Project 1: Single-source precursor synthesis of ceramic nanocomposites for (ultra)high-temperature applications

M.Sc. Jan Bernauer (1st cohort)
M.Sc. Minoo Boroojerdi (2nd cohort)

Supervisors: PD Dr. Emanuel Ionescu, Prof. Martin Heilmaier

The efficiency of combustion engines directly correlates with the temperature of combustion gases, wherein higher temperatures result in improved efficiency. Vital components operating at elevated temperatures, such as turbine blades or vanes, are constructed from highly refractory material composites with tailored property profiles. Typically, these composites consist of a nickel-based superalloy substrate coated with a YSZ ceramic layer. However, existing composite materials have reached their operational temperature thresholds, prompting recent efforts to investigate new materials to enhance turbine efficiency.

Project 1 aims to develop novel ceramic materials for the topcoat to shield a metallic substrate exposed to high temperatures and harsh environments. To achieve this, a polymer-derived ceramic (PDC) with adjustable composition is engineered. In the first cohort (P1.1), (nano)composites MC(N)/Si(B,N)C (M = Hf,Ta) were successfully synthesized. Both ceramic coatings and bulk ceramics were fabricated, and their processability and thermal properties were assessed [1,2].

The next phase of the project (2nd cohort, P1.2) focuses on advancing the system by synthesizing multinary Si(M,B)CN compositions, where M represents Hf, Ta, Al, and Y, with the goal of identifying the optimal formulation to meet the requirements for Thermal Barrier Coating (TBC) and Environmental Barrier Coating (EBC) applications. For this purpose, commercially available polysilazanes will be used as precursors, i.e. Durazane 1800 (Merck KGaA). Upon ceramization, the single-source precursor converts to SiCN-based ceramics containing in-situ formed transition metal compounds (carbides, borides, nitrides) with excess carbon. In order to prepare these systems, suitable chemical modification of the polysilazanes with metal amido complexes or other metal-organics is required, as developed during project P1.1.

The resulting amorphous ceramics as well as the ceramic nanocomposites obtained upon annealing at temperatures beyond 1100 °C will be investigated with respect to their chemical and phase composition as well as nano/microstructure.

The focus will be set on the preparation of amorphous monolithic samples, representing a shift from the SPS-focused studies in P1.1, in order to obtain materials exhibiting similar composition and structure with respect to the coatings produced in P2.2. These monoliths will be investigated in various conditions: as obtained, annealed at temperatures up to 1800 °C and after oxidation and corrosion experiments in cooperation with P3, P5 and P7. In addition to structural characterization, thermal, mechanical and thermomechanical properties such as CTE, thermal conductivity, hardness, and Young’s modulus will be determined in cooperation with P6 and P10 and used as input for P4, P9 and P12. Evaluation of the crack healing ability of the synthesized systems under corrosive conditions will be a further point of studies.

[1] Bernauer, J., Petry, N.-C., Thor, N., Kredel, S.A., Teppala, D.T., Galetz, M., Lepple, M., Pundt, A., Ionescu, E. and Riedel, R. (2024), Exceptional Hardness and Thermal Properties of SiC/(Hf,Ta)C(N)/(B)C Ceramic Composites Derived from Single-Source Precursor. Adv. Eng. Mater. 2301864.

[2] Bernauer, J., Kredel, S.A., Ionescu, E. and Riedel, R. (2024), Polymer-Derived Ceramic Coatings with Excellent Thermal Cycling Stability. Adv. Eng. Mater. 2301820.