Process for coating a turbomachine part

Abstract

The present invention relates to a method for coating a turbomachine part, comprising: fixing (S100) the turbomachine part to a support using a ceramic adhesive to obtain a solid assembly of the turbomachine part and the support, the support and / or the ceramic adhesive being made of graphite; applying (S300) a coating to a surface of the turbomachine part, the turbomachine part being held by the support; and heat treating (S400) the assembly in an oxidizing atmosphere. Fig. 5

Description

Title of the invention: Method for coating a turbomachine part Technical field

[0001] The present invention relates to the technical field of methods for applying a coating to a turbomachine part. More particularly, the present invention relates to the technical field of methods for applying a coating to a turbomachine part subjected to high temperatures and / or an oxidizing environment, such as a turbine. State of the art

[0002] Ceramic matrix composite (CMC) materials are increasingly used for the manufacture of turbomachine parts. These materials withstand high temperatures, potentially exceeding 1200 °C. Turbomachine parts made of CMC material require less cooling. Since this cooling generally comes from a sample in the compressor which impacts the efficiency of the turbomachine, turbomachine parts made of CMC material therefore make it possible to improve engine efficiency, which reduces fuel consumption. Furthermore, the low density of this material contributes to the reduction of the overall mass of turbomachines, leading to a further reduction in fuel consumption and therefore to a significant reduction in pollutant emissions.In order to improve the corrosion resistance of turbomachine parts, particularly at higher temperatures, the surface of these parts can be coated with a protective coating. This protective coating can form an environmental barrier layer and / or a thermal barrier layer. Generally, it is preferable to coat the entire surface of turbomachine parts with CMC in order to protect the CMC from the engine environment and from contact with other parts made of metallic materials.

[0003] The coating process typically comprises: - the application of a primer, for example by thermal spraying (TP) or chemical vapor deposition (CVD); - the application of a protective layer, for example by PT or by liquid means such as electrophoresis; and - sintering of the bonding undercoat and the protective layer in an air furnace at a temperature above 1200°C.

[0004] When applying the bonding undercoat and the protective layer, the CMC part must be held in place. Currently, this is achieved by the prior creation of one or more excess lengths on the part. These excess lengths must be removed prior to assembling the parts in the turbomachine. This removal step is generally carried out by machining. Since CMC material is difficult to machine, the removal step is therefore complex and costly.

[0005] Furthermore, the machined face is devoid of coating; it is therefore not protected from the engine environment. Summary of the invention

[0006] The present invention improves the situation. It proposes a method for coating a turbomachine part comprising: - fixing the turbomachine part to a support using a ceramic glue to obtain a solid assembly of the turbomachine part and the support, the support and / or the ceramic glue being made of graphite; - applying a coating to a surface of the turbomachine part, the turbomachine part being held by the support; - heat treatment of the assembly under an oxidizing atmosphere.

[0007] The support is intended to support the turbomachine part by bonding during the application of the coating. It allows the turbomachine part to be handled during the application of the coating. The support is preferably bonded to areas of its surface that are little exposed to the engine environment during its use. In particular, in the case of a distributor vane comprising a cavity, the support is preferably bonded to an area of ​​the surface of the part located in the cavity.

[0008] One of the advantages of the method is that chemical clamping does not present any risk of mechanical damage, such as scratches or indentations, to the turbomachine part, unlike mechanical clamping requiring tightening on it.

[0009] Furthermore, there is no need to disassemble the turbomachine part between different operations; the support is integral with the turbomachine part and follows it throughout the treatments to which the turbomachine part is subjected.

[0010] In certain cases, functionalization is obtained at the end of the coating process thanks to the ceramic glue whose ceramic layer plays the role of protection, for example anti-diffusion of chemical species.

[0011] Other optional features are as follows.

[0012] The ceramic glue can be chosen from an alumina-based glue, a mullite-based glue and a graphite-based glue; and the support is made of graphite.

