Method for forming a cathodic protection coating on a turbine component

Abstract

The present invention relates to a method for forming a cathodic protection coating on a substrate (1) forming a turbine component, the method comprising at least: - depositing particles (11) for cathodic protection of the substrate on the substrate, the deposition being carried out by electrophoresis with an organic electrolyte (10) containing at least said particles, and - forming an inorganic matrix in the pore regions of the resulting particle deposit, at least comprising: · impregnating the deposit with an impregnation composition, · thermally drying the deposit impregnated with the impregnation composition, and · densifying the deposit by mechanical compaction after the thermal drying treatment so that the deposit is electrically conductive.

Description

Technical Field

[0001] The present invention relates to a method for forming a cathodic protection coating on turbine components with an organic electrolyte. In particular, the present invention is interested in protecting compressor or turbine shafts used in aviation or industrial turbines. Background Art

[0002] Steels with high mechanical strength, usually greater than 1000 MPa, such as Maraging 250 or ML340, 40CDV12, can be used to form turbine components, such as compressor or turbine shafts. However, in use, such steels may be sensitive to corrosion.

[0003] To protect the components from corrosion, it is known to coat these components with an anti-corrosion coating by manual or automatic spraying. Using such methods, it may be relatively difficult to control the thickness of the applied coating, especially when the components have complex geometries. Therefore, coatings that do not meet the technical definition of the components may be obtained, and these coatings may have reduced properties (corrosion resistance when the thickness is insufficient, adhesion when the thickness is excessive).

[0004] Solutions have been proposed to try to solve the problem of the uniformity of deposits on complex components. To this end, patent US3787305 proposes depositing cathodic protection particles made of aluminum and resin (usually an acrylic resin) by electrophoretic deposition. The deposition is carried out by an aqueous electrolyte in which the resin is dissolved, and a voltage higher than the voltage of water electrolysis is applied, which causes a significant local change in the pH around the electrode and thus causes the resin containing aluminum particles to deposit on the surface of the working electrode. As described below, there are various problems with the electrolysis of water, which the inventors have observed in their research. In addition, the deposited resin is electrically insulating, which limits the deposition thickness that can be obtained by electrophoresis in a given deposition step to about twenty microns, a value that may not be sufficient to completely cover the surface defects of the substrate or ensure sufficient anti-corrosion. This method is carried out by calcining the organic resin using heat treatment at a relatively high temperature, which affects the microstructure of some substrates and causes additional pores in the coating. In addition, if a deposit of significant thickness is required, in other words, a thickness greater than or equal to 20 μm, it is necessary to repeat the deposition sequence of electrophoresis and calcining the resin one or more times after calcining the first layer of resin. This greatly prolongs the method and complicates it.

[0005] There is a need for a method for forming an anti-corrosion coating that overcomes the disadvantages of the prior art. Summary of the Invention

[0006] The present invention relates to a method for forming a cathodic protection coating on a substrate forming a turbine component, the method comprising at least:

[0007] - Depositing particles for cathodic protection of a substrate on the substrate, the deposition being carried out by electrophoresis with an organic electrolyte comprising at least said particles, and

[0008] - Forming an inorganic matrix in the pores of the particle deposit thus produced, comprising at least:

[0009] · Impregnating the deposit with an impregnating composition,

[0010] · Subjecting the deposit impregnated with the impregnating composition to a drying heat treatment, and

[0011] · After this drying heat treatment, densifying the deposit by mechanical compaction so that the deposit is electrically conductive.

[0012] Compared with the spray gun method, the electrophoresis technique can obtain a uniform deposit with a controlled thickness, even on parts with complex shapes or large sizes. The use of an organic electrolyte can overcome the harmful effects associated with water electrolysis. More specifically, research conducted by the present inventors has shown that if the deposition electrode corresponds to a cathode (- sign) made of steel, the water electrolysis that may occur during electrophoresis deposition with an aqueous electrolyte can cause hydrogen embrittlement of the part and lead to a foaming phenomenon that affects the uniformity of the deposit. In terms of anodic deposition of an aqueous electrolyte, it is necessary to enter the alkaline pH range to obtain negatively charged particles, which may cause corrosion of the deposited particles. The present invention also enables a large range of deposition thicknesses to be obtained during the same stage of electrophoresis deposition. Such thicknesses may be more difficult to obtain in a single deposition because the deposition is carried out by an aqueous electrolyte by applying a DC voltage. The inorganic matrix formed in the pores of the deposit constitutes a binding phase, enabling the cathodic protection particles to be held on the substrate and holding these particles together to ensure the cohesion of the deposit. The mechanical compaction of densification can bring the cathodic protection particles of the substrate into contact so that the coating is dense and electrically conductive. By compaction, the coating obtains a high-performance sacrificial property to prevent corrosion.

