Wear-resistant coating

Abstract

The present invention relates to a wear-resistant coating for a turbine, the wear-resistant coating comprising an inorganic compound having a Mohs hardness equal to or less than 6 and a melting temperature greater than 450 °C or even 800 °C, and a polymer compound in an amount between 40 vol% - 70 vol%.

Description

Technical Field

[0001] The present invention relates to a wear-resistant coating for a turbine, as well as a turbine module and a turbine including such a wear-resistant coating.

[0002] Such a wear-resistant coating can be used for any type of turbine, especially civil or military turbojet engines. In particular, such a wear-resistant coating is particularly useful in an environment where the temperature is up to 450 °C. Background Art

[0003] In many rotating machines, it is known to provide wear-resistant tracks on a stator ring opposite the tips of rotor blades.

[0004] Such tracks are made of a "wear-resistant" material that wears when the rotating blades contact these tracks.

[0005] This ensures a minimum clearance between the rotor and the stator, limits air leakage and improves the performance of the rotating machine, and there is no risk of damaging the blades if they rub against the stator.

[0006] The performance of a turbojet engine depends to a large extent on the control of these clearances between the stator and the rotor. For example, the clearance between the tip of the blade and the wear-resistant track must be kept to a minimum to reduce the pumping margin of the rotating machine.

[0007] In the case of a large diameter, these clearances can be effectively controlled by the wear-resistant tracks.

[0008] In the air duct, the clearance is reduced by the blade contacting the wear-resistant track. When contact is formed, the frictional force of the blade on the stator wears the wear-resistant track, and the blade follows its path with a minimum clearance opening. Therefore, the diameter of the stator ring is automatically adjusted to be as close to the rotor as possible.

[0009] Outside the air duct, a series of sliding pieces are machined into the rotor and pass through the wear-resistant track to form a labyrinth for air flow. This labyrinth has a sealing effect.

[0010] Currently, the wear-resistant seals used in the engine area where the temperature is lower than 450 °C are wear-resistant coatings based on an aluminum-silicon alloy (Al-Si) combined with a polyester-type polymer or a ceramic of hexagonal boron nitride (h-BN) type.

[0011] However, the corrosion resistance of these wear-resistant coatings is poor. The friction of the blade on the coating causes the generation of aluminum hydroxide compound (Al(OH)3), which causes the expansion of the wear-resistant coating, thereby causing delamination in the coating. These delaminations are clearly shown in Figure 1 shown in Figure 1Shows a wear-resistant coating 11 on a substrate 12. These coatings will next lose their wear-resistant function.

[0012] In addition, these wear-resistant coatings have poor wear resistance at low intrusion speeds.

[0013] Figure 2 Shows a wear map of an Al-Si and polymer-based wear-resistant coating obtained by a friction blade. This wear map shows the function of the rate of intrusion (Ti) into the wear-resistant coating varying with the blade speed (V). In this figure, region A corresponds to the transfer region of the coating on the blade, region B corresponds to the grooving region of the wear-resistant coating with weak transfer of aluminum on the blade, region C corresponds to the grooving region with micro-incisions of the wear-resistant coating, and region D corresponds to the region worn by fusion. The arrow indicates the wear mode when the wear-resistant coating is porous.

[0014] At low intrusion speeds (about 10 μm / s), we observe the transfer of the wear-resistant coating to the blade ( Figure 2 regions A and B), and thus excessive penetration (e.g., 246% penetration) and the appearance of grooves, as Figure 2 shown. These transfers result in a major loss of engine performance.

[0015] Therefore, there is indeed a need for wear-resistant coatings for turbines, turbine modules, and turbines including such wear-resistant coatings that do not have, or at least do not partially have, the inherent drawbacks of the above-known structures.

[0016] The object of the present invention is to propose a solution that can remedy at least some of these drawbacks. Summary of the Invention

[0017] To this end, the present invention relates to a wear-resistant coating for a turbine, which comprises an inorganic compound having a Mohs hardness less than or equal to 6 and a melting temperature greater than 450 °C and even 800 °C, and a polymer compound with a content of 40 vol% - 70 vol%.

