Coated nickel superalloy

Abstract

The invention relates to a part for an aircraft turbine engine (100), comprising: - a substrate (10) made of a nickel superalloy consisting of a γ phase and a γ' phase; - a coating (20) covering the substrate made of an alloy comprising, for more than 95% by volume, a γ' phase and having a chromium atomic content of between 2% and 5% and an aluminium atomic content of between 18% and 25%, wherein nickel accounts for the majority of the alloy; and - a thermal barrier layer (30); wherein the coating is arranged between the substrate and a thermal barrier layer.

Description

Description Title of the invention: Coated nickel superalloy. Technical Field

[0001] This presentation concerns the aeronautical field and more specifically 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 increased in recent decades, particularly thanks to the use of nickel superalloys.

[0004] These alloys in fact have good resistance to creep at high temperature 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 alloy, new superalloy compositions have been proposed to further increase their mechanical properties at high temperatures and thus envisage a further increase in the temperature of turbomachines.

[0007] In doing so, the composition of the superalloys experienced a significant decrease in chromium content compared to AMl, which 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 developing 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 turbomachine parts to protect them from temperature.

[0009] However, at the temperatures involved in the turbomachine, diffusion allows significant mobility of the atoms so that phase transformations are often observed in the coating.

[0010] These phase transformations result in the creation of surface undulations between the substrate and the coating, which promotes flaking of the thermal barrier.

[0011] We then speak of "rumpling", according to the established English term, to characterize the appearance of these surface undulations between the substrate and the coating causing a loss of adhesion of the thermal barrier placed on the coating.

[0012] For the most recent coated superalloys, richer in rhenium and poorer in chromium than AML, in addition to rumpling, the appearance of secondary reaction zones (or "SRZ" for the acronym in English "Secondary Reaction Zone") has been observed, which reduce the service life of the entire part.

[0013] Such zones are caused by the interdiffusion of elements from the coating and the substrate. Specifically, some of the elements from the coating migrate to the substrate and some of the elements from the substrate migrate to the coating, creating a zone between the substrate and the coating of a phase distinct from both the substrate and the coating. Such a zone significantly reduces the mechanical characteristics of the coated superalloy.

[0014] Indeed, these areas are associated with degradation of the microstructure and consequently a reduction in mechanical resistance properties, in particular poorer resistance to cracks, ultimately causing poor thermal barrier performance and therefore premature wear of the parts in operation.

[0015] Thus, there remains a need for a material with mechanical properties and resistance to oxidation allowing the increase in operating temperatures of aeronautical turbomachines compared to those permitted by AMl. Statement of the invention

[0016] The invention aims to provide a solution to the problems set out above.

[0017] For this, it concerns, according to a first of its aspects, a part for an aeronautical turbomachine comprising: - a substrate made of a nickel superalloy consisting of a y phase and a y' phase; - a coating covering the substrate in an alloy comprising more than 95% in volume a Y' phase and comprising an atomic content of chromium of between 2% and 5% and an atomic content of aluminum of between 18% and 25%, as well as nickel accounting for a majority of the alloy; and - a thermal barrier layer; the coating being disposed between the substrate and a thermal barrier layer.

[0018] The coating layer comprises more than 95% by volume of a Y'- phase

[0019] This prevents the appearance of surface undulations (sometimes called "rumpling" in the literature) between the coating and the substrate because the coating does not undergo microstructural changes during aging. The absence of these surface undulations allows for excellent thermal barrier performance, and thus a longer service life for the part as a whole.

[0020] Thus, the coating allows to meet not only environmental and mechanical requirements, offering on the one hand excellent protection against corrosion and oxidation and on the other hand mechanical characteristics compatible with the desired application.

[0021] In one embodiment, the substrate comprises a mass content of chromium less than or equal to 7% and a mass content of rhenium greater than or equal to 2.5% or even greater than or equal to 4.0%. Such contents are characteristic of the latest generation nickel superalloys which have less chromium and more rhenium than the alloys of the AM1 generation.

[0022] In these new generation alloys, the appearance of secondary reaction zones with prior art coatings is very marked, and the effects of a coating such as described above are all the more interesting.

