EP0848079A1 - Method for depositing a protective coating with great efficiency against corrosion at high temperatures for superalloys, protective coating and pieces protectes with such a coating - Google Patents

Abstract

A superalloy component is protected by forming on it a porous layer comprising a powdered alloy containing aluminium, chromium, an active ingredient, such as yttrium and rare earths of the yttric and lanthanidics groups. At least one platinum group metal, such as platinum, palladium, rhodium, ruthenium, osmium, iridium and alloys of these, is mixed with or applied on top of the layer and renders it impervious. Also claimed are a protective coating formed as above, in which the ingredients coexist throughout the thickness, and a superalloy component so coated.

Description

The invention relates to a method for producing coatings. protectors against high temperature oxidation and hot corrosion of superalloy parts, a coating protector obtained by such a process and parts made of superalloy protected by this coating. Application including the protection of hot parts of superalloy turbomachinery.

Turbine engine manufacturers, both terrestrial that aeronautics, have faced for more than thirty years imperatives to increase the efficiency of turbomachines, reduction in their specific fuel consumption as well as pollutant emissions of COx, SOx, NOx and unburnt. One of the ways to meet these imperatives is to get closer to the combustion stoichiometry fuel and therefore increase the gas temperature leaving the combustion chamber and impacting the first turbine stages. It is then necessary to return the turbine materials compatible with this elevation of flue gas temperature. One solution is to develop the refractoriness of the materials used to increase the temperature limit for use and service life by creep and fatigue. This solution has been widely implemented work during the appearance of superalloys based on nickel and / or cobalt. It has experienced a technical evolution considerable by the transition from equiaxed superalloys to monocrystalline superalloys (gain of 80 to 100 ° C in creep).

Another important development in the technology of turbines is linked to new sales and guaranteed in this area. The life of the turbines terrestrial and aeronautical are most often guaranteed customer. There is therefore considerable economic interest for a turbine engine manufacturer to increase so significant service life of the components, in particular the components of the so-called hot parts.

Such an evolution in technology poses the problem of improving the protection of the components of the hot part against oxidation at high temperature (T> 950 ° C. approximately) and hot corrosion (at intermediate temperature in the presence of SO ₂ / SO ₃ and deposits of molten salts such as sulfates and / or vanadates).

Among the protective coatings of superalloys against high temperature oxidation and hot corrosion, two large families of coatings are usually distinguished.

These two families are simple aluminum coatings and their derivatives and alloy coatings.

The coatings belonging to the family of simple aluminides and their derivatives essentially consist of a nickel aluminide alloy NiAl comprising an atomic percentage of aluminum of between 40 and 55%. This type of alloy forms by oxidation at high temperature a protective layer of aluminum oxide limiting the interaction of the coating with the environment (oxygen, molten salts, SO ₂ / SO ₃ ). These coatings can be deposited thermochemically by case hardening or in the vapor phase. They can also be obtained by depositing aluminizing paint followed by appropriate annealing. The main advantage of these coatings lies in their simplicity of implementation, low production costs, the possibility of homogeneously coating parts of complex shape.

However, the performance of these types of coating is limited. In the area of high temperatures, alumina formed is constrained and not very adherent; she flakes easily during thermal cycling causing aluminum consumption and depletion of the part external of the coating. This consumption seriously limits the life of the coating which turns out to be very short protective once the aluminum reserve has been consumed. In the field of hot corrosion, the layer of pure alumina formed can be dissolved by interaction with molten sulphate salts or mixtures sulfates / vanadates.

A good way to significantly increase lifespan of these coatings is to modify the simple aluminide NiAl by different elements such as chromium and / or certain precious metals from the platinum mine. The operation consists then to make a pre-deposit on the superalloy part or modifier metals, followed by aluminization. In in some cases, a specific heat treatment is carried out between the so-called pre-deposition step of the modifier metal and the actual aluminization step.

The use of chromium as a modifier metal is described for example in French patent 2,559,508 filed by SNECMA. In this patent chromium can be applied by way thermochemical. The role of chromium is then essentially limit the acidity or basicity of molten salts by so-called hot corrosion conditions, by dissolution of cations playing the acid-base role of buffer in salt molten.