[0018] In the present disclosure, "inorganic compound" refers to a solid compound having an ordered atomic structure and a definite chemical composition. In particular, such an inorganic compound may have a crystal structure characterized by the arrangement of its atoms according to a given periodicity and symmetry (crystal system and space group of the inorganic compound).

[0019] In the present disclosure, unless otherwise specified, the terms "lower than" and "higher than" should be understood in a broad sense, i.e., representing "less than or equal to" and "greater than or equal to" respectively.

[0020] The wear-resistant two-component polymer / inorganic coating according to the present invention advantageously has corrosion resistance and anti-grooving properties. In fact, due to their physicochemical properties, the polymer compound and the inorganic compound do not corrode.

[0021] The coating according to the invention provides very good wear resistance and generates low aerodynamic losses. This wear-resistant coating has a low production cost and offers a wide range of processing possibilities.

[0022] At a temperature below or equal to 450 °C, or even 350 °C, this wear-resistant coating can operate properly on the engine without time limit. In fact, the polymeric compound can withstand this temperature without reducing the wear resistance of the coating, and the inorganic compound can remain thermally stable up to 450 °C, or even 800 °C.

[0023] This wear-resistant coating has high-temperature stability, making it suitable for turbine modules exposed to high temperatures, such as high-pressure compressors and low-pressure compressors.

[0024] During engine operation, blades flush with or penetrating the wear-resistant coating can generate dust that may explode. The wear-resistant coating composed of polymers and inorganic substances according to the invention has a great lack of aluminum, which greatly reduces the sensitivity of the dust to self-explosion.

[0025] In addition, the wear debris is inert, which reduces its impact on the downstream components of the turbine. This coating reduces the risk of clogging the cooling channels of the module.

[0026] The inorganic compound is stable up to at least 450 °C, and possibly up to 800 °C.

[0027] By "stable" it is meant that when the inorganic compound is heated from room temperature to the relevant temperature, there is no change in physical state (such as melting or phase change) or chemical change (such as oxidation).

[0028] According to the invention, the inorganic compound can be selected from: calcium fluoride, hydroxyapatite, lanthanum phosphate, diatomaceous earth, muscovite or barium sulfate. These inorganic compounds are advantageously stable up to at least 450 °C, even 900 °C, and have a hardness suitable for providing satisfactory wear resistance, while exhibiting low roughness.

[0029] The polymeric compound can be a polyester, such as a liquid crystal, or a projectable polymer (i.e., a polymer that can be projected, especially a polymer that can be projected by thermal spraying).

[0030] Preferably, the porosity of the wear-resistant coating is less than 5%.

[0031] Porosity is defined as the ratio of the volume of voids present in the material to the total volume of the material. Due to the reduction of porosity, even without surface treatment, the roughness of the coating is reduced, which limits the aerodynamic losses.

[0032] The wear-resistant coating is preferably insoluble in water and acetone. The wear-resistant coating may be insoluble or slightly soluble in alcohol.

[0033] The invention also relates to a turbine module, which comprises:

[0034] - a rotor provided with a plurality of moving blades,

[0035] - a stator, and

[0036] - at least one wear-resistant coating according to the invention, provided at the interface between a part of the rotor and a part of the stator.

[0037] The module may be a high-pressure compressor or a low-pressure compressor for a turbine. The temperature in the module or in a compressor of this type is preferably below 350 °C.

[0038] The turbine module may include at least one underlying layer with a roughness Ra between 9 μm and 40 μm, which is preferably below the wear-resistant coating and above the said part of the rotor and the said part of the stator. This underlying layer enables the wear-resistant coating to adhere better to the substrate to be coated. Advantageously, the rougher the underlying layer, the better the adhesion of the wear-resistant coating.

