Part coated with a composition for protection against CMAS with controlled cracking, and corresponding treatment method

The invention relates to a turbomachine part comprising a substrate consisting of a metal material, or a composite material, and also comprising a layer of a coating for protection against the infiltration of CMAS-type compounds, at least partially covering the surface of the substrate, the protective coating layer comprising a plurality of elementary layers including elementary layers of a first assembly of elementary layers inserted between elementary layers of a second assembly of elementary layers, each elementary layer of the first assembly and each elementary layer of the second assembly comprising an anti-CMAS compound, and each contact zone between an elementary layer of the first assembly and an elementary layer of the second assembly forming an interface conducive to the spreading of cracks along said interface.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No. PCT/FR2018/053549 filed on Dec. 26, 2018, claiming priority based on French Patent Application No. 1763278 filed on Dec. 27, 2017. The entire contents of each of which are herein incorporated by reference in their entireties.

TECHNICAL FIELD OF THE INVENTION

The invention relates to a turbomachine part, such as a high-pressure turbine blade or a combustion chamber wall.

RELATED ART

In a turbojet engine, the exhaust gases generated by the combustion chamber can reach high temperatures, in excess of 1200° C. or even 1600° C. The parts of the turbojet engine in contact with these exhaust gases must be capable of maintaining their mechanical properties at these high temperatures. In particular, the components of high-pressure turbines, or HPT, must be protected against an excessive rise in surface temperature in order to guarantee their functional integrity and limit oxidation and corrosion.

It is known to manufacture certain parts of the turbojet engine in “superalloy”. Superalloys are a family of high-strength metal alloys that can work at temperatures relatively close to their melting points (typically 0.7 to 0.8 times their melting temperatures). It is also known to fabricate parts from ceramic matrix composites, or CMC.

It is known to cover the surface of parts made of said materials with a coating acting as a thermal barrier and/or an environmental barrier.

A thermal or environmental barrier generally comprises a thermally insulating layer whose function is to limit the surface temperature of the coated component, and a protective layer to protect the substrate from oxidation and/or corrosion. The ceramic layer generally covers the protective layer. By way of example, the thermally insulating layer can be made of yttriated zirconia.

A metallic undercoat can be deposited before the protective layer, and the protective layer can be formed by oxidation of the metallic undercoat. The metallic undercoat provides a bond between the surface of the superalloy substrate and the protective layer: the metal underlay is sometimes referred to as the “bond coat”.

In addition, the protective layer can be pre-oxidized prior to the deposition of the thermal insulation layer to form a dense alumina layer, usually called thermally-grown oxide (TGO), to promote the adhesion of the thermal insulation layer and enhance the protective function against oxidation and corrosion.

It is crucial to ensure a satisfactory service life of the thermal and environmental barriers throughout the operating cycles of the turbomachine parts. This service life is notably conditioned by the resistance of the barrier to thermal cycling on the one hand, and to environmental aggressions such as erosion and corrosion on the other. The thermal or environmental barrier is likely to degrade rapidly in the presence of particles rich in silica-type inorganic compounds, or if it is located in an atmosphere rich in compounds commonly known as CMAS, including in particular oxides of calcium, magnesium, aluminum and silicon. CMAS is likely to infiltrate the thermal or environmental barrier in the molten state, particularly in cracks formed in the internal volume of the barrier layers. Once infiltrated, particles of CMAS compounds can cause partial chemical dissolution of the barrier, or they can stiffen within the barrier and lower the mechanical strength properties of the thermal or environmental barrier.

To prevent the penetration of high-temperature liquid contaminants such as CMAS compounds into coating layers, anti-CMAS depositions are known to promote the formation of a tight barrier layer on the surface of the coated part by spontaneous chemical reaction between chemical species of anti-CMAS depositions and CMAS compounds. The tight barrier layer thus formed blocks the progress of the molten CMAS compounds within the part to be protected. Such anti-CMAS depositions can be applied either directly on the substrate to form a complete thermal or environmental barrier, or in a functionalization layer. The reaction kinetics between the anti-CMAS deposition and the CMAS compounds is then in competition with the infiltration kinetics of the CMAS compounds within the coating, and particularly within cracks in the coating.

However, the effectiveness of anti-CMAS depositions is reduced when the part to be protected presents a transverse crack.

