Modification of the Thermoset Injection Moulding Process for Shaping to Increase the Fibre Length in C/C-SiC Ceramics Produced by the LSI Process

Abstract

Ceramic-matrix composites (CMC) made of carbon and silicon carbide dual matrix reinforced with carbon fibres (C/C-SiC) have exceptional heat, thermal shock, creep, and wear resistance, while also having little density and high strength. In comparison to monolithic ceramics, CMC possess ductility and damage tolerance, which opens this material for severe applications. Starting in space applications, this material is today well established in friction applications, where lightweight high-performance brakes securely decelerate e.g. luxury cars or elevators. The high production costs still limit the broad application like as brake discs in standard passenger cars, although less weight, better performance and longer lifetime. The industrial used production process is the liquid silicon infiltration (LSI) with it three steps: green body shaping, pyrolysis and silicon infiltration. In this work, the shaping process of the carbon fibre reinforced plastic (CFRP) green body, is done by thermoset injection moulding. The application of plastic production processes like compounding and injection moulding in the liquid silicon infiltration process route, enables large-scale manufacturing. However, the screws and high shear forces inside the plastic processing machines significantly shorten the fibres. This paper describes the pros and cons of thermoset injection moulding in the LSI route, as well as the development and effect of different reinforcement types in dependence of their fibre length, since several energy dissipation mechanisms bases on a minimum length of reinforcement fibres in CMC. Various raw materials like short and chopped fibres with different length, rovings, and different approaches to receive longer fibres and their outcomes are presented. The mechanical properties show promising values and the micrographs display the infiltration status and crack development inside the specimen.