CN110592458A

CN110592458A - Aluminum-titanium alloy and turbine assembly

Info

Publication number: CN110592458A
Application number: CN201910958124.3A
Authority: CN
Inventors: 杨刚强
Original assignee: Jiangsu Guangkun Aluminum Co Ltd
Current assignee: Jiangsu Guangkun Aluminum Co Ltd
Priority date: 2019-10-10
Filing date: 2019-10-10
Publication date: 2019-12-20

Abstract

An aluminum titanium alloy and turbine component is disclosed, including a gamma titanium aluminide alloy consisting essentially of, in atomic percent, about 38 to about 50% aluminum, about 6% niobium, about 0.25 to about 2% tungsten, optionally up to about 1.5% boron, about 0.01 to about 3%. 1.0% carbon, optionally up to about 2% chromium, optionally up to about 2% vanadium, optionally up to about 2% manganese, the balance being titanium and incidental impurities. In some embodiments, the gamma titanium aluminide alloy forms at least a portion of a gas turbine component. In some embodiments, a gamma-titanium aluminide alloy consists essentially of, in atomic percent, about 40% to about 50% aluminum, about 3 to about 5% niobium, about 0.5 to about 1.5% tungsten, about 0.01 to about 1.5% boron, about 0.01 to about 1.0% carbon, optionally up to about 2% chromium, optionally up to about 2% vanadium, a manganese content of about 2%, the balance titanium and incidental impurities.

Description

Aluminum-titanium alloy and turbine assembly

Technical Field

The present disclosure relates to titanium aluminide alloys, particularly those that may be used in high temperature gas turbine applications, such as turbine blades and turbine wheels.

Background

The power output of an industrial gas turbine increases with each successive generation of power by the gas turbine. Associated with the turbine power is a parameter that determines the power output condition of the gas turbine. One of these parameters is defined in terms of the rotor speed of the turbine and the exhaust outlet annulus radius downstream of the last stage bucket. This parameter is set to AN2, where N is related to the rotor speed and A is related to the exit ring radius. As the AN2 area increases, the bucket tension increases. These increasing loads adversely affect the size of the rotor wheel and the stresses to which the metal, including the rotating components, is subjected and the volume of metal that needs to be supported.

In recent years, the AN2 value has increased sufficiently to warrant the use of expensive alloy 718, a precipitation hardenable nickel chromium alloy, also known as 718 (Huntington alloys corp., Huntington, w.va). Nickel-based alloys (e.g., alloy 718) are expensive, require the time required to manufacture the turbine assembly, and are relatively dense and heavy even when hollow sections are manufactured for internal cooling, thereby extending the service temperature range. The increase in size of gas turbines and the increase in weight of turbines both limit the further development of these machines and increase the cost of manufacturing the machines.

Disclosure of Invention

In an exemplary embodiment, the γ -titanium aluminide alloy consists essentially of, in atomic percent, about 38 to about 50% aluminum (Al), about 1 to about 6% niobium (Nb), about 0.25 to about 2% tungsten (W). Optionally up to about 1.5% boron (B), from about 0.01% to about 1.0% carbon (C), optionally up to about 2% chromium (Cr), optionally up to about 2% vanadium (V), optionally up to about 2% manganese (Mn), the remainder titanium (Ti) and incidental impurities.

In another exemplary embodiment, the turbine component comprises a gamma-titanium aluminide alloy comprising, substantially in atomic percent, about 38 to about 50% Al, about 1 to about 6% Nb, about 0.25 to about 2% W, optionally up to about 3%. 1.5% B, about 0.01 to about 1.0% C, optionally up to about 2% Cr, optionally up to about 2% V, optionally up to about 2% Mn, and the balance Ti and incidental impurities.

In another exemplary embodiment, the gamma-titanium aluminide alloy consists essentially of, in atomic percent, about 40 to about 50% Al, about 3 to about 5% Nb, about 0.5 to about 1.5% W, about 0.01 to about 1.5% B, about 0.01 to about 1.0% C, optionally up to about 2% Cr, optionally up to about 2% V, optionally up to about 2% Mn, and the balance Ti and incidental impurities.

