The invention relates to a turbine part such as a turbine blade or vane for example distributor used in aeronautics.

STATE OF THE ART

In a turbojet engine, the exhaust gases generated by the combustion chamber can reach high temperatures, exceeding 1200 ° C or 1600 ° C. Parts of the turbojet, in contact with the exhaust gases, such as turbine blades for example, must thus be able to retain their mechanical properties at such elevated temperatures.

A tentative, the east known fabriquer certaines de pièces du en phase "superalliage». Les superalliages constituent une famille d'Alliages métalliques high résistance inflation travailler à des températures relativement leurs near points of fusion (0.7 to 0.8 typiquement fois leurs températures de fusion).

To enhance the thermal resistance of these superalloys and to protect against oxidation and corrosion, it is known to cover with a coating acting as a thermal barrier.

1 schematically illustrates a section of a turbine part 1, for example a 6 blade turbine or a nozzle vane. The piece 1 comprises a substrate 2 of monocrystalline metal superalloy coated with a thermal barrier 10.

2 schematically illustrates a section of a part of the thermal barrier of the turbine part 1, overlying a substrate. The thermal barrier comprises a metal underlayer 3, a protective layer 4 and a thermally insulating layer 9. The metallic sub-layer 3 covers the substrate 2 in metallic superalloy. The metallic underlayer 3 is itself covered with the protective layer 4, formed by oxidation of the metal underlayer 3. The protective layer 4 to protect the superalloy substrate from corrosion and / or oxidation. The thermally insulating layer 9 covers the protective layer 4. The heat insulating layer can be ceramic, such as yttria-stabilized zirconia.

The underlayer 3 metal ensures a bond between the surface of the superalloy substrate and the protective layer: the undercoat layer metal is sometimes called "sub-adhesion layer". There are two major families of sub-layers of metal.

The first family of sub-layers includes metal underlayers simple nickel aluminide-based β-NiAl or platinum modified β-NiAIPt.

In the case of a simple aluminide nickel sublayer or modified platinum (β-NiAl or β-NiAIPt), the aluminum content (35-45 at%) of the sub-layer is sufficient to only form a protective layer of aluminum oxide (AI2O3) to protect the superalloy substrate against oxidation and corrosion.

However, when the part is subjected to high temperatures, unlike the nickel concentrations, and especially aluminum, between the superalloy substrate and the underlayer metal causes the diffusion of nickel in the sub-layer and that of the aluminum in the superalloy (called "inter-diffusion").

Moreover, aluminum is also consumed to form the protective layer of aluminum oxide.

These phenomena lead to a premature depletion of the sub-layer of aluminum, which promotes phase transformations in the sub-layer (β-NiAl → γ'-Ν ΐ3ΑΙ, martensitic transformation). These transformations generate cracks in the undercoat layer and favor the spalling of the aluminum oxide layer.

In addition, diffusion of certain elements of the superalloy, such as titanium, or of certain impurities, such as sulfur, results in a degradation of the adhesion of the aluminum oxide layer.

Finally, the inter-diffusion may result in the formation of secondary reaction zones (called "SRZ" or "Secondary Reaction Zone" in English) which greatly degrade the mechanical properties (creep, fatigue) of the coated superalloy.

Thus, inter-broadcasts between the superalloy substrate and the underlayer may have adverse consequences on the life of the superalloy.

The second family of sub-layers includes metal sub-layers based γ- (Νί) + γ '- (Νί3ΑΙ) simple or modified platinum.

These sub-layers have the advantage of limiting the harmful consequences of inter-diffusion, thereby increasing the life of superalloys coated.

Indeed, these sub-layers have a chemical composition close to that of the superalloy, which allows them to resist inter-diffusion phenomena at high temperature and to limit the phenomena of surface waviness (or rumpling English) which damaging the thermal barrier.

Through a chemical composition approximating that of the superalloys, these sub-layers also limit the formation of secondary reaction zones (SRZ).

However, a disadvantage of these sublayers is their low aluminum content (15 to 20 at%), which does not allow them to form a protective layer of aluminum oxide can remain throughout the life of a turbojet. In use of the turbine, the protective layer 4 can flake and / or be deteriorated, the underlayer 3 is then oxidized to form a new protective layer 4 or a new part of protective layer 4. The sublayer 3 metal is an aluminum reservoir for the formation of aluminum oxide surface: when decreasing, e.g. up to exhaustion,

amount of aluminum provided in the metallic sub-layer 3, and it is no longer possible to form a new protective layer 4. A peeling of the protective layer is for example observed from two hundred hours of use.

