Nickel base superalloy and single crystal castings

Abstract

Rhenium-bearing single crystal nickel base superalloy consisting essentially of, in weight %, about 12.5% to about 13.5% Cr, 9.0 to about 9.9% Co, about 4.7 to about 5.1% Ti, about 2.8 to about 3.2% Al, about 2.8 to about 4.3% W, about 1.4 to about 1.6% Mo, about 2.85 to about 3.1% Ta, about 1.0 to about 6.0% Re, about 0.08 to about 0.11% C, about 0.010 to about 0.015% B, up to about 0.15% Nb, up to about 0.15% Hf, up to about 0.003% Zr, and balance Ni and incidental impurities.

Description

This application claims the benefits and priority of Ser. No. 60/482,579 filed Jun. 25, 2003.

FIELD OF THE INVENTION

The present invention relates to a nickel base superalloy and to single crystal castings, such as single crystal airfoil castings, made from the superalloy.

BACKGROUND OF THE INVENTION

Superalloys are widely used as castings in the gas turbine engine industry for critical components, such as turbine airfoils including blades and vanes, subjected to high temperatures and stress levels. Such critical components oftentimes are cast using well known directional solidification (DS) techniques that provide a single crystal microstructure or columnar grain microstructure to optimize properties in one or more directions.

Directional solidification casting techniques are well known wherein a nickel base superalloy remelt ingot is vacuum induction remelted in a crucible in a casting furnace and poured into a ceramic investment cluster mold disposed in the furnace having a plurality of mold cavities. During directional solidification, the superalloy melt is subjected to unidirectional heat removal in the mold cavities to produce a columnar grain structure or single crystal in the event a crystal selector or seed crystal is incorporated in the mold cavities. Unidirectional heat removal can be effected by the well known mold withdrawal technique wherein the melt-filled cluster mold on a chill plate is withdrawn from the casting furnace at a controlled rate. Alternately, a power down technique can be employed wherein induction coils disposed about the melt-filled cluster mold on the chill plate are de-energized in controlled sequence. Regardless of the DS casting technique employed, generally unidirectional heat removal is established in the melt in the mold cavities.

SUMMARY OF THE INVENTION

The present invention provides in one embodiment a nickel base superalloy consisting essentially of, in weight %, about 12.5% to about 13.5% Cr, about 9.0 to about 9.9% Co, about 4.7 to about 5.1% Ti, about 2.8 to about 3.2% Al, about 2.8 to about 4.3% W, about 1.4 to about 1.6% Mo, about 2.85% to about 3.1% Ta, about 1.0 to about 6.0% Re, about 0.08 to about 0.11% C, about 0.010 to about 0.015% B, up to about 0.15% Nb, up to about 0.15% Hf, up to about 0.003% Zr, and balance Ni and incidental impurities. A preferred range for the Re concentration is about 2% to about 4% by weight.

A nickel base superalloy having a nominal composition pursuant to a particular embodiment of the invention consists essentially of, by weight, about 13.0% Cr, about 9.0% Co, about 4.9% Ti, about 3.0% Al, about 3.0% W, about 1.5% Mo, about 2.95% Ta, about 3.0% Re, about 0.09% C, about 0.012% B, up to about 0.15% Nb, up to about 0.15% Hf, up to about 0.003% Zr, and balance Ni and incidental impurities. Preferably, Nb, Hf, and Zr each are maintained at respective impurity level concentrations in the alloy.

The present invention provides in another embodiment a nickel base superalloy consisting essentially of, in weight %, about 9.5% to about 14.0% Cr, about 7.0 to about 11.0% Co, about 3.0 to about 5.0% Ti, about 3.0 to about 4.0% Al, about 3.0 to about 4.0% W, about 1.0 to about 2.5% Mo, about 1.0% to about 4.0% Ta, about 1.0 to about 6.0% Re, up to about 0.25% C, up to about 0.015% B, up to about 1.0% Nb, up to about 0.15% Hf, up to about 0.003% Zr, and balance Ni and incidental impurities. A preferred range for the Re concentration is about 2% to about 4% by weight. Preferably, Nb, Hf, and Zr each are maintained at respective impurity level concentrations in the alloy.

