EP4004250A1

EP4004250A1 - Abradable coating

Info

Publication number: EP4004250A1
Application number: EP20757631.5A
Authority: EP
Inventors: Guillaume FRADET; Laurent Paul Dudon; Serge Georges Vladimir SELEZNEFF
Original assignee: Safran Aircraft Engines SAS
Current assignee: Safran Aircraft Engines SAS
Priority date: 2019-07-26
Filing date: 2020-07-22
Publication date: 2022-06-01
Also published as: FR3099187B1; FR3099187A1; WO2021019154A1; US20220282633A1; CN114174548A

Abstract

Disclosed is an abradable coating for a turbomachine as well as a turbomachine module and a turbomachine comprising such an abradable coating, the abradable coating comprising, at a content of more than 50% by volume, a mineral compound having a Mohs' hardness of less than 6 and a melting point above 900°C.

Description

Title of the invention: Abradable coating

Technical area

This presentation relates to an abradable coating for a turbomachine as well as a turbomachine module and a turbomachine comprising such an abradable coating.

[0002] Such an abradable coating can be used in any type of turbomachine, and in particular civil or military turbojets. In particular, it is particularly useful in environments subject to very high temperatures.

Prior art

[0003] In many rotating machines, it is now known practice to provide the stator ring with abradable tracks facing the top of the rotor blades. Such tracks are made using so-called "abradable" materials which, when they come into contact with the rotating vanes, wear out more easily than the latter. This ensures a minimum clearance between the rotor and the stator, limiting air leaks and therefore improving the performance of the rotating machine, without risking damage to the blades in the event of friction of the latter on the stator. On the contrary, such friction abrades the abradable track, which automatically adjusts the diameter of the stator ring closest to the rotor.

[0004] Such abradable tracks can also be provided at the interface between the rotor and the stator fixed vanes in order to reduce air leakage also at this level.

[0005] A conventional way of making such an abradable material is to include in a matrix, metallic for example, porosities which will reduce the tenacity of the coating. Such porosities can for example be created by incorporation and then pyrolysis of polyester fillers. However, these porosities result in significant surface roughness, which increases the coefficient of aerodynamic friction in the boundary layer and therefore leads to performance losses.

[0006] Another possibility is to incorporate inert fillers with low mechanical strength into the matrix. However, in current configurations, the materials used for these fillers degrade at high temperature, currently limiting this option to temperature ranges below approximately 450 ° C.

[0007] Finally, another type of known abradable coating takes the form of a metallic honeycomb structure. However, while this type of coating is more resistant to high temperatures, it suffers from an abradability which leads to strong heating on contact as well as unwanted wear of the rotor.

[0008] There is therefore a real need for an abradable coating for

turbomachine, as well as a turbomachine module and a turbomachine comprising such an abradable coating, devoid, at least in part, of the drawbacks inherent in the aforementioned known configurations.

Disclosure of the invention

The present disclosure relates to an abradable coating for a turbomachine, comprising, with a content greater than 50% by volume, an inorganic compound whose Mohs hardness is less than 6 and whose melting temperature is greater than 900 ° C ° C. , preferably above 1000 ° C.

[0010] In the present description, the term “mineral compound” is understood to mean a solid compound having an ordered atomic structure and a defined chemical composition. In particular, such an inorganic compound can have a crystalline structure characterized by the arrangement of its atoms according to a given periodicity and symmetry (crystal system and space group of the mineral compound).

In the present disclosure, unless otherwise specified, the terms "lower" and "higher" should be understood in the broad sense, that is to say as meaning "lower or equal" and "higher or equal", respectively . [0012] Such a mineral compound offers very good abradability while benefiting from a lower surface roughness than the usual abradable coatings. Thus, in particular, it is possible to obtain a roughness Ra of less than 3 μm. Therefore, this coating generates much lower aerodynamic losses than the usual coatings.