Throughout the following description, a “transverse crack” refers to a plurality of cracks having a general orientation substantially orthogonal to the plane tangential to the surface of the coated part. AnnexedFIGS.1a,1band1cillustrate the phenomenon of capillary penetration of CMAS compounds from ambient air into a network of cracks within the external surface of a part. InFIG.1a, the part, which may be a high-pressure turbine blade of a turbomachine, has a layer2of anti-CMAS deposition, of substantially uniform thickness, on its surface. The anti-CMAS layer includes a substantially transverse crack4. This crack4is part of a larger network of transverse cracks comprising through cracks for the layer2, orthogonal to the surface and with little deviation. InFIG.1b, particles of CMAS compounds, melted due to the high surface temperature at the layer2during blade operation, form a liquid phase3at the surface of the layer2. This liquid phase3is partially infiltrated into the crack4. InFIG.1c, which represents the system in a later state than that ofFIG.1b, the chemical species present in the anti-CMAS deposition layer2have reacted with the infiltrated CMAS compounds to form a blocking phase5on the perimeter of the crack4. The blocking phase5is schematized here by a network of contiguous pentagonal shapes. This blocking phase5blocks the infiltration of the CMAS compounds of the liquid phase3. In addition, a secondary phase6can form in places, this secondary phase6being represented by the circular shapes shown inFIG.1c. Here, the crack4being substantially transverse, the liquid phase3rapidly infiltrates over the entire thickness of the anti-CMAS deposition layer2, the infiltration kinetics of the molten CMAS compounds outweighing the kinetics of the chemical reaction leading to the formation of the blocking phase. This weakens the layer2and reduces the service life of the part.

Thus, there is a need for a surface treatment of a turbomachine part, comprising the application of a thermal and/or environmental barrier having a guaranteed integrity throughout the life cycle of the part, in an environment loaded with CMAS compounds. In particular, a problem arises regarding the mechanical resistance of the anti-CMAS deposition layers arranged on the surface of turbine parts to the infiltration of molten CMAS compounds.

GENERAL PRESENTATION OF THE INVENTION

The invention responds to the abovementioned needs by providing a turbomachine part comprising a substrate made of a metallic material, or of a composite material, and comprising a protective coating layer against the infiltration of compounds of the calcium, magnesium, aluminum or silicon oxide type, or CMAS, the coating layer at least partially covering the surface of the substrate,the protective coating layer comprising a plurality of elementary layers, comprising elementary layers of a first set of elementary layers interposed between elementary layers of a second set of elementary layers,each contact zone between an elementary layer of the first set and an elementary layer of the second set forming an interface promoting the propagation of cracks along said interface.

A part according to the invention therefore has an anti-CMAS coating layer which promotes the deflection of possible cracks in a direction substantially parallel to the surface of the part. The capillary penetration of CMAS-type compounds melted during operation of the part is intended to be minimized. Indeed, the liquid phase formed by the molten CMAS compounds, instead of propagating within the cracks in a direction substantially orthogonal to the thickness of the successive layers of coating and rapidly reaching the substrate of the part, infiltrates into tortuosities formed by the cracks along the interfaces of elementary layers. The kinetics of the reaction of formation of a blocking phase involving chemical compounds of the coating is promoted over the infiltration kinetics of molten CMAS compounds.

Another advantage provided by the invention is to allow cracking of the anti-CMAS coating layers while ensuring good mechanical resistance due to the reduction of the infiltrated CMAS compounds. The presence of cracks within the coating allows to accommodate thermomechanical deformations on the surface of the part, without generating more important fractures which would harm the resistance of the part.

Additional and non-limiting features of a turbomachine part according to the invention are as follows, taken alone or in any of their technically possible combinations:the elementary layers of the first set have toughnesses which differ by at least 0.7 Mpa·m1/2from the toughnesses of the elementary layers of the second set,the elementary layers of the first set may for example have a toughness of between 0.5 and 1.5 MPa·m1/2and the elementary layers of the second set may have a toughness of between 1.5 and 2.2 MPa·m1/2.

