Fabrication process and mechanical properties of carbon nanotube/metal nanocomposites by molecular level mixing

Abstract

Since the first discovery of carbon nanotube in 1991, a window to new technological areas has been opened. One of the emerging applications of CNTs is the reinforcement of composite materials to overcome the performance limits of conventional materials. Recent developments in CNT/polymer composites have shown the potential for improving the strength of polymers, and this finding has encouraged researchers to use carbon nanotubes as reinforcement for metal and ceramic matrix. However, because of the difficulties in distributing CNTs homogeneously in metal matrix by means of traditional composite processes, it has been doubted whether CNTs can really reinforce metals. In this thesis, the novel fabrication process for carbon nanotube/metal (CNT/Metal) nanocomposites was developed and their mechanical properties were investigated. The novel process consists of fabrication of CNT/Metal nanocomposite powders based on molecular level mixing process and their consolidation. The molecular level mixing process for fabricating CNT/Metal composite powders involves suspending CNTs in a solvent by surface functionalization, mixing metal ions with CNT suspension, and heterogeneous nucleation of metal nanoparticles on CNT/Metal ion mixtures. In this study, this process produces CNT/Cu composite powders whereby the CNTs are homogeneously implanted within Cu powders or Cu nanoparticles are threaded by CNTs names as pearl-necklace structure. The CNT/Cu nanocomposite with 10vol.% CNTs, consolidated by spark plasma sintering of CNT/Cu composite powders, shows to be 3 times higher strength and 2 times higher Young’s modulus than Cu matrix. This extra-ordinary strengthening effect of carbon nanotubes in metal is higher than that of any other reinforcement ever used for metal matrix composites. It must be noted that the strengthening by carbon nanotube is parallel to other strengthening mechanisms including precipitation strengthening, grain refinement strengthening and work harden...