Method for manufacturing an environmental barrier crystallised in a thermodynamically stable form

Abstract

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 non-cracked crystalline β-Yb2Si2O7 environmental barrier layer (7) on an at least partially ceramic matrix composite material (3), wherein the environmental barrier layer is deposited by chemical vapour deposition from a gas phase comprising a precursor mixture of (a) a compound A of formula SiClxHy, in which x is an integer from 1 to 4 and y is an integer from 0 to 3, with x + y = 4, and (b) elementary ytterbium or ytterbium(III) chloride, and wherein, during deposition, a temperature between 1100°C and 1300°C and a pressure of 150 mbar or less are imposed.

Description

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

[0001] A particular area of ​​application of the invention is the protection of composite materials with at least partially ceramic matrix (“CMC materials”) forming hot parts of gas turbines, such as turbine distributors or turbine blades, for aircraft engines or industrial turbines. Previous technique

[0002] Improving efficiency and reducing pollutant emissions has led to consideration of ever-higher combustion chamber temperatures. It has therefore been proposed to replace metallic materials with CMC materials. Indeed, CMC materials are known for possessing both good mechanical properties, allowing their use in structural elements, and the ability to retain these properties at high temperatures. CMC materials can incorporate 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 temperatures in oxidizing and humid atmospheres, 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 lifespan. 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 can consist of a silicon bonding layer and a rare-earth silicate layer positioned on top of the bonding layer.The bonding layer serves two purposes: firstly, it improves the adhesion of the rare-earth silicate layer, and secondly, it forms a protective silica layer whose low oxygen permeability helps protect the CMC from oxidation. The rare-earth silicate layer, in turn, limits the diffusion of water vapor towards the silica layer formed by silicon oxidation, thus limiting its shrinkage. Environmental barriers can be... deposited by thermal spraying. 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 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 creating the environmental barrier through direct liquid injection of organometallic compound(s) using the chemical vapor deposition method (DLI-MOCVD). 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 and thus prevent layer evolution under service conditions. However, it is possible to further improve the protection provided to CMC materials in oxidizing and corrosive environments at high temperatures, particularly at 800°C or higher. Description of the invention

[0006] This description relates to a process for manufacturing a part with improved resistance to oxidation and high-temperature corrosion, comprising at least the deposition of an uncracked crystalline p-Yb2Si2O7 environmental barrier layer onto a composite material 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) compound A of formula SiCl x H y in which x is an integer between 1 and 4 and y an integer between 0 and 3 with x + y = 4, and (b) of 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 specific 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 natively crystallized in the crystallographic form most favorable to the EBC's performance in service, in this case the P form of ytterbium disilicate, denoted p-Yb2Si2O7. The crystallographic structure of p-Yb2Si2O7 has the advantage of not evolving in service under the influence of a high-temperature oxidizing environment (no harmful cracking or porosity developing), thus ensuring 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 beneficial 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 waterproof coating and to avoid oxidation of the underlying material due to the generation of high-temperature in-situ water, which can occur with prior art chlorinated deposition solutions. This oxidation is avoided by using a temperature of no more than 1300°C. A temperature of at least 1100°C, on the other hand, 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 general, compound A can be silicon tetrachloride (SiCl4, corresponding to x = 4 and y = 0 in the formula above), or trichlorosilane (SiHCl3, corresponding to x = 3 and y = 1 in the formula above).

[0010] 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 another embodiment, the pressure applied during the deposition of said environmental barrier layer is between 100 mbar and 150 mbar.

[0011] In one example embodiment, the precursor mixture is a mixture of compound A and elemental ytterbium.

[0012] In one embodiment, the gaseous phase further comprises (c) an oxygen-supplying gaseous source, and (d) a reducing gas.

[0013] The oxygen-supplying gaseous source can be carbon dioxide (CO2) or oxygen (O2). The reducing gas can be hydrogen (H2).

[0014] In general, the gaseous phase may essentially comprise, or even consist of, (a) compound A, (b) elemental ytterbium or ytterbium(III) chloride, (c) the oxygen-supplying gaseous source, and (d) the reducing gas.

[0015] In one embodiment example, the environmental barrier layer is deposited in a reaction chamber and a ratio [molar rate of introduction of compound A into the reaction chamber] / [molar rate of introduction of elemental ytterbium or ytterbium(III) chloride into the reaction chamber] of between 0.2 and 2 is imposed.