The change in toughness between two consecutive elementary layers induces preferential cracking in the direction of the interface between the consecutive layers, especially during operation and possibly at the end of manufacture after cooling;the elementary layers of the second set comprise a material from the following list: YSZ, Y2O3-ZrO2-Ta2O5, BaZrO3, CaZrO3, SrZrO3, or comprise a mixture of several of these materials;the elementary layers of the first set comprise a material taken from the following list: RE2Zr2O7 with RE a material of the rare earth family, Ba(Mg1/3Ta2/3)O3, La(Al1/4Mg1/2Ta1/4)O3, or comprise a mixture of several of these materials;the elementary layers of the first set have coefficients of thermal expansion which differ by at least 3.5 10−6K−1from the coefficients of thermal expansion of the elementary layers of the second set,the elementary layers of the first set being able to have a coefficient of thermal expansion of between 3.5 and 6.0 10−6K−1and the elementary layers of the second set being able to have a coefficient of thermal expansion of between 7.0 and 12.0 10−6K−1.

The change in the coefficient of thermal expansion between two consecutive elementary layers induces preferential cracking in the direction of the interface between the consecutive layers, especially during operation and possibly at the end of manufacture after cooling;the elementary layers of the second set comprise a material from the following list: YSZ, Y2O3-ZrO2-Ta2O5, BaZrO3, CaZrO3, SrZrO3, RE2Zr2O7 with RE a material of the rare earth family, Ba(Mg1/3Ta2/3)O3, La(Al1/4Mg1/2Ta1/4)O3, YAG, or comprise a mixture of several of these materials;the elementary layers of the first set comprise RE2Si2O7 or RE2SiO5 with RE a material of the rare earth family, or comprise a mixture of these materials;the ratio of the cumulative thickness of the elementary layers of the first set to the cumulative thickness of the elementary layers of the second set is comprised between 1:2 and 2:1;the total thickness of the protective coating layer is comprised between 20 and 500 μm, preferentially between 20 and 300 μm;the part is a turbine moving blade, or a high-pressure turbine nozzle, or a high-pressure turbine ring, or a combustion chamber wall.

According to a second aspect, the invention relates to a process for treating a turbomachine part comprising steps of depositing by thermal spraying a plurality of elementary layers on the surface of a substrate of the part, the substrate being formed of a metallic material, or of a composite material, to produce a protective coating layer against the infiltration of compounds of the CMAS type,the process comprising steps for depositing on the surface of the substrate elementary layers belonging to a first set, said steps being interposed between steps for depositing elementary layers belonging to a second set, the elementary layers of the first set having toughnesses which differ by at least 0.7 Mpa·m1/2from the toughnesses of the elementary layers of the second set,or the elementary layers of the first set having coefficients of thermal expansion which differ by at least 3.5 10−6K−1from the coefficients of thermal expansion of the elementary layers of the second set.

The process may have the following additional and non-limiting features:the steps for depositing elementary layers being carried out according to the suspension plasma spraying (SPS) technique, or according to one of the following other techniques: atmospheric plasma spraying (APS), solution precursor spraying plasma (SPPS), inert atmosphere or low pressure plasma spraying (IPS, VPS, VLPPS), PVD and EB-PVD, HVOF and Suspension HVOF (HVSFS), or according to a combination of several of these techniques;The process further comprises a step, preliminary to the deposition of elementary layers, of depositing on the surface of the substrate a coating layer forming a thermal barrier, and/or of depositing a coating layer forming an environmental barrier, and/or of depositing a bond coat promoting the adhesion of a coating layer;an elemental layer deposition step is carried out by a torch passage without cooling, and the directly subsequent elemental layer deposition step, or the directly preceding elemental layer deposition step, is carried out by a torch passage with cooling, the cooling being carried out by means of compressed air nozzles or by means of liquid carbon dioxide cryogenic nozzles,the coating layer can then be produced with inter-passes between torch passages without cooling and torch passages with cooling immediately following or preceding.

According to another aspect, the invention relates to a process for manufacturing a turbomachine part in which a thermal shock at the surface of the turbomachine part is caused between the deposition of a first elementary layer and the deposition of a second successive elementary layer, said thermal shock preferably being obtained by a torch passage without cooling after deposition of the first elementary layer, and a torch passage with cooling for the second elementary layer.

This last process allows the interface between the first elementary layer and the second elementary layer to be weakened in such a way as to promote the propagation of cracks within the plane of the interface.