[0013] In an exemplary embodiment, the organic electrolyte comprises an alcohol liquid medium in which the particles are suspended.

[0014] This feature is advantageous for depositing an electrolyte with good environmental and health compatibility and a large electroactive range.

[0015] In particular, the alcohol liquid medium can be formed with at least 50% by volume of propanol, such as propan - 2 - ol.

[0016] The use of propanol is advantageous because it eliminates the need for a dispersant in the electrolyte, thus simplifying the method.

[0017] In an exemplary embodiment, the thickness of the cathodic protection particle deposit on the substrate is greater than or equal to 40 μm.

[0018] The present invention is particularly advantageous in this case because it is able to obtain such a thickness in a single electrophoretic deposition step without having to interrupt the deposition.

[0019] In an exemplary embodiment, the cathodic protection particles are made of aluminum or an aluminum alloy. However, the present invention is not limited to the use of such materials, and other examples will be described below.

[0020] In an exemplary embodiment, the substrate is made of steel.

[0021] As for the particles, the present invention is not limited to a specific class of materials for the substrate. The substrate can more generally be metallic, for example made of a metal alloy, or even made of a composite material, provided that it has sufficient electrical conductivity to enable electrophoretic deposition.

[0022] In an exemplary embodiment, the impregnating composition comprises at least one alkali metal silicate or at least one alkaline earth metal silicate.

[0023] This feature is advantageous because it avoids the use of an acidic medium, in particular any risk of damage to certain substrates that could be incurred during sol-gel deposition. However, the use of the sol-gel route for forming the inorganic matrix remains within the scope of the present invention and will be described below.

[0024] In an exemplary embodiment, the formation of the inorganic matrix includes a stabilizing heat treatment of the deposit.

[0025] This feature advantageously enables the expulsion of the maximum possible amount of liquid medium and renders the deposit insoluble in water.

[0026] It should be noted that the drying heat treatment can be carried out at a first temperature and then the stabilizing heat treatment at a second temperature greater than the first temperature. In this case, the two treatments are separate and carried out at different temperatures. According to an alternative, a single and identical heat treatment can be carried out, in which the deposit is both dried and stabilized (in this case, the stabilizing and drying heat treatments are combined). According to another alternative, no stabilizing treatment is carried out and only the drying heat treatment is carried out.

[0027] In particular, the stabilizing heat treatment can be carried out before densification by mechanical compaction. However, carrying out the stabilizing heat treatment after this densification also does not depart from the scope of the present invention.

[0028] In particular, during the drying heat treatment and the optional stabilizing heat treatment, a temperature less than or equal to 500 °C, for example a temperature less than or equal to 450 °C, can be applied.

[0029] The fact that a limited temperature is applied during heat treatment can avoid any risk of damaging the substrate due to exposure to excessive temperatures.

[0030] In an exemplary embodiment, the substrate is a compressor shaft or a turbine shaft, for example made of high-strength steel. BRIEF DESCRIPTION OF THE DRAWINGS