[0016] More specifically, the following operating conditions relating to the gas introduction flow rates into the reaction vessel may be imposed during the deposition of the environmental barrier layer: - ratio [molar flow rate of introduction of compound A into the reaction vessel] / [molar flow rate of introduction of elemental ytterbium or ytterbium(III) chloride into the reaction vessel] between 0.2 and 2, - ratio [molar flow rate of introduction of the oxygen-supplying gas source into the reaction vessel] / [molar flow rate of introduction of elemental ytterbium or ytterbium(III) chloride into the reaction vessel] between 5 and 10, and - ratio [molar flow rate of introduction of reducing gas into the reaction vessel] / [molar flow rate of introduction of elemental ytterbium or ytterbium(III) chloride] between 10 and 100.

[0017] In general, molar flow rates are measured in mol / minute.

[0018] In one embodiment example, said environmental barrier layer has a thickness less than or equal to 50 pm.

[0019] In this case, the environmental barrier layer is thin, making it difficult to achieve by thermal spraying. Greater thicknesses can be obtained within the scope of the invention if this is acceptable for the intended application.

[0020] In one embodiment, the process 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.

[0021] In one embodiment, the process further comprises, after the deposition of said environmental barrier layer, the deposition, on said environmental barrier layer, of a second thermal barrier layer or protection layer against calcium and magnesium aluminosilicates.

[0022] In one example of implementation, the part is a turbomachine component.

[0023] In one embodiment example, the part is a turbine blade, or at least part of a turbine distributor. Brief description of the drawings [Fig. 1] Figure 1 schematically illustrates a first example of a part with improved resistance to oxidation and high-temperature corrosion that can be obtained by implementing the invention. [Fig. 2] Figure 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. [Fig. 3] Figure 3 schematically illustrates a second example of a part with improved resistance to oxidation and high-temperature corrosion that can be obtained by implementing the invention. Description of the implementation methods

[0024] The invention is now described by means of figures, which are provided for descriptive purposes to illustrate certain embodiments of the invention and which should not be interpreted as limiting the latter.

[0025] Figure 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.

[0026] The 3CMC material may include a fibrous reinforcement made of carbon (C) fibers or ceramic fibers, for example, silicon carbide (SiC) fibers or fibers composed primarily 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 names "Nicalon," "Hi-Nicalon," or "Hi-Nicalon Type-S," or by Ube Industries under the name "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% to 20% B, the remainder being C).

[0027] The fibrous reinforcement is densified by a matrix that is at least partially ceramic, for example, predominantly ceramic by volume. The ceramic matrix may include 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 infiltration (impregnation with a matrix precursor resin and transformation by crosslinking and pyrolysis, the process being repeatable) or by molten silicon infiltration (the "melt-infiltration" process). In the latter In this case, a powder is introduced into the possibly partially densified fibrous reinforcement. This powder may be carbon powder, ceramic powder, silicon carbide, or a mixture of such powders. A molten silicon-based metallic composition is then infiltrated to form a SiC-Si matrix. The fibrous reinforcement may 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 may be used.

[0028] 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 part of the surface S needs to be protected. In the example shown in Figure 1, the environmental barrier 2 comprises an environmental barrier layer 7 and an anchoring layer 5 located between the CMC material 3 and layer 7. In the example shown, the anchoring 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 anchoring layer 5.

[0029] The adhesion layer 5 can, in a known manner, 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.

[0030] Layer 7 is an environmental barrier layer providing protection against oxidation and high-temperature corrosion by limiting the diffusion of water vapor and oxygen to the bonding layer 5 and the CMC material 3. Layer 7 is an uncracked crystalline layer of p-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 between 20 µm and 50 µm.

[0031] We will now describe details relating to the fabrication of the environmental barrier. The passage that will now be addressed provides details relating to the formation of the tack layer 5.

[0032] The adhesion layer 5 can be formed by chemical vapor deposition from a silicon-containing precursor, such as a silane, monochlorosilane, dichlorosilane, and / or trichlorosilane. Two examples of adhesion layer 5 formation by chemical vapor deposition are described below.

[0033] According to a first example, the temperature applied during the deposition of the 5th adhesion layer 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, comprising 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, 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 from silicon with boron, oxygen and / or nitrogen dispersed inside.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 be between 300°C and 700°C or between 700°C and 1000°C, and the deposition pressure can be between 1.2 kPa and 1013 hPa. The operating conditions are chosen according to the precursor used. The processing temperature can be between 1000°C and 1400°C, for example, between 1200°C and 1350°C. During deposition, the silicon-containing precursor can be introduced into the reaction chamber in which the 3 CMC material is present with a flow rate of between 0.1 gram / minute and 2 gram / minute.

[0034] The description continues with details regarding the fabrication of layer 7 of the environmental barrier by chemical vapor deposition. As mentioned above, layer 7 is an uncracked crystalline layer of Yb2Si2O7.

