Strain Rate Sensitivity and Deformation Mechanism of Carbon Nanotubes Reinforced Aluminum Composites
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THE deformation mechanisms of ultrafine-grained (UFG) and nanocrystalline (NC) metals have been extensively studied recently for explaining, controlling, and optimizing the mechanical properties of metals.[1,2] In conventional coarse-grained metals, the plastic deformation is governed by the movement and interaction of intragranular dislocations. But as the grain size reduces to sub-micrometer and nanometer regimes, the intragranular dislocation process is weakened and the boundary-mediated deformation mechanisms gradually become a dominant factor.[3–5] Various grain boundary-mediated deformation mechanisms have been proposed to explain the deformation behaviors of UFG and NC metals, such as the dislocation-grain boundary
XIAOWEN FU, RUN XU, CHAO YUAN, ZHANQIU TAN, GENLIAN FAN, DING-BANG XIONG, QIANG GUO, ZHIQIANG LI, and DI ZHANG are with the State Key Laboratory of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China. Contact e-mails: [email protected], [email protected] GANG JI is with the Unite´ Mate´riaux et Transformations (UMET) CNRS UMR 8207, Universite´ de Lille, 59655 Villeneuve d’Ascq, France. Manuscript submitted December 2, 2018. Article published online May 21, 2019 3544—VOLUME 50A, AUGUST 2019
interaction,[6] grain boundary diffusion creep (Coble creep),[7] and grain boundary sliding.[3] In fact, all these deformation mechanisms are affected by the type, constituent, and structure of grain boundaries, which can be tailored to control dislocation activities and mechanical properties of the UFG and NC metals. Introducing heterogeneous phase(s) (‘‘nanofillers’’) into grain boundary regions to produce metal matrix composites is one of the effective methods to tailor the grain boundary structure. The mismatches of crystal type, lattice parameters, and chemical energy between nanofiller and matrix tend to distribute the nanofillers at the grain boundaries.[8] Therefore, unless some special preparation methods are employed,[9,10] the nanofillers are usually mainly distributed at the grain boundaries in the composites with UFG metal matrix.[10] For example, Kim et al.[11] obtained ultra-high strength in graphenemetal (Cu or Ni) nanolayered composites by introducing monolayer graphene into the grain boundaries to block dislocation propagation across the metal-graphene interface. Zhou et al.[12] observed a strong strain rate dependence of tensile ductility in the 5 vol pct Al2O3/Cu nanocomposite due to the transition of dominant deformation mechanism from lattice dislocation slip to co-operative grain boundary sliding during the nearly perfect deformation stage. Our group previously studied the influence of graphene on the deformation of UFG Cu by stress relaxation experiments. The critical
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resolved shear stress required for dislocation cross-slip and/or nucleation at/near grain boundaries in the graphene/Cu composite was found to be much higher than that of the UFG Cu matrix. This i
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