[0023] In fact, these secondary reaction zones can be avoided thanks to the coatings described which, in addition to the advantages already described, significantly improves the mechanical properties of the resulting part.

[0024] In one embodiment, the substrate may be selected from nickel superalloys commercially available under the names CMSX-4 PLUS, MCNG, CMSX-10.

[0025] In one embodiment, the coating is disposed directly in contact with the substrate.

[0026] 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 the thermal barrier, which is arranged directly in contact with the coating.

[0027] This embodiment is particularly advantageous, because it makes it possible to simply obtain a turbomachine part with a very simple constitution.

[0028] In one embodiment, the coating may comprise an atomic platinum content of between 1.0% and 6.0%.

[0029] This embodiment makes it possible to further extend the life of the alloy by increasing the resistance of the thermal barrier.

[0030] In one embodiment, the coating may comprise an atomic aluminum content of between 18% and 23%.

[0031] In one embodiment, the coating may further comprise a non-zero hafnium atomic content of between 0.0% and 1.0%.

[0032] In one embodiment, the coating may further comprise a non-zero atomic silicon content of between 0.0% and 1.0%.

[0033] In one embodiment, the coating may further comprise a non-zero atomic yttrium content of between 0.0% and 2.0%.

[0034] In one embodiment, the coating may further comprise a non-zero atomic zirconium content of between 0.0% and 2.0%.

[0035] These four elements have in fact been identified by the inventors as playing a positive role in improving the resistance to oxidation and corrosion conferred by the coating. In addition, these elements in these contents make it possible to ensure that the coating retains a structure comprising a y' phase for more than 95% by volume.

[0036] Finally, the inventors verified that these compositions allow excellent thermal barrier resistance on the turbomachine part.

[0037] The coating in fact makes it possible to avoid the appearance of phenomena causing delamination of the thermal barrier while guaranteeing excellent protection of the substrate against corrosion and oxidation, and this with substrates which are by nature more sensitive to corrosion and oxidation than AML.

[0038] In one embodiment, the substrate comprises a volume content of y-phase of between 25 and 35% and a complementary volume content of y'-phase.

[0039] By "in a complementary volume content" it is understood that the sum of the volume contents in phase y and phase y' is equal to 100% as the substrate is made up of phase y and phase y'.

[0040] It is known that the phase content 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.

[0041] The coating comprises a y' phase for more than 95% by volume, which ensures that the coating is not subject to microstructural changes throughout its lifetime.

[0042] Indeed, the evolution of the phase y' towards y does not create any surface undulation (rumpling) and is also extremely slow, because we are close to equilibrium with the substrate in the conditions encountered in the turbomachine.

[0043] By ensuring that the y' phase initially accounts for more than 95% of the coating volume, we guarantee that microstructural evolution has very little impact on the coating structure and therefore limits delamination of the thermal barrier.

[0044] In one embodiment, the coating comprises a y' phase for more than 99% by volume, or even consists of a y' phase.

[0045] As indicated above, the more the y' phase is present, the less microstructural evolution of the coating is to be feared.

[0046] In one embodiment, the coating does not comprise any other element in a content greater than or equal to 0.1 atomic % other than nickel, chromium, aluminum, and optionally platinum, hafnium, zirconium, silicon or yttrium.

[0047] This embodiment ensures that the coating obtains the desired beneficial effects while ensuring a volume content of phase y' greater than or equal to 95%.

[0048] In one embodiment, the thickness of the coating is between 5.0 μm and 50 μm, or even between 10 μm and 30 μm.

[0049] Such a thickness is lower than that of prior art coatings for comparable properties, which allows a weight saving for the parts.

[0050] In one embodiment, the average composition of the coating is homogeneous throughout the thickness of the coating after deposition. By this it is understood that the coating does not comprise a composition gradient.

[0051] Typically, the thermal barrier layer may comprise a layer of yttria-containing zirconia.

[0052] In one embodiment, the thermal barrier layer may comprise a layer of gadolinium zirconate (Gd2Zr2O7).

