EP1801251A1

EP1801251A1 - Nickel-based superalloy composition

Info

Publication number: EP1801251A1
Application number: EP06126538A
Authority: EP
Inventors: Ramgopal Darolia
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 2005-12-21
Filing date: 2006-12-19
Publication date: 2007-06-27
Anticipated expiration: 2026-12-19
Also published as: JP2007191791A; EP1801251B1; DE602006017324D1

Abstract

A nickel-based alloy composition and turbine vanes and blades including from about 8 % to about 18 % cobalt, from about 12 % to about 16 % chromium, from about 4 % to about 8 % aluminum, up to about 6 % tungsten, from about 0.5 % to about 3.5 % titanium, from about 2 % to about 6 % molybdenum, from about 0.05 % to about 0.25 % carbon, from about 0.005 % to about 0.025 % boron, from about 0.02 % to about 0.1 % zirconium, up to about 1.0% iron, up to about 2.0% rhenium, up to about 2.0% tantalum, up to about 1.0 % hafnium, balance essentially nickel and incidental impurities, wherein the sum weight percent of aluminum and titanium is from about 4.5 wt% to about 13 wt%. In addition, the ratio of the weight percentage of aluminum to titanium is greater than about 1:1, preferably greater than about 2:1.

Description

FIELD OF THE INVENTION

The present invention is directed to a nickel-based superalloy composition. In particular, the present invention is directed to a nickel-based superalloy composition for gas turbine engine components, such as low pressure turbine blades or vane segments, for use in gas turbine engines.

BACKGROUND OF THE INVENTION

In a gas turbine engine, air is pressurized in a compressor, mixed with fuel in a combustor and is ignited to generate hot combustion gases. The hot combustion gases flow into a turbine section of the engine. The turbine section of the engine typically includes a plurality of stages that may include a combination of turbine blades and turbine vanes. The expanding combustion gases drive the turbine by contacting the blades that rotate a turbine shaft. The rotation of the turbine shaft is utilized to power the compressor and other engine or accessory components. The vanes typically include an airfoil configuration and guide the combustion gases to the turbine blades of the next stage of the compressor. These combustion gases expose the turbine blades and vanes to high temperatures and corrosive atmospheres.
The turbine blades and vanes of a gas turbine engine may be fabricated from nickel-based superalloys. As used herein, "nickel-base", "nickel-based" or the similar, means that the composition has more nickel present than any other element. For example, alloys such as RENE^® 80 and RENE^® 77 may be used in the low pressure turbine section of the gas turbine engine as turbine blades and vanes. The compositions of RENE^® 80 and RENE^® 77 are known and have been utilized in the fabrication of a variety of gas turbine engine components. RENE^® is a trademark of Teledyne Industries, Inc., Los Angeles, CA for superalloy metals. RENE^® 77 and RENE^® 80 typically have the following nominal compositions in weight percent: TABLE 1

Alloy Ni Co Cr Al W Ti Mo C B Zr Fe Density (lbs/in³)

