PART FOR A TURBOMACHINE COMPRISING A GEOPOLYMER THERMAL BARRIER COATING

Abstract

The present invention relates to a part (10) for an aircraft turbomachine, this part (10) comprising a body and a thermal barrier coating (4) located on said body, this coating comprising: - a lower thermal insulation layer (42) which is located on said body and which comprises at least one geopolymer, - an intermediate metal heat dissipation layer (46) which is located on the lower layer, and - an upper thermal insulation layer (44) which is located on the intermediate metal layer and which comprises at least one geopolymer. Figure for abstract: Figure 2

Description

Title of the invention: PART FOR A TURBOMACHINE COMPRISING A GEOPOLYMER THERMAL BARRIER COATING Technical field of the invention

[0001] The invention relates to the field of thermal barrier coatings. More particularly, the present invention relates to a part for a turbomachine, in particular an aircraft turbomachine, comprising such a thermal barrier coating. Technical background

[0002] A turbomachine, as used for propulsion in the aeronautical field, comprises an atmospheric air inlet which communicates with one or more compressors, generally including a fan, driven in rotation around the same axis X. The primary flow of this air, after having been compressed, feeds a combustion chamber arranged in an annular manner around this axis X. This primary flow is mixed with a fuel and burned to provide combustion gases, downstream, to one or more turbines through which these gases are expanded, the rotors of the turbines driving the rotors of the compressors.

[0003] The engine of the turbomachines operates at a temperature of the combustion gases at the turbine inlet which is sought to be as high as possible, because this temperature conditions the performance of the turbomachine. For this purpose, the materials of the hot parts are selected to withstand these operating conditions and the walls of the parts swept by the combustion gases, such as the turbine casing, the distributors or the moving turbine blades, are provided with cooling means.

[0004] Generally, turbomachine parts can be made of metal or composite.

[0005] The use of composite materials is particularly advantageous in the field of turbomachines because they allow the reduction of the mass of the components associated with good mechanical properties.

[0006] A conventionally used composite material comprises a fibrous preform densified by a polymer resin. The preform may be the result of three-dimensional (3D) weaving or may be obtained by draping and superimposing several layers / plies (multi-layer). The resin may be injected into the preform or the preform may be pre-impregnated with the resin (also referred to as "pre-impregnated" or "prepreg").

[0007] Currently, turbomachine parts made from a composite material at Organic matrix resins (OMD) are increasingly used in the engine area. However, parts made from OMD are particularly sensitive to high heat. Indeed, the organic resin making up OMD parts is not very resistant to high temperatures (such as temperatures above 200°C or even 300°C for the most efficient ones).

[0008] Among the protections designed to enable these parts to withstand these extreme conditions, there is the deposition of several materials forming a “thermal barrier coating” on their external surface. This coating protects the part made from CMO from continuous exposure to high temperatures.

[0009] One solution would be to produce the thermal barrier coating in the form of silica wool encapsulated in metal strips (such as stainless steel or Inconel). Mechanical fasteners are also necessary to fix this type of coating to the turbomachine part. For example, these fasteners are rivet-type through fasteners with a titanium fitting or support to fix the periphery of the coating, or metal studs glued to the full surface of the CMO part. This type of coating can present an additional step and difficulty in positioning these fasteners for operators. Furthermore, the silica wool-based coating is thick (more than 4.0 mm) and can be bulky in a turbomachine.

[0010] It is also known to apply a thermal barrier coating formed of silicone in single or multi-layer form to the turbomachine part. However, this type of coating has the disadvantage of being expensive.

[0011] In this context, it is useful to at least partially overcome the aforementioned drawbacks by proposing a new, reliable and space-saving thermal barrier coating, particularly in a part for a turbomachine. Summary of the invention

[0012] The present invention thus provides a part for an aircraft turbomachine, this part comprising a body and a thermal barrier coating located on said body, this coating comprising: - a lower thermal insulation layer which is located on said body and which comprises at least one geopolymer, - an intermediate heat-dissipating metal layer which is located on the lower layer, and - an upper thermal insulation layer which is located on said intermediate metallic layer and which comprises at least one geopolymer.

[0013] The turbomachine part according to the invention has the advantage of being functional, in particular in a turbomachine engine, without limitation of duration to a tem high temperature. Indeed, the thermal barrier coating of the part benefits from high temperature stability (for example between 400 and 600°C), which makes it suitable for turbomachinery modules exposed to high temperatures, such as low pressure and high pressure compressors.

[0014] In particular, the thermal barrier coating according to the invention has a multi-layer architecture composed of several geopolymer layers and a metal layer. The metal layer is sandwiched between the lower and upper geopolymer layers.

