FR3097562A1 - Method of manufacturing an abradable part of a turbomachine and an abradable part - Google Patents

Abstract

Method of manufacturing an abradable part of a turbomachine and an abradable part Method of manufacturing a part of a turbomachine comprising a support (10) and an abradable coating (11) based on aluminum, the method comprising a step of depositing the coating abradable coating in which an abradable coating (11) is deposited on the support (10) and an anodizing step in which at least part of the abradable coating (11) is anodizing, the anodizing step taking place after the step of depositing the abradable coating. Turbomachine part comprising a support (10) and an abradable coating (11) based on aluminum. Figure for the abstract: Fig. 1.

Description

Method for manufacturing an abradable part of a turbomachine and abradable part

This presentation relates to a method of manufacturing an abradable part, in particular an abradable part of a turbomachine for an aircraft.

Within an aircraft turbomachine, several parts come into contact with other so-called “abradable” parts. Abradable parts have the particularity of wearing preferentially when in contact with another part, thus limiting the wear of the latter. In particular, the inner rings of the high pressure compressor may comprise abradable parts brought into contact with a rotor.

For example, abradable parts can be placed opposite the tips of turbomachine blades, and thus be subject to furrowing.

The groove comes from the local contact between the abradable and the tip of the blade. A drop of semi-molten abradable forms and settles on a tip of the blade, which grooves the track over its entire circumference. Most often this drop comes off after a few turns. The groove can sink a few millimeters deep. This tracking degrades both the sealing and the performance of the engine.

The abradable parts include a backing and an abradable coating. The support of current parts can be made of an alloy based on aluminum, titanium, iron or nickel.

On the other hand, the abradable part comprises an abradable coating which can for example be an alloy of aluminum and silicon or of aluminum and nickel. This coating can also be filled with a polymer, for example with a polyester. In addition, the abradable part can comprise an underlayer placed between the abradable coating and the support. The underlayer can for example be an alloy based on aluminum and/or nickel, for example NiAl, NiCrAl.

The environment of the high pressure compressor is exposed to corrosion, so abradable parts generally have protection against this phenomenon. Current techniques recommend manufacturing an abradable part for a turbomachine as follows. The one-piece support is anodized then an abradable coating is deposited on the support, for example by thermal spraying. The abradable coating is then machined which forms machining zones at the border between the abradable coating and the support where the anodized support is partially exposed. Finally, the support is touched up using a local chemical conversion, such as Alodine 1132 or 1200, on the junction parts between the abradable coating and the support to restore an anti-corrosion layer on the parts of the support that have been updated. bare by machining the abradable coating.

The parts obtained by this process have several drawbacks. First of all, the nickel-aluminum underlayer and the exposed aluminum form a galvanic stack, which prematurely corrodes the abradable coating, and can induce its detachment.

In addition, this process requires the use of a touch-up, which has less good corrosion resistance than the initial anodization of the support. Indeed, its maximum operating temperature is approximately 80°C, which is well below the operating temperature of the elements of the turbomachine comprising abradable parts. In addition, the surfaces to be retouched are large: this retouching is therefore time-consuming. Also, certain substances contained in local chemical conversions, such as Alodine 1132 or 1200, are impacted by the REACH list, which lists products that are dangerous for humans and/or the environment and will therefore be prohibited in the medium term.

There is therefore a need to improve the manufacturing process for abradable parts.

To this end, the present presentation concerns the manufacture of a turbomachine part comprising a support and an abradable coating based on aluminium, the method comprising a step of depositing the underlayer in which a metal underlayer is deposited on the support, a step of depositing the abradable coating provided after the step of depositing the underlayer in which an abradable coating is deposited on the underlayer, and an anodizing step in which the abradable coating is anodized, the step of anodization taking place after the step of depositing the abradable coating.

In the present disclosure, the abradable coating is a coating capable of being in contact with another part of the turbomachine and which is configured so that the contact between the abradable coating and the other part of the turbomachine preferentially wears the abradable coating.

In the present description, the expressions “part” and “abradable part” refer to an identical element, which is the abradable part manufactured by the process.

In the present description, the term “abradable coating based on aluminium” means abradable coatings in which the mass content of aluminum is the majority. It is understood that aluminum is therefore the element whose mass content of the abradable coating is the highest. The abradable coating based on aluminium, for example, has a mass content of at least 50% aluminium, preferably at least 60% aluminium, even more preferably at least 95% aluminium.

