Process for manufacturing a natively crystallized environmental barrier in a thermodynamically stable form

Abstract

Method for manufacturing a natively crystallized environmental barrier in a thermodynamically stable form The present invention relates to a method for manufacturing a part (1) with improved resistance to oxidation and corrosion at high temperature, comprising at least the deposition of a layer (7) of uncracked β-Yb2Si2O7 crystalline environmental barrier on a composite material (3) with an at least partially ceramic matrix, said environmental barrier layer being deposited by chemical vapor deposition from a gas phase comprising a precursor mixture of (a) silicon tetrachloride, and (b) elemental ytterbium or ytterbium (III) chloride, and imposing during the deposition a temperature of between 1100°C and 1300°C, and a pressure of less than or equal to 150 mbar. Figure for abstract: Fig. 1.

Description

Title of the invention: Method for manufacturing a natively crystallized environmental barrier in a thermodynamically stable form Technical field

[0001] A particular field of application of the invention is the protection of composite materials with an at least partially ceramic matrix ("CMC materials") forming hot parts of gas turbines, such as turbine nozzles or turbine blades, for aeronautical engines or industrial turbines. Prior art

[0002] Improving efficiency and reducing pollutant emissions leads to considering ever higher temperatures in combustion chambers. It has therefore been proposed to replace metallic materials with CMC materials. Indeed, CMC materials are known to have both good mechanical properties allowing their use for structural elements and the ability to retain these properties at high temperatures. CMC materials may comprise a fibrous reinforcement of refractory fibers, typically carbon or ceramic, which is densified by a ceramic matrix, for example silicon carbide.

[0003] Under the operating conditions of aeronautical turbines, i.e. at high temperature in an oxidizing and humid atmosphere, CMC materials are sensitive to the phenomenon of corrosion. Corrosion of CMC results from the oxidation of silicon carbide into silica which, in the presence of water vapor, volatilizes in the form of silicon hydroxides Si(OH)4. Corrosion phenomena cause a recession of the CMC and affect the lifetime of the latter. In order to limit this degradation in operation, it has been considered to form environmental barriers on the surface of the CMC materials ("Environmental Barrier Coating"; "EBC"). The environmental barriers may comprise a silicon bonding layer as well as a rare earth silicate layer positioned on the bonding layer.The bonding layer allows, on the one hand, to improve the adhesion of the rare earth silicate layer and, on the other hand, to form a protective silica layer, whose low permeability to oxygen contributes to the protection of the CMC against oxidation. The rare earth silicate layer allows, for its part, to limit the diffusion of water vapor towards the silica layer formed by oxidation of the silicon and consequently to limit its recession. Environmental barriers can be deposited. by thermal projection. In particular, US2019040761 is known, which describes the formation of an EBC by such a method.

[0004] Turbine and nozzle blades have a relatively complex shape and may require relatively thin environmental barriers to avoid affecting aerodynamic properties, so thermal spraying may not produce a coating that meets the required performance.

[0005] Application WO2022069812 proposes an alternative to thermal spraying by producing the environmental barrier by chemical vapor deposition of organometallic compound(s) by direct liquid injection (“Direct Liquid Injection-Metal Organic Chemical Vapor Deposition”; “DLLMOCVD”). This technique makes it possible to obtain a dense, thin layer with a controlled composition. This document recommends carrying out, after deposition of the environmental barrier, a high-temperature crystallization heat treatment in order to reduce the proportion of amorphous phase present and thus avoid an evolution of the layer under service conditions. It is nevertheless possible to further improve the protection conferred on CMC materials in an oxidizing and corrosive environment at high temperature, in particular greater than or equal to 800°C. Statement of the invention

[0006] The present disclosure relates to a method for manufacturing a part with improved resistance to oxidation and corrosion at high temperature, comprising at least the deposition of a crystalline environmental barrier layer of [3-Yb2Si2O7] not cracked on a composite material with an at least partially ceramic matrix, said environmental barrier layer being deposited by chemical vapor deposition from a gas phase comprising a precursor mixture of (a) silicon tetrachloride, and (b) elemental ytterbium or ytterbium (III) chloride, and imposing during the deposition a temperature of between 1100°C and 1300°C, and a pressure of less than or equal to 150 mbar.

