TURBOMACHINE BLADE INCLUDING A THERMAL BARRIER SYSTEM AND ITS MANUFACTURING PROCESS

Abstract

The present invention relates to a turbine blade (8) for a turbomachine (1), particularly an aircraft turbine, the blade (8) comprising a body (80) made of a metallic alloy and at least partially covered by at least one thermal barrier system (9), this body (80) comprising a blade (84) extending along a longitudinal axis and having an upper and lower surface connected by a leading edge and a trailing edge of the blade (84), and in which at least a portion of the thermal barrier system (9) is covered with at least one temporary water-repellent layer (90). Figure 3

Description

Title of the invention: BLADE FOR TURBOMACHINE COMPRISING A THERMAL BARRIER SYSTEM AND METHOD FOR MANUFACTURING SAME Technical field of the invention

[0001] The invention relates to the field of turbomachines, for example aircraft, and more particularly, to blades for these turbomachines which are subjected to high operating temperatures. Technical background

[0002] In a known manner, an aircraft turbomachine comprises from upstream to downstream, in the direction of gas flow, a fan, a low-pressure compressor, a high-pressure compressor, a combustion chamber, a high-pressure turbine and a low-pressure turbine. The rotor of the low-pressure compressor is driven by the rotor of the low-pressure turbine, and the rotor of the high-pressure compressor is driven by the rotor of the high-pressure turbine.

[0003] The turbomachine comprises moving blades and nozzles in the high pressure and low pressure turbines. The nozzles typically comprise fixed blades. Such moving blades and nozzles may comprise a body made of a metal alloy.

[0004] These moving blades and distributors are complex parts which must withstand high operating temperatures (in particular temperatures higher than those of the melting of metal conventionally forming these parts).

[0005] In order to better withstand this extreme temperature operating environment, these moving blades and turbomachine distributors are equipped with a cooling system. This cooling system comprises at least: - one or more ventilation circuits (or so-called cooling circuits) formed inside the blade body, - air passage holes on the blade to create a film of cold air around the blade, - a thermal barrier type protection system (also referred to hereinafter as a thermal barrier system) having a thermal insulation capacity and properties of resistance to attacks from the operating environment (for example, oxidation, erosion attacks by solid particles and / or hot gases, corrosion attacks by CMAS type oxide deposits (CaO-MgO-Al2O3-SiO2), etc.).

[0006] Thermal barrier systems can be multi-layer stacks complexes generally composed of the following different layers: - a bonding sub-layer, called alumino-forming, providing protection against oxidation and / or corrosion formed and / or deposited on the surface of a metal substrate (such as a turbomachine blade), - a thin layer of alumina (A12O3) on the bonding sub-layer, - a ceramic coating on the thin layer of alumina, the primary function of which is to limit the surface temperature of the coated components; and this ceramic coating can be multi-layer.

[0007] The lifetime of thermal barrier systems may depend on the superalloy nature, the bonding sub-layer (chemical composition, microstructure, and thickness) associated with its method of preparation, the resistance of the multi-layer stack to a thermal cycle, on the one hand, and the resistance of the external layer (namely the ceramic coating) to environmental aggressions (erosion by solid particles, chemical resistance, corrosion, etc.), on the other hand.

[0008] Thermal barrier systems can have the disadvantage of being sensitive to water (in liquid or gas form). Indeed, the blade body coated with the thermal barrier system is in contact with water either during prolonged storage in a humid environment or during operation in high-pressure and low-pressure turbines.

[0009] For example, the ceramic coating comprises zirconia partially stabilized with yttrium and can be deposited by physical vapor deposition (known by the acronym EB-PVD for Electron Beam Physical Vapor Deposition) or any other deposition process. In the presence of water, the thermal barrier system can flake and thus reduce its lifetime. Indeed, water molecules can initiate cracks at the interface between the bonding layer and the thin layer of alumina (A12O3) by chemical reaction with the bonding layer, leading to flaking of the thermal barrier system.

[0010] Furthermore, it may be necessary to carry out a retouching operation on the blade coated with the thermal barrier system, such as the air passage orifices of the cooling system. The retouching operation is notably carried out by electroerosion machining (known by the acronym EDM for Electrical Discharge Machining). However, this retouching operation requires partial immersion of the area of ​​the blade to be retouched in water. Thus, this retouching operation may degrade the thermal barrier system of the blade.

