Nickel-based alloy containing tantalum

Abstract

The present invention relates to a nickel-based alloy comprising, by mass percentage: - 4.0 to 20.0% cobalt; - 14.0 to 18.5% chromium; - 1.8 to 2.6% aluminum; - 1.3 to 1.9% titanium; - 5.5 to 6.5% tantalum; - 0.01 to 0.10% carbon; - 0.003 to 0.02% boron; and - 0.01 to 0.10% zirconium. The present invention also relates to a method for manufacturing a part from the nickel-based alloy, the method comprising: - the production of a billet having the composition of the nickel-based alloy; - the shaping of the part; and - the heat treatment of the part. Fig. 1

Description

Title of the invention: Nickel-based alloy comprising tantalum Scope of the invention

[0001] The present invention relates to nickel-based alloys. More particularly, the present invention relates to nickel-based alloys specifically designed for an application such as a turbine housing for an aircraft engine and comprising tantalum. State of the art

[0002] The objectives of ACARE in line with the European Green Deal of the Union European regulations, along with the cost-of-ownership reduction requirements imposed by aircraft manufacturers, are forcing engine manufacturers to significantly increase the performance of new-generation turbofan engines, particularly by drastically reducing specific fuel consumption. This translates into a need to improve engine efficiency by reducing the ventilation of hot components. Consequently, materials will have to withstand increasingly high operating temperatures.

[0003] For example, in the case of a low-pressure turbine housing, certain areas are subjected to both fatigue and scouring at very high temperatures, with a target of 800 °C and peaks at 850 °C for new-generation engines. Fatigue life is favored by a fine grain size (around 10 according to ASTM E12, hereafter abbreviated as ASTM), while the best scouring resistance is obtained on coarse-grained microstructures (around 0 ASTM). Therefore, a compromise must be found between these two opposing properties.

[0004] Today, the main alloys known for use in aircraft turbine housings are Inconel 718, 718 Plus, and Waspaloy. Their maximum operating temperatures are approximately 650 °C, 704 °C, and 750 °C, respectively. Beyond these temperatures, their mechanical properties decrease due to a softening of their microstructure. These alloys are therefore not designed to withstand temperatures of around 800 °C for extended periods.

[0005] Other alloys produced by powder metallurgy can achieve these high operating temperatures; for example, the alloy described in document EP 1 840 232 Bl. However, this alloy contains more than 43% by volume of γ' precipitates, and its ductility is insufficient for forming by circular rolling, a technique used to manufacture turbine housings for aircraft engines. The currently accepted upper limit is around 40% γ' precipitates.

[0006] Therefore, Waspaloy, an alloy containing 25% vol. of y' precipitates (whose nominal combination is in mass percentages Cr 18.00-21.00, Co 12.00-15.00, Mo 3.50-5.00, Al 1.20-1.60, Ti 2.75-3.25, B 0.003-0.01, C 0.02-0.10, Zr 0.02-0.08, Fe 0-2.00, Mn 0-0.10, Si 0-0.15, P 0-0.015, S 0-0.015 and Cu 0-0.10), is currently the one that allows the best compromise between fatigue life and resistance to high-temperature scouring. This compromise is achieved by using an intermediate grain size (between 2 and 6 ASTM) throughout the part. But again, this alloy was not designed to withstand an operating temperature of 800 °C for very long periods.

[0007] Certain alloys with 36% vol. of y' precipitates, such as FAD730TM or Rene65, could exhibit better properties than Waspaloy, but they do not currently allow for achieving an intermediate and homogeneous grain size on large parts. Their grain size, which is controlled solely by the primary y' precipitate populations, increases very rapidly when the temperature exceeds the y' solvus. Avoiding this excessive grain size growth would require controlling the heat treatment temperature to within one degree across the entire part, which is not feasible in an industrial furnace.

[0008] Thus, at present, there is no alloy which combines both better heat resistance than Waspaloy, the ability to be shaped by circular rolling, and the ability to achieve a homogeneous intermediate grain size throughout the part by heat treatment to ensure the compromise between resistance to fining and the fatigue life required for the intended application.

[0009] There is therefore a need for a new alloy that can meet the need to increase the operating temperature of the part, while maintaining a manufacturing method by circular rolling and without degrading the fatigue life compared to Waspaloy. Summary of the invention

[0010] Thus, one of the objectives of the present invention is to overcome at least one of the disadvantages mentioned above.

[0011] For this purpose, the present invention proposes a nickel-based alloy comprising tantalum, comprising by mass percentage: - 4.0 to 20.0% cobalt; - 14.0 to 18.5% chromium; - 1.8 to 2.6% aluminum; - 1.3 to 1.9% titanium; - 5.5 to 6.5% tantalum; - 0.01 to 0.10% carbon; - 0.003 to 0.02% boron; and - 0.01 to 0.10% zirconium.

[0012] Other optional and non-limiting features are as follows.

[0013] The nickel-based alloy may comprise 0.02 to 0.05% carbon by mass percentage.

[0014] The nickel-based alloy may comprise, by mass percentage: - 14.0 to 20.0% cobalt; - 2.0 to 2.5% aluminum; - 1.4 to 1.8% titanium; and - 5.7 to 6.4% tantalum.

