Method for manufacturing an environmental barrier that is natively crystallized 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 high-temperature corrosion, comprising at least the deposition of a layer (7) of uncracked crystalline β-Yb2Si2O7 environmental barrier on a composite material (3) with a matrix at least partially composed of ceramic, said environmental barrier layer being deposited by chemical vapor deposition from a gaseous phase comprising a precursor mixture of (a) silicon tetrachloride, and (b) elemental ytterbium or ytterbium(III) chloride, and by imposing during deposition a temperature between 1100°C and 1300°C, and a pressure less than or equal to 150 mbar. Figure for the 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 a matrix at least partially composed of ceramics (“CMC materials”) forming hot parts of gas turbines, such as turbine distributors or turbine blades, for aircraft engines or industrial turbines. Prior art

[0002] Improving efficiency and reducing pollutant emissions leads to the consideration of ever-higher temperatures in combustion chambers. It has therefore been proposed to replace metallic materials with CMC materials. Indeed, CMC materials are known to possess both good mechanical properties, allowing their use for structural elements, and the ability to retain these properties at high temperatures. CMC materials may include 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 aircraft turbines, i.e., at high temperature in an oxidizing and humid atmosphere, CMC materials are susceptible to corrosion. CMC corrosion results from the oxidation of silicon carbide to silica, which, in the presence of water vapor, volatilizes as silicon hydroxides, Si(OH)4. Corrosion causes the CMC to shrink and reduces its service life. To limit this degradation during operation, the application of environmental barrier coatings (EBCs) to the surface of the CMC materials has been considered. These environmental barriers may include a silicon bonding layer and a rare-earth silicate layer positioned on top of the bonding layer.The bonding layer improves the adhesion of the rare-earth silicate layer and forms a protective silica layer. The low oxygen permeability of this silica layer helps protect the CMC from oxidation. The rare-earth silicate layer, in turn, limits the diffusion of water vapor into the silica layer formed by silicon oxidation, thus limiting its shrinkage. Environmental barriers can then be applied. by thermal projection. In particular, US2019040761 is known to describe the formation of an EBC by such a method.

[0004] Turbine blades and distributors have a relatively complex shape and may require relatively thin environmental barriers so as not to affect aerodynamic properties, so thermal spraying may not produce a coating meeting the required performance.

[0005] Application WO2022069812 proposes an alternative to thermal spraying by creating the environmental barrier through direct liquid injection of organometallic compound(s) using the chemical vapor deposition method ("Direct Liquid Injection-Metal Organic Chemical Vapor Deposition"; "DLLMOCVD"). This technique produces a dense, thin layer with a controlled composition. This document recommends applying a high-temperature crystallization heat treatment after the environmental barrier has been deposited to reduce the proportion of amorphous phase present and thus prevent the layer from evolving under service conditions. It is nevertheless possible to further improve the protection provided to CMC materials in oxidizing and corrosive environments at high temperatures, particularly at or above 800°C. Description of the invention

[0006] The present description relates to a method for manufacturing a part with improved resistance to oxidation and high-temperature corrosion, comprising at least the deposition of an uncracked crystalline environmental barrier layer of [3-Yb2Si2O7] on a composite material with a matrix at least partially made of ceramic, said environmental barrier layer being deposited by chemical vapor deposition from a gaseous phase comprising a precursor mixture of (a) silicon tetrachloride, and (b) elemental ytterbium or ytterbium(III) chloride, and imposing during the deposition a temperature between 1100°C and 1300°C, and a pressure less than or equal to 150 mbar.