[0015] The term "geopolymer" means a material based on mineral matter composed for example of silica and alumina. Geopolymers are formed of chains or networks of mineral molecules linked by covalent bonds. The geopolymer may be entirely inorganic or may include a certain amount of organic matter. The geopolymer may be essentially a mineral chemical compound or a mixture of compounds consisting of units, for example silico-oxide (-Si-O-Si-O-), silico-aluminate (-Si-O-Al-O-), ferro-silico-aluminate (-Fe-O-Si-O-Al-O-) or alumino-phosphate (-A1-OPO), created by a geopolymerization process.

[0016] The geopolymer material, in particular due to its inorganic nature, offers very good resistance to high temperatures (in particular at a temperature above 300°C). The geopolymer layers of the coating of the invention thus have a thermal insulation function, and the metal layer, as a conductive material, can have a heat dissipating role.

[0017] In operation, the high temperature is attenuated by the upper geopolymer layer. This heat is then distributed uniformly over the surface of the intermediate metal layer, which makes it possible to locally avoid very hot spots. Finally, the lower geopolymer layer makes it possible to further reduce the temperature transmitted to the body of the turbomachine part. This therefore reduces the degradation of the part in operation.

[0018] The coating according to the invention can be easily applied to all types of shape of the part (for example, a flat shape and / or a shape with curvature), in particular without resorting to additional mechanical fixings. This coating therefore offers very good thermal protection and reduces the degradation of the part during operation. Such a coating is inexpensive to produce, compact and offers wide possibilities of use.

[0019] 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.

[0020] The thermal barrier coating according to the invention may comprise one or more of the following characteristics, taken in isolation from one another or in combination: combination with each other:

[0021] - the lower and upper layers comprise the same geopolymer;

[0022] - the geopolymer is based on potassium or sodium;

[0023] - the geopolymer comprises between 2 and 15%, and preferably between 5 and 10%, potassium hydroxide or sodium hydroxide;

[0024] - the geopolymer has the general formula K2O(Al2O3)(SiO2)6513.6(H2O);

[0025] - the heat dissipation layer is a metal foil, for example a copper foil or aluminum foil;

[0026] - the coating has a thickness E4 less than or equal to 3.0 mm, for example this E4 thickness is 2.0mm;

[0027] - each of the first and second thermal insulation layers has a thickness E42, E^ less than or equal to 1.0mm;

[0028] - the heat dissipation layer has a thickness E46 of between 15 and 35qm, for example this E46 thickness is about 25qm;

[0029] - the body of the part is made of organic matrix composite material or of metallic material;

[0030] — the heat dissipation layer is a metal foil having a thermal conductivity greater than or equal to 380 W / mK

[0031] The present invention also relates to an aircraft turbomachine comprising at least one turbomachine part as described above.

[0032] The present invention also relates to a method for producing a part according to one of the features of the invention. The method comprises the steps of: (a) formulate geopolymers for integration into lower and upper layers of thermal insulation, (b) depositing the lower layer of thermal insulation on at least a portion of the body of the turbomachine part, (c) depositing an intermediate heat-dissipating metal layer on the lower thermal insulation layer, and (d) depositing the top thermal insulation layer on the intermediate metal heat dissipation layer.

[0033] Before step (b), the method may comprise a step (i) of preparing the surface of the body of the part to be coated with said thermal barrier coating. For example, step (i) may be carried out by cleaning and / or sanding the body of the part to be coated. Brief description of the figures

[0034] The invention will be better understood and other details, features 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:

[0035] [Fig. 1] is a schematic axial sectional view of an aircraft turbomachine,

[0036] [Fig. 2] schematically represents in axial section a part for a turbomachine comprising a thermal barrier coating according to an embodiment of the invention,

[0037] [Fig.3a] schematically represents a side view of a test assembly for measuring the thermal reduction on a first sample heated without thermal barrier coating and on a second sample heated with thermal barrier coating,

[0038] [Fig.3b] is a top view of [Fig.3a],

[0039] [Fig.4] is a flowchart of a process for producing the part of [Fig.2]. Detailed description of the invention

[0040] 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 aircraft propulsion unit. The terms "radial" or "vertical" qualify 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 with reference to a positioning relative to the longitudinal axis. Thus, a structural element extending along the longitudinal axis comprises an inner surface facing the longitudinal axis and an outer surface, opposite its inner surface. Similarly, the terms "upstream" and "downstream" are defined with respect to the direction of air circulation in the turbomachine.