[0013] The ceramic adhesive may be a graphite-based adhesive; and the support may be made of a ceramic matrix composite material.

[0014] The fixing may comprise the formation of an intermediate space between the turbomachine part and the support, and the injection of the ceramic adhesive into the intermediate space.

[0015] The application of the coating may comprise: - the application of a bonding undercoat on the turbomachine part; and - the application of a protective layer on the bonding undercoat.

[0016] The application of the bonding undercoat can be carried out by thermal spraying or chemical vapor deposition.

[0017] The application of the protective layer can be carried out by thermal spraying, by chemical vapor deposition or by liquid means.

[0018] The heat treatment can be carried out at a temperature above 700°C, or even at a temperature above 1200°C.

[0019] The method may further comprise, prior to the application of the coating, the consolidation of the integral assembly by firing the ceramic adhesive, preferably at a temperature between 100°C and 400°C. Presentation of the drawings

[0020] Other objectives, characteristics and advantages will appear on reading the description given by way of example which follows and set out with reference to the drawings below, given for illustrative and non-limiting purposes, among which: Fig.l

[0021] [Fig.l] is a diagram illustrating a first example of embodiment of the coating method according to a first variant of the invention for coating a turbomachine part having a cavity. Fig. 2

[0022] [Fig.2] is a diagram illustrating a second example of embodiment of the coating method according to the first variant of the invention for coating a turbomachine part without a cavity. Fig. 3

[0023] [Fig.3] is a diagram illustrating a third example of embodiment of the coating method according to a second variant of the invention for the coating of a turbomachine part having a cavity. Fig. 4

[0024] [Fig.4] is a diagram illustrating a fourth example of embodiment of the coating method according to the second variant of the invention for coating a turbomachine part without a cavity. Fig. 5

[0025] [Fig.5] is a flowchart representing the steps of an exemplary embodiment of the coating method according to the invention. Fig. 6

[0026] [Fig.6] is a flowchart representing the steps of another exemplary embodiment of the coating method according to the first variant of the invention. Fig. 7

[0027] [Fig.7] is a flowchart representing the steps of an example of the realization of the step of fixing [Fig.5] and [Fig.6]. Fig. 8

[0028] [Fig.8] is a flowchart representing the steps of an exemplary embodiment of the actual coating step of [Fig.5] and [Fig.6]. Fig. 9

[0029] [Fig.9] is a diagram showing a section through the thickness of a piece of turbomachine coated according to the first variant of the coating method according to the invention. Fig. 10

[0030] [Fig. 10] is a diagram showing a section through the thickness of a turbomachine part coated according to the second variant of the coating method according to the invention. Detailed description

[0031] A method of coating a turbomachine part will be described in more detail below with reference to the figures.

[0032] The coating method comprises, as illustrated in [Fig.5], the fixing S100 of the turbomachine part 1 on a support 2 using a ceramic adhesive 3 to obtain a solid assembly of the turbomachine part 1 and the support 2, the application S300 of a coating 13, and the heat treatment S400 of the assembly under an oxidizing atmosphere. The support 2 and / or the ceramic adhesive 3 is made of graphite. During the heat treatment S400, the support 2 can thus be removed from the turbomachine part 1 without damaging it, either by disintegration of the ceramic adhesive 3, or by disintegration of the support 2.

[0033] This method is particularly advantageous for turbomachine parts requiring the application of a coating, particularly at high temperature. For example, turbomachine parts made of ceramic matrix composite intended to be used in an engine environment and therefore subjected to the flow of hot gas, must be protected from this environment by the application of a protective coating forming an environmental barrier layer, called Environmental Barrier Coating (EBC) in English, or a thermal barrier layer, called Thermal Barrier Coating (TBC) in English. This application is followed by a heat treatment step to sinter the protective coating.

[0034] The turbomachine part 1 may in particular be a distributor or a distributor sector, a blade, a ring or a ring sector, etc. In the example of [Fig.l], the turbomachine part 1 is a hollow distributor blade. It comprises a body 11 in which a cavity 14 is formed.

