Nickel-based superalloys, raw materials, components and methods

Abstract

The invention relates to a nickel-based superalloy comprising (in wt%) 4.5% to 5.5% cobalt (Co), 12% to 13% chromium (Cr), 1.6% to 2% molybdenum (Mo), 1.7% to 2.5% tungsten (W) 10, 4.6% to 5.2% aluminum (Al), 3.1% to 3.7% titanium (Ti), 1.1% to 1.7% niobium (Nb), 0.05% to 0.13% carbon (C), 0.01% to 0.02% boron (B) 15, 0.008% to 0.015% zirconium (Zr), 0.007% to 0.013% silicon (Si), up to 0.6% hafnium (Hf), nickel (Ni).

Description

[0001] The present invention relates to nickel-based superalloys, raw materials, components, and methods for casting them.

[0002] When the last-stage blade is designed for aero efficiency and resistance to creep, the design work is limited by LCF in the disk attachment due to the mass of the blade. All else being equal, reducing the density of the blade alloy will enable a design with better aero efficiency and / or allow a higher metal temperature, as it alleviates the LCF limitation. Improved aero efficiency and / or increased allowable metal temperature will, for example, be able to increase the thermal efficiency of a combined cycle power generation plant.

[0003] The last-stage blade operates at temperatures where the hot corrosion agent is particularly aggressive. To achieve fuel flexibility (including the use of corrosive fuels such as those containing biofuels) and to cope with airborne contaminants such as sea salt, it is advantageous to have good resistance to hot corrosion.

[0004] A general rule of thumb for good resistance to hot corrosion is to have a nominal composition with at least about 12 wt% chromium (Cr), at most about 2 wt% molybdenum (Mo), and no vanadium (V).

[0005] About 12 wt% Cr can form a continuous Cr2O3 layer in the oxide layer to slow down further oxidation and prevent corrosive elements from flowing into the alloy.

[0006] Molybdenum (Mo) and no vanadium (V) can react with the corrosion agent and accelerate the erosion from the corrosion agent.

[0007] Oxidation is generally not a major problem for the last-stage blade because the metal temperature is moderate by the standards of turbine hot-stage components. The last-stage blade typically operates in the range of 600 °C to 800 °C. Therefore, the ability to form a continuous and adherent Cr2O3 layer is sufficient.

[0008] IN792 with a nominal composition of Ni-8.5Co-12.5Cr-1.8Mo-4W-3.4Al-4Ti-4Ta-0.08C-0.02Zr-0.015B (in wt%) has a good combination of creep resistance and hot corrosion resistance, a γ' particle content of about 50 mol%, and is widely used for last-stage blades and other turbine components. Molybdenum (Mo) and no vanadium (V) are used to strengthen the γ matrix, while titanium (Ti) and tantalum (Ta) are used to strengthen the γ' particles.

[0009] Therefore, an object of the present invention is to improve the properties of nickel-based superalloys.

[0010] The said problem is solved by the alloy according to claim 1, by the raw material according to claim 13, the component according to claim 14, and the method according to claim 17.

[0011] Further advantageous features which can be combined with one another to produce additional advantages are listed in the dependent claims.

[0012] Although an increased γ'-content above a relatively high level as already seen in IN792 may be detrimental to the long-term creep strength as it may exacerbate the long-term coarsening of the γ'-structure, the coarsening is not a critical issue at the metal temperatures relevant to the posterior stage blades. Although the increased γ'-content may also be detrimental to all properties as it may exacerbate the precipitation tendency of unwanted phases such as Laves and Sigma, in the present invention, the increased γ'-content is balanced by reducing the strengthening elements, such that the phase stability is maintained.