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.

Drawings

FIG. 1 schematically depicts a gas turbine having components comprising a gamma-titanium aluminide alloy in an embodiment of the present disclosure.

Detailed Description

Exemplary titanium aluminide alloy compositions are provided. Embodiments of the present disclosure have a lower density than compositions that do not use one or more of the features described herein, while being able to withstand the stresses and creep/stress cracking resistance experienced by rotor wheels and turbine blades, a lower density than superalloy materials traditionally used for turbine components (e.g., rotor wheels and buckets), improved high temperature performance, improved high temperature creep resistance, improved high temperature elongation performance, improved high temperature oxidation resistance, improved high temperature ultimate tensile strength, improved high temperature yield strength,

as used herein, the term "high temperature" refers to a temperature within the operating temperature range of a gas turbine. The operating temperature is about 1093 ℃ (about 2000 ° F), or about 1093 to about 1540 ℃ (about 2000 to about 2800 ° F), or about 1093 to about 1200 ℃ (about 2000 to 200 ° F). About 2200 ° F), about 1200 ℃ (about 2200 ° F), about 1200 to about 1320 ℃ (about 2200 to about 2400 ° F), about 1320 ℃ (about 2400 ° F), or about 1320 to about 1430 ℃ (about 2400 to about 2600 ° F), or about 1430 ℃ (about 2600 ° F), or about 1430 to about 1540 ℃ (about 2600 ° F), about 1093 ℃ (about 2800 ° F), about 1200 to about 1430 ℃ (about 2200 to 2600 ° F), or any value, range

As used herein, the terms "substantially balanced titanium and incidental impurities" and "alloy substantially balanced titanium" refer to, in addition to titanium, minor impurities and other incidental elements inherent in titanium aluminide alloys that do not affect the advantageous aspects of the alloy in terms of characteristics and/or quantities. All compositional percentages identified herein are atomic percentages, unless otherwise specified.

In some embodiments, the compositions are used in high temperature applications where creep resistance and/or stress crack resistance is important. In some embodiments, the high temperature application is a gas turbine. In some embodiments, the composition is used in a gas turbine component. In some embodiments, the gas turbine component is a bucket or a wheel.

FIG. 1 illustrates a compressor section 105, a combustion section 130, and a turbine section 150 of a gas turbine 100. The compressor section 105 includes rotating blades 110 mounted on a wheel 112 and a non-rotating nozzle 115 configured to compress a fluid. Compressor portion 105 may also include a compressor discharge casing 125. The combustion section 130 includes a combustion can 135, a fuel nozzle 140, and a transition section 145. Within each combustion can 135, compressed air is received from compressor section 105 and mixed with fuel received from a fuel source. The mixture is ignited and a working fluid is generated. The working fluid generally flows downstream from the aft end of the fuel nozzle 140, downstream through the transition section 145, and into the turbine section 150. The turbine section 150 includes rotating blades 110 mounted on a wheel 112 and non-rotating nozzles 115. Turbine portion 150 converts the energy of the working fluid into mechanical torque. At least one of the turbine components includes a gamma titanium aluminide alloy composition. In some embodiments, the turbine component is a blade 110. In some embodiments, the turbine component is an impeller 112.

In some embodiments, the composition is a gamma titanium aluminide alloy. In some embodiments, the gamma-titanium aluminide alloy is an intermetallic alloy. In some embodiments, the gamma titanium aluminide alloy comprises, in atomic percent, about 38 to about 50% aluminum (Al), about 1 to about 6% niobium (Nb), about 0.25 to about 2.0% tungsten (W), optionally, to about 1.5% boron (B), about 0.01 to about 1% carbon (C), optionally, up to about 2% chromium (Cr), optionally, up to about 2% vanadium (V), optionally, up to about 2% manganese (Mn), with the remainder being substantially titanium (Ti) and incidental impurities.

