Effect of pre-twinning and heat treatment on formability of AZX311 Mg alloy

In this study,the effects of pre-strain-induced tensile twins(TTWs)and controlled heat treatment on the formability behavior of AZX311 Mg alloy sheets were investigated.A 4%compressive strain was applied to pre-strain the sheets using the in-plane compression(IPC)technique along the rolling direction(RD)to introduce TTWs.The pre-strained(PS)samples were subsequently heat-treated at 250℃,350℃,and 400℃ independently for 1 hr,and are termed as PSA1,PSA2,and PSA3,respectively.Erichsen cupping tests were conducted to assess the formability of the sheet samples under different initial conditions.The results showed that the PS sample heat-treated at 250℃ for 1hr exhibited a decrease in the Erichsen index(IE)compared to the as-rolled sample,whereas PSA2 and PSA3 samples showed an increase in IE values.Microtexture analysis revealed that most of the TTWs generated through pre-twinning were stable at 250℃;however,the twin volume fraction reduced to 41%at 350℃ compared to the PS samples due to enhanced thermal activity at that temperature.Furthermore,PSA2 samples showed severe grain coarsening in some areas of the sample,and the fraction of such grains increased in the PSA3 samples.The stretch formability(IE value)of PSA2 samples showed a 32.3%increase compared to the as-rolled specimens.Additionally,the analysis of the deformed specimen at failure under the Erichsen test indicated that considerable detwinning occurs in the PS and PSA1 samples,whereas dislocation slip activity dominates in the PSA2 and PSA3 samples during stretch forming.Apart from detwinning and dislocation slip,deformation twins were also observed in all samples after the Erichsen test.Thus,this work highlights the importance of texture control and its underlying mechanisms via pre-twinning followed by heat treatment and their impact on the room temperature(RT)stretch formability of AZX311 Mg alloy sheets.

Progress of Materials and Devices for Neuromorphic Vision Sensors

The latest developments in bio-inspired neuromorphic vision sensors can be summarized in 3 keywords:smaller,faster,and smarter.(1)Smaller:Devices are becoming more compact by integrating previously separated components such as sensors,memory,and processing units.As a prime example,the transition from traditional sensory vision computing to in-sensor vision computing has shown clear benefits,such as simpler circuitry,lower power consumption,and less data redundancy.(2)Swifter:Owing to the nature of physics,smaller and more integrated devices can detect,process,and react to input more quickly.In addition,the methods for sensing and processing optical information using various materials(such as oxide semiconductors)are evolving.(3)Smarter:Owing to these two main research directions,we can expect advanced applications such as adaptive vision sensors,collision sensors,and nociceptive sensors.This review mainly focuses on the recent progress,working mechanisms,image pre-processing techniques,and advanced features of two types of neuromorphic vision sensors based on near-sensor and in-sensor vision computing methodologies.

Effects of temperature on critical resolved shear stresses of slip and twining in Mg single crystal via experimental and crystal plasticity modeling

Magnesium(Mg)single crystal specimens with three different orientations were prepared and tested from room temperature to 733 K in order to systematically evaluate effects of temperature on the critical resolved shear stress(CRSS)of slips and twinning in Mg single crystals.The duplex non-basal slip took place in the temperature range from 613 to 733 K when the single crystal samples were stretched along the<0110>direction.In contrast,the single basal slip and prismatic slip were mainly activated in the temperature range from RT to 733 K when the tensile directions were inclined at an angle of 45°with the basal and the prismatic plane,respectively.Viscoplastic self-consistent(VPSC)crystal modeling simulations with genetic algorithm code(GA-code)were carried out to obtain the best fitted CRSSs of major deformation modes,such as basal slip,prismatic slip,pyramidalⅡ,{1012}tensile twinning and{1011}compressive twinning when duplex slips accommodated deformation.Additionally,CRSSs of the basal and the prismatic slip were derived using the Schmid factor(SF)criterion when the single slip mainly accommodated deformation.From the CRSSs of major deformation modes obtained by the VPSC simulations and the SF calculations,the CRSSs for basal slip and{1012}tensile twinning were found to show a weak temperature dependence,whereas those for prismatic,slip and{1011}compressive twinning exhibited a strong temperature dependence.From the comparison of previous results,VPSC-GA modeling was proved to be an effective method to obtain the CRSSs of various deformation modes of Mg and its alloys.

Recent advances in the in-plane shear testing of Mg alloy sheets

Sheet-metal products are integral parts of engineering industries and academia research. Various testing techniques have revealed the deformation behaviors of sheet metals under complex stress states. Information obtained from tensile and compression tests, however, are insufficient for the identification of material parameters relevant to modern constitutive laws, which require experimental setups capable of generating various loading conditions and applying great amounts of strain to sheet metals. In-plane shear testing has emerged as an important method to overcome the challenges associated with tension and compression tests and can provide additional information about deformation behaviors under large plastic strains. Materials such as Mg alloys with poor levels of both ductility and formability cannot accommodate large plastic strains. Therefore, tension and compression tests have limitations in explaining the material behaviors that occur during sheet metal forming where large plastic strains are introduced. Many studies have been conducted to explain the deformation behaviors of Mg alloys under shear deformation techniques. These include severe plastic deformation(SPD), especially the equal channel angular pressing(ECAP)and equal channel angular extrusion, rolling combined with shear deformation i.e. differential speed rolling(DSR), and also in-plane shear for sheet metals, particularly under large levels of plastic strain. These in-plane shear technique involves the Miyauchi shear test, ASTM shear test, and twin bridge shear tests. Moreover, many experimental results have revealed that the evolution of microstructure and texture during in-plane shear is closely related to the failure behavior of materials. Therefore, this review is focused on techniques for in-plane shear testing that have been reported thus far, on the effect of in-plane shear on the microstructure development of Mg alloy sheets, and on the usefulness of in-plane shear testing to evaluate the formability of Mg alloy sheets.

