COMPONENT PROTECTED BY AN ENVIRONMENTAL BARRIER

Background of the invention

The present invention relates to the general field of the protection against corrosion of parts made of composite material with ceramic matrix (CMC).

A particular field of application of the invention is the protection of parts made of ceramic matrix composite material (CMC) forming hot parts of gas turbines, such as combustion chamber walls, or turbine rings, distributors. turbine or turbine blades, for aeronautical engines or industrial turbines.

For such gas turbines, the concern to improve efficiency and reduce polluting emissions leads to consider ever higher temperatures in the combustion chambers.

It has therefore been proposed to replace metallic materials with CMC materials, in particular for the walls of combustion chambers or turbine rings. Indeed, CMC materials are known to have both good mechanical properties allowing their use for structural elements and the ability to maintain these properties at high temperatures. CMC materials include a fibrous reinforcement of refractory fibers, typically carbon or ceramic, which is densified by a ceramic matrix, for example SiC.

Under the operating conditions of aeronautical turbines, that is to say 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 SiC to silica which, in the presence of water vapor, volatilizes in the form of silicon hydroxides Si (OH) 4 . Corrosion phenomena cause CMC to recede and affect the life of the latter.

In order to limit this degradation in operation, it has been envisaged to form environmental barrier coatings on the surface of CMC materials. Such a solution of the state of the art is illustrated in FIG. 1.

Thus, as illustrated in FIG. 1, a substrate 1 made of a ceramic matrix composite material (CMC) is covered with a bonding layer 2 made of silicon, said bonding layer 2 itself being covered by an environmental barrier 3 which can be a layer of rare earth silicate. During operation of the turbomachine, a protective silica layer 2a forms between the silicon bonding layer 2 and the environmental barrier 3.

The bonding layer 2 makes it possible, on the one hand, to improve the grip of the environmental barrier 3 and, on the other hand, to form in operation the protective silica layer 2a, of which the low oxygen permeability is involved. the protection of the CMC substrate 1 against oxidation.

The environmental barrier 3 makes it possible, for its part, to limit the diffusion of water vapor towards the protective silica layer 2a formed by oxidation of the silicon of the bonding layer 2, and consequently to limit the recession of the latter. .

However, a problem encountered by this solution of the state of the art is that the accessibility of the protective silica layer 2a to water vapor and to air is locally very variable.

These local accessibility differences are due in particular to local differences in density of environmental barrier 3, the tortuosity of the network of microcracks and porosities in environmental barrier 3 responsible for preferred paths for oxygen, and local heterogeneities. composition or in the crystal lattice of the environmental barrier 3.

These local accessibility differences can induce local differences in thickness in the protective silica layer 2a potentially responsible for stress build-up and premature deterioration of the part by delamination.

There is therefore a need to have a new system for protecting a CMC substrate against corrosion, to increase the service life of CMC parts.

Object and summary of the invention

The main aim of the present invention is therefore to overcome such drawbacks by proposing a part comprising:

a substrate of which at least a part adjacent to a surface of the substrate is made of a material comprising silicon;

- a bonding sub-layer located on the surface of the substrate and comprising silicon,

- an environmental barrier which comprises an outer ceramic layer covering the bonding sub-layer,

said environmental barrier further comprising a self-healing inner layer located between the bonding sub-layer and the outer layer, said inner layer comprising a matrix in which silico-forming particles are dispersed, these particles being able to generate a phase for healing cracks in the matrix in the presence of oxygen.

Such an internal environmental barrier layer offers the advantage on the one hand of reducing the quantity of water and air reaching the bonding sub-layer, and on the other hand of reducing the heterogeneity in the amount of water and air passing through the environmental barrier.

Indeed, the particles being silico-forming, that is to say of a nature to form silica (S1O2) when they are oxidized, said particles dispersed in the matrix of the internal layer react in contact with oxygen. to generate a healing phase which seals said inner layer. The particles include silicon.

