Coated nickel superalloy

Abstract

Coated nickel superalloy. The invention relates to a part for an aeronautical turbomachine (100) comprising: - a substrate (10) made of a nickel superalloy consisting of a γ phase and a γ' phase, the substrate having a chromium content by mass of less than or equal to 7.0%; and - a coating (20) covering the substrate made of an alloy consisting of a γ phase and a γ' phase and comprising a chromium content by mass of between 6.0% and 14% and an aluminium content by mass of between 6.0% and 12%, and a platinum content by mass of between 0% and 17%, as well as nickel accounting for a majority of the alloy. Figure for the abstract: Fig. 3

Description

Title of the invention: Coated nickel superalloy. Technical field

[0001] This presentation concerns the aeronautical field and more precisely the metallic alloys used in this field and particularly the protective coatings of such alloys. Prior art

[0002] The efficiency of aeronautical turbomachines depends on their operating temperatures.

[0003] The operating temperature of turbomachines has been able to increase in recent decades, in particular thanks to the use of nickel superalloys.

[0004] These superalloys in fact have good resistance to high temperature fining together with resistance to corrosion and oxidation compatible with use in an aeronautical turbomachine.

[0005] One material used for this application is the alloy commercially available under the name AMI.

[0006] Since the success of this superalloy, new superalloy compositions have been proposed to further increase their high-temperature mechanical properties and thus enable a further improvement in the efficiency of turbomachines.

[0007] In doing so, the composition of the superalloys has seen a significant decrease in chromium content compared to AMl, which has jointly led to an increased sensitivity of the new alloys to the environment of an aeronautical turbomachine.

[0008] It has been proposed to compensate for this sensitivity by the development of new protective coatings, improving the resistance to oxidation or corrosion of the underlying substrate, and allowing excellent resistance of the thermal barrier, usually placed on the outside of the turbomachine parts to protect them from the temperature.

[0009] However, for the most recent coated superalloys, richer in rhenium and poorer in chromium than AMl, the appearance of secondary reaction zones (or "SRZ" for the acronym in English "Secondary Reaction Zone") has been observed which reduce the lifetime of the entire part.

[0010] Such areas are caused by interdiffusion of the elements of the coating and the substrate. More specifically, some of the elements of the coating migrate towards the substrate. and some of the elements of the substrate migrate to the coating, which creates between the substrate and the coating a zone of a phase distinct from both the substrate and the coating. Such a zone significantly reduces the mechanical characteristics of the coated superalloy.

[0011] Thus, there remains a need for a material having mechanical properties and resistance to oxidation allowing the operating temperatures of aeronautical turbomachines to be increased compared to those permitted by AM1. Statement of the invention

[0012] The invention aims to propose a solution to the problems set out above.

[0013] For this, it relates according to a first of its aspects to a part for an aeronautical turbomachine comprising: - a substrate made of a nickel superalloy consisting of a y phase and a y' phase, the substrate having a mass content of chromium less than or equal to 7.0%; and - a coating covering the substrate in an alloy consisting of a y phase and a y' phase and comprising a mass content of chromium of between 6.0% and 14% and an aluminum mass content of between 6.0% and 12%, and a platinum mass content of between 0% and 17%, as well as nickel accounting for a majority of the alloy.

[0014] The embodiment proposed above makes it possible to overcome the drawbacks of the coatings of the prior art and to propose a more advantageous solution than AM1 or other usual coated alloys for turbomachine parts.

[0015] By "accounting for a majority of the alloy" is meant that nickel is the most present element within the alloy.

[0016] The coating layer consists of a y phase and a y' phase which ensures excellent coherence with the substrate, thus limiting diffusion between the two phases.

[0017] Limiting diffusion is particularly advantageous because it limits the appearance of secondary reaction zones, which allows the coating layer to maintain excellent integrity and a very stable microstructure even at high temperatures.

[0018] Finally, the method is simplified compared to the methods of the prior art, because the proximity of structure between the coating and the substrate ensures excellent compatibility between the two.

[0019] In one embodiment, the coating is disposed directly in contact with the substrate.