[0039] Advantageously, the rough underlying layer is located between the said part of the stator and the wear-resistant coating.

[0040] The rough underlying layer may be composed of nickel-aluminum alloy or nickel-chromium-aluminum alloy.

[0041] The invention also relates to an aircraft turbine comprising a module according to the invention.

[0042] The invention also relates to a method for manufacturing a wear-resistant coating according to the invention, which method comprises the following steps:

[0043] - mixing a powder of an inorganic compound with a Mohs hardness less than or equal to 6 and a melting temperature greater than 450 °C, even 800 °C, with a powder of a polymer compound,

[0044] - forming a wear-resistant coating from the powder mixture, wherein the content of the polymer compound is 40 vol% - 70 vol% of the wear-resistant coating, and

[0045] - applying the wear-resistant coating to the interface between a part of the rotor with a plurality of moving blades of the turbine module and a part of the stator of the turbine module.

[0046] This ensures the chemical stability of the coating at up to at least 450 °C.

[0047] The wear-resistant coating can be formed by single-injection thermal spraying or double-injection thermal spraying, or by extrusion, or by hot molding. In particular, the wear-resistant coating can be obtained by double-injection thermal spraying for two components or by single injection in the case of premixed powder.

[0048] The application of the wear-resistant coating is carried out by bonding to the adhesive film or by direct injection between a part of the rotor and a part of the stator. At least one surface in contact with the adhesive is preferably roughened by appropriate treatment.

[0049] Then, the wear-resistant coating can be machined by turning and / or milling and / or grinding.

[0050] The process may further include the step of applying a base layer with a roughness Ra between 9 μm and 40 μm, preferably applying a base layer with a roughness Ra between 9 μm and 40 μm above the rotor part and the stator part and below the wear-resistant coating.

[0051] The rough base layer can be composed of nickel-aluminum alloy or nickel-chromium-aluminum alloy.

[0052] The rough base layer can be deposited on a part of the stator by plasma spraying in the area. In this case, the roughness Ra of the base layer can be 10 μm.

[0053] Alternatively, the rough base layer can be deposited on a part of the stator by arc wire spraying. In this case, the roughness Ra of the base layer is 40 μm. Description of the Drawings

[0054] After referring to the accompanying drawings and reading the following non-limiting example description, the present invention will be better understood, and further details, features, and advantages of the present invention will become clearer, wherein:

[0055] Already described Figure 1 Shows the microstructure of the wear-resistant coating composed of Al-Si and polyester after cyclic corrosion testing,

[0056] Already described Figure 2 Shows the wear map of the wear-resistant coating composed of Al-Si and polymer obtained by friction with the blade,

[0057] Already described Figure 3 Shows the traces left by the blade on the wear-resistant coating composed of Al-Si and h-BN after wear resistance testing,

[0058] Figure 4 Shows an axial sectional view of a turbine according to the present invention,

[0059] Figure 5 Shows a perspective view of a turbine according to the present invention,

[0060] Figure 6 Shows a front view of a turbine module according to the present invention,

[0061] Figure 7 Graph showing the variation of the corrosion resistance and anti-grooving properties of a wear-resistant coating according to the present invention with the ratio between an inorganic compound and a polymer compound,

[0062] Figure 8 Illustrates a dual-injection thermal spraying device,

[0063] Figure 9 and 10 Represents the microstructure of a wear-resistant coating composed of hydroxyapatite and polyester according to the present invention, and

[0064] Figure 11 Represents the traces left by the blade on a wear-resistant coating composed of hydroxyapatite and polyester according to the present invention after a wear resistance test.

[0065] Elements having the same function in different embodiments are provided with the same reference numerals in the figures. Detailed Description

[0066] Figure 4 and Figure 5 Illustrates a twin-spool turbojet engine 1 extending along a main axis A, which constitutes an example of a turbine according to the present invention. The turbojet engine 1 includes, from upstream to downstream in the direction of the air flow indicated by the arrow F, a fan 2, a low-pressure compressor 3, a high-pressure compressor 4, a combustion chamber 5, a high-pressure turbine 6, and a low-pressure turbine 7. The low-pressure compressor 3 and the high-pressure compressor 4 have several compression stages.

