WO2024023428A1

WO2024023428A1 - Coating application method and turbine blade with coating applied according to this method

Info

Publication number: WO2024023428A1
Application number: PCT/FR2023/051143
Authority: WO
Inventors: Amar Saboundji; Virginie JAQUET
Original assignee: Safran
Priority date: 2022-07-28
Filing date: 2023-07-21
Publication date: 2024-02-01
Also published as: FR3138451A1

Abstract

The present invention relates to a method for applying a coating to a substrate (100) made of a nickel-based superalloy and to a turbine blade made of a nickel-based superalloy with a coating applied according to this method. The coating application method comprises at least a first chemical vapour deposition step for depositing chromium and/or cobalt on a surface of the substrate (100) and a second chemical vapour deposition step, after at least partially diffusing, in an underlying layer (102) of the substrate (100), the chromium and/or the cobalt deposited in the first chemical vapour deposition step, for depositing aluminium on the underlying layer (102) of the substrate (100).

Description

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Description

Title of the invention: Process for applying coating and turbine blade with coating applied according to this process

Technical area

The present presentation concerns a process for applying a coating to a nickel-based superalloy substrate, as well as a nickel-based superalloy turbine blade with a coating applied according to this process. By nickel-based superalloy we mean a superalloy whose mass percentage of nickel is the majority. We understand that nickel is therefore the element with the highest mass percentage.

Prior art

[0002] It is known to use nickel-based superalloys for the hot parts of gas turbines for airplane or helicopter engines and in particular for the manufacture of fixed or mobile monocrystalline blades.

[0003] These materials have the main advantages of combining both high creep resistance at high temperatures as well as resistance to oxidation and corrosion.

[0004] Over time, nickel-based superalloys for single-crystal blades have undergone significant changes in chemical composition, with the aim in particular of improving their creep properties at high temperatures while maintaining environmental resistance. very aggressive in which these superalloys are used. These superalloys include an austenitic matrix of face-centered cubic structure, solid solution based on nickel, called gamma phase ("y"), with precipitates of gamma prime ("y'") hardening phase of ordered cubic structure L1 ₂ of type Ni ₃ Al The whole (matrix and precipitates) is therefore described as a y/y' superalloy. In general, at room temperature, these superalloys contain a high proportion of y' phase precipitates, approximately 60 to 70% by weight.

[0005] Furthermore, metallic coatings adapted to these superalloys have been developed in order to increase their resistance to the aggressive environment in which they are used, including resistance to oxidation and resistance to corrosion. Additionally, a ceramic coating of low thermal conductivity, performing a thermal barrier function, can be added to reduce the temperature on the metal surface.

[0006] Typically, a complete protection system comprises at least two layers. The first layer, also called sub-layer or bonding layer, is directly deposited on the nickel-based superalloy part to be protected, also called substrate, for example a blade. The deposition step is followed by a diffusion step of the sublayer in the superalloy. Deposit and distribution can also be carried out in a single step. The materials generally used to make this underlayer include aluminoforming metal alloys of the MCrAlY type (M = Ni (nickel) or Co (cobalt)) or a mixture of Ni and Co, Cr = chromium, Al = aluminum and Y = yttrium, or nickel aluminide type alloys (NixAly), some also containing platinum (NixAlyPtz). The second layer, generally called thermal barrier or "TBC" in accordance with the English acronym for "Thermal Barrier Coating", is a ceramic coating comprising for example yttriated zirconia, also called "YSZ" in accordance with the English acronym for " Yttria Stabilized Zirconia” or “YPSZ” in accordance with the English acronym for “Yttria Partially Stabilized Zirconia” and having a porous structure. This layer can be deposited by different processes, such as electron beam evaporation (“EB-PVD” in accordance with the English acronym for “Electron Beam Physical Vapor Deposition”), thermal spraying (“APS” in accordance with the English acronym for “Atmospheric Plasma Spraying” or “SPS” in accordance with the English acronym for “Suspension Plasma Spraying”), or any other process making it possible to obtain a porous ceramic coating with low thermal conductivity.