These γ TiAl alloys preferably provide the advantage of low density, allowing them to be particularly useful in applications such as turbine nozzles 115, turbine blades 110 and turbine wheels 112. These γ TiAl alloys preferably have a higher density advantage than the materials currently used, in particular nickel-based superalloys and high alloy steels, so that they can be used without the need to remove the metal, for example by hollowing.

Compared with nickel-based high-temperature alloy and high-alloy steel, the gamma TiAl alloy has obvious cost advantage. While γ TiAl alloys preferably include alloying elements, these alloying elements are preferably present in low amounts. Furthermore, these alloying elements are not strategic and readily available in most cases. When replacing superalloy turbine blades 110, the use of γ TiAl alloys may save approximately 100 ten thousand dollars in current per turbine stage. Since there may be up to 16 turbine stages in a gas turbine engine, the cost savings that can be achieved by replacing the superalloy with γ TiAl alloys is considerable.

In some embodiments, the gamma titanium alloy compositions useful in the turbine wheel 112 and turbine blade 110 consist essentially of, by atomic percentage, about 38 to about 50% aluminum (Al), about 1 to about 6% niobium (Nb). About 0.25 to about 2.0% tungsten (W), optionally up to about 1.5% boron (B), about 0.01 to about 1% carbon (C), optionally up to about 2% chromium (Cr), optionally up to about 2 vanadium (V) content, preferably about 2% manganese (Mn), with the remainder being essentially titanium (Ti) and incidental impurities.

In some embodiments, the gamma titanium aluminide alloy comprises, in atomic percent, about 40 to about 50% aluminum (Al), about 3 to about 5% niobium (Nb), about 0.5 to about 1.5% tungsten (W), about 0.01 to about 1.5% boron (B), about 0.01 to about 1% carbon (C), optionally up to about 2% chromium (Cr), optionally up to about 2% vanadium (V), optionally up to about 2% manganese (Mn), with the remainder being substantially titanium (Ti) and incidental impurities. In some embodiments, the total non-Al, non-Ti alloy content ranges from about 4.13% to about 12.13% by atomic percentage.

Al may be present in an amount in the range of about 38% to about 50%, or about 40% to about 50%, or about 45% to about 47%, or about 45.5% to about 46.5%, or about 4%, atomic percent. 46% or any number, range or subrange therebetween.

In this alloy, Nb may be added to improve the oxidation resistance of the alloy. Oxidation resistance is an important property for alloys used in the hot parts of turbines, such as for turbine blades 110 and vanes that are exposed to the hot oxidizing gases of combustion during operation. In these applications, the hot exhaust gases tend to deteriorate the alloys used for these components. Nb may be added in an amount of atomic percent ranging from about 1 to about 6%, alternatively from about 1 to about 5%, alternatively from about 2 to about 6%, alternatively from about 3 to about 5%, alternatively about 3%. 3%, or any number, range, or subrange therebetween.

Tungsten may be added to form fine, stable grains, thereby limiting grain growth during high temperature processing. Tungsten may also improve the oxidation and creep resistance of γ TiAl alloys, but may adversely affect ductility and fracture toughness. However, the overall effect of adding tungsten must be balanced by the application. For the turbine blade 110, creep resistance, stress cracking and oxidation resistance are important properties, and some reduction in ductility may be tolerated to improve these properties. Niobium may provide sufficient oxidation resistance, and thus tungsten may be included at or near the lower end of the tungsten range, not critical to the nozzle 115 resistance to creep and stress cracking. W may be added in an amount of atomic percent, in the range of about 0.25% to about 2%, or about 0.5% to about 1.5%, or about 1%, or any amount, range, or subrange therebetween.

The addition of boron can improve the high-temperature strength and creep resistance of the gamma titanium-aluminum alloy. The addition of boron forms a fine phase of TiB2 that limits grain growth during high temperature processing. Therefore, boron may be an important additive when γ TiAl requires high temperature processing for turbine blade 110 applications or both. B may be added in an amount up to about 1.5%, alternatively from about 0.01 to about 1.5%, alternatively about 0.1%, or any amount, range, or subrange therebetween, in atomic percent.

