The present invention relates to the general field of coatings thermal barrier used to thermally insulate the metallic parts in high temperature environments. The invention applies more particularly, but not exclusively, to thermal barrier used to protect parts in superalloys for aeronautical gas turbines.

The parts present in the hot parts of aircraft turbine engines operating in a desert environment or highly polluted, degrade very rapidly due to the attack of sand and alkali compounds in the air ingested by the engine. These compounds, known as "CMAS" (consisting in particular oxides of calcium, magnesium, aluminum and silicon) can degrade the coating acts as a thermal barrier covering some parts of the hot parts of the turbomachine.

Among the mechanisms of degradation of the thermal barrier by CMAS compounds being prominent infiltration in the liquid state of CMAS compounds in the thermal barrier and the dissolution-reprecipitation of the thermal barrier (traditionally consisting of a ceramic zirconia stabilized lYttrine YSZ), in isolated nodules of zirconia yttria depleted. Both mechanisms lower the mechanical properties of the thermal barrier which can lead to its cracking during the engine cooling phases. In addition, the ingestion of solid particles created the erosion of the thermal barrier flaking and then leaves the underlying metal substrate exposed, thus reducing the lifetime of the parts.

Solutions exist to limit the infiltration of CMAS in the thermal barrier. Examples include the use of a protective coating of the zirconia-based thermal barrier doped gadolinium (under the designation zirconate gadolinium, for example), or the use of alumina or titanium oxide. These coatings, by reacting with the CMAS, promote their precipitation and thus can limit their penetration into the thermal barrier. However, these coatings have the disadvantage of being sacrificial, requiring ongoing maintenance and regular monitoring of the condition of parts. In addition, the availability of the chemical elements (including rare earths) present in these coatings is increasingly limited, which is an additional constraint on their use.

There is therefore a need to have a part coated with a protective coating thermal barrier which has a long life in the environments and operating conditions of an aircraft turbine engine.

Purpose and Summary of the Invention

The present invention is thus a main object to overcome such drawbacks by providing a coated article comprising a metal substrate and / or intermetallic and a protective coating forming a thermal barrier covering said substrate, the protective coating comprising a first ceramic layer, characterized in that the protective coating further comprises a second layer present on the first layer, the second layer predominantly comprising by weight a first ore feldspar having a melting point of greater than or equal to 1010 ° C and having greater than or equal thickness to 10 pm.

By "coated" means that the piece of substrate is coated on all or part of its accessible surface or protect thermally.

Coating the coated part according to the invention is first characterized in that it comprises an impermeable outer layer CMAS, or in other words the sealed CMAS. Indeed, the second layer keeps a solid form at high temperature, and prevents the penetration of CMAS liquid in the first ceramic layer underlying (which constitutes the thermal insulating layer of the coating). By "high temperature" means temperatures of about 1000 ° C, as may be the case in an aviation turbomachine during operation.

Also, such a sacrificial layer is not as for coatings of the prior art, especially because it retains a solid form at high temperatures. the expression means "more sacrifice" that the layer thus deposited there from its development the ability to be chemically compatible (because of similar chemical composition) with the CMAS. The lifetime of such a layer is therefore increased compared to the prior art coatings.

In addition, the ore from the second layer is chemically stable with silica and alumina, which are compounds present in the CMAS and other sands or cements may be ingested by the turbomachine. Indeed, feldspars (or minerals from the feldspar family) are aluminosilicates which have a majority phase silica. In addition, these ores are compatible with the presence of water with which they degrade in a very slow decomposition reaction.

The composition of the first ceramic layer is not changed by the addition of the second layer which is independent of the first (in particular they can be deposited independently of one another). Thus, the performance of the first ceramic layer are not altered by the presence of the second protective layer, or by its deposition process.

The thickness greater than or equal to 10 μιτι of the second layer improves on the one hand the resistance to CMAS, but also the strength of the coating to erosion and impacts. The coated part according to the invention thus has a second controlled thickness coating layer and sufficient to obtain the aforementioned advantages. It is for example not the case for coatings comprising a protective layer which is formed in a turbomachine during operation, following for example a chemical reaction involving a thermal barrier layer and CMAS. Indeed, a protective layer formed in situ in the turbomachine, and not before the first use in the turbine engine, may have a smaller thickness, uncontrolled and inhomogeneous on the workpiece as it depends mainly on the diffusion of CMAS into the barrier thermal and environmental conditions (temperature, composition of CMAS) variables in the turbomachine.

