scholarly journals Stacking fault aggregation during cooling composing FCC–HCP martensitic transformation revealed by in-situ electron channeling contrast imaging in an Fe-high Mn alloy

2021 ◽  
Author(s):  
Motomichi Koyama ◽  
Misaki Seo ◽  
Keiichiro Nakafuji ◽  
Kaneaki Tsuzaki
Keyword(s):  
Martensitic Transformation ◽  
Stacking Fault ◽  
Contrast Imaging ◽  
Electron Channeling

Microcrack Nucleation and Crack Propagation in Equiaxed γ TiAl

2002 ◽  
Vol 753 ◽  
Author(s):  
Martin A. Crimp ◽  
Boon-Chi Ng ◽  
Benjamin A. Simkin ◽  
Thomas R. Bieler
Keyword(s):  
Ex Situ ◽  
Contrast Imaging ◽  
Active Deformation ◽  
Electron Channeling ◽  
Microcrack Initiation ◽  
Grain Orientations ◽  
Contrast Analysis ◽  
Defect Imaging

ABSTRACTTo gain a better understanding of the ductility limitations in TiAl alloys, the mechanisms involved in deformation strain transfer and/or microcrack initiation at grain boundaries have been examined in an equiaxed near-γ alloy. These studies have been carried out on both in-situ and ex-situ deformed bulk samples using scanning electron microscopy (SEM) techniques for both orientation analysis and deformation defect imaging. Selected area electron channeling patterns (SACPs) have allowed determination of grain orientations, eliminating ambiguity between the a and c axes. Deformation twins and dislocations have been imaged in the bulk samples using electron channeling contrast imaging (ECCI). A combination of ECCI contrast analysis and trace analysis based on orientations determined from SACP has allowed identification of the active deformation systems. Microcracks have been found to initiate at γ-γ boundaries as a result of an inability to adequately transfer twin strain from grain to grain. Once initiated, cracks propagate through cleavage and re-nucleation of grain boundary microcracks in front of the advancing crack. A geometric based predictive factor has been developed that accounts for microcrack initiation at γ-γ boundaries based in deformation twinning and strain accommodation by ordinary dislocations.

scholarly journals Novel −75°C SEM cooling stage: application for martensitic transformation in steel

Microscopy ◽  
2020 ◽  
Author(s):  
Kaneaki Tsuzazki ◽  
Motomichi Koyama ◽  
Ryosuke Sasaki ◽  
Keiichiro Nakafuji ◽  
Kazushi Oie ◽  
...  
Keyword(s):  
Martensitic Transformation ◽  
Electron Backscatter Diffraction ◽  
Dislocation Slip ◽  
In Situ Observation ◽  
Contrast Imaging ◽  
Cooling Stage ◽  
Electron Channelling ◽  
Electron Backscatter ◽  
Backscatter Diffraction

Abstract Microstructural changes during the martensitic transformation from face-centred cubic (FCC) to body-centred cubic (BCC) in an Fe-31Ni alloy were observed by scanning electron microscopy (SEM) with a newly developed Peltier stage available at temperatures to  −75°C. Electron channelling contrast imaging (ECCI) was utilized for the in situ observation during cooling. Electron backscatter diffraction analysis at ambient temperature (20°C) after the transformation was performed for the crystallographic characterization. A uniform dislocation slip in the FCC matrix associated with the transformation was detected at −57°C. Gradual growth of a BCC martensite was recognized upon cooling from −57°C to −63°C.

scholarly journals Electron channeling contrast imaging investigation of stacking fault pyramids in GaP on Si nucleation layers

2020 ◽  
Vol 532 ◽  
pp. 125422
Author(s):  
Markus Feifel ◽  
Jens Ohlmann ◽  
Ryan M. France ◽  
David Lackner ◽  
Frank Dimroth
Keyword(s):  
Stacking Fault ◽  
Contrast Imaging ◽  
Electron Channeling

scholarly journals Modelling Electron Channeling Contrast Intensity of Stacking Fault and Twin Boundary Using Crystal Thickness Effect