[0011] A laser can be used to retouch the blade coated with the thermal barrier system instead of EDM machining. However, this method can have a negative impact on the cavities forming the ventilation circuits of the blade. In addition, the laser does not allow for the creation of deep holes since the laser tends to de- focus before drilling the entire hole.

[0012] In these different contexts, it is interesting to propose a solution making it possible to protect the blade coated with a thermal barrier system against water, in particular during handling and / or operations before mounting this blade in an aircraft turbomachine. Summary of the invention

[0013] The present invention proposes a solution making it possible to remedy at least some of the aforementioned drawbacks.

[0014] To this end, the present invention proposes a blade for a turbomachine, in particular for an aircraft, the blade comprising a body made of a metal alloy and at least partly covered by at least one thermal barrier system, this body comprising a blade extending along a longitudinal axis A and having a lower surface and an upper surface connected to each other by a leading edge and a trailing edge of the blade.

[0015] According to the invention, at least part of the thermal barrier system is covered with at least one temporary water-repellent layer.

[0016] In the present application, the term "temporary" means a temporary layer which is not intended to be kept on the blade in operation in a turbomachine. This temporary layer is thus intended to be removed from the blade before its mounting or assembly in the turbomachine.

[0017] The term "water repellent" means a material that is waterproof and impermeable to water (in particular water in liquid or gaseous form) making it possible to protect the thermal barrier system against water projection.

[0018] Thus, the temporary water-repellent layer makes it possible to minimize the risks of attack on the thermal barrier system by water during the various handling and / or operations of the blade before its assembly in the turbomachine. Indeed, this water-repellent layer adheres easily to the thermal barrier system to form a watertight and waterproof barrier. In addition, the water-repellent layer can be easily removed without impacting and physically or chemically degrading the thermal barrier system or the blade.

[0019] The temporary water-repellent layer therefore makes it easier to carry out operations requiring the use of water on the blade coated with the thermal barrier system, such as the aforementioned retouching operation and / or a repair operation. Indeed, the water-repellent layer does not prevent the creation of electric discharge during EDM machining.

[0020] Consequently, the temporary water-repellent layer makes it possible to effectively protect the area(s) of the blade coated with the thermal barrier system that may come into contact with water.

[0021] The invention therefore has the advantage of being based on a simple design, offering very high reliability, and with little penalty in terms of cost and size.

[0022] The blade according to the invention may comprise one or more of the following characteristics, taken in isolation from one another or in combination with one another:

[0023] -said at least one thermal barrier system comprises a bonding layer located on the body of the blade, an alumina layer located on the bonding layer and a ceramic coating located on the alumina layer;

[0024] - said ceramic coating comprises a ceramic multilayer;

[0025] - said at least one water-repellent layer is a layer of wax, silicone and / or plasticizer;

[0026] - the wax layer is a layer of paraffin or beeswax;

[0027] - the blade further comprises an internal ventilation circuit connected to orifices of air passage, these orifices being located in an area devoid of said water-repellent layer;

[0028] - the blade is a blade of a high pressure turbine or a low pressure turbine of the turbomachine,

[0029] - the blade is a blade of a high pressure distributor of the turbomachine.

[0030] The present invention also relates to a method of manufacturing a blade for a turbomachine, in particular for an aircraft. The method comprises steps comprising: - a supply (a) of the blade comprising a body made of a metal alloy, this body comprising a blade extending along an axis of elongation A and having an intrados and an extrados connected to each other by a leading edge and a trailing edge of the blade, - a deposit (b) of the thermal barrier system on at least one part of the body, - a deposition (c) of at least one temporary water-repellent layer on said thermal barrier system to obtain a blade according to one of the particularities of the invention, and - a step (e) of total removal of said at least one layer of water repellent.