[0041] [Fig.l] shows a propulsion unit 1, in particular for an aircraft, comprising a turbomachine 2 and a nacelle 3 surrounding this turbomachine 2. The turbomachine 2, in particular for an aircraft, may be a turbojet or a turboprop ([Fig.l]).

[0042] This propulsion unit 1 can be fixed on a fuselage of an aircraft or mounted under a lifting wing of the aircraft (not illustrated in the figures).

[0043] With reference to [Fig.l], the turbomachine 2 extends along a longitudinal axis X and comprises, from upstream to downstream in the direction of flow of the gases, a fan S, a low-pressure compressor 2a, a high-pressure compressor 2b, an annular combustion chamber 2c, a high-pressure turbine 2d and a low-pressure turbine 2e, which define a flow path for a primary gas flow F1 (in particular a hot air flow).

[0044] The nacelle 3 of the propulsion unit 1 extends around the turbomachine 2 and defines around the latter an annular flow vein for an inlet flow F and a flow secondary gas flow F2 (in particular a cold air flow). After the inlet flow F passes through the blower S, it divides into primary flow Fl and secondary flow F2 in the turbomachine 2.

[0045] As described previously in the technical background of the invention, a thermal barrier coating is generally applied to one or more parts in the turbomachine 2, to protect the part subjected to high operating temperatures (in particular above 300°C).

[0046] Such a part is illustrated schematically in [Fig.2]. The part 10 therefore comprises a body and a thermal barrier coating 4. The body of the part 10 extends along a longitudinal axis A. This axis A may be parallel or transverse to the axis X of the turbomachine 2. The part 10 may have a generally planar shape and / or a shape with one or more curved zones.

[0047] The part 10 may be a casing (for example of the high pressure compressor and / or the low pressure compressor) or a wall (for example of the nacelle 3). More particularly, the part 10 is located in hot zones of the turbomachine. In this case, the part 10 may be a casing of at least one of the low pressure 2a and high pressure 2b compressors.

[0048] The part 10 may be made of metal (for example steel or aluminum) or of composite (such as organic matrix composite material).

[0049] With reference to [Fig.2], the thermal barrier coating 4 comprises a superposition of several layers. The coating 4 comprises: - a lower layer of thermal insulation 42, - an intermediate heat dissipation layer 46, and - a top layer of thermal insulation 44.

[0050] In the example, the lower layer 42 is located directly on the body of the part 10, the intermediate layer 46 is located on the lower layer 42 and the upper layer 44 is located on the intermediate layer 46. The body of the part 10 can thus form a substrate on which the coating 4 is deposited.

[0051] The intermediate layer 46 has a heat sink function. Indeed, the intermediate layer made of metal is a good thermal conductor. This makes it possible to distribute the heat, coming in particular from the upper layer 44, over its entire surface.

[0052] The intermediate layer 46 may be a metal foil. This intermediate layer 46 may be a copper foil or another metal foil having, for example, a thermal conductivity greater than or equal to 380 W / mK. Alternatively, another type of metal foil with a thermal conductivity less than 380 W / mK may be used provided that this metal foil is not degraded by chemical reaction with at least one of the geopolymer layers. Indeed, the layer intermediate may be an aluminum foil which has a lower thermal conductivity than a copper foil.

[0053] As described above, the lower 42 and upper 44 layers each have a thermal insulation function. Indeed, these layers 42, 44 make it possible to limit heat transfers, in particular between a hot zone of the turbomachine 2 and the part 10, so as to protect this part from thermal degradation. In order to reinforce the resistance to a high operating temperature (for example a temperature above 300°C), the layers 42, 44 each comprise a geopolymer. The geopolymer is an inorganic material which is stable at high operating temperatures (in particular, at least above 300°C).

[0054] The lower layer 42 may be similar to or different from the upper layer 44. In particular, the geopolymer composing the lower layer 42 may be identical to or different from the geopolymer of the upper layer 44.

[0055] The general formula of the geopolymer used in the lower layer 42 and / or the upper layer 44 may be: K2O(Al2O3)(SiO2)6513.6(H2O)

[0056] The geopolymer can be potassium-based or sodium-based.

[0057] For example, the geopolymer of formula K2O(Al2O3)(SiO2)6.513.6(H2O) may have a ratio of about 2:4:1. The sodium-based geopolymer may have a ratio of about 0.5 of sodium oxide (Na2O) to alumina (A12O3), a ratio of about 2.4 of silicon dioxide (SiO2), and a ratio of about 4.9 of water (H2O). The potassium-based geopolymer may have a ratio of about 0.5 of potassium oxide (K2O) to alumina (A12O3), a ratio of about 2.4 of silicon dioxide (SiO2), and a ratio of about 4.9 of water (H2O).