The use of platinum as a modifier metal is described in particular by patent FR 2 018 097. In this case platinum can be deposited electrolytically on the workpiece superalloy. This precious metal returns to proportions important in solid solution in the ß-NiAl phase of nickel aluminide. It gives both better adhesion to the protective alumina layer (oxidation cyclic) and good environmental resistance by presence of molten salts (hot corrosion).

An interesting alternative to the use of platinum as metal modifier for simple aluminide coatings consists of replacing it with palladium. The coatings thus obtained have, as the French patent teaches us FR 2 638 174, resistance to oxidation and corrosion to hot equivalent to that of aluminides modified by the platinum, for a much lower cost price.

Unlike simple aluminide coatings and their derivatives, alloy coatings are not obtained using processes involving high diffusion temperature between the superalloy substrate and the coating under development. For these coatings at on the contrary, an alloy is already deposited on the substrate made of a composition suitable for functionality sought such as resistance to oxidation and hot corrosion.

The most commonly used alloy coatings for high temperature protection applications for superalloy substrates are type coatings MCrAlY. For these coatings, the symbol M represents the base alloy which may be cobalt, nickel, iron, or a combination of these three metals. Chromium is present between 10 and 40% by mass and is mainly used to increase the resistance of coatings to hot corrosion. Aluminum is present in contents between 2 and 25 % by mass. Its major role is the hot forming of a protective layer of alumina which it is desired to be at slow growth, as chemically stable as possible to resist hot corrosion and extremely adherent so as to withstand the stresses of expansion differential during thermal cycling at temperature high. Yttrium Y is present at levels between a few tens of ppm and a few percent by mass. His role is twofold:

It is capable of trapping in the form of very stable sulphides the residual sulfur of the alloys, thus preventing it from diffusing hot towards the coating / oxide interface where it tends to segregate, thus greatly limiting the adhesion of the layer of alumina.
It is incorporated in the form of mixed oxides of yttrium and aluminum at the grain boundaries of the layer of alumina formed. These mixed oxides modify the diffusion mechanisms in alumina to lead to the formation of an alumina free from residual growth constraints, and therefore much more adherent to the coating.
In general, yttrium is a powerful promoter of coating / oxide adhesion in MCrAlY coatings.

Certain other elements such as hafnium, zirconium, cerium, lanthanides and generally most rare earths can play a role very similar to that of yttrium on the adhesion of protective alumina layers. In addition, the contribution of yttrium and related elements sometimes called active elements, to the effectiveness of protective coatings of superalloys is limited to only high temperature oxidation. No type effect active element could not be highlighted in the case of hot corrosion of coated superalloys.

La projection thermique plasma sous air, sous vide ou sous atmosphère contrôlée,

La projection thermique HVOF (en anglais : high velocity oxygene fuel) et autres procédés de projection thermique,

Le canon à détonation,

Le placage par explosion,

L'évaporation sous bombardement électronique,

L'évaporation par plasma multi-arc,

Les techniques de pulvérisation cathodique.

The alloy coatings can be deposited by techniques such as:

Plasma thermal spraying under air, under vacuum or under a controlled atmosphere,

HVOF thermal spraying (in English: high velocity oxygen fuel) and other thermal spraying processes,

The detonation cannon,

Explosion plating,

Evaporation under electronic bombardment,

Multi-arc plasma evaporation,

Sputtering techniques.

All these techniques have several disadvantages in common adults; they have a high cost of implementation, it is difficult to control the quality of the deposits, and it is difficult to control the deposit of MCrAlY on parts complex in shape because these are directional techniques which do not allow uniform coating of parts complex in shape.

To find alternatives to the use of the two families of coatings as described above, several solutions have been developed.

A first solution consists of the coatings of Aluminized MCrAlY.

Aluminization in pack or vapor phase on a MCrAlY coating deposited by one of the techniques mentioned above has the advantage of obtaining a external composition of the coating enriched with aluminum, this which extends the life of the coating, in particular by high temperature oxidation condition.