[0031] The manufacturing method according to the invention may comprise one or more of the following characteristics, taken in isolation from one another or in combination with one another:

[0032] - the removal step (e) is preceded by a step (d) of machining the blade with a view to make air passage holes;

[0033] - the machining step (d) is preceded by a step (i) of partial removal of said at least a layer of water repellent;

[0034] - the partial and / or total removal of said water-repellent layer is carried out manually, by a cutting tool and / or by heating to a predefined sublimation temperature of the water-repellent material;

[0035] - machining includes the sub-steps of: (di) immersing at least a portion of the blade in a container of water, and (d2) machining the blade by electroerosion to form the air passage orifices;

[0036] - the deposition of said at least one water-repellent layer comprises the sub-steps of: (ci) immersion of at least part of the blade in a bath containing a water-repellent material in liquid form, (c4) drying the blade to form said water-repellent layer;

[0037] - the method comprises, before sub-step (c4), a sub-step (c2) of vacuuming of the dawn comprising said water-repellent layer;

[0038] - the method comprises, before sub-step (c4) or before sub-step (c2), a sub- step (c3) of repeating sub-step (ci) or sub-steps (ci) and (c2). Brief description of the figures

[0039] The invention will be better understood and other details, characteristics and advantages of the invention will appear more clearly on reading the following description given by way of non-limiting example and with reference to the appended drawings in which:

[0040] [Fig.l] is a half schematic view in axial section of an aircraft turbomachine,

[0041] [Fig.2] is a schematic perspective view of a blade of the turbomachine of [Fig.l],

[0042] [Fig. 3] is a schematic perspective view of the blade of [Fig. 2] covered with a temporary water-repellent layer according to one embodiment of the invention,

[0043] [Fig.4] is a schematic perspective view of the blade of [Fig.2] covered with a temporary water-repellent layer according to another embodiment of the invention,

[0044] [Fig.5] is a partial schematic view in axial section of the blade of [Fig.3] or [Fig.4], in which is shown schematically and enlarged an example of a thermal barrier system covering at least part of the body of the blade of [Fig.3] or [Fig.4],

[0045] [Fig.6] is a diagram of the steps in the manufacturing process of the blade of [Fig.2],

[0046] Elements having the same functions in different implementations have the same references in the figures. Detailed description of the invention

[0047] By convention, in the description below, the terms “longitudinal” and “axial” qualify the orientation of structural elements extending in the direction of a longitudinal axis, such as a longitudinal axis of the engine of a turbomachine of an assembly aircraft propulsion. The terms "radial" or "vertical" describe an orientation of structural elements extending in a direction perpendicular to the longitudinal axis. The terms "inner" and "outer", and "internal" and "external" are used in reference to a positioning relative to the longitudinal axis. Thus, a structural element extending along the longitudinal axis has an inner surface facing the longitudinal axis and an outer surface, opposite its inner surface. Similarly, the terms "upstream" and "downstream" are defined in relation to the direction of airflow in the turbomachine.

[0048] In the following description, the invention applies to a blade for a turbomachine, in particular for an aircraft. For example, the turbomachine may be a turbojet ([Fig.l]), a turboprop or a turboshaft engine (not shown).

[0049] [Fig.l] represents a turbomachine 1 of the double-flow turbojet type constituting an example of a turbomachine according to the invention. The turbomachine 1 extends along a main axis X. The turbomachine 1 comprises, from upstream to downstream in the direction of circulation of the air flow represented 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 passage of an air inlet flow F in the fan 2 is divided into a primary flow F1 (called cold air flow) and a secondary flow F2 (called hot air flow) in the turbomachine 1.

[0050] The low pressure 6 and high pressure 7 turbines each comprise a plurality of blades 8, called mobile blades, mounted in particular on a disk linked to a drive shaft of the turbomachine 1.

[0051] The low pressure and high pressure turbines 7 may comprise one or more distributors. Each distributor may comprise blades, called fixed blades.

[0052] [Fig.2] illustrates an example of the movable blade 8 intended to be assembled in the turbomachine 1.

[0053] Although the following description relates to a moving blade 8 (for example high pressure and / or low pressure turbines), it can be applied to distributor blades.

[0054] This blade 8 comprises a body 80 made of a metal alloy. The body 80 comprises a blade 84.

[0055] The body 80 may also comprise a root 82 in the case of the moving blades, as illustrated in [Fig. 2]. Alternatively (not illustrated in the figures), the body 80 may comprise attachment platforms connected to the blade 84, for example in the case of the distributor blades. These attachment platforms are configured to each attach to a member of the turbomachine (such as a turbomachine casing).

[0056] The blade 84 (and in particular the vane 8) extends along an elongation axis A. This axis A is substantially perpendicular to the axis X. The blade 84 comprises a lower surface 842 and an extrados 844 connected to each other by a leading edge 846 and a trailing edge 848 of the blade 84.

