Nickel base superalloy with low shrinkage and a component

Abstract

A Nickel based superalloy comprising 12.0 to 15.0 wt% Chromium, 1.0% to 2.0% Molybdenum, 3.0-12.0 wt% Tungsten, 1.2 to 2.0 wt% Aluminium, 1.2 to 2.0 wt% Titanium 1.2 to 2 wt% Niobium, 0.03 to 0.13 wt%

Description

The invention relates to a Nickel based superalloy for higher temperature application having low shrinkage and a component. Superalloys based on Nickel are widely used in gas turbines in different applications, e.g. for blade, vanes, casings or rings in the hot gas path or combustion part. Classical alloys for rings, i.e. alloys straightforward to forge into rings, typically with a diameter in the 0.5 to 2.5m range, include y-alloys such as Haynes230 and Hasteloy-X, mildly y' strengthened alloys such as C-263, and moderately y' strengthened alloys such as Haynes282. y is Nickel (Ni) with elements such as Chromium (Cr), Iron (Fe), Cobalt (Co), Molybdenum (Mo) and Tungsten (W) in solid solution, y' is NisAl with elements like Titanium (Ti), Tantalum (Ta), Niobium (Nb) and Vanadium (V) in solid solution. Haynes230 has the nominal composition, in wt%: Ni-3Co-22Cr-2Mo-14W-0.3Al-0.lTi-0.5Mn-0.4Si-0.1C-0.01B-0.02La. Hasteloy-X has the nominal composition, in wt%: Ni-18Fe-22Cr-0.5Co-9Mo-0.2Al-0.lTi-0.4Mn-0.4Si-0.1C-0.005B. C-263 has the nominal composition, in wt%: Ni-20Co-20Cr-0.3Mn-6Mo-0.2Si-0.45Al-2.2Ti-0.06C-0.005B. Haynes282 has the nominal composition, in wt%: Ni-10Co-20Cr-8.5Mo-l.5Al-2.lTi-0T5Mn-0.08Si-0.06C-0.005B. Alloys for rings tend, as exemplified above, to contain very high levels of Chromium (Cr), mainly included for oxidation and corrosion resistance. Many such alloys also contain high levels of Molybdenum (Mo), typically in the 5wt% to 10wt% level, since this is beneficial for strength, and, for some important corrosive environments. Molybdenum (Mo) is however detrimental under the alkali salt dominated conditions often seen in gas turbines. This type of corrosion is known as hot corrosion for the gas turbine. A few alloys such as Haynes230 use Tungsten (W) rather than Molybdenum (Mo) as the major solution strengthening element since Tungsten (W) is less detrimental when the corrosive environment is dominated by alkali salts. The large scale use of alloys such as Hasteloy-X and C-263 in gas turbines implies that these high levels of Molybdenum (Mo) can be tolerated thanks to high levels of Chromium (Cr) as long as the hot corrosion conditions are not too severe. Most Ni base superalloys shrink when exposed in the 670K to 870K temperature range, and this is at the same time the range at which rings often are operated in gas turbines. Many Nickel (Ni) base rings in the turbine section accordingly suffer from shrinkage in service. This might ‘only’ cause a need to ‘use violence’ to remove said rings at inspections, and often a need to replace said rings with new ones since they cannot be mounted afterwards. But sometimes it contributes to failure of bolts and / or sealings where said rings are joined to the casing, to other rings, or, to the hot gas path stator components. In quite simplified terms, very fine Ni2(Cr, Mo, W) particles gradually precipitate in the 670K to 870K temperature range resulting in shrinkage. If there are also mechanical loadings there may be transformation plasticity such that the shrinkage is augmented. The diameter of some rings in gas turbines has been reduced by several mm in service. If the ratio Ni / (Cr+Mo+W), values given in at%, is close to 2, or even not too far from 2, in the y phase, significant shrinkage can and often will occur as this is ideal for formation of Ni2(Cr, Mo, W). This ratio is typically close to 2 for the compositions usually seen in ring alloys. It is therefore aim of the invention to overcome these problems. The problem is solved by an alloy according to claim 1 and a component according to claim 20. The dependent claims list up further features with given advantages which can be arbitrarily combined with each other to yield further synergy. The description discloses only embodiments of the invention. It was found that the Nickel base superalloy IN792 with 12.5 wt% Chromium (Cr) and 1.8 wt% Molybdenum (Mo) is widely used in gas turbine blades and vanes, including components not protected by coatings, which implies that this comparatively moderate level of Chromium (Cr) is sufficient when the Molybdenum (Mo) content is kept low. 12 wt% Chromium (Cr) is therefore to be seen as the threshold above which an alloy is able to form a protective layer of Chromia to withstand oxidation and corrosion. One example of the invention is given by, in wt%, Ring 1: Ni-13Cr-l.5Mo-4W-l.5Al-l.5Ti-l.5Nb-0.05C-0.015B-0.02Zr. Under gas turbine conditions, Chromium (Cr) can arguably be reduced as long as Molybdenum (Mo) is also reduced, and the alloy will still retain the hot corrosion resistance seen in alloys like C-263 (20 wt% Cr, 6 wt% Mo) and Hasteloy-X (22 wt% Cr, 9 wt% Mo). Secondly, the Ni / (Cr+Mo+W) ratio (elements in at%) can be shown to be well above 2 for Ringl. Ringl has a nominal y' equilibrium content, i.e. at 1123K, of about 12 mol%. The equilibrium content in the 670K to 870K range is higher, but the phase transformation in this range will be sluggish. It is not likely to reach more than about 20mol% y' in service. Chromium (Cr), Molybdenum (Mo) and Tungsten (W) are assumed, as usual, to partition mainly to the y phase while Aluminum (Al), Titanium (Ti) and Niobium (Nb) are assumed to partition mainly to the y' phase. Our result for the 20mol% case is 76.6 at% Nickel (Ni), 18 at% Chromium (Cr), 1.1 at% Molybdenum (Mo) and 1.5 at% Tungsten (W) in the y phase which gives a ratio of about 3.7. Ringl has a y' content’, at 1123K of about 12 mol%. Roughly estimated it would be in reality in the 670K to 870K range since the diffusion rates are too low to allow it to reach full equilibrium, it would to be about 20mol% for the estimation of the ratio above. Chromium (Cr), Molybdenum (Mo) and Tungsten (W) are assumed, as usual, to partition mainly to the y phase while Aluminum (Al), Titanium (Ti) and Niobium (Nb) are assumed to partition mainly to the y' phase. The result is 76.6 at% Nickel (Ni), 18 at% Chromium (Cr), 1.1 at% Molybdenum (Mo) and 1.5 at% Tungsten (W) in the y phase which gives a ratio of about 3.7. Even in the case of 30 mol% y‘ the ratio is reduced to 3.3, which is still far from the state of the art. Another solution by the invention would be Ring2 in [wt%]: Ni-13Cr-l.5Mo-8W-l.5Al-l.5Ti-l.5Nb-0.05C-0.015B-0.02Zr. Ring2 has a higher content of Tungsten (W) for increased strength, and this will obviously reduce the Ni / (Cr+Mo+W) ratio (elements in at%). Assuming 20 mol% y', the result is 67.2 at% Nickel (Ni), 27.3 at% Chromium (Cr), 1.1 at% Molybdenum (Mo) and 3.0 at% Tungsten (W) in the y phase. This gives a ratio of about 3.29 which is still well above 2. Tungsten (W) can be added at relatively high levels in wt% since the corresponding levels in at% will still be moderate for this heavy element. At least 12 wt% Chromium (Cr) is included to enable the formation of a protective Chromia layer. The upper limit is set to 15 wt% to ensure that the Ni / (Cr+Mo+W) ratio (values in at%) can be made to stay well above 2. Molybdenum (Mo) is an effective solution strengthening element and used for this at at least 1 wt%. An upper limit of 2 wt% is set to ensure that the hot corrosion resistance is not compromised. Elements like Cobalt (Co) and Iron (Fe) are often used as complementary base alloys in Nickel base superalloys, but their inclusion in alloys such as Ringl and Ring2 would reduce the Ni content and therefore reduce the Ni / (Cr+Mo+W) ratio (values in at%), hence they are avoided. Vanadium (V) and Tantalum (Ta) are possible alternatives to Ti and Nb for strengthening of the y' phase, but Vanadium (V) is well known as being detrimental for the hot corrosion resistance while Tantalum (Ta) is expensive. Hence they are avoided. Hafoium (Hf) is often added to high temperature alloys, but mainly to alloys designed for casting to mitigate issues such as hot tearing during said casting, and it is also very expensive. Hafnium (Hf) is thus also avoided. Tungsten (W) can be added at relatively high levels in wt% since it will still be present only at moderate levels as measured in at%, hence it will not significantly affect the Ni / Cr+Mo+W) Ratio (elements in at%). It is a very potent solution strengthening element and should be included at at least 3 wt%. An upper limit of 12 wt% is set to avoid a too significant reduction of the Ni / Cr+Mo+W) Ratio (elements in at%). Boron (B), Carbon (C) and Zirconium (Zr) are added at small measured values for grain boundary strengthening, consistent with essentially most Nickel base superalloys (except of course monocrystalline alloys). It can be observed that Zirconium (Zr) is not included in the nominal compositions for Haynes230, Hasteloy-X, C-263 and Haynes282 above. This element, which is beneficial for the grain boundary strength at small measured levels, is however seen at such beneficial levels in (sufficiently detailed) delivery certificates for such alloys since it is in fact difficult to avoid the inclusion of Zirconium (Zr) in the alloy production chain. Nevertheless, recognising the potential that it might at some point be found at a too low level in a batch of the new ring alloy, we have prudently set lower and upper limits on Zirconium (Zr). An at most moderate addition of Silicon (Si) can improve the oxidation resistance and weldability while not significantly reducing the grain boundary strength, and an upper limit of 0.2 wt% is set here. Manganese (Mn) is often used in Nickel base superalloys at levels up to about 1 wt% for Sulfur (S) scavenging and is often reported to be beneficial for the oxidation resistance. This limit of 1 wt% is set here.

