Showing papers in "JOM in 2019"

Ferroelectric Hf 0.5 Zr 0.5 O 2 Thin Films: A Review of Recent Advances

Abstract: Ferroelectricity in HfO2-based materials, especially Hf0.5Zr0.5O2 (HZO), is today one of the most attractive topics because of its wide range of applications in ferroelectric random-access memory, ferroelectric field-effect transistors, ferroelectric tunneling junctions, steep-slope devices, and synaptic devices. The main reason for this increasing interest is that, when compared with conventional ferroelectric materials, HZO is compatible with complementary metal–oxide–semiconductor flow [even back-end of the line thermal budget] and can exhibit robust ferroelectricity even at extremely thin (< 10 nm) thicknesses. In this report, recent advances in the ferroelectric properties of HZO thin films since the first report in 2011, including doping effects, mechanical stress effects, interface effects, and ferroelectric film thickness effects, are comprehensively reviewed.

Revealing the Effects of Powder Reuse for Selective Laser Melting by Powder Characterization

Abstract: In a selective laser melting process, it is common to reuse the powder in consecutive cycles of the route because it is more sustainable and cost effective. However, it is unknown whether reusing the material has an influence on the process. In this paper, Inconel 718, Ti6Al4V, AlSi10Mg and Scalmalloy are characterized to determine the impact of reusing powders on the additive manufacturing (AM) process under an argon high-purity atmosphere. Virgin powders were taken from the suppliers and compared to powders that had been used in the process for a long period of time with periodic ‘rejuvenation’. A well-structured characterization procedure, combining many existing techniques, is proposed, determining changes in the morphology, composition (chemical and microstructure) and flowability. Clear differences between the virgin and used state are revealed by the characterizations; AlSi10Mg, appears to be the most sensitive to reuse with changes in particle size distribution and morphology, and with an increase in the oxygen content. The main contribution of this paper is providing insight into the effects of reuse for four commonly used AM powders, by means of a simple but well-structured method that links the particle feature characterization process to the flowability of metal AM powders. The provided insights enable enhanced decision-making on recycling and reuse of powder for specific AM processes.

Comparison of Stainless Steel 316L Parts Made by FDM- and SLM-Based Additive Manufacturing Processes

Abstract: The selective laser melting (SLM) process is of great interest for fabrication of metal parts, and a number of studies have been conducted to provide in-depth understanding of how stainless steel 316L parts can be fabricated using this powder-bed-fusion-based additive manufacturing (AM) process. In comparison with SLM stainless steel 316L, this paper introduces an innovative AM process for making austenitic stainless steel 316L parts using a metal–polymer composite filament (Ultrafuse 316LX). Stainless steel 316L metal specimens were printed using a material extrusion (FDM)-based three-dimensional (3D) printer loaded with Ultrafuse filament, followed by an industry-standard debinding and sintering process. Tests were performed to understand the material properties, such as hardness, tensile strength, and microstructural characteristics. Part shrinkage was also analyzed based on the features of the FDM stainless steel 316L component. A preliminary guideline on how to select among these two alternative AM processes for fabrication of metal parts is discussed.

Powder Recycling Effects on the Tensile and Fatigue Behavior of Additively Manufactured Ti-6Al-4V Parts

Abstract: Additive manufacturing technology has enabled industries to generate functional parts with an increased level of complexity via layer-by-layer fabrication. In laser-powder bed fusion (L-PBF), powder is often recycled due to its high cost. However, there is no comprehensive study on how powder recycling affects its rheological properties, as well as the mechanical and fatigue behavior of the manufactured part. This study compares powder characteristics and mechanical performance of as-built and machined specimens fabricated from new and heavily used Ti-6Al-4V powder. Powder characteristics include particle size distribution and morphology, flowability, apparent density, compressibility, thermal conductivity, oxygen concentration, and more. Results indicate that particle size distribution becomes narrower and flowability increases with recycling. Not a significant effect of recycling was observed on the monotonic tensile and fatigue behavior of specimens in the as-built surface condition. However, machined specimens fabricated from used powder demonstrated longer fatigue lives in the high cycle regime.

