al ₂ O ₃ , smoothly passing through the eutectic point to a zirconia layer with high erosion resistance and heat insulating effect even in small (3-5 microns) thicknesses. A thin layer of zirconia is characterized by a fine-grained structure and high fracture toughness and has a stable chemical bond with Al ₂ O ₃ in the solid state.

When using the Al-Si-Y-Al ₂ O ₃ -ZrO _{2 system,} small additions (1-3%) of silicon primarily improve the wettability of the substrate with a condensable material, which increased the adhesion of the coating on high-temperature nickel alloys. In these amounts, silicon increases the resistance to gas corrosion of the diffusion zone by the substrate-gradient coating, and in combination with Al ₂ O ₃ oxide, it provides a two-three-fold increase in the durability of the gradient condensed coating under heat-exchange conditions at a maximum ambient temperature (gas stream) of 1100-1150 ^o C .

However, the diffusion of silicon into protected substrates from superalloys can reduce the creep resistance of the substrate-coating diffusion zone material; therefore, another composition is proposed for stable operation at high temperature: Al-Cr-Ni-Y-Al ₂ O ₃ -ZrO ₂ , which has an extremely high reliability when used as a bonding layer in the construction of heat-protective coatings, when the outer ceramic layer passes into a thermal barrier, obtained by sequential evaporation of the staff and the ceramic ingot from partially bilizirovannogo zirconia standard chemical composition ZrO ₂ - (7-8)% Y ₂ O _3.

A significant increase in the corrosion resistance of the gradient coating is achieved by the additional introduction of 0.5 - 2.5% platinum (Al- (Ni, Co) -Cr-Al ₂ O ₃ -Y-Pt-ZrO _{2 system} ) into the vaporized mixture, especially in media containing chloride and sodium sulfate. The addition of platinum 1.5-2 times increased the resistance to salt corrosion of gradient coatings, stabilizing the protective functions of the ceramic layer Al ₂ O ₃ -ZrO ₂ and limiting the diffusion mobility of individual components in the gradient structure of the condensed protective coating obtained by evaporation directly from the staff.

 Evaporation in vacuum of a given amount or final portion of heat-resistant materials with different vapor elasticities from one source is the most acceptable way to obtain coatings with a gradient structure, in particular, to obtain heat-protective coatings with an external ceramic layer.

 A smooth gradient of the chemical composition and structure of the protective layer in thickness ensures better coordination of the thermophysical characteristics (thermal coefficient of linear expansion, Young's modulus, etc.) of the structural components of a heat-resistant (corrosion-resistant) or heat-protective coating of stabilized zirconia. This made it possible to obtain high corrosion and thermocyclic durability of parts made of heat-resistant alloy with a gradient protective coating.

Upon evaporation of a bobbin alone from a separate source (crucible), a thin (δ ≈ 5-8 μm) gradient protective coating with an external layer of zirconia is characterized by high density, reliable adhesion to the surface to be protected and resistance to abrasive wear, and low roughness (R _a <0, 5 μm) of the surface of the ceramic layer.

Brief List of Drawings
The technical nature and principle of operation of the invention is illustrated by examples with reference to the accompanying drawings.

FIG. 1 shows the distribution curves of individual components over the thickness of a condensed protective coating with a gradient composition and structure obtained by direct evaporation of a sintered bead made from a mixture of components 13% Al-7% Al ₂ O ₃ -80% (ZrO ₂ -7% Y ₂ O ₃ ) - example 1; FIG. 2 - the same for the initial coating with a gradient composition and structure obtained by evaporation of the sintered bead, the components of which are selected in the ratio: 13% Al-1% Si-7% Al ₂ O ₃ -79% (ZrO ₂ -7% Y ₂ O ₃ ) - example 2; FIG. 3 - the same for the initial coating with a gradient composition and structure obtained by evaporation of the sintered bead, the components of which are selected in the ratio: 8% -Al-25% Cr-33% Ni-3% Al ₂ O ₃ -1% Y-30% (ZrO ₂ -7% Y ₂ O ₃ ) - example 3; FIG. 4 - the same for the initial coating with a gradient composition and structure obtained by evaporation of the sintered bead, the components of which are selected in the ratio: 8% Al-40% Co-15% Cr-2.5% Al ₂ O ₃ -0.8% Y -1.7% Pt-32% (ZrO ₂ -7% Y ₂ O ₃ ) - example 4; FIG. 5 depicts the thermocyclic durability of protective coatings with a gradient of chemical composition and thickness structure, having an external ceramic layer obtained by sequential evaporation of piles and a ceramic ingot of partially stabilized zirconia ZrO ₂ -7% Y ₂ O ₃ , on the end of which piles of various chemical composition were installed (examples 1, 2, 3), and the evaporation was carried out from one crucible.