However, this solution is not much better than applying a classic MCrAlY and suffers from the same limitations concerning the control of homogeneity on parts of complex shape and the cost of production.

A second solution is made up of electrophoretic MCrAlY coatings.
The process for producing this type of coating is described, for example, in patent FR 2,529,991 filed by SNECMA. The method consists in depositing on a substrate made of nickel-based superalloy a coating composed of agglomerated MCrAlY alloy powders, by a suitable electrophoresis technique. This porous deposit having no mechanical strength, it is necessary to fill the porosity by aluminization in the vapor phase. The aluminization plays the role of consolidation and filling of the pores left between the agglomerated MCrAlY powder grains. The final structure is very similar to that of a traditional aluminized MCrAlY coating.

The slightly directional electrophoretic technique allows evenly form shaped parts complex than turbine distributor vane doublets. This technique is much less expensive than a coating MCrAlY deposited by plasma then aluminized for a quality of equivalent protection. However the coating obtained has a limited performance gain compared to a MCrAlY coating alone.

(1) Dépôt d'alliage MCrAlY par projection thermique,

(2) Chromisation thermochimique optionnelle,

(3) Aluminisation thermochimique,

(4) Dépôt électrolytique de platine

(5) Traitement thermique de diffusion du dépôt de platine dans la partie externe du revêtement de MCrAlY aluminisé.

A third solution consists of the combination of an McrAlY coating deposited by plasma and a precious metal as described for example in European patent EP 0 587 341 A1. The coating is obtained by a process comprising the following steps:

(1) MCrAlY alloy deposition by thermal spraying,

(2) Optional thermochemical chromization,

(3) Thermochemical aluminization,

(4) Electrolytic deposition of platinum

(5) Heat treatment for diffusion of the platinum deposit in the external part of the coating of aluminized MCrAlY.

This coating has the major drawback of not comprising, by construction, platinum only in its external part. In done, it is the overlay of a coating of MCrAlY traditional and an aluminide coating modified by the platinum. The beneficial effects of MCrAlY coatings and platinum modified aluminide coatings are juxtaposed but not added. The synergy of effects does therefore cannot be obtained. Furthermore, the total thickness of the coating is at least equal to 100µm, which can pose problems with added mass when the coating is performed on rotating parts. In addition, such coating is, of a very high cost price (at least equal to the sum of the prices of a traditional MCrAlY coating and a platinum modified aluminide). Finally the problem coating of complex shaped parts always arises acutely.

• d'obtenir un revêtement protecteur combinant de manière synergique les effets bénéfiques du chrome et des éléments actifs d'une part, de l'ajout de métal précieux à la phase ß-NiAl, d'autre part,
• de s'affranchir des techniques de dépôt directionnelles, afin de pouvoir réaliser avec facilité un dépôt d'épaisseur et de qualité homogène sur des pièces de forme complexe,
• de limiter l'épaisseur totale du revêtement en dessous de 100 µm si nécessaire.

The object of the invention is to solve the drawbacks presented by the various known protective coatings and to determine a process for producing a protective coating against high temperature oxidation and hot corrosion of mechanical parts made of superalloys which allows :

• to obtain a protective coating synergistically combining the beneficial effects of chromium and the active elements on the one hand, of the addition of precious metal to the ß-NiAl phase, on the other hand,
• to overcome directional deposition techniques, in order to be able to easily carry out a deposit of uniform thickness and quality on parts of complex shape,
• limit the total thickness of the coating below 100 µm if necessary.

For this, the invention consists in carrying out on the surface of a superalloy a first deposit of an alloy powder agglomerated containing at least chromium, aluminum and a active element, and to fill the open porosity of the deposit of powder by a second electrolytic deposit of precious metal from the platinum mine. Appropriate heat treatment is then performed to allow inter-broadcast between the powder-based coating and electrolytic coating and obtain a coating comprising over its entire thickness chromium, an active element such as Yttrium, and a metal precious from the platinum mine.

Advantageously a thermochemical aluminization treatment can be done in a final step to bring a additional aluminum in the final coating and complete the filling of the residual gaps between grains of powder deposited.