DETAILED DESCRIPTION OF AN EMBODIMENT

A turbomachine part10has been shown inFIG.2ain a possible embodiment of the invention. The part10may comprise a substrate1of metallic material, for example a nickel-based or cobalt-based superalloy such as the known superalloys AM1, CM-NG, CMSX4 and its derivatives or the Rene superalloy and its derivatives. The part10may still include a ceramic matrix composite (also referred to as CMC) substrate1. The part can be any turbomachine part exposed to thermal cycling and exposed to CMAS compounds at high temperature. The part10may in particular be a turbine moving blade, or a high-pressure turbine nozzle, or a high-pressure turbine ring, or a combustor wall.

In addition, the substrate1can be covered (as well as the possible alumino-bonding layer) with a coating layer forming a thermal barrier, or forming an environmental barrier, or forming a thermal and environmental barrier. Such a coating layer is not shown inFIG.2a.

A thermal barrier may include yttriated zirconia, for example with a Y2O3 content of 7 to 8% by mass. Shaping of such a thermal barrier can be achieved by for example APS (atmospheric plasma spraying), SPS (suspension plasma spraying), SPPS (solution precursor plasma spraying), HVOF (high-velocity oxi-fuel), sol-gel process, HVSFS (high-velocity suspension flame spraying), EB-PVD (electron beam-physical vapor deposition), or any other known process for shaping thermal barriers.

An environmental barrier is advantageously used to protect a CMC substrate. A thermal and environmental barrier system may include one or more of the following group of materials: MoSi2, BSAS (BaO1-x—SrOx—Al2O3-2SiO2), Mullite (3Al2O3-2SiO2), rare earth mono- and di-silicates (rare earth=Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu), fully or partially stabilized or even doped zirconia, or any other composition known for an environmental thermal barrier.

According to the invention, the substrate1is partially or completely covered (together with the possible alumino-forming bonding layer, and/or the possible thermal and/or environmental barrier layer) with a layer2thickness of a protective coating against the infiltration of CMAS-type compounds. The protective layer2comprises a plurality of elementary layers. The term “elementary layer” is used hereinbelow to refer to a layer thickness having a substantially homogeneous chemical composition and substantially homogeneous physico-chemical characteristics (for example homogeneous toughness and homogeneous coefficient of thermal expansion). The layer2advantageously comprises a number of elementary layers between 3 and 50, and preferentially between 3 and 35. A total thickness of the layer2is advantageously between 20 and 500 micrometers, preferably between 20 and 300 micrometers.

If a thermal or environmental barrier coating layer is present on the substrate, the functionalization layer can be referred to as the CMAS2protective layer.

Alternatively, the layer2can be applied directly to the substrate1in the absence of any other thermal or environmental barrier coating.

Among the elementary layers within the layer2and according to the embodiment illustrated inFIG.2a, elementary layers20of a first set of elementary layers are distinguished from elementary layers21of a second set of elementary layers. The elementary layers20are inserted between the elementary layers21. In the example shown, the layer2has only alternating elementary layers20and elementary layers21. However, in an alternative not shown, elements belonging to a third type of layers, or more, could also be present within the layer2, either interspersed with elements20and21, or above or below a series of elements20and21. The thickness of an elementary layer20or21is preferably comprised between 0.1 micrometers and 50 micrometers. The three elementary layers20and the first three elementary layers21closest to the surface have been represented in enlarged size, and the remaining consecutive elementary layers have been represented with a lesser thickness; however, a part according to the invention does not necessarily have this difference in thickness between the elementary layers, this mode of representation being chosen here to illustrate cracks.

According to the invention, the contact interfaces between an elementary layer20and an elementary layer21are adapted to promote the propagation of cracks along said interface. With the orientation ofFIG.2, the cracks thus intended to form, along the wear of the part10or during cooling of the part10after manufacture, will present a substantially horizontal orientation. Each contact zone between an elementary layer20and an elementary layer21thus forms a mechanically weakened interface which promotes crack propagation. A detailed description of the elemental layers20and21is given below in relation to Example 1.

Due to the presence of the mechanically weakened interfaces between the layers20and21, as the part wears out, a cracking network is likely to develop with greater tortuosity than for a layer2, which would be made up of a uniform thickness of composition. Such a cracking network, comprising cracks42oriented in the plane of the interface between two successive layers, and cracks41oriented transversely in the direction of the thickness of the layer2, is shown inFIG.2a. Hereinbelow, the cracks42will be referred to as “horizontal” cracks and the cracks41as “transverse” cracks. The layer2thus forms a controlled-cracking CMAS protective layer. It is easy to understand that the part could also include cracks with other orientations.