[0058] Table 1 summarizes an example of the composition of the sodium-based geopolymer (NaOH) of the lower layer 42 and / or the upper layer 44.

[0059] [Tables 1] Sodium oxide -Na2O (% by weight) Alumina -A12O3 (% by weight) Silicon dioxide -SiO2 (% by weight) Water -h2o (%) Mass fraction (% by weight) Metakaolin clay -MK (metamax) 0 33.6 58.41 0 38.0 Silica fume - Condensil® s95dp 0 0 94.15 0 14.9 Binder - Betol® 39T 8.3 0 27.5 64.2 46.0 Sodium hydroxide - NaOH 77.5 0 0 22.5 5.1 Geopolymer content (in g / 100g) 7.8 12.8 48.8 30.6 104 (including 4.0g of impurity)

[0060] The geopolymer of the lower layer 42 and / or the upper layer 44 may comprise between 2 and 15% by weight of sodium hydroxide (NaOH). Preferably, the geopolymer comprises between 5 and 10% by weight of sodium hydroxide (NaOH). For example, the sodium hydroxide (NaO2) content is about 5.1% by weight in the geopolymer with reference to Table 1.

[0061] Table 2 summarizes an example of the composition of the potassium-based geopolymer (KOH) of the lower layer 42 and / or the upper layer 44.

[0062] [Tables2] Potassium oxide -K2O (wt%) Alumina -A12O3 (wt%) Silicon dioxide -SiO2 (wt%) Water -h2o (%) Mass fraction (wt%) Metakaolin clay -MK (metamax) 0 33.6 58.41 0 36.6 Silica fume -Condensil® s95dp 0 0 94.15 0 16.2 Binder - Kasil® 2135 11.0 0 24.0 65.0 43.4 Potassium hydroxide - KOH 83.1 0 0 16.9 7.7 Geopolymer content (in g / 100g) 11.2 12.3 47.0 29.5 103.9 (of which 3.9g impurity)

[0063] The geopolymer of the lower layer 32 and / or the upper layer 34 may comprise between 2 and 15% by weight of potassium hydroxide (KOH). Preferably, the geopolymer comprises between 5 and 10% by weight of potassium hydroxide (KOH). For example, the potassium hydroxide (KOH) content is about 7.7% by weight in the geopolymer with reference to Table 2.

[0064] The coating 4 may have a first thickness E4 which is measured radially relative to the axis A. This first thickness E4 is preferably less than or equal to 3.0 mm. For example, the first thickness E4 is 2.0 mm. This makes it possible to reduce the size of the part 4 in the turbomachine 2.

[0065] The lower layer 42 may have a second thickness E42. The upper layer 44 may have a third thickness E44. Each of the second and third thicknesses E42, E44 may be less than or equal to 1.0 mm.

[0066] The intermediate layer 46 may have a fourth thickness E46. This fourth thickness E46 is preferably between 15 and 35 μm. For example, the fourth thickness E46 is approximately 25 μm.

[0067] The thicknesses E42, E44 and E46 are also measured radially relative to the axis A of the part 10.

[0068] The Applicant was able to observe a thermal reduction of approximately 125°C corresponding to the temperature difference between a first test sample 5 not coated with the thermal barrier coating 4 and a second test sample 6 coated with the coating 4 of the invention. This temperature difference depends in particular on the thermal stress applied to the surface of the face exposed to the heat. For this, the Applicant carried out comparative tests between metal substrates (in particular a steel part 10) of the first 5 and second 6 samples, the assembly of which is illustrated in Figures 3a and 3b. The second sample 6 thus corresponds to the part 10 of [Fig.2].

[0069] With reference to figures 3a and 3b, the sample 5, 6 forms a plate of 100mm*100mm and has a thickness of approximately 2.0mm. The sample 5, 6 is supported on a base 7 and heated (in particular to approximately 450°C) by a heat source 8 for at least 15 minutes. The sample 5, 6 comprises a lower face 52, 62 (respectively not coated with the coating 4 and coated with the coating 4), and an upper face 54, 64 opposite the lower face 52, 62. The lower faces 52, 62 are heated directly by the heat source 8, and the upper faces 54, 64 are not heated directly by the heat source 8. The coating 4 deposited on the lower face 62 of the second sample 6 is therefore directly heated by the source 8. Then, the temperature is measured on the upper faces 54, 64 of the samples, for example with an infrared camera.Thus, the upper face 54 of the first sample 5 has a temperature of approximately 417°C, while the upper face 64 of the second sample 6 has a reduced temperature of approximately 292°C. The temperature difference between the upper faces 54, 64 of the first and second samples 5, 6 is therefore 125°C. It can thus be concluded that the coating 4 of the invention has made it possible to significantly reduce the temperature transmitted to the body of the second sample 6.

