Surface treatment method for a metal turbine blade of an aircraft turbomachine

Abstract

This surface treatment process for a metal turbine blade of an aircraft turbomachine comprises successive steps of nickel plating and vapor deposition aluminizing of the blade. Figure 2 (for the abbreviated version)

Description

Title of the invention: Surface treatment method for a metal turbine blade of an aircraft turbomachine technical field

[0001] The present invention relates to a method for surface treatment of a metallic turbine blade of an aircraft turbomachine. Previous techniques

[0002] Metals in the liquid state are susceptible to dissolving gases, a phenomenon known as gassing. During solidification, some of the dissolved gases are abruptly released by degassing, causing the formation of porosity in the cast parts.

[0003] The presence of these porosities has a detrimental effect on the suitability for surface treatments. In particular, the expansion of the gas contained in the porosities can generate blisters in a surface-applied coating. The coating no longer adheres to the substrate at the site of such blisters and is therefore no longer able to effectively protect the coated parts.

[0004] Preventive or remedial methods can be used to limit the level of gassing. For example, a hot isostatic compaction step can be added to reduce porosity, and / or heat treatments can be used to induce degassing before applying the coating. However, these methods can be time-consuming and are not always sufficient to control degassing problems.

[0005] Another solution could be to redesign the parts to eliminate the formation of porosity. However, this solution is not compatible with ongoing series production. Description of the invention

[0006] In this context, the invention aims at a surface treatment method for aircraft turbomachine blades compatible with current designs and making it possible to guarantee the reliability of protection provided by a substrate coating.

[0007] The invention relates to a surface treatment method for a metal turbine blade of an aircraft turbomachine. The method comprises successive steps of nickel plating and vapor deposition aluminizing the blade. This surface treatment method creates a nickel layer on the blade surface, effectively sealing pores. The resulting blade is thus more suitable for receiving an aluminum-based coating. able to fully perform its protective role, as it is no longer subject to the risk of blistering due to outgassing.

[0008] Preferably, the nickel plating step is carried out by a chemical bath.

[0009] For example, the nickel plating step is carried out by electrolysis in a bath.

[0010] According to one feature, the chemical bath is composed of an aqueous solution comprising nickel ions and a reducing agent.

[0011] According to another feature, the chemical bath further comprises a filler metal selected from hafnium, tantalum, molybdenum or zirconium.

[0012] For example, the chemical bath further includes the addition of at least one corrosion-resistant material to enhance the corrosion resistance of the blade. Advantageously, the chemical bath may include a material that improves the adhesion of the bonding layer produced in the aluminizing step.

[0013] According to another feature, the aluminizing step is carried out by vapor phase aluminizing treatment, such as chemical vapor deposition or physical vapor deposition.

[0014] Advantageously, the process includes a surface preparation step carried out before the nickel plating step.

[0015] For example, the process includes a surface smoothing post-treatment step carried out after the nickel plating step and before the aluminizing step.

[0016] According to another aspect, the invention relates to a metallic turbine blade of a turbomachine treated by a process as defined above. Brief description of the drawings

[0017] Other objects, features and advantages of the invention will become apparent from the following description, given solely by way of non-limiting example, and made with reference to the accompanying drawings in which:

[0018] [Fig. 1] is a partial longitudinal cross-sectional view of a low-pressure turbine of an aircraft turbomachine; and

[0019] [Fig.2] a flowchart of a surface treatment process for a blade according to an example of an embodiment of the invention. Detailed description of at least one embodiment

[0020] Fig. 1 partially represents in longitudinal section a low-pressure turbine 1 of an aircraft turbomachine, representative of turbine architectures comprising moving blades or rotors, and fixed blades or distributors.

[0021] The process according to the invention proposes a surface treatment of the blades comprising nickel plating followed by aluminizing.

[0022] It is understood that the present invention applies to any other aircraft turbomachine assembly equipped with movable and / or fixed blades.

[0023] Figure 1 more precisely represents five stages of a low-pressure turbine 1. Regarding the orientation with respect to the general direction of gas flow through the turbine, the first stage of the turbine is located upstream and the last stage of the turbine is located downstream.

[0024] The first stage comprises a movable wheel formed of a rotor disk 2 on which a plurality of movable blades 3 are radially mounted. The other stages each comprise a distributor formed of a plurality of fixed blades 4 and a movable wheel placed behind the distributor and formed of a rotor disk 2' on which a plurality of movable blades 3' are radially mounted.

[0025] The discs 2, 2' are fixed to each other by means of bolted links 5, making all the discs fixed in rotation around the longitudinal axis XX of the turbomachine.

[0026] Each disk 2, 2' has at least one annular flange 6 which extends towards the disks 2, 2' of the adjacent floors.

[0027] We will now describe, with reference to [Fig.2], a surface treatment process for an aircraft turbomachine blade, according to an example of implementation of the invention.

[0028] Here, the process begins with a step 7 of preparing the surface of the blade. This preparation step may include a degreasing phase and / or a pickling phase and / or a polishing phase.

[0029] For example, degreasing makes it possible to rid the surfaces to be treated of their contamination by organic or mineral impurities from the prior stages of manufacturing the parts or their storage.

[0030] For example, in the case of the renovation of metal parts, stripping makes it possible to remove the adherent layers of protective but degraded coatings.

[0031] Finally, polishing makes it possible in particular to eliminate geometric imperfections of the surface.

