Large plasticity in magnesium mediated by pyramidal dislocations

Liu, Bo Yu; Liu, Fei; Yang, Nan; Zhai, Xiao Bo; Zhang, Lei; Yang, Yang; Li, Bin; Li, Ju; Ma, Evan; Nie, Jian Feng; Shan, ZW

doi:10.1126/science.aaw2843

Cited by 320 publications

(58 citation statements)

References 30 publications

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“…As the onset of P → B transformation depends on the normal stresses on the prismatic/basal planes which, in most cases, translate to both a resolved shear stress and a normal stress on the twinning plane, twinning nucleation by the dual-step mechanism can also be critically affected by the normal stress on the twinning plane. Finally, a major advantage of nanoscale samples over bulk sample is that high-stress states can be attained 54 ; localized stress concentrations within bulk samples may provide equivalent stress condition for the activation of the dual-step mechanism. Moreover, our findings provide a solid fundamental basis for the twinning-based design and processing of advanced HCP alloys.…”

Section: Discussionmentioning

confidence: 99%

Direct observation of dual-step twinning nucleation in hexagonal close-packed crystals

Wang

et al. 2020

Nat Commun

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Design and processing of advanced lightweight structural alloys based on magnesium and titanium rely critically on a control over twinning that remains elusive to date and is dependent on an explicit understanding on the twinning nucleation mechanism in hexagonal close-packed (HCP) crystals. Here, by using in-situ high resolution transmission electron microscopy, we directly show a dual-step twinning nucleation mechanism in HCP rhenium nanocrystals. We find that nucleation of the predominant {1 0 −1 2} twinning is initiated by disconnections on the Prismatic│Basal interfaces which establish the lattice correspondence of the twin with a minor deviation from the ideal orientation. Subsequently, the minor deviation is corrected by the formation of coherent twin boundaries through rearrangement of the disconnections on the Prismatic│Basal interface; thereafter, the coherent twin boundaries propagate by twinning dislocations. The findings provide high-resolution direct evidence of the twinning nucleation mechanism in HCP crystals.

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Section: Discussionmentioning

confidence: 99%

Direct observation of dual-step twinning nucleation in hexagonal close-packed crystals

Wang

et al. 2020

Nat Commun

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“…It is to be noted that the proposed effects of the alloying elements are based exclusively on first-principles DFT calculations, as discussed in section A on pyramidal stacking faults, and they have not been examined by any MD simulations due to the lack of inter-atomic potentials for magnesium alloys. A very recent work based on in-situ transmission electron microscope mechanical testing, 3D image reconstruction, and atomistic simulations [38] demonstrated that the c þ a h i edge dislocation in pure Mg can glide on both pyramidal I and pyramidal II planes. A separate study of dislocations using weakbeam dark-field transmission electron microscopy reported that c þ a h i dislocations do not dissociate in hot-rolled AZ31 (Mg-3Al-1Zn-0.3Mn; wt pct) alloy.…”

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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“…This high stress coupled with promoted plasticity was also recently observed in microcompression of Mg with limited ductility at large scales. 55 Furthermore, the amorphous surface layer in FIB-machined pillars hinders surface selfdiffusion for dislocation nucleation and increases the required activation energy and activation volume 56 . The incoherent interface between crystalline core and amorphous shell also constricts the escape of dislocations at the surface, which then generates a back-stress which induces dislocation pile-ups and crack formation 57 .…”

Section: Discussionmentioning

confidence: 99%

Achieving micron-scale plasticity and theoretical strength in Silicon

et al. 2020

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As the backbone material of the information age, silicon is extensively used as a functional semiconductor and structural material in microelectronics and microsystems. At ambient temperature, the brittleness of Si limits its mechanical application in devices. Here, we demonstrate that Si processed by modern lithography procedures exhibits an ultrahigh elastic strain limit, near ideal strength (shear strength~4 GPa) and plastic deformation at the micron-scale, one order of magnitude larger than samples made using focused ion beams, due to superior surface quality. This extended elastic regime enables enhanced functional properties by allowing higher elastic strains to modify the band structure. Further, the micron-scale plasticity of Si allows the investigation of the intrinsic size effects and dislocation behavior in diamond-structured materials. This reveals a transition in deformation mechanisms from full to partial dislocations upon increasing specimen size at ambient temperature. This study demonstrates a surface engineering pathway for fabrication of more robust Si-based structures.

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Large plasticity in magnesium mediated by pyramidal dislocations

Cited by 320 publications

References 30 publications

Direct observation of dual-step twinning nucleation in hexagonal close-packed crystals

Direct observation of dual-step twinning nucleation in hexagonal close-packed crystals

Microstructure, Deformation, and Property of Wrought Magnesium Alloys

Achieving micron-scale plasticity and theoretical strength in Silicon

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