The same system is shown schematically inFIG.2b, in an environment where CMAS-type liquid contaminant compounds are present at high temperatures. Due to the high surface temperature at the layer2during blade operation, form a liquid phase3at the surface of the layer2. This liquid phase3gradually seeps through the thickness of the layer2over time via the cracks42and41. The presence of horizontal cracks42, in addition to transverse cracks41, causes a lengthening of the infiltration path of the liquid phase3. During exposure of the part1to molten CMAS compounds, it takes longer for the liquid phase3to reach the substrate1.

FIG.2cis a close-up schematic view of the interface between the liquid phase3and cracks42and41close to the surface of the part inFIG.2b. During the infiltration of the liquid phase3, there is competition between the kinetics of progression of said phase3within the cracks, and the reaction kinetics of the molten CMAS infiltrated with the anti-CMAS compounds within the elementary layers20and21—examples of anti-CMAS chemical compounds are given below. Said reaction between molten CMAS and anti-CMAS compounds, which may be, for example, a crystallization reaction, forms a “blocking” phase5on the periphery of the infiltration path of the molten CMAS. The blocking phase5blocks the progression of the molten CMAS compounds. This can still be referred to as a “tight barrier layer”. A secondary phase6can also be formed on the periphery of the cracks.

Compared with a part obtained by a crack-filling treatment, for example with a highly reactive ceramic, the part inFIGS.2ato2cis advantageous because the anti-CMAS deposition layer is not made mechanically rigid. In addition, the presence of cracks in the anti-CMAS coating makes it possible to accommodate thermomechanical deformations experienced by the part during operation, particularly those caused by thermal cycling. This constitutes an additional advantage of a part of the invention, compared with a part which would have undergone a treatment aimed at filling the cracks.

FIG.3shows a microscopic view of a cracked interface between an elemental layer20and an elemental layer21. It can be seen that the crack network formed during thermal cycling of the part may be more complex than the simplified shape shown inFIGS.2ato2c. In particular, horizontal cracks42can be formed at the interface, shown here as dotted lines around the perimeter of the microscope view, but can also be formed at positions offset from the interface.

Process for Manufacturing a Controlled-Cracking Part—Example 1

A treatment process40for obtaining a part with controlled cracking, i.e. promoting the formation of cracks at the interfaces between elementary layers of coating, according to a first example of implementation, is illustrated inFIG.4. It is considered that a substrate of the part to be treated is already formed upstream of said process, for example formed of metallic material or ceramic matrix composite (CMC).

In an optional step100, an alumino-forming bonding layer7is deposited on the surface of the substrate, to promote the adhesion of the next layer, as described above in relation toFIG.2a.

In an optional step200, a thermal barrier layer8, or environmental barrier (EBC), or thermal environmental barrier (TEBC) layer8is formed on the surface of the substrate, or on the surface of the bonding layer7. This layer8can be obtained in particular by any thermal spray deposition technique, as described above in relation toFIG.2a. In particular, step200is not essential if the subsequently deposited elemental layers act as a thermal barrier and/or environmental barrier.

A step300is then implemented to form a layer2of protective coating against the infiltration of CMAS-type compounds. Step300comprises a succession of sub-steps300(1),300(2) . . .300(N), each of these sub-steps comprising a deposition301of an elemental layer20, followed by a deposition302of an elemental layer21. The depositions301and302are preferably achieved by thermal spraying techniques, for example, APS, SPS, SPPS, HVOF, sol-gel process, HVSFS, EB-PVD, inert plasma spraying or reduced pressure plasma spraying (inert plasma spraying, or IPS; vacuum plasma spraying, or VPS; very low pressure plasma spraying, or VLPPS).

Here, the elementary layers20have different toughnesses from the elementary layers21, which creates mechanically weakened interfaces between said layers. Advantageously, the toughnesses of the elementary layers20differ by at least 0.7 MPa·m1/2from the toughnesses of the elementary layers21. By way of example, the elementary layers20have a tenacity of between 0.5 and 1.5 MPa·m1/2and the elementary layers21have a tenacity of between 1.5 and 2.2 MPa·m1/2. Not all the elementary layers20necessarily have the same toughness, as do the elementary layers21.