[0007] The invention is based on depositing, by chemical vapor deposition ("CVD"), an environmental barrier layer of particular composition, made of ytterbium disilicate Yb2Si2O7, using particular precursors and controlled temperature and pressure conditions so as to form, directly during deposition, an environmental barrier layer that is not cracked and natively crystallized in the crystallographic form most favorable to the performance of the EBC in service, in this case the [3] form of ytterbium disilicate which is noted [3-Yb2Si2O7. The crystallographic structure of [3-Yb2Si2O7 has the advantage of not changing in service under the effect of the high-temperature oxidizing environment (no appearance of harmful cracks or porosity) which provides stability of the protection provided over the life of the part. In addition, the non-cracked nature of the barrier during its development makes it possible to guarantee effective protection even if the deposit has a small thickness, which can be of particular interest in the case of a turbine blade or nozzle application. The invention corresponds to a specific selection of a deposition technique and particular precursors, as well as controlled temperature and pressure conditions during deposition which directly result in an equilibrium, non-cracked crystallized form, without requiring subsequent crystallization heat treatment. The invention makes it possible to obtain a dense and waterproof coating and to avoid oxidation of the underlying material due to the generation of in-situ water at high temperature which can be encountered with prior art chlorine deposition solutions.This oxidation is avoided by using a temperature of no more than 1300°C. Using a temperature of at least 1100°C allows a crystallized layer to be obtained.

[0008] The invention makes it possible to obtain a dense environmental barrier layer, which is not cracked during its production and is compatible with parts of complex geometry, in particular by making it possible to control the thickness and obtain a relatively thin coating.

[0009] In an exemplary embodiment, the temperature imposed during the deposition of said environmental barrier layer is between 1100°C and 1200°C, in particular between 1125°C and 1175°C. In an exemplary embodiment, the pressure imposed during the deposition of said environmental barrier layer is between 100 mbar and 150 mbar.

[0010] In an exemplary embodiment, the precursor mixture is a mixture of silicon tetrachloride and elemental ytterbium.

[0011] In an exemplary embodiment, said environmental barrier layer has a thickness less than or equal to 50 μm.

[0012] In this case, the environmental barrier layer is of thin thickness, difficult to achieve by thermal spraying. Greater thicknesses can be obtained within the scope of the invention if this is acceptable for the application considered.

[0013] In an exemplary embodiment, the method further comprises depositing a bonding layer comprising silicon on an external surface of the at least partially ceramic matrix composite material, and wherein the environmental barrier layer is deposited on said bonding layer.

[0014] In an exemplary embodiment, the method further comprises, after the deposition of said environmental barrier layer, the deposition, on said barrier layer environmental, a second layer of thermal barrier or protection against calcium and magnesium aluminosilicates.

[0015] In an exemplary embodiment, the part is a turbomachine part.

[0016] In one exemplary embodiment, the part is a turbine blade, or a part thereof less than one turbine distributor. Brief description of the drawings

[0017] [Fig-1] [Fig.l] illustrates, in a schematic manner, a first example of a part to improved resistance to oxidation and corrosion at high temperature obtainable by implementing the invention.

[0018] [Fig.2] [Fig.2] provides a test result showing a photograph obtained by scanning electron microscopy (SEM) of a deposit of ytterbium disilicate obtained within the framework of the invention.

[0019] [Fig.3] [Fig.3] illustrates, schematically, a second example of a part with improved resistance to oxidation and corrosion at high temperature obtainable by implementing the invention. Description of the embodiments

[0020] The invention is now described by means of figures, present for descriptive purposes to illustrate certain embodiments of the invention and which should not be interpreted as limiting the latter.

