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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

TEM observations of the Pt nanocrystalline thin film.(a) Bright-field transmission electron microscope (TEM) image of the Pt film, with a selected area diffraction pattern in the inset. (b) High-resolution TEM (HRTEM) image showing grains separated by high-angle grain boundaries (GBs). (c) Cross-sectional TEM image of the thin film. (d) Statistical distribution of the grain size. (e) Home-made testing device used for in situ tensile pulling of the Pt thin film in a TEM. Scale bars, 10 nm.
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f1: TEM observations of the Pt nanocrystalline thin film.(a) Bright-field transmission electron microscope (TEM) image of the Pt film, with a selected area diffraction pattern in the inset. (b) High-resolution TEM (HRTEM) image showing grains separated by high-angle grain boundaries (GBs). (c) Cross-sectional TEM image of the thin film. (d) Statistical distribution of the grain size. (e) Home-made testing device used for in situ tensile pulling of the Pt thin film in a TEM. Scale bars, 10 nm.

Mentions: As shown in the bright-field TEM image of Fig. 1a, the Pt film has nanometre-sized and equi-axed grains, with no obvious texture (see the selected area diffraction patterns in the inset and Supplementary Fig. 1). The HRTEM image in Fig. 1b shows that most grains are separated by high-angle GBs, without visible porosity or micro-cracks. The cross-sectional TEM images indicate that the thin film is ~10 nm in thickness, and consists of one or two grains in the thickness direction (Fig. 1c). The distribution of grain sizes, as measured for ~180 grains, is shown in Fig. 1d. The grain diameters range from 2 to 12 nm and most of the grains have a diameter below 10 nm, with an average d of ~6 nm. Tensile experiments were carried out using our TEM tensile stage as shown in the schematic in Fig. 1e. This special stage allows slow and gentle deformation of the electron-transparent film, and at the same time retains the double-tilt capability such that the grains can be oriented appropriately to a low-index crystallographic zone orientation for high-resolution imaging (see refs 28, 29 for details). The tensile pulling was realized by heating the sample holder to ~80 °C, causing bending of the bimetallic strips due to thermal expansion. The real-time evolution of the film was captured in situ along with deformation, in a JEOL-2010 field-emission TEM operating at 200 kV.


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)

TEM observations of the Pt nanocrystalline thin film.(a) Bright-field transmission electron microscope (TEM) image of the Pt film, with a selected area diffraction pattern in the inset. (b) High-resolution TEM (HRTEM) image showing grains separated by high-angle grain boundaries (GBs). (c) Cross-sectional TEM image of the thin film. (d) Statistical distribution of the grain size. (e) Home-made testing device used for in situ tensile pulling of the Pt thin film in a TEM. Scale bars, 10 nm.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f1: TEM observations of the Pt nanocrystalline thin film.(a) Bright-field transmission electron microscope (TEM) image of the Pt film, with a selected area diffraction pattern in the inset. (b) High-resolution TEM (HRTEM) image showing grains separated by high-angle grain boundaries (GBs). (c) Cross-sectional TEM image of the thin film. (d) Statistical distribution of the grain size. (e) Home-made testing device used for in situ tensile pulling of the Pt thin film in a TEM. Scale bars, 10 nm.
Mentions: As shown in the bright-field TEM image of Fig. 1a, the Pt film has nanometre-sized and equi-axed grains, with no obvious texture (see the selected area diffraction patterns in the inset and Supplementary Fig. 1). The HRTEM image in Fig. 1b shows that most grains are separated by high-angle GBs, without visible porosity or micro-cracks. The cross-sectional TEM images indicate that the thin film is ~10 nm in thickness, and consists of one or two grains in the thickness direction (Fig. 1c). The distribution of grain sizes, as measured for ~180 grains, is shown in Fig. 1d. The grain diameters range from 2 to 12 nm and most of the grains have a diameter below 10 nm, with an average d of ~6 nm. Tensile experiments were carried out using our TEM tensile stage as shown in the schematic in Fig. 1e. This special stage allows slow and gentle deformation of the electron-transparent film, and at the same time retains the double-tilt capability such that the grains can be oriented appropriately to a low-index crystallographic zone orientation for high-resolution imaging (see refs 28, 29 for details). The tensile pulling was realized by heating the sample holder to ~80 °C, causing bending of the bimetallic strips due to thermal expansion. The real-time evolution of the film was captured in situ along with deformation, in a JEOL-2010 field-emission TEM operating at 200 kV.

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