[0013] A blade alloy having creep resistance and corrosion resistance above the IN792 level and a reduced density will be able to achieve higher performance. Accordingly, it is an object of the present invention to provide an alloy having creep resistance and corrosion resistance at the IN792 level and a reduced density. Relative to IN792, the level of the strengthening elements is reduced, which is detrimental to the creep strength but will reduce the density. Al is increased, which will further reduce the density and increase the γ'-particle content, which is advantageous for the creep strength. Ta is replaced by Nb, which will further reduce the density. Si is included at a low measured level, while in most specifications for IN792, it is nominally set to zero. Such inclusion is to avoid the risk of reduced oxidation resistance and hot corrosion resistance that may occur if the production process of the component proves to result in an abnormally low level of silicon (Si), since silicon (Si) has a beneficial catalytic effect on the selective oxidation of the protective Cr2O3 even at low levels. Hafnium (Hf) values up to 2.0 wt% (the range visible in commercial alloys) can be added as required. If the alloy is directionally cast, higher hafnium (Hf) values will be used.

[0014] Some casting suppliers include hafnium (Hf) up to about 2.0 wt% to improve the casting yield. Whether hafnium (Hf) is an advantage, and if so, at what level, depends on the geometry of the component, as well as the specific casting method, die material, and equipment used by the supplier. When hafnium (Hf) is added, the level of one or more of the other alloy elements is slightly reduced to ensure that this does not cause an increased precipitation tendency of unwanted phases such as Laves and Sigma.

[0015] Tantalum (Ta) is usually added for oxidation resistance and strength in alloys for hot-stage blade manufacturing, while niobium (Nb) provides the same strengthening effect per atomic %, but does not improve oxidation resistance. Therefore, it is advantageous to replace tantalum (Ta) with niobium (Nb) in trailing-stage blades where a reasonable trade-off is made to reduce density at the cost of some oxidation resistance.

[0016] The nickel-based alloy of the present invention has the following composition:

[0017] It contains (by weight %), in particular consists of these elements:

[0018] Nickel-based superalloy,

[0019] It contains (by weight %):

[0020] 3.0% to 9.0% cobalt (Co),

[0021] In particular 4.0% to 9.0% cobalt (Co), 11.0% to 14.0% chromium (Cr),

[0022] In particular 11.5% to 13.5% chromium (Cr),

[0023] Very particularly 12.0% to 13.0% chromium (Cr), 1.0% to 3.5% molybdenum (Mo),

[0024] In particular 1.5% to 3.5% molybdenum (Mo), 4.0% to 6.0% aluminum (Al),

[0025] In particular 4.5% to 6.0% aluminum (Al),

[0026] Very particularly 5.0% aluminum (Al), 2.7% to 4.0% titanium (Ti),

[0027] In particular 3.0% to 4.0% titanium (Ti),

[0028] Very particularly 3.5% titanium (Ti), 0.03% to 0.15% carbon (C), in particular 0.08% to 0.15% carbon (C), 0.005% to 0.030% boron (B),

[0029] In particular 0.008% to 0.020% boron (B),

[0030] Very particularly 0.015% boron (B), 0.005% to 0.03% zirconium (Zr),

[0031] Particularly, 0.008% to 0.012% of zirconium (Zr), very particularly 0.01% of zirconium (Zr), nickel (Ni) and inevitable impurities, optional the following components: 1.5% to 3.0% of tungsten (W),

[0032] Particularly 1.5% to 2.5% of tungsten (W), 1.0% to 2.5% of niobium (Nb),

[0033] Particularly 1.0% to 2.0% of niobium (Nb),

[0034] 0.005% to 0.03% of silicon (Si),

[0035] Up to 2.0% of hafnium (Hf),

[0036] Particularly 0.5% to 1.5% of hafnium (Hf),

[0037] Up to 5 wt% of iron (Fe),

[0038] Particularly up to 3.0 wt% of iron (Fe),

[0039] Maximum 5 ppm of sulfur (S).

[0040] Particularly, it consists of these elements.

[0041] Particularly, only the said elements are used for the alloy.