In addition, such a reaction of particles with oxygen consumes part of the water and air passing through the internal layer of the environmental barrier, which limits the quantity of air and water transmitted to the sub. - bonding layer and reduces heterogeneities.

Furthermore, the particles of the internal layer may comprise ceramic particles, preferably particles of silicon carbide, or of silicon nitride, or of a MAX phase comprising silicon, or a mixture of such particles.

The particles of the internal layer can also comprise metallic particles, preferably particles of silicon element Si, or of a metallic silicide, or a mixture of such particles.

According to one possible characteristic, the particles of the internal layer have an average size less than or equal to 5μηη, and preferably less than or equal to 2μιτι.

The term “average size” denotes the dimension given by the statistical particle size distribution to half of the population, called D50.

In addition, the internal layer may comprise a level of particle volume load greater than or equal to 5% and less than 50%, and preferably between 20% and 40%.

According to an additional characteristic, the internal layer has a thickness between ΙΟμηι and 300μητι, and preferably between ΙΟΟμηι and 200μιτι.

The matrix of the internal layer can moreover be made of silicate, preferably a monosilicate or a rare earth disilicate, or an aluminosilicate such as mullite, or cordierite.

According to another characteristic, the matrix of the internal layer and the external layer are formed from the same material.

According to a second aspect, the invention proposes a method of manufacturing a part according to any one of the preceding characteristics, comprising the following steps:

deposition of the bonding sub-layer comprising silicon on the surface of the substrate;

depositing the internal layer of the environmental barrier on the bonding sub-layer;

- deposition of the outer layer of the environmental barrier on the inner layer, said outer layer being ceramic.

According to an additional characteristic, the deposition of the internal layer is carried out by plasma spraying in which a material intended to form the particles is introduced into a plasma jet in the form of a suspension in a liquid medium.

Furthermore, a material intended to form the matrix of the internal layer is introduced into the plasma jet in the form of powder.

According to another characteristic, the material intended to form the matrix of the internal layer is introduced into the plasma jet in the form of a suspension in liquid medium.

Brief description of the drawings

Other characteristics and advantages of the present invention will emerge from the description given below, with reference to the appended drawings which illustrate an exemplary embodiment thereof without any limiting nature. In the figures:

- Figure 1 shows an environmental barrier solution according to the state of the art;

- Figure 2 shows a sectional view of a part according to one embodiment of the invention;

- Figure 3 shows a detailed view of the inner layer of the environmental barrier;

- Figure 4 shows a first possible embodiment for the deposition of the internal layer of the environmental barrier;

- Figure 5 shows a second possible embodiment for the deposition of the internal layer of the environmental barrier;

- Figure 6 shows a third possible embodiment for the deposition of the internal layer of the environmental barrier;

- Figure 7 schematically shows the different steps of a manufacturing process according to an implementation of the invention.

Detailed description of the invention

In the following detailed description, the formation of an environmental barrier is envisaged on a substrate made of CMC material containing silicon. The invention is however applicable to substrates made of monolithic refractory material containing silicon and, more generally, to substrates at least one part of which adjacent to an external surface of the substrate is made of a refractory material (composite or monolithic) containing silicon. Thus, the invention relates in particular to the protection of refractory materials constituted by monolithic ceramics, for example of silicon carbide SiC or silicon nitride Si 3 N 4 , but more particularly the protection of refractory composite materials such as composite materials with a matrix.

ceramic (CMC) containing silicon, for example CMCs with a matrix at least partially of SiC.

As illustrated in FIG. 2, a part 10 according to the invention comprises a substrate 20 comprising a surface S. The substrate 20 comprises silicon on at least one part adjacent to the surface S. The part 10 can typically be a turbine ring. of a turbomachine.