Another nickel base superalloy having a nominal composition pursuant to a particular embodiment of the invention consists essentially of, by weight, about 11.75% Cr, about 9.0% Co, about 4.0% Ti, about 3.5% Al, about 3.5% W, about 1.75% Mo, about 2.5% Ta, about 3.0% Re, about 0.09% C, about 0.012% B, up to about 1.0% Nb, up to about 0.15% Hf, up to about 0.003% Zr, and balance Ni and incidental impurities.

A nickel base superalloy pursuant to embodiments of the invention possesses improved castability and improved mechanical properties.

Other advantages, features, and embodiments of the present invention will become apparent from the following description.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph representing the Larson-Miller parameter for invention alloys A and B pursuant to embodiments of the invention and for comparison CompSX, CMSX-4, PWA 1484, and Rene'N5 nickel base superalloys.

FIG. 2 is a graph representing the Larson-Miller parameter for invention alloy B pursuant to an embodiment of the invention and for comparison CompSX nickel base superalloy.

FIG. 3 is a bar graph showing stress rupture life for invention alloys A and B pursuant to embodiments of the invention and for comparison CompSx nickel base superalloy.

FIG. 4 is a bar graph representing the Larson-Miller parameter at different stress levels for invention alloys A and B pursuant to embodiments of the invention and for comparison CompSX nickel base superalloy.

FIG. 5 is a graph of ultimate tensile strength (UTS) versus temperature for invention alloy A pursuant to an embodiment of the invention and for comparison CompSX, CMSX-4, PWA 1484, and Rene'N5 nickel base superalloys.

FIG. 6 is a graph of 0.2% yield stress versus temperature for invention alloy A pursuant to an embodiment of the invention and for comparison CompSX, PWA 1484, and Rene'N5 nickel base superalloys.

FIG. 7 is a graph of percent elongation versus temperature for invention alloy A pursuant to an embodiment of the invention and for comparison CompSX, CMSX-4, PWA 1484, and Rene'N5 nickel base superalloys.

FIG. 8 is a graph of percent reduction in area versus temperature for invention alloy A pursuant to an embodiment of the invention and for comparison CompSX, CMSX-4, PWA 1484, and Rene'N5 nickel base superalloys.

DESCRIPTION OF THE INVENTION

The present invention provides a nickel base superalloy which is useful in directional solidification processes to make gas turbine engine components subjected to high temperatures and stress levels, such as turbine airfoils including blades and vanes, although the invention is not limited to use in such processes or to make such components. The nickel base superalloy is especially useful in directional solidification processes to make columnar grain castings or single crystal castings.

Pursuant to an embodiment of the invention, the nickel base superalloy consists essentially of, in weight %, about 12.5% to about 13.5% Cr, about 9.0 to about 9.9% Co, about 4.7 to about 5.1% Ti, about 2.8 to about 3.2% Al, about 2.8 to about 4.3% W, about 1.4 to about 1.6% Mo, about 2.85% to about 3.1% Ta, about 1.0 to about 6.0% Re, about 0.08 to about 0.11% C, about 0.010 to about 0.015% B, up to about 0.15% Nb, up to about 0.15% Hf, up to about 0.003% Zr, and balance Ni and incidental impurities. Such nickel base superalloy typically will exhibit a Pha Comp (N_v) value of about 2.37 or less.

The Pha Comp value corresponds to the electron vacany number (N_v), which is described in U.S. Pat. No. 6,054,096, the teachings of which are incorporated herein by reference to this end. The N_v value represents the propensity of the superalloy microstructure to be microstructurally unstable under elevated temperature and time service conditions where the instability relates to formation of brittle extraneous phases in the superalloy microstructure under the extended service conditions. Such extraneous phases are often referred to as TCP (topologically closed packed) phases, such as for example sigma phase and mu phase.

