Crack tip dislocations revealed by electron tomography in silicon single crystal

Tanaka, Masaki; Higashida, Kenji; Kaneko, Kenji; Hata, Satoshi; Mitsuhara, Masatoshi

doi:10.1016/j.scriptamat.2008.06.042

Cited by 83 publications

(46 citation statements)

References 16 publications

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“…After the tilt-series dataset acquisition, a 3D representation of the object is reconstructed and visualized using an algorithm such as the back-projection method. Recent advancements in ET technique enable a variety of 3D observations, such as 3D atomic arrangements and nanoparticle morphology, [1][2][3] morphology and spatial distribution of precipitates, [4][5][6] and dislocations [7][8][9][10] in crystalline materials.…”

Section: An Experimental Protocol Development Of Three-dimensional Trmentioning

confidence: 99%

An Experimental Protocol Development of Three-Dimensional Transmission Electron Microscopy Methods for Ferrous Alloys: Towards Quantitative Microstructural Characterization in Three Dimensions

et al. 2015

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The majority of engineering steels are ferromagnetic and structurally inhomogeneous on scales ranging from nanometers to micrometers, and their physical properties depend on the three-dimensional (3D) features in their microstructures. Thus, obtaining a 3D image with a large field of view is desirable for transmission electron microscopy (TEM) based microstructure characterization in order to establish the relationship between the microstructure and the physical properties with a reasonable statistical relevancy. Here, we use a conventional sample preparation process, i.e., mechanical polishing followed by electropolishing, and optimizing experimental protocols for electron tomography (ET) of ferromagnetic materials, to carry out microstructural characterization of engineering steel. We determined that the sample thickness after the mechanical polishing step is a critical experimental parameter affecting the success rate of tilt-series image acquisitions. For example, for ferritic heat-resistant 9Cr steel, mechanical thinning down to 30 μm or less was necessary to acquire an adequate tilt-series image of the carbide precipitates in the annular dark-field scanning TEM (ADF-STEM) mode. However, acquiring tilt-series images of dislocation structures remains a challenge due to an unavoidable, significant electron beam deflection during specimen tilt, even with a thinned sample. To overcome the electron beam deflection problem, we evaluated several relatively accessible approaches including the "Low-Mag STEM and Lorentz TEM" modes. Although rarely used for ET, both modes reduce or even zero the objective lens current, likely weakening the magnetic interference between the ferromagnetic specimen and the objective lens magnetic field. The advantages and disadvantages of these experimental components are discussed.

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Section: An Experimental Protocol Development Of Three-dimensional Trmentioning

confidence: 99%

An Experimental Protocol Development of Three-Dimensional Transmission Electron Microscopy Methods for Ferrous Alloys: Towards Quantitative Microstructural Characterization in Three Dimensions

et al. 2015

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“…[1][2][3] (2) Advances in developmental approaches using computational mechanics with respect to dislocation behaviours near a crack tip, 4,5) and microstructural analysis using transmission electron microscopy. [6][7][8][9] From the experimental point of view, the study on the brittle-to-ductile transition in Si single crystals by St John in 1975 10) and the suggestion of a dislocation free zone at the crack tip by Ohr in the 1980s 6) can be considered as the triggers for physical studies in this direction. Consequently, the field of the study on physical toughness was established after Thomson published 'Physics of Fracture' in 1986.…”

Section: Introductionmentioning

confidence: 99%

Mechanism behind Brittle-to-ductile Transition Understood by the Interaction between a Crack and Dislocations

Higashida

Tanaka

2012

ISIJ Int.

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Fundamental mechanism governing the fracture toughness of materials is reviewed in terms of a concept of the interaction between a crack and dislocations. The mechanism behind brittle-to-ductile transition (BDT) is demonstrated using a simple model based on dislocation dynamics and the theory of cracktip shielding by dislocations. The effects of dislocation mobility as well as dislocation sources on the BDT behavior are discussed, which enables us to understand the various factors such as grain refinement influencing fracture toughness.

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“…Recently, the diffraction contrast is rather used positively to obtain the three-dimensional structure of lattice defects, such as dislocations. [10][11][12][13][14] The three-dimensional structure of dislocations can be given by maintaining the diffraction constant during the acquisition of the tilting series. In the present study, crack tip dislocations in a silicon single crystal was observed by combining highvoltage electron microscopy [15][16][17] (HVEM) and electron tomography.…”

Section: Introductionmentioning

confidence: 99%

The Early Stage of Dislocation Process around a Crack Tip Observed by HVEM-Tomography in Silicon Single Crystals

et al. 2011

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Crack tip dislocations in silicon single crystals were observed by combining high-voltage electron microscopy and electron tomography. Cracks were introduced by an indentation method and dislocations were introduced around the crack tip by keeping the indented sample at high temperatures for several hours. The number of dislocations emitted from the crack tip was controlled by changing the holding time of the indented specimen at high temperatures. The dislocations observed were characterized in detail. It was found that primary emitted dislocations all had the same Burgers vectors and that some dislocation segments cross-slipped around the crack. The local stress intensity factor due to dislocations was calculated, basing on the dislocation character obtained in this study, indicating that emitted dislocations shields mode I, II and III stress intensity at the crack tip. After the emission of the number of those dislocations, dislocations with another Burgers vector were emitted around the crack. It was found that those dislocations accommodate mode II and III stress components which are the excess shielding fields due to the dislocations primary emitted from the crack tip.

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Crack tip dislocations revealed by electron tomography in silicon single crystal

Cited by 83 publications

References 16 publications

An Experimental Protocol Development of Three-Dimensional Transmission Electron Microscopy Methods for Ferrous Alloys: Towards Quantitative Microstructural Characterization in Three Dimensions

An Experimental Protocol Development of Three-Dimensional Transmission Electron Microscopy Methods for Ferrous Alloys: Towards Quantitative Microstructural Characterization in Three Dimensions

Mechanism behind Brittle-to-ductile Transition Understood by the Interaction between a Crack and Dislocations

The Early Stage of Dislocation Process around a Crack Tip Observed by HVEM-Tomography in Silicon Single Crystals

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