[0013] In addition, such an inorganic compound has an intrinsic abradable nature such that it is unnecessary to artificially incorporate porosities within the coating. Therefore, the surface roughness of the coating remains substantially the same, including after it has been scraped during operation of the

turbomachine. Consequently, the roughness of the coating, and therefore the aerodynamic losses, remain under control throughout the life of the coating.

[0014] This abradable coating also benefits from very high stability

temperature, which makes it suitable for the turbomachine modules exposed to the highest temperatures, and in particular the high pressure compressor or even the turbines.

[0015] Furthermore, the abrasion debris is inert, which reduces its impact on the downstream side of the turbomachine. Such a coating reduces the risk of clogging of the cooling channels of the module.

Finally, it should be specified that such an abradable coating is less expensive to

produce only the usual abradable coatings while offering such wide machining possibilities.

In some embodiments, the content of said mineral compound is greater than 55% by volume, preferably greater than 60% by volume.

[0018] In certain embodiments, the abradable coating has a porosity of less than 15%. The term “porosity” is understood to mean the ratio between the volume of the voids present in the material and the total volume of the material. Thanks to such reduced porosity, the roughness of the coating is reduced, even in the absence of surface treatment, which limits aerodynamic losses.

[0019] In some embodiments, the surface roughness Ra is less than 3 µm. The inventors have in fact observed that the aerodynamic losses remain reasonable below this threshold and then increase more sharply beyond this threshold. [0020] In certain embodiments, the inorganic compound is stable at least up to 900 ° C and preferably up to 1000 ° C. By “stable” is meant that the compound does not undergo a change in physical state (fusion or phase transformation for example) or chemical transformation (oxidation for example) when it is brought to the temperature in question from room temperature. .

[0021] In some embodiments, the mineral compound comprises a

alkaline earth element, preferably Calcium.

In certain embodiments, the mineral compound is chosen from:

Ca ₁₀ (PO ₄ ) 6 (OH) 2; LaP0 ₄ ; and kieselghur. These compounds are stable at least up to 900 ° C and have a hardness suitable for providing a satisfactory abradability while exhibiting low roughness.

[0023] In certain embodiments, the inorganic compound constitutes at least 95% by volume, preferably at least 99% by volume, of the material of the abradable coating. Of course, we do not intend to take the porosity of the material into account here in defining the composition of the material. The inventors have in fact observed during their experiments that such an inorganic compound alone provides the properties expected for a turbomachine abradable, without it necessarily being necessary to add another compound to it.

[0024] However, in other embodiments, the abradable coating

further comprises a metallic compound. This metallic compound forms a matrix for the mineral compound. This improves the resistance to erosion of the coating.

[0025] In certain embodiments, this metallic compound is chosen according to the application temperature.

In some embodiments, the metal compound is based on Nickel, Cobalt or Iron.

In some embodiments, the metal compound is chosen from:

NiAI; NiCrAI; CoNiCrAlY; and FeCrAlY. In some embodiments, the inorganic compound and the metal compound together constitute at least 95% by volume, preferably at least 99% by volume, of the material of the abradable coating.

This presentation also relates to a turbomachine module,

including

a rotor, fitted with a plurality of moving vanes,

a stator, and

at least one abradable coating according to any one of the preceding embodiments provided at the interface between a portion of the rotor and a portion of the stator.

[0030] In certain embodiments, at least one abradable coating of this type forms an abradable track provided on a stator ferrule, facing the moving blades of the rotor.

[0031] In some embodiments, the stator is provided with a plurality of fixed vanes.

[0032] In certain embodiments, at least one abradable coating of this type forms an abradable track provided at the inner end of the fixed blades of the stator, opposite the wipers carried by the rotor.

[0033] In certain embodiments, the module is a high-pressure compressor or a low-pressure turbine for a turbomachine.

[0034] This disclosure also relates to a turbomachine, comprising a module according to any one of the preceding embodiments.

