NICKEL BASE SUPERALLOY COMPOSITIONS AND SUPERALLOY ARTICLES

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This Application claims priority and benefit of U.S. Provisional Patent Application Serial No. 61/221,946, filed June 30, 2009, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

[0002] This invention relates generally to nickel-base superalloy compositions and superalloy articles and more particularly to such alloys for use in high pressure turbine (HPT) nozzle applications.

[0003] Currently known no-rhenium superalloys may exhibit inadequate stress rupture capability. Other known superalloys that provide desired stress rupture capability may include relatively high amounts of rhenium. It is desirable to provide an alloy able to provide sufficient stress rupture capability with a reduced rhenium level.

SUMMARY OF THE INVENTION

[0004] The above-mentioned need or needs may be met by exemplary embodiments that provide nickel-base superalloy compositions for use in high temperature applications. Exemplary embodiments exhibit sufficient stress rupture capability, at relatively low- or no- rhenium levels.

[0005] In an exemplary embodiment, a superalloy composition comprises, in weight percent: about 6.2-6.6 aluminum (Al), about 6.5-7.0 tantalum (Ta), about 6.0-7.0 chromium (Cr), about 6.25-7.0 tungsten (W), about 1.5-2.5 molybdenum (Mo), about 0.15-0.60 hafnium (Hf), 0.0-1.0 rhenium (Re), 6.5-9.0 cobalt (Co), optionally, 0.03-0.06 carbon (C), optionally, up to about 0.004 boron (B,) optionally up to about 0.03 total of one or more rare earth elements selected from yttrium (Y), lanthanum (La), or cerium (Ce), balance nickel (Ni), such that the superalloy composition exhibits a stress rupture capability improvement of at least about 15% over a base stress rupture capability of a base composition nominally comprising, in weight percent: 6.5 Al, 6.6 Ta, 6.0 Cr, 6.25 W, 1.5 Mo, 0.15 Hf, 0.0 Re, 7.5 Co, balance nickel.

[0006] In an exemplary embodiment, a superalloy composition consists of, in weight percent: about 6.2-6.6 aluminum (Al), about 6.5-7.0 tantalum (Ta), about 6.0 chromium (Cr), about 6.25-7.0 tungsten (W), about 2.0 molybdenum (Mo), about 0.6 hafnium (Hf), from 0.0 to 0.5 rhenium (Re), about 7.5 cobalt (Co), optionally, 0.03-0.06 carbon (C), optionally, up to about 0.004 boron (B), optionally up to about 0.03 total of one or more rare earth elements selected from yttrium (Y), lanthanum (La), or cerium (Ce), and a balance of nickel (Ni) and incidental impurities.

[0007] In an exemplary embodiment, an article formed from an exemplary superalloy composition is provided. The article may be a high pressure turbine nozzle, nozzle segment, or other gas turbine engine component.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the concluding part of the specification. The invention, however, may be best understood by reference to the following description taken in conjunction with the accompanying drawing figures in which:

[0009] FIG. 1 is a perspective view of a component article such as a gas turbine engine high pressure turbine (HPT) nozzle segment.

DETAILED DESCRIPTION OF THE INVENTION

[0010] Referring now to the drawings, FIG. 1 depicts an HPT nozzle segment 10 including at least one vane 12. In an exemplary embodiment, the nozzle segment 10 comprises a single crystal nickel-base superalloy composition as disclosed herein.

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Articles incorporating the disclosed superalloy composition include HPT nozzles or nozzle segments and may include other gas turbine engine components.

[0011] Exemplary nickel-base superalloy composition comprise reduced levels of rhenium (Re), defined herein as being from 0 up to about 0.5 weight %. Increased amounts of other strengthening alloying elements such as tantalum (Ta), tungsten (W) and molybdenum (Mo) may be utilized to offset the lower levels of Re. For example, tantalum may be present in amounts from about 6.5 to about 7.0 weight %, molybdenum may be present in amounts from about 1.5 to about 2.5 weight %, and tungsten may be present in amounts from about 6.25 to about 7.0 weight %. In other exemplary embodiments, tantalum may be present at levels of from about 6.5 to about 6.6 weight %. All percentages presented herein are percentages by weight, unless noted otherwise.

[0012] Table 1 provides a series of exemplary compositions. A theoretical stress rupture prediction generated by computer modeling for the compositions was compared with the predicted stress rupture (in hours) of a base, no-rhenium superalloy composition. As evidenced in Table 1, each of the enumerated compositions provided an improved predicted stress rupture, presented as % improvement.