RENE^® 80 Balance 9.5 14 3 4 5 4 0.17 0.015 0.03 0.295

RENE^® 77 Balance 15 14.6 4.3 0 3.35 4.2 0.07 0.015 0.04 0.5 0.287
Nickel-based superalloys, such as RENE^® 77 and RENE^® 80, are used in gas turbine engine components for the combination of properties that they provide. One of the drawbacks to the use of these nickel-based superalloys is the relatively high density of these alloys. The high density contributes to the total weight of the gas turbine engine. For example, in a known gas turbine engine, the low pressure turbine section may include six to seven stages of blades and vanes. One type of engine may include the first two stages having both the blades and vanes of these two stages made out of RENE^® 80, and the later four stages being made out of RENE^® 77. The use of RENE^® 80 and RENE^® 77 in the low pressure turbine section results in a relatively heavy turbine section, contributing to the total weight of the engine.
Aircraft and aircraft engine design have always strived for reduced weight and greater efficiency. Aircraft are becoming larger, requiring more thrust from the engines or additional engines. Reduced maintenance cost and initial cost can be achieved by enlarging the engine, increasing the thrust developed by the engines. However, as the engines grow in size, weight reduction becomes paramount as all the engine components within the engine, likewise, are required to grow. Further, additional engines on an aircraft in order to provide sufficient thrust likewise increase the total weight of the aircraft. In order to offset these problems, materials should be selected to minimize weight, while maintaining the required properties for gas turbine engine operation. A reduction in weight of individual components due to the use of lower density alloys provides significant advantages in engine efficiency, engine durability, payload capacity, lower fuel cost and other advantages relating to the lower total weight of the engine. The drawback to using lower density alloys previously has been that the lower density alloys do not have the combination of properties that are required for use in harsh, high-temperature conditions experienced in the turbine section of the gas turbine engine.
Other attempts to reduce weight in the engine include replacement of gas turbine engine components with lighter weight non-metallic materials, such as epoxy composite materials. These materials are lightweight and provide some desirable mechanical characteristics, particularly for lower temperature portions of the engine. However, these materials do not provide the combination of properties necessary for components of the gas turbine engine subject to higher temperatures and corrosive atmospheres, such as the low-pressure turbine portion of the engine.
Therefore, what is needed is a material suitable for use in the turbine section of a gas turbine engine having a reduced density with properties that are suitable for use in conditions present in the low pressure turbine section of the gas turbine engine.

SUMMARY OF THE INVENTION

The present invention includes a nickel-based alloy composition including from about 8 % to about 18 % cobalt, from about 12 % to about 16 % chromium, from about 4 % to about 8 % aluminum, up to about 6 % tungsten, from about 0.5 % to about 3.5 % titanium, from about 2 % to about 6 % molybdenum, from about 0.05 % to about 0.25 % carbon, from about 0.005 % to about 0.025 % boron, from about 0.02 % to about 0.1 % zirconium, up to about 1.0% iron, up to about 2.0% rhenium, up to about 2.0% tantalum, up to about 1.0 % hafnium, balance essentially nickel and incidental impurities, wherein the sum weight percent of aluminum and titanium is from about 4.5 wt% to about 13 wt%. In addition, the ratio of the weight percentage of aluminum to titanium is greater than about 1:1, preferably greater than about 2:1. In addition, the alloy has properties, including, but not limited to stress rupture life, fatigue strength, oxidation resistance and hot corrosion resistance that are equal to or greater than conventional polycrystalline equiaxed nickel-based superalloys, such as RENE^® 77 and RENE^® 80.
The present invention also includes gas turbine engine components, including, but not limited to compressor blades, compressor vanes, turbine vanes, and turbine blades. The gas turbine engine components fabricated from the nickel-based superalloys, according to the invention, have a lower density, providing a reduced total engine weight while providing acceptable mechanical properties and oxidation/corrosion resistance for use in the above-listed applications.

The present invention includes a lower density nickel-based superalloy and articles fabricated therefrom comprising, in weight percent, the composition shown in TABLE 2.

TABLE 2

Typical Alloy Compositions (in weight %)
Ni	Balance	Balance	Balance
Co	about 8 to about 11	about 9 to about 10	about 9.5
Cr	about 12 to about 16	about 13 to about 15	about 14
Al	about 4 to about 8	about 5 to about 7	about 6
W	about 4 to about 6	about 3 to about 5	about 4
Ti	about 0.5 to about 3.5	about 1 to about 3	about 1
Mo	about 2 to about 6	about 3 to about 5	about 4
C	about 0.05 to about 0.25	about 0.1 to about 0.2	about 0.17
B	about 0.005 to about 0.025	about 0.010 to about 0.020	about 0.015
Zr	about 0.02 to about 0.1	about 0.02 to about 0.05	about 0.05
Fe	up to about 1.0	up to about 0.5
Re	up to about 2.0	up to about 1.0
Ta	up to about 2.0	up to about 1.0
Hf	up to about 1.0	up to about 0.5
Al + Ti	about 4.5 to about 11.5	about 6 to about 10	about 7
Al:Ti	about 1.5:1 to about 6:1	about 2:1 to about 6:1	about 6:1

Another embodiment of the present invention includes a lower density nickel-based superalloy and articles fabricated therefrom comprising, in weight percent, having the composition shown in TABLE 3.