[0035] The attachment S100 of the support 2 to the turbomachine part 1 is preferably carried out on a surface 19 of the part relatively little subjected to the flow of hot gases coming from the combustion chamber. In this case, in the example of [Fig.l], the support 2 is attached to an area of ​​the surface of the part located in the cavity 14.

[0036] The thickness of the ceramic glue 3 is preferably less than 500 μm. Beyond this upper limit, the glue risks being excessively porous.

[0037] The fixing S100 may comprise the formation S110 of an intermediate space 9 between the turbomachine part 1 and the support 2 as well as the injection S120 of the ceramic glue 3 into this intermediate space 9 ([Fig.8]).

[0038] The interposed space 9 between the turbomachine part 1 and the support 2 corresponds to the thickness of glue to be obtained. It therefore preferably has a dimension less than 500 μm.

[0039] Preferably, the injection S120 is carried out at room temperature, in particular between 20 and 25°C.

[0040] The support 2 allows the turbomachine part 1 to be held during the application S300 of the coating and the heat treatment S400. The support 2 is typically a part having a bonding surface whose shape is complementary to that of the surface 19 of the turbomachine part 1, on which the support 2 is bonded. In the case of a turbomachine part 1 having a cavity 14 (see [Fig.l] and [Fig.3]) having an outer surface intended to support the machine environment and an inner surface which is not subjected to the flow of hot gases, the support 2 may be a counterform of the cavity 14 of the turbomachine part 1. In other cases, the support may be an elongated part (see [Fig.2] and [Fig.4]) having at one of its ends a relatively reduced bonding surface, that is to say that its area corresponds to less than 25% of the total surface 18 to be covered of the turbomachine part 1.

[0041] The support 2 may be made of a ceramic material, for example graphite. It may also be made of a composite material with a ceramic matrix, in particular a so-called oxide / oxide composite, in which the composition of the fibers of the fibrous reinforcement and that of the matrix comprise a ceramic based on one or more oxides, for example alumina.

[0042] The ceramic adhesive 3 can be chosen from alumina-based adhesives, mullite-based adhesives and graphite-based adhesives.

[0043] Furthermore, the fixing method described here also allows the attachment of a witness representative of the turbomachine part on a surface thereof not subjected to the flow of hot gases. Thus, the witness is integral with the turbomachine part during the treatments thereof. The monitoring of the part can therefore be ensured throughout its manufacture. Furthermore, the clamping of the witness on the turbomachine part 1 is resistant to the temperatures inflicted on the turbomachine part 1. This fixing results in an intermediate assembly comprising the turbomachine part 1, the witness and the ceramic adhesive 3 between a surface 19 of the turbomachine part 1 which is not intended to be subjected to the flow of hot gases, and the witness.

[0044] The application S300 of the coating may comprise the application S310 of a bonding underlayer 131 on the turbomachine part 1 and the application S320 of a protective layer 132 on the bonding underlayer 131 (see [Fig.8], [Fig.9] and [Fig.10]).

[0045] The bonding sub-layer 131 is for example made of silicon. It makes it easier to bond the protective layer 132 to the turbomachine part 1.

[0046] The application S310 of the bonding undercoat 131 can be carried out by thermal spraying or chemical vapor deposition. In the case of thermal spraying, the temperature is preferably greater than 500°C.

[0047] The protective layer 132 may be made of a material chosen from rare earth silicates. It makes it possible in particular to form an environmental barrier layer and / or a thermal barrier layer.

[0048] The application S320 of the protective layer 132 can be carried out by thermal spraying or by liquid means. In the case of thermal spraying, the temperature is preferably greater than 500°C. An example of a liquid means is electrophoresis.