According to a variant, the invention consists in depositing, at the surface of a superalloy, an agglomerated alloy powder containing at least chromium, aluminum, an element active and at least one precious metal from the platinum mine and to fill the open porosity of the agglomerated powder deposit by an aluminization treatment.

The deposition of the alloy powder can be carried out by a electrophoretic technique or by painting technique with a thermodegradable or volatile binder.

The active element is chosen from the group consisting of Yttrium, Yttric or lanthanidic rare earths such that Zr, Hf, La, Ce.

The element of the platinum mine is chosen from the group consisting of platinum, palladium, Rhodium, Ruthenium, Osmium, Iridium and combinations of these metals.

• dans une première étape, à effectuer sur la pièce à revêtir un premier dépôt d'un alliage pulvérulent contenant au moins du chrome, de l'aluminium et un élément actif et comportant une porosité résiduelle ouverte,
• dans une deuxième étape, à combler la porosité résiduelle ouverte du premier dépôt pulvérulent par un deuxième dépôt électrolytique métallique contenant au moins un élément de la mine du platine,
• dans une troisième étape, à effectuer un traitement thermique permettant d'assurer l'interdiffusion entre le premier dépôt pulvérulent et le deuxième dépôt électrolytique.

According to the invention, the process for producing a protective coating against high temperature oxidation and hot corrosion of parts made of superalloys, is characterized in that it consists:

• in a first step, to perform on the part to be coated a first deposit of a powdery alloy containing at least chromium, aluminum and an active element and comprising an open residual porosity,
• in a second step, filling the open residual porosity of the first powdery deposit with a second metallic electrolytic deposit containing at least one element of the platinum mine,
• in a third step, to carry out a heat treatment making it possible to ensure interdiffusion between the first powdery deposit and the second electrolytic deposit.

The invention also relates to a protective coating obtained by this production process and a superalloy part comprising this protective coating.

• la figure 1, des schémas montrant l'évolution de la structure du revêtement obtenu au cours des différentes étapes du procédé, selon l'invention,
• la figure 2, un tableau indiquant des exemples de compositions d'une poudre d'alliage de type MCrAlY pouvant être utilisées pour la réalisation du revêtement, selon l'invention,
• les figures 3 et 4, illustrent respectivement sous forme d'un tableau et de courbes, un exemple de répartition (en pourcentages atomiques), dans l'épaisseur du revêtement, des principaux éléments du revêtement, selon l'invention.

Other features and advantages of the invention will appear clearly in the following description given by way of nonlimiting example and made with reference to the appended figures which represent:

• FIG. 1, diagrams showing the evolution of the structure of the coating obtained during the different stages of the process, according to the invention,
• FIG. 2, a table showing examples of compositions of an MCrAlY type alloy powder which can be used for producing the coating, according to the invention,
• Figures 3 and 4 illustrate respectively in the form of a table and curves, an example of distribution (in atomic percentages), in the thickness of the coating, of the main elements of the coating, according to the invention.

The development of the coating according to the invention comprises several successive stages described below in conjunction with figure 1.

The coating is deposited on a sample 10 or a part nickel or cobalt-based superalloy, equiaxial, with directed or monocrystalline solidification, taking the place of substrate, such as for example and without limitation the superalloys known under the names: IN100, DS200, DS186, MAR M 247, DS247, MAR M 509, René 77, René 125, HS31, X40, AM1, AM3.

M est un métal de base Ni et/ou Co et/ou Fe,

Cr : entre 10 et 40 % massique

Al : entre 2 et 25 % massique

Y : entre 0 et 2,5 % massique

The first step 1 of the process for producing the coating consists in producing a first deposit 11 of alloy formed on the surface of the sample 10 or of the part to be coated, formed by the agglomeration of quasi-spherical powder grains, and having a residual porosity composed essentially of the space left between the grains of said powder. The alloy powder used is of the MCrAlY type and its composition is as follows:

M is a base metal Ni and / or Co and / or Fe,

Cr: between 10 and 40% by mass

Al: between 2 and 25% by mass

Y: between 0 and 2.5% by mass

It is preferable to use powders whose composition in mass percentages is reproduced in the table of figure 2.

