In the department “High Temperature and Functional Coatings” layers are developed 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.
One major goal is the development of thermal barrier coatings. 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 in 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 field 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. A wide variety of plasma sprayed, EB-PVD and diffusion aluminide bond coats are investigated underneath the ceramic top coat. Exact knowledge of the failure mechanisms is necessary for further improvement in the coatings and for development of life prediction methods. Characterization of the microstructure is one aspect, but close to reality tests are very important, too.
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 coatings (see there) and for titanium alloys. Application of titanium alloys and aluminides at high temperatures is restricted by insufficient lifetime in 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.
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 for those ceramic matrix composites stable ETBCs (environmental and thermal barrier 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. The research topics are fundamentally focused on material science related developments of catalytic and sensing coatings and their functioning principals, essentially regarding the turbine conditions. Complex oxides and nano-phase noble metal particles embedded in ceramic matrices are especially interesting relying on their high-temperature stability and implementation as catalysis. Both fabrication of these layers and characterization of their performance is carried out in order to optimize the performance of these coatings.
Head of Department
Dr.-Ing. Manfred Peters