Device for characterizing a coating and associated process

Abstract

The present invention relates to a method for characterizing the sealing of a protective coating covering a surface of a part (22) for a turbomachine (10), the method comprising the following steps: - diffusion (E1) of a gas into the protective coating, the gas comprising oxygen-18 (O18); and - determination (E2) of the location of oxygen-18 (O18) in the protective coating. Abstract figure: Fig. 3

Description

Title of the invention: Device for characterizing a coating and associated method FIELD OF THE INVENTION

[0001] The invention relates to the characterization of a turbomachine blade, in particular its sealing in an oxidizing environment. STATE OF THE ART

[0002] An aircraft turbomachine has a main direction extending along a longitudinal axis, and typically comprises, from upstream to downstream in the direction of gas flow, a fan and a primary body comprising a compression section which may comprise a low pressure compressor, a high pressure compressor, a combustion chamber, and a turbine section which may comprise a high pressure turbine and a low pressure turbine.

[0003] The turbomachine further comprises moving blades, for example mounted on a disk of the high-pressure turbine, and fixed blades, for example mounted between two platforms of a distributor of the high-pressure turbine. The blade comprises from upstream to downstream a leading edge, a blade corresponding to the aerodynamic surface of the blade and a trailing edge.

[0004] During operation of the turbomachine, these blades may be exposed to risks of corrosion caused by the flow of high-temperature air in contact with aerodynamic parts of the blade. Corrosion of ceramic matrix composite materials may result from the oxidation of silicon carbide (SiC) to silica, which in the presence of water vapor volatilizes in the form of silicon hydroxides (Si(OH)4).

[0005] In order to protect the blades against corrosion, in particular those made of ceramic matrix composite materials, an environmental barrier, comprising a layer of silicon and a layer of rare earth disilicate, is applied.

[0006] The different layers of the environmental barrier have distinct functions: - the silicon bonding layer makes it possible on the one hand to improve the adhesion of the yttrium disilicate layer and on the other hand to form a protective silica layer, the low permeability of which to oxygen contributes to the protection of the ceramic matrix composite material against oxidation; and - the rare earth disilicate layer (RE2Si2O7) limits the diffusion of water vapor towards the silica layer formed by oxidation of silicon and therefore prevents its recession. Furthermore, the latter can also play the role of thermal barrier, and / or abradable layer, and / or resistance to erosion depending on the desired properties.

[0007] The environmental barrier, in particular the rare earth disilicate layer, may comprise networks of connected porosities and / or cracks, which are detrimental to the sealing of the layer. One means of characterizing the sealing of the layer is an oxidation test in which a sample of the blade is immersed in an environment concentrated in a chosen type of oxidant for periods ranging from 500 h to 1000 h depending on the application. The sample is then removed from the environment to be examined in order to verify that it does not exhibit oxidation at the interface between the rare earth disilicate and the silicon, which would reflect permeability to oxidizing species and therefore poor protection of the substrate. Such an oxidation test has the disadvantage of being very long to carry out.

[0008] Another means of controlling the tightness of the rare earth disilicate layer consists of characterizing the network of porosities and cracks by imaging. A difficulty arises, however, from the fact that the porosities and / or cracks may have a size of the order of ten nanometers. The detection of porosities and / or cracks with such dimensions is complex to study over the entire extent of the part. In particular, a scanning electron microscope risks having insufficient resolution, while a transmission electron microscope will have sufficient but very localized resolution, involving a long analysis to study the entire surface of the part. In any case, these imaging means only make it possible to determine a two-dimensional network of porosities and / or cracks.However, a network of porosities and / or cracks can extend continuously in three-dimensional space while being discontinuous in a given plane. In order to determine whether a network of porosities and / or cracks extends continuously from the external surface of the environmental barrier to the bonding layer, it would therefore be necessary to produce a three-dimensional image of the environmental barrier with the desired resolution. Such a three-dimensional image is particularly difficult to produce.

[0009] An aim of the invention is therefore to improve the characterization of a part suitable for a turbomachine. Statement of the invention

[0010] To this end, the invention provides a method for characterizing the sealing of a protective coating covering a surface of a part for a turbomachine, the method comprising the following steps: - diffusion of a gas into the protective coating, the gas comprising oxygen 18; and - determination of the location of oxygen 18 in the protective coating.

