Patent Application
20100296962
The invention relates to nickel-base superalloys and to components containing these alloys.
Nickel-base superalloys are used in applications where a combination of high strength and a strong resistance to chemical attacks at high temperatures is needed. They are employed for the production of components of gas turbines such as blades and vanes. These parts are arranged in the hot section of a turbine and thus have to withstand high temperatures and an aggressive atmosphere.
Nickel-base superalloys and components of the above mentioned kind are disclosed for example in U.S. Pat. No. 6,818,077, U.S. Pat. No. 6,419,763, U.S. Pat. No. 6,177,046, EP 0 789 087 and EP 0 637 474.
It is an object of the present invention to provide a nickel-base superalloy, which combines high strength, high oxidation resistance, high corrosion resistance, microstructural stability and a large heat treatment window. It is a further object of the present invention to provide components, which comprise such a superalloy.
These objects are solved by the claims.
The nickel-base superalloy of the invention comprises in wt %:
Especially the superalloy consists of these elements.
Especially one, several or all optionally listed elements are present in the alloy. “Present” means that the amount of this element is measurable higher than the known impurity level of this element in a nickel based super alloy. That means that the amount of this element is at least twice the impurity level of this element in a nickel powder based alloy.
The alloy contains significant levels of Al, Cr and Ta to provide a combination of high strength, high oxidation resistance and high corrosion resistance.
Along Ta, other strengtheners of the gamma prime particles like Ti, Nb and V can be added to the superalloy, but since they are detrimental to the oxidation resistance, they should at most be added in limited quantities. The amount of Ti should not exceed 0.45, the amount of Nb should not exceed 0.28, and the amount of V should not exceed 1 wt % respectively.
The amount of matrix strengthening elements Mo, W, Re and Rh is between 2 and 8 wt %.
Other elements like Hf, C, B, Zr, Ca, Mg, Cu, Y, La, Sc, Ce, actinides and lanthanides, and Si can be present in the superalloy in order to adapt its properties to special needs such as grain boundary strengthening, oxide scale fortification, and compatibility with specific coating systems.
The content of Ti can be in the range (in wt %) of 0-0.40. Preferably it can be 0-0.35, more preferably 0-0.30 and most preferably 0-0.20.
It was also found that the content of Nb (in wt %) can be in the range of 0-0.25, preferably 0-0.20, more preferably 0-0.15 and most preferably 0-0.10.
According to another embodiment of the invention the content of C (in wt %) can be in the range of 0-0.15, preferably 0-0.08, more preferably 0.01-0.06 and most preferably 0.02-0.04.
The superalloy of the invention can also contain B in the range (in wt %) of 0-0.02, preferably 0-0.01, more preferably 0.001-0.008 and most preferably 0.003-0.007.
According to one aspect of the invention a conventional cast component, directionally solidified component and a single crystal component, which comprise the super alloy are provided.
According to another aspect of the invention, a conventional cast or a single crystal component consisting of a superalloy, which comprises in wt %:
Especially the superalloy consists of these elements.
The components of the invention can especially be part of a gas turbine, for example a turbine blade or vane, or as filler material, for example for laser welding of gas turbine components.
In the following one preferred embodiment of the invention is described. A superalloy was cast which has the composition given in Table 1.
Especially the superalloy comprises the elements Ni, Co, Cr, Mo, W, Al, Ta, Hf, C and B and very especially consists only of these elements.
In order to characterize the properties of the cast superalloy in Table 1 different experiments were conducted.
Solutioning experiments for 4 h at 1220, 1250, 1260, 1270 and 1300° C. followed by water quenching were done. At 1220° C. residual particles were seen and at 1250, 1260, 1270 and 1300° C. full solutioning without incipient melting was observed.
Further a heat treatment at 1250° C. for 8 h, 1100° C. for 4 h and 850° C. for 24 h was applied. SEM and TEM analysis showed a very regular microstructure with primary particles of ˜0.35 μm side length and a significant amount of secondary particles (see FIGS. 1 and 2).
No trace of TCP phases was found. The particle content was measured to be ˜60 vol %.
At this relatively high particle content it is usually difficult to obtain such a large heat treatment window, or, to include as much as 14% Cr without precipitation of brittle phases. Accordingly it was shown that this emphasis on Cr, Ta and Al
with at most moderate levels of other alloy elements provides a large heat treatment window and a good microstructural stability. Since Al is regarded as highly beneficial, Cr and Ta as beneficial, Mo and W as mildly detrimental (and Ti, Nb and V as detrimental) to oxidation resistance the composition in Table 1 will have a high oxidation resistance. With 14% Cr and a low level of the detrimental element Mo it will also have a high corrosion resistance.
With as much as 10% Ta supported by moderate levels of Mo and W is will also have a high strength, as Ta is a very potent strengthening element. Consequently it satisfies our requirements on high strength, high oxidation resistance, high corrosion resistance, microstructural stability and a large heat treatment window.
Table 2 shows a further preferred embodiment of the invention.
Especially the superalloy comprises the elements Ni, Co, Cr, Mo, W, Al, Ta, Hf, Zr, C and B and very especially consists only of these elements.
Most highly oxidation resistant alloys like e.g. CMSX-4 contain >5% Al and are cast with production processes to obtain <5 ppm S, and recently to levels as low as <0.5 ppm S.
The composition in Table 2 had an average content of sulphur (S) estimated to be ˜30 ppm, at which it should be severely detrimental, and the Al content is a comparatively moderate 4.5%. Cyclic oxidation tests on the superalloy in Table 2 nevertheless showed a stable response for 300 h under the severe test conditions of 1 h cycle time and 1100 C test temperature, which indicates an ability to form stable alumina, i.e. a high oxidation resistance. Accordingly it was shown that this emphasis on Cr, Ta and Al with at most moderate levels of other alloy elements provides a high oxidation resistance.
The composition in Table 2 has a lower particle content than the composition in Table 1, about 45 vol % rather than about 60 vol %, and should therefore have a larger heat treatment window, and be at least as stable. With 16% Cr and a low level of the detrimental element Mo it will also have a high corrosion resistance.
With as much as 10% Ta supported by moderate levels of Mo and W it will also have a high strength, as Ta is a very potent strengthening element.
Consequently it satisfies our requirements on high strength, high oxidation resistance, high corrosion resistance, microstructural stability and a large heat treatment window.
| Number | Date | Country | Kind |
|---|---|---|---|
| 06021724.7 | Oct 2006 | EP | regional |
This application is the US National Stage of International Application No. PCT/EP2007/059936, filed Sep. 20, 2007 and claims the benefit thereof. The International Application claims the benefits of European Patent Office application No. 06021724.7 EP filed Oct. 17, 2006, both of the applications are incorporated by reference herein in their entirety.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2007/059936 | 9/20/2007 | WO | 00 | 4/16/2009 |