The high temperature creep performance of gamma and gamma + beta titanium aluminide alloys can be greatly improved by adding a small amount of carbon. Creep resistance is an important attribute for turbine applications (e.g., turbine blades 110) that operate at high temperatures and high rotational speeds. The carbon content is tightly controlled because carbon also adversely affects ductility and fracture toughness. Thus, the presence of carbon may be desirable to provide a creep/stress rupture resistance 110 for a turbine bucket that operates at high rotational speeds and high temperatures as bucket 110, but may also be not limited to the lower end 115 of the carbon range for the turbine nozzle being substantially stationary while operating at high temperatures. The amount of C added may range from about 0.01 to about 1%, alternatively from about 0.01 to about 0.1%, alternatively about 0.03%, or any amount, range or sub-range therebetween, in atomic percent.

Chromium is an optional element added in an amount up to 2% to improve the creep/stress rupture resistance of γ TiAl alloys. Creep/stress crack resistance is a desirable characteristic of turbine blades 110 that rotate at high speeds in hot turbine exhaust. Creep resistance is less important in the turbine nozzle 115. When chromium is present in an amount greater than about 2%, the chromium adversely affects the toughness and ductility of the alloy due to the formation of an ordered chromium-rich B-2 phase. The amount of Cr added may be in atomic percent up to about 2%, or from about 1 to about 2%, or about 1%, or any amount, range, or subrange therebetween.

Vanadium is an optional element added in amounts up to about 2% to improve the toughness of the alloy. Toughness is the ability to absorb energy and plastically deform without breaking, for example, during an impact event such as from a foreign object. Toughness is an important characteristic in turbine blades 110 and nozzles 115. This is a particularly important property for the turbine blade 110 during transient power excursions when the blade 110 may contact the turbine casing while moving at high speeds. V may be added in an amount up to about 2%, or from about 1 to about 2%, or about 1%, or any amount, range or subrange therebetween, in atomic percent.

Manganese is an optional element added in amounts up to about 2%. Manganese is included when it is desired to increase the fracture toughness and higher ductility of the alloy, particularly when added in combination with at least one of vanadium and chromium. Mn may be added in an amount of atomic percent up to about 2%, or about 1%, or any amount, range, or subrange therebetween.

Molybdenum (Mo) is preferably specifically excluded in the formulation of the present alloy. Molybdenum is ductile and tough at lower temperatures. Molybdenum may also promote dissolution of the beta phase during high temperature extrusion, thereby providing a finer distribution of the beta phase within the matrix after extrusion. However, the present alloy is designed for turbine blades 110 and nozzles 115 that operate only at high temperatures. Although the addition of such dense refractory materials may be beneficial in certain applications, the addition of molybdenum is of little benefit in these contemplated applications due to the relatively high operating temperatures of the turbine blades 110 and nozzles.

Tantalum (Ta) is preferably specifically excluded in the formulation of the present alloy.

Reducing the Al content of the alloy to less than about 50% increases the amount of the second beta (β) phase that forms in the alloy at high temperatures. The beta phase can be further stabilized by the addition of beta stabilizers. As mentioned above, V, Nb, Mo, Ta, Cr, iron (Fe) and silicon (Si) are all beta stabilizers. Tantalum is not used in this alloy because of its cost and density as a strategic alloy. Iron is not used due to the density of the alloy. V, Nb and Mo are isomorphic β stabilizers that stabilize the β phase at lower temperatures. Cr is a eutectoid beta stabilizer that lowers the stabilization temperature of the beta phase to room temperature when Cr is present in sufficient concentration.

The amount of beta phase present in the gamma + beta titanium aluminide alloy at high temperatures is preferably controlled by careful composition control as described above, and the beta stabilizer can maintain the beta phase at a lower temperature. This is an important feature because the convenience of hot working can be increased by increasing the amount of beta phase that may be present. Thus, higher strain rate forging and hot extrusion can be achieved with a greater amount of beta phase. Of course, the amount of phase retained must be balanced by other properties that may include, but are not limited to, creep resistance, ultimate tensile strength, yield strength, elongation, toughness, density, and cost. Increasing the concentration of Ti increases the cost and density of the alloy.