[0035] Layer 7 is obtained from the precursor mixture in a gaseous state, which is drawn into the 3CMC material. The 3CMC material is heated to a temperature sufficient to allow the deposit to form, possibly in the presence of an oxygen-supplying gas and a reducing gas. This forms the environmental barrier layer 7 on the 3CMC material.

[0036] The precursor mixture can be a mixture of compound A, which is for example silicon tetrachloride SiCl4 or trichlorosilane SiHCl3, and elemental ytterbium Yb. Elemental ytterbium Yb can be obtained by evaporation in an internal preheating zone.

[0037] The precursor mixture can be a mixture of compound A, which is, for example, silicon tetrachloride (SiCl4) or trichlorosilane (SiHCl3), and ytterbium(III) chloride (YbCl3). Ytterbium(III) chloride can be obtained by chlorination of Yb with Cl2 or HCl, for example.

[0038] The oxygen-supplying gas can be carbon dioxide (CO2) or oxygen (O2). Carbon dioxide has the advantage of being less reactive than oxygen, thus allowing for finer control of the amount of oxygen introduced into the film. The reducing gas can be hydrogen (H2).

[0039] As mentioned above, temperature and pressure are controlled during the deposition of layer 7, that is, when material 3 is subjected to the precursor mixture in its 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, between 1125°C and 1175°C, or 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 deposition time of layer 7 is adjusted according to the desired thickness el.

[0040] The deposition of an uncracked p-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. The ratio [molar rate of SiCl4 introduction into the reaction chamber] / [molar rate of elemental ytterbium introduction into the reaction chamber] was 0.77, the ratio [molar rate of CO2 introduction into the reaction chamber] / [molar rate of elemental ytterbium introduction into the reaction chamber] was 7.25, and the ratio [molar rate of H2 introduction into the reaction chamber] / [molar rate of SiCl4 introduction into the reaction chamber] was 28.1. A photograph of the resulting coating is provided in Figure 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 led to degradation of the underlying substrate through active oxidation.

[0041] 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 one part of a distributor, at least one part of a nozzle or heat shield, a combustion chamber wall, a turbine ring sector, or a turbomachine blade.

[0042] 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 also be used in humid air.

[0043] 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 the 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 by an additional coating as will be described in connection with figure 3.

[0044] 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 layer 5 described above. The barrier 17 includes an environmental barrier layer 17a similar to the layer 7 described above. In the example in Figure 3, layer 17b was deposited after the deposition of layer 17a was complete, i.e., after the precursors used during 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.

[0045] The expression "between ... and ..." should be understood as including the boundaries.

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 p-Yb2Si2O7 crystalline environmental barrier on a composite material (3; 13) 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 compound A(a) of formula SiCl x Hy in which x is an integer between 1 and 4 and y an integer between 0 and 3 with x + y = 4, and (b) of 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.

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 method according to any one of claims 1 to 4, wherein the gas phase further comprises (c) an oxygen-supplying gaseous source, and (d) a reducing gas.

6. A method according to any one of claims 1 to 5, wherein the deposition of the environmental barrier layer is carried out in a reaction chamber and a ratio [molar rate of introduction of compound A into the reaction chamber] / [molar rate of introduction of elemental ytterbium or ytterbium(III) chloride into the reaction chamber] of between 0.2 and 2 is imposed.

7. A method according to claim 6, wherein the following operating conditions relating to the gas introduction rates into the reaction vessel are imposed during the deposition of the environmental barrier layer: - ratio [molar flow rate of introduction of compound A into the reaction vessel] / [molar flow rate of introduction of elemental ytterbium or ytterbium(III) chloride into the reaction vessel] between 0.2 and 2, - ratio [molar flow rate of introduction of the oxygen-supplying gas source into the reaction vessel] / [molar flow rate of introduction of elemental ytterbium or ytterbium(III) chloride into the reaction vessel] between 5 and 10, and - ratio [molar flow rate of introduction of the reducing gas into the reaction chamber] / [molar flow rate of introduction of compound A into the reaction chamber] between 10 and 100.

8. A process according to any one of claims 1 to 7, wherein the precursor mixture is a mixture of compound A and elemental ytterbium.

9. A method according to any one of claims 1 to 8, wherein said layer (7; 17a) of environmental barrier has a thickness (e) less than or equal to 50 pm.

10. A method according to any one of claims 1 to 9, 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.

11. A method according to any one of claims 1 to 10, 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 thermal barrier layer or protection layer against calcium and magnesium aluminosilicates.

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

13. Method according to claim 12, wherein the part (1; 11) is a turbine blade, or at least part of a turbine distributor.

Images