[0057] In the example of [Fig.2], the blade 84 has an aerodynamic profile, that is to say that the blade 84 has a curved profile of variable thickness between its leading edge 846 and its trailing edge 848.

[0058] [Fig.2] represents a platform 86 connecting the blade 84 to the foot 82, in such a way monobloc (i.e. made from material).

[0059] As described in the foregoing, in order to better withstand an extreme temperature operating environment, the blade body 8 may comprise at least one of the following elements: - one or more ventilation circuits 88 formed for example inside the blade body, - air passage orifices 89 on the blade which are for example through and formed on the blade 84 (such as on the trailing edge 848 in [Fig.2]), - at least one thermal barrier system 9 covering at least part of the blade body 8.

[0060] The internal ventilation circuit(s) 88 may be connected to the air passage orifices 89.

[0061] The thermal barrier system 9 may cover all or part of the blade 84 and / or the platform 86 and / or the root 82 (in the case of the moving blades) and / or at least one of the fixing platforms (in the case of the distributor blades).

[0062] Preferably, the air passage orifices 89 are in one or more zones of the blade 8 which are devoid of the thermal barrier coating 9.

[0063] The thermal barrier system 9 covering the blade body can be any type of water-sensitive material.

[0064] By way of non-limiting example ([Fig.5]), the thermal barrier system 9 comprises: - a bonding layer 92, - a layer of alumina (A12O3) 94, and - a 96 ceramic coating.

[0065] The bonding layer 92 (or otherwise called bonding sub-layer) may be located on the body of the blade 8. This bonding layer 92 may comprise a nickel-aluminium alloy (for example of the |3-NiAl type) which may or may not be modified by one of the elements chosen from platinum (Pt), hafnium (Hf), zirconium (Zr), yttrium (Y) and silicon (Si) or combinations of these elements. The bonding layer 92 may comprise aluminide alloys (for example of the y-Ni-y'-Ni3Al type) which may or may not be modified by one of the elements chosen from platinum (Pt), chromium (Cr), hafnium (Hf), zirconium (Zr), yttrium (Y) and silicon (Si) or combinations of these elements. The bonding layer 92 may comprise alloys of the MCrAlY type (with M can be nickel (Ni), cobalt (Co) or nickel and cobalt (NiCo)).

[0066] The bonding layer 92 makes it possible in particular to provide protection against oxidation and / or corrosion which may form on a surface of the body of the blade.

[0067] The bonding layer may have a first thickness.

[0068] The alumina layer 94 may be located on the bonding layer 92. This alumina layer 94 may be thin. For example, the alumina layer 94 may have a second thickness E94 less than the first thickness.

[0069] The ceramic coating 96 may be located on the alumina layer 94. This ceramic coating 96 may comprise several layers (or a multilayer) of ceramic material. The ceramic coating 96 may be based on zirconia, preferably stabilized with yttrium oxide. The ceramic coating 96 may have a third thickness E96.

[0070] The ceramic coating 96 can thus be the outermost layer of the thermal barrier system 9. This ceramic coating 96 makes it possible to ensure the thermal insulation of the blade coated with the thermal barrier system. The ceramic coating 96 can make it possible to resist attacks from the operating environment (for example oxidation, erosion attacks by solid particles and / or hot gases, corrosion attacks by CMAS type oxide deposits (CaO-MgO-Al2O3-SiO2), etc.).

[0071] The thermal barrier system 9 may also comprise an environmental protection type layer (not illustrated in the figures) located on the ceramic coating 96. For example, this environmental layer makes it possible to ensure protection of the thermal barrier system 9 (as well as the blade 8) against corrosion and / or oxidation.

[0072] One of the particularities of the invention lies in the fact that at least a portion of the thermal barrier system 9 is covered with at least one temporary water-repellent layer 90 (also referred to as a water-repellent layer 90 in the remainder of the application). This makes it possible to effectively protect the thermal barrier system 9 of the blade 8 against water (in liquid or gas form).

[0073] As described previously, the blade 8 comprising the water-repellent layer(s) 90 which cover at least part of the thermal barrier system, is not intended to be assembled in the turbomachine 1. This blade 8, which is illustrated in FIGS. 3 to 5, can be considered as an intermediate part of the final blade 8 of [Fig. 2] which will be assembled in the turbomachine 1.