Materials ◽  
2021 ◽  
Vol 14 (7) ◽  
pp. 1696
Author(s):  
Hana Kriaa ◽  
Antoine Guitton ◽  
Nabila Maloufi
Keyword(s):  
Twin Boundary ◽  
Theoretical Approach ◽  
Stacking Fault ◽  
Thickness Effect ◽  
Specimen Thickness ◽  
Crystal Thickness ◽  
Contrast Imaging ◽  
Electron Channeling ◽  
Electron Intensity ◽  
Backscattered Electron

In a scanning electron microscope, the backscattered electron intensity modulations are at the origin of the contrast of like-Kikuchi bands and crystalline defects. The Electron Channeling Contrast Imaging (ECCI) technique is suited for defects characterization at a mesoscale with transmission electron microscopy-like resolution. In order to achieve a better comprehension of ECCI contrasts of twin-boundary and stacking fault, an original theoretical approach based on the dynamical diffraction theory is used. The calculated backscattered electron intensity is explicitly expressed as function of physical and practical parameters controlling the ECCI experiment. Our model allows, first, the study of the specimen thickness effect on the channeling contrast on a perfect crystal, and thus its effect on the formation of like-Kikuchi bands. Then, our theoretical approach is extended to an imperfect crystal containing a planar defect such as twin-boundary and stacking fault, clarifying the intensity oscillations observed in ECC micrographs.

scholarly journals In Situ Macroscopic Tensile Testing in SEM and Electron Channeling Contrast Imaging: Pencil Glide Evidenced in a Bulk β-Ti21S Polycrystal

Materials ◽  
2019 ◽  
Vol 12 (15) ◽  
pp. 2479
Author(s):  
Meriem Ben Haj Slama ◽  
Nabila Maloufi ◽  
Julien Guyon ◽  
Slim Bahi ◽  
Laurent Weiss ◽  
...  
Keyword(s):  
Tensile Testing ◽  
Uniaxial Tensile ◽  
Uniaxial Tensile Test ◽  
Contrast Imaging ◽  
Bulk Specimen ◽  
Electron Channeling ◽  
Uniaxial Tensile Testing ◽  
Stress States ◽  
Tangled Dislocation

In this paper, we report the successful combination of macroscopic uniaxial tensile testing of bulk specimen combined with In situ dislocation-scale observations of the evolution of deformation microstructures during loading at several stress states. The dislocation-scale observations were performed by Accurate Electron Channeling Contrast Imaging in order to follow the defects evolution and their interactions with grain boundaries for several regions of interest during macroscopic loading. With this novel in situ procedure, the slip systems governing the deformation in polycrystalline bulk β-Ti21S are tracked during the macroscopic uniaxial tensile test. For instance, curved slip lines that are associated with “pencil glide” phenomenon and tangled dislocation networks are evidenced.

scholarly journals In-Situ Electron Channeling Contrast Imaging under Tensile Loading: Residual Stress, Dislocation Motion, and Slip Line Formation

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Keiichiro Nakafuji ◽  
Motomichi Koyama ◽  
Kaneaki Tsuzaki
Keyword(s):  
Residual Stress ◽  
Lattice Defect ◽  
Tensile Loading ◽  
Dislocation Motion ◽  
Contrast Imaging ◽  
Deformation Path ◽  
Deformation And Failure ◽  
Electron Channeling ◽  
Mechanical Field

AbstractElastoplastic phenomena, such as plastic deformation and failure, are multi-scale, deformation-path-dependent, and mechanical-field-sensitive problems associated with metals. Accordingly, visualization of the microstructural deformation path under a specific mechanical field is challenging for the elucidation of elastoplastic phenomena mechanisms. To overcome this problem, a dislocation-resolved in-situ technique for deformation under mechanically controllable conditions is required. Thus, we attempted to apply electron channeling contrast imaging (ECCI) under tensile loading, which enabled the detection of lattice defect motions and the evolution of elastic strain fields in bulk specimens. Here, we presented the suitability of ECCI as an in-situ technique with dislocation-detectable spatial resolution. In particular, the following ECCI-visualized plasticity-related phenomena were observed: (1) pre-deformation-induced residual stress and its disappearance via subsequent reloading, (2) heterogeneous dislocation motion during plastic relaxation, and (3) planar surface relief formation via loading to a higher stress.

Sign in / Sign up

Export Citation Format

Share Document