Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C19/00—Alloys based on nickel or cobalt
  • C22C19/03—Alloys based on nickel or cobalt based on nickel
  • C22C19/05—Alloys based on nickel or cobalt based on nickel with chromium
  • C22C19/051—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W
  • C22C19/057—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W with the maximum Cr content being less 10%

Definitions

• This invention relates generally to nickel-base superalloy compositions, articles, and methods, and more particularly to such alloys for use as single crystal articles at elevated temperatures wherein the superalloy composition includes a stabilizing amount of hafnium.
• a number of high temperature nickel base superalloys have been developed and reported for use in the form of single crystal articles at high temperature under severe load conditions. For example, such conditions exist in the turbine section of advanced gas turbine engines for aircraft use. Such single crystal articles are useful as airfoils in these turbine sections.
• hafnium acts as a stabilizer for nickel-base superalloys prone to formation of undesirable TCP phases.
• the hafnium- modified superalloys do not form the TCP phases to the extent that comparable unmodified nickel-base superalloys do under comparable conditions.
• the lowered propensity of TCP phase formation results in greater microstructure stability at high temperatures and increased alloying flexibility.
• Embodiments disclosed herein include Hf-modified nickel-base superalloys for high temperature applications. Further embodiments disclosed herein include a single crystal article formed from a Hf-modified nickel-base superalloy having an improved microstructural stability at elevated temperatures. Further embodiments disclosed herein provide a method of improving the microstructural stability of alloys prone to form TCP phases.
• a stabilized superalloy composition comprises tungsten, molybdenum, and optionally rhenium.
• the superalloy composition is modified with a stabilizing amount of hafnium sufficient to decrease the formation of topologically close packed (TCP) phases in a superalloy microstructure at elevated temperatures with respect to a comparable unmodified superalloy composition.
• TCP topologically close packed
• a nickel base superalloy single crystal article exhibiting improved microstructural stability.
• the superalloy single crystal article is formed from a hafnium-modified superalloy composition including tungsten, molybdenum, and optionally rhenium, and a stabilizing amount of hafnium sufficient to decrease the formation of topologically close packed (TCP) phases in a superalloy microstructure at elevated temperatures with respect to a comparable unmodified superalloy composition.
• a hafnium-modified superalloy composition including tungsten, molybdenum, and optionally rhenium, and a stabilizing amount of hafnium sufficient to decrease the formation of topologically close packed (TCP) phases in a superalloy microstructure at elevated temperatures with respect to a comparable unmodified superalloy composition.
• a method of improving the microstructural stability of a superalloy composition includes evaluating a propensity of a superalloy composition to form topologically close packed (TCP) phases in a superalloy microstructure at elevated temperatures by determining an associated TCP number. The method further includes; if the TCP number exceeds a predetermined TCP number, increasing an amount of hafnium in the superalloy composition to an amount sufficient to provide a hafnium-modified superalloy composition, wherein the hafnium-modified superalloy composition exhibits improved microstructural stability at the elevated temperatures.
• TCP topologically close packed
• FIG. 1 is a perspective view of a component article such as a gas turbine engine turbine blade.
• FIG. 2 is a bar graph comparison of 2000 0 F/ 18 ksi stress rupture life of various alloys, normalized to a second-generation superalloy.
• FIG. 3 is a bar graph comparison of 2100 0 F/ 10 ksi stress rupture life of various alloys, normalized to a second-generation superalloy.
• FIGS. 4-11 are a series of photomicrographs of the TCP phase in the dendrite primary core region after stress rupture testing at 2100 0 F/ 10 ksi for Alloys A, Al; B, Bl; C, Cl; and D, Dl, respectively.
• FIG. 12 is a bar graph showing the relationship between the change in TCP number and increased rupture life.
• FIG. 1 depicts a gas turbine blade 20.
• the gas turbine blade includes an airfoil 22 against which the flow of hot combustion gas impinges during service operation, a downwardly extending shaft 24, and an attachment in the form of a dovetail 26 which attaches the gas turbine blade 20 to a gas turbine disk (not shown) of the gas turbine engine.
• a platform 28 extends transversely outwardly at a location between the airfoil 22 and the shank 24 and dovetail 26.
• gas turbine blade 20 comprises a single crystal nickel-base superalloy composition as disclosed herein.
• rhenium rhenium
• Exemplary embodiments may include about 1.5 wt % rhenium.
• Other exemplary embodiments may include up to about 6 wt % rhenium.
• Increased amounts of other strengthening alloying elements such as tungsten (W) and molybdenum (Mo) may be utilized to offset the lower levels of Re in advanced turbine engine blade alloys.
• W tungsten
• Mo molybdenum
• the increased amounts of refractory elements provide alloys with heightened propensity to form TCP phases.
• the presence of the TCP phases reduces creep life over the part life upon repeated exposure to high temperature environments. All percentages presented herein are percentages by weight, unless noted otherwise.
• Hf hafnium
• TCP phases are refractory-rich needle — or dot-like phases (sigma, mu, or p) that deplete the superalloy matrix of refractory elements that are present to provide increased creep resistance.
• alloy pair B and Bl have similar creep rupture lives, as do alloy pair D and Dl.
• the micrograph of alloy B (FIG. 6) shows that this unmodified alloy composition is not prone to formation of TCP phases.
• the increased level of Hf in Hf-modified alloy Bl does not significantly affect formation of TCP phases (FIG. 7). Similar results are obtained for the alloy pair D and Dl, as shown in FIGS. 10-11.
• compositions including relatively high levels of refractory elements or Cr, which can promote formation of TCP phases may be stabilized by increased amounts of Hf.
• FIG. 12 illustrates the affect of the increased Hf additions on the rupture life at 2000 0 F of alloy compositions that tend to form an appreciable amount of TCP e.g., TCP numbers greater than 3.
• the TCP number is an analytical value based on alloy composition utilized to predict TCP phase precipitation.
• High TCP numbers indicate a propensity to form TCP phases.
• TCP numbers of 4 or less are generally required for acceptable stress rupture life.
• an improvement in creep rupture life at high temperatures >1800 0 F, 982 0 C
• An exemplary embodiment includes a method for increasing the micro structural stability of a nickel-base superalloy.
• an unmodified superalloy composition is evaluated for propensity to form TCP phases. If the unmodified superalloy composition exhibits a propensity to form TCP phases, for example a TCP number of greater than 3, the superalloy composition may be modified by the inclusion of a stabilizing amount of hafnium.
• the stabilizing amount of hafnium may be up to about 0.60 wt%. In other exemplary embodiments, the stabilizing amount of hafnium may be less than 0.60 wt%.
• the stabilizing amount of Hf may be greater than 0.60 wt%.
• a "stabilizing amount" of hafnium may be considered to be an amount of hafnium able to provide a -modified superalloy composition with a lower propensity to form TCP phases as compared to a comparable unmodified superalloy composition.
• the propensity for an unmodified superalloy composition to form TCP phases may be evaluated by experimental or analytical methods. For example, an unmodified superalloy composition may tend to form TCP phases at a hafnium content of about 0.15%. If the hafnium content in a comparable modified superalloy composition is increased to about 0.60 %, the propensity to form TCP phases may be reduced.
• the increased hafnium content is referred to herein as a stabilizing amount of hafnium

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Turbine Rotor Nozzle Sealing (AREA)

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• 2008
  • 2008-11-13 EP EP08867005A patent/EP2229462A1/en not_active Ceased
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  • 2008-11-13 WO PCT/US2008/083361 patent/WO2009085420A1/en active Application Filing
  • 2008-11-13 JP JP2010540690A patent/JP5697454B2/ja active Active

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