Variations in the composition of these powders can occur without departing from the scope of this invention, such as by example the replacement of all or part of the active element Y by one or more other active elements taken in the following list: Zr, Hf, La, Ce and more generally the yttrique or lanthanidic rare earths.

The particle size of the powder can be between 2 and 100 micrometers, preferably between 4 and 15 µm. It is particularly advantageous to use a particle size of fine powder, because it will on the one hand limit the final surface roughness of the coating and on the other hand limit the size of the residual porosities after the electrophoretic deposition. The risk of persistence of porosity in the coating after its final stage of development is finds decreased by the same amount.

This first deposit can be made using for example a painting technique with thermodegradable binder or volatile, or advantageously an electrophoretic technique.

The electrophoretic technique consists in carrying out a porous skeleton of metallic powders by immersing the parts to be coated in an insulating solution containing suspension of the powders to be deposited. The homogeneity of the suspension is ensured by agitation, which avoids sedimentation of particles at the bottom of the tank electrophoresis. The parts to be coated are positioned and cathode polarized. The anode consists of an electrode shaped arranged opposite and / or around the part to be coated, in order to obtain a homogeneous distribution of the electric field in the vicinity of the part, and thus the thicknesses of the deposit regular. The metallic particles are charged electrically in the electrostratic field and migrate quickly towards the surface of the room where they agglomerate by the Coulomb attraction. Parties not to be coated are protected by masking assemblies made in materials chemically compatible with the bath electrophoresis. Keeping parts in the tank and electrical connections of the parts are also ensured by the assembly comprising the mask (s). The difference of potential applied between anode and cathode, ensuring the migration of metallic particles, is between 200 and 500 V. The duration of deposit is between 1 second and 1 minute (typically less than 10 seconds) depending on the particle size of the powders to be deposited, and the thickness of the deposit wanted.

The deposited coating is not dense, but easily manipulated as shown in FIG. 1. The coating thicknesses can be between 20 and 200 μm at this stage, preferably between 30 and 60 μm. Depending on the density and particle size of the powder used, this corresponds to a mass of deposited alloy of between 10 and 100 mg / cm ² , preferably between 20 and 60 mg / cm ² .

Elle met en oeuvre un équipement simple et peu onéreux,

Elle assure un dépôt homogène, y compris sur des pièces de forme complexe,

La faible durée du dépôt autorise une cadence élevée en production automatisée, ce qui réduit le prix de revient de cette première étape,

Le rendement de dépôt (masse de poudre déposée sur masse de poudre utilisée) est voisin de 100 %, contrairement aux techniques classiques de dépôt à partir de poudre (projection thermique par exemple), ce qui est économiquement très attractif.

The electrophoretic technique is particularly well suited to the first step of the process according to the invention since:

It implements simple and inexpensive equipment,

It ensures a uniform deposit, including on pieces of complex shape,

The short duration of the deposit allows a high rate in automated production, which reduces the cost price of this first stage,

The deposition yield (mass of powder deposited on mass of powder used) is close to 100%, unlike conventional techniques of deposition from powder (thermal spraying for example), which is economically very attractive.

The second step 2 of the coating production process is a step of electroplating a metal alloy containing at least one platinum mine metal. Preferably, this platinum mine alloy is chosen from pure platinum or a platinum-rhodium alloy, or another palladium-nickel alloy. Sample or piece having previously undergone step 1 of the process is immersed in an electrolytic metal or alloy deposition bath selected. An anode system and / or current thieves, is arranged around the sample or the part to be coated with so that the distribution of current densities is homogeneous at all points of the room, this using the know-how of a person skilled in the art of electroplating. The cathodic current density to be applied is chosen, in depending on the operating parameters of the bath used. This current density is sufficiently low, in order to allow the penetration of the electrolytic deposit in all the gaps left between the grains of powder deposited during step 1. The duration of the electrolysis is adjusted by so that the mass of precious metal deposited is between 5 and 70%, preferably between 20 and 50% of the total mass of deposits made during steps 1 and 2.