DETAILED DESCRIPTION OF THE INVENTION
Using the effect of fractionation of a mixture of components of a certain composition in the process of its electron-beam heating in a single evaporator (crucible), condensed coatings having a variable chemical composition and structure in thickness were obtained. The initial coating layers adjacent to the substrate are enriched with a more volatile component, in the case under consideration heat-resistant and heat-protective coatings - aluminum and chromium. In the outer layers of coatings of this type, components with a lower vapor pressure and a higher melting point, for example silicon, aluminum oxides, cerium, yttrium, and a plate, predominate.

At the final stage of implementation, the predominant evaporation and condensation of substances with the highest melting point: yttrium oxide, zirconium dioxide. Since ZrO ₂ -7% Y ₂ O ₃ powder is used at the molecular level as zirconia dioxide, in this case, vaporization and vapor deposition of the ZrO ₂ -Y ₂ O ₃ ceramics of the initial composition take place.

 The mass of components of the evaporated mixture, pressed into a staff, is selected based on the required coating thickness. Stabik is pre-sintered and degassed in a vacuum.

 The last portions of oxide, in particular zirconium dioxide, condensing on the surface to be protected, can continuously (without a sharp gradient in composition and structure) transfer (transform) into a ceramic heat-insulating layer with a thickness of up to 250 μm (1350-150 μm), provided that the fixed staff is located at the end a ceramic ingot of stabilized zirconia placed in a water-cooled crucible. The evaporation of the ceramic ingot begins simultaneously with the completion of the evaporation of the billet.

The essence of the invention is illustrated by experimental data demonstrating the formation of coatings with a gradient of chemical composition and structure by thickness during the evaporation of pressed and sintered metal powders, heat-resistant alloys and oxides. Gradient coatings with a thickness of 6–8 μm were obtained on stationary substrates by evaporation and condensation of tablets weighing 6–15 g, and coatings of the same thickness with an external ceramic layer 135–150 μm thick were obtained on rotating substrates by evaporation of beads weighing 30–45 g and a standard ceramic ingot ZrO ₂ -7% Y ₂ O ₃ (initial density 4 ± 0.4 g / cm ³ ) for subsequent thermal cyclic tests of finger samples.

To obtain heat-resistant gradient coatings, the vapor phase was deposited on substrates of the EP-99 nickel alloy (see table 1). The substrates were used either without any intermediate coating or with a heat-resistant coating of Ni-11Co-18Cr-11Al- (Y). The temperature of the substrates was 850 - 900 ^o C.

When applying coatings to substrates rotating in a steam stream according to the claimed method, certain requirements are imposed on the quality of surface preparation of these substrates. The roughness R _a should not exceed 0.6 μm, more preferably 0.25 - 0.3 μm, which is achieved by surface treatment with standard grinding papers with abrasive N 320, N 500 or polishing washers.

The thermal cyclic durability of heat-resistant coatings with a gradient composition and structure obtained by evaporation from a single source was evaluated by testing finger samples from heat-resistant alloys (ZhS) EP-958 and Hastelloy-X (see table 1) in air at a maximum temperature of 1135 ^o C, the oxidation time in one cycle was 24 hours. Samples taken from the furnace were cooled with an intense air stream with a cooling rate of about 185 deg / min to room temperature (within 6-10 minutes). The time (the number of heat exchanges) was fixed before the destruction of the outer ceramic layer, which corresponded to the appearance of a corrosion spot or a branched microcrack visible to the naked eye, or ceramic detachment from 10% of the working surface of the samples.

 The nature of the gradient distribution of the components over the thickness determines the reliability and durability of the coatings: the obtained high functional characteristics of the coatings are an important indicator of the effectiveness of the proposed method.

Example 1: Al-Al ₂ O ₃ —ZrO _{2 system} .

A mixture of three components, 13% Al-7% Al ₂ O ₃ -80% (ZrO ₂ -7% Y ₂ O ₃ ) in the form of sticks weighing 6 g and 28 g, placed respectively in a copper water-cooled crucible and on the upper end of a ceramic ingot (⌀ 70 mm) from partially stabilized zirconia ZrO ₂ -7% Y ₂ O ₃ , also installed in a water-cooled crucible, was evaporated by direct exposure to an electron beam. Condensation was carried out in the first case (6 g bead) on a flat stationary substrate of EP-99 alloy. In the first case (28 g stock), the vapor stream was deposited onto rotating finger samples (⌀ 8 mm) from Hastella-X alloy. Using a CAMEBAX X-ray microanalyzer, a characteristic gradient distribution of the components over the thickness of the deposited coating was established (Fig. 1). At the presented concentrations of the distribution curves of the components, a smooth transition from aluminum to alumina and zirconia is observed. A metallographic study of the microstructure of the coating in cross section using a CAMSCAN scanning electron microscope, as expected, did not reveal the implementation of flat interfaces between Al ₂ O ₃ and ZrO ₂ • Y ₂ O ₃ .

