Week 47/2019

Heat shields for economical aircraft

Suspension spraying is used to specially coat components so that they can compensate for large thermal loads.
Suspension spraying is used to specially coat components so that they can compensate for large thermal loads.
Around 1,200 degrees Celsius (2,192 °F) – a temperature one-third as high as in the earth’s liquid core – that's the temperature required inside a turbine for an aircraft to fly. In fact, the higher the temperature, the more efficiently the turbine operates, saving fuel. Engineers are therefore looking for ways to increase the heat even further. The limiting element is the components; the materials they are made of tolerate significantly less heat and must be protected with special coatings. The Dresden-based Fraunhofer Institute for Material and Beam Technology IWS has now developed a new technology with which the components can be protected from heat even more quickly and cost-effectively.

To ensure that components such as turbine blades can withstand the extreme temperatures, they are given a thermal barrier coating. For decades, two processes have been deployed for this purpose, in which a thin metal layer and a slightly thicker ceramic layer – which together form what is called the thermal barrier coating – are applied in powder form. But neither of the two technologies used so far is perfect. Processing with electron beam evaporators, for example, results in very durable parts, but is extremely complex and expensive. Atmospheric plasma spraying, on the other hand, is inexpensive, but the layers produced in this way are not as resistant.

The best shielding layer

The Fraunhofer Institute has developed a new heat shield technology. A suspension is mixed from ceramic powder and water or alcohol and then is sprayed onto the aircraft parts. The crucial point: by using a suspension instead of powder, materials with particles as small as a thousandth of a millimeter can be processed that could not be used in previous methods. Using these particularly fine materials makes it possible to create layers with a special structure that can compensate well for huge thermal loads – and are therefore durable. What's more, even with large components, the new process is not very complex and therefore comparatively inexpensive.

Like the previous processes, the new coating also makes it possible to raise the operating temperature of a turbine by around 150 degrees Celsius (302 °F) without affecting the components. As a result, the turbine works more efficiently and the aircraft’s flight is more economical and environmentally friendly. The bottom line is a reduction in fuel consumption.

Already in use – and it goes even further

Together with the Swiss plant manufacturer AMT AG, the Dresden Fraunhofer Institute has now transferred this innovative process into industrial practice. The first manufacturers from the aviation industry are already using it. The stability and reproducibility of the coating process is significantly influenced by the properties of the suspension. In addition to other suspensions, some of which are commercially available, suspensions from Fraunhofer IKTS are used, which are specifically developed for this process and produced on a pilot scale.

However, the potential of the technology extends far beyond the aviation industry. For example, the technology developed in Dresden can also be used in machines for the production of semiconductors and chips and can provide better protection against corrosion. The technology is thus one of many examples of how innovations from the aviation industry can also foster progress in other industries.