Friction welding

Abstract

A method of bonding two materials by friction welding method. A first material may be made from a titanium aluminide intermetallic alloy and a second material may be made from a titanium alloy. The first material may be heated to a temperature between about 300° C. and about 800° C. The second material may be rotated relative to the first material. The first material and the second material may be pressed against each other while one of the first material, and the second material is rotated. The rotation of one of the first material and the second material may be stopped, and the first material and the second material may be pressed against each other after the rotation of one of the first material and the second material is stopped.

Description

U.S. GOVERNMENT RIGHTS[0001]This invention was made with government support under the terms of Contract No. DE-AC05-00OR22725 awarded by the Department of Energy. The government may have certain rights in this invention.TECHNICAL FIELD[0002]The present disclosure relates generally to a method of bonding different materials, and more particularly, to a method of bonding different materials by friction welding.BACKGROUND[0003]Titanium aluminide intermetallic alloys possess a favorable combination of low density and high temperature capabilities, and thus have emerged as potential high temperature materials to replace super-alloys in many applications, e.g. turbines and valves. The use of titanium aluminide intermetallic alloys, however, depends on the resolution of a critical issue, namely, integrating a titanium aluminide intermetallic alloy component successfully to its application system by bonding titanium aluminide intermetallic alloy to itself or a different material. Bonding ti...

AI Technical Summary

Benefits of technology

The present patent is about a method of bonding two materials, one made from titanium aluminide intermetallic alloy and the other made from titanium alloy, by heating the first material and rotating it while pressing it against the second material. This method can also be used to produce a turbine rotor assembly by heating the turbine rotor wheel and pressing the turbine rotor shaft against it while rotating it. Additionally, the patent describes an assembly made by friction welding process where a cavity is filled with at least one of the materials to be coupled to the other material.

Problems solved by technology

Bonding titanium aluminide intermetallic alloys is challenging mainly because of three reasons: high local thermal stress involved with bonding process, formation of brittle intermetallic phases at the bonding interface, and inherent low room temperature ductility of titanium aluminide intermetallic alloys.

Because of these reasons, the titanium aluminide intermetallic alloy components and the bonding interface are prone to crack during or after the bonding process and usually associated with inferior joint properties.

In some applications, because of specific geometry or large component size of the titanium aluminide intermetallic alloy components, the local thermal stresses can become extremely high and therefore render the bonding process even more challenging.

This rapid changing in geometry, in addition to the large thermal mass of turbine wheel, may cause a steep temperature gradient, and therefore, may cause large thermal stress which may exceed the strength of the titanium aluminide intermetallic alloy in the vicinity of the bonding interface.

However, in large size valves (for example, more than four inches (10.16 cm) in valve head diameter), the temperature change across the joining interface of the valve during bonding process may cause additional thermal stresses.

The method may not be capable of providing acceptable joint properties for joining components with relatively large size, e.g., large size valves, or joining components with special geometry shapes, e.g., turbine wheels, which may experience large thermal and stress changes during bonding process.

When the titanium aluminide intermetallic alloy component is heated beyond 900° C., the strength of titanium aluminide intermetallic alloy may decrease significantly, and therefore, may cause damage to the titanium aluminide intermetallic alloy component.

Heating titanium aluminide component, which may increase the burrs from the titanium aluminide generated from the friction welding process, however, may not reduce the burrs from titanium alloy.

Moreover, to avoid oxidation, thermal stress and other possible detrimental effects to the titanium aluminide intermetallic alloy component, heating the titanium aluminide intermetallic alloy component to 900-1100° C. has to be performed in a complicated manner, which may increase the cost.

Furthermore, the induction heating method in '910 patent might not be applicable in some applications, e.g. turbine wheels, due to the turbine wheels' special geometry.

Nevertheless, although the methods of the '188 publication and '910 patent may be used to join the Ti alloy with the titanium aluminide intermetallic alloy, they may have been only successful on components with relatively small scale and relatively simple geometry shape, e.g., small size valves having gradual geometry contour changes.

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