Cost effective processing of CMC composites by melt infiltration (LSI-process)

Kurzfassung

High performance ceramics are still largely produced via powder routes. The main disadvantage of these monlithic materials is their brittle failure behaviour and the thus dissatisfactory damage tolerance of ceramic components. The most favourable way to improve the fracture toughness of ceramics is the reinforcement with thermally stable continuous fibres. However, long manufacturing times, multiple reinfiltration steps and expensive raw materials lead to high material costs of these fibre reinforced ceramic matrix composites (CMC) which have prevented their breakthrough to terrestrial applications up until now. To overcome these restrictions and widen the applicability of CMCs - in particular, to enter in fields of mechanical engineering - a novel cost efficient manufacturing route has been developed by DLR. The process is based on the infiltration of a reactive fluid phase into porous carbon fibre preforms. Molten silicon is used as the reactive fluid which replaces the initial pore volume of the preform and reacts subsequently with the carbon matrix to form silicon carbide. A one-shot infiltration is sufficient for the densification of the matrix for this liquid silicon infiltration (LSI) process. Therefore short processing times can be achieved which lead, in addition to the use of commercially available uncoated to carbon fibres and cheap raw materials like phenolics and granules of silicon, to the lowest manufacturing costs of all CMC materials. This paper deals with the fabrication of so-called C/C-SiC composites and with design and cost aspects for the manufacture of C/C-SiC components.