In the second variant of coating deposition (on finger samples) during continuous evaporation of the bead and then the ceramic ingot, no interface was found in the zone corresponding to the completion of the bead evaporation and the beginning of the direct evaporation of the ZrO ₂ -7% Y ₂ O ₃ ceramic ingot. The total thickness of the thermal barrier layer was 135-150 μm (in two different experiments).

Finger samples with a gradient coating, including an external ceramic layer, were tested for thermocyclic durability according to the regime of 1135 ^o C ← → 50 ^o C (Fig. 5).

The gradient coating Al-Al ₂ O ₃ -ZrO _{2 was also} successfully implemented with a decrease in the content of zirconium dioxide to zero values (see Table 2). Coatings of the Al-Al ₂ O ₃ -ZrO _{2 system} can be effectively used to protect titanium alloys, for example VT-6C.

Example 2: system: Al-Si-Al ₂ O ₃ -Y-ZrO ₂ .

Silicon in an amount of 1-3% significantly increases the resistance to gas corrosion in coatings used to protect turbine blades using contaminated fuel. A mixture of four components, 13% -Al-1% Si-7% Al ₂ O ₃ -79% (ZrO ₂ -7% Y ₂ O ₃ ) is the same as in example 1, in the form of racks weighing 6 g and 30 g of the evaporator in the sequence analogous to example 1. The obtained distribution of the components over the thickness of the deposited coating is shown in FIG. 2 (in this case, gradient coatings were deposited on a substrate having a Ni-22Co-20Cr-11Al (Y) adhesive coating). Silicon evaporates from the staff following metallic aluminum almost simultaneously with Al ₂ O ₃ .

As a result of evaporation of the billet placed on the ZrO ₂ -7% Y ₂ O ₃ ceramic ingot in the gradient coating, no intermediate interfaces were found and an external thermal barrier layer with a thickness of up to 125-130 μm was formed directly after the evaporation of zirconia from the billet.

 In this embodiment of the gradient coating, cerium oxide may be used instead of alumina.

Example 3: system: Al — Cr — Ni — Al ₂ O ₃ —Y — ZrO ₂ .

A mixture of components containing 8% -Al-25% Cr-33% Ni-3% -Al ₂ O ₃ -1% Y-30% (ZrO ₂ -7% Y ₂ O ₃ ) in the form of racks weighing 15 g and 45 d was evaporated by direct exposure to an electron beam, similarly to the cases described above, and condensed onto stationary substrates.

The distribution of the components over the thickness of the gradient coating obtained by evaporation of the bead and ZrO ₂ - 7% Y ₂ O ₃ ingot is shown in FIG. 3. A characteristic peak is observed corresponding to alumina with a smooth transition to zirconium dioxide. The concentrated yttrium maximum falls on the branch of the curve of increasing concentration of zirconium dioxide in the outer layer of the gradient coating. The data of FIG. 3 confirm the absence of sharp interfaces between the individual coating zones in thickness.

The data of thermocyclic tests of finger samples (Fig. 5) confirmed the possibility of practical application of such a coating system. In the case of evaporation of the head and ZrO ₂ ceramic ingot - 7% Y ₂ O ₃ from one source, when the head was placed on the end of the ingot in one evaporator, the delamination of the ceramic thermal barrier layer in the conventional form was not obtained. Foci of corrosion damage (⌀ 2-3 mm) occurred in the ceramic thermal barrier coating after 1070 hours of testing.

 Localized, slowly proceeding corrosion of the gradient coating under the ceramic layer with a total area damage of not more than 5-6% was obtained on the surface of finger samples after ~ 1800 hours of testing (after which the tests were stopped).

The durability of condensed thermal barrier ceramic coatings ZrO ₂ - Y ₂ O ₃ on gradient coatings obtained by the present method from a single source is two to three times higher than the durability of two-layer metal / ceramic ceramic coatings obtained by standard industrial technology.

