EP4175929A1

EP4175929A1 - Method for manufacturing an environmental barrier

Info

Publication number: EP4175929A1
Application number: EP21740159.5A
Authority: EP
Inventors: Lisa PIN; Luc Patrice BIANCHI; Sophie Olivia Michele BOUDET; Jimmy James MARTHE
Original assignee: Safran Ceramics SA
Current assignee: Safran Ceramics SA
Priority date: 2020-07-02
Filing date: 2021-06-22
Publication date: 2023-05-10
Also published as: FR3112143A1; WO2022003273A1; US20230250034A1; CN115803306A

Abstract

The invention relates to a method for manufacturing (100) an environmental barrier comprising the steps of coating (102) a rare earth silicate powder with a precursor of a densification agent in order to form a rare earth silicate powder coated with the precursor of the densification agent, thermally spraying (104) the coated powder onto a substrate in order to obtain an at least partially amorphous environmental barrier on the substrate, and thermally treating (106) the environmental barrier in order to crystallise and densify same.

Description

PROCESS FOR MANUFACTURING AN ENVIRONMENTAL BARRIER

Technical area

This presentation relates to environmental barriers, also called "EBC)", in accordance with the acronym in English for "Environmental Barrier Coating", and 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 can for example be a turbine part of a turbomachine. The turbomachine can for example be a turbojet.

[0004] Under the operating conditions of aeronautical turbines, for example high temperature and corrosive environment, CMCs are generally sensitive 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 lifetime of CMCs, 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 adversely affect the performance of the EBC.

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

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

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

This disclosure relates to a method of manufacturing an environmental barrier, the method comprising the following steps: coating a rare earth silicate powder with a precursor of a densifying agent to form a silicate powder. rare earth 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 of crystallization and densification of the environmental barrier.

By coating the rare earth silicate powder with a precursor of a densifying agent, the precursor of the densifying agent, and therefore the densifying agent, is distributed homogeneously.

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

During thermal spraying, the precursor of the densifying agent will react to form the densifying agent on the rare earth silicate powder and promote densification of the environmental barrier. As a result, it can be envisaged to reduce the mass content of the densifying agent in comparison with a mixture obtained by mixing / grinding the two powders together.

By way of non-limiting examples, the densifying agent obtained during the thermal spraying of the coated powder can be magnesium oxide, calcium oxide, iron oxide, yttrium oxide, mullite, silica. [0014] In certain embodiments, the thermal spraying can be a plasma spraying in air, a plasma spraying under vacuum or HVOF in accordance with the acronym for "High Velocity Oxy Fuel".

[0015] In certain embodiments, the coating can be carried out by wet process.

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

In certain embodiments, the deagglomeration of the agglomerated powder can comprise a step of heat treatment of the agglomerated powder at a temperature of between 250 ° C (degree Celsius) and 600 ° C for 1 h (hour) to 4 h.

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

In some embodiments, the coating can be carried out by gas.

In some embodiments, the precursor of the densifying agent can be an organometallic precursor.

By way of non-limiting examples, the organometallic precursor can be a metal nitrate, a metal acetate, a metal chloride, a metal alkoxide or a metal phosphorus.

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

The use of a metal salt makes it possible to reduce the loss of silica during the thermal spraying of a rare earth silicate powder by the preferential oxidation of the metal salt which is placed 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. In some embodiments, the precursor of the densifying agent can be the densifying agent.

By way of non-limiting examples, the precursor of the densifying agent can be magnesium oxide or silica, the densifying agent being the same as the precursor.

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

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

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 envelope may 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.

In some 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 5 hours and less than or equal to 50 hours.

In certain embodiments, the substrate may be a substrate made of a composite material with a ceramic matrix.

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

In some embodiments, the environmental barrier can include a tie layer. By way of nonlimiting examples, the tie layer can be made of silicon.

It is understood that the tie layer is deposited on the substrate and is between the substrate and the layer of material.

Brief description of the drawings

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

[0036] [Fig. 1] Figure 1 is a schematic sectional view of a substrate and an environmental barrier according to one embodiment.

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

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

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

[0040] [Fig. 5] Fig. 5 is a flowchart showing the steps of a method of manufacturing an environmental barrier.

In all of the figures, the elements in common are identified by identical numerical references.

detailed description

Figure 1 is a schematic representation of a substrate 12 covered with an environmental barrier 10.

By way of non-limiting example, the substrate 12 can be a substrate made of a composite material with a ceramic matrix.