[0007] The invention is based on depositing, by chemical vapor deposition (CVD), an environmental barrier layer of a particular composition, made of ytterbium disilicate Yb2Si2O7, using specific precursors and controlled temperature and pressure conditions so as to form, directly during deposition, an uncracked environmental barrier layer that is natively crystallized in the crystallographic form most favorable to the EBC's performance in service, in this case the [3] form of ytterbium disilicate, denoted [3-Yb2Si2O7. The crystallographic structure of [3-Yb2Si2O7] has the advantage of not evolving in service under the effect of the oxidizing environment at high temperature (no harmful cracking or porosity occurs). This ensures the stability of the protection provided throughout the part's lifespan. Furthermore, the uncracked nature of the barrier during its fabrication guarantees effective protection even with a thin coating, which can be particularly advantageous in turbine blade or distributor applications. 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, uncracked crystalline form, without requiring subsequent crystallization heat treatment. The invention makes it possible to obtain a dense and watertight coating and avoids oxidation of the underlying material due to the generation of high-temperature in-situ water, a problem that can occur with prior art chlorinated 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 for the formation of a crystallized layer.

[0008] The invention makes it possible to obtain a dense environmental barrier layer, uncracked during its development and compatible with parts of complex geometry by allowing in particular to control the thickness and to obtain a relatively thin coating.

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

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

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

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

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

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

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

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

[0017] [Fig-1] Fig. 1 illustrates, schematically, a first example of a part with improved resistance to oxidation and high-temperature corrosion can be obtained by implementing the invention.

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

[0019] [Fig. 3] Fig. 3 schematically illustrates a second example of a part improved resistance to oxidation and high-temperature corrosion can be obtained by implementing the invention. Description of the implementation methods

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

[0021] Fig. 1 shows an example of part 1 comprising a CMC material 3 provided with an environmental barrier 2 which can be obtained by implementation of 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 (SiC) fibers or fibers essentially composed of SiC, including Si-C-0 or Si-CON fibers, i.e., fibers also containing oxygen and possibly nitrogen. Such fibers are produced by Nippon Carbon under the reference "Nicalon" or "Hi-Nicalon" or "Hi-Nicalon Type-S", or by 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.% B, the remainder being C).

[0023] The fibrous reinforcement is densified by a matrix that is at least partially ceramic, for example, predominantly ceramic by volume. The ceramic matrix may comprise silicon carbide or a Si-BC ternary system, for example. The matrix may be at least partially formed by CVI in a manner known per se. Alternatively, the matrix may be at least partially formed by liquid process (impregnation with a matrix precursor resin and transformation by crosslinking and pyrolysis, (the process can be repeated) or by molten silicon infiltration (the "Melt-Infiltration" process). In the latter case, a powder is introduced into the possibly partially densified fibrous reinforcement. This powder can be carbon powder, ceramic powder, silicon carbide, or a mixture of such powders, and a molten silicon-based metallic composition is then infiltrated to form a SiC-Si matrix. The fibrous reinforcement can be woven or non-woven; it remains within the scope of the invention when the fibrous reinforcement is in the form of short fibers dispersed in the material. Alternatively, a particulate reinforcement in the form of grains dispersed in the material can be used.

[0024] The environmental barrier 2 can be formed over the entire external surface S of the CMC material 3 or over only a portion of this surface S, for example, when only a part of the surface S needs to be protected. In the example illustrated in [Fig. 1], the environmental barrier 2 comprises an environmental barrier layer 7 and an adhesion layer 5 located between the CMC material 3 and layer 7. In the illustrated example, the adhesion layer 5 is in contact with the surface S of the composite material 3. Furthermore, in this example, layer 7 is in contact with the adhesion layer 5.

[0025] The adhesion layer 5 can, in a manner known per se, form a protective silica layer against oxidation during operation (the so-called "TGO" layer for "Thermally Grown Oxide"). The adhesion layer 5 can be made of silicon.

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

[0027] We will now describe details relating to the manufacture of the environmental barrier. The passage that will now be addressed provides details relating to the formation of the bonding layer 5.