The substrate 20 can be made of a CMC material containing silicon and which comprises a fibrous reinforcement which can be made from carbon fibers (C) or from ceramic fibers, for example from SiC fibers or formed essentially from SiC, including Si- fibers. C-0 or Si-CON, that is to say also containing oxygen and optionally 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 can 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 complement being C).

The fibrous reinforcement is densified by a matrix which is formed, in its entirety or at least in an external phase thereof, by a material containing silicon, such as a silicon compound, for example SiC or a ternary system Si -BC. By external phase of the matrix is ​​meant a phase of the matrix formed last, the furthest from the fibers of the reinforcement. Thus, the matrix can be formed from several phases of different natures, and can for example be:

a mixed C-SiC matrix (the SiC being on the external side), or a sequenced matrix with alternating SiC phases and matrix phases of lower rigidity, for example made of pyrolytic carbon (PyC), boron nitride (BN) or carbon doped with boron (BC), with a terminal phase of SiC matrix, or

a self-healing matrix with matrix phases in boron carbide (B 4 C) or in a ternary Si-BC system, optionally with free carbon (B 4 C + C, Si-BC + C), and with a phase terminal Si-BC or SiC.

The matrix can be at least partly formed by CVI in a manner known per se. As a variant, the matrix can be at least partly formed by the liquid route (impregnation with a precursor resin of the matrix and transformation by crosslinking and pyrolysis, the process being repeatable) or by infiltration of silicon in the molten state (process of "Melt-Infiltration"). In the latter case, a powder is introduced into the fibrous reinforcement optionally partially densified, this powder possibly being a carbon powder and possibly a ceramic powder, and a metallic composition based on silicon in the molten state is then infiltrated to form a matrix. of SiC-Si type.

A bonding sublayer 30 comprising silicon is located on the substrate 20. The bonding sublayer 30 is in contact with the substrate 20. The bonding sublayer 30 can typically be silicon (element Si ), or mullite (3AI203.2Si02). In operation, the bonding sub-layer 30 will oxidize and form a passivating layer of silica (Si0 2 ) (“Thermally Grown Oxide”).

An environmental barrier 40 is located on the bonding sub-layer 30 in order to protect said bonding sub-layer 30 and the substrate 20. The environmental barrier 40 comprises a self-healing inner layer 41 located on the sub-layer d. 'bonding 30, and an outer ceramic layer 42 located on the inner layer 41. The inner layer 41 is in contact on the one hand with the bonding sub-layer 30 and on the other hand with the outer layer 42.

By self-healing material is meant here a material forming, in the presence of oxygen, a vitreous composition capable, by changing to the pasty or fluid state in a certain temperature range, of healing cracks that have appeared within the material.

As can be seen in FIG. 3, the internal layer 41 comprises a matrix 41m in which particles 41p are dispersed. The matrix 41m is made of a material different from the material of the particles 41p. Furthermore, the matrix 41m comprises cracks 41f and other porosities.

The particles 41p are silico-forming particles, and therefore which are capable of generating a phase of healing of the cracks 41f of the matrix 41m in the presence of oxygen. The particles 41p are especially suitable for generating the healing phase when the temperature is above 800 ° C. The particles 41p comprise silicon.

Indeed, in operation, air and water flows 51 cross the outer layer 42 of the environmental barrier 40, and arrive at the inner layer 41 of said environmental barrier 40. The particles 41p being silico-forming, they react. with oxygen and form silica (S1O2). This silica generated by the particles 41p forms the healing phase and fills the cracks 41f and other porosities of the matrix 41m by capillary action, thus sealing the internal layer 41 by limiting the circulation of air and water flows 51 through said said. internal layer 41. Such a self-healing reaction of the internal layer 41 allows, that in contact with the air and water flows 51, said internal layer 41 becomes sealed, thus reducing the amount of air and water.

Moreover, in addition to sealing the internal layer 41 by filling the cracks 41f, such a self-healing effect makes it possible to consume a part of the water and of the air, thus reducing the quantity of air even more. and water in the outgoing streams 52 which reach the bonding sub-layer 30.

