5 years ago

Ultralarge Bending Strain and Fracture-Resistance Investigation of Tungsten Carbide Nanowires

Ultralarge Bending Strain and Fracture-Resistance Investigation of Tungsten Carbide Nanowires
Hao Cui, Yanmao Chen, Chengxin Wang, Jing Wang, Yong Sun
Hard tungsten carbide (WC) with brittle behavior is frequently applied for mechanical purposes. Here, ultralarge elastic bending deformation is reported in defect-rare WC [0001] nanowires; the tested bending strain reaches a maximum of 20% ± 3.33%, which challenges the traditional understanding of this material. The lattice analysis indicates that the dislocations are confined to the inner part of the WC nanowires. First, the high Peierls–Nabarro barrier hinders the movement of the locally formed dislocations, which causes rapid dislocation aggregation and hinders long-range glide, resulting in a dense distribution of the dislocation network. In this case, the loading is dispersed along multiple points, which is then balanced by the complex internal mechanical field. In the compressive part, the possible dislocations predominantly emerge in the (0001) plane and mainly slip along the axial direction. The disordered shell first forms at the tensile side and prevents the generation of nanocracks at the surface. The novel lattice kinetics make WC nanowires capable of substantial bending strain resistance. Analytical results of the force–displacement (F–d) curves based on the double-clamped beam model exhibit an obvious nonlinear elastic characteristic, which originates fundamentally from the lattice anharmonicity under moderate stress. A tungsten carbid nanowire remains globally elastic at bending strain of ≈20% maximally. Nonlinear stress–strain relationship is exposed based on double-clamped beam experiments. Ex situ high-resolution transmission electron microscopy shows that tensile side of the nanowire has experienced complex lattice evolution, including distortion, grain boundary sliding, and also surface amorphization, some of which behave reversible.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/smll.201700389

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