Effect of Spark Plasma Sintering in Fabricating Carbon Nanotube Reinforced Aluminum Matrix Composite Materials

Abstract

1. Intorduction Carbon nanotubes (CNT) are attractive next generation materials due to their unique properties, which lead to high mechanical, electrical, and thermal performance (Iijima, 1991; Endo et al., 1976; Niyogi et al., 2002; Komarov & Mirnov, 2004). This unique nano order material can not only be utilized on its own in precision industrial fields but can also provide high performance functionality in conjunction with conventional materials. For this reason, many researchers are investigating the fabrication of CNT reinforced metal, ceramic, and polymer matrix composite materials. Despite their research efforts, the fabrication of CNT-reinforced metal matrix composite materials, particularly with an aluminum (Al) matrix, is still facing several problems, such as difficulties in homogeneously dispersing the CNT in the Al matrix, (Salvetat-Delmotte and Rubio, 2002; Hilding et al., 2003; Xu et al., 1999) producing highly densified composite materials without any degradation of the CNT, (Kuzumaki et al., 1998; Sridhar & Narayana, 2009) and achieving enough interface strength between the Al matrix and reinforcement of CNT (Deng et al., 2007; Bakshi et al., 2009; Lahiri et al., 2009). To overcome these problems, Deng et al. fabricated the CNT-Al alloy composite materials by cold isostatic pressing and then subsequent hot extrusion techniques, with which they have achieved 45% incremental increase in tensile strength (Deng et al., 2007) Esawi et al. attempted to fabricate a CNT-Al matrix composite by mechanical milling and rolling or extrusion processes (Esawi & Morsi, 2007; Esawi & Borady, 2008; Esawi et al., 2009). Morsi et al. produced CNT-Al matrix composites by a unique powder metallurgy route using spark plasma extrusion (Morsi et al., 2009; 2010). Agawal et al. introduced several fabrication methods for CNT-Al and Al alloy composites based on thermal and cold spray forming technologies (Laha et al., 2004; Bakshi et al., 2008; Bakshi & Agarwal, 2010). Recently, we have also demonstrated the feasibility of making aluminum-carbon nanotube (Al-CNT) composite materials, producing not only a highly densified composite but also enhanced interface bonding between the Al matrix and CNT, by a combination of spark plasma sintering (SPS) followed by hot extrusion processes (Kwon et al., 2009; Kwon & Kawasaki, 2009; Kwon et al., 2010). However, the specific effect www.intechopen.com Advances in Composite Materials for Medicine and Nanotechnology 430 of SPS for the final product of Al-CNT composite is not yet clear. In the present study, we have fabricated CNT reinforced aluminum matrix composite materials with two different amounts of CNTs (1 and 5vol%), by a combination of SPS followed by hot extrusion processes. Pure Al bulks also have been fabricated using the same route for comparison. In particular, the SPS behavior of the Al-CNT mixture powder was discussed. Firstly, the morphologies of Al grains in spark plasma sintered (SPSed) Al-CNT and pure Al compacts were observed. The chemical stability between the Al and CNT and the real temperature between the each Al particles during the SPS process were discussed based on the two particles model. Finally, high resolution transmission electron microscopy was carried out to understand the materials at the boundary of the SPSed Al-CNT compact. Moreover, the tensile strength and elongation of the composites was measured and discussed in relation to the different amounts of CNT additions. 2. Experimental procedure