|Turbine blades from different services (from helicopter to stationary gas turbines) with a white ceramic EB-PVD thermal barrier coating based on zirconia
Coatings are used to protect materials and components against harmful attack of the environment. In the Institute of Materials Research both metallic and ceramic coatings are developed that protect metallic, ceramic, and composite materials.
Thermal barrier coatings (TBCs)
The surface temperature of turbine blades can be reduced in the order of 100 to 150°C by usage of only 0.2mm thick ceramic thermal barrier coatings of low thermal conductivity. This translates in modern aero engines in a reduction of the specific fuel consumption of about 2 to 3 % and a corresponding reduced emission.
DLR’s preferred manufacturing method, the electron beam physical vapour deposition (EB-PVD) creates very smooth and strain tolerant TBCs. They are the choice for highly loaded rotating aero engine blades due to the fact that the columnar microstructure provides excellent performance under rapid thermal cycling and thermo-mechanical straining conditions. Blade cooling is maintained because cooling holes stay opened. DLR is one of the world’s leading research organizations in the area of EB-PVD thermal barrier coatings. It develops in close cooperation with processing equipment manufacturers, coating companies, engine manufacturers, end users and other research cooperation partners new complex coatings.
Alloys used at elevated temperatures are mainly optimized with regard to their mechanical properties. In an oxygen containing or corrosive atmosphere, however, they suffer from insufficient performance. In the institute oxidation protective coatings are developed for both Nickel-based superalloys (mainly as bond coats for thermal barrier coationgs, siehe dort) see there) and for titanium alloys. Application of titanium alloys and aluminides at high temperatures is restricted by insufficient lifetime in an oxidizing atmosphere. Therefore, an effective protection of these materials is necessary for safe operation under various conditions. The main focus of our work is on magnetron sputtered coatings for application temperatures up to 900°C. more…
Environmental Barrier Coatings
Ceramic matrix composites such as WHIPOX often show substantial porosity, permeability for gases, and a rough surface caused by the manufacturing. For long-term application e.g. as combustion chamber shingles these materials must be protected against the extreme attack due to temperature, hot gas erosion and chemical reactions especially with water vapour. We develop stable ETBCs (environmental and thermal barrier coatings) for those ceramic matrix composites.
Multifunctional Emission Reducing Coatings
Combustion in post-modern lean-burn engines occurs under high air-to-fuel-ratios (A/F>15) and increases engine operating temperatures, leading to formation of higher NOx emissions. Under these new conditions, the currently applied materials and technologies have reached their uppermost limits. In order to ensure that NOx emission is effectively reduced and consequently to protect our environmental, it is essential to develop new catalytic materials i.e. catalytically active systems. Catalytic reduction of NOx can be achieved either by catalytic combustion as in primary systems or by selective catalytic reduction (SCR) as a part of the exhaust gas treatment technology which can be simultaneously controlled and monitored by gas sensors.
The principal aim of our team is to reduce NOx emission in turbines of airliners which are today, compared to their predecessors, more fuel-efficient and cleaner by employing advanced technology combustion systems. Current low-emission engines are based on in-furnace-control methods such as axially staged combustor with an LPP main module, dual annular combustor (DAC) as in CFM56 engines or those equipped with optimized injection systems and new diffuser design for lean-modules. As these technologies are still at low development levels to be considered for entry into service, there are some concerns about their applicability due to engine instabilities as well as a likelihood of a trade-off between NOx and low power HC and CO emissions. When these and the issues such as impact of NOx at altitude, NOx reduction during all phases of flight and difficulties in derivative engine design are merged, the importance of post-combustion NOx reduction becomes significant. Considering the exhaust gas temperatures, pressure and velocity, use of ceramic coatings that can reduce toxic gases effectively under net-oxidizing conditions is unavoidable. Manufacture of these material systems can be achieved by Magnetron-Sputtering, Sol- Gel Route und Electron-Beam Physical Vapor Deposition (EB-PVD).