Materials Science and Engineering A 430 (2006) 27–33 Microstructures and tensile behavior of carbon nanotube reinforced Cu matrix nanocomposites Kyung Tae Kim a , Seung Il Cha a , Seong Hyeon Hong b , Soon Hyung Hong a,∗ a Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, 373-1 Kusung-dong Yusung-gu, Daejeon 305-701, Republic of Korea b Nano P/M Group, Korea Institute of Machinery and Materials, 66 Sangnam-dong, Changwon, Kyungnam 641-010, Republic of Korea Received 25 January 2006; received in revised form 6 April 2006; accepted 27 April 2006 Abstract Carbon nanotubes (CNTs) have been considered as an ideal reinforcement to improve the mechanical performance of monolithic materials. However, the CNT/metal nanocomposites have shown lower strength than expected. In this study, the CNT reinforced Cu matrix nanocomposites were fabricated by spark plasma sintering (SPS) of high energy ball-milled nano-sized Cu powders with multi-wall CNTs, and followed by cold rolling process. The microstructure of CNT/Cu nanocomposites consists of two regions including CNT/Cu composite region, where most CNTs are distributed, and CNT free Cu matrix region. The stress–strain curves of CNT/Cu nanocomposites show a two-step yielding behavior, which is caused from the microstructural characteristics consisting of two regions and the load transfer between these regions. The CNT/Cu nanocomposites show a tensile strength of 281 MPa, which is approximately 1.6 times higher than that of monolithic Cu. It is confirmed that the key issue to enhance the strength of CNT/metal nanocomposite is homogeneous distribution of CNTs. © 2006 Elsevier B.V. All rights reserved. Keywords: Carbon nanotube; Cu; Nanocomposites; Microstructures; Two-step yielding 1. Introduction Carbon nanotubes have been expected as an ideal reinforce- ment to improve the mechanical performance of monolithic materials due to their high elastic modulus, strength and aspect ratio [1]. Recently, several researches have shown that the addi- tion of carbon nanotube can considerably enhance the strength, toughness and conductivities of polymers and ceramics [2–9]. In CNT/polymer nanocomposite, the addition of carbon nanotube as reinforcement improves the tensile strength of the polymer matrix by several times [2]. In case of CNT/silica nanocompos- ites fabricated by sol–gel process, the bending strength and frac- ture toughness increases by about two and three times, respec- tively, compared to monolithic silica [9]. Also, CNT/alumina nanocomposite processed by molecular level mixing shows strengthening and toughening by addition of CNTs [10]. However, CNT/metal nanocomposites have shown inferior mechanical properties than expected compared to CNT/polymer ∗ Corresponding author. Tel.: +82 42 869 3327; fax: +82 42 869 3310. E-mail address: shhong@kaist.ac.kr (S.H. Hong). or CNT/ceramic nanocomposites [11–15]. The inferior mechan- ical properties of CNT/metal nanocomposites are mainly due to severe agglomeration of CNTs and low relative densities, ranged 85–95%, which is caused by conventional powder metallurgy process, consisting of mixing of CNTs with metal powders and followed by sintering or hot pressing process [11–15]. Espe- cially Zhan et al. [4] demonstrated that the dispersion and homogenous mixing between CNT and ceramic matrix could be obtained by mixing nano-sized matrix powders with CNTs. They showed that the SPS process is very promising technique for full densification of CNT/ceramic nanocomposites, sepa- rately from no reliable mechanical data refuted by Wang et al. [7]. Also, we developed the CNT/Cu nanocomposites, which show remarkable enhancement of yield strength compared to that of unreinforced Cu [16], there have been little attempts to improve CNT/metal nanocomposites by modification of tradi- tional powder metallurgy process and to analyze the strengthen- ing mechanism of CNT/metal nanocomposites. In this study, the microstructure and tensile behavior of CNT/Cu nanocompos- ites, fabricated with nano-sized Cu powders by spark plasma sintering process, were investigated. The tensile deformation behavior of CNT/Cu nanocomposites was analyzed based on the 0921-5093/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2006.04.085