In the example of the process40, the layers20are formed of Gd2Zr2O7, with a toughness of 1.02 MPa·m1/2, and the layers21are formed of yttriated zirconia ZrO2—7-8% mass Y2O3(YSZ), with a toughness of 2.0 MPa·m1/2.

The layers20are formed by suspension plasma spraying (hereinafter SPS). A “Sinplex Pro” torch with a volume flow rate of 80/20/5 standard liters per minute (slpm) is used for the steps301. A YSZ/ethanol suspension with an injection rate of 40 to 50 grams per minute is used. The deposition rate of the YSZ is 2 micrometers of layer thickness20per deposition cycle, a cycle being defined as a round trip of the plasma torch in front of the surface to be treated of the part. Three deposition cycles are carried out for the deposition of an elemental layer20, which thus has a thickness of 6 micrometers.

The layer21is formed by SPS using a “Sinplex” torch with an argon/helium/dihydrogen volume flow rate of 80/20/5 slpm. A Gd2Zr2O7/ethanol suspension is used, with an injection rate of 40 to 50 grams per minute. The deposition rate of Gd2Zr2O7is 2 micrometers of layer thickness21per deposition cycle. Three deposition cycles are carried out for the deposition of an elemental layer21, which thus has a thickness of 6 micrometers.

The same suspension injector is used to perform steps301and302, with two separate suspension tanks open alternately for fluid communication with the suspension injector: a first tank is open for steps301and a second tank is open for steps302.

The layer2of anti-CMAS coating is produced by a sequence of 25 steps300(N=25), for a total thickness of 300 micrometers.

Alternatively, a thickness of the layer2can be between 20 and 500 micrometers, preferentially between 20 and 300 micrometers.

Alternatively, steps301and302can be implemented:Using a “Triplex Pro” torch with an argon/helium/dihydrogen volumetric flow rate with a slpm value selected from the following values: 80/20/0, 80/20/5, 80/0/5;Using a “Sinplex Pro” torch with an argon/helium/dihydrogen volumetric flow rate in slpm of one of the following values: 50/0/5, 40/0/5, 80/20/0, 80/20/5, 80/0/5;Using an “F4” torch with an argon/helium/dihydrogen volume flow rate in slpm of one of the following values: 45/45/3, 44/10/3, 45/30/5, 40/20/0, 30/50/5.

These values can also be used for processes50and60described below. Alternatively, the layers20can be formed from one of: RE2Zr2O7 with RE a rare earth material, Ba(Mg1/3Ta2/3)O3, La(Al1/4Mg1/2Ta1/4)O3, or a mixture of several of these materials.

Alternatively, the layers21can be formed from a material selected from: Y2O3-ZrO2-Ta2O5, BaZrO3, CaZrO3, SrZrO3, or a mixture of several of these materials.

According to an alternative, step300could include not only layer20deposition steps and layer21deposition steps, but could also include steps for the deposition of additional varieties of elementary layers.

In addition, a thermal shock can optionally be caused at the surface of the part between the deposition of an elementary layer20and the deposition of a successive elementary layer21, or vice versa, said thermal shock being obtainable by a torch passage without cooling after deposition of the first elementary layer, and a torch passage with cooling for the second elementary layer. This has the effect of further weakening the interface between the elementary layers20and21to promote horizontal cracking.

Process for Manufacturing a Controlled Cracking Part—Example 2

A treatment process50to obtain a controlled cracking part according to a second example is given inFIG.5.

Optional steps100and200are similar to the process steps40.

A step400is then carried out to form a layer2of protective coating against the infiltration of CMAS-type compounds. Step400comprises a succession of sub-steps400(1),400(2) . . .400(N), each of these sub-steps comprising a deposition501of an elemental layer22, followed by a deposition402of an elemental layer23.