[0042] A possible composition is given by Ni-5Co-12.5Cr-2Mo-2W-5Al-3.5Ti-1.5Nb-0.12C-0.015B-0.01Zr (in wt%) and has a density in the range of 7.8 kg / dm3 to 8 kg / dm3 and a γ' particle content of 67 mol% (at 850 °C).

[0043] It can be noted that the said alloy does not contain rhenium (Re) and tantalum (Ta), which are two elements commonly used in modern nickel-based superalloys, but unfortunately, these two elements significantly increase their density. Boron (B), carbon (C) and zirconium (Zr) are used for grain boundary strengthening and are included at normal values for high-strength nickel-based γ'-strengthened superalloys.

[0044] Furthermore, the said alloy should preferably be cast by a clean process such that, for example, the resulting sulfur content is less than 5 ppm. Sulfur (S) can severely reduce the protective ability and adhesion of the Cr2O3 layer, and therefore, despite the moderate use temperature, strict limitation of this element is prudent.

[0045] A possible embodiment is given by Ni-5Co-12.5Cr-1.8Mo-2.2W-5Al-3.5Ti-1.5Nb-0.1C-0.015B-0.01Zr-0.01Si (in wt%). It has a predicted density using the following extended Caron formula of about 7.9 kg / dm 3 and a predicted γ' particle content at 850 °C of 67 mol% based on ThermoCalc with TTNi8 as the database. The levels of the γ matrix elements Co and W are reduced relative to IN792. However, the reduction in γ matrix strength is small because the amount of the γ matrix to be strengthened by Mo and W is reduced relative to IN792. On an atomic basis, 1.5 wt% niobium (Nb) corresponds to about 3 wt% tantalum (Ta). Thus, the sum of the γ' strengthening elements titanium (Ti), tantalum (Ta), and niobium (Nb) is reduced relative to the very high levels of γ' strengthening elements used in IN792. Aluminum is increased to achieve a higher γ' content.

[0046] Hafnium (Hf) can be added as required for the production process requirements, as is currently done for IN792. In this case, one or more of the alloying elements need to be adjusted by those skilled in the art such that, for example, the precipitation tendency of unwanted phases does not increase. A higher upper limit of 2.0 wt% is selected relative to IN792 to also allow directional solidification casting. In addition, iron (Fe) can be added as required to reduce the γ' solvus line and thus increase the heat treatment window, for example, to control the inclusion of hafnium (Hf) which tends to reduce the heat treatment window.

[0047] Tungsten (W) within this range provides a useful strengthening effect and is low enough to avoid excessive formation of unwanted phases.

[0048] Aluminum (Al) is included at about 4 wt% to 6 wt%. Within this range, it is high enough to reduce the risk that the joint should be a weak link for oxidation and corrosion, high enough to contribute to the formation of γ' particles, and low enough to avoid excessive formation of unwanted phases.

[0049] Tantalum (Ta) is preferably not included.

[0050] Molybdenum (Mo) is an effective γ matrix strengthening element with low diffusivity.

[0051] Carbon (C) is an element with high diffusivity and at first glance might be thought to easily reach equilibrium with surrounding parts. However, internal experience does sometimes show joints that are essentially free of carbides (which are not usable) when BFM's that do not contain carbon (C) are used. Our explanation is that when boron (B) from the joint diffuses from the joint, carbon near the joint is at least temporarily incorporated in carboride. There should be a lower limit for carbon (C) to avoid joints that are completely free of carbon (C), but too high a level of carbon (C) means the risk of forming brittle carbide films and elongated carbides. Carbon (C) is included at 0.03 wt% to 0.15 wt%.

[0052] Zirconium (Zr) is an element that provides grain boundary strengthening and acts as a sulfur agglomerator at low measured levels. It needs to be capped at low levels because it tends to segregate, which can cause incipient melting because it is a melt depressant. It is included at 0.005 wt % to 0.03 wt %.