Finally, the second layer of the coating according to the invention can also block the macropores that may be present on the surface of the first ceramic layer. For example, when the first ceramic layer comprises zirconia stabilized lYttrine, it has a lamellar structure or sticks (columnar) with a non-zero surface roughness, and it becomes advantageous to provide a protective layer can the cover and clog its pores at the surface.

In an exemplary embodiment, the second layer of the coating has a thickness greater than or equal to 20 microns, for example greater than or equal to 50 pm.

In an exemplary embodiment, the second layer of the coating has a thickness greater than or equal to one third of the thickness of the first layer.

In an exemplary embodiment, the second layer has a crystallinity higher than or equal to 5%, for example greater than or equal to 10%. This degree of crystallinity can be measured, in a known per se, using techniques such as X-ray diffraction or Raman spectroscopy. The crystallinity of the second layer makes it possible in particular to improve the adhesion between the first layer and the second layer of the coating.

Preferably, the first ceramic layer comprises zirconia.

Also preferably, the first ceramic layer comprises zirconia stabilized lYttrine. Alternatively, the first ceramic layer may also comprise zirconia doped with rare earths or with a composition based on ternary oxides. In the family of ternary systems, there may be mentioned include zirconia based systems yttria doped with a separate third oxide such as an oxide of one of the following chemical elements: ytterbium (Yb), neodymium (Nd), dysprosium (Dy), gadolinium (Gd), niobium (Nb), tantalum (Ta), samarium (Sm).

In one embodiment, the second layer predominantly comprises by weight of anorthite. By "anorthosite" means the general composition of feldspar minerals CaAl 2 SI20 8 , the polymorphic ore anorthite are also included.

The anorthite has the advantage of having a high melting point (over 1500 ° C), its melting being congruent (that is to say the change of solid / liquid phase occurs without change in its composition chemical or dissociation into secondary compounds).

The anorthosite is also very stable and breaks down very little in the conditions of pressure and temperature imposed by example in an aviation turbomachine. Furthermore, anorthite has a low density (which reduces centrifugal mechanical forces on the rotating parts, with respect to denser coatings), a coefficient of thermal expansion close to that of the superalloy, and a thermal conductivity comparable to that of the insulating ceramic coating of the first layer (the thermal conductivity of anorthite is of the order of 2W.m "1 .K -1 ). Finally, the use of anorthite is easy, as several methods of synthesis and deposition of anorthite are known (eg, sol-gel, slurry, chemical vapor deposition, sputtering, thermal spraying, etc.).

In some embodiments, the coating further comprises a third layer predominantly comprising a second mass ore feldspar having a melting point of greater than or equal to 1010 ° C, the third layer being below the first layer. This deposit adds additional protection to the substrate if the first ceramic layer is allowed to degrade and cross molten CMAS to the underlying layers. Such deposition is possible because the material forming the second layer comprises an alumina phase, is then compatible with the bonding sub-layer (generally disposed between the substrate and the first ceramic layer), which is often rich in aluminum to have a alumino character.

In some embodiments, further the protective coating comprises a fourth layer overlying the second layer comprising alumina and / or titania. The alumina and titanium oxide (Ti0 2 ) are nucleating agents which allow to precipitate the molten CMAS before they attack the underlying layers of the coating.

Also, the second layer may comprise alumina and / or titania, for the same reasons as above. A deposition of alumina and / or titanium oxide can be done at the same time that the deposition of feldspar, in this case the second layer comprises alumina dispersed phases and / or titanium oxide in a stage feldspar majority.

A coated part according to the invention can be a piece of aviation turbomachine, for example a turbine blade, a turbine nozzle, a blade, a turbine ring, a combustion chamber, a kerosene jet nozzle, etc.