[0020] In one embodiment, the part may further comprise a layer of thermal barrier, for example placed on the coating.

[0021] In one embodiment, the turbomachine part does not comprise any layers other than the substrate, the coating, which is arranged directly in contact with the substrate and where appropriate a thermal barrier layer, which is preferably arranged directly in contact with the coating.

[0022] This embodiment is particularly advantageous, because it makes it possible to simply obtain a turbomachine part with a very simple constitution.

[0023] In one embodiment, the coating may comprise a chromium mass content of between 6.0% and 12%.

[0024] In one embodiment, the coating may comprise an aluminum mass content of between 6.0% and 9%.

[0025] In one embodiment, the coating may comprise a mass content of platinum of between 1.0% and 17%, or even 3.0% to 17%, 5.0% to 17% or even 8.0% to 17%.

[0026] In one embodiment, the coating may comprise a mass content of platinum of between 1.0% and 15%, or even 3.0% to 15%, 5.0% to 15% or even 8.0% to 15%.

[0027] This embodiment makes it possible to further extend the service life of the alloy by increasing its resistance to oxidation. In addition, the increase in the platinum content ensures excellent resistance to the thermal barrier possibly placed on the coating.

[0028] In one embodiment, the coating may further comprise a mass content of between 0.1% and 3% of one or more of the elements chosen from hafnium, silicon, zirconium and yttrium.

[0029] These four elements have in fact been identified by the inventors as playing a positive role in improving the resistance to oxidation / corrosion conferred by the coating. They also improve the resistance of the thermal barrier possibly placed on the coating.

[0030] Furthermore, these elements present in the indicated contents make it possible to ensure that the coating retains a structure consisting of a y phase and a y' phase.

[0031] In one embodiment, the coating does not comprise any element in a content greater than or equal to 0.1% by mass other than nickel, chromium, aluminum, and optionally platinum, hafnium, silicon, zirconium or yttrium.

[0032] This embodiment ensures that the coating obtains the desired beneficial effects while also ensuring that it is made up of a y phase and a Y'- phase.

[0033] In one embodiment, the substrate comprises a rhenium content greater than or equal to 2.5% or even greater than or equal to 4.0%. Such contents are characterized characteristics of the latest generation nickel superalloys which have less chromium and more rhenium than the alloys of the AML generation

[0034] In these new generation alloys, the appearance of secondary reaction zones with the coatings of the prior art are very marked, and the effects of a coating such as described above are all the more interesting.

[0035] In one embodiment, the substrate may be chosen from nickel superalloys commercially available under the names CMSX-4 PLUS, MCNG, CMSX-10.

[0036] In one embodiment, the substrate comprises a volume content of phase y of between 25% and 35% and a complementary volume content of phase y', preferably between 28% and 32% of phase y or even between 29% and 31%, or even precisely 30% of phase y.

[0037] In one embodiment, the coating comprises a volume content of phase y lower than that of y'.

[0038] In one embodiment, the coating comprises a volume content of phase y of between 25% and 35% and a volume content of complementary phase y' (i.e. between 65% and 75%), preferably between 28% and 32% of phase y or even between 29% and 31%.

[0039] It is known that the content of the phases varies depending on the temperature. The values ​​given are understood at the actual operating temperature of the part, for example between 1000°C and 1200°C.

[0040] By the expression "in a complementary volume content", it is understood that the sum of the volume contents in phase y and in phase y' is equal to 100%, because the substrate and the coating are made up of a phase y and in phase y'.

[0041] In one embodiment, the substrate comprises a y-phase volume content of between 25% and 35% and a complementary y'-phase volume content and the coating comprises a y-phase volume content of between 25% and 35% and a complementary y'-phase volume content.

[0042] In one embodiment, the turbomachine part is a turbomachine blade, and preferably a turbomachine hot part blade.

[0043] Indeed, the invention is very advantageous for such parts in particular because the invention makes it possible to reduce the thickness of the coatings for equivalent resistance properties, and turbomachine blades, the geometry of which is constrained for aerodynamic reasons, particularly benefit from this advantage.

