Processing and characterization of UHTCMCs via water based slurry impregnation and mild polymer infiltration and pyrolysis
SERVADEI F. 1, ZOLI L. 1, GALIZIA P. 1, SCITI D. 1
1 CNR-ISSMC (former ISTEC), Faenza, Italy
There is great interest in improving the capability and durability of Ceramic Matrix Composites (CMCs) to withstand more challenging conditions, such as temperatures above 2000 °C in corrosive atmospheres through new manufacturing technologies that involve a chemical modification of the matrix. The addition of borides and carbides of transition metals to the SiC matrix is the most promising solution. This new class of ceramic matrix composites is called Ultra-High Temperature Ceramic Matrix Composites (UHTCMCs) and can overcome the main limitations of currently used C/C and C/SiC composites, enabling higher temperature capability and ablation resistance. Technologies for manufacturing UHTCMCs are time consuming and energy-intensive with a strong impact on the environment, requiring high temperatures that lead to a strong adhesion of the fibres with the matrix. The use of coated fibres has been shown to partially solve this issue, but the high cost and long processing times for the coating deposition makes the process unappealing. Nowadays, finding the best trade-off to balance performance and cost-effectiveness of structural materials designed for extremely hot environments remains an open challenge.
In this talk, we present the manufacturing of uncoated PAN-based carbon fibre reinforced ultra-high temperature ceramic matrix composites via aqueous ZrB2 powder-based slurry impregnation coupled with polymer infiltration and mild pyrolysis (i.e. 1000 °C, a very low temperature to consolidate UHTCMCs), using allylhydrido polycarbosilane as source of amorphous SiC(O). Unidirectional (UD), two dimensional (2D) and needle punched (2.5D) cloths were impregnated to demonstrate the versatility of the process. Microstructure and mechanical properties were investigated and correlated with fibre properties and architecture. The good homogeneity of the fibre distribution into the matrix was found even using needle-punched 2.5D preform. The moderate temperature of pyrolysis allowed to reduce the process energy consumption and inhibited the degradation of fibre/matrix interphase even without the presence of a coating on fibres. The flexural strength was found over 250 MPa for unidirectional reinforced material, while the modulus exceeded 250 GPa for needle punched one. Such results were found to be in the same range of other CMCs obtained by more complex or more time-consuming energy-intensive processes. Therefore, the homogeneous distribution of UHTC phase around each single fibre due to the optimized water-based slurry impregnation and the weak fibre/matrix interface due to the mild pyrolysis conditions are the hallmark of this process and the key to improve durability and performance of materials for extreme environments.