The process of the formation of a carbon nanoscroll (CNS) from a planar monolayer graphene, initiated by a single-walled carbon nanotube (SWCNT), is investigated by using molecular dynamics simulations. The results show that once the radius of the SWCNT is above a critical value, the SWCNT can activate and guide the rolling of the graphene, and finally form a CNS with the SWCNT inside. During the process of forming the CNS, the van der Waals force plays an important role. The influences of nickel atoms on the formation and mechanical behavior of the CNS are also studied. The results show that there is no appreciable difference between the self scrolling of an ideal graphene (without nickel atoms) and that of a graphene with nickel atoms except for the different times required for the scrolling. The simulations also indicate that adding nickel atoms to two opposite edges (paralleling to the SWCNT axis) of the graphene before rolling is an effective strategy to increase the structural stability and critical buckling load of the CNS.

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Using molecular dynamics simulations, the plastic deformation behavior of nanocrytalline Ti has been investigated under tension and compression normal to the {0001}, { 1 ¯ 010 } , and { 1 ¯ 2 1 ¯ 0 } planes. The results indicate that the plastic deformation strongly depends on crystal orientation and loading directions. Under tension normal to basal plane, the deformation mechanism is mainly the grain reorientation and the subsequent deformation twinning. Under compression, the transformation of hexagonal-close packed (HCP)-Ti to face-centered cubic (FCC)-Ti dominates the deformation. When loading is normal to the prismatic planes (both { 1 ¯ 010 } and { 1 ¯ 2 1 ¯ 0 } ), the deformation mechanism is primarily the phase transformation among HCP, body-centered cubic (BCC), and FCC structures, regardless of loading mode. The orientation relations (OR) of {0001}HCP║{111}FCC and 〈 1 ¯ 210 〉 HCP | | 〈 110 〉 FCC , and { 10 1 ¯ 0 } HCP | | { 1 1 ¯ 0 } FCC and 〈 0001 〉 HCP | | 〈 010 〉 FCC between the HCP and FCC phases have been observed in the present work. For the transformation of HCP → BCC → HCP, the OR is 0001 α 1 | | { 110 } β | | { 10 1 ¯ 0 } α 2 (HCP phase before the critical strain is defined as α 1-Ti, BCC phase is defined as β-Ti, and the HCP phase after the critical strain is defined as α 2-Ti). Energy evolution during the various loading processes further shows the plastic anisotropy of nanocrystalline Ti is determined by the stacking order of the atoms. The results in the present work will promote the in-depth study of the plastic deformation mechanism of HCP materials.

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As a representative boundary, interphase-interface may affect the strength or ductility of multilayered composites dramatically. However, the effect of the interface with mismatch dislocations on the mechanical behavior of multilayered composites is still not clear. In the present work, we performed molecular dynamics simulations to investigate the effect of interface structures and layer spacing on the mechanical properties of the Ti/Al nanolaminate. The results indicate that there are two transitions of the plastic deformation mechanism in the Ti layer with the increase of layer spacing in the sample with a coherent interface. The plastic deformation mechanism evolves from one that is dominated by dislocation to the phase transformation from the hcp-Ti to the fcc-Ti mode, which transfers to the dislocation slip deformation again. For the samples with an incoherent interface, the plastic deformation is dominated by the transformation from hcp-Ti to fcc-Ti, regardless of the variation of layer spacing, while the plastic deformations in the Al layers are mainly dislocations confined in the layer slip in the samples with both coherent and incoherent interfaces. When the layer spacing is larger than 6.6 nm, an obvious second hardening is observed due to the superior dislocation storage ability of the Ti/Al laminate with the incoherent interface. Meanwhile, extraordinary ductility is obtained when optimal layer spacing is employed in the Ti/Al laminate. Moreover, the phase transformation mechanism of hcp-Ti to bcc-Ti has also been explicated in the present work. The general conclusions derived from this work may provide a guideline for the design of high-performance Ti/Al multilayer and alloy devices.

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