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Surface Pourbaix diagrams are critical to understanding the stability of nanomaterials in electrochemical environments. Their construction based on density functional theory is, however, prohibitively expensive for real-scale systems, such as several nanometer-size nanoparticles (NPs). Herein, with the aim of accelerating the accurate prediction of adsorption energies, we developed a bond-type embedded crystal graph convolutional neural network (BE-CGCNN) model in which four bonding types were treated differently. Owing to the enhanced accuracy of the bond-type embedding approach, we demonstrate the construction of reliable Pourbaix diagrams for very large-size NPs involving up to 6525 atoms (approximately 4.8 nm in diameter), which enables the exploration of electrochemical stability over various NP sizes and shapes. BE-CGCNN-based Pourbaix diagrams well reproduce the experimental observations with increasing NP size. This work suggests a method for accelerated Pourbaix diagram construction for real-scale and arbitrarily shaped NPs, which would significantly open up an avenue for electrochemical stability studies. Surface Pourbaix diagrams are critical to understanding the stability of nanomaterials. Here, the authors develop a bond-type embedded crystal graph convolutional neural network model and construct reliable Pourbaix diagrams for real-scale nanoparticles. [ABSTRACT FROM AUTHOR]

In vehicles with driving assistance systems, the responsibility of driving still lies with the driver. Therefore, active safety systems follow a design principle of avoiding intervention as long as possible. Decision making using this principle requires collision avoidance with surrounding objects during the evasive maneuvering of an ego vehicle. However, general decision-making methods for collision avoidance focus on preventing collisions with objects in front of the subject vehicle; the risk of collision with the following vehicle caused by emergency braking is not considered. This paper presents decision-making methods for such collision avoidance systems, wherein emergency braking and steering are considered as collision avoidance maneuvers. The risk of collision is predicted based on the braking model of a normal driver and several emergency braking strategies are designed to avoid collisions. A within-lane steering avoidance method to improve avoidance performance in small overlap collision scenarios and a general avoidance method of steering to change lanes are designed. Collisions with surrounding objects can be avoided using the designed evasive maneuvers; further, maneuvers that can be implemented at the last moment are determined. The results of computer simulations indicate an improved collision avoidance performance using the proposed methods. [ABSTRACT FROM AUTHOR]

Powder metallurgy (P/M) has been widely used in automobile, home appliances, and electronic devices, but its uses are very limited due to the low relative density of 85 to 95 pct. The Fe–Ni–B–C alloy system can mitigate the aforementioned issues by the liquid phase sintering, which results in a nearly full densification. However, the boron-containing alloys produced the brittle eutectic phases [Fe3(C, B) and Fe2B] along the grain boundaries, which are detrimental to the mechanical properties. The main objective of this study is to improve the ductility of boron-containing alloys through the microstructure modification. For this, the volume fraction of solidified phase was optimized by controlling the composition, and the coarsening of solidified α-Fe particles into the pearlite matrix was induced by a post annealing, which reduces the continuous network of eutectic phases and increased the grain continuity. In addition, the effect of microstructure modification on the mechanical properties of Fe–B–C and Fe–Ni–B–C alloys was comparatively investigated. As a result of microstructure modification, the post-annealed Fe–1Ni–0.4B–0.8C alloy exhibited a high elongation to failure of 5.2 pct. [ABSTRACT FROM AUTHOR]

Developing highly efficient electrochemical catalysts for carbon dioxide reduction reaction (CO2RR) provides a solution to battle global warming issues resulting from ever-increasing carbon footprint due to human activities. Copper (Cu) is known for its efficiency in CO2RR towards value-added hydrocarbons; hence its unique structural properties along with various Cu alloys have been extensively explored in the past decade. Here, we demonstrate a two-step approach to achieve intimate atomic Cu-Ag interfaces on the surface of Cu nanowires, which show greatly improved CO2RR selectivity towards methane (CH4). The specially designed Cu-Ag interfaces showed an impressive maximum Faradaic efficiency (FE) of 72% towards CH4 production at −1.17 V (vs. reversible hydrogen electrode (RHE)). [ABSTRACT FROM AUTHOR]

Within first-principles density functional theory (DFT) frameworks, it is challenging to predict the electronic structures of nanoparticles (NPs) accurately but fast. Herein, a machine-learning architecture is proposed to rapidly but reasonably predict electronic density of states (DOS) patterns of metallic NPs via a combination of principal component analysis (PCA) and the crystal graph convolutional neural network (CGCNN). With the PCA, a mathematically high-dimensional DOS image can be converted to a low-dimensional vector. The CGCNN plays a key role in reflecting the effects of local atomic structures on the DOS patterns of NPs with only a few of material features that are easily extracted from a periodic table. The PCA-CGCNN model is applicable for all pure and bimetallic NPs, in which a handful DOS training sets that are easily obtained with the typical DFT method are considered. The PCA-CGCNN model predicts the R2 value to be 0.85 or higher for Au pure NPs and 0.77 or higher for Au@Pt core@shell bimetallic NPs, respectively, in which the values are for the test sets. Although the PCA-CGCNN method showed a small loss of accuracy when compared with DFT calculations, the prediction time takes just ~ 160 s irrespective of the NP size in contrast to DFT method, for example, 13,000 times faster than the DFT method for Pt147. Our approach not only can be immediately applied to predict electronic structures of actual nanometer scaled NPs to be experimentally synthesized, but also be used to explore correlations between atomic structures and other spectrum image data of the materials (e.g., X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy). [ABSTRACT FROM AUTHOR]