[0021] [Fig.l] shows an example of part 1 comprising a CMC material 3 provided with an environmental barrier 2 which can be obtained by implementing the invention.

[0022] The 3 CMC material may comprise a fibrous reinforcement which may be made of carbon fibers (C) or ceramic fibers, for example silicon carbide fibers (SiC) or formed essentially of SiC, including Si-C-O or Si-CON fibers, i.e. also containing oxygen and possibly nitrogen. Such fibers are produced by the company Nippon Carbon under the reference "Nicalon" or "Hi-Nicalon" or "Hi-Nicalon Type-S", or by the company Ube Industries under the reference "Tyranno-ZMI". The ceramic fibers may be coated with a thin interphase layer of pyrolytic carbon (PyC), boron nitride (BN) or boron-doped carbon (BC, with 5% at. to 20% at. of B, the balance being C).

[0023] The fibrous reinforcement is densified by a matrix that is at least partially ceramic, for example predominantly ceramic in volume. The ceramic matrix may comprise silicon carbide or a Si-BC ternary system, for example. The matrix may be at least partly formed by CVI in a manner known per se. Alternatively, the matrix may be at least partly formed by liquid means (impregnation with a precursor resin of the matrix and transformation by crosslinking and pyrolysis, the process being repeatable) or by infiltration of silicon in the molten state (Melt-Infiltration process). In the latter case, a powder is introduced into the possibly partially densified fibrous reinforcement, this powder being able to be a carbon powder, a ceramic powder for example silicon carbide, or a mixture of such powders, and a metallic composition based on silicon in the molten state is then infiltrated to form a SiC-Si type matrix. The fibrous reinforcement can be woven or not, it is not outside the scope of the invention when the fibrous reinforcement is in the form of short fibers dispersed in the material 3. Alternatively, a particulate reinforcement can be used in the form of grains dispersed in the material 3.

[0024] The environmental barrier 2 may be formed on the entire external surface S of the CMC material 3 or on only a portion of this surface S, for example when only a portion of the surface S must be protected. In the example illustrated in [Fig.l], the environmental barrier 2 comprises an environmental barrier layer 7 and a bonding layer 5 present between the CMC material 3 and the layer 7. In the example illustrated, the bonding layer 5 is present in contact with the surface S of the composite material 3. Furthermore, in this example, the layer 7 is in contact with the bonding layer 5.

[0025] The bonding layer 5 can, in a manner known per se, form in operation a layer of silica which protects against oxidation (so-called “TGO” layer for “Therally Grown Oxide”). The bonding layer 5 can be made of silicon.

[0026] Layer 7 is an environmental barrier layer providing protection against oxidation and corrosion at high temperature by limiting in particular the diffusion of water vapor and oxygen towards the bonding layer 5 and the CMC material 3. Layer 7 is a non-cracked crystalline layer of [3-Yb2Si2O7. The thickness el of layer 7 may be less than or equal to 1000 pm, for example between 20 pm and 100 pm, for example between 20 pm and 50 pm.

[0027] Details relating to the manufacture of the environmental barrier will now be described. The passage which will now be discussed provides details relating to the formation of the bonding layer 5.

[0028] The bonding layer 5 may be formed by chemical vapor deposition from a precursor comprising silicon comprising, for example, a silane, a monochlorosilane, a dichlorosilane, and / or a trichlorosilane. Two examples of forming the bonding layer 5 by chemical vapor deposition are described below.

