Dislocation motion at a fatigue crack tip in a high-nitrogen steel clarified through in situ electron channeling contrast imaging

Habib, Kishan; Koyama, Motomichi; Tsuchiyama, Toshihiro; Nishikawa, Hiroshi

doi:10.1016/j.matchar.2019.109930

Cited by 16 publications

(11 citation statements)

References 25 publications

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“…Therefore, the ECCI technique has been used for the characterization of dislocation-driven phenomena such as the plastic deformation of metals [4,5]. Moreover, the ECCI technique has been recognized as a new pathway for in situ observations [6][7][8] because of two major points. First, bulk specimens are available for ECCI.…”

Section: Introductionmentioning

confidence: 99%

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

Koyama

Seo

Nakafuji

et al. 2021

Science and Technology of Advanced Materials

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To understand the mechanism of FCC–HCP martensitic transformation, we applied electron channeling contrast imaging under cooling to −51°C and subsequent heating to 150°C. The stacking faults were randomly extended and aggregated during cooling. The stacking fault aggregates were indexed as HCP. Furthermore, the shrink of stacking faults due to reverse motion of Shockley partials was observed during heating, but some SFs remained even after heating to the finishing temperature for reverse transformation (A f : 104°C). This fact implies that the chemical driving force of the FCC/HCP phases does not contribute to the motion of a single SF but works for group motion of stacking faults.

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Section: Introductionmentioning

confidence: 99%

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

Koyama

Seo

Nakafuji

et al. 2021

Science and Technology of Advanced Materials

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“…by using MBN [ 51 , 52 ]. The time-response histogram of the MBN signal can analyze the variation of magnetic properties on the grain and grain boundary during plastic deformation, especially the variation in inhomogeneity of magnetic properties before crack formation on a microscopic scale [ 2 ]. The high-sample-rate acquisition method improves the time to resolve DW motion detection, and the high-spatial-resolution magnetic probe improves the resolution for the characterization of the inhomogeneous material’s properties on the microscopic scale.…”

Section: Discussionmentioning

confidence: 99%

“…Stresses play a pivotal role in determining the durability and service life of components. [ 1 , 2 , 3 ]. Jun et al reported that components are vulnerable because of crack initiation caused by the generation of high tensile stresses [ 4 ].…”

Section: Introductionmentioning

confidence: 99%

Time-Response-Histogram-Based Feature of Magnetic Barkhausen Noise for Material Characterization Considering Influences of Grain and Grain Boundary under In Situ Tensile Test

Liu

Tian

Gao

et al. 2021

Sensors

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Stress is the crucial factor of ferromagnetic material failure origin. However, the nondestructive test methods to analyze the ferromagnetic material properties’ inhomogeneity on the microscopic scale with stress have not been obtained so far. In this study, magnetic Barkhausen noise (MBN) signals on different silicon steel sheet locations under in situ tensile tests were detected by a high-spatial-resolution magnetic probe. The domain-wall (DW) motion, grain, and grain boundary were detected using a magneto-optical Kerr (MOKE) image. The time characteristic of DW motion and MBN signals on different locations was varied during elastic deformation. Therefore, a time-response histogram is proposed in this work to show different DW motions inside the grain and around the grain boundary under low tensile stress. In order to separate the variation of magnetic properties affected by the grain and grain boundary under low tensile stress corresponding to MBN excitation, time-division was carried out to extract the root-mean-square (RMS), mean, and peak in the optimized time interval. The time-response histogram of MBN evaluated the silicon steel sheet’s inhomogeneous material properties, and provided a theoretical and experimental reference for ferromagnetic material properties under stress.

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“…47,48 Furthermore, because the specimen is a bulk specimen, in situ observation of dislocation motion under specific mechanical loading conditions can be performed. 49,50 Although the spatial resolution of ECCI is worse than that of transmission electron microscopy, it is sufficiently high to capture/characterize dislocation motion and associated microstructure evolution. Figure 10 shows the in situ ECCI results obtained near the fatigue crack tip in an austenitic steel.…”

Section: Damage-specific Microstructure Characterizationmentioning

confidence: 99%

Quantification and Characterization of Microdamage Resistance in Metals for Designing High-Strength Ductile Microstructures

Koyama

2021

Acc. Mater. Res.

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Conspectus Fractures in metallic materials such as ductile austenitic, ferritic, and dual-phase steels often occur after significant plastic deformation. The dislocation-driven plasticity enhances the microscopic stress concentration and induces vacancies (e.g., by the jogged screw dislocation motion), resulting in microstructure-scale cracks and voids at specific crystallographic planes or microstructure boundaries. (Hereafter, cracks and voids are referred to as damage.) In addition, plasticity plays important roles in microscopic damage growth in terms of damage tip blunting and coalescence. In fact, plasticity-related damage evolution in various fracture phenomena such as metal fatigue and hydrogen embrittlement still contains many uncertainties, particularly in high-strength materials containing fine and complex microstructures. Therefore, microscopy-based damage quantification and characterization are required for designing damage-resistant microstructures. In this context, because damage evolution is a multiscale phenomenon from atomistic to over millimeter scales, the target size of damage in the measurements is important to realize reliable analyses. The intrinsic origin of damage evolution is an atomistic/nanometer scale phenomenon, which requires transmission electron microscopy for its analysis. However, from mechanical viewpoints, revealing damage nucleation behavior is not necessary, because general mechanical analyses are performed for oversubmicrometer-sized damages that can be observed by optical microscopy and scanning electron microscopy. Hence, submicrometer/micrometer-sized damage is the major target in this damage quantification. As a post-mortem analysis method, the damage area fraction, the number of damages, the damage size, and the damage shape at various plastic strains can be quantified by observing micrometer-sized damages. In the case of monotonic tensile deformation, the number density of damages plotted against strain indicate the damage initiation probability. In addition, when damages stop growing, a strain range where the average damage size remains nearly constant appears. The strain range quantitatively indicates damage arrestability. For instance, dual-phase steel consisting of soft and hard body-centered cubic phases clearly shows three strain-dependent damage evolution regimes: (1) damage incubation regime (no damage appears), (2) damage arrest regime (damage initiates, but stops growing immediately), and (3) damage growth regime. Hydrogen uptake increases damage initiation probability and decreases damage arrestability. Specifically, a comparison of the quantified damage parameters between specimens with and without hydrogen revealed that large amounts of hydrogen in the dual-phase steel degrades the resistance to microscopic damage growth, which critically decreases the macroscopic ductility. In this case, the damage arrestability (damage growth resistance) is more important than crack initiation resistance, which is dependent on the dislocation-driven stress accommodatio...

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Dislocation motion at a fatigue crack tip in a high-nitrogen steel clarified through in situ electron channeling contrast imaging

Cited by 16 publications

References 25 publications

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

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

Time-Response-Histogram-Based Feature of Magnetic Barkhausen Noise for Material Characterization Considering Influences of Grain and Grain Boundary under In Situ Tensile Test

Quantification and Characterization of Microdamage Resistance in Metals for Designing High-Strength Ductile Microstructures

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