[0044] In one embodiment, the thickness of the coating may be between 5.0 μm and 100 μm, preferably between 20 μm and 50 μm.

[0045] The coating according to the invention in fact makes it possible to reduce the thickness of the diffusion zone in the substrate compared to the coatings of the prior art.

[0046] The coating effectively makes it possible to avoid secondary reaction zones which mechanically penalize walls which are too thin for prior art coatings.

[0047] According to another of its aspects, the invention also relates to a method for obtaining a turbomachine part as described above.

[0048] Such a method comprises: - a step of coating the external surface of a substrate with a nickel superalloy consisting of a y phase and a y' phase, the substrate having a mass content of chromium less than or equal to 7.0%, with a coating of an alloy consisting of a y phase and a y' phase and comprising a mass content of chromium of between 6.0% and 14% and an aluminum mass content of between 6.0% and 12%, and a platinum mass content of between 0% and 17%, as well as nickel accounting for a majority of the alloy.

[0049] In one embodiment, the method may further comprise, after the coating step, the following steps: - a homogenization diffusion heat treatment between 1000°C and 1200°C under vacuum or under an argon or oxygen atmosphere for 1 hour and 6 hours; and / or - a step of placing a thermal barrier on the coating.

[0050] In one embodiment, the coating step can be carried out by physical vapor deposition (PVD), for example under an electron beam (EB-PVD), by arc or by magnetron, by high-speed flame spraying (HVOF) or by a plasma process.

[0051] The homogenization treatment, if present, ensures excellent reproducibility of the part obtained. Such a step is not strictly necessary but can be carried out as a precaution to ensure that all the parts produced by the process have an identical thermal history, and that they thus have a homogeneity of composition.

[0052] All of these methods make it possible to manufacture the coating directly consisting of a y phase and a y' phase, which ensures a limitation of interdiffusion. Indeed, since the substrate and the coating both have y and y' phases, the only difference in chemical composition between the substrate and the coating is not sufficient for interdiffusion to be detrimental to the coating.

[0053] The very low interdiffusion between the substrate and the coating ensures the absence of secondary reaction zones, which makes it possible to obtain the technical effects described above for the coating, in particular excellent stability over time, unlike what can be observed for coatings of the prior art.

[0054] According to another of its aspects, the invention relates to an aeronautical turbomachine comprising a part as described above, said part being a blade.

[0055] Such a turbomachine can be used at higher temperatures than those of the prior art, which allows it to have better efficiency.

[0056] Indeed, the coated blades as described above offer better resistance to oxidation and better temperature resistance than the blades of the prior art, which overall allows the turbomachine to operate at a higher temperature. Brief description of the drawings

[0057] [Fig.l] [Fig.l] is a schematic representation of a turbomachine.

[0058] [Fig.2] [Fig.2] represents a coated turbomachine blade according to an embodiment of the invention.

[0059] [Fig.3] [Fig.3] represents tests carried out comparing samples according to the invention and outside the invention. Description of the embodiments

[0060] The invention is now described by means of figures, present for descriptive purposes to illustrate certain embodiments of the invention and which should not be interpreted as limiting the latter.

[0061] [Fig.l] represents, in section along a vertical plane passing through its main axis A, a double-flow turbojet 1. It comprises from upstream to downstream according to the circulation of the air flow, a fan 2, a low-pressure compressor 3, a high-pressure compressor 4, a combustion chamber 5, a high-pressure turbine 6, and a low-pressure turbine 7.

[0062] In the present application, the relative terms of positioning, for example “upstream”, “downstream”, “internal” and “external” will be understood relative to the horizontal axis A of the casing defining the axial direction, traveled in the direction of flow of the main and secondary air flows of the turbomachine.

[0063] Thus, a so-called “upstream” element will be crossed before a so-called “downstream” element and a so-called “internal” element will be closer to axis A than an “external” element.

[0064] [Fig.2] represents a moving blade, which can belong to a low pressure compressor 3, to a high pressure compressor 4, to a high pressure turbine 6, or to a low pressure turbine.