[0007] Due to the use of these materials at high temperature, for example from 650°C to 1250°C, inter-diffusion phenomena occur on the microscopic scale between the nickel-based superalloy of the substrate and the metal alloy of the underlayer. These inter-diffusion phenomena, associated with the oxidation of the sub-layer, modify in particular the chemical composition, the microstructure and therefore the mechanical properties of the sub-layer. from the manufacturing of the coating, then during the use of the blade in the turbine. These inter-diffusion phenomena also modify the chemical composition, the microstructure and consequently the mechanical properties of the superalloy of the substrate under the coating. In superalloys heavily loaded with refractory elements, particularly rhenium, a secondary reaction zone (ZRS) can thus form in the superalloy under the sub-layer to a depth of several tens, or even hundreds, of micrometers. The mechanical characteristics of this ZRS are significantly lower than those of the substrate superalloy. The formation of ZRS is undesirable because it leads to a significant reduction in the mechanical strength of the superalloy by facilitating the initiation of cracks at grain boundaries and interfaces, which is all the more critical at the level of the thin walls of the turbine blades. .

[0008] In order to avoid this problem, methods have been proposed, in particular in French patent application specifications FR 3201 643 A1 and FR 3 113260 A1, for applying by physical vapor deposition to nickel-based superalloys. , protective coatings more compatible with high rhenium contents. However, it may be difficult to use these methods for the application of such a protective coating in small internal cavities, such as for example the cooling channels of turbine blades, which may however also be exposed to the corrosion and oxidation.

Presentation of the invention

[0009] A first aspect of the present presentation concerns a process for applying a coating, which can be used even inside small cavities, and which makes it possible to protect a nickel-based superalloy substrate from oxidation and corrosion. even in aggressive environments, and in particular at very high temperatures, without mechanically weakening this substrate.

[0010] For this, the method according to this first aspect comprises at least a first chemical vapor deposition step, for depositing chromium and/or cobalt on a surface of the substrate, and a second chemical vapor deposition step. , after at least partial diffusion, in an underlying layer of the substrate, chromium and/or cobalt deposited during the first chemical vapor deposition step, to introduce aluminum into said underlying layer of the substrate.

[0011] The diffusion of chromium and/or cobalt in the underlying layer of the substrate after its chemical vapor deposition makes it possible to modify the microstructure of the superalloy in this underlying layer, and in particular to displace the rhenium capable of form a secondary reaction zone. The subsequent deposition of aluminum makes it possible to increase the concentration of aluminum in this underlying layer, possibly reaching between 5 and 12% by mass during the second chemical vapor deposition step, and thus form an aluminum coating. -former of phase 0 structures or combining phases 0, y and y'. This coating makes it possible to offer good environmental protection to the superalloy substrate, even in passages of restricted dimensions, such as for example cooling channels with a width of around a hundred micrometers. Chemical vapor deposition also makes it possible to reach difficult-to-access gaps with this treatment.

[0012] The nickel-based superalloy subject to this coating application process may comprise at least 3% by weight of rhenium. Rhenium makes it possible to slow down the diffusion of chemical species within the superalloy and to limit the coalescence of the y' phase precipitates during service at high temperatures, to thus improve the resistance of the superalloy to creep at high temperatures, but presents the disadvantage of facilitating, with conventional coatings, the formation of secondary reaction zones with the coating, in an underlying layer. With the coating deposition process according to the first aspect, it is possible to avoid this disadvantage of rhenium in the nickel-based superalloy.

The first chemical vapor deposition step can form a surface layer with a thickness of between 5 and 20 μm. This thickness makes it possible to obtain satisfactory protection against corrosion and oxidation without unduly encumbering narrow cooling channels. [0014] During the second chemical deposition phase, the aluminum can be doped with silicon and/or at least one rare earth, such as for example hafnium, yttrium or zirconium, in order to further increase the resistance. to oxidation.