Claims

1. Nickel based superalloy, comprising, especially consisting of: (in wt%)12,0% to 15,0% Chromium (Cr)1,0% to 2,0% Molybdenum (Mo)3,0% to 12,0% Tungsten (W)1,2% to 2,0% Aluminum (Al)1,2% to 2,0% Titanium (Ti)1,2% to 2,0% Niobium (Nb),0,03% to 0,13% Carbon (C)0,005 to 0,025% Boron (B)0,008% to 0,1% Zirconium (Zr).optionally:Silicon up to 0,2%and / orManganese (Mn) up to 1,0%.

2. Nickel based superalloy according to claim 1, comprising 3,0% to 5,0% Tungsten (W).

3. Nickel based superalloy according to claim 1, comprising 7,0% to 9,0% Tungsten (W)4. Nickel based superalloy according to any of the preceding claims, comprising no Iron (Fe).

5. Nickel based superalloy according to any of the preceding claims, comprising no Tantalum (Ta).

6. Nickel based superalloy according to any of the preceding claims, comprising no Hafnium (Hf).

7. Nickel based superalloy according to any of the preceding claims, comprising no Vanadium (V).

8. Nickel based superalloy according to any of the preceding claims, comprising no Cobalt (Co).

9. Nickel based superalloy according to any of the preceding claims, comprising12,5% to 13,5% Chromium (Cr)10. Nickel based superalloy according to any of the preceding claims, comprising1,2% to 1,7% Aluminum (Al).

11. Nickel based superalloy according to any of the preceding claims, comprising1,2% to 1,7% Titanium (Ti).

12. Nickel based superalloy according to any of the preceding claims, comprising1,2% to 1,7%Niobium (Nb).

13. Nickel based superalloy according to any of the preceding claims, comprising0,03% to 0,08% Carbon (C).

14. Nickel based superalloy according to any of the preceding claims, comprising0,01 to 0,02% Boron (B).

15. Nickel based superalloy according to any of the preceding claims, comprising0,008% to 0,05% Zirconium (Zr).

16. Nickel based superalloy according to any of the preceding claims, comprising0,05% to 0,15% Silicon (Si).

17. Nickel based superalloy according to any of the preceding claims 1-15, comprising no Silicon (Si).

18. Nickel based superalloy according to any of the preceding claims, comprising no Manganese (Mn).

19. Nickel based superalloy according to any of the preceding claims 1-17, comprising Manganese (Mn) 0.1% to 1,0%.

20. Component or raw materials comprising a Nickel based superalloy according to any of the preceding claims.