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Peek at the future of aerospace brazing

Posted: 03 Jan 2013 ?? ?Print Version ?Bookmark and Share

Keywords:gas turbine engines? sintered performs? braze alloys?

Morgan Technical Ceramics's Wesgo Metals site in Hayward, California, produces more than 15 braze alloy compositions for use in the compressor section. Nioro is used on Inconel X750 or 718 to meet the solution anneal temperature without excess grain growth that occurs from nickel-based alloys. Nioro is a high-purity gold/nickel alloy for vacuum brazing. Nickel braze alloys are used in compressor and turbine section brazing. In its foil form, it can be used for brazing honeycomb and metal seal strips.

In the stator section of a turbofan engine, the stator pulls the cold air in and bypasses the engine, creating the extra thrust. The stator also has a role in reducing turbulence, so air pitching and rolling is minimised.

Figure: A diagram of a typical turbofan engine, showing the most common locations for use of alloys, including those used for the engine's "cold section" (air inlet and compressor) and its "hot section" (turbine and combustion chamber).

In turbofan fuel systems, gold nickel and platinum gold nickel are used to braze the fuel system tubes and nozzles. The fuel nozzle, located where the first and second combustion stages take place, sees a considerable amount of heat. Ductility in the braze joints is needed to help with the expansion and vibration in the combustion section. Gold and platinum braze alloys also exhibit superior contrast in the braze joint, allowing the use of X-ray technology to check braze joint integrity. In addition, these alloys demonstrate extremely good corrosion resistance. This area is one where engine manufacturers have expressed a tremendous amount of interest in materials that can withstand highly extreme temperatures, where conventional super alloys fail.

Active metal brazing
An area of increasing interest is active metal brazing, which allows metal to be bonded directly to ceramic without metallisation, thereby eliminating several steps in the joining process and creating an extremely strong, hermetic seal that can reach higher operating temperatures. Aerospace applications include nozzles for aerospace and industrial turbine engines, new turbine vane systems and engine sensor components.

Active metal brazing can be performed with any combination of ceramics, carbon, graphite, metals and diamond. Active braze alloys (ABAs) are used for engine sensors that employ metal-to-ceramic strips to monitor engine functions. Brazing is done with a high temperature ABA so the sensor can withstand 1000C (1830F) in service.

Active metal brazing facilitates the joining of some materials and components that could never before be accomplished, and is especially beneficial in military and aerospace applications.

References
[1] National Aeronautics and Space Administration, http://www.grc.nasa.gov/WWW/K-12/airplane/aturbf.html, retrieved October 6, 2011

About the author
Tom Sandin is Morgan Technical Ceramics Wesgo Metals Brazing Product Manager.

To download the PDF version of this article, click here.


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