Researchers at University West in Sweden are using nanoparticles in the heat-insulating surface layer that protects aircraft engines from heat.
In tests, this is said to have increased the service life of the coating by 300 per cent and it is hoped that components with the new thermal barrier coating will be in production within two years.
To increase the service life of aircraft engines, a heat-insulating surface layer is sprayed on top of the metal components. The goal of the University West research group was to control the structure of the surface layer in order to increase its service life and insulating capability.
The thermal barrier coating is manufactured using thermal spray application, whereby a ceramic powder is sprayed onto a surface at a very high temperature –7,000 to 8,000 degrees C – using a plasma stream. The ceramic particles melt and strike the surface, where they form a protective layer that is approximately half a millimetre thick.
‘The base is a ceramic powder, but we have also tested adding plastic to generate pores that make the material more elastic,’ said Nicholas Curry, who has presented his doctoral thesis on the subject.
The ceramic layer is subjected to stress due to changes in temperature that make the material alternately expand and contract. Making the layer elastic became paramount and over the last few years the researchers have focused on further refining the microstructure in order to make the layer useful for industry.
‘We have tested the use of a layer that is formed from nanoparticles. The particles are so fine that we aren’t able to spray the powder directly onto a surface. Instead, we first mix the powder with a liquid that is then sprayed. This is called suspension plasma spray application,’ Curry said in a statement.
Curry and his colleagues have since tested the new layer thousands of times in thermal shock tests to simulate the temperature changes in an aircraft engine. Results showed that the new coating layer lasts at least three times as long as a conventional layer while it has low heat conduction abilities.
‘An aircraft motor that lasts longer does not need to undergo expensive, time-consuming service as often; this saves the aircraft industry money. The new technology is also significantly cheaper than the conventional technology, which means that more businesses will be able to purchase the equipment,’ said Curry.
One of the most important issues for the researchers to solve is how they can monitor what happens to the structure of the coating over time, and to understand how the microstructure in the layer works.
‘A conventional surface layer looks like a sandwich, with layer upon layer. The surface layer we produce with the new method can be compared more to standing columns. This makes the layer more flexible and easier to monitor. And it adheres to the metal, regardless of whether the surface is completely smooth or not. The most important thing is not the material itself, but how porous it is,’ said Curry.
The research was conducted in collaboration with GKN Aerospace and Siemens Industrial Turbomachinery.