[0070] The present application now describes an example of a method for producing the part 10, with reference to [Fig.4]. The method comprises the following steps: (a) formulation of geopolymers and their integration into the lower and upper layers of thermal insulation 42, 44, (b) depositing the lower thermal insulation layer 42 on at least a portion of the body of the part 10, (c) deposition of the intermediate heat dissipation layer 46 on the lower layer 42, and (d) depositing the upper thermal insulation layer 44 on the intermediate heat dissipation layer 46.

[0071] The method may comprise, before step (b), a step (i) of cleaning and / or sanding the body of the part 10.

[0072] An adhesive may be applied between the lower 42 and intermediate 46 layers and / or between the upper 44 and intermediate 46 layers.

[0073] The deposits of the layers 42, 44, 46 can be carried out manually by an operator.

[0074] By way of example, step (a) of formulating the geopolymer may comprise the following different steps: (aO production of a silicate solution (for example based on potassium or sodium) comprising a binder (such as Kasil® or Betol®), (a2) carrying out an initial preparation of a silica fume (for example by grinding (a20) the silica fume and sieving (a22) the ground silica fume), (a3) adding metakaolin to the initial preparation of step (a2) to produce an intermediate preparation comprising silica fume and metakaolin, (a4) pre-mixing and mixing the silicate solution of step (aj) with the intermediate preparation obtained in step (a3) ​​and one or more additives, to produce the geopolymer of at least one of the thermal insulation layers 42, 44.

[0075] The additive(s) may comprise boron nitride, zirconia, halloysite, polysilazane and / or silica carbide.

Claims

Claims

1. Method for producing a part (10) for an aircraft turbomachine, this part (10) comprising a body and a thermal barrier coating (4) located on said body, this coating comprising: - a lower thermal insulation layer (42) which is located on said body and which comprises at least one geopolymer, - an intermediate metal heat dissipation layer (46) which is located on the lower layer, and - an upper thermal insulation layer (44) which is located on the intermediate metal layer and which comprises at least one geopolymer, - the geopolymer has the general formula K2O(Al2O3)(SiO2)6513.6(H2O), the method comprising the steps of: (a) formulating geopolymers to integrate them into the lower and upper layers (42, 44), (b) depositing the lower layer (42) on at least a portion of the body of the turbomachine part, (c) depositing an intermediate metal layer (46) on the lower layer (42), (d) depositing the upper layer (44) on the intermediate metal layer (46), and before step (b), the method comprising a step (i) of surface preparation of the body of the part (10) to be coated with said thermal barrier coating (4).

2. Production method according to claim 1, characterized in that step (i) is carried out by cleaning and / or sanding the body of the part to be coated.

3. Production method according to claim 1 or 2, characterized in that an adhesive is applied between the lower (42) and intermediate (46) layers, and / or between the upper (44) and intermediate (46) layers.

4. Production method according to any one of the preceding claims, characterized in that step (a) of formulating the geopolymer comprises the following steps of: (a) producing a silicate solution comprising a binder, (a2) producing an initial preparation of a silica fume, (a3) adding metakaolin to the initial preparation of step (a2) to produce an intermediate preparation comprising silica fume and metakaolin, (a4) pre-mixing and mixing the silicate solution of step (aj) with the intermediate preparation obtained in step (a3) ​​and one or more additives, to produce the geopolymer of at least one of the thermal insulation layers 42, 44.

5. Manufacturing method according to claim 4, characterized in that step (a2) is carried out by grinding (a20) the silica fume and sieving (a22) the ground silica fume.

6. Manufacturing method according to claim 4 or 5, characterized in that the additive(s) of step (a4) comprise boron nitride, zirconia, halloysite, polysilazane and / or silica carbide.

7. Production method according to any one of the preceding claims, characterized in that the lower and upper layers (42, 44) comprise the same geopolymer.

8. Production method according to any one of the preceding claims, characterized in that the geopolymer comprises between 2 and 15%, and preferably between 5 and 10%, of potassium hydroxide.

9. Production method according to any one of the preceding claims, characterized in that the heat dissipation layer (46) is a metal foil, for example a copper foil or an aluminum foil.

10. Production method according to any one of the preceding claims, characterized in that the body of the part (10) is made of organic matrix composite material or of metal.

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