Coated turbo engine component with a nickel-based substrate containing hafnium

Description

Technical Field

[0001] The present invention relates to the field of nickel-based superalloys and more specifically to superalloys used in the aeronautical field. Previous technique

[0002] Nickel-based superalloys are known for their high mechanical strength, even at high temperatures, and good oxidation resistance. These two properties make them an ideal material for turbomachinery components used in the aerospace industry.

[0003] Among the known nickel-based superalloys, one can notably mention the alloy with the trade name AM-1, corresponding to the composition described in US patent 4,639,280. Patents EP1652964A1, EP2963135A1, and US2015 / 377037A1 concern other prior art materials. EP1652964A1, along with the René N5 material, presents the closest prior art, with a carbon mass content between 300 and 700 ppm.

[0004] The oxidation resistance of superalloys can be further enhanced by coatings applied to their surface. However, even with such coatings, currently available AM-1-based alloys eventually oxidize when used in turbomachinery. Therefore, further improvements in the oxidation resistance of superalloys for turbomachinery components remain desirable. Description of the invention

[0005] To this end, the inventors propose a turbomachine part according to claim 1.

[0006] Preferably, the hafnium mass content is less than or equal to 15000 ppm.

[0007] The invention proposes a turbomachine component formed from a substrate having a composition similar to AM-1 but modified to exhibit a relatively high hafnium content of at least 2000 ppm, and coated with a β-structured nickel aluminide. The inventors have observed that this component, formed from such a substrate coated with this specific coating, exhibits particularly high oxidation resistance. Without being bound by theory, the inventors believe that the limited carbon content in the substrate contributes to improving the component's oxidation resistance by allowing the hafnium to migrate to the surface and form a protective oxide, rather than being trapped as a carbide within the material.

[0008] Preferably, the hafnium mass content of the substrate may be greater than or equal to 4000 ppm.

[0009] In a preferred embodiment, the hafnium mass content of the substrate may be greater than or equal to 6000 ppm.

[0010] The inventors found that the higher the hafnium content, the better the resistance to oxidation.

[0011] In one embodiment, the superalloy is single-crystal. A single-crystal superalloy allows for faster and greater migration of hafnium to the surface because the hafnium is not trapped by the carbon typically introduced to stabilize the grain boundaries of a polycrystalline alloy. This further enhances the protection conferred by the hafnium and thus the oxidation resistance of the part.

[0012] In one embodiment, the β-structure nickel aluminide coating may be β-structure NiAl. It should be noted that, generally, the β-structure nickel aluminide coating may or may not be modified by one or more elements, for example, platinum, zirconium, or hafnium. Thus, suitable β-structure nickel aluminide coatings for the invention include, in particular, β-structure NiAl, β-structure NiPtAl, β-structure NiAlZr, and β-structure NiAlHf.

[0013] In one embodiment, the β-structure nickel aluminide coating is a β-structure NiAl coating or a β-structure NiPtAl coating.

[0014] The β-structure nickel aluminide coating can be formed by a method known per se. For example, the formation of β-structure nickel aluminide can notably be carried out by physical vapor deposition, chemical vapor deposition, box carburizing, or by slip.

[0015] In one embodiment, a turbomachine part according to the invention may further include a thermal barrier present on the β structure nickel aluminide coating.

[0016] Such a thermal barrier is known in itself, and makes it possible to protect the turbomachine part against the high temperatures it encounters during its use.

[0017] In one embodiment, the thermal barrier may be present in contact with the β structure nickel aluminide coating.

[0018] In one embodiment, the turbomachine component can be a turbomachine valve or a turbomachine valve sector. The valve can be a high-pressure valve or a low-pressure valve.

[0019] In alternative embodiments, the turbomachine part can also be a moving blade or a turbine ring sector.

[0020] According to another aspect, the invention also relates to a turbomachine comprising a part as described above. Brief description of the figures

[0021] [ Fig. 1 ] There figure 1 represents, schematically and partially, a portion of a turbomachine distributor according to an embodiment of the invention. Fig. 2 ] There figure 2 represents, schematically and partially, a cross-sectional view of a turbomachine component according to one embodiment of the invention. Fig. 3 ] There figure 3is a comparative test result showing the differences in oxidation resistance between parts according to the invention and parts outside the invention. Detailed description

[0022] The description will now be made by means of figures intended to better understand the invention but which should in no way be interpreted in a limiting way.

[0023] Typically, a turbomachine turbine consists of stationary and moving parts. The moving parts can be rotating rotors carrying blades and are generally positioned between sets of stationary blades, also called distributors. The distributor / rotating rotor assembly constitutes a turbine stage.