[0011] Thus, the method makes it possible to directly characterize the tightness of the protective coating without using a sample. The evaluation is rapid and may not be deduced from a destructive test.

[0012] The part can thus form a hot part of a turbomachine.

[0013] It may be provided that a material of the part is a ceramic matrix composite or a metal alloy.

[0014] It may be provided that the protective coating comprises a protective layer, and that for example a material of the protective layer comprises a rare earth silicate.

[0015] The rare earth silicate may be provided to be an ytterbium disilicate (Yb2Si2O7), or an yttrium disilicate (Y2Si2O7), or both.

[0016] The protective coating may therefore form an environmental barrier, i.e. a protective coating against the oxidizing and / or corrosive environment of turbomachines. The protective coating may also form a thermal barrier, i.e. a thermal insulation coating, instead of or in addition to forming an environmental barrier.

[0017] It may be provided that the protective coating further comprises a silicon bonding layer on the surface of the part to be protected, the protective layer being on the bonding layer.

[0018] Thus, the bonding layer has the effect of promoting the adhesion of the protective layer to the part.

[0019] It can be provided that the volume concentration of oxygen 18 is greater than or equal to 5% by volume of the gas, preferably greater than or equal to 20% by volume of the gas.

[0020] It may be provided that the coating comprises an oxide layer, for example a layer of ytterbium disilicate, comprising porosities occupying at most 5% of the volume of the layer.

[0021] It can be provided that the step of diffusion of the gas in the protective coating comprises: - placement of the part in an enclosure; - introduction of gas into the enclosure; and - heating of the room and the gas.

[0022] Thus, oxygen 18 diffuses into the room during heating.

[0023] A step of cooling the part can be provided, for example in the open air.

[0024] It can be expected that the step of determining the location of oxygen 18 in The protective coating includes: - a cut of the protective coating; and - obtaining an image in the cutting plane.

[0025] Thus the image highlights the oxygen 18 in the protective coating.

[0026] Heating can be expected to last at least ten hours.

[0027] It can be provided that the heating takes place at a temperature above 600°C, for example between 800°C and 1000°C.

[0028] It can be provided that the cutting of the protective coating is carried out by erosion of a volume extending over a thickness of the protective coating, the erosion being carried out for example by an ion gun.

[0029] It can be expected that the localization of oxygen 18 is carried out by mass spectrometry.

[0030] The part may be provided to be a turbine blade, a turbine ring sector or a turbine nozzle.

[0031] According to the invention, a characterization device is also provided comprising: - an enclosure designed to accommodate a room; - means for diffusing oxygen 18 into the enclosure; and - means of determining the location of oxygen 18 in the room. DESCRIPTION OF FIGURES

[0032] We will now present an embodiment of the invention by way of non-limiting example with the support of the drawings in which:

[0033] [Fig.l] is an axial half-sectional view of an aircraft turbomachine comprising blades capable of being characterized by the device according to the invention;

[0034] [Fig.2] illustrates a blade of the turbomachine of [Fig.l];

[0035] [Fig.3] is a flowchart illustrating a mode of implementation of the method according to the invention;

[0036] [Fig.4] illustrates a possible mode of implementation of a step of the method according to the invention;

[0037] [Fig.5] and [Fig.6] schematically illustrate a mode of diffusion of oxygen 18 in a coating of the blade;

[0038] [Fig.7] and [Fig.8] are scanning microscope micrographs of successive layers of a first oxidation-permeable coating and a second oxidation-impermeable coating of the blade;

[0039] [Fig.9] illustrates another possible variant of the method according to the invention;

[0040] [Fig. 10] and [Fig. 11] are ion mass spectrometry micrographs secondary successive layers of a first coating permeable to oxidation and a second coating impermeable to oxidation of the blade; and

[0041] [Fig.12] is a diagram illustrating a mode of implementation of an erosion of the re- dawn garment. DETAILED DESCRIPTION OF THE INVENTION

[0042] In the present example and with reference to [Fig. 1], the turbomachine 10 has a main direction extending along a longitudinal axis X, and comprises, from upstream to downstream in the direction of gas flow, a fan 102, a primary body comprising a compression section which may comprise a low-pressure compressor 103 as well as a high-pressure compressor 104, a combustion chamber 105, and a turbine section which may comprise a high-pressure turbine 106 as well as a low-pressure turbine 107. The fan 102 may be ducted and be housed in a retention casing and comprises a nacelle 101 defining an aerodynamic envelope of the engine. Alternatively, the fan may be unducted. The airflow entering the turbomachine 10 is divided into a primary flow configured to pass through the primary body and a secondary flow which bypasses the primary body and is propelled by the fan 102.