[0015] The nickel-based alloy may comprise 5.0 mass % or less of molybdenum.

[0016] The nickel-based alloy may comprise 5.0% by mass or less of iron, of preference 2.0% by mass or less.

[0017] The nickel-based alloy may comprise 9.0 wt% or less of tungsten, preferably 6.2 wt% or less.

[0018] The nickel-based alloy may comprise 1.0 wt% or less of niobium, preferably 0.5 wt% or less.

[0019] Furthermore, the present invention proposes a process for treating such an alloy comprising: - the manufacture of a billet whose composition is that of the nickel-based alloy; - the shaping of the part; and - the heat treatment of the part.

[0020] Other optional and non-limiting features are as follows.

[0021] The manufacture of the billet may include: - the production of an ingot, preferably by melting materials; and - the conversion of the ingot into billets, preferably by cutting the ingot and then forging.

[0022] The part's shaping may include: - the forging of the billet, preferably by crushing; - rolling of the forged billet, preferably by circular rolling.

[0023] The heat treatment of the part may include at least one of the following treatments: - a supersolvus y' type solution, preferably at a temperature 10 to 40 °C higher than solvus y'; and - a subsolvus y' type solution, preferably at a temperature 10 to 40 °C lower than solvus y'.

[0024] The heat treatment may further include: - a precipitation sludge of M23C6 type carbides, preferably by heating to a temperature between 825 and 870 °C; and - optionally a stabilization income for precipitate populations y', preferably at a temperature between 760 and 825 °C.

[0025] The present invention also provides an aeronautical part in the alloy described above, in particular a turbine housing.

[0026] Nickel-based alloys comprising tantalum according to the invention are suitable for the manufacture of parts intended to withstand temperatures of around 800 °C in the hottest parts thereof and temperature peaks of up to 850 °C, while maintaining good fatigue resistance over the whole of them.

[0027] This compromise is made possible by controlling grain size through heat treatment and forging, which allows for an intermediate grain size of ASTM 2 to 6. The alloy is also suitable for production by vacuum casting and shaping by ring rolling, techniques that limit manufacturing costs compared to other methods such as powder metallurgy or direct manufacturing. Presentation of the drawings

[0028] Other objectives, features and advantages will become apparent from reading the description with reference to the drawings shown below.

[0029] [Fig. 1] is a diagram showing the steps of the process of manufacturing a part in a nickel-based alloy comprising tantalum according to the invention.

[0030] [Fig.2] is a diagram showing an example of sub-steps of billet manufacturing of the process according to the invention.

[0031] [Fig.3] is a diagram showing an example of ingot production sub-steps of the billet manufacturing step.

[0032] [Fig.4] is a diagram showing an example of sub-steps of the ingot conversion into billets of the billet manufacturing step.

[0033] [Fig.5] is a diagram showing an example of sub-steps of part shaping of the process according to the invention.

[0034] [Fig.6] is a diagram showing a first example of sub-steps of the heat treatment of the process according to the invention.

[0035] [Fig.7] is a diagram showing a second example of sub-steps of the heat treatment of the process according to the invention.

[0036] [Fig.8] is a diagram showing a third example of sub-steps of the heat treatment of the process according to the invention.

[0037] [Fig.9] is a diagram showing grain boundaries and carbide precipitates in an alloy according to the invention after treatment according to the treatment process of one of Figures 1 to 8.

Claims

Demands

1. Nickel-based alloy, comprising in mass percentages of: - 4.0 to 20.0% cobalt; - 14.0 to 18.5% chromium; - 1.8 to 2.6% aluminium; - 1.3 to 1.9% titanium; - 5.5 to 6.5% tantalum; - 0.01 to 0.10% carbon; - 0.003 to 0.02% boron; and - 0.01 to 0.10% zirconium; - 0 to 5.0% molybdenum; - 0 to 5.0% iron; - 0 to 9.0% tungsten; - 0 to 1.0% niobium; nickel representing the balance to reach 100%.

2. Nickel-based alloy according to claim 1, comprising by mass percentage: - 0.02 to 0.05% carbon.

3. Nickel-based alloy according to claim 1 or claim 2, comprising by mass percentage: - 14.0 to 20.0% cobalt; - 2.0 to 2.5% aluminium; - 1.4 to 1.8% titanium; and - 5.7 to 6.4% tantalum.

4. A method for manufacturing a part from a nickel-based alloy according to any one of claims 1 to 3, the method comprising: - manufacturing a billet having the composition of the nickel-based alloy; - shaping the part; and - heat treating the part.

5. A method according to claim 4, wherein the heat treatment of the part comprises at least one treatment among: - a supersolvus y' type solution treatment, preferably at a temperature 10 to 40 °C higher than solvus y'; and - a subsolvus y' type solution treatment, preferably at a temperature 10 to 40 °C lower than solvus y'.

6. A process according to any one of claims 4 to 5, wherein the heat treatment may further comprise: - a precipitation tempering of M23C6 type carbides, preferably by heating at a temperature between 825 and 870 °C; and - optionally a stabilization tempering of the y' precipitate populations, preferably at a temperature between 760 and 825 °C.

7. Aeronautical part in an alloy according to any one of claims 1 to 3, in particular a turbine housing.

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