Review of Organic/Inorganic Thin Film Encapsulation by Atomic Layer Deposition for a Flexible OLED Display

Abstract: Recent trends in thin film encapsulations (TFEs), fabricating organic/inorganic encapsulation films are reviewed. Atomic layer deposited inorganic films have superior barrier performance and have advantages of excellent uniformity over large scales at relatively low deposition temperatures. However, organic film should be combined with a hybrid structure for improved flexibility and longer lag time. We introduce various organic deposition methods and mechanisms for enhancing barrier performance. However, stress engineering is required to achieve high performance TFEs for flexible devices, new materials and deposition methods. First, modulating the internal stress in TFEs should be considered to increase flexibility by adopting other layers that can reduce internal stress. Second, controlling the configuration of the hybrid structure can prevent degradation due to cracks. Third, the introduction of a neutral plane as the middle layer decreases the strain. The results summarize how the device can improve barrier performance under external stress. This paper can guide the improvements in barrier performance.

A Simulation Work for the Influences of Aggregation/Agglomeration of Clay Layers on the Tensile Properties of Nanocomposites

Abstract: This study examines the aggregation/agglomeration of layered clay in polymer nanocomposites and discusses their influences on nanoparticle characteristics and mechanical properties using appropriate equations. The effective volume fraction, specific surface area, and aspect ratio of layers are calculated in samples containing both single and aggregated/agglomerated nanoparticles. The Young’s modulus and yield strength of nanocomposites are predicted based on the effective characteristics of layers. The aggregation/agglomeration decreases the effective levels of volume fraction, aspect ratio, and specific surface area of nanoparticles. As a result, researchers should prevent the accumulation of clay layers in nanocomposites and encourage the exfoliation of single layers causing optimal properties.

Prediction of the Composition and Hardness of High-Entropy Alloys by Machine Learning

Abstract: Machine learning with artificial neural network (ANN)-based methods is a powerful tool for the prediction and exploitation of the subtle relationships between the composition and properties of materials. This work utilizes an ANN to predict the composition of high-entropy alloys (HEAs) based on non-equimolar AlCoCrFeMnNi in order to achieve the highest hardness in the system. A simulated annealing algorithm is integrated with the ANN to optimize the composition. A bootstrap approach is adopted to quantify the uncertainty of the prediction. Without any guidance, the design of new compositions of AlCoCrFeMnNi-based HEAs would be difficult by empirical methods. This work successfully demonstrates that, by applying the machine learning method, new compositions of AlCoCrFeMnNi-based HEAs can be obtained, exhibiting hardness values higher than the best literature value for the same alloy system. The correlations between the predicted composition, hardness, and microstructure are also discussed.

Evaluation of the Tensile Strength in Carbon Nanotube-Reinforced Nanocomposites Using the Expanded Takayanagi Model

Abstract: In this study, we used the Takayanagi model expanded by Loos and Manas-Zloczower for the tensile modulus to assess the tensile strength of polymer/carbon nanotube nanocomposites (PCNTs). The new model assumes the strengthening and percolating efficiencies of the interphase between the polymer matrix and the nanoparticles. We evaluated the suggested model with the experimental data of two PCNTs and found that this model successfully calculated the average levels of the percolation threshold, interphase thickness (t), and interphase strength (σiN). The percolation threshold > 0.004, interphase volume fraction 30 nm caused the lowest relative tensile strength, less than the strength of the polymer matrix. Among the studied variables, the t and σiN parameters most significantly affected the tensile strength of PCNTs; when t = 25 nm and σiN = 17 GPa, there was 1300% improvement in the strength of the PCNT. This model can be applied in future studies to accelerate the material design process.

Recent Advances in LPSO-Containing Wrought Magnesium Alloys: Relationships Between Processing, Microstructure, and Mechanical Properties

Abstract: Development of strong and ductile lightweight magnesium (Mg) alloys has been the subject of enormous research breakthroughs since 2000. This review describes the most significant progress on the design and processing of high-strength wrought Mg alloys containing long-period stacking order (LPSO) phases. It first focuses on the typical atomic structure, transformation, and morphology of various LPSO phases, then explores the key contributions of thermomechanical processing techniques to the metallurgical structure, morphology, spatial dimension, and distribution of diverse LPSO phases and discusses the LPSO-derived strengthening mechanisms of Mg alloys. Finally, future research opportunities for LPSO-containing wrought Mg alloys are proposed on the basis of the mechanistic relationships between the evolution of LPSO phase particles and strengthening mechanisms.