In addition, as illustrated in FIG. 3, the quantity of air and water is heterogeneous in the flows 51 which arrive on the internal layer 41. The fact that part of the water and of the air either consumed by the reaction of the particles 41p makes it possible to homogenize the outgoing flows 52 of air and water which arrive on the bonding sub-layer 30. Such homogenization of the outgoing flows 52 makes it possible to reduce the local differences in thickness in the protective silica layer generated by the bonding sub-layer 30, thus reducing the risk of accumulation of stresses and of premature deterioration of the part 10 by delamination.

Moreover, in addition to the oxidation reaction, the particles

41p can corrode in the presence of water and air, and generate HxSiyOz gas. Such a corrosion reaction of the particles 41p also makes it possible to consume water and air, thus reducing the quantity of water and air arriving on the bonding sub-layer 30.

The particles 41p can be ceramic particles. The particles 41p are preferably particles of silicon carbide (SiC), particles of silicon nitride (S13N4), or particles of a max phase comprising silicon, or a mixture of such particles. Silicon carbide is in particular one of the preferred materials.

The particles 41 p can also be metallic particles. The particles 41p are preferably particles of silicon (element Si), particles of a metal silicide, or a mixture of such particles.

The particles 41p preferably have an average size (D50) which is less than or equal to 5 μm. It is in fact advantageous that the particles 41p have an average size less than or equal to 5 μm because this allows the internal layer 41 to be more reactive for the generation of the healing phase in Si0 2 and for the consumption of air and some water. Indeed, the use of particles of small size makes it possible to increase the surface available for the oxidation and corrosion reaction of the particles 41p. Preferably, the particles 41p have an average size less than or equal to 2μιη, for example between Ο, ΐμηη and 2pm, in order to further increase the reactivity and the efficiency of the internal layer 41.

As will be described below, the use of particles having a size less than 5μιη is allowed in particular by a deposition by plasma spraying where the material intended to form the particles 41p is introduced by liquid route.

The internal layer 41 advantageously comprises a volume load rate of particles 41p greater than or equal to 5% and less (strictly) than 50%. This makes it possible, on the one hand, to ensure better reactivity of the internal layer 41 for the generation of the healing phase and the consumption of water and air as well as to ensure a sufficient service life for the internal layer 41. , and on the other hand to sufficiently keep the properties provided by the matrix 41m. Preferably, the internal layer 41 comprises a degree of volume charge of the particles 41p of between 20% and 40%.

The matrix 41m is advantageously made of silicate, and preferably a monosilicate or a rare earth disilicate, or an aluminosilicate such as mullite, or cordierite. It should be noted that the matrix 41m is preferably not made of barium and strontium aluminosilicate (BSAS), because the BSAS reacts with the silica. A matrix 41m in monosilicate or rare earth disilicate is a preferred embodiment. A matrix 41m in Y 2 Si 2 0 7 , RE 2 Si 2 0 7 , or in RE 2 Si0 5 are

preferred variants of the embodiment according to which the matrix 41m is in monosilicate or in rare earth disilicate.

The internal layer 41 has a thickness E which can be between 10 pm and 300 pm. Such a thickness allows the internal layer 41 to perform its role of protecting the bonding sub-layer 30. In addition, when the internal layer 41 has a significant thickness, for example between 200 μm and 300 μm, it can ensure it alone has the function of sealing against water and air for the environmental barrier 40, the upper layer 40 then being able to fulfill only the role of abradable. Furthermore, the thickness E of the internal layer 41 is preferably between lOOpm and 200μιη.

The outer layer 42 of the environmental barrier 40 is ceramic. The outer layer 42 can be a conventional environmental barrier layer. The outer layer 42 can be a monosilicate or a rare earth disilicate, or an aluminosilicate such as mullite or barium and strontium aluminosilicate (BSAS), or else cordierite.

