Coated turbine components having a nickel-based substrate containing hafnium

Abstract

The present invention relates to a turbine component (20) comprising: (i) a nickel-based superalloy substrate (21) comprising, by mass, 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 at a mass content greater than or equal to 2000 ppm, and optionally niobium at a mass content less than or equal to 1.5%, and at least one of carbon, zirconium and boron, optionally each at a mass content less than or equal to 100 ppm, the remainder consisting of nickel and unavoidable impurities; and (ii) a β-structured nickel-aluminate coating (22) covering the substrate.

Description

Technical Field

[0001] This invention relates to the field of nickel-based superalloys, and more precisely to superalloys for use in the aerospace field. Background Art

[0002] As is well known, nickel-based superalloys possess both high mechanical strength even at high temperatures and excellent oxidation resistance. Due to these two properties, they are the preferred material for turbine components in the aerospace field.

[0003] Among known nickel-based superalloys, one alloy with the trade name AM-1 can be specifically mentioned, which corresponds to the composition described in document US 4639280.

[0004] The oxidation resistance of superalloys can be further improved by forming coatings on their surfaces. However, even with such coatings, currently available AM-1-based alloys eventually oxidize when used in turbines. Therefore, further improvements in the oxidation resistance of superalloys for turbine components remain necessary. Summary of the Invention

[0005] To this end, the inventors provide a turbine component comprising:

[0006] (i) A nickel-based superalloy substrate, comprising, by mass, 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 at a mass content greater than or equal to 2000 ppm, and optionally niobium at a mass content less than or equal to 1.5%, and optionally at least one of carbon, zirconium, and boron, each at a mass content less than or equal to 100 ppm, the remainder consisting of nickel and unavoidable impurities; and

[0007] (ii) A β-structured nickel-aluminate coating covering the substrate.

[0008] Preferably, the hafnium content is less than or equal to 15,000 ppm.

[0009] This invention provides a turbine component formed from a substrate coated with a β-structured nickel-aluminate compound, the substrate having a composition similar to AM-1 but modified to have a relatively high hafnium content (at least 2000 ppm). The inventors have observed that the component formed from this substrate coated with this particular coating exhibits exceptionally high oxidation resistance. Not wishing to be limited by theory, the inventors believe that by ensuring hafnium can migrate to the surface and form a protective oxide, rather than being trapped as a carbide within the material, the limited carbon content in the substrate contributes to improved oxidation resistance of the component.

[0010] Preferably, the hafnium content in the substrate can be greater than or equal to 4000 ppm.

[0011] In a preferred embodiment, the hafnium mass content in the substrate can be greater than or equal to 6000 ppm.

[0012] The inventors have discovered that the higher the hafnium content, the better the antioxidant properties.

[0013] In one implementation, the superalloy is single-crystal. Single-crystal superalloys allow hafnium to migrate to the surface in greater quantities and at a faster rate because hafnium is not trapped by carbon, which is typically introduced to stabilize the grain boundaries of polycrystalline alloys. This further improves the protection imparted by hafnium, thereby enhancing the oxidation resistance of the component.

[0014] In one embodiment, the β-structured nickel-aluminate coating may be β-structured NiAl. It should be noted that the β-structured nickel-aluminate coating may or may not be modified by one or more elements, such as platinum, zirconium, or hafnium. Therefore, as a β-structured nickel-aluminate coating suitable for the present invention, it may specifically be made of β-structured NiAl, β-structured NiPtAl, β-structured NiAlZr, and β-structured NiAlHf.

[0015] In one embodiment, the β-structured nickel-aluminate coating is a β-structured NiAl coating or a β-structured NiPtAl coating.

[0016] β-structured nickel-aluminate coatings can be formed using methods known in the art. For example, the formation of β-structured nickel-aluminate coatings can specifically be achieved through physical vapor deposition, chemical vapor deposition, solid carburizing, or via a slurry process.

[0017] In one embodiment, the turbine component according to the invention may further include a thermal barrier present on a β-structured nickel-aluminate coating.

[0018] The thermal barrier itself is known and can protect turbine components from the high temperatures encountered during their use.

[0019] In one embodiment, the thermal barrier may exist in contact with a β-structured nickel-aluminate coating.

[0020] In one implementation, the turbine component may be a turbine distributor or a turbine distributor sector. The distributor may be a high-pressure distributor or a low-pressure distributor.

[0021] In alternative implementations, turbine components may also be moving vanes or turbine ring sectors.

[0022] According to another aspect, the invention also relates to a turbine comprising the components described above. Attached Figure Description

[0023] [ Figure 1 ] Figure 1 A portion of a turbine distributor according to one embodiment of the present invention is shown schematically and in part.