[0049] The S400 heat treatment is carried out in an oxidizing atmosphere, for example in air. Advantageously, it is carried out at a temperature above 1200°C, allowing the oxidation of the graphite. Since the ceramic adhesive 3 and / or the support 2 are made of graphite, the S400 heat treatment leads to the elimination of this graphite element, which results in a separation between the support 2 and the turbomachine part 1.

[0050] The S400 heat treatment can also allow the sintering of the protective layer 132.

[0051] The coating method described here has mainly two implementation variants.

[0052] In a first variant of the invention, the support 2 is made of graphite. Thus, the support 2 is removed during the heat treatment step S400 and forms a sacrificial element. In this variant, the ceramic adhesive 3 can be chosen from alumina-based adhesives, mullite-based adhesives and graphite-based adhesives.

[0053] If the ceramic adhesive chosen is alumina-based or mullite-based, it is ceramized during the S400 heat treatment and forms a protective layer 12 (see [Fig.l], [Fig.2] and [Fig.9]), in particular an anti-diffusion protective layer, which will remain on the finished turbomachine part. Indeed, during their use, the turbomachine parts can come into contact with metal parts. This contact leads to diffusion of elements between the metal and the ceramic. Thus, the method has the advantage, not only of simplifying the method of coating the turbomachine part 1, and in particular its surface intended to be subjected to the engine environment, but also makes it possible to apply a protective layer 12 to another surface.

[0054] If the ceramic glue 3 is graphite-based, it is also removed during the S400 heat treatment (see [Fig. 10]).

[0055] In an embodiment illustrated in [Fig.6], the method may further comprise, prior to the application S300 of the coating, the consolidation S200 of the integral assembly by baking the glue, preferably between 100°C and 400°C, for a duration of between 1 hour and 3 hours.

[0056] In a second variant of the invention, the support 2 is not sacrificial and is recovered at the end of the process for subsequent use. In this case, the support 2 may be made of a ceramic matrix composite material, for example oxide / oxide.

[0057] The ceramic glue 3 is then a graphite-based glue.

[0058] In each of the two variants of the invention, the elimination of the support 2 and / or the ceramic glue 3 during the heat treatment S400 avoids a machining step to remove the link between the turbomachine part 1 and the support 2.

Claims

Claims

1. Method for coating a turbomachine part (1), comprising: - fixing (S 100) the turbomachine part on a support (2) using a ceramic adhesive (3) to obtain a solid assembly of the turbomachine part and the support, the support and / or the ceramic adhesive being made of graphite; - applying (S300) a coating (13) to a surface of the turbomachine part, the turbomachine part being held by the support (2); - heat treating (S400) the assembly in an oxidizing atmosphere.

2. A method according to claim 1, wherein the ceramic adhesive is selected from an alumina-based adhesive, a mullite-based adhesive and a graphite-based adhesive; and the support is made of graphite.

3. A method according to claim 1, wherein the ceramic adhesive is a graphite-based adhesive; and the support is made of a ceramic matrix composite material.

4. Method according to one of claims 1 to 3, in which the fixing comprises the formation (SI 10) of an intermediate space (9) between the turbomachine part and the support, and the injection (S 120) of the ceramic glue into the intermediate space.

5. Method according to one of claims 1 to 4, in which the application of the coating comprises: - the application (S310) of a bonding undercoat on the turbomachine part; and - the application (S320) of a protective layer on the bonding undercoat.

6. Method according to claim 5, in which the application of the bonding undercoat is carried out by thermal spraying or chemical vapor deposition.

7. A method according to claim 5 or claim 6, wherein the application of the protective layer is carried out by thermal spraying, by chemical vapor deposition or by liquid means.

8. Method according to one of claims 1 to 7, in which the heat treatment is carried out at a temperature above 700°C, or even at a temperature above 1200°C.

9. Method according to one of claims 1 to 8, further comprising, prior to the application of the coating, the consolidation (S200) of the integral assembly by firing the ceramic glue, preferably at a temperature between 100°C and 400°C. Title: Process for coating a turbomachine part

Images