The aforementioned characteristics and advantages, as well as others, will become apparent on reading the following detailed description of embodiments of the abradable coating and of the proposed module. This detailed description refers to the accompanying drawings.

Brief description of the drawings

The accompanying drawings are schematic and are intended above all to illustrate the principles of the disclosure. In these drawings, from one figure to another, identical elements (or parts of elements) are identified by the same reference signs.

[0038] [Fig. 1] Figure 1 is an axial sectional view of a turbomachine according to the disclosure.

[0039] [Fig. 2] Figure 2 is a sectional view of a module according to the disclosure.

[0040] [Fig. 3] Figure 3 is a photograph illustrating the microstructure of a

first example of coating according to the description.

[0041] [Fig. 4] Figure 4 is a graph illustrating the aerodynamic losses within a module as a function of the roughness of the abradable coating.

[0042] [Fig. 5] Figure 5 schematically illustrates an abradability test.

Description of embodiments

In order to make the description more concrete, an example of an abradable coating is described in detail below, with reference to the accompanying drawings. It is recalled that the invention is not limited to this example.

[0044] Figure 1 shows, in section along a vertical plane passing through its main axis A, a bypass turbojet 1, constituting an example of a turbomachine according to the disclosure. It comprises, from upstream to downstream according to the circulation of the air flow, a fan 2, a low pressure compressor 3, a high pressure compressor 4, a combustion chamber 5, a high pressure turbine 6, and a low pressure turbine 7.

[0045] Figure 2 shows, schematically, a stage of the high pressure compressor 4, the high pressure compressor 4 comprising a succession of stages of this type.

The rotor 10 of each stage comprises a plurality of movable vanes 1 1, mounted on a disc 12 coupled to the high pressure shaft of the

turbomachine 1. In addition, a ferrule 13 connects the disc 12 to the disc 12 'of the preceding stage. The stator 20 of each stage comprises for its part a ferrule 21, provided vis-à-vis the movable vanes 11, and a plurality of fixed vanes 22 provided vis-à-vis the ferrule 13 of the rotor 10. The ferrule 21 of the stator carries abradable tracks 31 against which rubs the outer ends of the movable blades 1 1. Furthermore, another abradable track 32 is provided on the inner end of each fixed blade 22; wipers 15 provided on the ferrule 13 of the rotor then rub against this abradable track 32.

Examples of abradable coatings, making it possible to form these abradable tracks 31 and 32, will now be described.

In a first example, the abradable coating is made of

hydroxyapatite, mineral compound with the formula Ca ₁₀ (PO ₄ ) 6 (OH) 2. With the exception of possible impurities, this abradable coating does not include any other component.

[0050] This inorganic compound has a hexagonal crystal system and a space group of 6 / m. It is stable up to at least 900 ° C and has a hardness of 5 on the Mohs scale. Plus, it is insoluble in water, acetone, and alcohol.

It is deposited by thermal spraying on the substrate to be coated, in this case the ferrule 21 and the ring 32, from a powder having a particle size of between 45 and 90 μm. In the present example, a thickness of 1.5 mm is desired for the coating.

After surface machining, a coating is obtained, the microstructure of which is visible in FIG. 3: its porosity is less than 15% and its roughness Ra less than 3 μm.

In this regard, Figure 5 shows the aerodynamic losses suffered by the air stream circulating in a high pressure compressor equipped with abradable tracks, depending on the roughness of the coating forming these abradable tracks. This curve 50 was drawn by comparing several materials on a test bench. Points 51 and 52 correspond to the cases of two abradable coatings currently preferred for a high pressure compressor: it is a raw Metco 2043 coating for point 51 and a Metco 2043 coating with Alumina slip for point 52.

Point 53 corresponds for its part to the case of this coating produced in

hydroxyapatite: it is therefore observed that this coating benefits from a roughness approximately three times lower than those of the known Metco 2043 coatings and therefore causes practically two times less aerodynamic losses than these coatings of the state of the art.