Thus, since the anodizing step is carried out after the machining of the abradable coating, no part of the support of the part is exposed. It is therefore not necessary to carry out retouching during the manufacture of an abradable part, which makes it possible to circumvent all the disadvantages listed above and linked to the use of this substance.

In particular, the protection against corrosion is more effective. In addition, the aeronautical performance of the part is improved since the sudden variation in profile generated by the step created during the retouching stage disappears.

In this presentation, the performances of abradables are evaluated using the A/S ratio (abradability over overpenetration) which is measured as follows. Three mock vanes are arranged projecting from the perimeter of a rotating wheel. An abradable sample to be tested is placed below the rotating wheel. The rotating wheel advances at constant speed towards the abradable sample and penetrates it to a set depth. The depth actually dug in the abradable is then measured and the ratio setpoint depth / dug depth is calculated. This ratio is called A/S ratio and is expressed as a percentage. The test parameters are as follows. The rotation speed at the tip of the simulacrum blades is 210 m/s, the speed of advance of the rotating wheel towards the sample is 150 µm/s and the set depth is 1 mm.

The abradable parts obtained by the method described above also have better A/S ratios than parts obtained by prior techniques. The performance of the abradable parts is therefore improved.

As a non-limiting example of an abradable coating based on aluminium, mention may be made of an alloy of aluminum and silicon, filled with particles of polyester, boron nitride, graphite or clay.

In some embodiments, the volume content of the filler is about 50 vol%.

In certain embodiments, the method comprises a machining step provided between the step of depositing the abradable coating and the anodizing step, in which the abradable coating is shaped.

Thus, the abradable coating can be machined according to the needs and geometric constraints that the abradable part must respect.

In certain embodiments, the method comprises a sanding step provided before the step of depositing the underlayer and in which the support is cleaned.

Thus, the impurities which could hinder or weaken the manufacture of the abradable part can be removed. In addition, this step improves the roughness of the support, and therefore improves the mechanical grip of the abradable coating on the support.

In certain embodiments, the method comprises a sealing step provided after the anodizing step and in which the abradable part is treated with chromium.

In some embodiments, the underlayer is made of aluminum, the part support is an aluminum-based alloy, and the support is anodized at the same time as the abradable coating during the anodizing step.

Thus, the abradable coating and the support are anodized simultaneously, for example by a sulfuric anodic oxidation bath. In addition, the underlayer provided in pure aluminum is resistant to the conditions of the anodizing stage and it is not deteriorated during the latter.

As a non-limiting example, the aluminum-based alloy can be a 2000, 5000, 6000 or 7000 series aluminum alloy.

In certain embodiments, the underlayer is made of aluminum or an aluminum-based alloy and the abradable coating is anodized by a local anodizing process.

Thus, the abradable coating can be anodized independently of the support, which makes it possible not to expose and possibly damage the support during the anodizing step.

As a non-limiting example, the underlayer can be made of pure aluminum or an alloy based on aluminum and nickel.

As a non-limiting example of support, the support can be an alloy based on titanium, nickel, magnesium, aluminum or iron.

In certain embodiments, the abradable coating has a thickness greater than or equal to 1 mm, preferably greater than or equal to 1.5 mm, preferably greater than or equal to 2 mm, preferably greater than or equal to 2.5 mm, preferably greater than or equal to 3mm and less than or equal to 5mm, preferably less than or equal to 4.5 mm, preferably less than or equal to 4 mm, preferably less than or equal to 3.5 mm, preferably less than or equal at 3mm.

In certain embodiments, the underlayer has a thickness greater than or equal to 50 μm, preferably greater than or equal to 100 μm, preferably greater than or equal to 150 μm, preferably greater than or equal to 200 μm, preferably greater than or equal to equal to 250 μm and less than or equal to 500 μm, preferably less than or equal to 450 μm, preferably less than or equal to 400 μm, preferably less than or equal to 350 μm, preferably less than or equal to 300 μm.

In certain embodiments, the anodized layer of the support has a thickness greater than or equal to 4 μm, preferably greater than or equal to 5 μm, preferably greater than or equal to 6 μm, preferably greater than or equal to 7 μm, preferably greater than or equal to 8 μm and less than or equal to 20 μm, preferably less than or equal to 19 μm, preferably less than or equal to 18 μm, preferably less than or equal to 17 μm, preferably less than or equal to 16 μm.