[0074] [Fig. 3] illustrates an example of a blade 8 in which the entire blade 84 and platform 86 are covered by the water-repellent layer 90. In this case, the entire blade 84 and platform 86 may be covered with the thermal barrier system 9, or only a portion of the blade 84 and / or platform 86 may be covered with the thermal barrier system 9 and it is the entire blade 84 and platform 86 which is covered with the water-repellent layer 90 to facilitate its deposition.

[0075] [Fig. 4] illustrates another example of the blade 8 in which the water-repellent layer 90 covers a portion of the blade 84. In particular, the air passage orifices 89 are located in an area of ​​the blade (namely at the trailing edge 848) devoid of the water-repellent layer 90.

[0076] [Fig. 5] illustrates a non-limiting example of an arrangement of the water-repellent layer 90 on the thermal barrier system 9 which covers the body of the blade 8.

[0077] The water-repellent layer 90 may have a fourth thickness E90. This fourth thickness E90 may be equal to or less than the third thickness E96 of the ceramic coating 96. This may be sufficient to insulate and protect the thermal barrier system from water. The thicknesses E90, E94, E96 are measured relative to a plane transverse to the axis A.

[0078] Advantageously, the water-repellent layer 90 is a layer of wax, silicone and / or plasticizer. These materials have the advantages of having good mechanical properties (namely waterproof, easy adhesion to the thermal barrier coating and does not prevent EDM machining), high covering power and easy removal without damaging the thermal barrier system 9 (in particular the ceramic coating 96). For example, the wax layer is a layer of paraffin or beeswax.

[0079] The present application will now describe a method of manufacturing the blade 8 for the turbomachine 1.

[0080] The method comprises steps consisting of: (a) providing a blade 8 comprising a body 80 made of a metal alloy, (b) depositing the thermal barrier system 9 on at least a portion of the body 80, (c) depositing at least one temporary water-repellent layer 90 on the thermal barrier system 9 to obtain the blade 8 described above with reference to figures 3 to 5, and (e) complete removal of the water repellent layer(s) 90.

[0081] As described with reference to Figures 2 to 4, the body 80 of step (a) therefore comprises the blade 84 having the intrados 842 and the extrados 844 connected to each other by its leading edge 846 and its trailing edge 848. The body 80 may comprise the root 82 with reference to the blade of [Fig.2]. As a variant, the body 80 may comprise fixing platforms, for example in the case of the distributor blades.

[0082] [Fig.6] illustrates all the steps of the manufacturing process of the blade 8 intended to be assembled in the turbomachine 1. The preferred steps of the process are shown in dotted lines in [Fig.6].

[0083] Step (c) of depositing the water-repellent layer(s) 90 may comprise the following sub-steps of: (ci) immersion of at least part of the blade 8 in a bath containing a water-repellent material in liquid form, (c4) drying the blade 8 to form the water repellent layer 90 on at least a portion of the thermal barrier system 9 (as illustrated in Figures 3 and 4).

[0084] Step (c4) can be carried out with a drying time of between 30 minutes and 1 hour.

[0085] For example, for a water-repellent layer based on paraffin wax, step (ci) is carried out by immersing the area(s) to be protected (for example the entire blade and the platform with reference to [Fig. 3]) in a paraffin-type wax bath. This wax bath is composed of 100% wax by volume and at a temperature of 60°C. Then, the drying time is approximately 1 hour at room temperature.

[0086] Step (c) may also comprise a sub-step (c2) of placing the blade 8 comprising the water-repellent layer 90 under vacuum. This sub-step (c2) is carried out before the sub-step (c4), in particular in a vacuum chamber. For example, the sub-step (c2) is carried out with a predetermined pressure of approximately 10 mbar. This sub-step (c2) makes it possible to facilitate the deposition of water-repellent material inside the air passage orifices 89.

[0087] Step (c) may also comprise a sub-step (c3) of repeating sub-step (ci) alone or sub-steps (ci) and (c2). This sub-step (c3) is before sub-step (c4) of total removal of the water-repellent layer 90 or before sub-step (c2) of vacuuming. In order to obtain the fourth thickness E90 sufficient to form a water-tight barrier, at least one of sub-steps (ci) and (c2) are repeated one or more times.

[0088] The manufacturing method may further comprise a step (d) of machining the blade 84, for example to produce (or re-machine) air passage orifices 89. This step (d) is carried out before step (e).

