Monocrystalline alloys with controlled partitioning
Nickel-based superalloys, for fabrication of monocrystalline turbine components to be used in industrial and aircraft turbine engines, having the following composition (in wt %): 5.6-8.1% Al, 4.1-14.1% Ru, 6.1-9.9% Ta, 3.6-7.5% Re, and the remaining balance Ni. The partitioning of alloying elements can be controlled to achieve a wide range of precipitate shapes and exceptional resistance to degradation under high temperature exposure conditions.
This application claims the benefit of U.S. Provisional Application No. 60/537,481, filed on Jan. 16, 2004. The disclosure of the above application is incorporated herein by reference.
FIELD OF THE INVENTIONThe present invention relates to alloys and, more particularly, relates to nickel-based superalloys for the manufacture of monocrystalline structures.
BACKGROUND AND SUMMARY OF THE INVENTIONThe present invention generally relates to advanced materials for high temperature components in industrial power and aircraft turbines and, specifically, monocrystalline superalloy blades and vanes. To maximize the efficiency of these turbine systems, the operating temperatures of blades and vanes must be maximized to prevent damage and premature failure. By way of background, it should be recognized that premature damage accumulation may occur along grain boundaries when such components are operated near their melting point. Accordingly, Bridgman-type processes may be utilized to eliminate boundaries and, thus, permit use of superalloys in monocrystalline form. At high temperatures, monocrystalline blades and vanes undergo degradation due to creep, phase instabilities, or oxidation and, consequently, must be periodically replaced. It is desirable in many cases to minimize these characteristics in order to maximize the useful life and operating properties of turbines.
The addition of refractory alloying elements, such as rhenium (Re) and tungsten (W), are desirable for improving the maximum temperature capability of these monocrystalline alloys. As a result, the addition of refractory alloying elements serves to strengthen the monocrystal and, thus, delay the onset of creep damage. However, conversely, high levels of refractory alloying elements may lead to phase instabilities. One form of phase instability is the formation of brittle topologically close packed phases (TCPs). These phases form during long-term, elevated-temperature exposures and tend to degrade mechanical properties. To avoid precipitation of detrimental TCP phases during service, low levels of chromium (Cr) are recommended. Low levels of Cr, however, may result in poor oxidation and corrosion resistance. That being said, it has recently been shown that the addition of small amounts of ruthenium (Ru) decreases the propensity for the precipitation of detrimental TCP phases. Another consequence of refractory alloying additions is their tendency to cause a breakdown of single crystal solidification. It is essential to design alloys within composition ranges where it is possible to produce them as monocrystals to avoid the disadvantages of the prior art.
Phase instability may further occur in monocrystalline alloys when the directional coarsening or “rafting” of the Ni3Al-γ′ precipitates under the action of an externally applied stress. Rafting is enhanced by high levels of Re, which increase the lattice parameter of the y matrix to higher values than the γ′ precipitate phase. In commercial monocrystalline alloys stressed in tension along an applied stress A-A (see
The present invention goes well beyond the prior art in the use of higher levels of ruthenium (Ru) (up to about 14.1 wt %) to control precipitate morphology and rafting behavior, suppress precipitation of TCP phases, and improve creep properties. This is possible through controlled partitioning, where differing amounts of Ru affect the partitioning of elements in the alloy, particularly the Re and W, to the gamma and gamma prime phases. The exceptional aspect of the present invention is that alloys with positive, zero, or negative misfit, no TCP phases and high levels of Re can be designed. This is significant because rafting can be completely suppressed or rafts parallel to or normal to the applied tension applied stress A-A can form with zero, positive, or negative misfit, respectively.
Furthermore, it has been demonstrated that with higher levels of Ru, higher ratios of Cr/Re can be achieved, simultaneously improving oxidation and creep behavior. Cr is important in controlling partitioning. Since the three major mechanisms of high temperature degradation (TCP phase formation, creep damage, and oxidation) are improved, the alloys of the present invention are capable of increasing the useful life and temperature capability of critical turbine components.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGSThe present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:
The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.
With initial reference to Table 1, a plurality of embodiments are illustrated that are within the scope of the present invention. However, it should be appreciated that these examples are non-limiting and, thus, additional compositions may be used or the values enumerated modified.
A first preferred embodiment defined by the principles of the present invention include a class of high refractory content single crystals with spherical precipitates that exhibit no rafting when subjected to external stresses. All current commercial single crystal alloys possess microstructures with γ′ cuboidal precipitates that arise due to lattice misfit between the matrix and precipitates. This misfit occurs due to strong partitioning of the Re and W to the gamma matrix phase. When subjected to tensile stresses along the applied stress A-A (see
With brief reference to
As seen in
Likewise, alloy UM-F9 of the present invention results in spherical precipitates with no rafting following application of temperature and stress. It should be emphasized that stable, spherical precipitates have never before been reported in strong, Re-containing alloys. This stabilization of precipitate morphology under stress occurs in response to a low ratio of Cr/Ru and high ratio of Ru/(Re+W), from about 0-0.4 and about 0.7-1.2, (in wt %), respectively. Within this composition range, the alloys can be solidified as monocrystals using conventional Bridgman growth techniques.
