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Bi-crystallographic lattice structure directs grain boundary motion under shear stress.

Wan L, Han W, Chen K - Sci Rep (2015)

Bottom Line: Shear stress driven grain boundary (GB) migration was found to be a ubiquitous phenomenon in small grained polycrystalline materials.Here we show that the GB displacement shift complete (DSC) dislocation mechanism for GB shear coupled migration is still functioning even if the geometry orientation of the GBs deviates a few degrees from the appropriate coincidence site lattice (CSL) GBs.We conclude that the CSL-DSC bi-crystallographic lattice structure in GB is the main reason that GB can migrate under shear stress.

View Article: PubMed Central - PubMed

Affiliation: Center for Advancing Materials Performance from the Nanoscale, State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an 710049, China.

ABSTRACT
Shear stress driven grain boundary (GB) migration was found to be a ubiquitous phenomenon in small grained polycrystalline materials. Here we show that the GB displacement shift complete (DSC) dislocation mechanism for GB shear coupled migration is still functioning even if the geometry orientation of the GBs deviates a few degrees from the appropriate coincidence site lattice (CSL) GBs. It means that any large angle GB can have a considerable chance to be such a "CSL-related GB" for which the shear coupled GB migration motion can happen by the GB DSC dislocation mechanism. We conclude that the CSL-DSC bi-crystallographic lattice structure in GB is the main reason that GB can migrate under shear stress.

No MeSH data available.


Related in: MedlinePlus

Snapshots of the final atomic configurations for shear of the bicrystals with the vicinal GBs.(a) Shear of the vicinal GB “Σ11-113A” along the Y-axis of the simulation cell. (b) Shear of the vicinal GB “Σ11-113B” along the X-axis of the simulation cell. (c) Shear of the vicinal GB “Σ9-221A” along the X-axis of the simulation cell. (d) Shear of the vicinal GB “AS-1-15/111A” along the X-axis of the simulation cell. Only the atoms which do not have the face centered cubic structural order (i.e., all the defects such as surfaces, GBs, point defects, etc.) are displayed. The shear directions are indicated by the red dotted arrows. The initial positions of the GBs are marked by the dashed frames.
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f2: Snapshots of the final atomic configurations for shear of the bicrystals with the vicinal GBs.(a) Shear of the vicinal GB “Σ11-113A” along the Y-axis of the simulation cell. (b) Shear of the vicinal GB “Σ11-113B” along the X-axis of the simulation cell. (c) Shear of the vicinal GB “Σ9-221A” along the X-axis of the simulation cell. (d) Shear of the vicinal GB “AS-1-15/111A” along the X-axis of the simulation cell. Only the atoms which do not have the face centered cubic structural order (i.e., all the defects such as surfaces, GBs, point defects, etc.) are displayed. The shear directions are indicated by the red dotted arrows. The initial positions of the GBs are marked by the dashed frames.

Mentions: As can be seen in the Fig. 2, these vicinal GBs can migrate upward or downward by shear of them along appropriate directions parallel to the GB plane (see also the Supplementary Table S1 and the Supplementary Movies). The stress-strain response for those shear simulations with shear directions aligned with the X- or Y- axes of the simulation cell has also been calculated, and the curves are given in the Supplementary Figure S2. For the study of the migration mechanisms, the structures of these vicinal GBs need to be analyzed first. Figure 3 gives some typical examples of the structure of the vicinal GBs studied. It shows that the structure of the vicinal GBs generally consists of areas of “good fit” intervened by GB secondary dislocations (marked by the red arrows and oval/rectangular frames in Fig. 3) distributed within the GB plane. Here, the area of “good fit” means that the arrangement of atoms in this area is almost the same as that of the reference CSL GBs. Take the vicinal GB “Σ11-113A” for example. As shown in Fig. 3a, the lower grain of this GB has been rotated around the [] by 4° as compared with that of the Σ11 [] (1 1 3) symmetric tilt GB. The red arrows in Fig. 3a,b shows that a number of GB secondary dislocations aligned parallel to [] have been introduced to accommodate the deviations in misorientation and inclination. A step structure can also be formed by the GB secondary dislocations of this GB. On the other hand, the other areas in the GB plane have an atomistic structure the same as that of the Σ11 [] (1 1 3) symmetric tilt GB.