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[0047] Figure 1 and Figure 2 represent the deposition of the cathodic protection particles 11 on the substrate 1 within the scope of the exemplary method according to the present invention. This deposition is carried out by electrophoresis with the organic electrolyte 10, which contains the particles 11 suspended in the organic liquid medium. The particles 11 and the organic liquid medium can have different compositions, as described below. The particles 11 can be the only particles suspended in the organic liquid medium, but when the electrolyte 10 also contains other particles different from the particles 11 suspended in the organic liquid medium, it does not deviate from the scope of the present invention. The average size D50 of the additional particles can be smaller than the average size D50 of the particles 11. Compared with the particles 11, the other particles can be present in small amounts. Advantageously, other particles with limited hardness can be selected so as to deform during the mechanical compaction process and not interfere with this step. The other particles can be metallic or ceramic. The substrate 1 to be coated is immersed in the organic electrolyte 10. The surface of the substrate 1 intended to be coated with the particles 11 can be prepared in a conventional manner by chemical and / or mechanical stripping in advance. The surface of the substrate 1 includes a conductive material. The substrate 1 can be made of a metallic material (such as aluminum or aluminum alloy), or made of steel. A substrate 1 made of a composite material can also be used as long as its conductivity is sufficient for the deposition of the particles 11 by electrophoresis. The substrate 1 is a turbine component, such as a component of an aircraft turbine engine or an industrial turbine. The substrate 1 can be a compressor shaft or a turbine shaft. The substrate 1 can be used at a temperature less than or equal to 1000 °C, for example less than or equal to 500 °C, depending on the material used for the substrate.

[0048] As Figure 1 and Figure 2 shown, the substrate 1 includes an electrode connected to the first terminal of the generator G. The counter electrode 15 faces the surface of the substrate 1 to be coated and is also immersed in the electrolyte 10. The counter electrode 15 is connected to the second terminal of the generator G different from the first terminal. A stirring device (not shown) may be present in the electrolyte 10 to ensure the mixing of the bath during deposition. Due to the application of an electric field between the substrate 1 and the counter electrode 15, the charged particles 11 move and deposit on the substrate 1 to obtain a deposit 6 of the particles 11. The particles 11 may deposit in contact with the substrate 1. In the illustrated embodiment, the substrate 1 is negatively charged during deposition while the particles 11 are positively charged. However, it does not depart from the scope of the present invention if the substrate 1 is positively charged and the particles 11 are negatively charged.

[0049] The average size D50 of the particles may be less than or equal to 30 μm, for example between 10 nm and 30 μm. Various forms of particles may be used. According to one embodiment, the particles 11 have a shape factor substantially equal to 1, for example having a substantially spherical geometry. The particles 11 may be in solid form and the particles 11 may be metallic. The material of the particles 11 is selected according to the material of the substrate 1 for cathodic protection of the substrate 1. Thus, the particles 11 constitute a sacrificial material that preferentially corrodes compared to the underlying substrate 1 to protect the substrate 1. The cathodic protection coating obtained after mechanical compaction is conductive, thereby allowing conduction between the coating and the substrate and obtaining this preferential corrosion of the cathodic protection particles 11. The material of the particles 11 is selected to allow an oxidation / reduction pair having a standard potential strictly less than that formed by the material of the substrate 1. For example, for a substrate 1 made of steel, cathodic protection particles 11 made of aluminum or aluminum alloy may be used, but particles 11 made of, for example, zinc or zinc alloy, or magnesium or magnesium alloy may also be used for the same substrate 1.

[0050] Before starting deposition by electrophoresis, the mass content of the particles 11 in the electrolyte 10 may be greater than or equal to 0.1%, for example between 0.1% and 20%.

[0051] Before starting deposition by electrophoresis, the mass content of the organic liquid medium in the electrolyte 10 may be greater than or equal to 75%, for example between 75% and 99.9%.

[0052] At least 50% by volume of the organic liquid medium can be formed by an organic compound or a mixture of organic compounds. The organic compound or the mixture of organic compounds can be present in the organic liquid medium at a volume content of greater than or equal to 75%, for example greater than or equal to 95%. The organic liquid medium can be substantially anhydrous or have a limited water content such that deposition is substantially not affected by the phenomenon of water electrolysis. The volume content of water in the organic liquid medium can generally be less than or equal to 5%.

[0053] According to one example, at least 50% by volume of the organic liquid medium is formed by an alcohol or a mixture of alcohols. The alcohol or the mixture of alcohols can be present in the organic liquid medium at a volume content of greater than or equal to 75%, for example greater than or equal to 95%. One or more alcohols used can be C2 or C3 alcohols, for example selected from ethanol and propan-2-ol. It should be noted that the organic liquid medium is not necessarily an alcohol. According to one example, the medium can contain acetone or can be formed only of acetone.