[0029] According to a first example, the temperature imposed during the deposition of the bonding layer 5 may be between 900°C and 1150°C, for example between 1100°C and 1150°C, and the pressure imposed during this deposition may be between 15.3 kPa and 20 kPa, for example between 16.7 kPa and 18 kPa. During the deposition, the precursor comprising silicon can be introduced into the reaction chamber in which the 3 CMC material is present with a flow rate of between 0.05 grams / minute and 0.3 grams / minute, for example between 0.1 grams / minute and 0.2 grams / minute. According to this first example, the bonding layer 5 obtained has a crystalline microstructure. In particular, the bonding layer 5 can be made of silicon, this bonding layer 5 comprising for example columnar grains of crystalline silicon. Alternatively, the bonding layer 5 can be made of silicon alloy, for example eutectic silicon alloy or silicide. According to a second example, the bonding layer 5 comprises an amorphous silicon phase having crystalline silicon grains distributed therein, these grains possibly having an average size of between 0.03 pm and 3 pm.The amorphous silicon phase may be formed from pure silicon or silicon with boron, oxygen and / or nitrogen dispersed therein. According to this second example, the bonding layer 5 may be formed at a deposition temperature that prevents crystallization of the deposited silicon, followed by heat treatment of the bonding layer at a treatment temperature higher than the temperature imposed during deposition in order to form the crystalline silicon grains distributed in the amorphous silicon phase. The temperature imposed during deposition may be between 300°C and 700°C or between 700°C and 1000°C, and the pressure imposed during deposition may be between 1.2 kPa and 1013 hPa. The operating conditions are chosen according to the precursor used. The treatment temperature may be between 1000°C and 1400°C, for example between 1200°C and 1350°C.During deposition, the precursor comprising silicon can be introduced into the reaction chamber in which the 3 CMC material is present with a flow rate of between 0.1 grams / minute and 2 grams / minute.

[0030] The description continues by providing details relating to the manufacture of the environmental barrier layer 7 by chemical vapor deposition. As indicated above, the layer 7 is a crystalline layer of [3- Yb2Si2O7 uncracked.

[0031] The layer 7 is obtained from the precursor mixture in the gaseous state entrained towards the 3 CMC material. The 3 CMC material is heated to a temperature sufficient to allow the formation of the deposit in the optional presence of a gaseous source providing oxygen. The environmental barrier layer 7 is thus formed on the 3 CMC material.

[0032] The precursor mixture may be a mixture of silicon tetrachloride SiCl4 and elemental ytterbium Yb. The elemental ytterbium Yb may be obtained by evaporation in an internal preheating zone.

[0033] The precursor mixture may be a mixture of silicon tetrachloride SiCl4 and ytterbium(III) chloride (YbCl3). Ytterbium(III) chloride may be obtained by chlorination of Yb with Cl2 or HCl for example.

[0034] The gaseous source providing oxygen can be carbon dioxide CO2, or dioxygen O2. Carbon dioxide has the advantage of being less reactive than dioxygen and therefore allows more precise control of the quantity of oxygen introduced into the film.

[0035] As indicated above, the temperature and the pressure are controlled during the deposition of the layer 7, that is to say when the material 3 is subjected to the precursor mixture in the gaseous state. Thus, the temperature imposed during the deposition of the layer 7 is between 1100°C and 1300°C, for example between 1100°C and 1200°C, for example between 1125°C and 1175°C, for example between 1140°C and 1160°C. The pressure imposed during the deposition of the layer 7 is less than or equal to 150 mbar, for example between 100 mbar and 150 mbar. The duration of the deposition of the layer 7 is adjusted according to the desired thickness el.

[0036] The deposition of an uncracked [3-Yb2Si2O7] layer was carried out under hot wall CVD conditions, from gaseous elemental Yb and SiCl4 (QYb = 4.3 standard cubic centimeters per minute (sccm), QSiCl4 = 4.3 sccm, QH2 = 120 sccm, QCO2 = 40 sccm, P = 20 mbar, duration: 40 minutes), at 1150°C. A photograph of the resulting coating is provided in [Fig. 2]. Other tests were carried out at different temperatures. The comparative test at 1030°C led to a deposit that was not crystallized in the correct crystallographic form (mixture of ytterbium disilicate in alpha and beta form). The comparative test at 1350°C led to degradation of the underlying substrate by active oxidation.

[0037] The part 1 thus manufactured may be a part for aeronautical or aerospace application. The part 1 may be a hot part of a gas turbine of an aeronautical or aerospace engine or of an industrial turbine. The part 1 may be a turbomachine part. The part 1 may constitute at least a part of a distributor, at least a part of a nozzle or a thermal protection coating, a wall of a combustion chamber, a turbine ring sector or a turbomachine blade.

