Fiber-reinforced composites offer good mechanical properties with low weight and high damage tolerance. The most well-known type of fiber-reinforced composites is fiber-reinforced plastics (FRP), which can only be used up to a maximum of 300°C. Much higher temperatures are possible with ceramics reinforced with ceramic fibers, known as Ceramic Matrix Composites (CMCs), which can reach operating temperatures of well over 1000°C. The interplay between reinforcing fibers and the surrounding ceramic is adjusted to make the CMCs behave in a quasi-ductile manner. Similar to metals, they do not break suddenly and catastrophically, but can stretch up to one percent before failure. However, the production costs of conventional CMCs are very high, with the prices of the required ceramic reinforcing fibers ranging from a few hundred to several thousand euros per kilogram. This limits the use of CMCs to a few high-priced applications such as aerospace or energy technology. Therefore, Fraunhofer Center HTL is also developing low-cost CMCs that use glass or basalt fibers, which are one to two orders of magnitude cheaper than ceramic reinforcing fibers. The maximum operating temperature of these new CMCs is limited to around 900°C to 1000°C.

Processing Through Automated Processes
Prepreg Plant
© Mathis AG
Prepreg System at Fraunhofer Center HTL

In the processing of the reinforcement fibers into CMCs, consistently cost-effective automated processes must be used to limit manufacturing costs. The fiber coating, for example, is done through a rapid dipping process, while the production of fiber preforms utilizes modern textile machines, and the impregnation with the ceramic matrix is done through roll-to-roll processes. The latter produces flexible prepregs that can be cut, laminated, and shaped using standard methods.

The final manufacturing step is a thermal treatment, which is carried out at temperatures below 1000°C to avoid damaging the reinforcement fibers. This process uses geopolymer materials, among others, which can be cured at low temperatures.

Application between 300°C and 1000°C

The cost-effective CMCs can be used for operating temperatures between 300°C and approximately 1000°C. These include, for example, many processes in foundry technology. For steam power plants, metal-ceramic composites can be produced with the new CMCs that are particularly creep-resistant and yet gas-tight. Due to the low manufacturing costs, many other applications are also conceivable.

Service Offering:

  • Application-specific material selection and development
  • Sampling with low-cost CMC materials
  • Manufacturing studies for cost-optimized prototypes and small series
  • Selection of cost-effective manufacturing steps
  • Development of textile 2D and 3D semifinished products in final contour
  • Investigation and selection of cost-effective reinforcement fibers
  • Development of ceramic matrices that sinter at low temperatures
  • Development of continuous manufacturing steps
  • Optimized component production in final contour without post-processing
  • Development of a robot-assisted quality control for series testing of components
  • Technology transfer of processes and material formulations to manufacturers