Thus, ultimately, these types of metal sublayers may have performance in terms of resistance to oxidation and corrosion much lower than those sublayers metal β-NiAIPt type.

SUMMARY OF THE INVENTION

An object of the invention is to propose a solution to effectively protect a turbine part in the oxidation of superalloy and corrosion while having a longer life than the known metal sublayers.

This object is achieved through the present invention by a turbine component comprising:

- a substrate base superalloy monocrystalline nickel, and

- a metal sublayer overlying the substrate,

characterized in that the sublayer comprises at least two elementary layers, including a first primary layer and a second sub-layer, the first elementary layer being disposed between the substrate and the second individual layer, each individual layer comprising a stage γ'- Ν ΐ3ΑΙ and in that the average atomic fraction of aluminum of the second individual layer is strictly greater than the average atomic fraction of aluminum of the first elementary layer.

As the metal underlayer is formed of several individual layers, it is possible to gradually vary the aluminum concentration of a basic layer to the other, so as to limit the phenomena of inter-diffusion between two elementary layers.

Moreover, the aluminum concentration of the second individual layer can be selected to form a protective layer of aluminum oxide having a life greater than that of known metallic sublayers of the second family.

The invention is advantageously completed by the following characteristics, taken individually or in any of their technically possible combinations:

at least one elementary layer comprises a γ-Ni phase;

average atomic fraction of aluminum of the first individual layer is strictly greater than the average atomic fraction of aluminum of the substrate;

the first elemental layer comprises a γ'-phase and an Νΐ3ΑΙ γ-Ni phase and the metal underlayer comprises at least one other elementary layer solely comprising a γ-Ni phase;

the metal underlayer comprises a plurality of individual layers, each individual layer comprises a γ'-Ν ΐ3ΑΙ phase and optionally a γ-Ni phase and the average atomic fraction of aluminum of the elementary layers is increasing as it is away from the substrate;

average atomic fraction of aluminum of the elementary layer furthest from the substrate is between 0.22 and 0.35;

average atomic fraction of aluminum of the nearest elementary layer of the substrate is less than 0.2;

the difference between the average atomic fraction of the aluminum substrate and the average atomic fraction of aluminum of the nearest elementary layer of the substrate is less than 0.08;

the difference between the average atomic fraction of aluminum of two successive elementary layers is less than 0.06;

each individual layer comprises at least one additive selected from chromium and hafnium, and the average atomic fraction additive of the elementary layers is increasing as one moves away from the substrate;

each elementary layer comprises hafnium and the difference between the average atomic fraction of hafnium two successive elementary layers is less than 0.001;

average atomic fraction of hafnium in the most distant elementary layer of the substrate is less than 0.03 and the average atomic fraction of hafnium to the nearest elementary layer of the substrate is greater than 0.0005.

This object is also achieved within the framework of the present invention by a method for manufacturing a turbine component comprising the steps of: depositing a first individual layer comprising a phase γ'- N 13AI and optionally a Phase γ-Ni, and having an average atomic fraction x of aluminum, on a substrate of metal superalloy single crystal nickel base;

- depositing a second sub-layer comprising a phase γ'- N 13AI and optionally a γ-Ni phase and having an average atomic fraction strictly greater X2 aluminum xi on the first elemental layer.

The first basic layer may have an average atomic fraction aluminum xi strictly greater than the average atomic fraction aluminum xo nickel superalloy substrate base.

PRESENTATION OF DRAWINGS

Other characteristics and advantages will emerge from the following description which is purely illustrative and non-limiting and should be read with reference to the appended figures, in which:

- Figure 1 illustrates schematically a section of a turbine component, for example a turbine blade or a nozzle vane;

- Figure 2 illustrates schematically a section of a part of the thermal barrier of the turbine part;

- Figure 3 schematically illustrates a substrate 2 coated with an undercoat layer according to one embodiment of the invention and

- Figure 4 schematically illustrates a method of manufacturing a one piece impeller.

DEFINITIONS

By the term means "superalloy" a complex alloy having, at high temperature and high pressure, a very good resistance to oxidation, corrosion, creep and cyclic stress (especially mechanical or thermal). Superalloys have particular application in the manufacture of parts used in the aircraft, for example turbine blades, because they are a family of high strength alloys that can operate at relatively temperatures near their melting points (typically 0 7 to 0.8 times their melting temperatures).

