The microstructure of SCS-6 SiC fiber
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A thorough investigation of the microstructure of single SCS-6 SiC fibers widely used as reinforcements in metal-matrix and ceramic-matrix composites has been made. Various techniques of electron microscopy (EM) including scanning (SEM), conventional transmission (TEM), high resolution (HREM), parallel electron energy loss spectroscopy (PEELS), and scanning Auger microscopy (SAM) have been used to analyze and characterize the microstructure. The fiber is a complicated composite consisting of many different layers of SiC deposited on a carbon core and different carbonaceous coatings covering the SiC layers. The structural and chemical aspects of each layer are characterized and discussed.
I. INTRODUCTION SiC fibers are of considerable interest as reinforcements for metal- and ceramic-matrix composites. The microstructural features of the fibers, which arise from the method of production, affect the mechanical and physical properties of the composite. In a fiber-reinforced metal-matrix composite, where the composite strength is generally determined by the ceramic component while its fracture properties are controlled by the metallic component, the strength of the fiber is of primary importance. As a result, the microstructure of the inner part of the fiber, which controls its strength, plays a major role. On the other hand, in a fiber-reinforced ceramic-matrix composite, where strengths of both fiber and matrix are high and of comparable value, both components are brittle and it is the fracture properties that need to be addressed. Of particular importance in this respect is the adhesion of the fibers to the matrix in which they are embedded. To a large extent, the fracture properties of a fiber-reinforced ceramic composite are determined by how strongly the fibers adhere to the matrix.1"5 In general, a relatively weak interface is desirable in this case because it stops the propagation of a crack in the matrix from crossing into the fiber and causing catastrophic failure of the composite. For this reason, in ceramicmatrix composites, it is the fiber/matrix interface that is of prime concern. The fiber/matrix interface is either sharp, in which case it is defined by a plane, or, alternatively, it is diffuse, in which case an interfacial region exists. The former is the usual case for ceramic-matrix composites where there is small reactivity between the fibers and the matrix at the temperature at which the composite is processed. On the other hand, in the case of fiber-reinforced metal-matrix composites, a reaction layer often forms between the outermost regions of the fiber and the adjacent matrix. This reaction layer constitutes the interfacial region and 2234
J. Mater. Res., Vol. 6, No. 10, Oct 1991
http://journals.cambridge.org
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the interface is then diffuse and not clearly defined. In either case, the microstructure of the outermost section of the fiber, or of the fiber/matrix interface itself, is of particular importance. Some of the most widely used commercial fibers are the SCS seri