[0053] Additional examples of the present invention are listed here:

[0054] Cr Co Mo W Al Ti Nb Hf C B Zr Fe Si 1 12.5％ 5％ 2％ 2％ 5％ 3.5％ 1.5％ 0.12％ 0.015％ 0.01％ 2 12.5％ 5％ 2％ 2％ 5％ 3.5％ 1.5％ 0.12％ 0.015％ 0.01％ 3 12.5％ 5％ 3％ 5％ 3.5％ 1.5％ 0.12％ 0.015％ 0.01％ 4 12.5％ 5％ 1.8％ 2.2％ 5％ 3.3％ 1.4％ 0.5％ 0.1％ 0.015％ 0.01％ 0.01％ 5 12.5％ 5％ 1.8％ 2.2％ 5％ 3.5％ 1.5％ 0.1％ 0.015％ 0.01％ 0.01％ 6 12％ 3％ 2％ 2％ 4.2％ 3.0％ 1.0％ 0.5％ 0.05％ 0.015％ 1％ 7 14％ 8％ 2％ 2.1％ 5.5％ 3.9％ 1.5％ 0.08％ 0.015％ 0.01％ 0.02％ 8 12％ 7％ 1.8％ 2.2％ 6％ 2.8％ 0.8％ 0.08％ 0.015％ 0.008％ 0.5％ 0.008％

Claims

1. A nickel-based superalloy, Comprising (by weight %), in particular consisting of these elements: 3.0% to 9.0% cobalt (Co), In particular, 4.0% to 9.0% cobalt (Co), 11.0% to 14.0% chromium (Cr), In particular, 11.5% to 13.5% chromium (Cr), Very particularly, 12.0% to 13.0% chromium (Cr), 1.0% to 3.5% molybdenum (Mo), In particular, 1.5% to 3.5% molybdenum (Mo), 4.0% to 6.0% aluminum (Al), In particular, 4.5% to 6.0% aluminum (Al), Very particularly, 5.0% aluminum (Al), 2.7% to 4.0% titanium (Ti), In particular, 3.0% to 4.0% titanium (Ti), Very particularly, 3.5% titanium (Ti), 0.03% to 0.15% carbon (C), In particular, 0.08% to 0.15% carbon (C), 0.005% to 0.030% boron (B), In particular, 0.008% to 0.020% boron (B), Very particularly, 0.015% boron (B), 0.005% to 0.03% zirconium (Zr), In particular, 0.008% to 0.012% zirconium (Zr), Very particularly, 0.01% zirconium (Zr), Nickel (Ni) and inevitable impurities, Optional following components: 1.5% to 3.0% tungsten (W), In particular, 1.5% to 2.5% tungsten (W), 1.0% to 2.5% niobium (Nb), In particular, 1.0% to 2.0% niobium (Nb), 0.005% to 0.03% silicon (Si), Up to 2.0% hafnium (Hf), In particular, 0.5% to 1.5% hafnium (Hf), Up to 5 wt% iron (Fe), In particular, up to 3.0 wt% iron (Fe), Maximum 5 ppm sulfur (S).

2. The nickel-based superalloy according to claim 1, Not containing tungsten (W) and / or tantalum (Ta).

3. The nickel-based superalloy according to claim 1 or 2, Containing niobium (Nb) or hafnium (Hf).

4. The nickel-based superalloy according to any one of claims 1, 2 or 3, Containing 1.5% to 2.5% molybdenum (Mo), In particular, 2.0% molybdenum (Mo).

5. The nickel-based superalloy according to any one of claims 1, 2 or 3, Containing 2.5% to 3.5% molybdenum (Mo), In particular, 3.0% molybdenum (Mo).

6. The nickel-based superalloy according to any one of claims 1, 2, 3, 4 or 5, containing (by weight): 4.5% to 5.5% cobalt (Co) 12% to 13% chromium (Cr) 1.6% to 2% molybdenum (Mo) 1.7% to 2.5% tungsten (W) 4.6% to 5.2% aluminum (Al) 3.1% to 3.7% titanium (Ti) 1.1% to 1.7% niobium (Nb) 0.05% to 0.13% carbon (C) 0.01% to 0.02% boron (B) 0.008% to 0.015% zirconium (Zr) 0.007% to 0.013% silicon (Si) Hafnium (Hf) up to 0.6% Nickel (Ni).

