Development of a cost-effective manufacturing process for C/C composites using pultrusion

C/C composites (carbon fiber reinforced carbon) belong to the ceramics class of materials and have unique properties in the range of high-temperature applications between 500 and 1000 °C. These include high thermal stability, high mechanical strength, thermal shock resistance, and low distortion. These properties are required, for example, in the heat treatment of metal alloys. With a density of less than 2 g/cm³, these materials can be used to manufacture significantly lighter material carriers (so-called charging racks), which require up to 85% less energy for a heat treatment cycle than steel charging racks due to their lower thermal mass.

Challenge

Currently, the production of these high-performance materials is very expensive. Another obstacle is their open porosity, which allows quenching media (e.g., oil) to penetrate the material and damage it during frequent cooling. Their susceptibility to oxidation when in contact with oxygen is also a critical factor.

Solution approach

The IGF project KOPRA addresses these challenges by producing carbon fiber-reinforced phenolic resin profiles using the pultrusion process at Fraunhofer IWU. These profiles are subsequently converted into C/C and C/C-SiC composites at the Chair of Composite Materials and Material Composites at Chemnitz University of Technology. In parallel, the Chair of Materials and Surface Technology is developing and validating a coating that increases the material’s resistance to wear, diffusion, and oxidation under the harsh conditions of heat treatment processes. The project will culminate in a charging rack demonstrator showcasing the advantages of the new manufacturing approach.

A particular challenge for Fraunhofer IWU is the production of graded profile structures via pultrusion through the targeted addition of reactive silicon to the polymer matrix. The resulting profiles feature a silicon-rich surface and a silicon-poor core. This innovative approach enables the formation of silicon carbide during pyrolysis and is a prerequisite for achieving the high adhesive strength of the developed surface coating.