TABLE 3

Typical Alloy Compositions (in weight %)
Ni	Balance	Balance	Balance
Co	about 12 to about 18	about 13 to about 16	about 15
Cr	about 13 to about 16	about 14 to about 15	about 14.3
Al	about 4 to about 8	about 5 to about 7	about 6
W	up to about 1	up to about 0.5	about 0
Ti	about 1 to about 3	about 2 to about 3	about 3
Mo	about 2 to about 6	about 3 to about 5	about 4.2
C	about 0.05 to about 0.25	about 0.1 to about 0.2	about 0.07
B	about 0.005 to about 0.025	about 0.010 to about 0.020	about 0.015
Zr	about 0.01 to about 0.1	about 0.05 to about 0.1	about 0.05
Fe	up to about 1.0	up to about 0.75	about 0.5
Re	up to about 2.0	up to about 1.0
Ta	up to about 2.0	up to about 1.0
Hf	up to about 1.0	up to about 0.5
Al + Ti	about 4.5 to about 11	about 7 to about 11	about 9
Al:Ti	about 1:1 to about 5:1	about 1.5:1 to about 3:1	about 2:1

The nickel-based superalloys according to the present invention include conventionally cast polycrystalline equiaxed microstructure containing alloys. The alloys may be formed by vacuum melting alloy constituents, as shown in TABLES 2 and 3 and conventionally casting the melt. Subsequent heat treatment may be used to desirably precipitate the gamma-prime (i.e., γ') phase into the gamma (i.e., γ) phase matrix. The casting process for forming the alloy of the present invention may include conventional investment casting to polycrystalline substantially equiaxed alloy having sufficient γ' phase to provide stress rupture life, fatigue strength, oxidation resistance and hot corrosion resistance equal to or greater than conventional polycrystalline equiaxed nickel-based superalloys, such as RENE^® 77 and RENE^® 80.
An advantage of the present invention is that the nickel-based superalloy of the present invention has a density that is less than the density of nickel-based superalloys that have been previously used in the turbine section of the gas turbine engine.
Another advantage of the present invention is that the nickel-based superalloy composition maintains an aluminum to titanium ratio that provides sufficient aluminum to form an aluminum oxide containing coating on the alloy surface, which further protects the alloy from oxidation and hot corrosion and forms a surface suitable for additional coatings, while also allowing the γ' phase to form.
Still another advantage of the present invention is that the properties of the alloys equal or exceed the properties of substantially equiaxed, conventionally cast alloys, such as RENE^® 77 and RENE^® 80. The meeting or exceeding of the mechanical properties and oxidation/corrosion resistance properties of RENE^® 77 and RENE^® 80 permits the replacement of turbine engine components with lower density materials, while maintaining or exceeding operating parameters for the gas turbine engine.
Still another advantage of the present invention is that gas turbine engines fabricated using the alloys of the present invention are lighter, providing significant advantages in, among other things, engine efficiency, engine durability, payload capacity, and lower specific fuel consumption.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention includes lower density nickel-based superalloys for use in gas turbine engine components. In particular, the present invention includes gas turbine engine turbine blades and vanes fabricated from lower density nickel-based superalloys.
One embodiment of the present invention includes a nickel-based superalloy comprising, in weight percent, from about 8 % to about 11 % cobalt, from about 12 % to about 16 % chromium, from about 4 % to about 8 % aluminum, from about 4 % to about 6 % tungsten, from about 0.5 % to about 3.5 % titanium, from about 2 % to about 6 % molybdenum, from about 0.05 % to about 0.25 % carbon, from about 0.005 % to about 0.025 % boron, from about 0.02 % to about 0.1 % zirconium, up to about 2.0% rhenium, up to about 2.0% tantalum, up to about 1.0 % hafnium, balance essentially nickel and incidental impurities.
Another embodiment of the present invention includes a nickel-based superalloy comprising, in weight percent, from about 12 % to about 18 % cobalt, from about 13 % to about 16 % chromium, from about 4 % to about 8 % aluminum, from about 1 % to about 3 % titanium, from about 2 % to about 6 % molybdenum, from about 0.05 % to about 0.25 % carbon, from about 0.005 % to about 0.025 % boron, from about 0.01 % to about 0.1 % zirconium, up to about 1.0 % iron, up to about 2.0% rhenium, up to about 2.0% tantalum, up to about 1.0 % hafnium, balance essentially nickel and incidental impurities.