The invention also provides a method of manufacturing a coated article comprising a metal substrate and / or intermetallic and a protective coating forming a thermal barrier covering said substrate, the method comprising forming a first ceramic layer on the metal substrate and / or intermetallic, characterized in that it further comprises the formation on the first layer a second layer of ceramic, the second layer predominantly comprising a mass feldspar ore having a melting point of greater than or equal to 1010 ° C and having a thickness greater than or equal to 10 pm.

The workpiece coated method of the invention may be carried out prior to a first use of the workpiece in a turbomachine. In other words, the coating of the coated part of the invention may be formed prior to the first use of the workpiece in a turbomachine. In this way, the part of the protective coating according to the invention may be homogeneous in composition and thickness across the entire room, regardless of the subsequent conditions of use of the room.

Finally, the invention provides a method of using a coated article such as defined above, comprising the use of the part in an oxidizing environment to a temperature above 1000 ° C and in the presence of aluminosilicates of calcium and magnesium (CMAS). These conditions may correspond to conditions found in an operating turbine engine.

Brief Description of Drawings

Other features and advantages of the present invention will emerge from the description made below, with reference to the accompanying drawings which illustrate examples of embodiment thereof without any limiting character. In the figures:

- Figures 1 to 4 illustrate the various parts comprising substrates coated with a protective coating forming a thermal barrier according to various embodiments of the invention.

Detailed Description of the Invention

Figure 1 shows a sectional view of a coating 2 of protection for forming a thermal barrier on a metal substrate (and / or intermetallic) 1 of a coated part of the invention. The part may for example be an aeronautical turbine engine turbine blade. The substrate 1 may typically comprise a superalloy based on iron, cobalt or nickel. Note that the substrate 1 may also include an intermetallic material of the titanium aluminide type, or niobium silicides, molybdenum silicides, etc. The coating 2 covers the substrate 1, and is in direct contact thereof.

In known manner, the coating 2 comprises first of all a so-called tie layer 20 which provides in particular protection against corrosion and oxidation of the substrate 1. The bonding layer 20, known per se, partially oxide on its surface over a certain thickness when heated to high temperature to form an oxide layer 21 (also referred to TGO "Thermally Grown oxide"). The bonding layer 20 may for example comprise a simple or modified aluminide.

A first ceramic layer 22 then covers the oxide layer 21. The first layer 22 is here in direct contact with the oxide layer 21 which acts as a coupling layer for the first layer 22.

Typically, this first layer 22 may comprise stabilized zirconia lYttrine (YSZ) having a columnar structure or in sticks. The first layer 22 may have a non-zero roughness on its outer surface (that is to say, its surface opposite to the substrate 1). The first layer 22 provides thermal insulation of the lining 2 and the thermal barrier protects the substrate 1 of the heat of the gas from the gas flow stream in the turbine engine. This is also the first layer 22 which can be degraded by the action of high temperature CMAS. The coating 2 of the coated part of the invention allows to limit this degradation.

Alternatively, the first layer 22 can comprise doped zirconia with rare earths, or with a composition based on ternary oxides. In the family of ternary systems, there may be mentioned include zirconia based systems yttria doped with a separate third oxide such as an oxide of one of the following chemical elements: ytterbium (Yb), neodymium (Nd), dysprosium (Dy), gadolinium (Gd), niobium (Nb), tantalum (Ta), samarium (Sm).

According to the invention, the coating 2 further comprises a second layer 23 mainly comprising by weight feldspar ore having a melting point of greater than or equal to 1010 ° C. This layer has a greater thickness e2 or equal to 10 microns, for example greater than 20 mm, or greater than or equal to 50 μηη. The thickness e2 of the second layer 23 may be greater than or equal to one third of the thickness el of the first layer 22.

The second layer 23 or protective layer 23 protects the first layer 22 made of ceramic, in particular forming a tight barrier CMAS, and chemically compatible with the CMAS. Indeed, the minerals of the feldspar family having a melting point of 1010 ° C are all solid first high temperatures they are exposed in the turbine engine. In addition, they have a chemical structure based on alumina and silica as main phase, which ensures a good chemical compatibility with CMAS in the environment of the turbomachine. Such ore may for example be of anorthite, or one of its polymorphs.

