Reinforcement/Matrix Interaction in Sic Fiber-Reinforced Ni 3 a1 Matrix Composites
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REINFORCEMENT/MATRIX INTERACTION IN SiC FIBER-REINFORCED Ni 3A1 MATRIX COMPOSITES J.-M. Yang*, W. H. Kao** and C. T. Liu*** *Department of Materials Science and Engineering, University of California Los Angeles, CA 90024 "**MaterialsScience Laboratory, The Aerospace Corporation, El Segundo, CA 90245 ***Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 ABSTRACT The interfacial reaction characteristics of two different types of SiC fibers with Ni3 A1 (Ni-Al-Cr-Zr-B) matrix have been investigated. The microstructure and chemical compositions across the reaction zone have been analyzed quantitatively using microscopy and electron probe microanalysis. In both types of SiC/Ni 3 AI composites, it was found that Ni was the dominant diffusing species responsible for the overall reaction. The C-rich layer outside the SCS-6 fiber provided an incubation period, but could not stop the inward diffusion of Ni. It could, however, effectively stop the diffusion of Al, Zr and Cr. No significant increase in reaction zone thickness after exposure at temperatures below 900 "C for up to 100 hours was observed. When the C-rich layer was depleted, a rapid increase in reaction zone thickness and the formation of multilayer reaction products occurred. In the case of Sigma/Ni 3 A1 composite, extensive reaction between the fiber and the matrix occurred at all the temperatures studied. Diffusion barrier coating for both types of fibers is required to develop nickel aluminide matrix composites. INTRODUCTION Nickel aluminides based on Ni 3 Al are attractive materials for high temperature structural applications due to their high stiffness and high strength retention at elevated temperature, combined with low density and good oxidation resistance [1]. However, the inherent brittle intergranular fracture had limited the wide spread applications of polycrystalline aluminides as engineering materials. Nevertheless, significant improvement in the ductility and toughness has been achieved recently through various metallurgical techniques such as microalloying, macroalloying, grain refinement, etc [2-8]. It has been found that the addition of small amount of boron dramatically increases the ductility, suppresses brittle intergranular fracture at ambient temperatures. A tensile elongation greater than 50% with virtually 100% transgranular failure has been achieved in Ni-24 at.% Al containing about 0.5 at.% B [6]. The incorporation of ceramic reinforcements into the intermetallic alloy matrix should produce a composite which possesses a lower density, improved tensile strength and stiffness, as well as enhanced creep resistance [9]. Potential applications of these novel intermetallic composites include hypersonic aircraft, space vehicles, propulsion system of jet engines, etc., where sufficient stiffness, corrosion resistance and strength at elevated-temperature are required. Various approaches have been employed to consolidate nickel aluminide matrix composites with continuous fibers and particulates, such as powder metall
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