[0065] More specifically, the blade 100 comprises: - a substrate 10 made of a nickel superalloy consisting of a y phase and a y' phase, the substrate having a mass content of chromium less than or equal to 7.0%; and - a coating 20 covering the substrate 10 in an alloy consisting of a y phase and a y' phase and comprising a mass content of chromium of between 6.0% and 14% and an aluminum mass content of between 6.0% and 12%, and a platinum mass content of between 0% and 17%, as well as nickel accounting for a majority of the alloy.

[0066] In the embodiment described in [Fig.l] and although this is not necessary, the blade 100 further comprises a thermal barrier 30.

[0067] As described above, such a blade offers better temperature resistance and better grip of the thermal barrier resulting in a longer service life of the part compared to the turbomachine parts of the prior art.

[0068] [Fig.2] further illustrates what is meant by the “thickness” ei of the coating 20.

[0069] This word takes here and in the application its classical meaning, namely the smallest distance that it is necessary to travel to cross the coating from one side to the other.

[0070] In the present application, the y and y' phases of a nickel superalloy will have the usual meaning in the field.

[0071] Nickel-based superalloys consist of a y-Ni face-centered cubic austenitic phase (or matrix), possibly containing α-substitution solid solution additives (Co, Cr, W, Mo), and a y'-Ni3X type y'-Ni3X phase (or precipitates), with X = Al, Ti or Ta. The y' phase has an ordered Li2 structure, derived from the face-centered cubic structure, consistent with the matrix, i.e. having an atomic mesh very close to it.

[0072] The determination of a phase quantity in a given substrate or coating can be made by methods known to those skilled in the art, for example by X-ray diffraction or by the succession of an analysis step under an EDS microscope to determine the chemical composition and a simulation step carried out on the basis of the exact chemical composition determined by the EDS analysis.

[0073] The simulation is carried out by tools known as such, for example by means of the THERMOCALC ® software.

[0074] As described above, the coating 20 also consists of a y phase and a y' phase.

[0075] In one embodiment, the substrate may be chosen from nickel superalloys commercially available under the names CMSX-4 PLUS, MCNG, CMSX-10.

[0076] Preferably, the thermal barrier layer 30 is an external surface of the blade 100.

[0077] The thermal barrier layer is a layer chosen according to the needs of the invention and according to general practices in the field.

[0078] In one embodiment, the thermal barrier layer may comprise a layer of yttria-containing zirconia.

[0079] In one embodiment, the thermal barrier layer may comprise a layer of gadolinium zirconate (Gd2Zr2O7).

[0080] In one embodiment the thermal barrier layer may comprise a layer of yttria zirconia and a layer of gadolinium zirconate disposed directly in contact with each other.

[0081] [Fig.2] illustrates the thickness e2 of the thermal barrier 30.

[0082] For illustration purposes, the thermal barrier layer is here represented by a single layer 30.

[0083] In one embodiment, the thickness e2 of the thermal barrier 30 may be between 100 μm and 200 μm.

[0084] Preferably, the thermal barrier layer 30 is an external surface of the blade 100.

[0085] [Fig.3] shows results of mass loss tests carried out for 3 samples subjected to the same cyclic oxidation conditions. Each of the samples was placed at 1150°C in a controlled air atmosphere, and the mass variation was observed as a function of the number of temperature variation cycles (heating, holding at 1150°C and cooling).

[0086] Conventionally for the field, the mass variation is associated with oxidation and it is considered that a sample resists oxidation less the more rapidly its mass decreases.

[0087] The first sample (curve 201, outside the invention) is a nickel superalloy consisting of a y phase and a y' phase having a mass content of chromium less than or equal to 7.0%.

[0088] In this case, it is a sample commercially available under the reference CMSX-4 PLUS.

[0089] The second sample (curve 202) consists of a nickel superalloy substrate comprising a y phase and a y' phase, the substrate having a chromium mass content of less than or equal to 7.0%, further comprising a coating being made of an alloy consisting of a y phase and a y' phase and comprising a chromium mass content of between 6.0% and 14% and an aluminium mass content of between 6.0% and 12%, a hafnium mass content of 0.1%, the remainder of the coating being nickel and the coating does not comprise any element other than those mentioned above in a content greater than 0.1%.