The concentrations of Cr, Co, W, and Mo are closely controlled within the above ranges to achieve the above PhaC Comp (N_v) value so as to improve microstructural stability of the superalloy in service at anticipated elevated temperatures and times experienced by airfoils in a gas turbine engine.

The Re alloying element preferably is present in amount of about 2% to about 4% by weight and more preferably about 3.0% Re. Re is present in the superalloy to increase strength of single crystal castings made of the superalloy. Preferably, Nb, Hf, and Zr each are maintained at respective impurity level concentrations in the alloy.

The invention contemplates a nickel base superalloy having a nominal composition that consists essentially of, by weight, about 13.0% Cr, about 9.0% Co, about 4.9% Ti, about 3.0% Al, about 3.0% W, about 1.5% Mo, about 2.95% Ta, about 3.0% Re, about 0.09% C, about 0.012% B, up to about 0.15% Nb, up to about 0.15% Hf, up to about 0.003% Zr, and balance Ni and incidental impurities. Such nickel base superalloy typically exhibits a Pha Comp (N_v) value of about 2.37.

Pursuant to another embodiment of the invention, the nickel base superalloy consists essentially of, in weight %, about 9.5% to about 14.0% Cr, about 7.0 to about 11.0% Co, about 3.0 to about 5.0% Ti, about 3.0 to about 4.0% Al, about 3.0 to about 4.0% W, about 1.0 to about 2.5% Mo, about 1.0% to about 4.0% Ta, about 1.0 to about 6.0% Re, up to about 0.25% C, up to about 0.015% B, up to about 1.0% Nb, up to about 0.15% Hf, up to about 0.003% Zr, and balance Ni and incidental impurities. A preferred range for the Re concentration is about 2% to about 4% by weight. Preferably, Nb, Hf, and Zr each are maintained at respective impurity level concentrations in the alloy.

The invention contemplates another nickel base superalloy having a nominal composition pursuant to a particular embodiment of the invention consisting essentially of, by weight, about 11.75% Cr, about 9.0% Co, about 4.0% Ti, about 3.5% Al, about 3.5% W, about 1.75% Mo, about 2.5% Ta, about 3.0% Re, about 0.09% C, about 0.012% B, up to about 1.0% Nb, up to about 0.15% Hf, up to about 0.003% Zr, and balance Ni and incidental impurities. Such nickel base superalloy typically exhibits a Pha Comp (N_v) value of about 2.20.

The nickel base superalloys pursuant to the invention will be production-castable from the standpoint that it can be cast into complex single crystal shapes including solid and/or hollow components, such as single crystal gas turbine engine airfoils including blades and vanes. The castings will be generally free from casting scale that is formed on single crystal castings made from low carbon single crystal nickel base superalloys.

Single crystal test bars for mechanical property testing were cast using a superalloy pursuant to an embodiment of the invention having the nominal composition, in weight %, 13.3% Cr, 9.1% Co, 4.83% Ti, 3.06% Al, 2.99% W, 1.49% Mo, 2.97% Ta, 2.98% Re, 0.087% C, 0.012% B, 0.0012% Nb, 0.0007% Hf, 0.0001% Zr, and balance Ni and incidental impurities (designated invention alloy A).

Additional single crystal test bars for mechanical property testing were cast using a superalloy pursuant to an embodiment of the invention having the nominal composition, in weight %, 13.9% Cr, 9.4% Co, 4.9% Ti, 3.0% Al, 3.85% W, 1.58% Mo, 2.94% Ta, 0.09% C, 0.012% B, LAP Zr, LAP Nb, LAP Hf, and balance Ni and incidental impurities wherein LAP is low as possible impurity level (designated invention alloy B).

