Damping behavior of 6061Al/Gr metal matrix composites
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INTRODUCTION
T H E damping capacity o f a material refers to its ability to convert mechanical vibration energy into thermal energy. When utilized effectively in a structural application, this property allows undesirable noise and vibration to be passively attenuated and removed to the surroundings as heat. Accordingly, investigators have sought to improve the damping capacity o f metals and alloys through the use o f innovative processing techniques. With the advent o fmetalmatrix composite (MMC) technology, it became possible to modify the physical and mechanical properties o f metals and alloys by combining them with nonmetallic phases.' Ceramic-reinforced metals, for example, may combine the ductility, toughness, and environmental resistance o f the matrix metal with the high strength and high modulus characteristics o f the ceramic reinforcement, t~J The behavior o f MMCs is largely dictated by the microstructure o f the constituents as well as the characteristics o f the metal/ceramic interface. As a result, effective metal/ceramic c o m p o sitions are generally limited by the thermodynamic compatibility o f the combined phases and the thermal conditions present during processing, t2] For instance, incorporation o f graphite particulates into AI at elevated temperatures, such as those present during casting, may result in the extensive formation o f carbide phases, with an associated degradation o f mechanical properties, tin1 In view o f such limitations and in an effort to expand the range o f possible metal/ceramic combinations, there have been extensive research efforts aimed toward the development o f novel synthesis techniques for MMCs.~I.3 -5] Recently, spray atomization and codeposition processing has received considerable attention for the synthesis o f discontinuously reinforced M M C s . This interest R.J, PEREZ, Graduate Student Researcher, J. ZHANG, Graduate Student Researcher, and E.J. LAVERNIA, Associate Professor, are with the Department of Mechanical and Aerospace Engineering, University of California-Irvine, Irvine, CA 92717. M.N. G U N G O R , Senior Engineer, is with the Department of Advanced Materials Technology, Westinghouse S c i e n c e and Technology Center, Westinghouse Electric Corporation, Pittsburgh, P A 15235. Manuscript submitted May 2 2 , 1992. METALLURGICAL TRANSACTIONS A
has arisen as a result o f several promising characteristics o f the technique, tl,6"Tj F i r s t , because o f highly efficient heat convection during atomization, the M M C is rapidly cooled immediately following introduction o f the reinforcing particulates, thereby minimizing reaction kinetics at the matrix/reinforcement interface. This provides an opportunity to process metal/ceramic combinations which would otherwise r e a c t extensively when exposed to elevated temperatures. Second, spray-atomized and deposited materials have been reported to exhibit characteristics associated with rapid solidification, n a m e l y , fine-grained microstructures, increased solid solubility, nonequilibrium phases,
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