Selective Laser Melting of Al0.3CoCrFeNi High-Entropy Alloy: Printability, Microstructure, and Mechanical Properties

Abstract: Al0.3CoCrFeNi high-entropy alloy (HEA) was additively manufactured by powder-bed selective laser melting (SLM) with emphasis on its microstructure and tensile properties. Al0.3CoCrFeNi showed excellent printability, enabling fabrication of fully dense products. The microstructure of the SLM as-built HEA consisted of a single-phase disordered face-centered cubic solid solution with fine columnar grains elongated along the build direction. The characteristic features of the as-built microstructure were a fiber texture aligned toward the build direction and a large dislocation density. As a consequence, printed Al0.3CoCrFeNi HEA exhibited superior tensile strength in comparison with as-cast or wrought counterparts.

Current Status of Titanium Recycling and Related Technologies

Abstract: The major resource for recycling Ti is currently in-house Ti scrap generated in smelting and fabrication processes instead of postconsumer Ti products, and the actual recycling rate including cascade recycling in the smelting and fabrication industry is high. The major impurities in Ti scrap are O and Fe. High-grade Ti scrap with low O and Fe concentrations is remelted to obtain Ti and its alloys. On the other hand, low-grade Ti scrap with high O and Fe concentrations is used as ferrotitanium for the steel industry. However, if demand for Ti drastically increases, the amount of low-grade Ti scrap generated would exceed the demand for ferrotitanium. Before this happens, technologies for anti-contamination or for efficient O and Fe removal must be developed for efficient utilization of Ti. Herein, the current status of Ti scrap generation and its recycling flow are reviewed. New developments in Ti recycling technology are also discussed.

Disassembly Automation for Recycling End-of-Life Lithium-Ion Pouch Cells

Abstract: Rapid advances in the use of lithium-ion batteries (LIBs) in consumer electronics, electric vehicles, and electric grid storage have led to a large number of end-of-life (EOL) LIBs awaiting recycling to reclaim critical materials and eliminate environmental hazards. This article studies automatic mechanical separation methodology for EOL pouch LIBs with Z-folded electrode-separator compounds (ESC). Customized handling tools are designed, manufactured, and assembled into an automatic disassembly system prototype that consists of three modules. Verification experiments utilizing dummy cells prove that the main components of pouch LIBs (cathode sheets, anode sheets, separators, and polymer-laminated aluminum film housing) can be automatically separated and extracted with well-preserved integrity using our proposed disassembly strategy.

Sulfation Roasting Mechanism for Spent Lithium-Ion Battery Metal Oxides Under SO2-O2-Ar Atmosphere

Abstract: Sulfation roasting followed by water leaching has been proposed as an alternative route for recycling valuable metals from spent lithium-ion batteries (LIBs). In the present work, the reaction mechanism of the sulfation roasting of synthetic LiCoO2 was investigated by both thermodynamic calculations and roasting experiments under flowing 10% SO2-1% O2-89% Ar gas atmosphere at 700°C. The products and microstructural evolution processes were characterized by x-ray diffraction, scanning electron microscope and energy dispersive x-ray spectrometer, and atomic absorption spectroscopy. It was confirmed that Co3O4 was formed as an intermedia product, and the final roasted products were composed by Li2SO4, Li2Co(SO4)2, and CoO. The leaching results indicated that 99.5% Li and 17.4% Co could be recovered into water after 120 min of roasting. The present results will provide the basis and solid guidelines for recycling of Li and Co from spent LIBs.

Uncertainty Quantification in Metallic Additive Manufacturing Through Physics-Informed Data-Driven Modeling

Abstract: The complicated metal-based additive manufacturing (AM) process involves various sources of uncertainty, leading to variability in AM products. For comprehensive uncertainty quantification (UQ) of AM processes, we present a physics-informed data-driven modeling framework, in which multilevel data-driven surrogate models are constructed based on extensive computational data obtained by multiscale multiphysics AM models. It starts with computationally inexpensive surrogate models for which the uncertainty can be readily quantified, followed by global sensitivity analysis for comprehensive UQ study. Using AM-fabricated Ti-6Al-4V components as examples, this study demonstrates the capability of the proposed data-driven UQ framework for efficient investigation of uncertainty propagation from process parameters to material microstructures, then to macrolevel mechanical properties through a combination of advanced AM multiphysics simulations and data-driven surrogate modeling. Model correction and parameter calibration for the constructed surrogate models using limited amounts of experimental data are discussed.