[0067] The rotor of each compression stage includes a plurality of moving blades, which are mounted on a disk connected to the high-pressure shaft of the turbojet engine 1. A shroud connects the disk to the disk of the previous stage.

[0068] The stator of each stage includes a shroud disposed opposite the moving blades of the rotor, and a plurality of fixed blades disposed opposite the rotor shroud. The shroud of the stator has a wear-resistant track, against which the outer ends of the moving blades of the rotor rub.

[0069] In Figure 5 and Figure 6 the contact area 8 between the moving blade 9 of the rotor 13 and the wear-resistant track 14 of the stator 15 is particularly visible. The wear-resistant track 14 engages the top of the blade 9 of the rotor 13. The contact area 8 corresponds to the clearance between the top of the blade 9 of the rotor 13 and the wear-resistant track 14.

[0070] An example of a wear-resistant coating for forming these wear-resistant tracks will now be described.

[0071] The wear-resistant coating comprises an inorganic compound and a polymer compound. More specifically, the wear-resistant coating may consist of an inorganic compound and a polymer compound. Except for any impurities, this wear-resistant coating does not include any other components. In particular, this wear-resistant coating does not include metal compounds.

[0072] The Mohs hardness of the inorganic compound is less than or equal to 6, and the melting temperature is greater than 450 °C, even 800 °C. In other words, the inorganic compound is stable at least up to 450 °C or 800 °C.

[0073] The inorganic compound may be selected from: calcium fluoride (CaF2), hydroxyapatite (Ca 10 (PO4)6(OH)2), lanthanum phosphate (LaPO4), diatomaceous earth (SiO2), muscovite (KAI2(AlSi3O 10 )(OH,F)2) or barium sulfate (BaO4S).

[0074] Hydroxyapatite has a hexagonal crystal system and a 6 / m space group. This inorganic compound is stable up to at least 900 °C and has a Mohs hardness of 5. In addition, this inorganic compound is insoluble in water, acetone and alcohol.

[0075] The polymer compound can be a polyester, such as a liquid crystal, or a sprayable polymer, such as a thermal spray polymer.

[0076] The volume average polymer compound content of the wear-resistant coating is between 40% and 70%.

[0077] The proportion of the polymer compound in the wear-resistant coating depends on the function of the engine component. For example, the polyester content of the wear-resistant coating for a high-pressure compressor is low (about 40 vol% of the wear-resistant coating), while the polyester content for a low-pressure compressor is high (about 70 vol% of the wear-resistant coating).

[0078] Figure 7 The corrosion resistance (R e ), i.e., the corrosion resistance property, and the grooving resistance (R S ), i.e., the grooving resistance property, of the wear-resistant coating are shown as a function of the ratio (R P ) between the inorganic compound and the polymer compound.

[0079] For a wear-resistant coating containing 0%-80% of the polymer compound and 20%-100% of the inorganic compound, the grooving resistance R S (represented by curve a) is stable, while the corrosion resistance R e(represented by curve b) increases as the percentage of the polymer compound in the wear-resistant coating increases (the polymer compound in the wear-resistant coating ranges from 0% by volume to 80% by volume), and thus increases as the percentage of the inorganic compound in the wear-resistant coating decreases (the inorganic compound in the wear-resistant coating ranges from 100% by volume to 20% by volume).

[0080] In Figure 7 , region Z1 corresponds to the optimal percentage of the polymer compound in the wear-resistant coating. This region Z1 ranges from 40% to 70% by volume of the polymer compound in the wear-resistant coating. The wear-resistant coating including such a volume percentage of the polymer compound exhibits optimal corrosion resistance and anti-grooving performance.

