By National Research Council, Division on Engineering and Physical Sciences, National Materials Advisory Board, Commission on Engineering and Technical Systems, Committee on Advanced Fibers for High-Temperature Ceramic Composites
High-temperature ceramic fibers are the foremost elements of ceramic matrix composites (CMCs). Ceramic fiber houses (strength, temperature and creep resistance, for example)-along with the debonding features in their coatings-determine the houses of CMCs. This file outlines the state-of-the-art in high-temperature ceramic fibers and coatings, assesses fibers and coatings by way of destiny wishes, and recommends promising avenues of study. CMCs also are mentioned during this report back to supply a context for discussing high-temperature ceramic fibers and coatings.
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Extra resources for Advanced Fibers for High-Temperature Ceramic Composites: Advanced Materials for the Twenty-First Century
The CVD β-SiC fibers have grain sizes on the order of 4 to 10 times larger than the Hi-Nicalon fiber, but creep rates are 10 to 100 times those of Hi-Nicalon. Lowering the boron content of the Sylramic fiber appears to improve creep resistance, but the effect has not been quantified. Thus, fundamental questions remain about what controls the creep rates of SiC-based materials. What is the role of carbon, of solid solution dopants? Do the stacking faults in β-SiC grains play a role? Is the α-SiC microstructure intrinsically more creep resistant?
Comparison of Fiber Categories As a class, polymer-derived SiC-based fibers are the strongest ceramic fibers known. , greater than 1 percent). As the β-SiC grain size increases or the amorphous phase content decreases, the carbon content increases in some fibers (Hi-Nicalon, Tyranno Lox E) resulting in a decrease in strength and an increase in the modulus, thus sacrificing strain-to-failure. These microstructural changes are induced by (1) using a curing step during fiber processing that incorporates very little oxygen into the structure and (2) by conducting pyrolysis at higher temperatures.
These test results are presented as a function of temperature for many of the commercially available and developmental fibers (the higher the m value the more creep resistant the material). The Carborundum fiber has the highest creep resistance (except for the annealed Hi-Nicalon S); the Hi-Nicalon S and the Dow Corning fiber follow. The highest ranked production fiber is Hi-Nicalon. 2 primary creep occurs after the initial elastic extension (or strain) of the material under load and continues until the creep rate reaches a steady state.
Advanced Fibers for High-Temperature Ceramic Composites: Advanced Materials for the Twenty-First Century by National Research Council, Division on Engineering and Physical Sciences, National Materials Advisory Board, Commission on Engineering and Technical Systems, Committee on Advanced Fibers for High-Temperature Ceramic Composites