E-beam-enhanced solid-state mechanical amorphization of alpha-quartz: Reducing deformation barrier via localized excess electrons as mobile anions

Under hydrostatic pressure, alpha-quartz undergoes solid-state mechanical amorphization wherein the interpenetration of SiO4 tetrahedra occurs and the material loses crystallinity. This phase transformation requires a high hydrostatic pressure of 14 GPa because the repulsive forces resulting from the ionic nature of the Si-O bonds prevent the severe distortion of the atomic configuration. Herein, we experimentally and computationally demonstrate that e-beam irradiation changes the nature of the interatomic bonds in alpha-quartz and enhances the solid-state mechanical amorphization at nanoscale. Specifically, during in situ uniaxial compression, a larger permanent deformation occurs in alpha-quartz micropillars compressed during e-beam irradiation than in those without e-beam irradiation. Microstructural analysis reveals that the large permanent deformation under e-beam irradiation originates from the enhanced mechanical amorphization of alpha-quartz and the subsequent viscoplastic deformation of the amorphized region. Further, atomic-scale simulations suggest that the delocalized excess electrons introduced by e-beam irradiation move to highly distorted atomic configurations and alleviate the repulsive force, thus reducing the barrier to the solid-state mechanical amorphization. These findings deepen our understanding of electron-matter interactions and can be extended to new glass forming and processing technologies at nano- and microscale.Comment: 24 pages, 6 figure

Strongly adhesive dry transfer technique for van der Waals heterostructure

That one can stack van der Waals materials with atomically sharp interfaces has provided a new material platform of constructing heterostructures. The technical challenge of mechanical stacking is picking up the exfoliated atomically thin materials after mechanical exfoliation without chemical and mechanical degradation. Chemically inert hexagonal boron nitride (hBN) has been widely used for encapsulating and picking up vdW materials. However, due to the relatively weak adhesion of hBN, assembling vdW heterostructures based on hBN has been limited. We report a new dry transfer technique. We used two vdW semiconductors (ZnPS3 and CrPS4) to pick up and encapsulate layers for vdW heterostructures, which otherwise are known to be hard to fabricate. By combining with optimized polycaprolactone (PCL) providing strong adhesion, we demonstrated various vertical heterostructure devices, including quasi-2D superconducting NbSe2 Josephson junctions with atomically clean interface. The versatility of the PCL-based vdW stacking method provides a new route for assembling complex 2D vdW materials without interfacial degradation.Comment: Accepted for publication in 2D Material

Practical microstructure-informed dual-scale simulation for predicting hole expansion failure of hyper-burring steel

A practical dual-scale finite element model is developed to enable the formability prediction in the hole expansion of a hyper-burring steel sheet. This numerical approach resorts to the isotropic macroscale hole expansion simulation for calculating the deformation histories near the hole edge, since they are known to be the potential fracture initiation site. The deformation histories are used as boundary conditions in the lower microscale model for calculating the local fracture of the steel sheet. The microscale simulation utilizes the dislocation density based constitutive model and a microstructure-based representative volume element (RVE), with realistic grain morphology taken from experimental microscopy. The fracture initiation at the hole edge region is evaluated from the microscale simulation using four frequently employed uncoupled ductile fracture models, which enable the definition of the critical fracture strain. The proposed dual-scale model can better predict the failure initiation and location near the hole edge when the modeling parameters are calibrated taking into account not only the deformation histories of the hole edge, but also the local stress triaxiality. Moreover, the proposed dual-scale model is applied to analyze the microstructure effect on the hole expansion ratio by providing the insights into the effect of grain size and grain boundary characteristics.N

New approach to hole-expansion ratio in complex phase and martensitic steels: Understanding the role of punching damage

Although advanced high-strength steel (AHSS) demonstrates excellent uniaxial tensile formability, its application in automotive parts is limited due to inferior flange formability. Despite extensive efforts to enhance the flange formability of AHSS, our understanding of it remains limited. In this study, we propose a novel approach to enhance the hole-expansion ratio (HER), which is an indicator of flange formability. Firstly, we correct the existing misconception that the HER does not correlate with uniaxial tensile formability. It was verified through the artificial neural network technique that the uniaxial tensile formability has a strong correlation only with the HER in holes fabricated by electrical discharge machining. However, in the case of punched holes, minimizing the damage accumulated during punching is more important than enhancing uniaxial tensile formability. As an example, the MT steel used in this study showed a decrease in uniaxial tensile formability due to tempering embrittlement after heat treatment. However, this microstructural characteristic effectively reduced punching damage, resulting in a nearly twofold improvement in the HER of punched holes. Consequently, the approach to improving the HER should differ depending on the hole fabrication method. Specifically, to increase the HER of a punched hole, it is crucial to design the material with microstructural characteristics that minimize punching damage

Atomic-scale characterization of V-shaped interface structure of η1 precipitates in Al–Zn–Mg alloy

Al–Zn–Mg alloys have attracted significant interest in the automotive industry owing to their high strength and light weight. Precipitation hardening is the primary mechanism by which these alloys are strengthened, meaning the analysis of the shape, size, and fraction of the precipitates is crucial. In this study, the interfacial structure of precipitates, which influences the mechanical properties of alloys, was investigated. Aberration-corrected scanning transmission electron microscopy studies revealed the atomic structure of the unique V-shaped interface structure of the η1 precipitates, which are the most prevalent among the η precipitates produced in this alloy. The structure was investigated from an energetic perspective using first-principles calculations, which revealed that the formation of the V-shaped interface structure increased the stability through strain relaxation in both the aluminum matrix and η1. The results provide valuable insights into the formation and growth mechanisms of precipitates, paving the way for further advancements in this field

Strongly adhesive dry transfer technique for van der Waals heterostructure

© 2020 IOP Publishing Ltd. That one can stack van der Waals materials with atomically sharp interfaces has provided a new material platform of constructing heterostructures. The technical challenge of mechanical stacking is picking up the exfoliated atomically thin materials after mechanical exfoliation without chemical and mechanical degradation. Chemically inert hexagonal boron nitride (hBN) has been widely used for encapsulating and picking up vdW materials. However, due to the relatively weak adhesion of hBN, assembling vdW heterostructures based on hBN has been limited. We report a new dry transfer technique. We used two vdW semiconductors (ZnPS(3)and CrPS4) to pick up and encapsulate layers for vdW heterostructures, which otherwise are known to be hard to fabricate. By combining with optimized polycaprolactone (PCL) providing strong adhesion, we demonstrated various vertical heterostructure devices, including quasi-2D superconducting NbSe(2)Josephson junctions with atomically clean interface. The versatility of the PCL-based vdW stacking method provides a new route for assembling complex 2D vdW materials without interfacial degradation11sciescopu