[0090] In other words, the second sample comprises a substrate similar to the first sample coated with a protective coating as envisaged above.

[0091] The third sample (curve 203) is similar to the second sample (curve 202), and differs in that the coating additionally comprises a mass content of 15% platinum.

[0092] The thickness of the coating for the production of the second and third samples is approximately 30 μm.

[0093] [Fig.3] illustrates that the coating according to the invention (curves 2 and 3) effectively provides excellent resistance to oxidation.

[0094] It can indeed be seen that more than 3500 cycles are required for a coated sample to exhibit a mass loss comparable to that achieved for 500 cycles with the bare substrate of the first sample (curve 201).

[0095] The third sample illustrates the additional protective effect obtained by adding platinum to the coating.

[0096] Indeed, to achieve the same mass loss as a coated sample without platinum (curve 202) at 3500 cycles, more than 5000 cycles are required for a coated sample comprising platinum (curve 203).

Claims

Claims

1. Part for an aeronautical turbomachine (100) comprising: - a substrate (10) made of a nickel superalloy consisting of a y phase and a y' phase, the substrate having a mass content of chromium less than or equal to 7.0%; and - a coating (20) covering the substrate made of an alloy consisting of a y phase and a y' phase and comprising a mass content of chromium of between 6.0% and 14% and an aluminum mass content of between 6.0% and 12%, and a platinum mass content of between 0% and 17%, as well as nickel accounting for a majority of the alloy.

2. Part for an aeronautical turbomachine (100) according to claim 1, in which the substrate (10) comprises a volume content of phase y of between 25% and 35% and a complementary volume content of phase y' and in which the coating (20) comprises a volume content of phase y of between 25% and 35% and a complementary volume content of phase y'.

3. Part for an aeronautical turbomachine (100) according to claim 1 or 2, further comprising a thermal barrier (30) disposed on the coating.

4. Part for an aeronautical turbomachine (100) according to any one of claims 1 to 3, said part comprising only the substrate (10), the coating (20), which is arranged directly in contact with the substrate and where appropriate a thermal barrier (30), arranged directly in contact with the coating.

5. Part for an aeronautical turbomachine (100) according to one of claims 1 to 4, in which the coating (20) comprises a mass content of platinum of between 1.0% and 17%.

6. Part for an aeronautical turbomachine (100) according to one of claims 1 to 5, in which the coating (20) further comprises a mass content of between 0.1% and 3% of one or more of the elements chosen from hafnium, silicon, zirconium and yttrium.

7. Part for an aeronautical turbomachine (100) according to one of claims 1 to 6, in which the coating (20) does not comprise any element in a content greater than or equal to 0.1% by mass other than nickel, chromium, aluminum, and possibly platinum, hafnium, silicon, zirconium and yttrium.

8. Part for an aeronautical turbomachine (100) according to one of the claims- indications 1 to 7, wherein the thickness of the coating (20) may be between 5.0 pm and 100 pm, preferably between 20 pm and 50 pm.

9. Method for obtaining a turbomachine part (100) according to one of claims 1 to 8, which comprises: - a step of coating the external surface of a substrate (10) in a nickel superalloy consisting of a y phase and a y' phase, the substrate having a mass content of chromium less than or equal to 7.0%, by a coating (20) in an alloy consisting of a y phase and a y' phase and comprising a mass content of chromium of between 6.0% and 14% and an aluminum mass content of between 6.0% and 12%, and a platinum mass content of between 0% and 17%, as well as nickel accounting for a majority of the alloy.

10. The method of claim 9, wherein the coating step is carried out by physical vapor deposition (PVD) optionally under an electron beam (EB-PVD), by high velocity oxygen fuel (HVOF) or by a plasma process.

11. Aeronautical turbomachine comprising a part (100) according to one of claims 1 to 8, said part being a turbomachine blade.

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