Unexpected partial dislocations within stacking faults in a cold deformed Mg−Bi alloy

He, Chao; Zhang, Y.; Liu, C.Q.; Yuan, Yue; Chen, H.W.; Nie, Jian Feng

doi:10.1016/j.actamat.2020.02.010

Cited by 36 publications

(9 citation statements)

References 59 publications

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“…These alloys were prepared from high-purity Mg, Bi, and Pb metals by induction melting in a mild steel crucible at 760 °C under a mixed gas atmosphere (SF 6 + CO 2 ) and casting into a preheated steel mold. To avoid any local melting 39 , the solution heat-treatment of the Mg–Bi alloy was performed at 320 °C for 24 h and then at 450 °C for 24 h while that of the Mg–Pb alloy at 300 °C for 24 h and then at 370 °C for 24 h, followed by cold water quenching. Small cylinder-shaped samples were uniaxially compressed to strains ranging from 3% to 20% at ambient temperature.…”

Section: Methodsmentioning

confidence: 99%

Unusual solute segregation phenomenon in coherent twin boundaries

Chen

et al. 2021

Nat Commun

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Interface segregation of solute atoms has a profound effect on properties of engineering alloys. The occurrence of solute segregation in coherent twin boundaries (CTBs) in Mg alloys is commonly considered to be induced by atomic size effect where solute atoms larger than Mg take extension sites and those smaller ones take compression sites in CTBs. Here we report an unusual solute segregation phenomenon in a group of Mg alloys—solute atoms larger than Mg unexpectedly segregate to compression sites of {10$$\overline 1$$ 1 ¯ 1} fully coherent twin boundary and do not segregate to the extension or compression site of {10$$\overline 1$$ 1 ¯ 2} fully coherent twin boundary. We propose that such segregation is dominated by chemical bonding (coordination and solute electronic configuration) rather than elastic strain minimization. We further demonstrate that the chemical bonding factor can also predict the solute segregation phenomena reported previously. Our findings advance the atomic-level understanding of the role of electronic structure in solute segregation in fully coherent twin boundaries, and more broadly grain boundaries, in Mg alloys. They are likely to provide insights into interface boundaries in other metals and alloys of different structures.

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Section: Methodsmentioning

confidence: 99%

Unusual solute segregation phenomenon in coherent twin boundaries

Chen

et al. 2021

Nat Commun

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“…Precaution has to be taken when imaging and analyzing I 1 faults in scanning transmission electron microscopy (STEM), as a Frank partial may react with a basal a h i dislocation to form a complex configuration where an I 1 fault is bounded by a Frank partial at one end and a Shockley partial at the other end. [8] It has been recognized that solute atoms may segregate to I 1 faults, but there are few experimental studies made by Z-contrast STEM. Most reports were based on first-principles density functional theory (DFT) calculations and considered only one solute atom in the fault plane.…”

Section: A Dislocations and Stacking Faultsmentioning

confidence: 99%

“…[39] Other experimental observations made by atomic-resolution STEM indicated that c þ a h i dislocations dissociate in cold deformed samples of Mg-Bi and Mg-Sn alloys. [8,40] Detailed and systematic characterization of more alloy systems and alloys subjected to different deformation conditions is needed in the future to resolve the controversial reports. Equally, more computation-based studies are needed in the future on solute-dislocation interactions and quantitative effects of solutes on dislocation slip activities in different slip systems.…”

Section: B Slip Twinning and Grain Boundary Slidingmentioning

confidence: 99%

Microstructure, Deformation, and Property of Wrought Magnesium Alloys

Nie

Shin

Zeng

2020

Metall Mater Trans A

156

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Pure magnesium (Mg) develops a strong basal texture after conventional processing of hot rolling or extrusion. Consequently, it exhibits anisotropic mechanical properties and is difficult to form at room temperature. Adding appropriate alloying elements can weaken the basal texture or even change it, but the improvement in formability and mechanical properties is still far from expectations. Over the past 20 years, considerable efforts have been made and significant progress has been made on wrought Mg alloys at the fundamental and technological levels. At the fundamental level, textures formed in sheets and extrusions of different alloy compositions and produced under different strain paths or thermomechanical processing conditions are relatively well established, with the assistance of the advanced characterization technique of electron backscatter diffraction. At the technological level, room temperature formability of sheet has been significantly improved, and tension-compression yield asymmetry of extrusion is also remarkably reduced or eliminated. This paper starts with an overview of dislocations, stacking faults and twins, and deformation of single crystals of pure Mg along different orientations and under different loading conditions, followed by a review of microstructure (texture and grain size) and deformation of polycrystalline pure Mg with different textures, grain sizes, and loading conditions. With this information as a base, texture, grain size, and deformation of polycrystalline Mg alloy sheets and extrusions produced under different processing conditions are systematically examined and compared. Remaining and emerging scientific and technology issues are then highlighted and discussed in the context of texture and grain size. The need for better-resolution diffraction and spectroscopy techniques is also discussed in the relationship between texture change and grain boundary solute segregation.

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“…A closer examination of the defect substructure inside the twin in figure 12 reveals that the point where a SF intersects the twin boundary almost invariably coincides with a corner of a BP or PB facet. Such SFs have also been observed experimentally in {1012} twins [47,48], and their possible origins and the character of their bounding defects have been studied in detail [49,64,65]. The bounding defect in the twin boundary is specifically known to have disconnection character; the Burgers vectors and the step heights of the disconnections in figure 12 are given in the conventional notation b ±µ/±κ used in interfacial defect theory [66].…”

Section: Revising the Micromechanical Modelmentioning

confidence: 97%

Energetic contributions to deformation twinning in magnesium

Kapan

Alkan

Aydıner

et al. 2023

Modelling Simul. Mater. Sci. Eng.

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Modeling deformation twin nucleation in magnesium has proven to be a challenging task. In particular, the absence of a heterogeneous twin nucleation model which provides accurate energetic descriptions for twin-related structures indicates a need to more deeply understand twin energetics. To address this problem, molecular dynamics simulations are performed to follow the energetic evolution of {1012} tension twin embryos nucleating from an asymmetrically-tilted grain boundary. The line, surface and volumetric terms associated with twin nucleation are identified. A micromechanical model is proposed where the stress field around the twin nucleus is estimated using the Eshelby formalism, and the contributions of the various twin-related structures to the total energy of the twin are evaluated. The reduction in the grain boundary energy arising from the change in character of the prior grain boundary is found to be able to offset the energy costs of creating the other interfaces. The defect structures bounding the stacking faults that form inside the twin are also found to possibly have significant energetic contributions. These results suggest that both of these effects could be critical considerations when predicting twin nucleation sites in magnesium.

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Unexpected partial dislocations within stacking faults in a cold deformed Mg−Bi alloy

Cited by 36 publications

References 59 publications

Unusual solute segregation phenomenon in coherent twin boundaries

Unusual solute segregation phenomenon in coherent twin boundaries

Microstructure, Deformation, and Property of Wrought Magnesium Alloys

Energetic contributions to deformation twinning in magnesium

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