[0054] The organic liquid medium can contain a dispersant. The dispersant can be a steric, ionic or electrosteric dispersant. Among ionic dispersants, metal salts can be used, such as chlorides and nitrates, for example: AlCl3.6(H2O), MgCl2.6(H2O), Mg(NO3)2.6(H2O), and Al(NO3)3.9(H2O). The dispersant can be present in the organic liquid medium at a concentration greater than or equal to 0.1 mmol.L -1 , for example between 0.1 mmol.L -1 and 2.5 mmol.L -1 . Other salts can be considered; such as sulfates or phosphates. Other types of ionic dispersants are also possible, such as diiodides, mixtures of diiodides and acetone (see publication: Journal of the European Ceramic Society (2011), Volume 31, pages 1075 - 1086) or triethylamine (TEA). Electrosteric dispersants can be used, such as polyelectrolytes, such as polyethyleneimine or polyacrylic acid. As mentioned above, it is advantageous to use propanol in electrolyte 10 as this makes the use of a dispersant redundant.

[0055] The deposition of particles 11 can be carried out by applying a DC or pulsed voltage. During deposition, an electric field greater than or equal to 5 V.cm -1 , for example between 5 V.cm -1 and 200 V.cm -1 , or even between 5 V.cm -1 and 60 V.cm -1 can be applied.

[0056] According to an alternative, a DC or pulsed current can be applied during the deposition of the particles 11. A surface current density greater than or equal to 10 nA.cm -2 can be applied during the deposition, for example between 10 nA.cm -2 and 10 mA.cm -2 .

[0057] The deposition of the particles 11 on the substrate 1 can be carried out for a time greater than or equal to 10 seconds, for example between 10 seconds and 1 hour.

[0058] The thickness e of the deposit 6 of the particles 11 on the substrate 1 can be greater than or equal to 1 μm, for example greater than or equal to 40 μm. This thickness e can generally be between 1 μm and 300 μm, for example between 40 μm and 300 μm. The volume porosity of the deposit 6 of the particles 11 on the substrate 1 can be greater than or equal to 50%, for example between 50% and 60%. The thickness e and the porosity of the deposit 6 are controlled by the electrophoretic deposition time and the voltage or current applied during the electrophoretic deposition. The electrical parameters employed are determined by those skilled in the art according to the electrolyte 10 used.

[0059] Details related to the electrophoretic deposition step of the particles 11 have just been described. The following attempts to describe in combination Figure 3 details related to the formation of the inorganic matrix in the pores of the deposit 6.

[0060] The impregnating composition 20 is impregnated into the pores of the deposit 6 of the particles 11 to form the inorganic matrix 40. Figure 3 The example shown in illustrates the impregnation by the soaking and removal technique. In this technique, the substrate 1 coated with the deposit 6 of the particles 11 is connected to a movable device 30 to immerse the substrate 1 in a bath of the impregnating composition 20 for impregnation. Generally, the impregnating composition 20 can be in liquid form. For example, the speed of removing the substrate 1 by the device 30 can be between 1 mm.min -1 and 1000 mm.min -1 . The viscosity of the impregnating composition 20 at 20 °C can be between 1 mPa.s and 500 mPa.s, for example between 1 mPa.s and 200 mPa.s. The viscosity is measured using a rheometer with a shear rate of 644 s -1 . Those skilled in the art will readily recognize that other impregnation methods are possible, such as impregnation by manual or automatic spraying. The impregnating composition 20 can fill at least 50% of the volume of the pores of the deposit 6, for example at least 75% of this volume, or even substantially the entire volume.

[0061] The impregnating composition 20 may comprise at least one sol-gel precursor or an alkali metal silicate or an alkaline earth metal silicate. The impregnating composition 20 may, for example, comprise sodium silicate Na2SiO3 or calcium silicate or magnesium silicate. The sol-gel precursors may be selected from: silanols such as TEOS (tetraethoxysilane) and TMOS (tetramethoxysilane), sol-gel precursors containing aluminum such as aluminum tri-sec-butyrate and aluminum triisopropoxide, or sol-gel precursors containing zirconium such as zirconium tetrapropoxide. Like the cathodic protection coating 50 to be obtained, the impregnating composition 20 may be phosphate-free, in particular free of aluminum phosphate. Like the cathodic protection coating 50 to be obtained, the impregnating composition 20 may be free of chromium-based compounds in the +VI oxidation state. Like the cathodic protection coating 50 to be obtained, the impregnating composition 20 may be free of chromates or lead compounds. These properties make it possible to comply with environmental regulations.