[0081] The wear-resistant coating according to the present invention does not contain more than 70% by volume of the polymer compound. In fact, when the polymer compound in the wear-resistant coating exceeds 70% by volume, the adhesion of the wear-resistant coating to the substrate will be insufficient, especially in the case where the wear-resistant coating is obtained by thermal spraying. In Figure 7 , region Z2 corresponds to the percentage of the above-mentioned polymer compound in the wear-resistant coating, and for such a percentage, the wear-resistant coating does not have sufficient adhesion to the substrate.

[0082] The wear-resistant coating according to the present invention does not contain less than 40% by volume of the polymer compound. In fact, when the polymer compound in the wear-resistant coating is less than 40% by volume, the corrosion resistance of the wear-resistant coating will be insufficient. In Figure 7 , region Z3 corresponds to the percentage of the above-mentioned polymer compound in the wear-resistant coating, and for such a percentage, the corrosion resistance of the wear-resistant coating is insufficient.

[0083] Preferably, the porosity of the wear-resistant coating is less than 5%. Such porosity can be evaluated by observation with a microscope magnified 200 times.

[0084] The wear-resistant coating is insoluble in water and acetone, slightly soluble in alcohol, and soluble in engine cleaning agents. In particular, the inorganic compound dissolves significantly at pH 3 and below (lower than the pH value of acid rain).

[0085] The wear-resistant coating can be deposited on the substrate to be coated by thermal spraying using powder. For the wear-resistant coating composed of hydroxyapatite and polyester, the powder particle size range of the inorganic compound before spraying is -130 μm to +45 μm, and the powder particle size range of the polyester before spraying is -150 μm or -145 μm to +45 μm.

[0086] In the case of single-injection thermal spraying, the powders of the inorganic compound and the polymer compound are pre-mixed and then the powder mixture is sprayed onto the substrate to be coated through a plasma torch.

[0087] In the case of double-injection thermal spraying, powders of inorganic compounds and powders of high molecular compounds are mixed during the process of being sprayed onto the substrate to be coated. Figure 8 A double-injection thermal spraying device is shown. The device 20 includes an inorganic compound injector 21, a high molecular compound injector 22, and a plasma torch 23. The inorganic compound and the high molecular compound are injected into a plasma torch beam, which sprays them onto the substrate to be coated.

[0088] The wear-resistant coating can be processed by any known technique, including turning, milling, or grinding. After surface processing, a wear-resistant coating as shown in Figure 9 is obtained, and its microstructure is as shown in Figure 10 The porosity of such a wear-resistant coating is less than or equal to 5%.

[0089] The wear resistance of such a wear-resistant coating (evaluated according to DMC 0420) is in the range of 100% - 130%. With such a wear-resistant coating, there is no blade wear.

[0090] The DMC 0420 test uses the A / O (wear resistance / overpenetration) ratio to evaluate the performance of the wear-resistant coating, and this ratio is measured using a measuring device not shown in the figure: Three simulated blades are arranged to protrude from the periphery of a rotating wheel. The wear-resistant sample to be tested is placed under the rotating wheel. The rotating wheel advances towards the wear-resistant sample at a constant speed and penetrates it to a set depth. Then the actual depth dug into the wear-resistant sample is measured, and the ratio of the set depth to the dug-in depth is calculated. This ratio is called the A / O ratio and is expressed as a percentage.

[0091] According to another technique, a wear-resistant coating composed of hydroxyapatite and polyester can be deposited on the substrate to be coated, preferably on a low-pressure compressor. The hydroxyapatite powder and the polyester powder are mixed and then extruded or thermo-molded into a ring. This ring is a wear-resistant track blank, which is then bonded to the substrate to be coated or directly injected onto the substrate, such as the housing of a low-pressure compressor. The wear-resistant track blank can be bonded through an adhesive film. Alternatively, to minimize the thickness of the bonding seal and ensure better adhesion of the wear-resistant coating to the substrate, the ring can be cold inserted. Then bonding is carried out by baking in an oven, for example, at a temperature of about 175°C. Then the wear-resistant track is processed to the required dimensions.