Comparative Studies on Degradation Behavior of Pure Zinc in Various Simulated Body Fluids

Abstract: The initial corrosion behavior of pure zinc during 168 h of immersion in Hanks’ solution, simulated body fluid (SBF), Dulbecco’s modified Eagles’ medium (DMEM), and DMEM with 10% fetal bovine serum (FBS) was investigated. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization were performed on samples after immersion. The morphology and chemical composition of corrosion products were determined by environment scanning electron microscope, x-ray diffraction, x-ray photoelectron spectroscopy, and Fourier transform infrared spectrometer. The results demonstrated that pure Zn degraded at a rate of 0.01 mm yr−1 to 0.02 mm yr−1 in DMEM and DMEM + FBS and exhibited the highest corrosion rate in SBF. It was shown that the composition of solution was crucial for the evaluation of degradation behavior in vitro. Insoluble salts formation and organic components in DMEM retarded the degradation of Zn. The presence of proteins increased the polarization resistance while it also exacerbated localized corrosion.

Microstructure and Corrosion Characteristics of Selective Laser-Melted 316L Stainless Steel: The Impact of Process-Induced Porosities

Abstract: The microstructure and corrosion susceptibility of selective laser-melted (SLM) 316L stainless steel on planes aligned and perpendicular to the building direction in aqueous 3.5 wt.% NaCl solution were investigated and compared with their conventionally wrought counterpart. Cyclic potentiodynamic polarization results confirmed a superior pitting resistance and a reduced rate of metastable pitting for the SLM-fabricated samples regardless of the sample’s orientation compared to the wrought alloy. Although the process-induced porosities in the SLM samples did not affect the corrosion and pitting potentials of the alloy at the initial immersion time, they likely contributed to the reduced re-passivation potential of the surface. Furthermore, at longer immersion times, the electrochemical impedance spectroscopy and immersion testing results confirmed a more detrimental impact of the process-induced porosities on lowering the electrochemical stability of the SLM-316L surface perpendicular to the building direction, where larger size and higher density of crevice-like porosities were detected.

Effect of Post-heat Treatment on the Corrosion Behavior of AlSi10Mg Alloy Produced by Additive Manufacturing

Abstract: Additive manufacturing processes are becoming attractive technologies for producing complex components in relatively a short time and at reasonable cost. The present study aims to evaluate the effect of post-heat treatment on the corrosion performance of AlSi10Mg alloy produced by selective laser melting (SLM). Heat treatment up to 400°C for 2 h was tested. Microstructure evaluation was carried out using optical and scanning electron microscopy, along with x-ray diffraction assessment and photoelectron spectroscopy analysis. Corrosion performance was studied by salt spray testing, potentiodynamic polarization and electrochemical impedance spectroscopy for general corrosion assessment, while slow strain rate testing and low cycle corrosion fatigue were employed for stress corrosion examination. The obtained results indicated that relatively improved corrosion performance was achieved by heat treatment at 200–300°C. This was mainly attributed to the preservation of the fine Si net embedded in the α-Al matrix that was obtained during the SLM process and the adequate residual stress relief conditions.

Effect of Hollow Glass Microspheres on the Morphology, Rheology and Crystallinity of Short Bamboo Fiber-Reinforced Hybrid Polypropylene Composite

Abstract: Light-weight and high-strength polymer composites have attracted the special attention of automotive and aerospace sectors since they offer advantages such as less fuel consumption and higher fuel efficiency. In the present study, an effort has been made to prepare such polymer composites using natural fiber and very low-density hollow inorganic particles. The use of hollow glass microspheres (HGM) as a potential filler particle for making light-weight hybrid polymer composites was investigated. Polypropylene (PP) and maleic anhydride-grafted-polypropylene (in 9:1 ratio) constituted the base matrix (BM). For strength reinforcement, alkali-treated short bamboo fibers (SBF) were employed, while for making the composite material light in weight, HGM were incorporated. Silane treatment of HGM by (3-aminopropyl)triethoxysilane was performed to enhance interfacial adhesion with BM. Adequate wetting of HGM and SBF was evident from the SEM images of cryo-fractured samples. A 14% increase in tensile strength was observed in comparison to virgin PP for the composite with 5 wt.% HGM, and a desirable decrease in density was observed for all the composite samples with increasing HGM content. Improvement in hardness but a marginal decrease in impact strength due to HGM fillers was observed. Rheological analysis of the composite melt samples showed an apparent increase in the complex modulus with increasing HGM content. Thermal analysis of the composites revealed a significant impact of hybrid fillers on the crystallinity, with SBF showing a minimal effect while HGM reducing it significantly. Wide-angle x-ray diffraction spectra showed changes in the crystal structure of the composite with noticeable β-form peaks.