A superalloy has a two-phase microstructure comprising a first phase (known as "Phase γ ') forming a matrix, and a second phase (called" Phase γ' ") forming hardening precipitates in the matrix.

The "base" of the superalloy means the principal metal component of the matrix. In most cases, superalloys include an iron base, cobalt, or nickel, but also sometimes a titanium base or aluminum.

The "nickel-based superalloys" have the advantage of offering a good compromise between oxidation resistance, tensile strength at high temperature and weight, which justifies their use in the hottest parts of jet engines.

Nickel base superalloys consist of a γ phase (or matrix) of cubic austenitic face-centered γ-Ni, optionally with additives in solid substitution solution (Co, Cr, W, Mo), and a γ-phase (or precipitated) type γ'-Ν ΐ3Χ, where X = Al, Ti or Ta.

Phase γ 'has an ordered L12 structure derived from the cubic face centered structure, coherent with the matrix, that is to say having an atomic mesh very close to it.

De par son caractère ordonné, the phase γ 'présente la propriété remarquable d'avoir une résistance mécanique augmente here with the temperature point approximately 800 ° C. The phrase très forte entre les phases Y and γ 'Confere a holding mécanique k des très élevée superalliages a nickel base, here À elle-même du ratio γ / γ' et de la taille des précipités durcissants.

Superalloys nickel base and generally have a high mechanical resistance to 700 ° C and mechanical strength which decreases sharply above 800 ° C.

The terms "atomic fraction" means the concentration. All concentrations are expressed as atomic concentration (at%).

DETAILED DESCRIPTION OF THE INVENTION

Referring to Figure 3, a substrate 2 is covered by a thermal barrier.

The elements shown in Figure 3 may independently represent the elements of a turbine blade, a nozzle vane, or any other member, part or piece of a turbine.

The substrate 2 is formed by nickel base superalloy.

The thermal barrier comprises a metal underlayer 3, a protective layer 4 and a thermally insulating layer (not shown in Figure 3).

The substrate 2 is covered by the metallic underlayer 3, itself covered by the protective layer 4.

According to one aspect of the invention, the underlayer 3 metal comprises at least two elementary layers 5. Figure 3 illustrates a

embodiment wherein the sub-layer 3 comprises four elementary layers 5.

Generally, the one or more interfaces between the individual layers 5 have the advantage to limit or prevent metal diffusion and / or oxygen at high temperature between the individual layers, thereby limiting or preventing a phenomenon inter-diffusion.

The sub-layer 3 includes a first elemental layer 7 and a second elemental layer 8. The first elemental layer 7 is disposed between the substrate 2 and the second elementary layer 8. In general, the average atomic fraction of aluminum of the second elementary layer 8 is strictly greater than the average atomic fraction of aluminum of the first elementary layer 7.

Thus, an aluminum atomic fraction gradient may be generated in a sub-layer 3.

Generally, each individual layer comprises a γ'-Νΐ3ΑΙ stage and optionally a γ-Ni phase.

According to one aspect of the invention, the first elementary layer comprises a phase γ'-Νΐ3ΑΙ and γ-Ni phase and another elementary layer only comprises a γ-Ni phase. Advantageously, a plurality of elementary layers comprises a phase γ'-Ν ΐ3ΑΙ and γ-Ni phase and a plurality of elementary layers solely comprises a γ-Ni phase. The average atomic fraction of aluminum of the elementary layers is increasing as one moves away from the substrate; in other words, a positive gradient of the atomic fraction of aluminum, in a direction directed from the substrate to the protective layer 4, can thus be generated in the sub-layer 3.

This feature has two effects concomitantly: · the average atomic fraction of aluminum of the elementary layer 5 furthest from the substrate is sufficient to only form a protective layer 4 of aluminum oxide

so as to protect the superalloy substrate 2 against oxidation and corrosion, and

• the average atomic fraction of aluminum of the elementary layer 7 closest to the substrate is sufficiently low to limit the diffusion of aluminum from the elementary layer 7 (that is to say the elementary layer into contact with the substrate 2) to the substrate 2.

The average atomic fraction of aluminum of the elementary layer furthest from the substrate (that is to say the elementary layer thereby forming the protective layer 4) may be between 0.22 and 0.35 and preferably between 0.25 and 0.3.

