High-performance materials from ceramic fibers
Ceramic fiber composites, so-called CMCs (Ceramic Matrix Composites), are a special material: they are resistant to high temperatures and, due to their reinforcement with ceramic fibers, resist rapid and strong temperature changes without damage - in contrast to conventional ceramics. This opens up special technical fields of application for these materials.
The German Institutes of Textile and Fiber Research in Denkendorf have been developing ceramic fibers with special property profiles for decades. Recently, considerable investments have been made in plant technology, as the aim of the research activities is to transfer the manufacturing process to industrial production. The focus is on the development of oxide ceramic fibers based on mullite and corundum.
Best values in high temperature resistance
The decisive property of these fibers is their excellent high temperature resistance. The so-called OXCEFI ceramic fibers developed at the DITF already achieve values that exceed those of the best commercially available fibers. In this respect, interest in their economical implementation is also growing. Industry is already showing great interest in transferring the manufacturing technology into industrial production.
In order to process the ceramic fibers into composites, so-called textile preforms have to be produced: Three-dimensional contours can then be formed from fabrics impregnated with ceramic matrix, which are then fired into fiber-ceramic components in a further step. The DITF have now succeeded for the first time in producing the fabrics for the preforms in high and reproducible manufacturing quality. What may sound unspectacular is anything but trivial when it comes to ceramic fibers. Although the fibers convince by high strength values in the longitudinal direction of the fibers, they are very susceptible to breakage under mechanical loads transverse to the fiber axis. Conventional weaving processes are far too stressful for the yarn. This results in filament breaks which hinder fabric production or, in the worst case, make it completely impossible.
Demanding fabric production
These problems are avoided by using a special DITF weaving machine to ensure particularly gentle weft insertion of the yarn. An unusual gripper technology specially adapted to this type of fiber enables the ceramic fibers to be processed without tearing. In this way, for the first time, larger fabric webs can be produced flawlessly from the ceramic fibers developed in-house. The respective adaptation of the device parameters of the weaving machine to the properties of each fiber type to be processed is demanding. Even small differences in the mechanical parameters of the fiber material are immediately noticeable in the result of the weaving process. DITF's strength lies in the synergies resulting from its cross-departmental expertise in the manufacture of fibers and the mechanical processing of fabrics within the same research facility.
The ceramic fiber-reinforced composites produced from the textile preforms are impressively break-resistant - even under high mechanical loads and sudden temperature changes. The property profiles of those CMCs that are already commercially available are likely to be surpassed by the particularly good high-temperature resistances of the fibers
developed at the DITF.
Ceramic composites are used in high-temperature lightweight construction, where, for example, they can replace metallic superalloys and outperform them in terms of temperature resistance, specific strengths and modules. One field of application is the development of new types of aircraft gas turbines and stationary gas turbines with reduced emission values and higher efficiencies.