This presentation also relates to a turbomachine part comprising a support, an abradable coating based on aluminum provided on the support and an underlayer placed between the support and the abradable coating, in which the abradable coating is anodized.

It is therefore understood that the anodization step is carried out after the step of depositing the abradable coating.

In certain embodiments, the turbomachine part is an aircraft turbomachine part.

The invention and its advantages will be better understood on reading the detailed description given below of various embodiments of the invention given by way of non-limiting examples. This description refers to the pages of appended figures, on which:

FIG. 1 represents a part according to one embodiment obtained by a manufacturing method according to one embodiment.

FIG. 2 represents a part according to another embodiment obtained by a manufacturing method according to another embodiment.

FIG. 3 schematically represents the steps of a method according to one embodiment.

FIG. 4 represents a part obtained by a manufacturing method according to an embodiment of the prior art.

Figure 5 shows a device configured to measure the A/S ratio.

Figure 6 shows a graph illustrating a thermal cycle applied for adhesion tests.

This presentation concerns a method for manufacturing an abradable part of a turbomachine. Although this presentation takes the example of an inner ring of a high pressure or low pressure compressor, the process described can be used to manufacture any abradable part of a turbomachine. However, for reasons of clarity of the presentation, examples which are not intended to be limiting are described.

Manufacture of an abradable part according to a method of the prior art

FIG. 4 represents an abradable part obtained by a method of the prior art. The part comprises a support 20, an abradable coating 21 and an underlayer 22. The support is a 2000, 5000, 6000 or 7000 series aluminum alloy, for example 2219 or 2618. The abradable coating 21 is based on aluminum , composed of 88% aluminum and 12% silicon. It is also loaded to 40% by mass with a polymer (for example a polyester). The underlayer 12 is an aluminum alloy, composed of 95% aluminum and 5% nickel.

In addition, the part includes an anodized layer 23, a retouched layer 24 and a step 25 between layer 24 and anodized layer 23.

The method of manufacturing such an abradable part is as follows. The support 20 is first anodized during an anodization step. This anodization can be carried out in a sulfuric anodic oxidation bath (SAO) in the presence of an electric current. During this step, the anodized layer 23 is formed over a depth comprised between 6 μm and 20 μm, preferably between 8 μm and 13 μm.

Then the part undergoes a sanding step in which the support 20 is cleaned by mechanical projection. In addition, sandblasting makes it possible to increase the roughness of the treated area in order to deposit the abradable.

Then, the underlayer 22 is deposited during a step of depositing the underlayer. This deposition is carried out by thermal spraying. In this way, the underlayer 22 is deposited over a thickness of between 100 μm and 200 μm.

Then, the abradable coating 21 is deposited during the step of depositing the abradable coating. This deposition is carried out by thermal spraying.

Then, the abradable coating 21 which has been deposited is machined during the machining step. In this way, the excess abradable coating 21 is removed so that the final abradable coating 21 has a thickness of between 2 mm and 3 mm. During this step, part of the anodized layer 23 is removed from the support 10, which exposes part of the support 20 and creates the step 25. This step measures between 0.20 mm and 0.30 mm.

A touch-up is therefore applied to the parts of the support 20 which have been exposed by the machining step. This retouching creates layer 24 on support 20.

Manufacture of a part according to a first method

FIG. 1 represents an abradable part according to a first embodiment. In the embodiment of FIG. 1, the part comprises a support 10, an abradable coating 11 and an undercoat 12. The support is a 2000, 5000, 6000 or 7000 series aluminum alloy. aluminum base, composed of 88% aluminum and 12% silicon. It is moreover filled to 50% by mass with a polymer (for example a polyester). The underlayer 12 is made of aluminum.

FIG. 3 represents a diagram illustrating the various stages of the manufacturing process of the part of FIG. 1. Initially, the part undergoes a sandblasting step E1 in which the support 10 is cleaned and its roughness is increased, for example by corundum particles or glass ball. After this step, the support 10 has a roughness of between Ra=1.6 μm and Ra=4 μm according to the ISO 4288 standard.