Effect of Al and Ti on High-Temperature Oxidation Behavior of CoCrFeNi-Based High-Entropy Alloys

Abstract: CoCrFeNiAlxTiy high-entropy alloys were produced by the induction melting method and their oxidation behavior investigated when exposed to 1000°C for different durations. One or more body-centered cubic phases were found in all alloys, except CoCrFeNiTi0.5. In the CoCrFeNiTi0.5 alloy, two different face-centered cubic phases and one tetragonal sigma phase were detected. Scanning electron microscopy elemental analysis showed that all the alloys exhibited homogeneous microstructure. Energy-dispersive x-ray spectroscopy analysis revealed that Cr and Fe elements were enriched in one phase and Al-Ni-Ti elements in another. The presence of Ti negatively affected the oxidation behavior. According to the oxidation test results, dominant Al2O3 formation was observed in the CoCrFeNiAl0.5 and CoCrFeNiAlTi0.5 alloys. As a result, these two alloys exhibited the best performance among the five high-entropy alloys in terms of mass gain and oxide thickness.

Effect of Solidification Defects and HAZ Softening on the Anisotropic Mechanical Properties of a Wire Arc Additive-Manufactured Low-Carbon Low-Alloy Steel Part

Abstract: Wire arc additive manufacturing (WAAM) is a pioneer additive-based technology for fabrication of large-scale engineering components. Despite the many advances in the field of additive manufacturing, formation of solidification defects, including discontinuities and microstructural imperfections, in the fabricated components is still inevitable, regardless of the feedstock material or fabrication process applied. In this study, the effects of solidification defects on the anisotropic mechanical properties of a low-carbon low-alloy steel (ER70S-6) wall produced by WAAM have been investigated. Analysis of the microstructure and mechanical properties of the fabricated part confirmed the formation of various solidification defects, i.e., interpass lack of fusions, localized brittle zones, and grain coarsening in the heat-affected zones, leading to anisotropic behavior in the ductility along the deposition versus building directions of the component. The effect of discontinuities on the anisotropic mechanical properties was minimized through microstructural modifications of the fabricated part using postprinting normalizing heat treatment.

Use of an Abrasive Water Cavitating Jet and Peening Process to Improve the Fatigue Strength of Titanium Alloy 6Al-4V Manufactured by the Electron Beam Powder Bed Melting (EBPB) Additive Manufacturing Method

Abstract: Metal components made by additive manufacturing have large inherent surface roughness, and, as such, their strength and fatigue life can be reduced significantly versus wrought products. In order to improve these properties, a novel mechanical surface treatment that introduces compressive residual stress while simultaneously reducing the surface roughness is proposed. The proposed treatment uses cavitation peening combined with an abrasive slurry. The impact of the kinetic energy-charged abrasive particles, induced by collapsing water cavitation vapor bubbles, produces compressive residual stress, while the abrasive reduces the surface roughness. Plane-bending fatigue tests were carried out to determine the effectiveness of this treatment on the fatigue life and strength of titanium alloy Ti6Al4V manufactured by electron beam melting. It was demonstrated that the fatigue strength of an as-built specimen was improved from 169 MPa to 280 MPa by the proposed treatment.

Selective Laser Melting of 316L Stainless Steel: Physics of Melting Mode Transition and Its Influence on Microstructural and Mechanical Behavior

Abstract: A combined computational–experimental study is performed to investigate the effect of melting modes (conduction, transition and keyhole) on 316L stainless steel parts fabricated by selective laser melting. A high-fidelity mesoscale model is developed using the LIGGGHTS and OpenFOAM open-source codes to describe the physical phenomena (convection, melting, evaporation and solidification), melt flow dynamics and melting mode transition. The developed model helps to understand laser/matter interaction, melting of particles, the effect of recoil pressure and the formation of fusion zone. The computational results were found consistent with the single-track experimental results. Furthermore, for establishing the influence of melting mode on microstructural and mechanical properties, bulk samples with different melting modes were fabricated and characterized by comparing the microstructure, microhardness, nanohardness and tensile behavior. The experimental results showed that the stable keyhole mode results in higher hardness, higher elongation and finer cellular grains compared with the conduction mode.

