Analysis, influencing and optimisation of the microstructure and characterisation of the process-structure-property correlation (PSP) of C/SiC composites, produced by thermoset injection molding in the 1st process stage (IM-CMC)

• Applicant: Professorin Dr.-Ing. Daisy Nestler
• Subject Area: Glass, Ceramics and Derived Composites ; Lightweight Construction, Textile Technology
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 501805773

The aim of the project is the analysis of process-related microstructure changes and the resulting failure mechanisms of C/C-SiC ceramic-matrix composites. The special feature of this project is the use of the thermoset injection moulding process as the first process stage in the three-stage LSI route (liquid silicon infiltration). This so-called IM-LSI process (injection moulding and liquid silicon infiltration) enables the mass production of CFRP preforms, but changes the microstructure by separating fibre structures, shortening them and reorienting them during injection. This requires an evaluation of the energy dissipation mechanisms for generating the quasi-ductility. The focus is on the effects of the three main process steps (injection moulding, pyrolysis, silicon filtration) on the microstructure. In the short fibre compound, the carbon fibres are predominantly isolated, but are reproducibly arranged in thermoset injection moulding. The resulting microstructure, the adjustment of the fibre orientation by sprue design and the influence of weld lines on structure and properties are the subject of the investigations. In addition, silicon powder should already be mixed into the granules during compounding. This enables intrinsic silicification with the advantage of precisely controlling the SiC content in the matrix. The direct impregnation of textile semi-finished products as inserts in thermoset injection moulding serves to compensate for the short fibre length of the compound and should lead to a significant increase in mechanical properties, in particular quasi-ductility. The change of the microstructure due to the formation of the crack network during pyrolysis differs from the state of the art. The individual reinforcing fibres cause the formation of a fine crack network, which is subsequently infiltrated with silicon. The investigation of the effect of this microstructure in contrast to a coarse woven-based microstructure on the energy dissipating mechanisms and thus on the quasi-ductility is a main focus of this project. The relationships between process, microstructure and properties will be investigated, represented and optimised.

• DFG Programme: Research Grants