The nickel-based superalloy according to an embodiment of the invention is preferably a composition having a low density compared to conventional polycrystalline equiaxed microstructure cast alloys. The alloy of the present invention includes a conventionally cast alloy having a polycrystalline substantially equiaxed microstructure. To form the alloy, the elemental composition is first melted. Melting for casting purposes may take place using any suitable melting process, including vacuum-induction melting or vacuum-arc melting. Additional remelting steps may also be applied to remove impurities from the melt, including additional vacuum-arc remelting, electroslab remelting and combinations thereof. Subsequent heat treatment may be applied to provide the desired microstructure. In one embodiment of the present invention, a lower density is provided by maintaining a ratio of aluminum to titanium in the alloy composition greater than about 1:1 by weight. The ratio is preferably sufficiently large to provide a lower density alloy, but sufficiently low to provide the nickel-based superalloy with the properties.
The ratio of the aluminum to titanium and the total amount of aluminum and titanium is provided to increase the amount of γ' phase precipitated into the alloy matrix as compared to conventionally cast alloys. The γ' phase precipitate typically includes Ni₃(Al,Ti) or Co₃(Al,Ti), which provides the primary strengthening phase of the alloy, without significant lowering the fracture toughness of the alloy. As the amount of titanium and aluminum increases, the amount of titanium and aluminum available to form the γ' phase likewise increases. In addition, the greater the ratio of aluminum to titanium the greater the presence of the γ' phase in the alloy matrix. The presence of γ' phase provides properties that are desirable in alloys used in gas turbine engine components. The nickel-based superalloy preferably includes a combined weight percent of aluminum and titanium greater than about 5 wt%. The combination of the sum of the aluminum and titanium in addition to the ratio of aluminum and titanium also permits the alloy to have a density lower than conventional cast alloys, such as RENE^® 80 and RENE^® 77.
In addition to increasing the presence of the γ' phase and the lowering of the density of the alloy, the increase in the amount of aluminum and the ratio of aluminum to titanium, preferably greater than about 1:1, permits an excess amount of aluminum to be available to form aluminum oxide-containing layers on the exterior surface of the alloy. These oxide-containing layers provide protections against the atmosphere, providing oxidation resistance and hot corrosion resistance, as well as forming a surface favorable to providing subsequent coatings, such as thermal barrier coatings. In addition, the excess aluminum provides self-healing coating properties, wherein aluminum oxide containing coatings regenerate in locations on the surface where the coatings have been damaged or eroded.
In another embodiment of the present invention, strengthening elements may be added to the alloy composition. High density elements, such as W and Mo, add significant weight to the overall component formed of the nickel-based superalloy. The concentrations of these high density elements may be reduced by the addition of smaller amounts of strengthening elements including Re, Ta, Hf and combinations thereof. The addition of Re, Ta, Hf and combinations thereof increases the strength of the material. Ta and Hf present in the alloy provide further strengthening of the alloy by solid solution strengthening of the γ' phase. Re present in the alloy provides further strengthening of the alloy by solid solution strengthening of the γ matrix. The addition of relatively small amounts of these strengthening elements permits reduction in the use of W and Mo in the alloy composition. The reduction of W and Mo and the ability to strengthen the alloy composition with smaller amounts of strengthening elements, such as Re, Ta, Hf, has the overall effect of reducing the density of the alloy. The concentrations of W may be reduced to as low as 2 % in the alloy by introduction of these alternate strengthening elements. The concentrations of Mo may be reduced or eliminated in the alloy by introduction of these alternate strengthening elements. In a preferred embodiment, the density of the alloy is reduced an additional 2% from the alloy having the Al:Ti ratio of the present invention by substitution of these alternate strengthening elements for W and/or Mo.