[0062] Once impregnation has been carried out with the impregnating composition 20, the deposit 6 impregnated with the impregnating composition 20 may be heat-treated to consolidate the deposit of cathodic protection particles impregnated with the impregnating composition and to stabilize the deposit. This heat treatment comprises at least one drying heat treatment such that it is possible to consolidate the deposit by expelling most of the liquid medium present in the impregnating composition and retaining the solid part binding the particles 11. During the drying heat treatment, a temperature greater than or equal to 70°C, for example between 70°C and 100°C, may be applied. The duration of the drying heat treatment may be greater than or equal to 1 hour, for example between 1 hour and 3 hours.

[0063] If necessary, a stabilizing heat treatment may be carried out to completely remove the liquid medium and obtain a water-insoluble protective coating. As described above, drying and stabilization may be carried out during a common heat treatment, or a second stabilizing heat treatment may be carried out at a higher temperature after a first drying heat treatment. In the latter case, during the stabilizing heat treatment, a temperature greater than or equal to 250°C, or even between 250°C and 500°C, may be applied.

[0064] The heat treatment (including drying and optional stabilization techniques) may lead to a chemical transformation of the impregnating composition, for example to its polymerization in the case of sol-gel precursors. The chemical transformation of the impregnating composition experienced during the heat treatment may be different from pyrolysis.

[0065] During the heat treatment, a temperature less than or equal to 500°C, for example less than or equal to 450°C, may generally be applied. A temperature greater than or equal to 200°C, for example between 200°C and 500°C or between 200°C and 450°C, is generally applied during the heat treatment. The heat treatment may be carried out for at least one hour, for example at least ten hours. The heat treatment may be carried out in air.

[0066] After the dry heat treatment, the impregnated impregnation composition 20 can be compacted to further densify the deposit of the particles 11. This compaction can be carried out by spraying organic or inorganic particles, such as particles made of corundum, glass or sodium bicarbonate. Water-soluble particles can be sprayed to produce compaction, such as particles made of sodium bicarbonate. The document FR 3102 694 describes a usable compaction technique.

[0067] A conductive cathodic protection coating 50 is obtained, which comprises an inorganic matrix 40 derived from the impregnation composition 20, and this inorganic matrix 40 holds the particles 11 together and ensures their attachment to the substrate 1. As described above, if the compaction is carried out after drying but before stabilization, this does not depart from the scope of the present invention.

[0068] Examples

[0069] Example 1: Obtaining a covered electrophoretic deposition with a significant thickness

[0070] A deposit 6 of aluminum particles 11 is produced on the surface of a substrate made of steel by electrophoresis. The covered substrate is as Figure 4 shown. Deposition is carried out using an electrolyte 10 formed by a suspension of aluminum particles 11 in pure propan-2-ol (without adding any additives). The deposition is carried out for 10 minutes while applying an electric field of 30 V / cm -1 . The deposit is covered, uniform and has a significant thickness, which is equal to 100 μm in this case. Figure 4 The resin shown corresponds to the epoxy resin used to coat the samples so that the samples can be observed with a scanning electron microscope.

[0071] Example 2: Influence of time on the deposition of cathodic protection particles

[0072] Multiple depositions of aluminum particles (10 g / L) are carried out in an electrolyte of pure propan-2-ol by applying a constant electric field of 10 V / cm -1 and by varying the deposition time between 3 minutes and 20 minutes.

[0073] The thickness of the obtained deposits varies from 15 μm to 90 μm with the change of the deposition time ( Figure 5 ). Within this deposition time range, no decrease in the deposition rate is observed, which indicates that higher thicknesses can be obtained at longer deposition times. The only theoretical limitation on the coating thickness would come from the depletion of the particles in the suspension. No peeling of the deposit is observed until the thickness is about 200 μm. Throughout the deposition time range, the measured porosity of the deposits is similar and in the range of 50% to 60%, as Figure 6 shown. The porosity is independent of the deposition time.

