Process for manufacturing an environmental barrier 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 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 of organometallic compound(s) by imposing during the deposition a temperature of between 1200°C and 1400°C and a pressure of less than or equal to 40 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. 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 of organometallic compound(s) by imposing during the deposition a temperature of between 1200°C and 1400°C and a pressure of less than or equal to 40 mbar.

[0007] The invention is based on depositing, by chemical vapor deposition of organometallic compound(s) ("Metal Organic Chemical Vapor Deposition"; "MOCVD"), an environmental barrier layer of particular composition, made of ytterbium disilicate Yb2Si2O7, under 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 conferred during 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 low thickness, which can be of particular interest in the case of a turbine blade or nozzle application. The use of a temperature lower than 1200°C leads to an amorphous layer with lower performance, and the use of a temperature higher than 1400°C can result in damage or melting of the underlying elements, in particular of any silicon bonding layer present. The use of a pressure higher than 40 mbar can affect the repeatability of the deposits. The invention corresponds to a specific selection, a deposition technique, a particular composition and controlled temperature and pressure conditions during deposition which directly result in an equilibrium, non-cracked crystallized form, without requiring subsequent crystallization heat treatment.For illustration purposes, if the composition were modified by depositing yttrium disilicate Y2Si2O7 under the same temperature and pressure conditions, either a cracked or highly porous coating would be obtained, or a crystallographic organization evolving in service to reach the most thermodynamically stable crystallographic organization, resulting in both cases in poorer performance. The invention makes it possible to obtain a dense environmental barrier layer, non-cracked during its production and compatible with parts of complex geometry, in particular by making it possible to control the thickness and obtain a relatively thin coating.

[0008] In an exemplary embodiment, the temperature imposed during the deposition of said environmental barrier layer is between 1200°C and 1250°C.

[0009] In particular, the temperature imposed during the deposition of said environmental barrier layer may be between 1210°C and 1250°C.

[0010] In an exemplary embodiment, the pressure imposed during the deposition of said environmental barrier layer is between 2 mbar and 10 mbar.

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

[0012] In an exemplary embodiment, said environmental barrier layer is deposited in a cold wall reactor.

[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 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 environmental barrier layer, of a second thermal barrier layer or protection against calcium and magnesium aluminosilicates.

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

[0016] In particular, the part may be a turbine blade, or at least part of a turbine nozzle.

[0017] Brief description of the drawings [Fig.l] [Fig.l] illustrates, schematically, a first example of a part with improved resistance to oxidation and corrosion at high temperature which can be obtained by implementing the invention.

[0018] [Fig.2] [Fig.2] provides a comparative test result showing photographs obtained by scanning electron microscopy (SEM) of ytterbium disilicate deposits before and after heat treatment. [Fig.3] [Fig.3] illustrates, schematically, a second example of a part with improved resistance to oxidation and corrosion at high temperature which can be obtained by implementing the invention. Description of the embodiments

[0019] 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.

[0020] [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.

[0021] 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).

[0022] The fibrous reinforcement is densified by an at least partially ceramic matrix, 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. In 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 able to be repeated) 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 may 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 may be used in the form of grains dispersed in the material 3.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] According to a first example, the temperature imposed during the deposition of the bonding layer 5 can 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 may be introduced into the reaction chamber in which the material 3 CMC 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 may be made of silicon, this bonding layer 5 comprising, for example, columnar grains of crystalline silicon. Alternatively, the bonding layer 5 may 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 which prevents crystallization of the deposited silicon, followed by a 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 can 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.

[0029] The description continues by providing details relating to the manufacture of the environmental barrier layer 7 by chemical vapor deposition of organometallic compound(s), a technique referred to hereinafter as "MOCVD" for the sake of brevity. As indicated above, the layer 7 is a non-cracked crystalline layer of [3-Yb2Si2O7.

[0030] The layer 7 is obtained from one or more molecular precursors in the gaseous state entrained by a carrier gas (such as argon or nitrogen) towards the 3 CMC material. The 3 CMC material is heated to a temperature sufficient to allow the decomposition of the molecular precursors in the optional presence of a gaseous source providing oxygen. The environmental barrier layer 7 is thus formed on the 3 CMC material. The reaction chamber may be a hot-walled or cold-walled reactor. The latter case is advantageous in order to promote at high temperature the rapid formation of the deposit on the 3 CMC material and not the homogeneous reactions in the gas phase while respecting the degradation temperature of the precursors.

