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Atomistic simulation of tensile deformation behavior of ∑5 tilt grain boundaries in copper bicrystal.

Zhang L, Lu C, Tieu K - Sci Rep (2014)

Bottom Line: The results show that the ∑5 asymmetric GBs with different inclination angles (φ) are composed of only two structural units corresponding to the two ∑5 symmetric GBs.Tensile deformation is applied under both 'free' and 'constrained' boundary conditions.Simulation results revealed different mechanical properties of the symmetric and asymmetric GBs and indicated that stress state can play an important role in the deformation mechanisms of nanocrystalline materials.

View Article: PubMed Central - PubMed

Affiliation: School of Mechanical, Materials and Mechatronic Engineering, University of Wollongong, Wollongong, NSW 2522, Australia.

ABSTRACT
Experiments on polycrystalline metallic samples have indicated that Grain boundary (GB) structure can affect many material properties related to fracture and plasticity. In this study, atomistic simulations are employed to investigate the structures and mechanical behavior of both symmetric and asymmetric ∑5[0 0 1] tilt GBs of copper bicrystal. First, the equilibrium GB structures are generated by molecular statics simulation at 0K. The results show that the ∑5 asymmetric GBs with different inclination angles (φ) are composed of only two structural units corresponding to the two ∑5 symmetric GBs. Molecular dynamics simulations are then conducted to investigate the mechanical response and the underlying deformation mechanisms of bicrystal models with different ∑5 GBs under tension. Tensile deformation is applied under both 'free' and 'constrained' boundary conditions. Simulation results revealed different mechanical properties of the symmetric and asymmetric GBs and indicated that stress state can play an important role in the deformation mechanisms of nanocrystalline materials.

No MeSH data available.


Related in: MedlinePlus

Snapshots of Cu bicrystal with ∑5 (φ = 0°) GB at different deformation stage under free tension boundary condition.Images are colored according to the CNA parameter. Atoms with perfect fcc structures are removed to facilitate viewing of the defective structures. Atoms colored with yellow organize the GB plane and the dislocation core, while the blue atoms represent the stacking fault.
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f4: Snapshots of Cu bicrystal with ∑5 (φ = 0°) GB at different deformation stage under free tension boundary condition.Images are colored according to the CNA parameter. Atoms with perfect fcc structures are removed to facilitate viewing of the defective structures. Atoms colored with yellow organize the GB plane and the dislocation core, while the blue atoms represent the stacking fault.

Mentions: Visual inspection of the MD simulation results indicates that the maximum tensile stress corresponds to the nucleation of partial dislocations, in agreement with results for uniaxial tensile of Cu bicrystal by Spearot et al.2736. Fig. 4 shows the snapshot of atoms in Cu bicrystal with ∑5 (φ = 0°) GB at different deformation stages under free tension boundary condition. Images are colored according to the CNA parameter. Atoms with perfect fcc structures are removed to facilitate viewing of the defective structures. Atoms colored with yellow organize the GB plane and the dislocation core, while the blue atoms represent the stacking fault. The dislocation extraction algorithm (DXA)3738 is used to compute their Burgers vectors. The GB region becomes coarsening when the tensile deformation is increasing until the maximum tensile stress has been reached. In Fig. 4 (b), at the beginning of the stress drop (ε = 8.9%), the image shows that partial dislocation loops with both edge and screw character are nucleated from the bicrystal interface into the upper grain and the lower grain simultaneously. DXA analysis indicates that Shockley partial dislocation with Burger's vectors b = (1/6)[1 1 2] and b = (1/6)[1 1 −2] nucleated from the bicrystal interface and slip on the (1 1 1) and (1 1 −1) plane. According to the Schmid factor analysis, they are the most favorable slip system. The tensile stress required to nucleate the first partial dislocation from the ∑5 (φ = 0°) GB at 10 K is calculated as 6.28 GPa, which corresponds to a critical resolved shear stress of approximately 3.08 GPa for the given lattice orientation. The result is comparable to the maximum resolved shear stress under the uniaxial tensile deformation of bicrystal Cu at 300 K by Spearot39. With the increase in the tensile strain, dislocations nucleate continuously from the GB plane and slip in each grain, as seen in Fig. 4 (c).