[0092] An adhesion primer layer can be added between the substrate to be coated and the wear-resistant coating. The rougher the primer layer is, the stronger the adhesion of the wear-resistant coating will be. Preferably, the roughness Ra of the primer layer is between 9 μm and 40 μm. For example, the primer layer can be composed of a nickel-aluminum (NiAl) alloy or a nickel-chromium-aluminum (NiCrAl) alloy deposited on the substrate by plasma spraying in air. The roughness Ra of such a primer layer is about 10 μm. The primer layer can be composed of NiAl or NiCrAl deposited by arc spraying. The roughness Ra of such a primer layer is about 40 μm.

Claims

1. A wear-resistant coating for a turbine (1), comprising an inorganic compound with a Mohs hardness less than or equal to 6 and a melting temperature greater than 450 °C, and a high molecular compound with a content between 40% and 70% by volume, characterized in that The inorganic compound is selected from: calcium fluoride, hydroxyapatite, lanthanum phosphate, diatomaceous earth, muscovite or barium sulfate, wherein the porosity of the wear-resistant coating is less than 5%.

2. The wear-resistant coating according to claim 1, wherein, The melting temperature of the inorganic compound is greater than 800 °C.

3. The wear-resistant coating according to claim 1, wherein, The polymer compound is polyester.

4. The wear-resistant coating according to claim 1, wherein, The polymer compound is a sprayable polymer.

5. The wear-resistant coating according to any one of claims 1 to 4, wherein, The inorganic compound is hydroxyapatite and the polymer compound is polyester.

6. The wear-resistant coating according to any one of claims 1 to 4, wherein, The coating is insoluble in water and acetone.

7. A turbine module, comprising: - a rotor (13) provided with a plurality of moving blades (9), - a stator (15), and - at least one wear-resistant coating according to any one of claims 1-6, the wear-resistant coating being provided at an interface between a part of the rotor and a part of the stator.

8. The module according to claim 7, comprising at least one underlying layer with a roughness Ra between 9 μm and 40 μm, the underlying layer being below the wear-resistant coating and above the part of the rotor (13) and the part of the stator (15).

9. The module according to claim 8, wherein, The underlying layer is located between the part of the stator (15) and the wear-resistant coating.

10. The module according to claim 8 or 9, wherein, The underlying layer is composed of nickel-aluminum alloy or nickel-chromium-aluminum alloy.

11. An aircraft turbine (1), comprising the module according to any one of claims 7-10.

12. A method of manufacturing a wear-resistant coating according to any one of claims 1-6, comprising the steps of: - mixing a powder of an inorganic compound having a Mohs hardness less than or equal to 6 and a melting temperature greater than 450 °C with a powder of a polymer compound, - forming a wear-resistant coating from the powder mixture, wherein the content of the polymer compound is between 40 vol% and 70 vol% of the wear-resistant coating, - applying the wear-resistant coating to an interface between a part of a rotor (13) having a plurality of moving blades (9) and a part of a stator (15) of a turbine module.

13. The method according to claim 12, wherein, The formation of the wear-resistant coating is carried out by single-injection thermal spraying or double-injection thermal spraying, extrusion or thermoforming.

14. The method according to claim 12 or 13, wherein The application of the wear-resistant coating is carried out by bonding with an adhesive film or by direct injection between the part of the rotor (13) and the part of the stator (15).

15. The method according to claim 12 or 13, wherein, A rough underlying layer is deposited on the part of the stator (15) by plasma spraying in a region, the roughness Ra of the underlying layer being 10 μm, and the underlying layer being composed of nickel-aluminum alloy or nickel-chromium-aluminum alloy.

16. The method according to claim 12 or 13, wherein A rough underlying layer is deposited on the part of the stator (15) by arc wire spraying, the roughness Ra of the underlying layer being 40 μm, and the underlying layer being composed of nickel-aluminum alloy or nickel-chromium-aluminum alloy.

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