Synthetically, coating 2 comprises the layer closest to farthest from the substrate 1: a bonding layer 20 directly in contact with the substrate 1, an oxide layer 21 directly in contact with the bonding layer 20 a first ceramic layer 22 directly in contact with the oxide layer 21 and a second protection layer 23 directly in contact with the first ceramic layer 22.

2 shows another embodiment of a workpiece comprising a substrate 1 coated with a coating 2 'according to the invention. In this example, the coating 2 'further comprises a third

protective layer 24 overlying the oxide layer 21 and disposed below the first layer 22 of ceramic. The third protective layer 24 is here in direct contact with the oxide layer 21 and first layer 22 of ceramic.

This arrangement is advantageous in that it allows to have another barrier layer 24 or third layer 24 sealed in the first layer 22 made of ceramic, and prevents, in the case where the CMAS cross the layer 22, that they reach the substrate 1 and degrade. The third layer 24 has a composition of the same type as that of the second layer 23 and may comprise primarily bulk a second ore feldspar having a melting point of greater than or equal to 1010 ° C. The second feldspar ore may be identical to the first ore the second layer 23, or different from one.

Such an arrangement is not possible with the protective layers of the prior art because these layers are generally not compatible with the oxide material layer 21. For example, a protective layer of prior art based on doped zirconia gadolinium degrades by reaction with alumina to form an aluminide gadolinium. The formation of this aluminide gadolinium leads to an increase in volume and also in the formation of pores, which significantly weakens the entire coating. The third layer 24 according to the invention in turn is compatible with the alumina of the oxide layer 21 because it includes an alumina phase.

The coating 2 "of Figure 3 comprises a fourth layer 25 overlying the second layer 23 for protection with the aim to further increase the protection layer 22 made of ceramic. The fourth layer 25, in contact with the second layer 23, comprises alumina and / or titania. the alumina and titanium oxide are compounds capable of reacting with the CMAS liquid and facilitating their precipitation. Note that it is also conceivable to use for the fourth layer 25 of the rare earth oxides, for example, a yttrium oxide, zirconium, gadolinium, lanthanum, samarium, etc. Thus, with such an additional layer, it further increases the life of the coating 2 ".

Alternatively, may be added alumina and / or titanium oxide in the second layer 26 of protection (such as in the coating 2 " 'of Figure 4) to increase the effectiveness of the protection of the coating . for example, alumina and / or titanium oxide may be added in powder form during the deposition of the second protective layer.

Example

In the following examples, we are interested in the use of anorthite as feldspar ore the second layer 23 or the third protection layer 24, and one of its deposition processes.

The anorthite, of general formula CaAl 2 If 2 0 8 presents additional advantages over other feldspars, including a congruent melting point over 1500 ° C which still gives it a better chemical stability at high temperatures. Also, it has a coefficient of thermal expansion close to that of a superalloy, and a thermal conductivity comparable to that of ceramic forming the first layer 22.

In general, stoichiometric anorthite comprises by weight: 20.16% calcium oxide (CaO) 36.66% alumina

(Al 2 0 3 ) and 43.19% silica (Si0 2 ). This composition is advantageous for the following reasons.

In desert regions, the calcium oxide is present in the sand up to 15% by weight and silica is the primary compound. When such sands are ingested by the turbomachine, the second protective layer 23 is chemically compatible with such compounds. This layer mainly comprising 23 by weight of anorthite retains a crystallized form and remains tight

CMAS.

In addition, it is known that aluminosilicates compounds may react with water which may be present as residual moisture when the turbomachine is stopped or generated during the combustion of fuel with air. However, anorthite decomposition reaction with water is very slow under the conditions of operation of the turbomachine. Likewise, other degradation reactions of anorthite are known, but have equally slow kinetics in pressure and temperature conditions considered, and therefore irrelevant in a turbo application.

A process for depositing a second protective layer 23 based on anorthite will now be described briefly.