7. The nickel-based superalloy according to any one of claims 1, 2, 3, 4 or 5, comprising (by weight%): 4.5% to 5.5% cobalt (Co) 12% to 13% chromium (Cr) 1.6% to 3.4% molybdenum (Mo) 4.6% to 5.4% aluminum (Al) 3.1% to 3.7% titanium (Ti) 0.07% to 0.15% carbon (C) 0.01% to 0.02% boron (B) 0.008% to 0.015% zirconium (Zr) Nickel (Ni), optionally the following components: 1.7% to 2.5% tungsten (W) 1.0% to 2.0% hafnium (Hf) 1.1% to 1.7% niobium (Nb).

8. The nickel-based superalloy according to any one of claims 1, 2, 3, 4, 5 or 7, comprising (by weight%): 5% cobalt (Co) 12.5% chromium (Cr) 2% molybdenum (Mo) 2% tungsten (W) 5% aluminum (Al) 3.5% titanium (Ti) 1.5% niobium (Nb) 0.12% carbon (C) 0.015% boron (B) 0.01% zirconium (Zr) Nickel (Ni).

9. The nickel-based superalloy according to any one of claims 1, 2, 3, 4, 5 or 7, comprising (by weight%): 5% cobalt (Co) 12.5% chromium (Cr) 2% molybdenum (Mo) 2% tungsten (W) 5% aluminum (Al) 3.5% titanium (Ti) 1.5% hafnium (Hf) 0.12% carbon (C) 0.015% boron (B) 0.01% zirconium (Zr) Nickel (Ni).

10. The nickel-based superalloy according to any one of claims 1, 2, 3, 4, 5 or 7, comprising (by weight%): 5% cobalt (Co) 12.5% chromium (Cr) 3% molybdenum (Mo) 5% aluminum (Al) 3.5% titanium (Ti) 1.5% hafnium (Hf) 0.12% carbon (C) 0.015% boron (B) 0.01% zirconium (Zr) Nickel (Ni).

11. The nickel-based superalloy according to any one of claims 1, 2, 3, 4, 5 or 6, comprising (by weight%): 5% cobalt (Co) 12.5% chromium (Cr) 1.8% molybdenum (Mo) 2.2% tungsten (W) 5% aluminum (Al) 3.3% titanium (Ti) 1.4% niobium (Nb) 0.1% carbon (C) 0.015% boron (B) 0.01% zirconium (Zr) 0.01% silicon (Si) 0.5% hafnium (Hf) Nickel (Ni).

12. The nickel-based superalloy according to any one of claims 1, 2, 3, 4, 5 or 6, comprising (by weight%): 5% cobalt (Co) 12.5% chromium (Cr) 1.8% molybdenum (Mo) 2.2% tungsten (W) 5% aluminum (Al) 3.5% titanium (Ti) 1.5% niobium (Nb) 0.1% carbon (C) 0.015% boron (B) 0.01% zirconium (Zr) 0.01% silicon (Si) Nickel (Ni).

13. A raw material, comprising the composition according to any one of claims 1 to 12, in particular consisting of the composition according to any one of claims 1 to 12, wherein the raw material is a powder, in particular a powder comprising a binder or ceramic particles or wherein the raw material is in the form of a bar, rod or billet.

14. A component, having the composition according to any one of claims 1 to 12, the component being in particular a component of a turbine, very particularly a blade or vane.

15. The component according to claim 14, wherein the component is cast, in particular cast into an equiaxed microstructure.

16. The component according to claim 14, wherein the component is cast, in particular cast into a columnar microstructure or a single crystal microstructure.

17. A method for producing the component according to claim 14, 15 or 16, wherein the alloy is melted, in particular cast into an equiaxed microstructure or a directionally solidified structure.