Research Training Group MatCom – ComMat: High-temperature oxidation behavior of ceramic coatings based on polymer-derived ceramic nanocomposites

The Research Training Group 2561 “Material Compounds from Composite Materials” is funded by the Deutsche Forschungsgemeinschaft (DFG) and comprises 12 PhD students from 3 research institutes: DECHEMA-Forschungsinstitut (DFI), Technical University Darmstadt (TUD) and Karlsruher Institute of Technology (KIT).

The Research Training Group aims to develop, characterize and model new composite materials for high-temperature application above 1300°C. This allows for a higher working temperature of combustion engines thus increasing performance and efficiency. Therefore, materials are required which can withstand harsh working environments. The underlying idea is to combine two material systems (composite materials) into material compounds, thereby combining their respective intrinsic characteristics and advantages.

One of these material systems consists of polymer-derived ceramic nanocomposites, which serve as thermal/environmental barrier coatings (T/EBCs) for the underlying metallic/intermetallic refractory metal silicide substrates.

Polymer-derived ceramic nanocomposites (PDC-NCs) provide an attractive combination of high-temperature properties (e.g. high thermal stability, self-healing capability and low intrinsic thermal conductivity), which makes PDC-NCs a promising candidate for thermal barrier coatings for harsh operation conditions beyond 1300 °C. However, the oxidation behaviour, which plays a crucial role for the assessment and selection of materials for TBCs, has not been investigated systematically. In general, silicon-based PDC-NCs rely on a thermally grown SiO₂ layer, which provides protection against further oxidation at high temperatures. However, the presence of water vapor at high temperatures leads to evaporation of the protective SiO₂ scale due to formation of volatile Si(OH)₄. By variation of the chemical composition oxidation behaviour of PDC-NCs can be further enhanced.

The major goal of this project is to systematically examine the influence of the chemical composition of PDC-NCs on the high-temperature oxidation behaviour (T ≥ 1300 °C). Therefore, the chemical composition of the polymeric precursor will be selectively modified, while measuring the effect on the oxidation kinetics and the microstructure of the resulting oxide scales. First, monolithic ceramic samples will be investigated in dry atmospheres. In addition, the reactions in wet atmospheres and the oxidation behaviour of PDC-NC coatings will be evaluated including the interaction of the coatings with the underlying substrate. The experimental results will be combined with thermodynamic modeling to get a deeper understanding of the underlying oxidation processes. Concluding, the interaction between the coating and the underlying substrate will be evaluated.

Further information can be found on the GRK website

Funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) - GRK2561/1