Example 4: system: Al- (Ni, Co) -Cr-Al ₂ O ₃ -Y-Pt-ZrO ² /
Platinum was introduced into the mixture (staff) of evaporated materials as a component that increases the heat resistance of protective coatings. Stackes weighing 15 g were evaporated from a water-cooled copper crucible onto a stationary substrate. The mixture of the starting components contained: 8% Al-40% Co-15% Cr-2.5% Al ₂ O ₃ -0.8% Y-1.7% Pt-32% (ZrO ₂ -7% Y ₂ O ₃ ) Distribution curves of individual elements in a platinum-containing gradient coating, obtained by X-ray microanalysis and shown in FIG. 4 show the presence of platinum in a layer adjacent to the outer ZrO ₂ layer. Coatings of this type can be recommended for surface protection in oxidative and erosion-active gas flows. The deposition of a thick ceramic layer of ZrO ₂ turns these coatings into heat-shielding.

Industrial applicability
The greatest effect of applying the method according to the invention is expressed when obtaining protective coatings with a smooth gradient of chemical composition and thickness structure with an external ceramic layer on the substrate, when high quality and reliability of the formation of thermal barrier protective coatings with increased corrosion resistance under conditions of frequent heat exchange are required.

Claims (3)

 1. The method of obtaining a protective coating on the substrate with a gradient of chemical composition and structure in thickness with an external ceramic layer, comprising placing a stabilized zirconia ceramic ingot in a water-cooled crucible, electron beam evaporation and subsequent vapor stream condensation on a heated substrate in vacuum, characterized in that preliminarily extruded a staff from a mixture of metals or alloys and oxides having different vapor pressure at an evaporation temperature, anneal it in a vacuum and place it on end of ceramic ingot, followed by successive electron beam evaporation of bars and ceramic ingot. 2. The method according to p. 1, characterized in that the head is pressed from a mixture containing Al-Al ₂ O ₃ - ZrO ₂ , in the following ratio, wt.%:
Al - 5 - 40
Al ₂ O ₃ - 1 - 60
ZrO ₂ - Else
3. The method according to p. 1, characterized in that the staff is pressed from a mixture containing Al-Si-Y-Al ₂ O ₃ -ZrO ₂ in the following ratio, wt.%:
Al - 5 - 40
Si - 0.3 - 3
Y - Up to 1.5
Al ₂ O ₃ - 3 - 84
ZrO ₂ - Else
4. The method according to p. 1, characterized in that the head is pressed from a mixture containing Al-Cr-Ni-Al ₂ O ₃ -Y-ZrO ₂ , in the following ratio, wt.%:
Al - 2 - 18
Cr - 5 - 40
Ni - Up to 40
Al ₂ O ₃ - 2 - 58
Y - Up to 1.5
ZrO ₂ - Else
5. The method according to p. 1, characterized in that the head is pressed from a mixture containing Al-Cr- (Ni, Co) -Al ₂ O ₃ -Y-Pt-ZrO ₂ , in the following ratio, wt.%:
Al - 4 - 12
Cr - 10 - 25
Ni, Co - 25 - 45
Al ₂ O ₃ - 1 - 60
Y - 0.5 - 2.5
Pt - 0.5 - 2.5
ZrO ₂ - Else
6. A method of producing a protective coating on a substrate with a gradient of chemical composition and thickness structure with an external ceramic layer, comprising electron beam evaporation of a material placed in a water-cooled crucible and condensation of a vapor stream on a heated substrate in a vacuum, characterized in that as evaporated The material used is a staff pre-compressed from a mixture of metals and oxides having different vapor elasticities at the evaporation temperature, and annealed in vacuum. 7. The method according to p. 6, characterized in that the staff is pressed from a mixture containing Al-Al ₂ O ₃ -ZrO ₂ in the following ratio, wt.%:
Al - 5 - 40
Al ₂ O ₃ - 1-60
ZrO ₂ - Else
8. The method according to p. 6, characterized in that the staff is pressed from a mixture containing Al-Si-Y-Al ₂ O ₃ -ZrO ₂ in the following ratio, wt.%:
Al - 5 - 40
Si - 0.3 - 3
Y - Up to 1.5
Al ₂ O ₃ - 3 - 84
ZrO ₂ - Else
9. The method according to p. 6, characterized in that the head is pressed from a mixture containing Al-Cr-Ni-Al ₂ O ₃ -Y-ZrO ₂ , in the following ratio, wt.%:
Al - 2 - 18
Cr - 5 - 40
Ni - Up to 40
Al ₂ O ₃ - 2 - 58
Y - Up to 1.5
ZrO ₂ - Else
10. The method according to p. 6, characterized in that the staff is pressed from a mixture containing Al-Cr- (Ni, Co) -Al ₂ O ₃ -Y-Pt-ZrO ₂ , in the following ratio of components, wt.%:
Al - 4 - 12
Cr - 10 - 25
Ni, Co - 25 - 45
Al ₂ O ₃ - 1 - 60
Y - 0.5 - 2.5
Pt - 0.5 - 2.5
ZrO ₂ - Else

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