Predicting Microstructure-Sensitive Fatigue-Crack Path in 3D Using a Machine Learning Framework

Abstract: The overarching aim of this paper is to explore the use of machine learning (ML) to predict the microstructure-sensitive evolution of a three-dimensional (3D) crack surface in a polycrystalline alloy. A convolutional neural network (CNN)-based methodology is developed to establish spatial relationships between micromechanical/microstructural features in a cyclically loaded, uncracked microstructure and the 3D crack path, the latter quantified by the vertical deviation (i.e., z-offset) of the crack along a specified axis. The proposed methodology consists of (i) a feature selection and reduction scheme to identify a lower-dimensional representation of the experimentally measured microstructure and computed micromechanical fields, which allows for computational feasibility in predicting the z-offsets; (ii) a CNN model to compute the z-offset as a function of the local, lower-dimensional feature data; and (iii) a radial basis function smoothing spline to ensure spatial continuity between the independently predicted z-offsets. The proposed CNN-based methodology is shown to improve on the accuracies obtained using existing ML models such as XGBoost and to provide a definitive way of quantifying model uncertainty associated with CNN predictions. To further investigate the applicability of ML models, multiple prediction strategies with which to deploy ML algorithms are proposed and the relative performance of ML algorithms corresponding to each prediction strategy are analyzed. The presented work thus provides a framework to find an encoded representation of 3D microstructure and micromechanical data and develop methods to predict microstructure-sensitive crack evolution based on this encoded representation, while quantifying associated prediction uncertainties.

Integrated Simulation Framework for Additively Manufactured Ti-6Al-4V: Melt Pool Dynamics, Microstructure, Solid-State Phase Transformation, and Microelastic Response

Abstract: To accelerate the establishment of fundamental understanding of the additive manufacturing (AM) process and its influence on microstructural evolution and related properties, we develop a multiphysics and multiscale modeling framework that integrates: (1) a high-fidelity powder-scale three-dimensional simulation of transient heat transfer and melt flow dynamics, (2) cellular automaton simulation of solidification grain structure and texture, (3) phase-field modeling of precipitation and dissolution of second-phase precipitate during repeated thermal cycles, and (4) microstructure-based micro- and mesoscopic elastic response calculation. Using Ti-6Al-4V as a model system, we demonstrate the application of the integrated framework to simulate complex microstructure evolution during a single-track laser powder bed fusion process and the associated mechanical response. Our modeling framework successfully captures the solidification β grain structure as a function of laser power and scanning speed, α precipitation upon subsequent cooling with different rates, and elastic response of the resulting (α + β) two-phase microstructure. The key features of solidification and second-phase precipitate microstructures, and their dependence on processing parameters, agree well with existing experimental observations. The established modeling framework is generally applicable to other metallic materials fabricated by AM.

Review of Recent Advances in Applications of Vapor-Phase Material Infiltration Based on Atomic Layer Deposition

Abstract: Polymer–inorganic hybrid nanocomposites exhibit enhanced material properties, combining the advantages of both their organic and inorganic subcomponents. Extensive research is being carried out to functionalize polymers towards various improved physicochemical characteristics such as electrical, optical, and mechanical properties for various applications. Vapor-phase material infiltration is an emerging hybridization route, derived from atomic layer deposition, which facilitates uniform incorporation of inorganic entities into a polymer matrix, leading to novel applications in fields such as microelectronics, energy storage, smart coatings, and smart fabrics. In this article, recent advances in employing vapor-phase material infiltration as a hybridization and nanopatterning technique for various application avenues are reviewed.

Numerical Simulation of Steel and Argon Gas Two-Phase Flow in Continuous Casting Using LES + VOF + DPM Model

Abstract: A coupled three-dimensional model, including Large Eddy Simulation model, Lagrangian Discrete Phase Model and VOF multiphase model was developed to investigate the transient two-phase flow and bubble distribution in continuous casting strand. A two-way coupling model including the effect of the drag force, lift force, virtual mass force and pressure gradient force was adopted. The lift force was added via user defined function. A Rosin–Rammler bubble size distribution base on the water model was employed. The results show that the effect of the lift force cannot be ignored during the calculation of the steel and argon gas two-phase flow. Only the bubbles smaller than 2 mm would be brought to near the narrow face. With the increase of the argon flow rate, the transformation of the flow pattern from the double roll to complex flow and single roll was successfully predicted.