The single crystal test bars were made by casting the above-described invention alloys A and B at a temperature of alloy melting point plus 350-400 degrees F. into a shell mold preheated to 2750-2850 degrees F. The superalloy test bars were solidified as single crystal test bars using the conventional directional solidification withdrawal technique and a pigtail crystal selector in the shell molds. Directional solidification processes for making single crystal castings are described in U.S. Pat. Nos. 3,700,023; 3,763,926; and 4,190,094. The solidified as-cast test bars of both invention alloys A and B were subjected to a primary aging heat treatment at 2050 degrees F. for 2 hours, gas fan cooled at greater than 75 degrees F./minute to a final aging heat treatment at 1550 degrees F. for 16 hours and then gas fan cooled at greater than 25 degrees F./minute to room temperature for mechanical property testing.

Similar single crystal comparison test bars were made from a known comparison CompSX nickel base superalloy, PWA 1484 nickel base superalloy, N5 nickel base superalloy, and CMSX-4 nickel base superalloy also using the conventional directional solidification withdrawal technique. These nickel base superalloys are in commercial use in the manufacture of single crystal airfoil castings for use in gas turbine engines. The CompSX nickel base superalloy is described in U.S. Pat. No. 6,416,596; the PWA 1484 nickel base superalloy is described in U.S. Pat. No. 4,719,080; the N5 nickel base superalloy is described in U.S. Pat. No. 6,074,602; and the CMSX-4 nickel base superalloy is described in U.S. Pat. No. 4,643,782. The CMSX-4 nickel base superalloy limits carbon to a maximum of 60 ppm by weight. The CompSX nickel base superalloy used in the mechanical property testing had a nominal composition, in weight %, 13.9% Cr, 9.4% Co, 4.9% Ti, 3.0% Al, 3.85% W, 1.58% Mo, 2.94% Ta, 0.09% C, 0.012% B, less than 50 ppm by weight Zr, LAP Nb, LAP Hf, and balance Ni and incidental impurities wherein LAP is low as possible impurity level. The CompSX test bars were single crystal cast and heat treated in the same manner as the invention alloy A and B test bars.

The test bars were tested at different elevated temperatures for stress rupture resistance using test procedure ASTM E139 and tensile tested at room temperature and elevated temperatures for ultimate tensile strength (UTS), 0.2% yield strength, percent elongation, and reduction in area using ASTM test procedure ASTM E8 for room temperature tests and ASTM E21 for elevated temperatures.

Referring to FIGS. 1 and 2, comparison of the Larson-Miller parameters for the invention alloy A and B test bars pursuant to the invention and the comparison CompSX, PWA 1484, N5, and CMSX-4 nickel base superalloys is shown. The Larson-Miller parameter, P, is used to compare stress rupture characteristics of the nickel base superalloys shown in FIGS. 1 and 2. The Larson-Miller parameter is a time-temperature dependent parameter, P=T(° K.)(20+log t)1000 where T is test temperature and t is time to rupture, widely used to extraplote stress rupture data as described in MECHANICAL METALLURGY, section 3-13, pages 483-486, Copyright 1961, 1976 by McGraw-Hill, Inc. FIGS. 1, 2 and 3 reveal that the invention alloy A pursuant to the invention is an improvement over the CompSX test bars with either a single crystal or equiaxed grain structure. FIG. 1 also includes several commercially available third generation single crystal superalloy data points as a reference. It is important to point out the data provided on the superalloy systems including PWA 1484, N5, and CMSX-4, represent a fully solutioned microstructure obtained by heat treatments that have been optimized over time to enhance the mechanical properties of those superalloys.

FIG. 3 is a bar graph comparing the stress rupture lives for the invention alloys A and B pursuant to the invention and the comparison CompSX nickel base superalloy. It is apparent that the invention alloy A pursuant to the invention exhibited a dramatic increase in stress rupture life compared to the comparison CompSX nickel base superalloy under all testing conditions shown in FIG. 3.