In the example of the process50, the layers22are formed from Y2Si2O7, with a coefficient of thermal expansion of 3.9 10−6K−1, and the layers23are formed from yttriated zirconia ZrO2—7-8% mass Y2O3(YSZ), with a coefficient of thermal expansion of 11.5 10−6K−1. The layers22and23are formed by SPS using a “Sinplex Pro” torch with an argon/helium/dihydrogen volume flow rate of 40/0/5 slpm. A Y2Si2O7/ethanol suspension is used for the layer22and YSZ/ethanol for the layer23, with an injection rate of 40 to 50 grams per minute. The deposition rate of YSZ is 2 micrometers of the layer23thickness per injection cycle. Three injection cycles are carried out for the deposition of an elemental layer23, which thus has a thickness of 6 micrometers. The deposition rate of Y2Si2O7is 1 micrometer layer22thickness per injection cycle. Three injection cycles are carried out for the deposition of an elementary layer22, which thus has a thickness of 3 micrometers. The same suspension injector is used to carry out steps401and402, with two separate suspension tanks open alternately for fluid communication with the suspension injector.

The layer2of anti-CMAS coating is produced by a sequence of 34 iterations of 400 steps (N=34), for a total thickness of about 300 micrometers. As for the process40, thermal shocks can be induced to further weaken the interfaces between elementary layers.

Alternatively, the elemental layers22comprise RE2Si2O7or RE2SiO5with RE a material of the rare earth family, or comprises a mixture of these materials.

Alternatively, the elementary layers23include a material from the following list: YSZ, Y2O3-ZrO2-Ta2O5, BaZrO3, CaZrO3, SrZrO3, RE2Zr2O7 with RE a material of the rare earth family, Ba(Mg1/3Ta2/3)O3, La(Al1/4Mg1/2Ta1/4)O3, YAG, or comprise a mixture of these materials.

Process for Manufacturing a Controlled Cracking Part—Example 3

A treatment process60to obtain a controlled cracking part according to a third example is given inFIG.6.

Optional steps100and200are similar to the steps of the process40.

A step500is then carried out to form a layer2of protective coating against CMAS. Step600comprises a succession of sub-steps500(1) . . .500(N) depending on the desired layer2thickness in particular. Each of said sub-steps comprises a first deposition501of elementary layer24, and a second deposition502of elementary layer24according to a different protocol from the deposition501.

Between a step501and a successive step502, or vice versa, a thermal shock is caused by a torch passage without cooling at the end of step501, and a torch passage with cooling at the end of step502.

Cooling is achieved by means of compressed air nozzles, for example 6 nozzles at 6 bar of the carp tail type, or by means of liquid carbon dioxide cryogenic nozzles, for example two nozzles at 25 bar.

A deposition500is carried out here with inter-passes, with slow deposition kinematics (illumination speed less than 300 millimeters per second) and with a high mass loading rate (more than 20% by mass of solid particles in suspension).

In the particular example of the process60, the layers24are formed from YSZ. Steps501and502are carried out with an “F4—MB” torch with an argon/helium/dihydrogen volume flow rate of 45/45/6 slpm, with a YSZ/ethanol suspension.

The depositions501are made with a mass loading rate of 12% and an injection rate of 25 to 30 grams per minute, for a thickness of 10 micrometers (2 micrometers per cycle). The depositions502are made with a mass loading rate of 20% and an injection rate of 45 to 50 grams per minute, for a thickness of 9 micrometers (3 micrometers per cycle). Preferentially, two separate suspension injectors are used to perform steps501and502, with two separate, alternatively open suspension tanks.

In the example of process60, N=16 iterations of steps500are carried out, for a total thickness of about 300 micrometers for the layer2.

Examples of Controlled Cracking Turbomachine Parts

FIGS.7ato7dschematically represent several examples of layer stacks implemented for turbomachine parts according to the invention.

The anti-CMAS deposition layers2shown inFIGS.7ato7dare obtained for example by any of the processes described above.

FIG.7arepresents a part comprising a metal alloy substrate1coated with a layer2of anti-CMAS coating. In this example, the layer2can act as both a thermal barrier and an anti-CMAS coating.

InFIG.7c, a thermal barrier layer8is interposed between the bonding layer7and the anti-CMAS2layer. The anti-CMAS2deposition can be a functionalization layer that does not act as a thermal barrier.

InFIG.7d, the substrate1is formed as a ceramic matrix composite (CMC). The substrate is coated with a bonding layer7, a thermal and environmental barrier (TEBC) layer9and an anti-CMAS deposition layer2.

The parts shown inFIGS.7ato7dhave, as described above, mechanically weakened interfaces which promote cracking in planes substantially parallel to the surface of the part.