TURBOMACHINE COMPONENT MADE OF SUPER ALLOY WITH OPTIMIZED HAFNIUM CONTENT

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] It is desirable to optimize the resistance of these alloys to oxidation. Description of the invention

[0005] In this respect, it is to the inventors' credit that they have succeeded in optimizing the composition of a turbomachine component to obtain improved oxidation resistance properties. To this end, the inventors propose a turbomachine component according to claim 1.

[0006] The invention proposes a turbomachine part comprising an alloy of composition close to AM-1 but with an optimized hafnium content, so as to exhibit better resistance to oxidation.

[0007] The inventors observed that such a component exhibits particularly high oxidation resistance. Without being bound by theory, the inventors believe that when the hafnium content is too low, little Hf oxidation occurs, and the HfO₂ oxide does not fulfill its role as an anchoring structure for the oxide layer on the superalloy surface. Similarly, if the hafnium content is too low, the hafnium does not sufficiently block the outward diffusion of cations, thus preventing the formation of protective oxide layers such as α-Al₂O₃. At hafnium concentrations exceeding 1100 ppm, excessively large HfO₂ hafnium oxides can form, reducing the oxide / metal interface toughness and thus compromising the oxide's protective function.

[0008] In one embodiment, the mass content of hafnium in the substrate can be between 670 ppm and 780 ppm.

[0009] The inventors found that this hafnium content made it possible to obtain a part with the best resistance to oxidation.

[0010] Furthermore, the inventors have found that a part with an optimized hafnium content has good mechanical properties, close to those of an AM1 part, and can therefore be used in the same engine component applications as AM1. It is possible to shape a part of the invention using prior art forming processes already applicable to AM1 parts. In particular, the proposed optimized hafnium content does not compromise the feasibility of the turbomachinery component homogenization steps that can be performed at the end of the AM1 part forming process.

[0011] In one embodiment, the superalloy can define an external surface of the part. In other words, it is not necessary to coat the part to benefit from the oxidation resistance properties conferred by the part described above.

[0012] In another embodiment, a β-structured nickel aluminide coating may be present on the surface of a superalloy as described above. Thus, in one embodiment, a turbomachine component may comprise: a substrate formed by the nickel-based superalloy, and a β-structure nickel aluminide coating present on the substrate.

[0013] It should be noted that, generally speaking, β-structure nickel aluminide coatings 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.

[0014] In one embodiment, the β-structure nickel aluminide coating is a β-structure NiAl coating or a β-structure NiPtAl coating.

[0015] The β-structure nickel aluminide coating can be formed by a method known per se. For example, β-structure nickel aluminide can be formed by physical vapor deposition, chemical vapor deposition, box carburizing, or by slip deposition.

[0016] In the preceding embodiment, a turbomachine part according to the invention may further include a thermal barrier present on the nickel aluminide coating of β structure.

[0017] 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.

[0018] In one embodiment, the thermal barrier may be present in contact with the β structure nickel aluminide coating.

[0019] 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.

[0020] In one embodiment, the turbomachine component can be a turbomachine blade, a turbomachine distributor, a turbomachine turbine ring, or a turbomachine combustion chamber. The distributor can be a high-pressure or low-pressure distributor.

[0021] In a preferred embodiment, the turbomachine part can be a turbomachine blade, or a high-pressure turbomachine distributor.

[0022] According to another aspect, the invention also relates to a turbomachine comprising a part as described above. Brief description of the figures

[0023] [ Fig. 1 ] There figure 1 represents, schematically and partially, a cross-sectional view of a turbomachine component according to one embodiment of the invention. Fig. 2 ] There figure 2 represents, schematically and partially, a cross-sectional view of a turbomachine component according to another embodiment of the invention. Fig. 3 ] There figure 3 is a result of comparative tests showing the differences in terms of oxidation resistance between parts according to the invention and parts outside the invention. Detailed description

[0024] 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.

[0025] There figure 1represents a first embodiment of the invention, in which a turbomachine part 20 is made entirely of a superalloy 21 without any coating being applied to it. In this embodiment, the superalloy forms the outer part of the part.

[0026] On the figure 2 , illustrating another particular embodiment of the invention, a turbomachine part 24 is schematically represented as consisting of a superalloy substrate 21 and a nickel aluminide coating 22 of β structure which covers the underlying superalloy substrate 21.

[0027] In the embodiment shown, the turbomachine part 24 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 between 500 ppm and 1100 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. 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, then twice a week thereafter.

[0035] The samples tested in this example are uncoated. In other words, the side of the sample that undergoes the oxidation cycles is made of superalloy.

[0036] 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 when a specific mass loss of 20 mg / cm² is observed.

[0037] There figure 3 illustrates the results obtained for each sample. The mass concentrations of hafnium in the samples shown on the figure 3 are for curves 11a and 11b of 340 ppm, curves 12a and 12b of 670 ppm, curve 13a of 780 ppm, curves 16a and 16b of 1300 ppm, curves 15a and 15b of 2100 ppm, curves 14a and 14b of 4700 ppm and curves 17a and 17b of 8000 ppm.

[0038] There is no difference in composition between the samples whose results are represented with a number followed by the letter a and the composition of the sample whose results are represented with the same number followed by the letter b.

[0039] It can be observed on the figure 3 Samples with a hafnium mass concentration between 500 ppm and 1100 ppm (12a, 12b, and 13a) also exhibit the lowest mass loss. This optimized hafnium content therefore provides better resistance to oxidation.

[0040] The expression "between ... and ..." should be understood as including the boundaries.

Claims

1. A turbomachine part (20) comprising a nickel-based superalloy (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 between 500 ppm and 1100 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.

2. The turbomachine part (20) according to claim 1, wherein the hafnium mass content in the superalloy (21) is between 670 ppm and 780 ppm.

3. The turbomachine part (20) according to claim 1 or 2, wherein the superalloy (21) defines an outer surface of the part.

4. The turbomachine part (24) according to claim 1 or 2, comprising: - a substrate formed by the nickel based superalloy (21), and - a β-structured nickel aluminide coating (22) present on the substrate.

5. The turbomachine part (24) according to claim 4, wherein the β-structured nickel aluminide coating (22) is a β-structured NiAl coating or β-structured NiPtAl coating.

6. The turbomachine part (24) according to claim 4 or 5, wherein a thermal barrier (23) is present on the β-structured nickel aluminide coating (22).

7. The turbomachine part (20) according to any one of claims 1 to 6, wherein the superalloy (21) is monocrystalline.

8. The turbomachine part (20) according to any one of claims 1 to 7, wherein said part is a turbomachine vane, a turbomachine distributor, a turbomachine turbine ring, or a turbomachine combustion chamber.

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