Referring to FIGS. 4, 5, 6, and 7, the tensile testing data is shown for the invention alloy A pursuant to the invention and the comparison CompSX, PWA 1484, N5, and CMSX-4 nickel base superalloys. It is apparent that the invention alloy A pursuant to the invention is comparable to the comparison nickel base superalloys in tensile strength (e.g. ultimate tensile strength-UTS and 0.2% yield stress-0.2% YS), elongation, and reduction of area over the temperatures tested (e.g. room temperature to 1100° C.).

The nickel base superalloys pursuant to the invention exhibited reduced casting scale and reduced non-metallic inclusions as a result of the inclusion of the carbon concentrations of 0.087 weight %. For example, the invention alloy A and B investment cast test bars pursuant to the invention had reduced casting scale and reduced non-metallic inclusion levels as compared to the CMSX-4 nickel base superalloy and exhibited improved castability from the standpoint that vacuum investment cast test bars pursuant to the invention exhibited less exterior scale as compared to vacuum investment cast test bars of the comparison CMSX-4 nickel base superalloy.

Although the invention has been shown and described with respect to detailed embodiments thereof, it will be understood by those skilled in the art that various changes in form and detail thereof may be made without departing from the spirit and scope of the claimed invention.

Claims

1. Nickel base superalloy consisting essentially of, in weight %, about 12.5% to about 13.5% Cr, 9.0 to about 9.9% Co, about 4.7 to about 5.1% Ti, about 2.8 to about 3.2% Al, about 2.8 to about 4.3% W, about 1.4 to about 1.6% Mo, about 2.85 to about 3.1% Ta, about 1.0 to about 6.0% Re, about 0.08 to about 0.11% C, about 0.010 to about 0.015% B, up to about 0.15% Nb, up to about 0.15% Hf, up to about 0.003% Zr, and balance Ni and incidental impurities.

2. The superalloy of claim 1 having a Re content of about 2 to about 4 weight %.

3. The superalloy of claim 2 having an Nv value of less than 2.37.

4. Nickel base superalloy consisting essentially of, in weight %, about 13.0% Cr, 9.0% Co, about 4.9% Ti, about 3.0% Al, about 3.03% W, about 1.5% Mo, about 2.95% Ta, about 3.0% Re, about 0.09% C, about 0.012% B, up to about 0.15% Nb, up to about 0.15% Hf, up to about 0.003% Zr, and balance Ni and incidental impurities and an Nv of about 2.33.

5. A turbine airfoil comprising the superalloy of claims 1, 2, 3, or 4.

6. A turbine airfoil of claim 5 which is a directionally solidified columnar grain or single crystal cast airfoil.

7. Nickel base superalloy consisting essentially of, in weight %, about 9.5% to about 14.0% Cr, 7.0 to about 11.0% Co, about 3.0 to about 5.0% Ti, about 3.0 to about 4.0% Al, about 3.0 to about 4.0% W, about 1.0 to about 2.5% Mo, about 1.0 to about 4.0% Ta, about 1.0 to about 6.0% Re, up to about 0.25% C, up to about 0.015% B, up to about 1.0% Nb, up to about 0.15% Hf, up to about 0.003% Zr, and balance Ni and incidental impurities.

8. The superalloy of claim 7 having a Re content of about 2 to about 4 weight %.

9. The superalloy of claim 8 having an Nv value of less than 2.37.

10. Nickel base superalloy consisting essentially of, in weight %, about 11.75% Cr, 9.0% Co, about 4.0% Ti, about 3.5% Al, about 3.5% W, about 1.75% Mo, about 2.5% Ta, about 3.0% Re, about 0.09% C, up to about 0.012% B, up to about 0.15% Nb, up to about 0.15% Hf, up to about 0.003% Zr, and balance Ni and incidental impurities and an Nv of about 2.33.

11. A turbine airfoil comprising the superalloy of claims 7, 8, 9, or 10.

12. A turbine airfoil of claim 11 which is a single crystal cast airfoil.