[0074] Example 3: Influence of the electric field on the deposition of cathodic protection particles

[0075] Multiple depositions of aluminum particles were carried out in a pure propanol - 2 electrolyte, while applying a deposition time of 10 minutes and varying the applied electric field between 5 V.cm -1 and 60 V.cm -1 . The results obtained are as shown in Figure 7 and Figure 8 . Aluminum powder deposits with a thickness controllable in the range of 5 μm to 220 μm can be produced by electrophoresis ( Figure 7 ), while maintaining a similar microstructure with a porosity of 50% to 60% ( Figure 8 ). Higher thickness values up to 500 μm can be obtained by applying higher electric field values.

[0076] Example 4: Proof of cathodic protection provided by the coating obtained by implementing the present invention

[0077] A deposit 6 of aluminum particles 11 was obtained on a substrate made of steel by applying an electric field of 10 V.cm -1 for 10 minutes. Then, the deposit was impregnated with sodium silicate by soaking and removing at a rate of 300 mm.min -1 . Heat treatment was carried out at 400 °C for 3 hours, and then the deposit was densified by mechanical compaction by spraying sodium bicarbonate particles with a particle size between 100 μm and 300 μm under a relative pressure of 3 bar.

[0078] A current coupling experiment was carried out for a time of 5 minutes to prove that the coating thus obtained indeed has cathodic protection for the underlying steel substrate. The assembly 100 used is as shown in Figure 9 . The test coating 50 was electrically connected to the bare steel substrate 110 via a zero - resistance ammeter (ZRA). The current flowing between the two electrodes was measured, which corresponds to the current coupling current. The common potential (potentiel commun) taken by the electrodes was also measured and plotted as a function of time. As shown in Figure 9 , the working electrode WE was connected to a substrate made of 15CDV6 bare steel. The counter electrode CE was either bare steel 1 (used as a reference) or the coating 50 ( Figure 9 the symbol 1 / 50 in Figure 9 indicates the bare substrate 1 or the coating 50). The reference electrode 120 was an Ag / AgCl electrode. The electrode assembly was immersed in a bath 130 of 0.05 M sodium chloride.

[0079] As shown in Figure 10As shown, the common potential (curve "A") taken by the bare substrate connected to the coating 50 is a more cathodic potential compared to the substrate (curve "B") connected to the same bare substrate 1. The greater the negative current coupling potential indicates that the cathodic protection is indeed effective. According to Figure 11 , the measured current coupling current density stabilizes at -30 μA·cm -2 value (curve "A"), which indicates that the coating 50 provides electrons to the bare substrate 110 through its oxidation, thereby cathodically polarizing it and thus being protected.

[0080] Images of various electrodes were taken after the current coupling test. When two substrates made of bare steel are the same and connected to each other, no significant current is observed, and there are obvious corrosion points on both substrates after the test ( Figure 12 and 13 ). In the case where the bare substrate is connected to the test coating, no corrosion points can be seen on the steel after the current coupling test ( Figure 14 ). The tested coating no longer shows obvious degradation ( Figure 15 ).

[0081] Example 5: Effect of mechanical compaction

[0082] On a substrate made of 15CDV6 steel, a deposit of aluminum particles is obtained by electrophoresis from a suspension of aluminum particles dispersed in propan-2-ol (without additives). The deposition is carried out by applying a series of pulsed voltage cycles that alternate between a zero potential difference and a +10 V potential difference, with a duty cycle of 1 / 6. The application frequency of the pulses is equal to 1 Hz, and the total treatment time is 30 minutes.

[0083] Then the deposit is impregnated with sodium silicate by immersion and removal at a rate of 300 mm·min -1 . Then, the assembly is heat-treated at 400 °C for 3 hours and then densified by mechanical compaction by spraying sodium bicarbonate particles with a particle size between 100 μm and 300 μm at a relative pressure of 3 bar. A reference deposit corresponding to the aforementioned deposit in all aspects is also carried out using the same procedure, except that the compaction is omitted. The thickness of the uncompacted deposit is 22 μm, and the thickness of the compacted deposit is 18 μm.

[0084] The corrosion test is carried out under the following conditions: immersion in a solution of water + 0.05 M NaCl or 3 g / L NaCl. The test tubes are continuously monitored with regularly taken photos.