[0043] Furthermore, the turbomachine 10 may comprise more than two bodies. The turbomachine 10 comprises at least two drive shafts, typically a high-pressure shaft 109 and a low-pressure shaft 108. The high-pressure shaft 109 is connected to the high-pressure turbine 106 and is configured to drive the high-pressure compressor 104. The low-pressure shaft 108 is connected to the low-pressure turbine 107 and is configured to drive the low-pressure compressor 103. The low-pressure shaft 108 further drives the fan 102, either directly via the low-pressure turbine or via a reduction mechanism that may comprise an epicyclic reduction gear of the planetary or star type (see [Fig.l]). The invention also applies to turbomachines comprising a third shaft connected to an intermediate turbine extending between the high-pressure turbine 106 and the low-pressure turbine 107.The intermediate turbine drives the low pressure compressor 103. The blower 102 is driven by the low pressure turbine 107.

[0044] In the present application, upstream and downstream are defined with respect to the normal flow direction of the gas in the machine 10. The axial direction corresponds to the direction of the X axis and a radial direction is a direction perpendicular to this axis and passing through it. Unless otherwise specified, internal (respectively, inside) and external (respectively, outside), respectively, are used with reference to a radial direction such that the internal part or face of an element is closer (respectively further) from the X axis than the external part or face of the same element.

[0045] The turbomachine 10 comprises blades 22 configured to be mounted for example on a disk of the high-pressure turbine 116, the disk 116 being configured to be movable in rotation around the longitudinal axis X. According to another example, the blades 22 are configured to be mounted on a distributor of the high pressure turbine 126, the distributor 126 being configured to be fixed about the longitudinal axis X.

[0046] A blade 22 comprises a root 23 configured to be, for example, fixed to the disk 116 of the high-pressure turbine 106, a blade head 25 radially external and opposite the root 23, an aerodynamic profile blade 24 capable of extending in a radial direction in the air flow from the root 23 to the head 25, as well as a leading edge 27 and a trailing edge 28. The leading edge 27, corresponding to the front part of the aerodynamic profile 24 which faces the air flow in normal operation of the engine and which divides the air flow into a pressure flow and an extrados flow, is configured to extend opposite the flow of gases entering the machine 2. The trailing edge 28 corresponds to the rear part of the profile 24, where the pressure and extrados flows meet.

[0047] In the following, the invention is particularly described in the case of a turbine blade 22. This is not, however, limiting, the invention applying to any part of a turbomachine 10.

[0048] As illustrated in [Fig. 2], the blade 22 may be made of a composite material 3, in this case with a ceramic matrix, or of a metal alloy and have a protective coating composed of a bonding layer 2 of silicon and an external protective layer 1 covering the previous one. The protective layer 1 may in particular be made of rare earth oxide, for example yttrium disilicate or ytterbium disilicate. It may also be made of yttria-containing zirconia, mullite, rare earth zirconate, and / or alumina.

[0049] As illustrated in [Fig.4], the protective coating may have cracks and / or porosities 4, in particular at the level of the protective layer 1.

[0050] In order to locate and characterize at least part of the cracks and / or porosities 4, a characterization device is provided comprising: - an enclosure designed to receive the blade 22; - means for diffusing oxygen 18 018 into an enclosure of the device; and - means for determining a location of oxygen 18 018 in the blade 22.

[0051] The enclosure is configured to house the blade 22 in a compartment. For example, the compartment is parallelepipedal in shape having a length and a width greater than several tens of centimeters, typically 50 cm. According to another example, the blade 22 can be positioned vertically in the enclosure having a height and a length greater than 5 m. In addition, the enclosure can comprise a door configured to hermetically close the enclosure after having housed the blade 22 in the compartment.

