METHOD FOR MANUFACTURING AN ENVIRONMENTAL BARRIER

Abstract

A method of manufacturing (100) an environmental barrier comprising the steps of coating (102) a rare earth silicate powder with a precursor of a densifying agent to form a rare earth silicate powder coated with the precursor of the densifying agent, thermally spraying (104) the coated powder onto a substrate to obtain an at least partially amorphous environmental barrier on the substrate and thermally treating (106) the environmental barrier to crystallize and densify. Figure for abstract: Fig. 5

Description

Title of the invention: METHOD FOR MANUFACTURING AN ENVIRONMENTAL BARRIER Technical field

[0001] This disclosure relates to environmental barriers, also called "EBCs", in accordance with the acronym in English for "Environmental Barrier Coating", and to their manufacturing process. Prior art

[0002] FR3059323 discloses an environmental barrier for a CMC (ceramic matrix composite) part of a turbomachine.

[0003] The CMC part may, for example, be a turbine part of a turbomachine. The turbomachine may, for example, be a turbojet.

[0004] Under the operating conditions of aeronautical turbines, for example high temperature and corrosive environment, CMCs are generally susceptible to corrosion. Corrosion of CMC generally results in the oxidation of silicon carbide to silica. In the presence of water vapor, silica volatilizes in the form of Si(OH)4 hydroxides. These corrosion phenomena lead to premature degradation of the CMC. Also, in order to guarantee the service life of the CMCs, the CMCs are protected against wet corrosion by an environmental barrier (EBC).

[0005] EBCs are usually produced by thermal spraying. However, this process generally produces a coating comprising a set of defects generating a 3D network of porosity / cracks which impair the performance of the EBC.

[0006] On the other hand, it has been demonstrated that the effectiveness of an EBC is closely linked to its hermeticity, in order to block the molecular diffusion of oxidizing and corrosive species.

[0007] Various solutions exist to improve the sealing of one or more layers of an EBC, such as the addition of sintering agents or healing agents. However, it can be complicated to obtain a homogeneous distribution of the sintering and / or healing agents. Statement of the invention

[0008] The present disclosure aims to remedy at least in part these drawbacks.

[0009] The present disclosure relates to a method of manufacturing an environmental barrier, the method comprising the steps of: coating a rare earth silicate powder with a precursor of a densifying agent to form a rare earth silicate powder coated with the precursor of the densifying agent; thermal spraying of the coated powder onto a substrate to obtain an at least partially amorphous environmental barrier on the substrate; and heat treatment for crystallization and densification of the environmental barrier.

[0010] By coating the rare earth silicate powder with a precursor of a densifying agent, the precursor of the densifying agent, and thus the densifying agent, is distributed homogeneously.

[0011] It is understood that coating the rare earth silicate powder with a precursor of the densifying agent makes it possible to obtain a better distribution and better control of the dosage of the densifying agent than conventional mixing / grinding methods. The method makes it possible to obtain a homogeneous distribution and in very finely dispersed form of the densifying agent in the rare earth silicate powder matrix.

[0012] During thermal spraying, the precursor of the densifying agent will react to form the densifying agent on the rare earth silicate powder and promote the densification of the environmental barrier. Therefore, it may be considered to reduce the mass content of the densifying agent in comparison to a mixture obtained by mixing / grinding the two powders together.

[0013] By way of non-limiting examples, the densifying agent obtained during the thermal projection of the coated powder may be magnesium oxide, calcium oxide, iron oxide, yttrium oxide, mullite, silica.

[0014] In some embodiments, the thermal spraying may be air plasma spraying, vacuum plasma spraying, or HVOF, which stands for High Velocity Oxy Fuel.

[0015] In some embodiments, the coating may be carried out wet.

[0016] In some embodiments, the rare earth silicate powder may be immersed in a solution comprising a solvent and the precursor of the densifying agent, the solvent may be evaporated to form an agglomerated coated powder and the agglomerated coated powder may be deagglomerated to form the coated powder.

[0017] In some embodiments, the deagglomeration of the agglomerated powder may comprise a step of heat treating the agglomerated powder at a temperature between 250°C (degrees Celsius) and 600°C for 1h (hour) to 4h.

[0018] In some embodiments, the rare earth silicate powder may be fluidized in a solution comprising a solvent and the precursor of the densifying agent.

[0019] In certain embodiments, the coating can be carried out by gaseous means.