EXAMPLES

Table 3

Alloy	Al + Ti	Al:Ti	Density Lbs/in3
Comparative Example 1*	8	3:5	0.295
Example 1	8	3:1	0.287

* Comparative Example 1 includes a nominal composition of RENE^® 80

Example 1: Table 3 shows the Comparative Example 1 having a nominal composition of RENE^® 80 and Example 1 having the shown amounts of Ti and Al. Aluminum and titanium are both γ' formers and form the γ' phase structure, which strengthens the alloy. Comparative Example 1 includes 5 wt % Ti and 3 wt % Al, and has a density of 0.295 lbs/in³. Example 1 includes a nickel-based alloy that includes, in weight percent, about 9.5 % cobalt, about 14 % chromium, about 6 % aluminum, about 4 % tungsten, about 2 % titanium, about 4 % molybdenum, about 0.17 % carbon, about 0.015 % boron, about 0.03 % zirconium, balance essentially nickel and incidental impurities. Example 1 includes a total of 8 wt % Al + Ti, with an Al:Ti ratio of about 3:1. As shown in Table 3, Example 1 has a density of 0.287 1bs/in³. The density of Example 1 is about 3% less than the density for Comparative Example 1. The 3% density reduction in the alloy may correspond to a reduction in total weight of the assembled engine of about 81 lbs more. This reduction in density yields significant reductions in the total weight of the component fabricated from the alloy of Example 1. Table 4

Alloy Al + Ti Al:Ti Density lbs/in³

Comparative Example 2* 7.65 4.3:3.35 0.286

Example 2 9 2 0.279

* Comparative Example 2 includes a nominal composition of RENE^® 77
Example 2: Table 4 shows the relative presence of titanium and aluminum and density of Example 2 in comparison to the density of Comparative Example 2, which is a nominal composition of RENE^™ 77. Comparative Example 2 includes 3.35 wt % Ti and 4.3wt % Al, and has a density of 0.286 lbs/in³. Example 2 includes a nickel-based alloy that includes, in weight percent, about 15 % cobalt, about 14.3 % chromium, about 6 % aluminum, about 3 % titanium, about 4.2 % molybdenum, about 0.07 % carbon, about 0.015 % boron, about 0.04 % zirconium and about 0.5 % iron. Example 2 includes a total of 9 wt % Al+Ti, with an Al:Ti ratio of about 2:1, has a density of 0.279 lbs/in³. The density of Example 2 is about 3 % less than the density for Comparative Example 2. The 3% density reduction in the alloy may correspond to a reduction in total weight of the assembled engine of about 81 lbs more. This reduction in density yields significant reductions in total weight of the component fabricated from the alloy of Example 2.
In a gas turbine engine having six low pressure turbine stages, such as the GE-92B, the substitution of the lower density alloys of Examples 1 and 2 for the higher density RENE^® 77 and RENE^® 80 of Comparative Examples 1 and 2 results in a weight savings of about 81 lbs, which is a significant weight savings for a gas turbine engine.
While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims

A nickel-based alloy composition having a polycrystalline substantially equiaxed microstructure comprising:
from about 8 % to about 18 % cobalt, from about 12 % to about 16 % chromium, from about 4 % to about 8 % aluminum, up to about 6 % tungsten, from about 0.5 % to about 3.5 % titanium, from about 2 % to about 6 % molybdenum, from about 0.05 % to about 0.25 % carbon, from about 0.005 % to about 0.025 % boron, from about 0.02 % to about 0.1 % zirconium, up to about 1.0% iron, up to about 2.0% rhenium, up to about 2.0% tantalum, up to about 1.0 % hafnium, balance essentially nickel and incidental impurities; and

wherein the sum weight percent of aluminum and titanium is from about 4.5 wt% to about 13 wt% and the ratio of aluminum to titanium is greater than about 1:1.
The alloy of claim 1 wherein the ratio of aluminum to titanium is at least about 2:1
The alloy of claim 1 comprising, in weight percent, from about 8 % to about 11% cobalt, from about 12 % to about 16 % chromium, from about 4 % to about 8 % aluminum, from about 4 % to about 6 % tungsten, from about 0.5 % to about 3.5 % titanium, from about 2 % to about 6 % molybdenum, from about 0.05 % to about 0.25 % carbon, from about 0.005 % to about 0.025 % boron, from about 0.02 % to about 0.1 % zirconium, up to about 2.0% rhenium, up to about 2.0% tantalum, up to about 1.0 % hafnium, balance essentially nickel and incidental impurities.
The alloy of claim 3 comprising, in weight percent, from about 9 % to about 10 % cobalt, from about 13 % to about 15 % chromium, from about 5 % to about 7 % aluminum, from about 3 % to about 5 % tungsten, from about 1 % to about 3 % titanium, from about 3 % to about 5 % molybdenum, from about 0.1% to about 0.2 % carbon, from about 0.010 % to about 0.020 % boron, from about 0.02 % to about 0.05 % zirconium, up to about 1.0% rhenium, up to about 1.0% tantalum, up to about 1.0 % hafnium, balance essentially nickel and incidental impurities.
The alloy of claim 4 comprising, in weight percent, about 9.5 % cobalt, about 14 % chromium, about 6 % aluminum, about 4 % tungsten, about 1 % titanium, about 4 % molybdenum, about 0.17 % carbon, about 0.015 % boron, about 0.05 % zirconium, balance essentially nickel and incidental impurities.
The alloy of claim 1 comprising, in weight percent, from about 12 % to about 18 % cobalt, from about 13 % to about 16 % chromium, from about 4 % to about 8 % aluminum, from about 1 % to about 3 % titanium, from about 2 % to about 6 % molybdenum, from about 0.05 % to about 0.25 % carbon, from about 0.005 % to about 0.025 % boron, from about 0.01 % to about 0.1 % zirconium, up to about 1.0 % iron, up to about 2.0% rhenium, up to about 2.0% tantalum, up to about 1.0 % hafnium, balance essentially nickel and incidental impurities.
The alloy of claim 6 comprising, in weight percent, from about 13 % to about 16 % cobalt, from about 14 % to about 15 % chromium, from about 5 % to about 7 % aluminum, from about 2 % to about 3 % titanium, from about 3 % to about 5 % molybdenum, from about 0.10 % to about 0.20 % carbon, from about 0.010 % to about 0.020 % boron, from about 0.02 % to about 0.05 % zirconium, up to about 0.75 % iron, up to about 1.0% rhenium, up to about 1.0% tantalum, up to about 1.0 % hafnium, balance essentially nickel and incidental impurities.
The alloy of claim 7 comprising, in weight percent, about 15 % cobalt, about 14.3 % chromium, about 6 % aluminum, about 3 % titanium, about 4.2 % molybdenum, about 0.07 % carbon, about 0.015 % boron, about 0.05 % zirconium, about 0.5 % iron, balance essentially nickel and incidental impurities.
The alloy of claim 1, wherein the alloy has a density less than about 0.287 1bs/in3.
The alloy of claim 1, wherein the alloy has a density of less than about 0.279 lbs/in3.