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Grain rotation mediated by grain boundary dislocations in nanocrystalline platinum.

Wang L, Teng J, Liu P, Hirata A, Ma E, Zhang Z, Chen M, Han X - Nat Commun (2014)

Bottom Line: Grain rotation is a well-known phenomenon during high (homologous) temperature deformation and recrystallization of polycrystalline materials.In recent years, grain rotation has also been proposed as a plasticity mechanism at low temperatures (for example, room temperature for metals), especially for nanocrystalline grains with diameter d less than ~15 nm.Our atomic-scale images demonstrate directly that the evolution of the misorientation angle between neighbouring grains can be quantitatively accounted for by the change of the Frank-Bilby dislocation content in the grain boundary.

View Article: PubMed Central - PubMed

Affiliation: 1] Institute of Microstructure and Property of Advanced Materials, Beijing University of Technology, Beijing 100124, China [2].

ABSTRACT
Grain rotation is a well-known phenomenon during high (homologous) temperature deformation and recrystallization of polycrystalline materials. In recent years, grain rotation has also been proposed as a plasticity mechanism at low temperatures (for example, room temperature for metals), especially for nanocrystalline grains with diameter d less than ~15 nm. Here, in tensile-loaded Pt thin films under a high-resolution transmission electron microscope, we show that the plasticity mechanism transitions from cross-grain dislocation glide in larger grains (d>6 nm) to a mode of coordinated rotation of multiple grains for grains with d<6 nm. The mechanism underlying the grain rotation is dislocation climb at the grain boundary, rather than grain boundary sliding or diffusional creep. Our atomic-scale images demonstrate directly that the evolution of the misorientation angle between neighbouring grains can be quantitatively accounted for by the change of the Frank-Bilby dislocation content in the grain boundary.

No MeSH data available.


Related in: MedlinePlus

HRTEM images taken at different points of time showing the GB dislocation-mediated grain rotation.(a) Two GB dislocations (as marked with ‘T’) at GB1–3. (b–d) During straining, the number of the dislocations increased, leading to the GB angle at G1–2 increasing from 8.3° to 13.5°. Scale bars, 2 nm.
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f2: HRTEM images taken at different points of time showing the GB dislocation-mediated grain rotation.(a) Two GB dislocations (as marked with ‘T’) at GB1–3. (b–d) During straining, the number of the dislocations increased, leading to the GB angle at G1–2 increasing from 8.3° to 13.5°. Scale bars, 2 nm.

Mentions: Figure 2 is a series of HRTEM images, showing the GB dislocation-mediated grain rotation process observed at the atomic scale. For convenience, we define the in-plane motion about the axis parallel to the electron beam as ‘rotation’ and the out-of-plane rotation around an axis in the film plane as ‘tilt’. We define Gi–j as the GB between grains Gi and Gj. As shown in Fig. 2a, both G1 and G2 exhibit a clear [110] (axis) lattice and the GB angles are 8.3° and 6.4° for G1–2 and G1–3, respectively. In the figure, the double-ended arrow indicates the loading axis, relative to the grains G1, G2 and G3. As revealed in Fig. 2b–d, during the straining, the number of the dislocations at G1–2 increases and the average spacing of the GB dislocations decreases from 3.1 to 1.2 nm. This increased number of GB dislocations leads to the increased misorientation angle of G1–2, from 8.3° to 13.5°, as well as that of G1–3, from 6.4° to 10.6°. No dislocations were observed inside the small grains throughout the deformation process. During the straining, G1 and G2 exhibit no obvious lattice fringe change, indicating that the grain rotation is not caused by a global tilt of specimen during deformation.


Grain rotation mediated by grain boundary dislocations in nanocrystalline platinum.

Wang L, Teng J, Liu P, Hirata A, Ma E, Zhang Z, Chen M, Han X - Nat Commun (2014)

HRTEM images taken at different points of time showing the GB dislocation-mediated grain rotation.(a) Two GB dislocations (as marked with ‘T’) at GB1–3. (b–d) During straining, the number of the dislocations increased, leading to the GB angle at G1–2 increasing from 8.3° to 13.5°. Scale bars, 2 nm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4109021&req=5

f2: HRTEM images taken at different points of time showing the GB dislocation-mediated grain rotation.(a) Two GB dislocations (as marked with ‘T’) at GB1–3. (b–d) During straining, the number of the dislocations increased, leading to the GB angle at G1–2 increasing from 8.3° to 13.5°. Scale bars, 2 nm.
Mentions: Figure 2 is a series of HRTEM images, showing the GB dislocation-mediated grain rotation process observed at the atomic scale. For convenience, we define the in-plane motion about the axis parallel to the electron beam as ‘rotation’ and the out-of-plane rotation around an axis in the film plane as ‘tilt’. We define Gi–j as the GB between grains Gi and Gj. As shown in Fig. 2a, both G1 and G2 exhibit a clear [110] (axis) lattice and the GB angles are 8.3° and 6.4° for G1–2 and G1–3, respectively. In the figure, the double-ended arrow indicates the loading axis, relative to the grains G1, G2 and G3. As revealed in Fig. 2b–d, during the straining, the number of the dislocations at G1–2 increases and the average spacing of the GB dislocations decreases from 3.1 to 1.2 nm. This increased number of GB dislocations leads to the increased misorientation angle of G1–2, from 8.3° to 13.5°, as well as that of G1–3, from 6.4° to 10.6°. No dislocations were observed inside the small grains throughout the deformation process. During the straining, G1 and G2 exhibit no obvious lattice fringe change, indicating that the grain rotation is not caused by a global tilt of specimen during deformation.

Bottom Line: Grain rotation is a well-known phenomenon during high (homologous) temperature deformation and recrystallization of polycrystalline materials.In recent years, grain rotation has also been proposed as a plasticity mechanism at low temperatures (for example, room temperature for metals), especially for nanocrystalline grains with diameter d less than ~15 nm.Our atomic-scale images demonstrate directly that the evolution of the misorientation angle between neighbouring grains can be quantitatively accounted for by the change of the Frank-Bilby dislocation content in the grain boundary.

View Article: PubMed Central - PubMed

Affiliation: 1] Institute of Microstructure and Property of Advanced Materials, Beijing University of Technology, Beijing 100124, China [2].

ABSTRACT
Grain rotation is a well-known phenomenon during high (homologous) temperature deformation and recrystallization of polycrystalline materials. In recent years, grain rotation has also been proposed as a plasticity mechanism at low temperatures (for example, room temperature for metals), especially for nanocrystalline grains with diameter d less than ~15 nm. Here, in tensile-loaded Pt thin films under a high-resolution transmission electron microscope, we show that the plasticity mechanism transitions from cross-grain dislocation glide in larger grains (d>6 nm) to a mode of coordinated rotation of multiple grains for grains with d<6 nm. The mechanism underlying the grain rotation is dislocation climb at the grain boundary, rather than grain boundary sliding or diffusional creep. Our atomic-scale images demonstrate directly that the evolution of the misorientation angle between neighbouring grains can be quantitatively accounted for by the change of the Frank-Bilby dislocation content in the grain boundary.

No MeSH data available.


Related in: MedlinePlus