[0015] For the first and/or second chemical vapor deposition step, it is in particular possible to use any one of the plasma-enhanced chemical vapor deposition processes (in English: “Plasma-Enhanced Chemical Vapor Deposition”). " or PECVD), low pressure chemical vapor deposition (in English: "Low Pressure Chemical Vapor Deposition" or LPCVD), chemical vapor deposition under ultra-high vacuum (in English: "Ultra-High Vacuum Chemical Vapor Deposition » or UHVCVD) and atomic layer chemical vapor deposition (in English: “Atomic Layer Chemical Vapor Deposition” or ALCVD). In particular, the first and/or the second chemical vapor deposition step may be low pressure chemical vapor deposition, thus taking place at a temperature of between 900 and 1150° C., for example between 1000 and 1100°C, and at a pressure of between 2 and 50 kPa. More particularly, the first chemical vapor deposition step can be carried out at a temperature of between 1040 and 1060° C. and at a pressure of between 5 and 20 kPa or at a pressure of between 15 and 25 kPa, preferably between 18 and 22 kPa, while the second chemical vapor deposition step is carried out at a temperature of between 1050 and 1070°C and at a pressure of approximately 20 kPa.

[0016] A second aspect of the present presentation concerns a turbine blade made of nickel-based superalloy with a coating applied according to the process of the first aspect. In particular, this blade may comprise one or more cooling channels, and the coating be applied inside the cooling channels, which is facilitated by the use of chemical vapor deposition steps.

[0017] A third aspect of the present presentation concerns a turbomachine comprising the turbine blade according to the second aspect. The turbomachine may in particular be a fan turbojet (in English: “turbofan”). Other types of turbomachine, such as for example a turboprop, a turboshaft engine, or a single-flow turbojet (in English: “turbojet”). Brief description of the drawings

The aforementioned characteristics and advantages, as well as others, will appear on reading the following description of embodiments, given by way of non-limiting examples, with reference to the appended figures.

[0019] [Fig. 1] Figure 1 is a schematic view in longitudinal section of a turbomachine.

[0020] [Fig. 2] Figure 2 schematically illustrates a turbine blade of the turbomachine of Figure 1, with cooling channels.

[0021] [Fig. 3] Figure 3 schematically illustrates a nickel-based superalloy substrate with a layer of metal deposited on the surface of the substrate during a first chemical vapor deposition step.

[0022] [Fig. 4] Figure 4 schematically illustrates the nickel-based superalloy substrate after diffusion, in an underlying layer of the substrate, of the metal deposited during the first chemical vapor deposition step.

[0023] [Fig. 5] Figure 5 schematically illustrates the nickel-based superalloy substrate with a layer of aluminum deposited on the surface of the substrate during a second chemical vapor deposition step.

detailed description

[0024] Single-crystal nickel-based superalloys consist of precipitates y' Ni ₃ (AI, Ti, Ta) dispersed in a matrix y of cubic structure with centered feces, solid solution based on nickel, and have mechanical properties, particularly at high temperatures, which make them interesting candidates for the manufacture of monocrystalline parts intended for the hot parts of turbojet engines. These superalloys may in particular have rhenium concentrations equal to or greater than 3% by weight in order to slow down the diffusion of chemical species within the superalloy and to limit the coalescence of phase y' precipitates during service at high temperatures, a phenomenon which causes a reduction in mechanical resistance. Rhenium thus makes it possible to improve the creep resistance at high temperatures of the nickel-based superalloy. Among the nickel-based superalloys also rich in rhenium, we include CMSX-4 Plus Mod C ®, CMSX-10 ®, and MC-NG. These alloys have the following compositions, where the 100% complement consists of nickel and unavoidable impurities:

[0025] [Table 1]

[0026] In particular, these nickel-based superalloys can be intended for the manufacture of single-crystal blades by a directed solidification process in a thermal gradient. The use of a monocrystalline seed or a grain selector at the start of solidification makes it possible to obtain this monocrystalline structure, oriented for example in a crystallographic direction <001> which is the orientation which confers, in general, the properties optimal mechanics of superalloys.