[0038] Once obtained, the part 1 is used at high temperature, greater than or equal to 800°C, in an oxidizing and corrosive atmosphere. In particular, it can be used at a temperature between 800°C and 1500°C, or even between 800°C and 1300°C. The part 1 can, in particular, be used in humid air.

[0039] The example which has just been described concerns a layer 7 of environmental barrier which forms the external surface of the coated part, that is to say forming the coating layer furthest from the material 3. However, it does not go beyond the scope of the invention if this is not the case, the environmental barrier layer being able to be coated with an additional coating as will be described in connection with [Fig.3].

[0040] [Fig. 3] shows a variant of part 11 comprising a CMC material 13 provided with a protective coating 12 which can be obtained by implementing the invention. The coating 12 comprises a barrier 17 and a bonding layer 15 present between the CMC material 13 and the barrier 17. The material 13 and the layer 15 have characteristics similar to the material 3 and the layer 5 described above. The barrier 17 comprises an environmental barrier layer 17a similar to the layer 7 described above. In the example of [Fig. 3], the layer 17b was deposited once the deposition of the layer 17a was complete, that is to say after removal of the precursors used during the CVD deposition. Layer 17b is a thermal barrier layer, known per se, for example in yttria zirconia (YSZ: ZrO2 + 8% at. Y2O3), or a protective layer against calcium and magnesium aluminosilicates (CMAS), for example in rare earth zirconate, for example in Gd2Zr2O7.Layer 17b is deposited using techniques known per se. This deposition is carried out while layer 17a is in an uncracked state and layer 17a remains uncracked during this deposition.

[0041] The expression “between ... and ...” must be understood as including the limits.

Claims

Claims

1. A method of manufacturing a part (1; 11) with improved resistance to oxidation and corrosion at high temperature, comprising at least the deposition of a layer (7; 17a) of non-cracked crystalline environmental barrier of [3-Yb2Si2O7] on a composite material (3; 13) with an at least partially ceramic matrix, said environmental barrier layer being deposited by chemical vapor deposition from a gas phase comprising a precursor mixture of (a) silicon tetrachloride, and (b) elemental ytterbium or ytterbium (III) chloride, and imposing during the deposition a temperature of between 1100°C and 1300°C, and a pressure of less than or equal to 150 mbar.

2. Method according to claim 1, wherein the temperature imposed during the deposition of said environmental barrier layer (7; 17a) is between 1100°C and 1200°C.

3. Method according to claim 2, wherein the temperature imposed during the deposition of said environmental barrier layer (7; 17a) is between 1125°C and 1175°C.

4. Method according to any one of claims 1 to 3, wherein the pressure imposed during the deposition of said environmental barrier layer (7; 17a) is between 100 mbar and 150 mbar.

5. A method according to any one of claims 1 to 4, wherein the precursor mixture is a mixture of silicon tetrachloride and elemental ytterbium.

6. Method according to any one of claims 1 to 5, wherein said environmental barrier layer (7; 17a) has a thickness (e0) less than or equal to 50 pm.

7. A method according to any one of claims 1 to 6, wherein the method further comprises depositing a bonding layer (5; 15) comprising silicon on an external surface (S) of the at least partially ceramic matrix composite material (3; 13), and wherein the environmental barrier layer (7; 17a) is deposited on said bonding layer.

8. A method according to any one of claims 1 to 7, wherein the method further comprises, after the deposition of said environmental barrier layer (7; 17a), the deposition, on said environmental barrier layer, of a second environmental barrier layer (17b). thermal or protection against calcium and magnesium aluminosilicates.

9. Method according to any one of claims 1 to 8, in which the part (1; 11) is a turbomachine part.

10. A method according to claim 9, wherein the part (1; 11) is a turbine blade, or at least part of a turbine nozzle.

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