[0024] [ Figure 2 ] Figure 2 A schematic, and partially illustrated, cross-sectional view of a turbine component according to one embodiment of the present invention is shown.

[0025] [ Figure 3 ] Figure 3 These are comparative test results showing the difference in antioxidant properties between components according to the present invention and components outside the present invention. Detailed Implementation

[0026] The invention will now be described with reference to the accompanying drawings, which are intended to provide a better understanding of the invention and should not be interpreted in a restrictive manner.

[0027] Typically, a turbine consists of stationary elements and movable elements. The movable element can be a movable wheel that carries the blades and is usually inserted between the stationary blade sets, also known as a distributor. The distributor / movable wheel pair forms the turbine stage.

[0028] Figure 1 A portion of the turbine distributor 10 is shown.

[0029] The turbine distributor 10 may include an outer platform 2 and an inner platform 4, with fixed blades 6 extending between the outer platform 2 and the inner platform 4, intended to guide airflow in a direction that facilitates the drive of adjacent movable wheels (not shown).

[0030] Figure 2 The schematic diagram shows a turbine component 20 comprising a substrate 21 and a β-structured nickel-aluminate coating 22 covering the lower substrate 21.

[0031] Furthermore, in the illustrated embodiment, the turbine component 20 also includes a thermal barrier 23 in contact with the β-structured nickel-aluminate coating 22. The thermal barrier 23 may define the outer surface of the component 20.

[0032] In one embodiment, the thickness e1 of the coating 22 can be from 40 μm to 90 μm.

[0033] Similarly, the thickness e2 of the thermal barrier 23 can be from 50 μm to 300 μm.

[0034] In one embodiment, the thermal barrier may be selected from zirconium oxide partially stabilized with yttrium oxide or one or more other rare earth oxides, dysprosium-doped zirconium oxide, gadolinium zirconate, or perovskite.

[0035] In an alternative embodiment, the thermal barrier 23 may be absent. In this case, the β-structured nickel-aluminate coating 22 may define the outer surface of the component.

[0036] Example

[0037] Multiple AM-1 samples were enriched with hafnium mass contents ranging from 340 ppm to 8000 ppm. Therefore, samples according to the invention were produced when the hafnium level was greater than or equal to 2000 ppm, and other samples outside the scope of the invention were also produced.

[0038] The sample only had its hafnium mass content changed.

[0039] The hafnium content of the samples prepared in this manner was determined by mass spectrometry. The samples were coated with a platinum-modified β-structured nickel aluminum oxide (NiPtAl) coating. Subsequently, each sample underwent oxidation cycling, and the mass change of each sample was measured three times per week for the first 200 cycles, and then twice per week thereafter.

[0040] The oxidation cycle corresponds to very rapid heating to the oxidation temperature (1150℃ ± 5℃), holding at 1150℃ for 60 minutes under atmospheric pressure, and finally forced cooling with dry air for 15 minutes to ensure room temperature is below 150℃ ± 3℃. After 6000 oxidation cycles, a concentration of 20 mg / cm³ was observed. 2 Stop the test when the specific mass changes.

[0041] Figure 3 The results obtained for each sample are shown. Figure 3 The hafnium mass content of the samples shown is as follows: 340 ppm for curve 11, 780 ppm for curve 12, 670 ppm for curve 13, 1300 ppm for curve 14, 2100 ppm for curve 15, 4700 ppm for curve 16, and 8000 ppm for curve 17.

[0042] Depend on Figure 3 It is evident that samples with hafnium content greater than 2000 ppm (15, 16, 17) also exhibited the lowest mass loss. Therefore, high hafnium content allows for better antioxidant properties.

[0043] The term “...to…” should be understood to include the end value.

Claims

1. A turbine component comprising: (i) A nickel-based superalloy substrate, comprising, by mass, 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 at a mass content greater than or equal to 4000 ppm, and niobium at a mass content of 0% to 1.5%, and at least one of carbon, zirconium, and boron, each at a mass content of 0 ppm to 100 ppm, the remainder consisting of nickel and unavoidable impurities; and (ii) A β-structured nickel-aluminate coating covering the substrate.

2. The turbine component as claimed in claim 1, wherein, The hafnium content in the substrate is greater than or equal to 6000 ppm.

3. The turbine component of claim 1, wherein the turbine component further comprises a thermal barrier present on a β-structured nickel-aluminate coating.

4. The turbine component as claimed in claim 1, wherein, The β-structured nickel-aluminate coating is either a β-structured NiAl coating or a β-structured NiPtAl coating.

5. The turbine component as claimed in claim 1, wherein, Superalloys are single crystals.

6. The turbine component as claimed in claim 1, wherein, The component is a turbine distributor or a turbine distributor sector.

7. A turbine comprising the components as claimed in claim 1.

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