[0089] Step (d) may comprise the following sub-steps: (di) immersing at least a portion of the blade 8 in a container of water, and (d2) machining of the blade 8 by electroerosion (EDM) to form in particular the air passage orifices 89.

[0090] A step (i) of partial removal of the water-repellent layer 90 can be carried out before step (d), in particular by removing the water-repellent layer 90 located at the air passage orifices 89 ([Fig.4]). This step (i) makes it possible to facilitate the creation of an electric discharge for EDM machining.

[0091] By way of example, the partial and / or total removal of the water-repellent layer 90 can be carried out by at least one of the following methods: - manually by operator, - a cutting tool, - heating to a predefined sublimation temperature of the water-repellent material.

[0092] For example, for a paraffin wax-based water repellent layer, the sublimation temperature is approximately 600°C to remove the water repellent layer 90 without damaging the thermal barrier system 9.

[0093] Advantageously, the water-repellent material is chosen with a sublimation temperature lower than approximately 800°C.

[0094] The invention is however not limited to a moving blade 8 of turbines 6, 7, and can be applied to all turbomachine blades or vanes which are covered at least in part with a thermal barrier system and need to be protected against water. For example, the invention can be applied to blades (not illustrated in the figures) of a high-pressure distributor (located in particular in the high-pressure turbine 6) of the turbomachine.

Claims

Claims

1. Method for manufacturing a blade (8) for a turbomachine (1), in particular an aircraft, the method comprising steps comprising: - a supply (a) of the blade (8) comprising a body (80) made of a metal alloy, this body (80) comprising a blade (84) extending along an elongation axis (A) and having a lower surface (842) and an upper surface (844) connected to each other by a leading edge (846) and a trailing edge (848) of the blade (84), - a deposition (b) of at least one thermal barrier system (9) on at least one part of the body (80), - a deposition (c) of at least one temporary water-repellent layer (90) on at least one part of the thermal barrier system (9), and - a step (e) of total removal of said at least one water-repellent layer (90),and characterized in that the deposition of said at least one water-repellent layer (90) comprises the sub-steps of: (ci) immersion of at least a portion of the blade (8) in a bath containing a water-repellent material in liquid form, (c4) drying of the blade (8) to form said water-repellent layer (90).,

2. Manufacturing method according to claim 1, characterized in that said at least one thermal barrier system (9) comprises a bonding layer (92) located on the body (80) of the blade, an alumina layer (94) located on the bonding layer (92) and a ceramic coating (96) located on the alumina layer (94).

3. Manufacturing method according to claim 2, characterized in that said ceramic coating (96) comprises a ceramic multilayer.

4. Manufacturing method according to any one of claims 1 to 3, characterized in that said at least one water-repellent layer (90) is a layer of wax, silicone and / or plasticizer.

5. Manufacturing method according to claim 4, characterized in that the wax layer is a layer of paraffin or beeswax.

6. Manufacturing method according to one of the preceding claims, characterized in that it further comprises an internal ventilation circuit (88) connected to air passage orifices (89), these orifices (89) being located in an area devoid of said water-repellent layer (90).

7. A manufacturing method according to any one of the preceding claims- preceding, characterized in that the step (e) of removal is preceded by a step (d) of machining the blade (84) in order to produce air passage orifices (89).

8. Manufacturing method according to the preceding claim, characterized in that the machining step (d) is preceded by a step (i) of partial removal of said at least one water-repellent layer (90).

9. Manufacturing method according to any one of the preceding claims, characterized in that the partial and / or total removal of said water-repellent layer (90) is carried out manually, by a cutting tool and / or by heating to a predefined sublimation temperature of the water-repellent material.

10. Manufacturing method according to claim 8 or 9, characterized in that the machining comprises the sub-steps of: (di) immersing at least a portion of the blade (8) in a container of water, and (d2) machining the blade (8) by electroerosion to form the air passage orifices (89).

11. Manufacturing method according to any one of the preceding claims, characterized in that it comprises, before sub-step (c4), a sub-step (c2) of placing the blade (8) comprising said water-repellent layer (90) under vacuum.

12. Manufacturing method according to any one of the preceding claims, characterized in that it comprises, before sub-step (c4) or before sub-step (c2), a sub-step (c3) of repeating sub-step (ci) or sub-steps (ci) and (c2).

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