Bi-crystallographic lattice structure directs grain boundary motion under shear stress.

Wan L, Han W, Chen K - Sci Rep (2015)

Snapshots of the final atomic configurations for shear of the bicrystals with the vicinal GBs.(a) Shear of the vicinal GB “Σ11-113A” along the Y-axis of the simulation cell. (b) Shear of the vicinal GB “Σ11-113B” along the X-axis of the simulation cell. (c) Shear of the vicinal GB “Σ9-221A” along the X-axis of the simulation cell. (d) Shear of the vicinal GB “AS-1-15/111A” along the X-axis of the simulation cell. Only the atoms which do not have the face centered cubic structural order (i.e., all the defects such as surfaces, GBs, point defects, etc.) are displayed. The shear directions are indicated by the red dotted arrows. The initial positions of the GBs are marked by the dashed frames.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4548247&req=5

f2: Snapshots of the final atomic configurations for shear of the bicrystals with the vicinal GBs.(a) Shear of the vicinal GB “Σ11-113A” along the Y-axis of the simulation cell. (b) Shear of the vicinal GB “Σ11-113B” along the X-axis of the simulation cell. (c) Shear of the vicinal GB “Σ9-221A” along the X-axis of the simulation cell. (d) Shear of the vicinal GB “AS-1-15/111A” along the X-axis of the simulation cell. Only the atoms which do not have the face centered cubic structural order (i.e., all the defects such as surfaces, GBs, point defects, etc.) are displayed. The shear directions are indicated by the red dotted arrows. The initial positions of the GBs are marked by the dashed frames.
Mentions: As can be seen in the Fig. 2, these vicinal GBs can migrate upward or downward by shear of them along appropriate directions parallel to the GB plane (see also the Supplementary Table S1 and the Supplementary Movies). The stress-strain response for those shear simulations with shear directions aligned with the X- or Y- axes of the simulation cell has also been calculated, and the curves are given in the Supplementary Figure S2. For the study of the migration mechanisms, the structures of these vicinal GBs need to be analyzed first. Figure 3 gives some typical examples of the structure of the vicinal GBs studied. It shows that the structure of the vicinal GBs generally consists of areas of “good fit” intervened by GB secondary dislocations (marked by the red arrows and oval/rectangular frames in Fig. 3) distributed within the GB plane. Here, the area of “good fit” means that the arrangement of atoms in this area is almost the same as that of the reference CSL GBs. Take the vicinal GB “Σ11-113A” for example. As shown in Fig. 3a, the lower grain of this GB has been rotated around the [] by 4° as compared with that of the Σ11 [] (1 1 3) symmetric tilt GB. The red arrows in Fig. 3a,b shows that a number of GB secondary dislocations aligned parallel to [] have been introduced to accommodate the deviations in misorientation and inclination. A step structure can also be formed by the GB secondary dislocations of this GB. On the other hand, the other areas in the GB plane have an atomistic structure the same as that of the Σ11 [] (1 1 3) symmetric tilt GB.

Bottom Line: Shear stress driven grain boundary (GB) migration was found to be a ubiquitous phenomenon in small grained polycrystalline materials.Here we show that the GB displacement shift complete (DSC) dislocation mechanism for GB shear coupled migration is still functioning even if the geometry orientation of the GBs deviates a few degrees from the appropriate coincidence site lattice (CSL) GBs.We conclude that the CSL-DSC bi-crystallographic lattice structure in GB is the main reason that GB can migrate under shear stress.

View Article: PubMed Central - PubMed

Affiliation: Center for Advancing Materials Performance from the Nanoscale, State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an 710049, China.

ABSTRACT
Shear stress driven grain boundary (GB) migration was found to be a ubiquitous phenomenon in small grained polycrystalline materials. Here we show that the GB displacement shift complete (DSC) dislocation mechanism for GB shear coupled migration is still functioning even if the geometry orientation of the GBs deviates a few degrees from the appropriate coincidence site lattice (CSL) GBs. It means that any large angle GB can have a considerable chance to be such a "CSL-related GB" for which the shear coupled GB migration motion can happen by the GB DSC dislocation mechanism. We conclude that the CSL-DSC bi-crystallographic lattice structure in GB is the main reason that GB can migrate under shear stress.

No MeSH data available.


Related in: MedlinePlus