Nanocarbon-reinforced metal-matrix composites for structural applications

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troduction Metal matrix composites (MMCs) typically incorporate hard (usually ceramic) reinforcement into a metal matrix, enabling mechanical properties that are unattainable with the individual constituents of either the filler material or the metal matrix. Traditional methods such as solid-solution and precipitate strengthening can significantly increase the strength of an alloy, but often do not cause a pronounced change in modulus, which is a direct measure of the chemical bond stiffness of the metal. In MMCs, on the other hand, the reinforcing agent effectively improves the modulus as a result of its load-bearing capability upon mechanical loading. The development of MMCs is always accompanied by the search, discovery, and subsequent use of more advanced reinforcements. In the past decade, with the emergence of nanocarbon materials such as carbon nanotubes (CNTs), graphene, and their derivatives, research efforts have been dedicated to the fabrication and characterization of nanocarbon-reinforced MMCs.1–3 In their pristine, single-crystalline form, nanocarbon materials are reported to have extremely high strengths (130 GPa)4 and high Young’s modulus (1 TPa).4 Even if these nanocarbon materials contain a certain concentration of crystalline defects, their intrinsic properties still prevail over

those of conventional fiber and particle reinforcements.5 Furthermore, property enhancement from the nanocarbon reinforcements can well exceed that predicted by the “rule-ofmixture,” owing to the confinement of dislocations imposed by the interface between the metal matrix and the nanocarbon fillers.6–8 This article highlights and reviews recent important research progress in the field of the mechanical behavior of nanocarbon-reinforced MMCs. State-of-the-art developments regarding the fabrication and processing of these composites are discussed. Particular emphasis is given to the structure and properties relation of the nanocarbon–metal interfaces, since the interfaces not only transfer external load from the matrix to the reinforcement, but also affect the deformation mechanism of the composite.6–8 Finally, perspectives and challenges are proposed and identified for the further advancement of this field.

Fabrication and processing The greatest difficulty in fabricating nanocarbon-reinforced MMCs is the uniform dispersion of these nanoscale reinforcements in the metal matrix. The high surface-to-volume ratio of CNTs and graphene is a “double-edged sword,” which may

Qiang Guo, State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University, China; [email protected] Katsuyoshi Kondoh, Department of International Affairs, Osaka University, Japan; [email protected] Seung Min Han, Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Republic of Korea; [email protected] doi:10.1557/mrs.2018.321

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• VOLUME 44 • JANUARY 2019 • www.mrs.org/bulletin © 2019 Materials Downloaded MRS fromBULLETIN https://www.cambridge.org/core. University of New England, on

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