Electrospun Flexible Nanofibres for Batteries:Design and Application

Flexible and free-standing electrospun nanofibres have been used as electrode materials in electrochemical energy storage systems due to their versatile properties,such as mechanical stability,superb electrical conductivity,and high functionality.In energy storage systems such as metal-ion,metal-air,and metal-sulphur batteries,electrospun nanofibres are vital for constructing flexible electrodes and substantially enhancing their electrochemical properties.The need for flexible batteries has increased with increasing demand for new products such as wearable and flexible devices,including smartwatches and flexible displays.Conventional batteries have several semirigid to rigid components that limit their expansion in the flexible device market.The creation of flexible and wearable batteries with greater mechanical flexibility,higher energy,and substantial power density is critical in meeting the demand for these new electronic items.The implementation of carbon and carbon-derived composites into flexible electrodes is required to realize this goal.It is essential to understand recent advances and the comprehensive foundation behind the synthesis and assembly of various flexible electrospun nanofibres.The design of nanofibres,including those comprising carbon,N-doped carbon,hierarchical,porous carbon,and metal/metal oxide carbon composites,will be explored.We will highlight the merits of electrospun carbon flexible electrodes by describing porosity,surface area,binder-free and free-standing electrode construction,cycling stability,and performance rate.Significant scientific progress has been achieved and logistical challenges have been met in promoting secondary battery usage;therefore,this review of flexible electrode materials will advance this easily used and sought-after technology.The challenges and prospects involved in the timely development of carbon nanofibre composite flexible electrodes and batteries will be addressed.

Finite element analysis using elasto-visco-plastic self-consistent polycrystal model for E-form Mg sheet subjected to bending

The mechanical behavior of a magnesium alloy E-form under bending was investigated using the elasto-visco-plastic polycrystal model(ΔEVPSC) and its finite element(FE) implementation(ΔEVPSC-FE) developed in Jeong et al. and Jeong and Tomé. The crystallographic orientation distribution(COD) obtained from X-ray diffraction was used to represent the initial texture, and the Voce hardening parameters were calibrated by fitting the uniaxial tension and the compression flow stress curves. A quasi-static FE analysis of a miniaturized V-bending operation was conducted using the ΔEVPSC-FE model. The bending induced an inhomogeneous stress response along the through-thickness and the lateral directions, which was well captured by the model. Moreover, the predictive capability of the model was validated by comparing with various experimental results such as(1) force vs. displacement curves;(2) the through-thickness variations in the twin volume fraction;and(3) the changes in crystallographic texture as a function of displacement. Additional bending simulation was performed using an isotropic texture, the result of which suggests that the potential improvement in bendability of the magnesium alloy is attainable by weakening the initial texture. Moreover, the simulation results imply that the crystallographic texture, which may affect the twin activation across the thickness direction, plays a significant role in the shifting direction of the neutral layer.

Discovery of Pb-free hybrid organic-inorganic 2D perovskites using a stepwise optimization strategy

The current status of 2D organic–inorganic hybrid perovskites for use in photovoltaic(PV)and light-emitting diode(LED)applications lags far behind their 3D counterparts.Here,we propose a computational strategy for discovering novel perovskites with as few computing resources as possible.A tandem optimization algorithm consisting of an elitism-reinforced nondominated sorting genetic algorithm(NSGA-II)and a multiobjective Bayesian optimization(MOBO)algorithm was used for density functional theory(DFT)calculations.The DFT-calculated band gap and effective mass were taken as objective functions to be optimized,and the constituent molecules and elements of a Ruddlesden–Popper(RP)structure(n=2)were taken as decision variables.Fourteen previously unknown RP perovskite candidates for PV and LED applications were discovered as a result of the NSGA-II/MOBO algorithm.Thereafter,more accurate DFT calculations based on the HSE06 exchange correlation functional and ab initio molecular dynamics(AIMD)were conducted for the discovered 2D perovskites to ensure their validity.

Mixed-phase composites derived from cobalt terephthalate as efficient battery-type electrodes for high-performance supercapattery

Interfacial engineering of two-dimensional(2D)monometallic phosphides enables remarkable structural and electrochemical properties in energy storage devices.Herein,2D nanosheets(NSs)of FeP_(2)/Co_(2) P were grown on Ni-foam(FCP)using a solution-based and phosphorization approach to be used as freestanding for high-performance energy storage devices.An effective phosphorization strategy is successfully de-veloped to improve the overall crystalline phase,tailor the morphology,and boost the electrochemical performances of electrodes.The FCP NSs electrode exhibits a battery-type redox behavior with a maxi-mum high areal capacity of 1.96 C cm^(-2) at 4 mA cm^(-2) in 6 M KOH aqueous electrolyte compared to the other counterparts.The superior electrochemical performance was achieved by increasing the electroac-tive sites and high conductivity via surface tailoring and fast redox reactions.Moreover,a supercapattery was assembled utilizing FCP and activated carbon(AC)electrodes and it revealed maximum specific en-ergy(E_(s))and specific power(P_(s))of 41.2 Wh kg^(-1) and 7578 W kg^(-1) with good cycling stability of 91%after 10,000 cycles at 5 A g^(-1).Eventually,the supercapattery has been explored in practical applications by lighting up light-emitting diodes(LEDs),representing the real-time performance of superior energy storage devices.