Then, the underlayer 12 is deposited during the step of depositing the underlayer E2. This deposition is carried out by thermal spraying. In this way, the underlayer 12 is deposited over a thickness of between 100 μm and 200 μm. The role of the underlayer 12 is to increase the roughness of the surface of the material in order to guarantee good adhesion between the abradable coating 11 and the support 10. In addition, the underlayer 12 makes it possible to ensure mechanical accommodation, more particularly vis-à-vis the thermomechanical stresses generated by the difference between the coefficients of expansion of the abradable coating 11 and of the support 10.

Then, the abradable coating 11 is deposited during the step of depositing the abradable coating E3. This deposition is carried out by thermal spraying.

Then in the embodiment of FIG. 1, the abradable coating 11 which has been deposited is machined during the machining step E4. In this way, the excess abradable coating 11 is removed so that the final abradable coating 11 has a thickness of between 2 mm and 3 mm.

Finally, the part is anodized during an E5 anodization step. This anodization can be carried out in a sulfuric anodic oxidation bath (SAO) in the presence of an electric current. During this anodization step E5, the entire surface of the support 10 and of the abradable coating 11 is anodized, thus creating an anodized layer 13. Under these conditions, the anodized layer 13 has a thickness of between 5 μm and 20 µm, preferably between 8 µm and 13 µm.

This anodization step E5 makes it possible to form an anodic layer of alumina on the abradable coating.

Thanks to the particular composition of the undercoat 12 which is only aluminum, the undercoat 12 is not degraded by the anodizing conditions.

In certain configurations, the abradable part undergoes a clogging step E6 provided after the anodizing step and in which the abradable part is immersed in a bath containing corrosion inhibiting salts, for example chromium salts. This improves the anti-corrosion properties of the entire anodized surface

Manufacture of a part according to a second method

FIG. 2 illustrates an abradable part according to a second embodiment obtained by a second manufacturing process.

In this method, the support 10 is provided in materials such as titanium, iron or nickel alloys. The underlayer 12, for its part, is provided in an alloy composed of 95% aluminum and 5% nickel.

This process is similar to the process for manufacturing the part of the first embodiment concerning the steps of sandblasting E1, deposition of the underlayer E2, deposition of the abradable coating E3 and machining E4.

However, in this case, the anodization step E5 is carried out locally, only on the abradable coating 11. The anodization is then carried out, for example, using a pad which is applied locally at selected locations. Thus, the abradable coating 11 can be anodized without interacting and possibly damaging the support 10. An anodized layer 13 is therefore created, only on the abradable coating 11. The anodized layer 13 is alumina.

Parts Performance Comparison abradable

Initially, the methods of the present disclosure make it possible to dispense with the retouching step and the formation of a step 25 on the finalized abradable part, between the abradable coating 21 and the anodized layer 23. Indeed, the presence of this step 25 on the abradable parts obtained by the method of the prior art reduces the aerodynamics. In addition, the removal of the retouching step also saves time when manufacturing an abradable part.

In addition, the performance of abradables is evaluated using the A/S ratio (abradability over overpenetration) which is measured as follows: three simulated blades are arranged projecting from the perimeter of a rotating wheel. An abradable sample to be tested is placed below the rotating wheel. The rotating wheel advances at constant speed towards the abradable sample and penetrates it to a set depth. This measuring device is illustrated in Figure 5. The depth actually dug in the abradable is then measured and the ratio setpoint depth/dug depth is calculated. This ratio is called A/S ratio and is expressed as a percentage. The test parameters are as follows. The rotation speed at the tip of the simulacrum blades is 210 m/s, the speed of advance of the rotating wheel towards the sample is 150 µm/s and the set depth is 1 mm.

The following table presents comparative tests of abradability of abradable parts obtained by a process of the prior art and the process of the present presentation.

Process for obtaining the part Prior art test No. 1 Prior art test No. 2 Process of this presentation test n°1 Process of this presentation test n°2 Maximum measured A/S ratio 171% 170% 137% 133% Minimum measured A/S ratio 126% 116% 104% 107%

Table 1 represents abradability tests carried out on two parts obtained by a process of the prior art and on two parts obtained by a process of the present description. Each test of each part is associated with a value of the maximum and minimum A/S ratio representing respectively the greatest and the lowest penetration measured during the test. Initially, it appears that the average difference between the largest and the smallest A/S ratio measured is lower for the parts obtained by the process of this presentation.