[0013] Certain of the exemplary compositions presented in Table 1 are highlighted. These exemplary compositions exhibit excellent improvement in the predicted stress rupture as compared to the Base composition. These exemplary compositions may provide desired outcomes with reduced rhenium levels (0.0-0.5 weight %). Other exemplary compositions include rhenium in levels up to about 1.0 weight %.

[0014] Alloys 25 and 27 listed in Table 1 are provided as comparative examples and include about 1.5 weight % rhenium. Exemplary embodiments disclosed herein consider the contributions of various alloying elements to the thermal mechanical properties and oxidation resistance of the superalloy composition. 58-2

[0015] Certain exemplary embodiments disclosed herein include from about 6.2 to about 6.6 weight percent aluminum. In other exemplary embodiments, the aluminum may be present in amounts from about 6.3 to about 6.5 percent.

[0016] Certain embodiments disclosed herein include at least about 6 to about 7 weight % chromium (Cr) sufficient to provide hot corrosion resistance, but not high enough to detrimentally lead to TCP phase instability and poor cyclic oxidation resistance.

[0017] Certain embodiments disclosed herein include from about 6.5% to about 9%, and more preferably about 7% to about 8% cobalt (Co). Lower amounts of cobalt may reduce alloy stability. Greater amounts may reduce the gamma prime solvus temperature thus impacting high temperature strength and oxidation resistance.

[0018] Certain embodiments disclosed herein include molybdenum (Mo) in amounts from about 1.5 to 2.5 weight %. The minimum value is sufficient to impart solid solution strengthening. Amounts exceeding the maximum may lead to surface instability. Greater amounts of Mo may also negatively impact both hot corrosion and oxidation resistance.

[0019] Certain embodiments disclosed herein include tungsten (W) in amounts from about 6.25 to about 7.0 weight %. Lower amounts of W may decrease strength. Higher amounts may produce instability with respect to TCP phase formation. Higher amounts may also reduce oxidation capability.

[0020] Certain embodiments disclosed herein provide reduced levels of rhenium, preferably from 0.0 to about 1.0 weight percent, and more preferably not greater than about 0.5 weight %. It is contemplated that some or all of the rhenium may be provided as revert from scrap material. Compositions 25 and 27 illustrate significant improvement in predicted stress rupture capability with the addition of 1.5 weight % rhenium. It is desired to provide improved performance at reduced rhenium levels. [0021] Hafnium (Hf) may be included at relatively low levels of about 0.15 weight % up to higher levels of about 0.6 weight %. Hafnium can improve oxidation resistance and the adherence of thermal barrier coatings when utilized. However, hafnium can degrade the corrosion resistance of uncoated alloys. Hafnium additions of about 0.7% can be satisfactory, but additions of greater than about 1% adversely impact stress rupture properties and the incipient melting temperature.

[0022] Optional additions may include about 0.03-0.06 weight % carbon (C), up to about 0.004 weight % boron (B), or up to about 0.03 weight% of one or more rare earth elements such as yttrium (Y), lanthanum (La), and cesium (Ce).

[0023] Boron provides strength for low angle boundaries and enhanced acceptability limits for components having low angle grain boundaries. The lower limit for carbon provides sufficient carbon to improve alloy cleanliness since carbon provides de-oxidation. Beyond the upper 0.06% amount, the carbide volume fraction increases, reducing fatigue life. Rare earth additions, i.e., yttrium (Y), lanthanum (La), and cerium (Ce), may be provided in certain embodiments in amounts up to about 0.03%. These additions may improve oxidation resistance by enhancing the retention of the protective alumina scale. Greater amounts may promote mold/metal reaction at the casting surface, increasing the component inclusion content.

[0024] Exemplary embodiments disclosed herein include each of the enumerated compositions in Table 1 with the exception of the base composition, and comparative alloys 25 and 27. Additionally, exemplary embodiments disclosed herein include compositions employing the endpoints of disclosed ranges and all intermediate values. For example, a range of aluminum from about 6.2 to about 6.6 weight percent is defined to include 6.2 weight percent, 6.6 weight percent, and any intervening percentage between 6.2 and 6.6 weight percent.

[0025] Exemplary embodiments disclosed herein provide improved stress rupture capability of at least 15% as compared to a base stress rupture capability of a base

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composition nominally comprising, in weight percent: 6.5 Al, 6.6 Ta, 6.0 Cr, 6.25 W, 1.5 Mo, 0.15 Hf, 0.0 Re, 7.5Co, balance Ni, identified as "Base" in Table 1.

[0026] EXAMPLES

TABLE 1

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[0027] This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to make and use the invention. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.