At the end of step 2, the coating 12 obtained is composed of the juxtaposition of the MCrAlY powder and the alloy metallic containing at least one platinum mine metal.

Du superalliage substrat,

De la composition de la poudre MCrAlY,

De la granulométrie de la poudre de MCrAlY,

De la composition de l'alliage métallique électrodéposé,

De l'éventualité d'un traitement ultérieur défini dans une étape 4 décrite ci-dessous.

The third step 3 is an annealing with the aim of interdiffusion between the grains of MCrAlY powder and the metal alloy containing at least one metal from the electrodeposited platinum mine. This annealing must imperatively be carried out under a neutral atmosphere (argon for example), reducing atmosphere (hydrogen for example), or under a vacuum better than 10 ^-4 Torrs. The temperature and the duration of the annealing are dependent on:

Substrate superalloy,

The composition of the MCrAlY powder,

The particle size of the MCrAlY powder,

The composition of the electrodeposited metal alloy,

The possibility of further processing defined in step 4 described below.

The annealing temperature can be between 750 and 1250 ° C and its duration between 15 minutes and 48 hours (preferably between 2 and 4 p.m.). In the event that none further processing is not planned, it is necessary that the annealing completely closes the residual porosity of the coating and that the interdiffusion between the powder grains of MCrAlY and the deposition of the electrodeposited metal alloy be complete. It is then necessary to apply the highest annealing temperatures and / or durations of anneals the longest. In the event that a treatment later described in step 4 below is planned, the densification of the coating and the interdiffusion between grains of MCrAlY powder and deposition of the alloy metallic electrodeposited is partly ensured by step 4. The temperatures and / or the annealing times can then to be weaker.

Step 4 of the method according to the invention is optional. She consists of aluminizing the coating according to conventional methods known to those skilled in the art. To this end, it is possible to use vapor phase aluminization or aluminization by applying paint aluminizing. It is also possible to apply checkout aluminization techniques.

This fourth step enriches the aluminum outer surface of the coating, thereby extending the life lifetime of this coating under high oxidation conditions temperature. This fourth step also makes it possible to complete the filling of the interstices left between the grains of powder deposited during the first stage.

According to a variant of the method for producing a protective coating, the first deposit made in step 1 is made from an MCrAlY type alloy powder additionally containing one or more metals from the mine of platinum.

The addition of one or more metals from the platinum mine can be done in different ways. It is possible to directly produce powders whose composition corresponds to the formula MCrAlY + MP where MP is a metal of the platinum mine or an alloy thereof. The techniques of manufacture of such powders are those corresponding to the state of the art in powder metallurgy. It is exhaustively, casting the alloy followed by a atomization step by arc or by rotating electrode. he it is also possible to use MCrALY powders conventional, having undergone a surface treatment subsequent so as to deposit on the periphery of the grains a alloy containing the metal of the MP platinum mine. This subsequent surface treatment can be for example a autocatalytic chemical deposit or not, a deposit electrolytic, an organometallic PVD or CVD type deposit. MCrALY + MP type powders are further characterized by the metal content of the MP platinum mine. In the framework of the invention, the metal of the platinum MP mine can represent between 2 and 60% by mass (preferably between 20 and 50%) relative to the total mass of the powder.

This first deposit is then directly followed by a deposit coating aluminization according to step 4 of process, steps 2 and 3 being omitted. In this case, for the aluminization depot, only aluminization techniques in vapor phase or by application of aluminizing paint can be used. Aluminization techniques in body are not possible because the friction of the powders aluminization cement on a powdery deposit directly from step 1 and not yet consolidated risks destroying the porous layer.