[0085] The results obtained after this test are as shown in Figure 16As shown, the photos related to the uncompacted reference coating are provided in the left column, and the pictures related to the compacted coating are provided in the right column. In the uncompacted case, the coating acts as a barrier. However, the inherent defects in the deposit leave channels for the corrosive product to reach the substrate and initiate corrosion of the steel substrate. Compaction enables densification of the deposit by bringing the aluminum particles contained in the deposit into contact. Bringing the aluminum particles into contact ensures the formation of a dense conductive film, and the aluminum acts as a sacrificial anode, thereby improving corrosion resistance and slowing the appearance of corrosion sites, as Figure 16 shown.

[0086] The expression "between... and..." shall be understood to include the limiting values.

Claims

1. A method for forming a cathodic protection coating (50) on a substrate (1) for forming a turbine component, the cathodic protection coating (50) being free of chromium-based compounds in the +VI oxidation state, the method comprising at least: - depositing particles (11) for cathodic protection of the substrate on the substrate, the deposition being carried out by electrophoresis through an organic electrolyte (10), the organic electrolyte (10) comprising at least the particles suspended in an organic liquid medium, and due to the application of an electric field between the substrate and a counter electrode (15), the charged particles move and deposit on the substrate to obtain a deposition of particles, and - forming an inorganic matrix (40) in the pores of the resulting particle deposit (6), at least comprising: · impregnating (20) the deposit with an impregnating composition by an immersion and removal technique, · subjecting the deposit impregnated with the impregnating composition to a dry heat treatment, and · after the dry heat treatment, densifying the deposit by mechanical compaction to render the deposit conductive.

2. The method according to claim 1, wherein, The organic electrolyte (10) comprises an alcohol liquid medium in which the particles (11) are suspended.

3. The method according to claim 2, wherein At least 50 vol% of the alcohol liquid medium is formed by propanol.

4. The method according to any one of claims 1 to 3, wherein, The thickness (e) of the deposit (6) of cathodic protection particles (11) on the substrate (1) is greater than or equal to 40 μm.

5. The method according to any one of claims 1-3, wherein, The cathodic protection particles (11) are made of aluminum or an aluminum alloy.

6. The method according to claim 4, wherein, The cathodic protection particles (11) are made of aluminum or an aluminum alloy.

7. The method according to any one of claims 1-3 and 6, wherein, The substrate (1) is made of steel.

8. The method according to claim 4, wherein, The substrate (1) is made of steel.

9. The method according to claim 5, wherein, The substrate (1) is made of steel.

10. The method according to any one of claims 1-3, 6 and 8-9, wherein, The impregnating composition comprises at least one alkali metal silicate or alkaline earth metal silicate.

11. The method according to claim 4, wherein, The impregnating composition comprises at least one alkali metal silicate or alkaline earth metal silicate.

12. The method according to claim 5, wherein The impregnating composition comprises at least one alkali metal silicate or alkaline earth metal silicate.

13. The method according to claim 7, wherein, The impregnating composition comprises at least one alkali metal silicate or alkaline earth metal silicate.

14. The method according to any one of claims 1-3, 6, 8-9 and 11-13, wherein, The formation of the inorganic matrix comprises a stabilizing heat treatment of the deposit, the dry heat treatment being carried out at a first temperature and then the stabilizing heat treatment being carried out at a second temperature greater than the first temperature; or a single and identical treatment step is carried out, in which case the deposit is both dried and stabilized, and in this case the stabilization and the dry heat treatment are combined.

15. The method according to claim 14, wherein, The stabilizing heat treatment is carried out before densification by mechanical compaction.

16. The method according to claim 14, wherein, A temperature of less than or equal to 500 °C is applied during the dry heat treatment and the optional stabilizing heat treatment.

17. The method according to claim 15, wherein, A temperature of less than or equal to 500 °C is applied during the dry heat treatment and the optional stabilizing heat treatment.

18. The method according to any one of claims 1-3, 6, 8-9, 11-13 and 15-17, wherein, The densification of the deposit by mechanical compaction is carried out by jetting particles.

19. The method according to any one of claims 1-3, 6, 8-9, 11-13 and 15-17, wherein, The substrate (1) is a compressor shaft or a turbine shaft.

20. The method according to claim 18, wherein The substrate (1) is a compressor shaft or a turbine shaft.

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