[0020] In some embodiments, the precursor of the densifying agent may be an organometallic precursor.

[0021] As non-limiting examples, the organometallic precursor may be a metal nitrate, a metal acetate, a metal chloride, a metal alkoxide or a metal phosphorus.

[0022] By way of non-limiting example, the organometallic precursor may be a metal salt of magnesium, iron, aluminum and / or silicon and / or aluminophosphate and / or a sol of magnesia, iron oxide, boehmite, silica.

[0023] The use of a metal salt makes it possible to reduce the loss of silica during the thermal projection of a rare earth silicate powder by the preferential oxidation of the metal salt which is arranged outside the particle. The oxidizing species of the plasma will therefore react preferentially with the metal salt and form a protective oxide matrix around the rare earth silicate powder, thus limiting the volatilization of the silica.

[0024] In some embodiments, the precursor of the densifying agent may be the densifying agent.

[0025] As non-limiting examples, the precursor of the densifying agent may be magnesium oxide or silica, the densifying agent being the same as the precursor.

[0026] When silica is present as a precursor to the densifying agent, the silica present in the outer layer of the powder particles will "saturate" the plasma and thus prevent or reduce the volatilization of the silica present in the rare earth silicate powder.

[0027] In some embodiments, the coated powder may have a core-shell structure.

[0028] A core-shell structure can be obtained, also called "core-shell" in English, in which the powder particles comprise a core of rare earth silicate powder coated by an outer layer (or shell) formed by the precursor of the densifying agent. The shell can have a thickness of the order of a nanometer and the distribution of the precursor of the sintering agent as well as the control of the dosage of the precursor of the sintering agent are improved.

[0029] In certain embodiments, the heat treatment can be carried out at a temperature greater than or equal to 1100°C, preferably greater than or equal to 1200°C and less than or equal to 1350°C, preferably less than or equal to 1300°C with a plateau greater than or equal to 5h and less than or equal to 50h.

[0030] In some embodiments, the substrate may be a ceramic matrix composite material substrate.

[0031] The CMC material substrate is generally made from 2D or 3D woven ceramic fibers. These ceramic fibers can then be subjected to gas densification (also called "CVI" according to the English acronym for "Chemical Vapor Infiltration"), alone or in combination with another technique, such as infiltration by a melt (also called "MI" according to the English acronym for "Melt Infiltration") in order to obtain the CMC material substrate.

[0032] In some embodiments, the environmental barrier may comprise a tie layer.

[0033] As non-limiting examples, the bonding layer may be made of silicon.

[0034] It is understood that the bonding layer is deposited on the substrate and is comprised between the substrate and the layer of material. Brief description of the drawings

[0035] Other characteristics and advantages of the subject of the present disclosure will emerge from the following description of embodiments, given as non-limiting examples, with reference to the appended figures.

[0036] [Fig.l] [Fig.l] is a schematic cross-sectional view of a substrate and an environmental barrier according to one embodiment.

[0037] [Fig.2] [Fig.2] is a schematic cross-sectional view of a substrate and an environmental barrier according to a detailed embodiment.

[0038] [Fig.3] [Fig.3] is a schematic sectional view of a coated powder according to one embodiment.

[0039] [Fig.4] [Fig.4] is a schematic cross-sectional view of a powder coated according to another embodiment.

[0040] [Fig.5] [Fig.5] is a flowchart representing the steps in a manufacturing process for an environmental barrier.

[0041] Throughout the figures, the elements in common are identified by identical numerical references. Detailed description

[0042] [Fig.l] is a schematic representation of a substrate 12 covered with an environmental barrier 10.

[0043] By way of non-limiting example, the substrate 12 may be a substrate made of ceramic matrix composite material.

[0044] By way of non-limiting example and as shown schematically in [Fig.2], the environmental barrier 10 may comprise a silicon bonding layer 14 and a layer of yttrium disilicate 16.

[0045] At the interface between the bonding layer 14 and the yttrium disilicate layer 16 there is a silica layer 18. The silica layer 18 is a silicon oxide layer formed by oxidation of the silicon bonding layer 14.

[0046] The yttrium 16 disilicate layer comprises a densifying agent.

[0047] As non-limiting examples, the densifying agent may be a sintering agent and / or a healing agent.

[0048] As non-limiting examples, the sintering agent may be magnesium oxide or iron oxide.

[0049] By way of non-limiting example, the healing agent is mullite, silica or an aluminophosphate.