[0052] According to one embodiment, the diffusion means comprise a gas reservoir, such as a bottle, placed in fluid communication with the enclosure. It can be provided that the reservoir is hydraulically connected to a gas spray nozzle oriented into the enclosure. Thus, the nozzle makes it possible to distribute the gas homogeneously in the enclosure.

[0053] The reservoir may contain a gas, for example air, the gas comprising oxygen 18 molecules, i.e. oxygen whose mass number is equal to 18. Provision may be made for the reservoir to contain a gas, the gas consisting solely of oxygen 18.

[0054] It can also be provided that instead of a gas, the reservoir contains a liquid comprising oxygen molecules 18.

[0055] The characterization device also comprises means for heating the interior of the enclosure configured to increase the temperature of the gas or liquid comprising oxygen 18, as well as that of the blade 22. Thus, the thermal agitation of the gas or liquid facilitates the diffusion of oxygen 18 in the porous network and the cracks of the protective coating and allows the substitution of the oxygen 16 present in this protective coating by oxygen 18.

[0056] The means for locating the oxygen 18 018 make it possible to locate the networks of cracks and / or porosities 4 in the protective coating opening onto an external surface of the protective coating. Indeed, as illustrated in [Fig.5], the oxygen 18 018 will penetrate each continuous network of porosities and / or fractures extending from the external surface of the protective coating, replace the oxygen 16 of the protective coating in contact with the oxygen 18, and remain trapped in the protective coating after the temperature has decreased. Locating the oxygen 18 018 in the protective coating therefore also amounts to locating the cracks and / or porosities 4 of the protective coating opening onto the outside. The locating means may comprise a secondary ion mass spectrometer (SIMS), for example directly integrated into the compartment.

[0057] Method for characterizing the tightness of a protective coating

[0058] An embodiment of the method for characterizing the tightness of a protective coating is described with reference to [Fig. 3]. The characterization device described above is configured to implement the characterization method. For example, it is considered that the protective coating covers the surface of a turbine blade.

[0059] During a step E1, a gas comprising oxygen 18 018 is diffused into the protective coating.

[0060] During a step E2, a location of oxygen 18 018 is determined in the protective coating.

[0061] With reference to [Fig.4], the step E1 of diffusion of the gas into the protective coating may comprise the following steps.

[0062] During a step E10, the blade 22 is placed in the enclosure.

[0063] During a step El 1, the gas or liquid is introduced into the enclosure comprising oxygen 18 018. For example, the gas from the cylinder is introduced such that a volume concentration of oxygen 18 018 is greater than or equal to 5% by volume of the gas in the enclosure, preferably greater than or equal to 20% by volume of the gas in the enclosure. Provision may be made to introduce the gas consisting solely of oxygen 18 018 such that a volume concentration of oxygen 18 018 is equal to 100% by volume of the gas in the enclosure.

[0064] During a step E12, the gas and the blade 22 are heated to a temperature greater than 600°C, preferably between 800°C and 1000°C.

[0065] The heating step E12 lasts at least ten hours so that the oxygen 18 018 has sufficient time to diffuse into most of the crack and / or porosity networks 4.

[0066] During a step E13, the blade 22 is extracted from the enclosure to cool, for example in the open air so as to better observe the networks of cracks and / or porosities 4 by reducing the thermal excitation within the protective layer 1.

[0067] [Fig. 5] schematically illustrates an example in which the oxygen 18 018 diffuses into a crack 4 of the protective layer 1 of the blade 22. The protective layer 1 being an oxide comprising oxygen 16 isotopes, the oxygen 18 018 replaces the oxygen 16 in the crack 4. Thus, as schematically illustrated in [Fig. 6], the isotopes 18 in the enclosure are inserted into the coating of the blade 22 and are found around the crack 4 after diffusion.

[0068] It is understood that diffusion in the coating means that the 018 isotopes can be found at any location in a volume delimited by the protective coating, in particular in the case of a coating having a significant thickness, i.e. the thickness is between 5 qm and 2 mm.

[0069] With reference to [Fig.7], step E2 of determining a location of oxygen 18 018 in the protective coating is now described.

[0070] During a step E21, a cut is made in the protective coating.

[0071] According to one embodiment, the cut can be made in a plane perpendicular dicular to the protective coating. A slice of the blade is therefore obtained, the slice highlighting the networks of porosity and / or cracks 4 over a thickness of the protective coating.

