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Dislocation-twin boundary interactions induced nanocrystalline via SPD processing in bulk metals.

Zhang F, Feng X, Yang Z, Kang J, Wang T - Sci Rep (2015)

Bottom Line: This report investigated dislocation-twin boundary (TB) interactions that cause the TB to disappear and turn into a high-angle grain boundary (GB).The evolution of the microstructural characteristics of Hadfield steel was shown as a function of severe plastic deformation processing time.These reactions induced atomic steps on the TB and led to the accumulation of gliding dislocations at the TB, which resulted in the transition from coherent TB to incoherent GB.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, China.

ABSTRACT
This report investigated dislocation-twin boundary (TB) interactions that cause the TB to disappear and turn into a high-angle grain boundary (GB). The evolution of the microstructural characteristics of Hadfield steel was shown as a function of severe plastic deformation processing time. Sessile Frank partial dislocations and/or sessile unit dislocations were formed on the TB through possible dislocation reactions. These reactions induced atomic steps on the TB and led to the accumulation of gliding dislocations at the TB, which resulted in the transition from coherent TB to incoherent GB. The factors that affect these interactions were described, and a physical model was established to explain in detail the feasible dislocation reactions at the TB.

No MeSH data available.


Related in: MedlinePlus

HRTEM images showing dislocations at the TB of the sample subjected to HSP for 4 × 104 times: (a) macroscopic view of twins; (b) a close view of Frank partial dislocation at the TB; (c) a close view of unit dislocation at TB and corresponding 1D Fourier-filtered image of the red-boxed selected area.Continuous lines indicate the location of the axis of symmetry of twins. Red circles show the location of steps in the TB associated with unit dislocation, whereas blue rectangular boxes indicate the location of Frank partial dislocation.
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f3: HRTEM images showing dislocations at the TB of the sample subjected to HSP for 4 × 104 times: (a) macroscopic view of twins; (b) a close view of Frank partial dislocation at the TB; (c) a close view of unit dislocation at TB and corresponding 1D Fourier-filtered image of the red-boxed selected area.Continuous lines indicate the location of the axis of symmetry of twins. Red circles show the location of steps in the TB associated with unit dislocation, whereas blue rectangular boxes indicate the location of Frank partial dislocation.

Mentions: Figures 1 and 2 reveal that the nanocrystallization process includes the disappearing of deformation twins, which is found to be the ubiquitous in the SPD process. The dislocation–TB interactions are the leading grain refinement mechanism in Hadfield steel. Considering that this finding answers the aforementioned first question, we attempted to find the answers to the other questions. A close observation of the dislocations at the TB is shown in Fig. 3. A narrow twin (≈20 nm) is clearly observed in Fig. 3(a). Detailed analysis of the image reveals the presence of numerous dislocations, which introduce steps at the TB. Fig. 3(b) shows the presence of Frank partial dislocation at the TB with a Burgers vector of . A unit dislocation is present at the TB with a Burgers vector of , thereby inducing a step with a height of one (111) atomic layer (Fig. 3c). Importantly, the glide plane of the unit dislocation is not parallel to any {111} glide plane in both the twin and the matrix. This result indicates that the unit dislocation is sessile. A 1D Fourier-filtered image of the selected area marked in Fig. 3(c) shows a disorientation angle of approximately 3° between the left and right parts of the step at the TB, which is marked in Fig. 3(c) by two white lines parallel to the (111) of the twin and the matrix. These sessile dislocations at the TB cause distortion at the core of the dislocations, thereby breaking the coherence of the atomic arrangement at the TB.


Dislocation-twin boundary interactions induced nanocrystalline via SPD processing in bulk metals.

Zhang F, Feng X, Yang Z, Kang J, Wang T - Sci Rep (2015)

HRTEM images showing dislocations at the TB of the sample subjected to HSP for 4 × 104 times: (a) macroscopic view of twins; (b) a close view of Frank partial dislocation at the TB; (c) a close view of unit dislocation at TB and corresponding 1D Fourier-filtered image of the red-boxed selected area.Continuous lines indicate the location of the axis of symmetry of twins. Red circles show the location of steps in the TB associated with unit dislocation, whereas blue rectangular boxes indicate the location of Frank partial dislocation.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4355667&req=5

f3: HRTEM images showing dislocations at the TB of the sample subjected to HSP for 4 × 104 times: (a) macroscopic view of twins; (b) a close view of Frank partial dislocation at the TB; (c) a close view of unit dislocation at TB and corresponding 1D Fourier-filtered image of the red-boxed selected area.Continuous lines indicate the location of the axis of symmetry of twins. Red circles show the location of steps in the TB associated with unit dislocation, whereas blue rectangular boxes indicate the location of Frank partial dislocation.
Mentions: Figures 1 and 2 reveal that the nanocrystallization process includes the disappearing of deformation twins, which is found to be the ubiquitous in the SPD process. The dislocation–TB interactions are the leading grain refinement mechanism in Hadfield steel. Considering that this finding answers the aforementioned first question, we attempted to find the answers to the other questions. A close observation of the dislocations at the TB is shown in Fig. 3. A narrow twin (≈20 nm) is clearly observed in Fig. 3(a). Detailed analysis of the image reveals the presence of numerous dislocations, which introduce steps at the TB. Fig. 3(b) shows the presence of Frank partial dislocation at the TB with a Burgers vector of . A unit dislocation is present at the TB with a Burgers vector of , thereby inducing a step with a height of one (111) atomic layer (Fig. 3c). Importantly, the glide plane of the unit dislocation is not parallel to any {111} glide plane in both the twin and the matrix. This result indicates that the unit dislocation is sessile. A 1D Fourier-filtered image of the selected area marked in Fig. 3(c) shows a disorientation angle of approximately 3° between the left and right parts of the step at the TB, which is marked in Fig. 3(c) by two white lines parallel to the (111) of the twin and the matrix. These sessile dislocations at the TB cause distortion at the core of the dislocations, thereby breaking the coherence of the atomic arrangement at the TB.

Bottom Line: This report investigated dislocation-twin boundary (TB) interactions that cause the TB to disappear and turn into a high-angle grain boundary (GB).The evolution of the microstructural characteristics of Hadfield steel was shown as a function of severe plastic deformation processing time.These reactions induced atomic steps on the TB and led to the accumulation of gliding dislocations at the TB, which resulted in the transition from coherent TB to incoherent GB.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, China.

ABSTRACT
This report investigated dislocation-twin boundary (TB) interactions that cause the TB to disappear and turn into a high-angle grain boundary (GB). The evolution of the microstructural characteristics of Hadfield steel was shown as a function of severe plastic deformation processing time. Sessile Frank partial dislocations and/or sessile unit dislocations were formed on the TB through possible dislocation reactions. These reactions induced atomic steps on the TB and led to the accumulation of gliding dislocations at the TB, which resulted in the transition from coherent TB to incoherent GB. The factors that affect these interactions were described, and a physical model was established to explain in detail the feasible dislocation reactions at the TB.

No MeSH data available.


Related in: MedlinePlus