[0050] By way of non-limiting example, the yttrium 16 disilicate layer may comprise between 0.1 and 5% by mass of sintering agent, for example 0.4% by mass of sintering agent.

[0051] The environmental barrier 10 can be obtained by the manufacturing method 100 of [Fig.4].

[0052] The manufacturing method 100 of the environmental barrier 10 comprises a step 102 of coating a rare earth silicate powder 22 with a precursor of a densifying agent 24 to form a rare earth silicate powder 20 coated with the precursor of the densifying agent.

[0053] The coated powder 20 may have a core-shell structure, as shown in [Fig. 3], the coated powder 20 comprising a core of rare earth silicate powder 22 coated by an outer layer (or shell) formed by the precursor of the densifying agent 24.

[0054] Alternatively, the coated powder 20 may have particles formed by the precursor of the densifying agent 24 present on the surface of the rare earth silicate powder 22, as shown in [Fig.4].

[0055] These two types of structures can be obtained by wet or gaseous means.

[0056] Example of coating

[0057] Rare earth disilicate powder, magnesium acetate and distilled water.

[0058] In 1 L (liter) of distilled water, dissolve 5% by mass of magnesium acetate (typically between 0.1 and 10% by mass).

[0059] Pour 1 kg of rare earth disilicate powder into the aqueous magnesium acetate solution.

[0060] Mix with a magnetic bar.

[0061] Drying at 90°C in an oven.

[0062] On the agglomerated powder blocks, carry out a heat treatment at 400°C for 1 hour in air so that the blocks become friable.

[0063] Coated powder 20 is available.

[0064] The coated powder 20 is sprayed by a thermal spraying method 104 onto the substrate 12 to obtain an at least partially amorphous environmental barrier 10 on the substrate 12.

[0065] In the example of the organometallic precursor of the densifying agent described above, the organometallic precursor of the densifying agent, i.e., magnesium acetate, will dehydrate and oxidize during thermal spraying to form the densifying agent around the rare earth disilicate powder, in a desired and controlled concentration. A partially amorphous environmental barrier 10 can be obtained with flattened grains (also called "splats") of rare earth disilicate and the densifying agent uniformly distributed around the flattened grains of rare earth disilicate.

[0066] The environmental barrier 10 then undergoes a heat treatment step 106 of crystallization and densification.

[0067] By way of non-limiting example, the heat treatment 106 for crystallization and densification may comprise a temperature increase at 100°C / h (degrees Celsius per hour) up to 1300°C, a 50-hour hold at 1300°C and a temperature decrease at 100°C / h down to room temperature, i.e. approximately 20°C.

[0068] As a non-limiting example, the heat treatment 106 for crystallization and densification may comprise a temperature increase of 300°C / h (degrees Celsius per hour) up to 1350°C, a 5-hour hold at 1350°C and a temperature decrease of 100°C / h down to room temperature, i.e. approximately 20°C.

[0069] Although the present disclosure has been described with reference to a specific exemplary embodiment, it is obvious that various modifications and changes may be made to these examples without departing from the general scope of the invention as defined by the claims. Furthermore, individual features of the various embodiments recited may be combined in additional embodiments. Therefore, the description and drawings should be considered in an illustrative rather than restrictive sense.

Claims

Claims

1. A method of manufacturing (100) an environmental barrier (10), the method comprising the following steps: coating (102) a rare earth silicate powder (22) with a precursor of a densifying agent (24) to form a rare earth silicate powder (20) coated with the precursor of the densifying agent, the coating (102) being carried out by gaseous means; thermal spraying (104) of the coated powder (20) onto a substrate (12) to obtain an at least partially amorphous environmental barrier (10) on the substrate (12); and heat treatment (106) for crystallization and densification of the environmental barrier (10).

2. The manufacturing method (100) of claim 1, wherein the rare earth silicate powder (22) is fluidized in a solution comprising a solvent and the precursor of the densifying agent (24).

3. A manufacturing method (100) according to any one of claims 1 or 2, wherein the precursor of the densifying agent (24) is an organometallic precursor.

4. A manufacturing method (100) according to any one of claims 1 to 3, wherein the coated powder (20) has a core-shell structure.

5. A manufacturing method according to any one of claims 1 to 4, wherein the substrate (12) is a ceramic matrix composite material substrate.

6. A manufacturing method according to any one of claims 1 to 5, wherein the environmental barrier (10) comprises a bonding layer (14).

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