[0027] Figure 1 represents, in section along a vertical plane passing through its main axis A, a fan turbojet 10. Such a fan turbojet 10 can comprise, from upstream to downstream depending on the circulation of the air flow, a blower 12, a low pressure compressor 14, a high pressure compressor 16, a combustion chamber 18, a high pressure turbine 20, and a low pressure turbine 22.

The high pressure turbine 20 may comprise a plurality of blades 20A rotating with the rotor and fixed blades 20B, also called rectifiers, mounted on the stator. The stator of the turbine 20 may comprise a plurality of stator rings 24 arranged opposite the rotating blades 20A of the turbine 20.

It is therefore possible to manufacture a blade 20A, 20B for a turbomachine comprising a nickel-based superalloy. However, despite the good resistance of these superalloys to high temperatures, those prevailing within the hot parts of turbomachines may require cooling of the 20A blades, 20B. To ensure this cooling, such a blade 20A, 20B may include internal cavities, in particular in the form of cooling channels 21, to allow the circulation of a cooling fluid such as, for example, air taken from the compressors 14, 16. The width of the cooling channels 21 is however restricted by the shape and dimensions of these blades 20A, 20B, and can be of the order of a tenth of a millimeter, that is to say a hundred of micrometers.

[0030] In order to protect the surface of the superalloy around these cavities from oxidation and corrosion, a coating can be applied to this surface following a process comprising two consecutive stages of chemical vapor deposition. These two consecutive steps can be carried out in the same chemical vapor deposition device. In a first chemical vapor deposition step, chromium can be deposited, for example at a temperature of between 1040 and 1060°C and at a pressure of between 15 and 25 kPa, preferably between 18 and 22 kPa, on the surface of this nickel-based superalloy substrate 100, as illustrated in Figure 3, to form a surface layer 101, superimposed on the substrate 100, with a thickness ei of, for example, between 5 and 20 pm. Cobalt can, however, be deposited alternatively or in addition to chromium during this first chemical vapor deposition step.

The chromium and/or cobalt deposited during the first chemical vapor deposition step can then diffuse into the substrate 100, to form an underlying layer 102, rich in chromium and/or cobalt and poor in rhenium. . Thus, after a first step of chemical deposition of chromium in the vapor phase on a substrate 100 in CMSX-4 Plus Mod C ® superalloy and the subsequent diffusion of this chromium in the underlying layer 102, this underlying layer 102, being able to have a thickness 62 normally less than the initial thickness ei of the surface layer 101 before diffusion, as illustrated in Figure 4, can have a composition, in mass percentages, of 40 to 55% of nickel, 10 to 30% of chromium, 7 to 8% cobalt, 1 to 2% aluminum, and practically no rhenium, this having been displaced from this underlying layer 102 by the chromium. This diffusion can in particular be facilitated by a heat treatment, for example at a temperature greater than 1000°C and a pressure of between 10 ^-3 and 10 ^-4 Pa for up to 4 hours or under a partial pressure of a neutral gas such as Argon of between 0.1 to 1 Pa for 2 at 4 a.m. During this heat treatment, although elements of the underlying layer 102 of the substrate 100 can also rise towards the surface layer 101 during this heat treatment to replace the copper and/or cobalt diffused towards the surface layer, the thickness of the surface layer 101 can decrease significantly.

