NICKEL BASED ALLOY

Abstract

A nickel based superalloy, including: Chromium (Cr) 12.0%-14.0%, Molybdenum (Mo) 1.5%-3.0%, Tungsten (W) 2.5%-4.5%, Aluminum (Al) 4.0%-5.0%, Titanium (Ti) 1.8%-2.8%, Niobium (Nb) 1.5%-3.5%, Hafnium (Hf) 0.8%-1.8%, Carbon (C) 0.03%-0.13%, Boron (B) 0.005%-0.025%, Silicon (Si) 0.005%-0.05%, and optionally: Cobalt (Co) 0.0%-10.0%, Tantalum (Ta) 0.0%-3.0%, Zirconium (Zr) 0.0%-0.03%, especially remainder Nickel.

Claims

1. Nickel based alloy, comprising (in wt %): Chromium (Cr) 12.0%-14.0%, especially 12.0%-13.0%, Molybdenum (Mo) 1.5%-3.0%, especially 1.6%-2.7%, very especially 1.6%-2.0%, Tungsten (W) 2.5%-4.5%, especially 3.6%-4.0%, Aluminum (Al) 4.0%-5.0%, especially 4.3%-4.7%, Titanium (Ti) 1.8%-2.8%, especially 2.0%-2.6%, Niobium (Nb) 1.5%-3.5%, especially 2.0%-3.4%, Hafnium (Hf) 0.8%-1.8%, especially 0.8%-1.4%, Carbon (C) 0.03%-0.13%, especially 0.07% Carbon (C), Boron (B) 0.005%-0.025%, especially 0.01% Boron (B), Silicon (Si) 0.005%-0.05%, especially 0.01% Silicon (Si), and optionally: Cobalt (Co) 0.0%-10.0%, especially 4.0%-6.0%, very especially 5.0%, Tantalum (Ta) 0.0%-3.0%, especially 0.5%-3.0%, very especially 2.0%-2.4% Tantalum (Ta), Zirconium (Zr) 0.0%-0.03%, especially 0,001%-0.03% Zirconium (Zr); and especially no Rhenium (Re) or Ruthenium (Ru) and/or no Yttrium (Y), remainder Nickel.

2. Nickel based alloy according to claim 1, comprising (in wt %): TABLE-US-00003 Cr 12.5% Co  5.0% Mo  1.8% W  3.8% Al  4.5% Ti  2.2% Ta  2.2% Nb  2.2% Hf  1.0% C 0.07% B 0.01% Zr 0.01% Si 0.01%.

3. A Nickel based alloy according to claim 1, comprising (in wt %): TABLE-US-00004 Cr 12.5% Co  5.0% Mo  1.8% W  3.8% Al  4.5% Ti  2.4% Nb  3.2% Hf  1.2% C 0.07% B 0.01% Zr 0.01% Si 0.01% especially no Tantalum (Ta).

4. The Nickel based alloy according to claim 1, comprising 2.0 wt %-2.4 wt % Niobium (Nb), especially 2.2 wt % Niobium (Nb).

5. The Nickel based alloy according to claim 1, comprising 3.0 wt %-3.4 wt % Niobium (Nb), especially 3.2 wt % Niobium (Nb).

6. The Nickel based alloy according to claim 1, comprising 0.8 wt % 1.2 wt % Hafnium (Hf), especially 1.0 wt % Hafnium (Hf).

7. The Nickel based alloy according to claim 1, comprising 1.0 wt %-1.4 wt % Hafnium (Hf), especially 1.2 wt % Hafnium (Hf).

8. The Nickel based alloy according to claim 1, comprising 2.2 wt % Tantalum (Ta).

9. The Nickel based alloy according to claim 1, comprising 0.1 wt % Zirconium (Zr).

10. The Nickel based alloy according to claim 1, comprising no Tantalum (Ta).

11. The Nickel based alloy according to claim 1, comprising 2.2 wt % Titanium (Ti).

12. The Nickel based alloy according to claim 1, comprising 2.4 wt % Titanium (Ti).

13. The Nickel based alloy according to claim 1, comprising 1.8 wt % Molybdenum (Mo).

14. The Nickel based alloy according to claim 1, comprising 3.8 wt % Tungsten (W).

15. The Nickel based alloy according to claim 1, comprising 4.5 wt % Aluminum (Al).

16. The Nickel based alloy according to claim 1, comprising 12.5 wt % Chromium (Cr).

17. The Nickel based alloy according to claim 1, wherein the Nickel based alloy consists of (in wt %) the listed elements.

18. The Nickel based alloy according to claim 2, wherein the Nickel based alloy consists of (in wt %) the listed elements.

19. The Nickel based alloy according to claim 3, wherein the Nickel based alloy consists of (in wt %) the listed elements.

Description

DETAILED DESCRIPTION OF INVENTION

[0044] Following best modes are listed here below (in wt %).

TABLE-US-00001 Alloy A Cr 12.5 Co 5.0 Mo 1.8 W 3.8 Al 4.5 Ti 2.2 Ta 2.2 Nb 2.2 Hf 1.0 C 0.07 B 0.01 Zr 0.01 Si 0.01

TABLE-US-00002 Alloy B Cr 12.5 Co 5.0 Mo 1.8 W 3.8 Al 4.5 Ti 2.4 Nb 3.2 Hf 1.2 C 0.07 B 0.01 Zr 0.01 Si 0.01, especially no Tantalum (Ta).