[0031] The person skilled in the art knows how to choose the molecular precursors to be used as well as the relative proportions in the MOCVD technique in order to obtain the layer 7 having the specific composition indicated above. According to one example, the layer 7 is formed at least from a molecular precursor of silicon oxide, and a molecular precursor of ytterbium oxide in the presence of a gaseous source providing oxygen. The molecular precursor of silicon oxide may be an alkoxysilane, for example tetraethyl orthosilicate (TEOS) or di-t-butoxydiacetoxysilane (DADBS). The molecular precursor of ytterbium oxide may be chosen from: ytterbium alkoxides or ytterbium beta-diketonates. An example of a usable ytterbium alkoxide is Yb(mmp)3, where the (mmp) group denotes l-methoxy-2-methyl-2-propanolato.As an example of a usable ytterbium beta-diketonate, we can cite Yb(thd)3 where the group (thd) denotes 2,2,6,6-tetramethyl-3,5-heptanedionate. The gaseous source providing oxygen can comprise at least one of the following gases: O2, N2O, H2O, CO2, O3.

[0032] 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 molecular precursor(s) in the gaseous state. Thus, the temperature imposed during the deposition of the layer 7 is between 1200°C and 1400°C, for example between 1200°C and 1250°C, for example between 1210°C and 1250°C or between 1200°C and 1230°C, for example between 1210°C and 1230°C. The pressure imposed during the deposition of the layer 7 is less than or equal to 40 mbar, for example between 2 mbar and 40 mbar or even between 2 mbar and 10 mbar. The duration of the deposition of layer 7 is adjusted according to the desired thickness el, it can for example be between 3 hours and 10 hours.

[0033] [Fig.2] provides a comparative test result showing the advantages of the invention. The three photographs in the upper part illustrate three deposits of ytterbium disilicate each deposited by MOCVD by imposing a distinct temperature, namely: 1130°C (outside the invention), 1230°C (according to the invention) and 1280°C (according to the invention). The pressure imposed during each of the deposits was 5 mbar and the molecular precursors used were DADBS: Di-t-butoxydiacetoxysilane and Yb(thd)3: Ytterbium(III) tris(2,2,6,6-tetramethyl-3,5-heptanedionate). The deposits were carried out in a cold wall reactor. The deposits according to the invention obtained at 1230°C and 1280°C are deposits of crystallized [3-Yb2Si2O7 having a columnar and non-cracked microstructure. The deposit outside the invention obtained at 1130°C is a deposit of a mixture of alpha, beta and amorphous phases of ytterbium disilicate which will evolve during the temperature change. The three photographs in the lower part illustrate the structure obtained after subjecting each of these deposits to a heat treatment at a temperature of 1350°C, for a period of 10 hours in air. Following the heat treatment, the appearance of porosities is observed in the deposit outside the invention, and not in the deposits according to the invention which fully retain their protective character.

[0034] 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.

[0035] 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.

[0036] The example which has just been described concerns an environmental barrier layer 7 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].

[0037] [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 molecular precursor(s) used during the MOCVD 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 made of rare earth zirconate, for example 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.

[0038] The expression “between ... and ...” must be understood as including the limits.

Claims

Claims

1. Method for 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 of organometallic compound(s) by imposing during the deposition a temperature of between 1200°C and 1400°C and a pressure of less than or equal to 40 mbar.

2. Method according to claim 1, wherein the temperature imposed during the deposition of said environmental barrier layer (7; 17a) is between 1200°C and 1250°C.

3. Method according to claim 2, wherein the temperature imposed during the deposition of said environmental barrier layer (7; 17a) is between 1210°C and 1250°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 2 mbar and 10 mbar.

5. Method according to any one of claims 1 to 4, wherein said environmental barrier layer (7; 17a) has a thickness (e0) less than or equal to 50 pm.

6. A method according to any one of claims 1 to 5, wherein said environmental barrier layer (7; 17a) is deposited in a cold wall reactor.

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 layer (17b) of thermal barrier or protection against calcium and magnesium aluminosilicates.

9.

10. Method according to any one of claims 1 to 8, in which the part (1; 11) is a turbomachine part. Method according to claim 9, in which the part (1; 11) is a turbine blade, or at least part of a turbine nozzle.

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