In addition, an abradable part is considered efficient when its A/S ratio of this abradable part is less than 140%. As shown in the previous diagram, the abradable parts of the prior art do not make it possible to present an A/S ratio lower than this setpoint value. However, thanks to the anodic layer of alumina formed during the anodization step E5, the A/S ratio of the abradable coating 11 of a part obtained by the method of this presentation is of the order of 135%. The anodized abradable coating therefore has better performance than an abradable part obtained by a method of the prior art.

In addition, tests have been carried out to check the mechanical strength of sub-layers 12 made of pure aluminum. More specifically, adhesion tests were carried out by subjecting parts to several hundred thermal cycles. The thermal cycle is represented in FIG. 6. First of all, an abradable part according to the first embodiment obtained by a method of the present description is heated linearly from 75° C. to 270° C. in 5 minutes. Then, the part is maintained at 270° C. for 10 minutes. Then, the part is cooled to 150°C in 40 minutes, then maintained at this temperature for 30 minutes. Finally, the part is cooled to 75°C in 90 minutes. The total duration of a cycle is 2 hours and 55 minutes. The results of these tests are as follows.

Number of thermal cycles undergone 0 60 143 273 Adhesion (MPa) 10.7 10.1 9.6 10.8

The adhesion therefore remains greater than 5.0 MPa, which therefore meets the operating requirements in a turbomachine.

The roughness of the aluminum sub-layers 12 was also tested. The sub-layers 12 have characteristic roughness dimensions of around Ra=3.2 μm and Rz=26.5 μm. These measurements were carried out according to the ISO 4288 standard.

The corrosion resistance of the abradable part obtained by a method of the present disclosure was also tested. The following table summarizes various corrosion tests carried out with neutral salt spray according to standard NF EN ISO 9227.

Process Thermal aging 168h 336h 408h Prior art 1 hour at 270°C then 3 hours at 150°C Generalized corrosion Generalized corrosion Generalized corrosion none Corrosion on the abradable coating Corrosion on the abradable coating Generalized corrosion First process 1 hour at 270°C then 3 hours at 150°C white dots white dots white dots none RAS RAS white dots

Thus, the abradable parts obtained by the methods of the present disclosure are more resistant to corrosion even after more than 400 hours of testing. It is also found that thermal aging has an influence on the anti-corrosion properties of the parts tested.

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 features of the different illustrated/mentioned embodiments can be combined in additional embodiments. Accordingly, the description and the 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 method.

Claims (10)

Method for manufacturing a turbomachine part comprising a support (10) and an abradable coating (11) based on aluminium, the method comprising a step of depositing the underlayer (E2) in which an underlayer (12) metal is deposited on the support, a step of depositing the abradable coating (E3) provided after the step of depositing the underlayer (E2) in which an abradable coating (11) is deposited on the underbase (12), and an anodization step (E5) in which the abradable coating (11) is anodized, the anodization step (E5) taking place after the step of depositing the abradable coating (E3). Method according to claim 1, comprising a machining step (E4) provided between the step of depositing the abradable coating (E3) and the anodizing step (E5), in which the abradable coating (11) is form. Method according to claim 1 or 2, comprising a sandblasting step (E1) provided before the step of depositing the underlayer (E2). Method according to one of Claims 1 to 3, in which the underlayer (12) is made of aluminium, the support (10) of the part is an aluminum-based alloy, and in which the support (10) is anodized together with the abradable coating (11) during the anodizing step (E5). Method according to one of Claims 1 to 3, in which the undercoat (12) is made of aluminum or an aluminum-based alloy and the abradable coating (11) is anodized by a local anodizing process. Method according to one of Claims 1 to 5, in which the anodized layer of the support (10) has a thickness greater than 4 µm, preferably greater than 5 µm, preferably greater than 6 µm, preferably greater than 7 µm, preferably greater than 8 μm and less than 20 μm, preferably less than 19 μm, preferably less than 18 μm, preferably less than 17 μm, preferably less than 16 μm. Turbomachine part comprising a support (10), an abradable coating (11) based on aluminum provided on the support (11) and an underlayer (12) placed between the support (10) and the abradable coating (11), wherein the abradable coating (11) is anodized. Part according to Claim 7, in which the underlayer (12) is made of aluminum or an aluminum-based alloy. Part according to Claim 7 or 8, in which the support (10) is an aluminum-based alloy and the entire surface of the part is anodized. Part according to Claim 7 or 8, in which the support (10) is made of a titanium, iron or nickel alloy.