Preferably, in order to ensure better mechanical and chemical compatibility between the internal layer 41 and the external layer 42 of the environmental barrier 40, the matrix 41m of the internal layer 41 and the external layer 42 are formed from the same material. Such a characteristic is all the more advantageous when the internal layer 41 and the external layer 42 are directly in contact with one another. Preferably, the matrix 41m of the inner layer 41 and the outer layer 42 are made of monosilicate or rare earth disilicate. Furthermore, the outer layer 42 may be loaded with fibers or inclusions depending on the properties wishing to be given to said outer layer 42.

Environmental barrier 40 may also include additional layers located on outer layer 42.

As illustrated in FIG. 7, according to one possible implementation, the method of manufacturing part 10 comprises the following steps:

E1: deposition of the bonding sub-layer 30 comprising silicon on the surface S of the substrate 20;

- E2 deposition of the internal layer 41 of the environmental barrier 40 on the bonding sub-layer 30;

- E3 deposition of the outer layer 42 of the environmental barrier 40 on the inner layer 41, said outer layer 42 being ceramic.

According to a preferred implementation of the method for manufacturing part 10, the deposition of the internal layer 41 is carried out by plasma spraying in which the material intended to form the particles 41p dispersed in the internal layer 41 is introduced into the plasma jet. in the form of a suspension in liquid medium.

The fact of introducing the material intended to form the particles 41p into the plasma jet in the form of a suspension in a liquid medium makes it possible to use particles 41p with a low average size, in particular with an average size less than 5 μm. Indeed, if the particles are not introduced into the plasma jet in the form of a suspension in a liquid medium, for example by being introduced in the form of a powder, the particles are liable to rebound on the plasma jet. because of their too small size, thus making it difficult to control the deposition of the internal layer 41.

In addition, the introduction of the material intended to form the particles 41p into the plasma jet in the form of a suspension in a liquid medium makes it possible to use a wider choice of particles 41p. Indeed, certain materials, including silicon carbide (SiC) in particular, may not withstand the introduction in the form of a powder into the plasma jet with difficulty and may in particular risk sublimating. Controlling the deposition of the internal layer 41 with particles 41p made of such materials, in particular silicon carbide (SiC), is therefore made difficult. The introduction into the plasma jet in the form of a suspension of the particles 41p in a liquid medium makes it possible to protect these materials against the plasma jet, and thus makes it easier to control the deposition of the internal layer 41.

According to a first possible embodiment for the deposition of the internal layer 41 which is illustrated in FIG. 4, said internal layer 41 of the environmental barrier 40 is produced by plasma spraying using a plasma torch 60 which generates a plasma jet 61. Plasma projection can be carried out at atmospheric pressure in air.

The material intended to form the matrix 41m of the inner layer 41 is injected into the plasma jet 61 using an injector 70 in the form of a powder 71. The powder 71 may, according to one example, be a Y2S12O7 powder with an average size of 30pm.

The material intended to form the particles 41p of the internal layer 41 is injected into the plasma jet 61 by an injector 80 in the form of a suspension 81 in a liquid medium. The suspension 81 can be, according to one example, an aqueous suspension loaded at 20% by mass of silicon carbide (SiC) particles with an average size of Ιμιτι.

In the example presented in FIG. 4, an internal layer 41 comprising a matrix 41m in Y 2 Si 2 0 7 and SiC particles with an average size of Ιμιτι is formed on the bonding sub-layer 30. The rate of particle volume charge 41p is 30% in this internal layer 41, and the thickness E of said internal layer is 150 μm.

According to a second embodiment shown in FIG. 5, the material intended to form the matrix 41m of the internal layer 41 is not injected into the plasma jet in powder form, but in the form of a suspension 91 in powder form. liquid medium comprising both the material intended to form the matrix 41m and the material intended to form the particles 41p. This suspension 91 is injected into the plasma jet 61 by a single injector 90.