Piassava Fiber as an Epoxy Matrix Composite Reinforcement for Ballistic Armor Applications

Abstract: The ballistic performance of piassava fiber-reinforced epoxy matrix composites was evaluated as an intermediate layer in multilayered armor systems (MASs). The composites were produced varying the volumetric fractions of piassava fibers, in a range of 10–50 vol.%, embedded in DGEBA/TETA as the epoxy matrix. These composites were adhesive bonded to a MAS composed of a frontal Al2O3 ceramic tile and an aluminum sheet alloy as the third layer. Ballistic tests were conducted using 7.62-mm-high velocity ammunition. The evaluation of the ballistic performance of the system was measured by the depth of penetration caused in a clay witness, which simulates the consistency of the human body, in accordance to some requirements of the NIJ standard 0101.06. The fractured materials were analyzed after the ballistic tests by scanning electron microscopy. The ballistic results showed that MASs using piassava fiber composites as a second layer are within the depth of penetration bounds to be considered as an efficient protection. This indicates that piassava fiber, a green material, is a promising material to be used in composites for ballistic armor applications.

Atomistic Study of the Effect of Magnesium Dopants on the Strength of Nanocrystalline Aluminum

Abstract: Atomistic simulations have been used to study the deformation mechanisms of nanocrystalline pure Al and Al-Mg binary alloys. Voronoi tessellation was used to fully create a three-dimensional polycrystalline model with a grain size of 10 nm, while hybrid Monte Carlo and molecular dynamic simulations were used to achieve both mechanical and chemical equilibriums in nanocrystalline Al-5 at.%Mg. The results of tensile tests show an improved strength, including the yield strength and ultimate strength, through doping 5 at.%Mg into nanocrystalline aluminum. The results of atomic structures clearly reveal the multiple strengthening mechanisms related to doping in Al-Mg alloys. At the early deformation stage, up to an applied strain of 0.2, the strengthening mechanism of the dopants exhibits as dopant pinning grain boundary (GB) migration. However, at the late deformation stage, which is close to failure of nanocrystalline materials, dopants can prohibit the initiation of intergranular cracks and also impede propagation of existing cracks along the GBs, thus improving the flow stress of Al-Mg alloys.

Effect of Oleic Acid Coating of Iron Oxide Nanoparticles on Properties of Magnetic Polyamide-6 Nanocomposite

Abstract: This work reports the development and testing of a magnetic polymer (Polyamide 6, PA6) nanocomposite capable of melting when exposed to an external magnetic field. Addition of high concentrations of iron oxide nanoparticles (NPs) can induce quick melting but is detrimental to the mechanical properties of the polymer. To reduce the amount of NPs required for achieving efficient melting, they should be well dispersed in the polymer. In this study, the oleic acid loading on the surfaces of the NPs was varied to study the effect of variations in coatings on the dispersion in the polymer and on the polymer melting time. The NPs functionalized with oleic acid were added to melted monomer e-caprolactam and polymerized using ring-opening polymerization. The resulting PA6 nanocomposite was characterized by Fourier-transform infrared spectroscopy, differential scanning calorimetry, x-ray diffraction and transmission electron microscopy. The results confirmed that the PA6 nanocomposite showed a decrease of 8–10% in its glass-transition temperature compared to commercial PA6. The crystallinity of the synthesized samples were found to vary between 42% and 57%. The 55 wt.% oleic acid-loaded NPs were found to disperse most efficiently in the PA6 matrix; however, some large agglomerates were formed due to excessive oleic acid. Therefore, the 22 wt.% oleic acid coating showed overall superior dispersion. Additionally, the magnetic induction response was tested by observing a melt-characteristic of the magnetic polymer composite using a model set-up. Oleic acid concentration is found to affect the dispersion, melting time and crystallinity of the nanocomposite.

Artificial Intelligence Predicts Body-Centered-Cubic and Face-Centered-Cubic Phases in High-Entropy Alloys

Abstract: For the first time, an artificial intelligence approach, the adaptive neuro fuzzy interface system (ANFIS), has been used for phase predictions in high-entropy alloys. The phase predictions were carried out using two different approaches. The first one was constructed using the composition of elements as the input parameters. The second one was constructed using six parameters, which are found to be crucial in the formation of these alloys. The accuracy of these models was verified using a testing dataset and was found to be 84.21% and 80%, respectively. The discussion demonstrates the application of ANFIS for designing these alloys.