Non-oxide ceramic fibers are of considerable interest due to the ability to combine the high performance, especially high temperature thermal and creep resistance, with the structural advantages of fibers including their use as reinforcements for metal (MMCs) and ceramic matrix composites (CMCs). In this paper the development of CVD SiC fibers and three generations of polymer derived SiC fibers over the past 50 years are discussed, illustrating the effect of fiber precursor and processing on the microstructure and physical properties of the non-oxide ceramic fibers. Additionally recent advances in research and development related to fibers from SiC and SiCN systems are presented with discussion of the current focus on reducing the costs of the fiber processing, while increasing their thermostructural stability.
Aluminum phosphate was deposited onto bundles of carbon fibers and flat glassy carbon substrates using atomic layer deposition by exposing them to alternating pulses of trimethylaluminum and triethylphosphate vapors. Energy dispersive X-ray spectroscopy (EDXS) and solid state nuclear magnetic resonance (SS-NMR) spectra confirmed that the coating comprises aluminum phosphate (orthophosphate as well as other stoichiometries). Scanning electron microscopic (SEM) images revealed that the coatings are uniform and conformal. After coating, the fibers are still separated from each other like the uncoated fibers. Thermogravimetric analysis (TGA) indicates an improvement of oxidation resistance of the coated fibers compared to uncoated fibers.
Layers of alumina were deposited on to bundled carbon fibers in an atomic layer deposition (ALD) process via sequential exposure to vapors of aluminium chloride and water, respectively. Scanning electron microscopic (SEM) images of the coated fibers revealed that each individual fiber within a bundle was coated evenly and separately, fibers are not bridged by the coating. SEM and transmission electron microscopic (TEM) images indicate that the coating was uniform and conformal with good adhesion to the fiber surface. Average deposition rate, measured from SEM images, was 0.06 nm per cycle at 500 °C. SEM also revealed that at deposition temperatures of 500 °C few of the fibers were damaged. At temperatures of 300 °C, no damaged fibers were observed, the average deposition rate decreased down to 0.033 nm per cycle. Oxidation resistance of the alumina-coated fibers was characterized by thermogravimetric analysis (TGA). The alumina coating improved oxidation resistance of the carbon fiber significantly. Oxidation onset temperature was 600 °C for fibers coated with a 45 nm thick alumina. Uncoated fibers, on the other hand, started to oxidize at temperatures as low as 250 °C.
The research and development of new materials such as particle-reinforced aluminum matrix composites (AMCs) will only result in a successful innovation if these materials show significant advantages not only from a technological, but also from an economic point of view. Against this background, in the Collaborative Research Center SFB 692, the concept of an integrated technology, user, and market analysis and forecast has been developed as a means for assessing the technological and commercial potential of new materials in early life cycle stages. After briefly describing this concept, it is applied to AMCs and the potential field of manufacturing aircraft components. Results show not only technological advances, but also considerable economic potential-the latter one primarily resulting from the possible weight reduction being enabled by the increased yield strength of the new material.
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