According to one example, the suspension 91 is an aqueous suspension loaded to 20% by mass with the materials intended to form the matrix 41m and the particles 41p. The proportion of the mixture between these two materials is adapted so that the volume charge rate of the particles 41p in the internal layer 41 is 30%. The suspension 91 comprises particles of Y2S12O7, with an average size of 30 μm, which are intended to form the matrix 41 m (which will therefore be made of Y2S12O7), and particles of SiC, with an average size of 1 μm, and which are intended to form the matrix. form the 41p particles (which will therefore be SiC). The internal layer 41 formed has a thickness E of 150μητι.

According to a third embodiment illustrated in FIG. 6, the material intended to form the matrix 41m and the material intended to form the particles 41p are not injected into the plasma jet 61 in the same suspension, but in two suspensions 101a and 101b distinct.

The first suspension 101a is an aqueous suspension which is loaded with 20% by mass of particles of Y2S12O7 to form the

matrix 41m which have an average size of 5μιη. The first suspension 101a is injected into the plasma jet 61 by a first injector 100a.

The second suspension 101b is an aqueous suspension which is charged to 20% by mass of SiC particles to form the particles 41p, these particles having an average size of 1pm. The second suspension 101b is injected into the plasma jet 61 by a second injector 100b. The internal layer 41 formed has a thickness E of 150 μm.

The expression "between ... and ..." should be understood as including the limits.

CLAIMS

1. Piece (10) comprising:

- a substrate (20) of which at least a part adjacent to a surface (S) of the substrate is made of a material comprising silicon;

- a bonding sub-layer (30) located on the surface (S) of the substrate and comprising silicon,

- an environmental barrier (40) which comprises an outer layer (42) of ceramic covering the bonding sub-layer (30), characterized in that said environmental barrier (40) further comprises an inner layer (41) self- healing located between the bonding sub-layer (30) and the outer layer (42), said inner layer (41) comprising a matrix (41m) in which silico-forming particles (41p) are dispersed, these particles (41p ) being able to generate a phase of healing of cracks (41f) of the matrix (41m) in the presence of oxygen, the internal layer comprising a volume charge rate of particles (41p) of between 20% and 40%.

2. Part (10) according to claim 1 wherein the particles (41p) of the inner layer (41) comprise ceramic particles, preferably particles of silicon carbide, or of silicon nitride, or of a MAX phase comprising silicon, or a mixture of such particles.

3. Part (10) according to claim 1 or 2 wherein the particles (41p) of the inner layer (41) comprise metal particles, preferably particles of silicon element Si, or of a metal silicide, or a mixture of such particles.

4. Part (10) according to any one of claims 1 to 3, in which the particles of the inner layer have an average size less than or equal to 5 μm, and preferably less than or equal to 2 μm.

5. Part (10) according to any one of claims 1 to 4, wherein the inner layer has a thickness between ΙΟμιη and 300μητι, and preferably between ΙΟΟμητι and 200 m.

6. Part (10) according to any one of claims 1 to 5, wherein the matrix of the inner layer is made of silicate, preferably a monosilicate or a rare earth disilicate, or an aluminosilicate such as mullite, or cordierite. .

7. Part (10) according to any one of claims 1 to 6, wherein the matrix of the inner layer and the outer layer are formed of the same material.

8. A method of manufacturing a part (10) according to any one of claims 1 to 7, comprising the following steps:

(E1) deposition of the bonding sublayer (30) comprising silicon on the surface (S) of the substrate (20);

- (E2) deposition of the internal layer (41) of the environmental barrier (40) on the bonding sub-layer (30);

(E3) depositing the outer layer (42) of the environmental barrier (40) on the inner layer (41), said outer layer (42) being ceramic.

9. The method of claim 8, wherein the deposition of the internal layer (41) is carried out by plasma spraying in which a material intended to form the particles is introduced into a plasma jet in the form of a suspension in a liquid medium. .