[0024] There figure 1 represents a portion of a turbomachine distributor 10.

[0025] A turbomachine distributor 10 may include an outer platform 2 and an inner platform 4, between which extend fixed vanes 6, intended to direct the airflow in a direction favorable to the drive of the adjacent moving wheel, not shown.

[0026] On the figure 2 is schematically represented a turbomachine part 20 composed of a substrate 21 and a nickel aluminide coating 22 of β structure which covers the underlying substrate 21.

[0027] Furthermore, in the embodiment shown, the turbomachine part 20 further comprises a thermal barrier 23 in contact with the nickel aluminide coating 22 of β structure. The thermal barrier 23 may define the external surface of the part 20.

[0028] In one embodiment, the coating 22 can have a thickness e 1 between 40 µm and 90 µm.

[0029] Similarly, the thermal barrier 23 can have a thickness e 2 between 50 µm and 300 µm.

[0030] In one embodiment, the thermal barrier can be chosen from yttrium-stabilized zirconia or one or more other rare earth oxide(s), dysprosium-doped zirconia, gadolinium zirconate, or perovskite.

[0031] In an alternative embodiment, the thermal barrier 23 may be absent. In which case, the nickel aluminide coating 22 with β structure may define the external surface of the part. Example

[0032] Several AM-1 samples were enriched with hafnium concentrations ranging from 340 ppm to 8000 ppm. Samples according to the invention are thus produced when the hafnium concentration is greater than or equal to 2000 ppm, and others not according to the invention.

[0033] The samples vary only in their mass concentrations of hafnium.

[0034] The hafnium content of the samples thus prepared is measured by mass spectrometry. The samples are coated with a platinum-modified nickel aluminide (NiPtAl) coating with a β structure. Each sample is then subjected to oxidation cycles, and the mass change of each sample is measured three times a week for the first 200 cycles, and then twice a week thereafter.

[0035] An oxidation cycle consists of very rapid heating to the oxidation temperature (1150°C ±5°C), holding at 1150°C under atmospheric air pressure for 60 minutes, and finally forced cooling with dry air for 15 minutes to ensure that the room temperature is below 150°C ± 3°C. The test is stopped after 6000 oxidation cycles or when a specific mass change of 20 mg / cm² is observed.

[0036] There figure 3illustrates the results obtained for each sample. The mass concentrations of hafnium in the samples shown on the figure 3 are for curve 11 of 340 ppm, curve 12 of 780 ppm, curve 13 of 670 ppm, curve 14 of 1300 ppm, curve 15 of 2100 ppm, curve 16 of 4700 ppm and curve 17 of 8000 ppm.

[0037] It can be observed on the figure 3 Samples with a hafnium content exceeding 2000 ppm (15, 16, 17) also exhibited the lowest mass loss. Therefore, a high hafnium content provides better resistance to oxidation.

[0038] The expression "between ... and ..." should be understood as including the boundaries.

Claims

1. A turbomachine part (20) comprising: (i) a nickel-based superalloy substrate (21) comprising, in mass content, 5.0% to 8.0% cobalt, 6.5% to 10% chromium, 0.5% to 2.5% molybdenum, 5.0 % to 9.0% tungsten, 6.0% to 9.0% tantalum, 4.5% to 5.8% aluminum, hafnium in a mass content greater than or equal to 2000 ppm, and comprising niobium in a mass content comprised between 0% and 1.5%, and at least one of carbon, zirconium and boron each in a mass content comprised between 0 ppm and 100 ppm, the remainder being composed of nickel and unavoidable impurities; and (ii) a β-structured nickel aluminide coating (22) covering the substrate.

2. The turbomachine part (20) according to claim 1, wherein the hafnium mass content in the substrate (21) is greater than or equal to 4000 ppm.

3. The turbomachine part (20) according to claim 2, wherein the hafnium mass content in the substrate (21) is greater than or equal to 6000 ppm.

4. The turbomachine part (20) according to any one of claims 1 to 3, further comprising a thermal barrier (23) present on the β-structured nickel aluminide coating.

5. The turbomachine part (20) according to any one of claims 1 to 4, wherein the β-structured nickel aluminide coating (22) is a β-structured NiAl coating or β-structured NiPtAl coating.

6. The turbomachine part (20) according to any one of claims 1 to 5, wherein the superalloy is monocrystalline.

7. The turbomachine part (20) according to any one of claims 1 to 6, wherein said part is a turbomachine distributor (10) or a turbomachine distributor sector.

8. A turbomachine comprising a part (20) according to any one of claims 1 to 7.