We first performed the synthesis of anorthosite. Reagents such as kaolin (source of silicon and aluminum), alumina or aluminum hydroxide (aluminum source), and the lime or calcium carbonate (calcium source) are prepared. Table 1 below provides two examples (El, E2) of the quantities of each component to be used to achieve about 90g anorthite (the yield obtained with the procedure described hereinafter is of the order of 90%). In order to improve the yield, it is for example possible to add boric acid H 3 B0 3 1% by mass.

Table 1

The powder form reactants are mixed by means of a lubricated mill with distilled water. The mixture is then subjected to a compression pressure by means of ceramic balls (zirconia for example), the relevant parameters are: a pressure between Loompa and 150MPa, a rotation speed ranging between 100 revolutions / minute and 500 revolutions / minute, and a milling time of between 20 min and 60 min. These values ​​are of course given as an illustration.

Then, drying is carried out of the mixture which has been ground to remove any residual moisture, generally at a temperature between 100 and 120 ° C.

Then, the synthesis process is completed calcining the ground mixture and dried at a temperature between 900 ° C and 1080 ° C for a dwell time between 1 hour and 6 hours. Cooling is then carried out in dry air.

Finally, one can carry out the deposition of anorthite thus synthesized by various means known to those skilled in the art, such as the sol-gel, the slurry, the chemical vapor deposition, spraying, thermal spraying (and its derivatives: SPS or "Suspension Plasma spraying" SPPS or "Precursor Plasma Spray Solution"), the type of HVOF projection (or "High Velocity Oxy Fuel"), or by physical vapor deposition with electron beam ( EB-PVD). For these deposits, anorthite synthesized is preferably in the form of a powder having an average particle size of a few microns. Following the deposition of anorthite, it is possible to perform a heat treatment to complete the formation of the protective coating on the substrate and to control the crystallinity of the second layer 23 protection.

Note that during the deposition of the anorthite powder to produce a second layer 23 (Figures 1 and 2) or a third layer 24 (Figure 3), it is possible to incorporate an alumina powder and / or titanium oxide to the anorthite powder when depositing to form a fourth layer 26 (Figure 4) multiphasic.

CLAIMS

1. A coated substrate comprising a metal and / or intermetallic (1) and a protective coating (2; 2 '; 2 "; 2"') forming a thermal barrier covering said substrate, the protective coating comprising a first ceramic layer (22), characterized in that it further comprises a second layer (23; 26) present on the first layer, the second layer predominantly comprising a first mass ore feldspar having a melting point of greater than or equal to 1010 ° C and having a thickness (e2) greater than or equal to 10 pm.

2. Part according to claim 1, characterized in that the second layer has a thickness (e2) greater than or equal to 20 pm.

3. Part according to any one of claims 1 and 2, characterized in that the first ceramic layer (22) comprises zirconia.

4. Part according to claim 3, characterized in that the first ceramic layer (22) comprises zirconia stabilized lYttrine.

5. Part according to any one of claims 1 to 4, characterized in that the second layer (23; 26) predominantly comprises by weight of anorthite.

6. Part according to any one of claims 1 to 5, characterized in that the coating (2 further comprises a third layer (24) mainly comprising a second mass ore feldspar having a melting point of greater than or equal to 1010 ° C, the third layer being located below the first layer (22).

7. Part according to any one of claims 1 to 6, characterized in that the coating (2 ") further comprises a

fourth layer (25) overlying the second layer (23; 26) comprising alumina and / or titania.

8. Component according to any one of claims 1 to 7, characterized in that the second layer (26) further comprises alumina and / or titania.

9. A method of manufacturing a coated article comprising a metal substrate and / or intermetallic (1) and a protective coating (2; 2 '; 2 "; 2"') forming a thermal barrier covering said substrate, the method comprising forming a first ceramic layer (22) on the metal substrate and / or intermetallic, characterized in that it further comprises forming on the first layer of a second ceramic layer (23; 26), the second layer mass predominantly comprising a feldspar ore having a melting point of greater than or equal to 1010 ° C and having a thickness greater than or equal to 10 μιτι.

10. A method of using a coated article according to any one of claims 1 to 8, comprising the use of the part in an oxidizing environment to a temperature above 1000 ° C and in the presence of aluminosilicates of calcium and magnesium.