High Modulus and High Strength C/C-SiC Ceramic Matrix Composites by Fiber-Matrix Interface Tailoring via Modification of Fiber Surface and Matrix Precursor - Kerafam 2

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Based on the knowledge gained in the previous KeraFaM project, KeraFaM 2 aims to bring the mechanical properties of C/C-SiC materials closer to the theoretical limits expected from standard and high performance fibers.So far, the following insights were obtained:•Protection of the fibers against conversion during the siliconisation can be achieved by precise tailoring of the fiber-matrix-bonding (FMB). This prevents fiber-matrix-delamination (FMD) and favors segmentation cracks (SC) between fiber bundles, resulting in dense C/C-blocks separated by SiC matrix. Mechanical properties of the resulting C/C-SiC composites are below the theoretical limits. The low utilization rate of fiber properties is attributed to the C/C block structure favoring a fiber bundle pullout.•The formation of the crack structure of the samples observed after carbonization does already start during curing of the resin.•The choice of matrix resin influences the microstructure. The essential difference between the resins are the phenolic and solvent content.•The Ultra High Modulus (UHM) fibers used during the project could not be processed after desizing due to their brittleness.•The micro crack formation for different FMBs during pyrolysis can be modeled employing the Finite Element Method (FEM).The collaboration between the team ceramic composites and structures at the DLR in Stuttgart, the DITF in Denkendorf and the chair of experimental physics 2 at the University of Augsburg has proven to be complementery and effective during KeraFaM. Based on this successful collaboration, the following goals will be pursued in KeraFaM 2:•To raise the fiber utilization rate substructuring of the C/C blocks is intended. This could be achieved by a multilayer sizing. This sizing is used to obtain a more defined tailoring of the FMB and to protect the fibers from conversion. In a second approach a microporous C-matrix will be produced. Both concepts are expected to favor single fiber pullout over fiber bundle pullout.•Analysis of cross-linking reactions, in situ acoustic emissions analysis and nano-CT examination starting at the curing stage of the resin addresses understanding of the microstructure formation. This will ultimately lead to better control of the microstructure and the resulting C/C-SiC composite properties.•The FE-Model will be refined by taking into account experimentally obtained material parameters in order to realistically represent microstructure development for different FMB values. The resulting model will be validated by acoustic emissions analysis and SEM measurements.•The impact of phenolic content of the matrix resins on residual carbon mass, shrinkage and microstructure after carbonization will be evaluated varying the proportion of aromatic compounds of the matrix resin.•To allow further processing and to protect fibers from conversion to SiC, UHM fibers will be modified by applying an additional sizing on top of the as-received sizing.