One hot working process that attempts to maintain the workpiece at its highest elevated temperature throughout the operation is isothermal forging. Alloys that inherently have low forgeability, such as the titanium aluminide alloys of the present invention, may be difficult to form and their mechanical properties may vary greatly over a small temperature range. Isothermal forging may be used to help overcome these properties when including alloying additions as described above. Isothermal forging is achieved by heating the die to a temperature at or slightly below the temperature of the starting workpiece. For example, the die may be preheated prior to forging and maintained at temperature by an external heat source, such as a quartz lamp, or the die may include a controlled heating element that maintains the temperature at a preset level. When the force exerted by the die is used to form the workpiece, cooling of the workpiece between the die working interfaces is eliminated or at least substantially reduced, thus greatly improving the flow characteristics of the metal. Isothermal forging may or may not be performed in a vacuum or controlled atmosphere. The equipment cost of the manufacturing process is high and the additional cost of such an operation is contingent on circumstances.

To function in gas turbine applications where the alloys are used as turbine wheels 112 or turbine blades 110 attached to the turbine wheels 112, the alloys must have high temperature creep resistance as well as satisfactory high temperature Ultimate Tensile Strength (UTS), Yield Strength (YS), and elongation. The alloys disclosed herein may also be used as seals in turbine applications. High temperature creep resistance is not as important since the seal is stationary, but the alloy must have a high temperature Ultimate Tensile Strength (UTS), Yield Strength (YS) and elongation.

In some embodiments, the amounts of Al, Nb, W, B, C, Cr, V, Mn, and Ti are selected to provide a predetermined amount of at least one property to the gamma titanium aluminide alloy. In some embodiments, the at least one property is material cost, density, high temperature creep resistance, high temperature elongation, high temperature oxidation resistance, high temperature ultimate tensile strength, high temperature yield strength, or a combination thereof.

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

1. An aluminum titanium alloy and turbine assembly consisting essentially of, in atomic percent: about 38% to about 50% aluminum (Al), about 1 to about 6% niobium (Nb), about 0.25 to about 2% tungsten (W), optionally up to about 1.5% boron (B); about 0.01 to about 1.0% carbon (C); optionally up to about 2% chromium (Cr), optionally up to about 2% vanadium (V), optionally up to about 2% manganese (Mn), and the balance titanium (Ti) and other impurities.

2. The gamma-titanium aluminide alloy of claim 1, wherein the gamma-titanium aluminide alloy is absent molybdenum (Mo) and tantalum (Ta).

3. The gamma-titanium aluminide alloy of claim 1, wherein said Cr is present in an atomic percent of from about 1 to about 2%.

4. The gamma-titanium aluminide alloy of claim 1, wherein the Mn is present in an amount of about 1 to about 2 atomic percent.

5. The gamma-titanium aluminide alloy of claim 1, wherein said V is present in an amount of about 1 to about 2 atomic percent.

6. The gamma-titanium aluminide alloy of claim 1, wherein Al is present in an amount, in atomic percent, of about 45.5% to about 46.5%, Nb is present in an amount of about 3% to about 5%, and W is present in an amount of about 0.5% to about 1.5%.

7. The gamma-titanium aluminide alloy of claim 1, wherein Al is present in atomic percent, Al is present in an amount of about 45% to about 47%, and Nb is present in an atomic percent of about 5%.

8. The gamma titanium aluminide alloy of claim 1, wherein W is present in an atomic percentage of about 1%.

9. A turbine component comprising a gamma-titanium aluminide alloy consisting essentially of, in atomic percent: about 38% to about 50% aluminum (Al), about 1 to about 6% niobium (Nb), about 0.25 to about 2% tungsten (W);

optionally, the boron (B) content is up to about 1.5%; about 0.01 to about 1.0% carbon (C); optionally up to about 2% chromium (Cr), optionally up to about 2% vanadium (V), optionally up to about 2% manganese (Mn), and the balance titanium (Ti) and other impurities.

10. The turbine component of claim 9, wherein the turbine component is a wheel or a vane.