Mechanical strength in hierarchically polycrystalline graphene with dislocation arrays-embedded grains

ZD Han and Q Shi and H Gong and ZS Zhang and JY Wu, MATERIALS RESEARCH EXPRESS, 5, 115019 (2018).

DOI: 10.1088/2053-1591/aadde0

Nanotwinning lamellae within crystalline grains strengthens 3D polycrystalline solids due to inactive dislocation-slips by nanotwinning. 2D graphene with twin grain boundaries formed by pentagon- heptagon dislocation lines (PHDLs) exhibits high strength comparable to pristine lattice. However, the role of PHDLs embedded within 2D polycrystalline grains on the mechanical properties of graphene remains unknown yet. Here, hierarchically polycrystalline graphene comprising of a variety of PHDLs-embedded grains are constructed and their tensile properties are explored by atomistic simulations. Relaxed hierarchical polycrystals composed of PHDLs-contained grains are hierarchically wrinkled, with unique surface wrinkles of grains nested within irregularly global wrinkles, in contrast to the conventional counterparts. Tensile strengths of PHDLs-contained polycrystals are type of PHDLs dependent; those with robust PHDLs are as strong as the intragain PHDLs-free counterpart. All hierarchical polycrystals demonstrate inverse pseudo Hall-Petch-like strength relations to grain size, analogous to the counterpart yet in contrast to nanotwinned polycrystals. However, depending on the type of PHDLs, either monotonous or 'flipped' variation in the breaking strains with grain size is observed. Four distinct cracking behaviors are identified relying on the robustness of PHDLs. Particularly, tension-induced broken bonds shared by hexagon-heptagon near the PHDLs are recoverable. These findings shed new light in the optimal performance of 2D materials through dislocation engineering for practical applications in flexible systems.

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