Method for manufacturing an environmental barrier natively crystallized in thermodynamically stable form

Abstract

The present invention relates to a method for manufacturing a part (1) with improved resistance to oxidation and corrosion at high temperatures, involving at least the deposition of a non-cracked β-Yb2Si2O7 crystalline environmental barrier layer (7) onto an at least partially ceramic matrix composite material (3), said environmental barrier layer being deposited by chemical vapor deposition of organometallic compound(s), at an imposed temperature, during the deposition, of between 1200°C and 1400°C and an imposed pressure of less than or equal to 40 mbar.

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 a matrix at least partially made of ceramic (“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. Consequently, this limits its recession. Environmental barriers can be deposited by thermal spraying. US2019040761, in particular, describes the formation of an EBC using 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) (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. 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] The present presentation 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 on a composite material with a matrix at least partially made of ceramic, said environmental barrier layer being deposited by chemical vapor deposition of organometallic compound(s) by imposing during the deposition a temperature between 1200°C and 1400°C and a pressure less than or equal to 40 mbar.

[0007] The invention is based on the fact of depositing, by chemical vapor deposition of organometallic compound(s) (“Metal Organic Chemical Vapor Deposition”; "MOCVD"), an environmental barrier layer of specific composition, made of ytterbium disilicate Yb2Si2O7, is applied under controlled temperature and pressure conditions to form, directly upon deposition, an uncracked environmental barrier layer that is natively crystallized in the crystallographic form most favorable to the EBC's in-service performance, namely the P-form of ytterbium disilicate, denoted -Yb2Si2O7. The crystallographic structure of p-Yb2Si2O7 has the advantage of not evolving in service under the effect of the high-temperature oxidizing environment (no harmful cracking or porosity), thus ensuring the stability of the protection. conferred over the part's lifetime. Furthermore, the uncracked nature of the barrier during its fabrication ensures effective protection even with a thin coating, which can be particularly advantageous for turbine blade or distributor applications. Applying a temperature below 1200°C results in an amorphous layer with reduced performance, while applying a temperature above 1400°C can cause damage to or melting of the underlying elements, especially any existing silicon bonding layer. Using a pressure above 40 mbar can affect coating repeatability.The invention relates to a specific selection of a deposition technique, a particular composition, and controlled temperature and pressure conditions during deposition that directly result in an equilibrium, uncracked crystalline form, without requiring subsequent heat treatment for crystallization. For example, if the composition were modified by depositing yttrium disilicate (Y₂Si₂O₇) under the same temperature and pressure conditions, one would obtain either a cracked or highly porous coating, or a crystallographic organization that evolves in service to reach the most thermodynamically stable crystallographic organization, resulting in both cases in lower performance.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.

[0008] In one example implementation, 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 can be between 1210°C and 1250°C.

[0010] In one example implementation, the pressure imposed during the deposition of said environmental barrier layer is between 2 mbar and 10 mbar.

[0011] In one embodiment, the environmental barrier layer has a thickness of 50 µm or less. In this case, the environmental barrier layer is thin and 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.

[0012] In one embodiment example, said environmental barrier layer is deposited in a cold-walled reactor.

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

[0014] 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.

[0015] In one example of implementation, the part is a turbomachine component.

[0016] In particular, the part may be 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 comparative test result showing photographs obtained by scanning electron microscopy (SEM) of ytterbium disilicate deposits before and after heat treatment. [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

[0017] 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.

[0018] 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.

[0019] 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 layer of pyrolytic carbon interphase. (PyC), in boron nitride (BN) or in boron-doped carbon (BC, with 5%at. to 20%at. of B, the complement being C).

[0020] 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 process (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 case, a powder is introduced into the possibly partially densified fibrous reinforcement; this powder may be carbon powder, ceramic powder, silicon carbide powder, or a mixture of such powders, and a molten silicon-based metallic composition is then infiltrated to form a SiC-Si type matrix.The fibrous reinforcement may be woven or not; it does not depart from 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 in the form of grains dispersed in the material 3 may be used.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] In a first example, the temperature applied during the deposition of the 5-layer adhesion can range from 900°C to 1150°C, for example, from 1100°C to 1150°C, and the pressure applied during this deposition can range from 15.3 kPa to 20 kPa, for example, from 16.7 kPa to 18 kPa. During deposition, the silicon-containing precursor can be introduced into the reaction chamber containing the 3-CMC material at a flow rate of between 0.05 grams / minute and 0.3 grams / minute, for example, from 0.1 grams / minute to 0.2 grams / minute. In this first example, the resulting 5-layer adhesion has a crystalline microstructure. In particular, the 5-layer adhesion can be made of silicon, and this 5-layer adhesion can, for example, consist of columnar grains of crystalline silicon. Alternatively, the 5th bonding layer can be made of silicon alloy, for example a eutectic silicon alloy or silicide.According to a second example, the adhesion layer 5 comprises an amorphous silicon phase containing crystalline silicon grains with an average grain size ranging from 0.03 µm to 3 µm. The amorphous silicon phase can be composed of pure silicon or silicon with boron, oxygen, and / or nitrogen dispersed within it. In this second example, the adhesion layer 5 can be formed at a deposition temperature that prevents crystallization of the deposited silicon, 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 treatment 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 grams / minute and 2 grams / minute.

[0027] The description continues with details regarding the fabrication of layer 7 of the environmental barrier by chemical vapor deposition of organometallic compound(s), a technique hereafter referred to as "MOCVD" for brevity. As mentioned above, layer 7 is an uncracked crystalline layer of O-Yb2Si2O7.