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

[0029] According to a first example, the temperature applied during the deposition of the adhesion layer 5 can be between 900°C and 1150°C, for example between 1100°C and 1150°C, and the pressure applied during this deposition can be between 15.3 kPa and 20 kPa, for example between 16.7 kPa and 18 kPa. During deposition, the precursor A material containing silicon can be introduced into the reaction chamber containing the CMC material 3 at 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 resulting adhesion layer 5 has a crystalline microstructure. In particular, the adhesion layer 5 can be made of silicon, this adhesion layer 5 comprising, for example, columnar grains of crystalline silicon. Alternatively, the adhesion layer 5 can be made of a silicon alloy, for example, a silicon eutectic alloy or a silicide. According to a second example, the adhesion layer 5 comprises an amorphous silicon phase with crystalline silicon grains distributed within it, these grains having an average size of between 0.03 µm and 3 µm.The amorphous silicon phase can be formed from pure silicon or silicon with boron, oxygen, and / or nitrogen dispersed within it. According to this second example, the adhesion layer (5) can be formed at a deposition temperature that prevents crystallization of the deposited silicon. This is followed by heat treatment of the adhesion layer at a processing temperature higher than the deposition temperature to form the crystalline silicon grains distributed within the amorphous silicon phase. The deposition temperature can range from 300°C to 700°C or from 700°C to 1000°C, and the deposition pressure can range from 1.2 kPa to 1013 hPa. The operating conditions are chosen according to the precursor used. The processing temperature can range from 1000°C to 1400°C, for example, from 1200°C to 1350°C.During deposition, the silicon-containing precursor can be introduced into the reaction chamber containing the 3CMC material at a flow rate of between 0.1 gram / minute and 2 gram / minute.

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

[0031] Layer 7 is obtained from the precursor mixture in a gaseous state, which is drawn towards the CMC material 3. The CMC material 3 is heated to a temperature sufficient to allow the formation of the deposit, possibly in the presence of an oxygen-supplying gaseous source. This forms the environmental barrier layer 7 on the CMC material 3.

[0032] The precursor mixture can be a mixture of silicon tetrachloride SiCl4 and elemental ytterbium Yb. Elemental ytterbium Yb can 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 oxygen source can be carbon dioxide (CO2) or dioxygen (O2). Carbon dioxide has the advantage of being less reactive than dioxygen and therefore allows for finer control of the amount of oxygen introduced into the film.

[0035] As mentioned above, the temperature and pressure are controlled during the deposition of layer 7, that is, when the material 3 is subjected to the precursor mixture in the gaseous state. Thus, the temperature applied during the deposition of 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 applied during the deposition of layer 7 is less than or equal to 150 mbar, for example between 100 mbar and 150 mbar. The duration of the deposition of 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, starting 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 resulted in a deposit that did not crystallize in the correct crystallographic form (a mixture of ytterbium disilicate in alpha and beta forms). The comparative test at 1350°C resulted in degradation of the underlying substrate by active oxidation.

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

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

[0039] The example just described concerns an environmental barrier layer 7 which forms the external surface of the coated part, i.e. forming the coating layer furthest from material 3. However, we do not leave 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] Figure 3 shows a variant of part 11 comprising a CMC material 13 with a protective coating 12 that can be obtained by implementing the invention. The coating 12 includes a barrier 17 and an adhesion layer 15 located 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 includes an environmental barrier layer 17a similar to the layer 7 described above. In the example of Figure 3, the layer 17b was deposited after the deposition of the layer 17a was complete, i.e., after the precursors used during the CVD deposition had been removed. Layer 17b is a thermal barrier layer, known in itself, 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 takes place while layer 17a is in an uncracked state, and layer 17a remains uncracked during this deposition.

[0041] The expression "between ... and ..." should be understood as including the bounds.

Claims

Demands

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

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

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

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

6. A method according to any one of claims 1 to 5, wherein said layer (7; 17a) of environmental barrier 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 the deposition of a bonding layer (5; 15) comprising silicon on an external surface (S) of the composite material (3; 13) with a matrix at least partially ceramic, 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 barrier layer (17b). thermal or protective against calcium and magnesium aluminosilicates.

9. A method according to any one of claims 1 to 8, wherein the part (1; 11) is a turbomachine part.

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

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