Brazing project promises better aircraft engines

Brazing is a process used to join even dissimilar and difficult to weld materials, and is capable of creating complex, high strength joints. The process works by heating an alloy, known as a Brazing Filler Metal (BFM), between the parts to be joined, to form a bond.

However, as the range of applications in which these brazes are used increases, so to do the demands placed upon them, according to Dr Russell Goodall at Sheffield University, who is leading an EPSRC-funded project to develop BFMs with improved performance.

For example, the team, which also includes the UK Atomic Energy Authority, Rolls-Royce, Johnson Matthey and the University of Limerick, among others, hope to improve the strength of BFMs.

Joining two dissimilar metals with a different alloy can lead to the formation of metallic compounds, which can be brittle and limit the strength of the joint, said Goodall.

So the researchers will investigate a new type of alloy, known as a High Entropy Alloy, in which similar amounts of many elements are combined, unlike conventional materials that consist of one main solvent and small additions of other elements. By using these new alloys, they hope to create tougher, higher strength joints without the brittleness.

Some applications, meanwhile, require filler metals that are able to operate at higher or lower temperatures, said Goodall.

“We want engines to be hotter, so we need filler metals that can withstand higher temperatures,” he said. “But there are also areas where we need the temperature to be lower, such as for use with functional ceramics that are very highly engineered to have particular electrical behaviours,” he said.

One application the researchers will be investigating is aircraft engines, where stronger alloys with improved temperature resistance could be used for more load-bearing and critical components, said Goodall.

“Some of the best-performing high temperature brazes also currently use precious metals in these applications, so if we can find alternatives that have a higher base metal content then that will make them cheaper,” he said.

The team will also be investigating the use of new filler metals in nuclear fusion reactors.

The inner walls of fusion reactors are likely to be covered by water-cooled armour tiles, which consist of thin tungsten blocks with copper alloy water-cooling pipes inside them.

These pipes are brazed using a gold-based alloy, which is expensive and has a low melting temperature, limiting the operating temperature and heat load capacity of the components.

An alloy that operates at a higher temperature without damaging the microstructure in the copper pipes would allow heat to be drawn out of the reactor more quickly, improving its efficiency.

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