Atomistic simulation of tensile deformation behavior of ∑5 tilt grain boundaries in copper bicrystal.

Zhang L, Lu C, Tieu K - Sci Rep (2014)

Snapshots of Cu bicrystal with ∑5 (φ = 0°) GB at different deformation stage under free tension boundary condition.Images are colored according to the CNA parameter. Atoms with perfect fcc structures are removed to facilitate viewing of the defective structures. Atoms colored with yellow organize the GB plane and the dislocation core, while the blue atoms represent the stacking fault.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4118255&req=5

f4: Snapshots of Cu bicrystal with ∑5 (φ = 0°) GB at different deformation stage under free tension boundary condition.Images are colored according to the CNA parameter. Atoms with perfect fcc structures are removed to facilitate viewing of the defective structures. Atoms colored with yellow organize the GB plane and the dislocation core, while the blue atoms represent the stacking fault.
Mentions: Visual inspection of the MD simulation results indicates that the maximum tensile stress corresponds to the nucleation of partial dislocations, in agreement with results for uniaxial tensile of Cu bicrystal by Spearot et al.2736. Fig. 4 shows the snapshot of atoms in Cu bicrystal with ∑5 (φ = 0°) GB at different deformation stages under free tension boundary condition. Images are colored according to the CNA parameter. Atoms with perfect fcc structures are removed to facilitate viewing of the defective structures. Atoms colored with yellow organize the GB plane and the dislocation core, while the blue atoms represent the stacking fault. The dislocation extraction algorithm (DXA)3738 is used to compute their Burgers vectors. The GB region becomes coarsening when the tensile deformation is increasing until the maximum tensile stress has been reached. In Fig. 4 (b), at the beginning of the stress drop (ε = 8.9%), the image shows that partial dislocation loops with both edge and screw character are nucleated from the bicrystal interface into the upper grain and the lower grain simultaneously. DXA analysis indicates that Shockley partial dislocation with Burger's vectors b = (1/6)[1 1 2] and b = (1/6)[1 1 −2] nucleated from the bicrystal interface and slip on the (1 1 1) and (1 1 −1) plane. According to the Schmid factor analysis, they are the most favorable slip system. The tensile stress required to nucleate the first partial dislocation from the ∑5 (φ = 0°) GB at 10 K is calculated as 6.28 GPa, which corresponds to a critical resolved shear stress of approximately 3.08 GPa for the given lattice orientation. The result is comparable to the maximum resolved shear stress under the uniaxial tensile deformation of bicrystal Cu at 300 K by Spearot39. With the increase in the tensile strain, dislocations nucleate continuously from the GB plane and slip in each grain, as seen in Fig. 4 (c).

Bottom Line: The results show that the ∑5 asymmetric GBs with different inclination angles (φ) are composed of only two structural units corresponding to the two ∑5 symmetric GBs.Tensile deformation is applied under both 'free' and 'constrained' boundary conditions.Simulation results revealed different mechanical properties of the symmetric and asymmetric GBs and indicated that stress state can play an important role in the deformation mechanisms of nanocrystalline materials.

View Article: PubMed Central - PubMed

Affiliation: School of Mechanical, Materials and Mechatronic Engineering, University of Wollongong, Wollongong, NSW 2522, Australia.

ABSTRACT
Experiments on polycrystalline metallic samples have indicated that Grain boundary (GB) structure can affect many material properties related to fracture and plasticity. In this study, atomistic simulations are employed to investigate the structures and mechanical behavior of both symmetric and asymmetric ∑5[0 0 1] tilt GBs of copper bicrystal. First, the equilibrium GB structures are generated by molecular statics simulation at 0K. The results show that the ∑5 asymmetric GBs with different inclination angles (φ) are composed of only two structural units corresponding to the two ∑5 symmetric GBs. Molecular dynamics simulations are then conducted to investigate the mechanical response and the underlying deformation mechanisms of bicrystal models with different ∑5 GBs under tension. Tensile deformation is applied under both 'free' and 'constrained' boundary conditions. Simulation results revealed different mechanical properties of the symmetric and asymmetric GBs and indicated that stress state can play an important role in the deformation mechanisms of nanocrystalline materials.

No MeSH data available.


Related in: MedlinePlus