Strengthening behavior of few-layered graphene/ aluminum composites S.E. Shin a , H.J. Choi b , J.H. Shin a , D.H. Bae a, * a Department of Materials Science and Engineering, Yonsei University, Seoul 120-749, Republic of Korea b School of Advanced Materials Engineering, Kookmin University, Seoul 136-702, Republic of Korea ARTICLE INFO Article history: Received 26 February 2014 Accepted 17 October 2014 Available online 25 October 2014 ABSTRACT Strengthening behavior of composite containing discontinuous reinforcement is strongly related with load transfer at the reinforcement–matrix interface. We selected multi-walled carbon nanotube (MWCNT) and few-layer graphene (FLG) as a reinforcing agent. By varying a volume fraction of the reinforcement, aluminum (Al) matrix composites were produced by a powder metallurgy method. Uniform dispersion and uniaxial alignment of MWCNT and FLG in the Al matrix are evidenced by high-resolution transmission electron micro- scope analysis. Although the reinforcements have a similar molecular structure, FLG has a 12.8 times larger specific surface area per volume more than MWCNT due to geometric difference. Therefore an increment of a yield stress versus a reinforcement volume fraction for FLG shows 3.5 times higher than that of MWCNT Consequently, for both reinforce- ments, the composite strength proportionally increases with the specific surface area on the composite, and the composites containing 0.7 vol% FLG exhibit 440 MPa of tensile strength. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Graphene has attracted interest as a reinforcing agent for metal matrix composites due to excellent mechanical proper- ties based on the strong sp 2 CAC bonds, which are similar to fullerene and carbon nanotube [1,2]. Furthermore, it has mer- its over other carbon-based nano materials, which originate from its inherent two-dimensional (2-D) morphology; the pla- nar structure is more favorable to load transfer as well as to impeding atomic diffusion at high temperatures, as compared to its 0-D and 1-D counterparts. Consequently, it provides superior strength for composites at both room temperature and high temperatures. In order to transmit the excellent properties of graphene to composites, uniform dispersion of an individually-exfoliated graphene is one key factor. Several processes have been intro- duced to exfoliate graphite to single-layer or few-layer graph- ene by mechanical and/or chemical means [3–5]. Mechanical exfoliation using a tape dispenser [2] or atomic force micros- copy (AFM) [6] has exhibited inadequate productivity for large-scale industrial applications. Although large-scale syn- thesis of graphene by gas phase techniques (e.g., thermal chemical vapor deposition) [7–9] is actively ongoing, this pro- cess is still costly and has restrictions in terms of the selec- tion of the substrate materials. Chemical exfoliation by a solution process has been suggested as a relatively cheap pro- cess [10–12], and yet presents difficulties for scalable synthe- sis due to complex synthesis steps and the requirement for a large amount of chemicals and acid. Recently, solid phase techniques, combined with ball-milling processes, have http://dx.doi.org/10.1016/j.carbon.2014.10.044 0008-6223/Ó 2014 Elsevier Ltd. All rights reserved. * Corresponding author. E-mail address: donghyun@yonsei.ac.kr (D.H. Bae). CARBON 82 (2015) 143 –151 Available at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/carbon