Example 1

The coating is produced on a sample in the form of wafers of dimensions 20 × 30 × 2 mm ³ made of DS200 + Hf alloy. This sample underwent a first electrophoretic deposition from a powder of CoNiCrAlY alloy, the composition of which is given in the table shown in FIG. 2. The particle size of the powder is centered on approximately 15 μm. The quantity of powder deposited corresponds to a mass gain of 15 mg / cm ² . This sample then underwent a second electroplating of Pd-20% mass Ni alloy. The current density used for this second deposit is 1 A / dm ² for a duration of approximately 45 minutes. The amount of palladium alloy deposited in this way is approximately ⁸ mg / cm ² (ie approximately 35% of the metallic mass deposited in total during these first two stages). In a third step, a two-hour secondary vacuum diffusion annealing at 850 ° C was carried out. Finally, in a fourth step, aluminization in the vapor phase using a cement alloy of Cr-30% by mass Al, and an activator of the NH ₄ F type was carried out at 1100 ° C. for 10 h. The coating obtained is dense, single-phase with a total thickness of approximately 80 μm. It is essentially composed of a ß (Ni, Co) Al phase containing in solid solution chromium, palladium and yttrium. Figures 3 and 4 illustrate the distribution of the main elements in the thickness of the coating. The atomic percentages were determined by electron microprobe analysis. The yttrium cannot be validly detected by this type of measurement but is detected with the electron microscope at higher magnification. Figures 3 and 4 show that the composition of the coating varies little in its thickness and in particular that the metal of the platinum mine is present in significant quantity throughout the thickness of the coating.

Example 2

The procedure is as in Example 1 except during the electrolytic deposition step where the amount of palladium alloy deposited corresponds to 12 mg / cm ² by increasing the duration of the electrolytic deposition in proportion. The mass of the palladium alloy then corresponds to approximately 44% of the metal mass deposited in total during the two deposition operations. The structure of the coating obtained is identical to that of Example 1, but the amount of palladium is greater (15 atomic% on average).

Claims (13)

Process for producing a protective coating against high temperature oxidation and hot corrosion of parts made of superalloys, characterized in that it consists: in a first step, to perform on the part to be coated a first deposit of a powdery alloy containing at least chromium, aluminum and an active element and comprising an open residual porosity, in a second step, filling the open residual porosity of the first powdery deposit with a second metallic electrolytic deposit containing at least one metal of the platinum mine, in a third step, to carry out a heat treatment making it possible to ensure interdiffusion between the first powdery deposit and the second electrolytic deposit so that the metal of the platinum mine is present throughout the thickness of the protective coating. Method for producing a protective coating according to the claim 1, characterized in that it further comprises a fourth step consisting in carrying out an aluminization of the coating obtained in step 3 so as to enrich this aluminum cladding and to complete the filling of its porosity. Method for producing a protective coating according to any one of claims 1 or 2, characterized in that the platinum mine metal deposited in the second stage is in proportion between 5 and 70% by mass per relative to the total mass of deposits made in the two first steps. Method for producing a protective coating according to any one of claims 1 to 3, characterized in that that the third stage heat treatment is performed at a temperature between 750 and 1250 ° C for a period of between 15 minutes and 48 hours. Method for producing a protective coating according to the claim 2, characterized in that the powdered alloy filed in the first step further contains at least one platinum mine metal and in that the second and third steps are omitted. Method for producing a protective coating according to the claim 5, characterized in that the metal of the mine of platinum is in proportion between 2 and 60% by mass relative to the total mass of the powder. Method for producing a protective coating according to any one of the preceding claims, characterized in that the deposition of a powdery alloy is carried out by an electrophoretic technique. Method for producing a protective coating according to any one of claims 1 to 6, characterized in that that the deposition of a powdery alloy is carried out by a painting technique comprising a thermodegradable binder or volatile. Method for producing a protective coating according to any one of the preceding claims, characterized in that the active element of the powdery alloy is chosen in the group consisting of Yttrium, rare earths Yttriques and rare earth lanthanides. Method for producing a protective coating according to any one of the preceding claims, characterized in that the element of the platinum mine is chosen from the group consisting of Platinum, Palladium, Rhodium, Ruthenium, Osmium, Iridium, and combinations of these metals. Protective coating obtained by the process of realization according to any one of the claims previous, characterized in that it comprises at least the Cr, Al elements, an active element and a metal from the Platinum, all these elements coexisting throughout the thickness of the coating. Protective coating according to claim 11, characterized in that it is used as an underlay of thermal barrier of a superalloy part. Superalloy part, characterized in that it comprises a protective coating according to claim 11.

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