[0045] The levels of the matrix strengthening in these alloys elements Molybdenum (Mo) and Tungsten (W) are on at least the IN792 level. In terms of particle strengthening, Tantalum (Ta) has been partly or completely replaced by Niobium (Nb) and Hafnium (Hf), and in addition Aluminum (Al) has been reduced to enable inclusion of Titanium (Ti), resulting in a significantly increased strength. Niobium (Nb) and Hafnium (Hf) provide strengthening per at % on about the same level as Tantalum (Ta), but because of the difference in density between Tantalum (Ta), Niobium (Nb) and Hafnium (Hf), we only need about 1 wt % Niobium (Nb) to replace 2 wt % Ta and 1 wt % Hafnium (Hf) to replace 1.5 wt % Tantalum (Ta). Hence 8 wt % Tantalum (Ta) can be especially replaced by 3.2 wt % Niobium (Nb) and 1.1 wt % Hafnium (Hf). We have further limited Titanium (Ti) to levels at which enable a high HTW resulting in good homogenization and no residual eutectics, as this is regarded as important for good mechanical properties.

[0046] The alloys have at least a 15K in advantage in absolute creep strength and we should also get 10K to 15K in advantage thanks to a reduced density relative to IN792. Hence we get an overall density corrected advantage of about 30K in density corrected creep capability relative to IN792.

[0047] The composition is limited by following consideration:

[0048] Cobalt (Co) is allowed to vary within rather wide limits although there might be a risk for partial ordering degradation at blade root temperatures at the low end and TCP precipitation at 1023K or so at the higher end, hence the intermediate level of especially 5% in the trial alloys.

[0049] It is within the especially 12% to 14% Chromium (Cr) range we are able to find alloys with high creep strength and a reasonable corrosion resistance. Below 12% Chromium (Cr) the corrosion resistance falls fast because the ability to form a protective Cr.sub.2O.sub.3 layer is lost, and above 14% Chromium (Cr) the creep strength falls fast because we will be forced to reduce levels of particles and/or strengthening elements. Going below 12% Chromium (Cr) is also a case of diminishing returns in terms of creep strength, because even if less Chromium (Cr) allows for more strengthening elements in terms of ‘equilibrium calculation TCP resistance’, the HTW will fall and this will cause more residual segregation which is detrimental to the mechanical properties, and more strengthening elements also means a higher density.

[0050] Molybdenum (Mo) is advantageous to Tungsten (W) in terms of density, but too much Molybdenum (Mo) will reduce the hot corrosion resistance. The trial alloys above have especially 1.8% Molybdenum (Mo) just as IN738LC and IN792, and going higher might be detrimental, but let's allow ourselves 3% in the application and see if this could at best be used.

[0051] Since 3% Molybdenum (Mo) is not sufficient, we will have to utilize Tungsten (W) even if it increases the density. It is however kept at reasonably moderate levels.

[0052] If we want almost 60 mol % of strong particles according to the Titanium (Ti)+Tantalum (Ta)+Niobium (Nb)+Hafnium (Hf) recipe outlined above, this is simply where we end up in terms of Aluminum (Al) content. It is lower than in truly oxidation resistant alloys such as CM247CC with their ability to form protective Al.sub.2O.sub.3 layers, but it is nevertheless higher than in most classical industrial gas turbine alloys like Rene80 (3 wt % Al), IN738LC (3.4 wt % Al) and IN792 (3.4 wt % Al) which should provide an advantage over them.

[0053] The balance between Titanium (Ti), Tantalum (Ta), Niobium (Nb) and Hafnium (Hf) in terms of ‘strengthening with a low density’ was outlined above, as was the need to limit Titanium (Ti) to enable a high HTW. In addition, a high Hafnium (Hf) level is usually regarded as good for castability, especially by providing hot tearing resistance. Furthermore, while the main idea is that this should be a new CC alloy, the high Hafnium (Hf) content promotes DS castability.

[0054] The combination of Carbon (C), Boron (B) and Zirconium (Zr) is chosen to provide good grain boundary strengthening while not resulting on hot tearing, and the hot tearing issue is why Zirconium (Zr) is at a low level. Low Zirconium (Zr) also helps with DS castability.

[0055] Silicon (Si) is usually not included in specification for high creep strength superalloys, because it tends to reduce the grain boundary strength, at least when used at 0.05% and above. It is however almost present as a ‘contaminant’ at levels in the order of 0.01% or so when master heats are done. There are papers indicating that if the master heat producers managed to actually reduce it even lower, to ‘almost zero’, then this could seriously impair the oxidation and corrosion resistance, because Silicon (Si) is apparently a catalyst in the formation of a protective Cr.sub.2O.sub.3 layer within the oxide scale. So it's a safety measure to include it but at a small controlled level.

[0056] The balance between Titanium (Ti), Tantalum (Ta), Niobium (Nb) and Hafnium (Hf) to get high strength and low density while maintaining a good HTW despite a high particle content.