Thus, the protective formed exclusively of protective aluminum oxide layer may be formed on the underlayer 3 in order to protect the superalloy against oxidation and corrosion.

The average atomic fraction of aluminum of the elementary layer closest to the substrate 5 may be less than 0.2 and preferably may be between 0.15 and 0.2. Preferably, the average atomic fraction of aluminum of the first individual layer is strictly greater than the average atomic fraction of aluminum of the substrate. The difference between the average atomic fraction of the aluminum substrate and the average atomic fraction of aluminum of the individual layer closest to the substrate may also be less than 0.08 and preferably less than 0.06.

Thus, the diffusion of aluminum to the substrate is limited or prevented.

According to another aspect of the invention, the difference in average atomic fraction of aluminum between two successive elementary layers 5 is limited. It can advantageously be less than 0.06. Thus, the diffusion of aluminum between two successive elementary layers 5 can be limited or prevented. Indeed, the more the average atomic fraction of aluminum between two elementary layers is close, the lower the diffusion of aluminum between these two layers is high.

Table 1 shows the allotropic phase, the atomic fraction of aluminum Xj and the thickness of each ' -th element layer 5 according to one embodiment of the invention) being between 1 and m, m being a natural number designating the total number of elementary layers forming the metallic underlayer 3.

Table 1

Each individual layer may comprise further of nickel Ni and aluminum Al, other chemicals or additives, such as chromium Cr and hafnium Hf. In the embodiment corresponding to Table 1, the average atomic fractions Cr and Hf, not shown, are equal between the different elementary layers. In contrast, the average atomic fraction of aluminum of an elementary layer is growing, that is to say is increasing, as the elementary layer 5 remote from the substrate. Conversely, the average atomic fraction of an elementary nickel layer decreases, that is to say decreases, as the elementary layer 5 remote from the substrate.

Table 2 shows the allotropic phase, the atomic fraction of aluminum Xj and the thickness of each ' -th element layer 5 according to an example particularly suitable for use of the superalloy AM1 and wherein m = 7.

Table 2

Generally, the thickness of each individual layer is between 100 nm and 20 μιτι.

According to one embodiment of the invention, a gradient of average atomic fraction of chromium and / or hafnium is generated in the sub-layer 3. Each of the individual layers 5 comprises at least one additive selected from chromium and / or hafnium, and the average atomic fraction of chromium and / or hafnium of each of the elementary layers is increasing, that is to say is increasing as one moves away from the substrate.

Thus, the chromium inter-diffusion and / or hafnium of an elementary layer 5 to the other is limited or prevented.

According to one aspect of the invention, the difference in average atomic fraction hafnium between two consecutive individual layers is preferably less than 2 × 10 "4 and preferably less than 10 " 4 . The average atomic fraction of hafnium elementary layer 5 closest to the substrate is preferably less than 10.10 4 , preferably less than 5.10 "4 . The average atomic fraction of hafnium elementary layer 5 closest to the protective layer 4 is advantageously between 0.005 and 0.03, preferably between 0.01 and 0.02.

In one aspect of the invention in which a chromium gradient is formed in the undercoat layer, the difference in average atomic fraction of chromium between two consecutive individual layers is advantageously between 0.001 and 0.02 and preferably between 0.005 and 0.01. The average atomic fraction of chromium elementary layer 5 closest to the substrate is preferably less than 0.07. The average atomic fraction of chromium elementary layer 5 closest to the protective layer 4 is preferably greater than 0.1.

Figure 4 schematically illustrates the steps of a method of manufacturing a one piece impeller. Such a method comprises at least two steps:

- a first step consists in depositing a first elemental layer 7 on a substrate of metal superalloy single crystal nickel base. The first individual layer deposited comprises a γ'-Νΐ3ΑΙ stage and optionally a γ-Ni phase. The first layer is deposited with an atomic fraction in controlled aluminum xi. The first basic layer material may be an alloy or a metallic nickel base superalloy. Advantageously, the average aluminum fraction x is strictly greater than the average fraction aluminum xo of the substrate 2;

- a second step consists in depositing a second sub-layer 8 of the first elementary layer 7. The second elementary layer 8 deposited comprises a γ'-ΝίβΑΙ stage and optionally a γ-Ni phase. The second elementary layer 8 deposited has an average atomic fraction

X2 strictly greater than x.

The steps are repeated to deposit a number m of elementary layers so that the last elementary layer 5 deposited has a predetermined average atomic fraction. The predetermined average atomic fraction is between 0.22 and 0.35.