Furthermore, the performance of this abradable coating was evaluated using the A / S ratio (abradability on overpenetration) which is measured using a measuring device 90 illustrated in FIG. 6: three Simulacral vanes 91 are disposed projecting on the perimeter of a rotating wheel 92. An abradable sample 93 to be tested is placed below the rotating wheel 92. The rotating wheel 92 advances at constant speed towards the abradable sample 93 and penetrates it. up to a set depth. We then measure the depth actually dug in the abradable and we calculate the set depth / dug depth ratio. This ratio is called the A / S ratio and is expressed as a percentage. The test parameters are as follows. The speed of rotation at the end of the sham vanes 91 is 210 m / s, the speed of advance of the rotating wheel 92 towards the sample 93 is 150 pm / s and the set depth is 0.5mm.

[0056] Therefore, this hydroxyapatite coating has shown during these tests an A / S ratio of between 110% and 120%, without the blades being subjected to wear.

[0057] In addition, an erosion test according to the ASTM G76 standard was carried out on this

abradable coating. An erosion of 1.7 mm ³ / g for an angle of 90 ° was then measured for this hydroxyapatite coating.

[0058] Although the present invention has been described with reference to specific embodiments, it is obvious that modifications and

changes can be made to these examples without departing from the general scope of the invention as defined by the claims. In particular, individual characteristics of the different embodiments

illustrated / mentioned may be combined in additional embodiments. Therefore, description and drawings should be

considered in an illustrative rather than restrictive sense.

It is also obvious that all the characteristics described with reference to a method can be transposed, alone or in combination, to a device, and conversely, all the characteristics described with reference to a device can be transposed, alone or in combination, to a process.

Claims

[Claim 1] Abradable coating for a turbomachine, comprising, with a content greater than 50% by volume, an inorganic compound whose Mohs hardness is less than 6 and whose melting point is greater than 900 ° C, preferably greater than 1 000 ° C,

wherein the surface roughness Ra is less than 3 µm.

[Claim 2] An abradable coating according to claim 1, wherein the content of said inorganic compound is greater than 55% by volume, preferably greater than 60% by volume.

[Claim 3] An abradable coating according to claim 1 or 2, wherein the porosity is less than 15%.

[Claim 4] An abradable coating according to any one of

claims 1 to 3, wherein the inorganic compound is selected from:

Cai ₀ (PO ₄ ) ₆ (OH) ₂ ; LaP0 ₄ ; and kieselghur.

[Claim 5] An abradable coating according to any one of

claims 1 to 4, wherein the inorganic compound constitutes at least 95% by volume, preferably at least 99% by volume, of the material of the abradable coating.

[Claim 6] An abradable coating according to any one of

claims 1 to 4, further comprising a metallic compound.

[Claim 7] An abradable coating according to claim 6, wherein the metal compound is based on Nickel, Cobalt or Iron.

[Claim 8] An abradable coating according to claim 6 or 7, wherein the metallic compound is selected from: NiAl; NiCrAI;

CoNiCrAlY; and FeCrAlY.

[Claim 9] An abradable coating according to any one of

Claims 6 to 8, wherein the inorganic compound and the metallic compound together constitute at least 95% by volume, preferably at least 99% by volume, of the material of the abradable coating.

[Claim 10] Assembly, comprising

a substrate and an abradable coating (31, 32) according to any one of claims 1 to 9 provided on the substrate.

[Claim 11] Turbomachine module, comprising

a rotor (10), provided with a plurality of mobile vanes (11),

a stator (20), and

at least one abradable coating (31, 32) according to any one of claims 1 to 10 provided at the interface between a portion of the rotor (10) and a portion of the stator (20).

[Claim 12] Turbomachine, comprising a module (4) according to

claim 11.

[Claim 13] A method of manufacturing a coating according to one

any of claims 1 to 12, wherein the inorganic compound is deposited by thermal spraying from a powder having a

particle size between 45 and 90 μm.