The diffusion of chromium and/or cobalt in the underlying layer 102 can be followed by the second chemical vapor deposition step. In this second chemical vapor deposition step, which can take the form of a “flash” type aluminization, and which can for example be carried out at a temperature of between 900 and 1150° C, in particular between 1050 and 1070 °C, at a pressure of between 2 and 50 kPa, for example at approximately 20 kPa, and/or for a period of between 30 minutes and 8 hours, in particular between 30 and 60 minutes, aluminum can be introduced up into the underlying layer 102, as illustrated in Figure 5, where it can reach a concentration of 5 to 12% by weight. In the surface layer 101, the concentration of aluminum could even reach up to 20%. This aluminum in the surface 101 and underlying 102 layers can then, in service, form alumina, thus helping to protect the other alloy elements. In the second physical vapor deposition step, the aluminum can be deposited pure or doped with silicon and/or one or more rare earths, such as for example hafnium, yttrium or zirconium, which can thus reach each mass concentrations of, for example 0.5 to 2% in the surface layers 101 and underlying layers 102.

[0033] It is conceivable that the part forming the substrate 100 is extracted, before the second chemical vapor deposition step, from an enclosure in which the first chemical deposition step has been carried out, in particular if said first and second steps chemical vapor deposition must be carried out in two different enclosures to meet industrial constraints. In this case, the heat treatment for the diffusion, towards the underlying layer 102, of the chromium and/or cobalt deposited during the first chemical vapor deposition step could be carried out in an enclosure used for the second stage of chemical vapor deposition, during its rise in temperature prior to the implementation of the second stage of chemical vapor deposition.

Alternatively, however, the first and second chemical vapor deposition steps could be carried out in the same enclosure, maintained at the required temperature and pressure for the appropriate time for the heat treatment used for diffusion, in the interval between the first and second chemical vapor deposition steps.

[0035] Although the present presentation has been described with reference to specific examples of 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. Furthermore, individual features of the different embodiments discussed may be combined in additional embodiments. Therefore, the description and drawings should be considered in an illustrative rather than a restrictive sense.

Claims

[Claim 1] Method for applying a coating to a nickel-based superalloy substrate (100), the method comprising at least: a first chemical vapor deposition step, for depositing chromium and/or cobalt on a surface of the substrate (100), and a second step of chemical vapor deposition, after at least partial diffusion, in an underlying layer (102) of the substrate (100), of the chromium and/or cobalt deposited during the first step of chemical vapor deposition, to introduce aluminum into said underlying layer (102) of the substrate (100).

[Claim 2] A method according to claim 1, wherein the nickel-based superalloy comprises at least 3% by weight of rhenium.

[Claim 3] A method according to any one of claims 1 or 2, wherein the first chemical vapor deposition step forms a surface layer (101) with a thickness (e ₁ ) of between 5 and 20 pm.

[Claim 4] Method according to any one of claims 1 to 3, in which the aluminum reaches a concentration of between 5 and 12% by weight in said underlying layer (102) during the second chemical deposition step in vapor phase.

[Claim 5] Method according to any one of claims 1 to 4, in which, during the second chemical deposition phase, the aluminum is doped with silicon and/or at least one rare earth.

[Claim 6] Method according to any one of claims 1 to 5, in which the first and/or second chemical vapor deposition step is carried out at a temperature of between 900 and 1150°C and at a pressure between 2 and 50 kPa.

[Claim 7] Method according to any one of claims 1 to 6, wherein the first chemical vapor deposition step is carried out at a temperature of between 1040 and 1060°C and at a pressure of between 15 and 1060°C. 25 kPa, preferably between 18 and 22 kPa.

[Claim 8] A method according to any one of claims 1 to 7, wherein the second chemical vapor deposition step is carried out at a temperature of between 1050 and 1070°C and at a pressure of approximately 20 kPa .

[Claim 9] Turbine blade (20A, 20B) made of nickel-based superalloy with a coating applied according to the method of any one of claims 1 to 8.

[Claim 10] A turbine blade (20A, 20B) according to claim 9, comprising one or more cooling channels (21), and wherein the coating is applied inside the cooling channels (21).

[Claim 11] Turbomachine comprising the turbine blade (20A, 20B) of any one of claims 9 or 10.