The different elementary layers 5 of the sub-layer 3 may be deposited physically in the vapor phase (PVD method, acronym of the English term Physical Vapor Deposition). Various PVD methods may be used for making the elementary layer 5 such as sputtering, evaporation joule, laser ablation and the physical vapor deposition assisted by electron beam.

Two distinct methods may be used to precisely control the atomic fractions in each element of each successive elementary layers 5:

- several materials of targets may be used sequentially (that is to say one after the other), using a target to deposit an elementary layer. Each target comprises a material whose chemical composition is that of a corresponding elementary layer 5;

- several materials of targets may be used in parallel, simultaneously, during the deposition of one or more elementary layers. Each target may for example comprise a particular chemical element.

Each layer may be deposited by co-evaporation or co-sputtering, in which case, the rate of evaporation or sputtering respectively imposed on each target during the deposition of an elementary layer 5 then determines the stoichiometry of said layer.

CLAIMS

1. Component (1) of turbine comprising:

- a substrate (2) based superalloy monocrystalline nickel, and - a sub-layer (3) metal overlying the substrate (2), characterized in that the metal underlayer comprises at least two elementary layers (5), including a first individual layer (7) and a second sub-layer, the first elementary layer being disposed between the substrate and the second individual layer, each individual layer comprising a γ'-Ν ΐ3ΑΙ phase and that the average atomic fraction of aluminum second elementary layer is strictly greater than the average atomic fraction of aluminum of the first elementary layer.

2. Part (1) of turbine according to claim 1, wherein at least one elementary layer comprises a γ-Ni phase.

3. Item (1) of turbine according to claim 1 to 2, wherein the average atomic fraction of aluminum of the first individual layer is strictly greater than the average atomic fraction of aluminum of the substrate.

4. Part (1) of turbine according to one of claims 1 to 3, wherein the first elementary layer comprises a γ'-Νΐ3ΑΙ phase and a V-Ni, and the metal underlayer comprises at least one further layer elementary comprising only a γ-Νί phase.

5. Part (1) of turbine according to one of claims 1 to 4, wherein the metal underlayer comprises a plurality of individual layers, each individual layer comprising a γ'-Νΐ3ΑΙ phase and optionally a γ-phase -Ni, and in that the atomic fraction

average aluminum of the elementary layers is increasing as one moves away from the substrate.

6. Item (1) of turbine according to one of claims 1 to 5, wherein the average atomic fraction of aluminum of the elementary layer furthest from the substrate is between 0.22 and 0.35.

7. Item (1) of turbine according to one of claims 1 to 6, wherein the average atomic fraction of aluminum of the nearest elementary layer of the substrate is less than 0.2.

8. Item (1) of turbine according to one of claims 1 to 7, wherein the difference between the average atomic fraction of the aluminum substrate and the average atomic fraction of aluminum of the nearest elementary layer of the substrate is less than 0.08.

9. Item (1) of turbine according to one of claims 1 to 8, wherein the difference between the average atomic fraction of aluminum of two successive elementary layers is less than 0.06.

10. Item (1) of turbine according to one of claims 1 to 9, wherein each individual layer comprises at least one additive selected from chromium and duhafnium, and wherein the average atomic fraction additive of the elementary layers is increasing as one moves away from the substrate.

11. Item (1) of turbine according to claim 10, wherein each elementary layer comprises hafnium, and wherein the difference between the average atomic fraction of hafnium two successive elementary layers is less than 0.001.

12. Item (1) of turbine according to one of claims 10 to 1 1, wherein the average atomic fraction of elemental hafnium layer furthest from the substrate is less than 0.03 and the average atomic fraction of hafnium the nearest elementary layer of the substrate is greater than 0.0005.

13. A method of making a turbine component (1) comprising the steps of:

a) depositing a first individual layer (7) comprising a V'-Ni3AI phase and optionally a γ-Ni phase and having an average atomic fraction x of aluminum, on a substrate (2) of metallic superalloy single crystal nickel base;

b) depositing a second sub-layer (8) comprising a phase-V'Ni3AI and optionally a γ-Ni phase and having an average atomic fraction strictly greater X2 aluminum xi on the first elemental layer.

14. Method according to the preceding claim, wherein the first individual layer has an average atomic fraction aluminum xi strictly greater than the average atomic fraction aluminum xo nickel superalloy substrate base.