[0053] In one embodiment the thermal barrier layer may comprise a layer of yttria zirconia and a layer of gadolinium zirconate disposed in direct contact with each other.

[0054] In one embodiment, the turbomachine part is a turbomachine blade, and preferably a turbomachine hot end blade.

[0055] 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.

[0056] According to another of its aspects, the invention also relates to a method for obtaining an aeronautical turbomachine part as described above.

[0057] Such a method includes: - a step of coating the external surface of a substrate with a nickel superalloy consisting of a y phase and a y' phase, with a coating of an alloy comprising for more than 95% by volume a y' phase and comprising an atomic content of chromium of between 2% and 5% and an atomic content of aluminium of between 18% and 25%, as well as nickel accounting for a majority of the alloy; and - a step of placing a thermal barrier on the coating.

[0058] In one embodiment, the coating step may 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.

[0059] All of these processes make it possible to manufacture the coating directly consisting of more than 95% by volume of a y' phase, which ensures a limitation of interdiffusion.

[0060] The very low interdiffusion between the substrate and the coating ensures the absence of secondary reaction zones which ensures obtaining the technical effects described above for the coating, in particular better stability over time of the barrier. thermal insulation provided on the coating than that which can be observed for coatings of the prior art.

[0061] Furthermore, these methods ensure that the coating is deposited and is not itself obtained by diffusion of elements from the substrate to the coating, which ensures the absence of secondary reaction zones.

[0062] In one embodiment, the method may further comprise, between the coating step and the step of providing a thermal barrier, 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.

[0063] The homogenization treatment, if present, ensures excellent reproducibility of the resulting part. Such a step is not strictly necessary but can be carried out as a precaution to ensure that all parts produced by the process have an identical thermal history, and that they therefore present a homogeneity of composition.

[0064] The thermal barrier may be deposited on the coating by methods known per se and preferably identical to those used for depositing the coating.

[0065] The process proposed here then makes it possible, unlike the processes of the prior art, to obtain the coating in a single deposition step, carried out in a single machine.

[0066] Conventionally, prior art deposition processes include an initial step of electrolytic platinum deposition followed by an aluminization step carried out by chemical vapor deposition which requires changing machines between the two steps.

[0067] This embodiment allows for time savings and improved simplicity of deposition compared to prior art methods.

[0068] The characteristics of the coating, both the composition and the microstructure, ensure excellent resistance over time of the coating and the thermal barrier placed on the coating.

[0069] According to another of its aspects, the invention relates to an aeronautical turbomachine comprising a part as described above, said part being a blade.

[0070] Such a turbomachine can be used at higher temperatures than those of the prior art, which allows it to have better efficiency.

[0071] 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

[0072] [Fig. 1] Figure 1 is a schematic representation of a turbomachine.

[0073] [Fig. 2] Figure 2 represents a coated turbomachine blade according to one embodiment of the invention. Description of the embodiments

[0074] 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.

[0075] Figure 1 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.

[0076] In the present application, the relative terms of positioning, for example “upstream”, “downstream”, “internal” and “external”, will be understood in relation 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.

[0077] Thus, an element called "upstream" will be crossed before an element called "downstream" and an element called "internal" will be closer to axis A than an "external" element.

[0078] Figure 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.

[0079] More specifically, Dawn 100 includes: - a substrate 10 made of a nickel superalloy consisting of a y phase and a y' phase; and - a coating 20 covering the substrate 10 in an alloy comprising for more than 95% by volume a y' phase and comprising an atomic content of chromium of between 2% and 5% and an atomic content of aluminum of between 18% and 25%, as well as nickel accounting for a majority of the alloy; - a thermal barrier layer 30.

[0080] 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 prior art turbomachine parts.

[0081] Figure 2 further illustrates what is meant by the “thickness” ei of the coating 20.

[0082] This word takes on 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.

[0083] In the present application, the y and y' phases of a nickel superalloy will have the usual meaning in the art.

