Al-SiC Nanocomposites Produced by Ball Milling and Spark Plasma Sintering
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Al-SiC Nanocomposites Produced by Ball Milling and Spark Plasma Sintering R.C. Picu,1 J.J. Gracio,2 G.T. Vincze,2 N. Mathew,1 T. Schubert,3 A.B. Lopez,4 C. Buchheim2 1
Department of Mechanical, Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180, U.S.A. 2 Center for Mechanical Technology and Automation, Department of Mechanical Engineering, University of Aveiro, 3810-193, Portugal. 3 Fraunhofer Institute for Manufacturing Technologies and Advanced Materials IFAM, Dresden, Germany. 4 CICECO, Department of Ceramic and Glass, University of Aveiro, 3810-193, Portugal. ABSTRACT In this work Al-SiC nanocomposites were prepared by high energy ball milling followed by spark plasma sintering of the powder. For this purpose Al micro-powder was mixed with 50 nm diameter SiC nanoparticles. The final composites had grains of approximately 100 nm dimensions, with SiC particles located mostly at grain boundaries. To characterize their mechanical behavior, uniaxial compression, micro- and nano-indentation were performed. Materials with 1vol% SiC as well as nanocrystalline Al produced by the same means with the composite were processed, tested and compared. AA1050 was also considered for reference. It was concluded that the yield stress of the nanocomposite with 1 vol% SiC is 10 times larger than that of regular pure Al (AA1050). Nanocrystalline Al without SiC and processed by the same method has a yield stress 7 times larger than AA1050. Therefore, the largest increase is due to the formation of nanograins, with the SiC particles’ role being primarily that of stabilizing the grains. This was demonstrated by performing annealing experiments at 150oC and 250oC for 2h, in separate experiments. INTRODUCTION Metal matrix nanocomposites have been studied over the past decade with the hope of reproducing the interesting property improvements observed in the field of polymer nanocomposites. Metal matrix nanocomposites are mixtures of (e.g.) ceramic nanoparticles with a metal or metallic alloy base. The particles are supposed to act as obstacles to dislocation motion and to effectively pin grain boundaries, conferring therefore microstructural stability to the composite. Since fillers have high melting point and good thermal stability, it has been discussed that such nanocomposites can be used as materials for high temperature applications. Currently, there are two ways to produce metal matrix nanocomposites. The melt technology requires that nanoparticles are dispersed in the melt of the matrix metal. The most important challenge in this method is related to the poor wettability of the particles by the melt [1]. This limits the concentration of fillers that can be properly dispersed. Also, chemical reactions between fillers and matrix may take place. The other class of methods is powder metallurgy-based, e.g. [2]. This requires mixing the two materials in powder form, mechanical alloying by ball milling, followed by pressing, sintering and/or hot pressing (e.g. extrusion). The method avoids miscibility issu
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