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

At the interface between the tie layer 14 and the yttrium disilicate layer 16 is present a silica layer 18. The silica layer 18 is a silicon oxide layer formed by oxidation of the silicon bonding layer 14.

The yttrium disilicate layer 16 comprises a densifying agent.

By way of non-limiting examples, the densifying agent can be a sintering agent and / or a healing agent.

By way of non-limiting examples, the sintering agent can be magnesium oxide or iron oxide.

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

By way of nonlimiting example, the yttrium disilicate layer 16 may comprise between 0.1 and 5% by mass of sintering agent, for example 0.4% by mass of sintering agent.

The environmental barrier 10 can be obtained by the manufacturing process 100 of Figure 4.

The manufacturing process 100 of the environmental barrier 10 comprises a coating step 102 of 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 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. densifying agent 24.

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

These two types of structures can be obtained by the wet route or by the gas route.

Example of enrobaae

Rare earth disilicate powder, magnesium acetate and distilled water.

In 1 L (liter) of distilled water, dissolve 5% by mass of magnesium acetate (typically between 0.1 and 10% by mass). Pour 1 kg of rare earth disilicate powder in the aqueous solution of magnesium acetate.

Mix with a magnetic bar.

Drying at 90 ° C in an oven.

On the blocks of agglomerated powder perform a heat treatment at 400 ° C for 1 hour in air so that the blocks become friable.

The coated powder 20 is available.

The coated powder 20 is projected by a thermal spraying process 104 on the substrate 12 to obtain an environmental barrier 10 at least partially amorphous on the substrate 12.

In the example of the organometallic precursor of the densifying agent described above, the organometallic precursor of the densifying agent, that is to say magnesium acetate, will dehydrate and s' oxidize during thermal spraying to form the densifying agent around the rare earth disilicate powder at a desired and controlled concentration. A partially amorphous environmental barrier can be obtained with flattened grains (also called "splats") of rare earth disilicate and the densifying agent evenly distributed around the flattened grains of rare earth disilicate.

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

As a non-limiting example, the heat treatment 106 of crystallization and densification can include a temperature rise at 100 ° C / h (degrees Celsius per hour) up to 1300 ° C, a level of 50 hours at 1300 ° C and a drop in temperature at 100 ° C / h to room temperature, that is to say around 20 ° C.

As a non-limiting example, the heat treatment 106 of crystallization and densification may include a temperature rise at 300 ° C / h (degrees Celsius per hour) up to 1350 ° C, a level of 5 hours at 1350 ° C and a drop in temperature to 100 ° C / h to room temperature, that is to say around 20 ° C.

Although the present disclosure has been described with reference to a specific embodiment, it is obvious that various modifications and changes can be made to these examples without departing from the general scope of the invention as defined by the claims. In addition, individual characteristics of the various embodiments mentioned can be combined in additional embodiments. Therefore, the description and the drawings should be taken in an illustrative rather than a restrictive sense.

Claims

[Claim 1] A method of manufacturing (100) an environmental barrier (10), the method comprising the steps of: coating (102) of a rare earth silicate powder (22) with a precursor of a protective agent. densifying (24) to form a rare earth silicate powder (20) coated with the precursor of the densifying agent; 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) to crystallize and densify the environmental barrier (10).

[Claim 2] The manufacturing method (100) according to claim 1, wherein the coating (102) is wet.

[Claim 3] The manufacturing method (100) according to claim 2, wherein the rare earth silicate powder (22) is immersed in a solution comprising a solvent and the precursor of the densifying agent (24), the solvent. is evaporated to form an agglomerated coated powder and the agglomerated coated powder is deagglomerated to form the coated powder (20).

[Claim 4] The manufacturing method (100) according to claim 2, wherein the rare earth silicate powder (22) is fluidized in a solution comprising a solvent and the precursor of the densifying agent (24).

[Claim 5] The manufacturing method (100) according to claim 1, wherein the coating (102) is carried out by gas.

[Claim 6] The manufacturing method (100) according to any one of claims 1 to 5, wherein the precursor of the densifying agent (24) is an organometallic precursor.

[Claim 7] The manufacturing method (100) according to any one of claims 1 to 6, wherein the coated powder (20) has a core-shell structure.

[Claim 8] The manufacturing method according to any one of claims 1 to 7, wherein the substrate (12) is a ceramic matrix composite material substrate. [Claim 9] The manufacturing method according to any of claims 1 to 8, wherein the environmental barrier (10) comprises a tie layer (14).