In another embodiment of the present invention, rafts in a Re-containing alloy align parallel to the direction of the applied tensile stress A-A. An example of this is illustrated in
An additional embodiment of the present invention illustrates that if partitioning can be controlled, creep acceleration and strength degradation as a result of rafting can be avoided. Ruthenium additions permit these objectives to be achieved in Re and W-containing alloys.
Turning now to
In another embodiment of the present invention, high oxidation resistance is combined with high creep strength and a high resistance to TCP phase precipitation in Ru-containing alloys.
The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.
Claims
1. A superalloy comprising:
- about 5.6 to about 8.1 percent by weight of aluminum (Al);
- about 4.1 to about 14.1 percent by weight of ruthenium (Ru);
- about 6.1 to about 9.9 percent by weight of tantalum (Ta);
- about 3.6 to about 7.5 percent by weight of rhenium (Re); and
- nickel (Ni).
2. The superalloy according to claim 1, further comprising:
- about 0.1 to about 12.4 percent by weight of tungsten (W).
3. The superalloy according to claim 1, further comprising:
- about 0.1 to about 9.6 percent by weight of cobalt (Co).
4. The superalloy according to claim 1, further comprising:
- about 0.1 to about 6.9 percent by weight of chromium (Cr).
5. The superalloy according to claim 1, further comprising:
- about 0.1 to about 0.7 percent by weight of silicon (Si).
6. The superalloy according to claim 1, further comprising:
- about 0.1 to about 1.5 percent by weight of molybdenum (Mo).
7. The superalloy according to claim 1, further comprising:
- about 0.1 to about 0.8 percent by weight of titanium (Ti).
8. The superalloy according to claim 1, further comprising spherical precipitates.
9. The superalloy according to claim 1 wherein said superalloy forms a monocrystalline structure.
10. A turbine article comprising:
- a monocrystalline alloy having about 5.6 to about 8.1 percent by weight of aluminum (Al), about 4.1 to about 14.1 percent by weight of ruthenium (Ru), about 6.1 to about 9.9 percent by weight of tantalum (Ta), about 3.6 to about 7.5 percent by weight of rhenium (Re), and nickel (Ni).
11. The turbine article according to claim 10 wherein said monocrystalline alloy further comprises about 0.1 to about 12.4 percent by weight of tungsten (W).
12. The turbine article according to claim 10 wherein said monocrystalline alloy further comprises about 0.1 to about 9.6 percent by weight of cobalt (Co).
13. The turbine article according to claim 10 wherein said monocrystalline alloy further comprises about 0.1 to about 6.9 percent by weight of chromium (Cr).
14. The turbine article according to claim 10 wherein said monocrystalline alloy further comprises about 0.1 to about 0.7 percent by weight of silicon (Si).
15. The turbine article according to claim 10 wherein said monocrystalline alloy further comprises about 0.1 to about 1.5 percent by weight of molybdenum (Mo).
16. The turbine article according to claim 10 wherein said monocrystalline alloy further comprises about 0.1 to about 0.8 percent by weight of titanium (Ti).
17. The turbine article according to claim 10 wherein said monocrystalline alloy further comprises spherical precipitates.
18. A superalloy comprising:
- about 5.6 to about 6.3 percent by weight of aluminum (Al);
- about 4.1 to about 9.7 percent by weight of ruthenium (Ru);
- about 6.1 to about 9.9 percent by weight of tantalum (Ta);
- about 3.6 to about 7.5 percent by weight of rhenium (Re); and
- nickel (Ni).
19. The superalloy according to claim 18, further comprising:
- about 0.1 to about 12.4 percent by weight of tungsten (W).
20. The superalloy according to claim 18, further comprising:
- about 0.1 to about 9.6 percent by weight of cobalt (Co).
21. The superalloy according to claim 18, further comprising:
- about 0.1 to about 6.9 percent by weight of chromium (Cr).
22. The superalloy according to claim 18, further comprising:
- about 0.1 to about 0.7 percent by weight of silicon (Si).
23. The superalloy according to claim 18, further comprising:
- about 0.1 to about 1.5 percent by weight of molybdenum (Mo).
24. The superalloy according to claim 18, further comprising:
- about 0.1 to about 0.8 percent by weight of titanium (Ti).
25. The superalloy according to claim 18, further comprising spherical precipitates.
26. The superalloy according to claim 18 wherein said superalloy forms a monocrystalline structure.
Type: Application
Filed: Nov 19, 2004
Publication Date: Oct 13, 2005
Inventors: Tresa Pollock (Ann Arbor, MI), Qiang Feng (Ann Arbor, MI), Laura Rowland (Ann Arbor, MI), Maxim Konter (Klingnau), Peter Holmes (Winkel)
Application Number: 10/994,202