[0032] The process continues with a nickel plating step 8. Preferably, the nickel plating step is carried out by a chemical bath, for example by immersing the part in a liquid bath which results in a metallic deposit being brought about by an autocatalytic chemical process.

[0033] The chemical nickel plating bath consists of an aqueous solution comprising nickel ions and a reducing agent. A layer of nickel then forms on the surface of the blade, which acts as a catalyst for the chemical reaction.

[0034] For example, the reducing agent is hypophosphite or a boron compound.

[0035] In the case of hypophosphite baths, a basic medium is used, a temperature ranging from 70°C to 100°C and salt concentrations ranging from 10 to 25 g / L.

[0036] In the case of baths using boron compounds, either borohydrides are used in an alkaline medium, or dimethylamine-borane in a neutral or slightly acidic medium, with a temperature ranging from 70°C to 100°C.

[0037] Preferably, the chemical bath also includes an addition of at least one corrosion-resistant material to enhance the corrosion resistance of the blade. For example, this addition could be chromium or platinum.

[0038] Depending on the required mechanical characteristics of the blade, the chemical bath may further include a filler metal such as hafnium, tantalum, molybdenum, or zirconium. Such a filler metal improves the mechanical characteristics of the part. For example, such a filler metal fills dislocations in the treated part and delays crack propagation.

[0039] Alternatively, the nickel plating step may be carried out by electrolysis in a bath. For example, nickel sulfate baths or Watts baths, nickel chloride baths, or nickel sulfamate baths may be used.

[0040] In the case of sulfate baths, the concentration of nickel sulfate ranges from 225 g / L to 400 g / L and the concentration of nickel chloride ranges from 30 g / L to 60 g / L, for a temperature between 45°C and 55°C and a current density of approximately 1 A / dm². The efficiency varies between 93%, corresponding to a pH of 2, and 99%, corresponding to a pH of 5.

[0041] In the case of chloride baths, an all-chloride bath or, preferably, a pre-nickel plating bath with chloride, also known as a Wood's bath, can be used. For example, in a pre-nickel plating bath, the nickel chloride concentration ranges from 30 g / L to 250 g / L, at a temperature between 20°C and 30°C and a current density between 1 and 2 A / dm². The yield varies between 99%, corresponding to a pH of 2, and 99.5%, corresponding to a pH of 5.

[0042] In the case of sulfamate baths, the nickel sulfamate concentration is on the order of 650 g / L, for a temperature between 40°C and 60°C and a current density between 1 and 20 A / dm². The efficiency varies between 95.5%, corresponding to a pH of 2.5, and 99.5%, corresponding to a pH of 4.

[0043] It should be noted that the pH and temperature of the bath used influence the process yield. For an electrolytic bath, it is possible to lower the pH value by using boric acid. For a chemical bath, it is possible to raise the pH value by using sodium hydroxide.

[0044] After nickel plating step 8, the process continues with a surface smoothing post-treatment step 9, so as to obtain a blade surface having a predetermined maximum roughness. For example, the smoothing post-treatment of The surface is mechanically treated, including sandblasting or polishing. For example, the maximum predetermined roughness is on the order of 3.2 pm.

[0045] Alternatively, it remains possible not to perform a surface post-treatment step.

[0046] The process ends with a step 10 of vapor deposition aluminizing the blade, in which an aluminum coating is deposited on the blade. In other words, an aluminoform bonding layer is deposited. For example, the bonding layer is produced by vapor deposition of aluminum, according to the vapor deposition treatment known as APVS for "Snecma Vapor Deposition." This APVS treatment is described, in particular, in French patent FR 1433497. More generally, this deposition can be carried out by any method within the grasp of those skilled in the art, such as chemical vapor deposition (CVD) or physical vapor deposition (PVD).

[0047] According to one embodiment, it is possible to include an additional heat treatment step carried out between nickel plating step 8 and before aluminizing step 10. By way of example, the heat treatment may include tempering the blade for one hour at 1000°C followed by tempering the blade for one hour at 1100°C.

[0048] Alternatively, a tempering step can be carried out after the aluminizing step. As an example, a tempering of 10 minutes at 1050°C can be provided.

Claims

Demands

1. A surface treatment method for a metallic aircraft turbomachine blade (3, 3', 4) characterized in that it comprises successive nickel plating steps of said blade (3, 3', 4) and vapor phase aluminizing of said blade (3, 3', 4).

2. A method according to claim 1, wherein the nickel plating step is carried out by a chemical bath.

3. A method according to claim 1, wherein the nickel plating step is carried out by electrolysis in a bath.

4. A method according to claim 2, wherein the chemical bath is composed of an aqueous solution comprising nickel ions and a reducing agent.

5. A method according to claim 4, wherein the chemical bath further comprises a filler metal selected from hafnium, tantalum, molybdenum or zirconium.

6. A method according to claim 4 or 5, wherein the chemical bath further comprises an addition of at least one corrosion-resistant material so as to enhance the corrosion resistance of the blade (3, 3', 4).

7. A method according to any one of claims 1 to 6, wherein the aluminizing step is carried out by vapor phase aluminizing treatment, such as chemical vapor deposition or physical vapor deposition.

8. A method according to any one of claims 1 to 7, comprising a surface preparation step carried out before the nickel plating step.

9. A method according to any one of claims 1 to 8, comprising a surface smoothing post-treatment step carried out after the nickel plating step and before the aluminizing step.

10. Metallic aircraft turbomachine blade (3, 3', 4) treated by a process according to any one of claims 1 to 9.

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