[0084] Nickel-based superalloys can consist of a y-Ni face-centered cubic austenitic y phase (or matrix), possibly containing a-substitution solid solution additives (Co, Cr, W, Mo), and a y'-Ni3X type y' phase (or precipitates), with X = Al, Ti or Ta. The y' phase has an L structure 12 ordered, derived from the face-centered cubic structure, consistent with the matrix, i.e. having an atomic mesh very close to it.

[0085] 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 statistical determination on samples observed by scanning electron microscopy 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. The simulation is carried out by tools known as such, for example by means of the THERMOCALC ® software.

[0086] In one embodiment, the substrate may be selected from nickel superalloys commercially available under the names CMSX-4 PLUS, MCNG, CMSX-10.

[0087] As described above, the coating 20 is a nickel alloy and comprises for more than 95% by volume a y' phase.

[0088] The blade 100 further comprises a thermal barrier layer 30 disposed on the coating.

[0089] Preferably, the thermal barrier layer 30 is an outer surface of the blade 100.

[0090] The thermal barrier layer is a layer chosen according to the needs of the invention and according to general customs in the field.

[0091] In one embodiment, the thermal barrier layer may comprise a layer of yttria-containing zirconia.

[0092] In one embodiment, the thermal barrier layer may comprise a layer of gadolinium zirconate (Gd2Zr2O7).

[0093] In one embodiment the thermal barrier layer may comprise a layer of yttria zirconia and a layer of gadolinium zirconate disposed in direct contact with each other.

[0094] For illustration purposes, the thermal barrier layer is here represented by a single layer 30.

[0095] Figure 2 illustrates the thickness e2 of the thermal barrier 30.

[0096] In one embodiment, the thickness e2 of the thermal barrier 30 may be between 100 μm and 200 μm.

[0097] Preferably, the thermal barrier layer 30 is an outer surface of the blade.

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; - a coating (20) covering the substrate in an alloy consisting of a y' phase and comprising an atomic content of chromium of between 2% and 5% and an atomic content of aluminum of between 18% and 25%, as well as nickel accounting for a majority of the alloy; and - a thermal barrier layer (30); the coating being disposed between the substrate and a thermal barrier layer.

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'.

3. Part for an aeronautical turbomachine (100) according to claim 1 or 2, which does not comprise layers other than the substrate (10), the coating (20), which is arranged directly in contact with the substrate and the thermal barrier (30), which is arranged directly in contact with the coating.

4. An aeronautical turbomachine part (100) according to any one of claims 1 to 3, wherein the coating (20) comprises a platinum atomic content of between 1.0% and 6.0%.

5. Part for an aeronautical turbomachine (100) according to one of claims 1 to 4, in which the coating (20) further comprises: a non-zero atomic content of hafnium and comprised between 0.0% and 1.0%; a non-zero atomic content of silicon and comprised between 0.0% and 1.0%; a non-zero atomic content of zirconium and comprised between 0.0% and 2.0%; and / or a non-zero atomic content of yttrium and comprised between 0.0% and 2.0%.

6. Part for an aeronautical turbomachine (100) according to one of claims 1 to 5, in which the coating (20) does not comprise any other element in a content greater than or equal to 0.1 atomic% than nickel, chromium, aluminum, and possibly platinum, hafnium, zirconium, silicon and yttrium.

7. Part for an aeronautical turbomachine (100) according to one of claims 1 to 6, in which the thickness (ei) of the coating (20) can be between 5.0 pm and 50 pm, preferably between 10 pm and 30 pm.

8. Method for obtaining an aeronautical turbomachine part (100) according to one of claims 1 to 7, 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, with a coating (20) in an alloy comprising for more than 95% by volume a Y' phase and comprising an atomic content of chromium of between 2% and 5% and an atomic content of aluminum of between 18% and 25%, as well as nickel accounting for a majority of the alloy; - a step of arranging a thermal barrier (30) on the coating.

9. Method according to claim 8, in which the coating step is carried out by physical vapor deposition (PVD) for example under an electron beam (EB-PVD), by arc or by magnetron, by high velocity flame spraying (HVOF) or by a plasma process.

10. Aeronautical turbomachine comprising a part (100) according to one of claims 1 to 7, and in which said part is a blade.

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