Stock material or miscellaneous articles – All metal or with adjacent metals – Having metal particles
Reexamination Certificate
1998-03-03
2001-04-17
Jenkins, Daniel J. (Department: 1742)
Stock material or miscellaneous articles
All metal or with adjacent metals
Having metal particles
C419S008000, C419S029000, C419S049000, C419S009000
Reexamination Certificate
active
06218026
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to the design and fabrication of a lightweight titanium member having stiffness and temperature characteristics that could allow the design of lighter, simpler and more cost effective mechanical arrangements. More particularly, the present invention has one form wherein a high performance shaft is formed of a titanium alloy tube having a gamma titanium aluminide alloy core metallurgically bonded therein. This high performance hybrid shaft has significantly increased stiffness over conventional titanium alloy shafts with no effective increase in density. Although the invention was developed for use in a gas turbine engine, certain applications may be outside of this field.
It is well known that a gas turbine engine integrates a compressor and a turbine that have components that rotate at extremely high speeds and the components are generally subjected to elevated temperatures. The rotatable components are coupled to shafts which are also subjected to the temperatures and loading inherent to most gas turbine engines. The necessity for reliable and durable shafts has resulted in the utilization of steel and nickel based alloy materials. In spite of their relatively high density and the cost and difficulty associated in manufacturing shafts from these materials they have been utilized extensively to produce gas turbine engine shafts. However, gas turbine engine designers continuously strive to decrease the weight of rotating gas turbine engine components which provides many benefits including a reduction in the centrifugal forces generated by these components. Further, the reduction in weight of the components in an aircraft gas turbine engine reduces the power consumed in the propulsion of these components.
Designers of gas turbine engines are fully cognizant that one technique for reducing the weight of gas turbine components is to use lower density materials. As a result, the designers of gas turbine engine shaft systems have become interested in titanium alloys in order to produce a relatively lightweight shaft design. However, an inherent limitation with the use of titanium alloys for many designs is the relatively low stiffness which traditional titanium alloys exhibit.
The relatively recent development of titanium alloys based on an intermetallic compound, gamma titanium aluminide (TiAl), having good high temperature (to about 1600° F.) properties makes them ideal candidates for high temperature components within a gas turbine engine. This is because they exhibit improved stiffness characteristics. Further, because of their high strength to weight ratios, gamma titanium aluminides may be used to fabricate parts having substantially lighter weight then parts fabricated from steel or nickel based super alloy parts.
Although gamma titanium aluminides have material properties that are very desirable from a component design standpoint, they are brittle at room temperature and are considered generally hard to fabricate. For many applications involving gamma titanium aluminides, either fusion welding or brazing would probably be the most desirable techniques for joining the gamma titanium aluminide details to a similar material or to other high temperature materials. However, existing welding and brazing techniques have proved unsatisfactory in many respects for providing reliable high temperature joints for titanium aluminide alloys. Therefore, a need exists for a fabrication technique that can lead to a lightweight high stiffness shaft that can utilize the material characteristics of titanium aluminide in combination with dissimilar material combinations such as steel, nickel or conventional titanium where there unique toughness and hardness characteristics might be dictated by a multi-alloy fabricated system by design requirements.
Although the migration from contemporary steel and nickel based shafts to titanium alloy shafts is a step in the right direction, the need for additional improvement in producing a lightweight high stiffness shaft still remains. The present invention satisfies this need in a novel and unobvious way.
SUMMARY OF THE INVENTION
One form of the present invention contemplates a method for manufacturing an apparatus. The method, comprising: providing a member having in its interior a gamma titanium aluminide core having a modulus of elasticity greater than the modulus of elasticity of the member; and creating a metallurgical bond between the member and the gamma titanium aluminide core so that the apparatus has a modulus of elasticity greater than the modulus of elasticity that the member would have without the core being bonded to it.
Another form of the present invention contemplates an apparatus, comprising: a member having a core of gamma titanium aluminide material positioned within the member and the core is metallurgically bonded to the member, wherein the apparatus has a room temperature modulus of elasticity greater than the room temperature modulus of elasticity the member would have without the core bonded thereto and a density about equal to the density of the member.
Another form of the present invention contemplates a member, comprising: a tube; and a gamma titanium aluminide core positioned within and metallurgically bonded to the tube, wherein the member has a room temperature modulus of elasticity greater than the room temperature modulus of elasticity that the tube would have without the core bonded thereto and the member has a density about equal to the density of the tube.
Another form of the present invention contemplates an apparatus, comprising: a first segment comprising a first member having a first core of gamma titanium aluminide material positioned therein and metallurgically bonded thereto; a second segment comprising a second member having a second core of gamma titanium aluminide material positioned therein and metallurgically bonded thereto; and the first segment and the second segment are fixidly joined together, and further the apparatus has a room temperature modulus of elasticity greater than the room temperature modulus of elasticity that the first member or the second member would have without their respective core bonded therein and a density about equal to the density of the members.
One object of the present invention is to provide an improved lightweight high stiffness high temperature shaft and method of manufacture.
Related objects and advantages of the present invention will be apparent from the following description.
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Ewing Bruce Allan
Ress, Jr. Robert Anthony
Roessler James Ronald
Allison Engine Company
Jenkins Daniel J.
Woodard Emhardt Naughton Moriarty & McNett
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