[0028] Layer 7 is obtained from one or more gaseous molecular precursors carried by a carrier gas (such as argon or nitrogen) to the 3CMC material. The 3CMC material is heated to a temperature sufficient to allow the decomposition of the molecular precursors, possibly in the presence of an oxygen-supplying gaseous source. This forms the environmental barrier layer 7 on the 3CMC material. The reaction chamber can be a hot-walled or cold-walled reactor. The latter is advantageous because it promotes rapid formation of the deposit on the 3CMC material at high temperatures, rather than homogeneous gas-phase reactions, while still maintaining the precursor degradation temperature.

[0029] A person skilled in the art knows how to select the appropriate molecular precursors and their relative proportions in the MOCVD technique to obtain layer 7 with the specific composition indicated above. For example, layer 7 is formed from at least one silicon dioxide molecular precursor and one ytterbium dioxide molecular precursor in the presence of an oxygen-supplying gas and possibly a carrier gas. The silicon dioxide molecular precursor can be an alkoxysilane, for example, tetraethyl orthosilicate (TEOS) or di-t-butoxydiacetoxysilane (DADBS). The ytterbium dioxide molecular precursor can be chosen from ytterbium alkoxides or ytterbium beta-diketonates. As an example of a usable ytterbium alkoxide, we can cite Yb(mmp)3, where the (mmp) group designates l-methoxy-2-methyl-2-propanolato.An example of a usable ytterbium beta-diketonate is Yb(thd)3, where the (thd) group designates 2,2,6,6-tetramethyl-3,5-heptanedione. The oxygen-supplying gaseous source can include at least one of the following gases: O2, N2O, H2O, CO2, or O3. The carrier gas can be nitrogen (N2). The molecular precursors are injected as a solution into the reactor and evaporated within it.

[0030] As mentioned above, temperature and pressure are controlled during the deposition of layer 7, that is, when material 3 is subjected to the molecular precursor(s) in the gaseous state. Thus, the temperature imposed during the deposition of 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 applied during the deposition of 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 deposition time for layer 7 is adjusted according to the desired thickness; for example, it can be between 3 and 10 hours.

[0031] Figure 2 provides a comparative test result demonstrating the advantages of the invention. The three photographs at the top illustrate three ytterbium disilicate deposits, each deposited by MOCVD at a distinct temperature: 1130°C (not part of the invention), 1230°C (according to the invention), and 1280°C (according to the invention). The pressure applied during each deposition 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 depositions were carried out in a cold-walled reactor.In this experiment, the ratio [molar flow rate of introduction of the DADBS solution into the reactor] / [molar flow rate of introduction of the Yb(thd)3 solution into the reactor] was 1.07, the ratio [molar flow rate of introduction of the oxygen-supplying gas source into the reactor] / [molar flow rate of introduction of the Yb(thd)3 solution into the reactor] was 1887 and the ratio [molar flow rate of introduction of the carrier gas into the reactor] / [molar flow rate of introduction of the Yb(thd)3 solution into the reactor] was 6981. The deposits according to the invention obtained at 1230°C and 1280°C are deposits of crystallized p-Yb2Si2O7 having a columnar and uncracked microstructure. The off-invention deposit 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 at the bottom illustrate the structure obtained after each of these coatings was subjected to heat treatment at a temperature of 1350°C for 10 hours in air. Following the heat treatment, porosity appeared in the coating not described in the invention, but not in the coatings according to the invention, which retained their protective character entirely.

[0032] In general, the following operating conditions can be imposed for depositing the environmental barrier layer by MOCVD: - ratio [molar flow rate of introduction of the silicon oxide molecular precursor solution into the reactor] / [molar flow rate of introduction of the ytterbium oxide molecular precursor solution into the reactor] between 0.8 and 1.3, - ratio [molar flow rate of introduction of the oxygen-supplying gas source into the reactor] / [molar flow rate of introduction of the ytterbium oxide molecular precursor solution into the reactor] between 1500 and 2000, - injection frequency of precursor solutions into the reactor between 0.5 Hz and 3 Hz, and - evaporation temperature of precursors between 170°C and 250°C, and optionally - when a carrier gas is used, the ratio [molar flow rate of introduction of the carrier gas into the reactor] / [molar flow rate of introduction of the solution of the molecular precursor of ytterbium oxide into the reactor] is between 3000 and 10000.

[0033] In general, molar flow rates are measured in mol / minute.

[0034] In combination with the characteristics described in the previous paragraph, the following conditions may also apply: - concentration of the silicon oxide molecular precursor in the associated solution between: 0.01 mol / L and 0.1 mol / L, and - concentration of the molecular precursor of ytterbium oxide in the associated solution between: 0.015 mol / L to 0.15 mol / L.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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. Top. In the example in Figure 3, layer 17b was deposited after the deposition of layer 17a was complete, that is, after the removal of the molecular precursor(s) used during the MOCVD deposition. Layer 17b is a thermal barrier layer, known per se, for example, yttria-stabilized zirconia (YSZ: ZrO2+ 8 at.% Y2O3), or a protective layer against calcium magnesium aluminosilicates (CMAS), for example, rare-earth zirconate, such as 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.

[0039] The expression "between ... and ..." should be understood as including the boundaries.

Claims

Claims

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 made of ceramic, said environmental barrier layer being deposited by chemical vapor deposition of organometallic compound(s) by imposing during the deposition a temperature between 1200°C and 1400°C and a pressure less than or equal to 40 mbar.

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

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

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

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

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 thermal barrier layer or protection layer 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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