Fabrication of Carbon Nanofibers/A356 Nanocomposites by High-Intensity Ultrasonic Processing
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DUCTION
HIGH-STRENGTH light structural materials have many applications, such as in construction, automotive, aviation, and many other industries. As a novel material, carbon nanofibers (CNFs) have attracted much attention due to their exceedingly high elastic modulus and tensile strength. In addition, most CNFs have a smooth surface, low curvature, and almost the same size of diameter, which promotes CNF dispersion uniformly in the matrix and provides great opportunities for industrial applications.[1,2] Therefore, the CNFs are a candidate with great potential as reinforcement of composites for mass production. At present, various efforts have been made to develop CNFs as a reinforcement for metal matrix. Patchara et al.[3] produced a Ti64/CNFs composite by a powder metallurgy process. They reported that the addition of nanofibers improved the tensile strength of composites. However, the elongation decreased due to the formation of brittle phases and microcracks. Fumio et al.[4] fabricated CNF-reinforced aluminum matrix composites using sintering and hot extrusion. They reported that the mechanical properties of fabricated composites were also
QING-JIE WU and HONG YAN are with the School of Mechanical and Electrical Engineering, Nanchang University, Nanchang, 330031, China and also with the Key Laboratory of Light Alloy Preparation & Processing in Nanchang City, Nanchang, 330031, China. Contact e-mail: [email protected] Manuscript submitted April 24, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
significantly improved due to the CNFs, and the properties can be accurately predicted by proposed theoretical models. At present, metal casting and power metallurgy are commonly used for the preparation of metal-based composite materials.[5,6] However, powder metallurgy is not suitable for large-scale industrial production because of its high cost and processing difficulties. In contrast, the casting process has the advantages of low cost and easy operation, making it easier to adapt to modern industrial production requirements. However, a limited number of studies have been conducted on the fabrication of CNF-reinforced aluminum matrix composites produced by melt casting. Conventional agitation casting is a relatively simple alternative process that can be used to produce metal matrix composites with complex shapes. Micron-sized particles can be successfully entrained into the melt by agitating vortex.[7] However, nanosized reinforcements are difficult to disperse into the melt by the conventionally used stirring, due to their large surface area-to-volume ratio.[8,9] When treated by high-intensity ultrasound, the melt can generate acoustic cavitation and acoustic convection. The sound pressure gradient causes microstirring of the solution at high temperatures. The alternating pressure produced by ultrasound creates numerous cavities in the liquid metal. Parts of these cavities collapse under the compression stresses of the sound wave. When these cavities collapse, small areas of high pressure differences are generated, resulti
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