[0072] According to another embodiment, the cutting can be carried out by erosion of a volume extending over a thickness of the protective coating. The erosion consists of removing a layer of the protective coating in order to reveal the networks of porosities and / or cracks 4 under the layer. Erosion can for example be implemented by an ion gun ([Fig. 12]).

[0073] A beam diameter of the ion gun is for example less than 5 pm.

[0074] Thus, the characterization of the tightness of the protective coating is not deduced from a destructive test.

[0075] During a step E22, an image in a plane of the section is obtained. The image may for example be a micrograph obtained by secondary ion mass spectrometry (SIMS) in which the coating is scanned by a beam of energetic ions sputtering the coating and then the material is analyzed by mass spectrometry to obtain the image.

[0076] Thus, the image obtained corresponds to a micrograph in which oxygen 18 018 is highlighted. It is then possible to visualize on the image the networks of porosity and / or cracks 4.

[0077] Two coatings are tested in order to verify that the oxygen 18 018 is located in the networks of porosity and / or cracks 4 and to characterize an oxidation tightness of each coating. The first coating, a scanning microscope micrograph of which is illustrated in [Fig.8], is not oxidation tight and comprises a first layer of ytterbium disilicate DSY comprising porosities occupying 8% of the volume of the DSY layer above a silicon Si layer. The second coating, a scanning microscope micrograph of which is illustrated in [Fig.9], is oxidation tight and comprises the first DSY layer superimposed on a second layer of ytterbium disilicate DSYb comprising porosities occupying 4% of the volume of the DSYb layer, the second layer being on the silicon Si layer.

[0078] The protective layer 1 made of ytterbium disilicate is impervious to oxidation for a quantity of porosities occupying at most 5% of the volume of the layer 1, a protective layer 1 comprising porosities occupying 4% of the volume of the layer being a preferred value.

[0079] [Fig. 10] and [Fig. 11] illustrate secondary ion mass spectrometry micrographs of a section of the protective coating of the blade 22 obtained following the section of the blade 22 in which the oxygen 18 018 has diffused. The oxygen 18 018 is located in the pore networks 4 visible in [Fig. 8] and [Fig. 9]. In addition, the location of the oxygen 18 018 confirms that the first coating of [Fig. 8] is permeable to oxidation and that the second coating of [Fig. 9] is impermeable to oxidation.

[0080] These results are consistent with oxidation tests at 500 h and 1000 h carried out on the two coatings.

[0081] Of course, numerous modifications can be made to the invention without to go beyond the framework of this one.

Claims

Claims

1. Method for characterizing the tightness of a protective coating covering a surface of a part (22) for a turbomachine (10), the method comprising the following steps: - diffusion (El) of a gas in the protective coating, the gas comprising oxygen 18 (018); and - determination (E2) of a location of the oxygen 18 (018) in the protective coating.

2. The method of claim 1, wherein a volume concentration of oxygen 18 is greater than or equal to 5% by volume of the gas, preferably greater than or equal to 20% by volume of the gas.

3. Method according to one of claims 1 to 2, in which the coating comprises a layer (1) of oxide, for example a layer (1) of ytterbium disilicate, comprising porosities occupying at most 5% of the volume of the layer (1).

4. Method according to one of claims 1 to 3, in which the step of diffusion (El) of the gas in the protective coating comprises: - a placement (E10) of the part (22) in an enclosure; - an introduction (El 1) of the gas into the enclosure; and - a heating (E12) of the part (22) and of the gas (O18).

5. Method according to one of claims 1 to 4, in which the step of determining (E2) the location of oxygen 18 (O18) in the protective coating comprises: - a section (E21) of the protective coating; and - obtaining an image (E22) in a plane of the section.

6. A method according to claim 5, wherein the cutting of the protective coating is carried out by erosion of a volume extending over a thickness of the protective coating, the erosion being carried out for example by an ion gun.

7. Method according to one of claims 5 to 6, in which the image is obtained by secondary ion mass spectrometry.

8. Method according to one of claims 1 to 7, in which the part (22) is a turbine blade, a turbine ring sector or a turbine nozzle.

9. Characterization device comprising: - an enclosure arranged to receive a part, - means for diffusing oxygen 18 (018) into the enclosure; and - means for determining the location of oxygen 18 (018) in the room.

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