Globally, safety has become an increasingly important issue in the automotive industry. In an attempt to reduce traffic fatalities, UNECE launched a new EU Road Safety Program which aims to decrease the number of road deaths by half by 2020. AEB (Autonomous Emergency Braking) is a very effective active safety system intended to reduce fatalities. This study involves the design of a multi-sensor data fusion strategy and decision-making algorithm for AEB pedestrian. Possible collision avoidance scenarios according to the EuroNCAP protocol are analyzed and a robust pedestrian tracking strategy is proposed. The performance of the AEB system is enhanced by using a braking model to predict the collision avoidance time and by designing the system activation zone according to the relative speed and possible distance required to stop for pedestrians. The AEB activation threshold requires careful consideration. The test results confirm the advantages of the proposed algorithm, the performance of which is described in this paper. [ABSTRACT FROM AUTHOR]

Lowering the sintering temperature of nanoparticles in the electrode deposition process holds both academic and industrial interest because of the potential applications of such electrodes in polymer devices and flexible electronics. In addition, achieving uniform electrode formation after ligand exchange is equally important as lowering the sintering temperature. Here, we report a simple chemical treatment by the addition of ligand-exchanging interfaces to lower the sintering temperature; we also determine the optimum extent of ligand exchange for crack-free electrode formation. First, we investigated the structural change of Ag thin films with respect to the concentration of acrylic acid (AA) solutions. Second, we used thermal analysis to evaluate the effects of changes in the sintering temperature. We observed that the resulting conductivity of the Ag patterns was only one order of magnitude lower than that of bulk Ag when the patterns were sintered at 150 °C. The simple chemical treatment developed in this work for solution-processed Ag electrode formation can be adopted for flexible electronics, which would eliminate the need for vacuum and high-temperature processes. [ABSTRACT FROM AUTHOR]

The thermal decomposition synthesis of long copper nanowires (CuNWs) was achieved by controlling the synthesis parameters. A detailed study was performed to determine the effect of the molar ratio of copper chloride to nickel acetylacetonate, temperature, and stirring rate on the final shape of the products. Transparent electrodes (TEs) were fabricated by wet treatment with acetic acid (AA), without using a sintering process. The low oxidation stability and high surface roughness are the main disadvantages of the CuNW TEs, which limit their applications. In order to overcome these issues, we prepared CuNW/polymer composite TEs by partial embedding of the CuNWs into poly(methyl methacrylate) (PMMA) on poly(ethylene terephthalate) (PET) substrates. The CuNW/PMMA composite TEs exhibit excellent optoelectronic performance (91.3% at 100.7 Ω/sq), low surface roughness (4.6 nm in height), and good mechanical and chemical stability as compared with CuNW TEs. On the basis of these properties, we believe that CuNW-based composite TEs could serve as low-cost materials for a wide range of new optoelectronic devices. [ABSTRACT FROM AUTHOR]

Sn whiskers are becoming a serious reliability issue in Pb-free electronic packaging applications. Sn whiskers are also observed in connector parts of electronics as well as on electroplated surface finishes. Sn whiskers found in connector parts are known to behave differently from the typical Sn whiskers reported on electroplated Sn surfaces. In this study, Sn whiskers on plastically deformed Sn-rich films were investigated to understand their growth behavior to establish mitigation strategies for Sn-rich films used in connectors. Therefore, a microhardness indentation technique was applied to plastically deform electroplated matte Sn samples, followed by temperature/humidity (T/H) testing (30°C, dry air). Each sample was examined by scanning electron microscopy at regular time intervals up to 4000 h. Various morphologies of Sn whiskers on plastically deformed matte Sn films were observed, and their growth statistics and kinetics are analyzed in terms of the plating conditions and plastic deformation by using transmission electron microscopy, x-ray diffraction, and the focused ion-beam technique. Sn whiskers were observed on plastically deformed regions of thin (2- μm) and thick (10- μm) matte Sn films, regardless of the current density applied. Plastic deformation was found to promote whisker formation on matte Sn films. A high density of dislocations and newly formed fine Sn subgrains were observed in deformed grains. In addition, the recrystallized grains and CuSn intermetallic compound grew further with increasing time. Finally, a growth mechanism for deformation-induced Sn whiskers is proposed based on a recrystallization model combined with the formation of CuSn. [ABSTRACT FROM AUTHOR]

Backside illumination complementary metal oxide semiconductor image sensors (BSI CISs) represent an advanced technology that produces high-quality image sensors. However, BSI CISs are limited by high dark signals and noise signals on the backside. To address these problems, backside junctions are commonly used. High-dose backside junctions effectively reduce dark signals and noise signals. The depth of the implantation profile is a key factor in determining the junction depth. A laser thermal annealing process is conducted only near the surface to the activation, and thus broader doping profiles are limitations to be activation of dopants. Changing the dopant from B to BF can decrease the implant projected range. However, there are abnormal activation rates for BF in applications involving laser thermal annealing processes for shallow junctions. Although the need for BF is increasing, a mechanism for its slow activation and low activation rates has not yet been confirmed. Here, we identify the mechanism by which BF undergoes low activation after a melting threshold temperature and explain why this phenomenon occurs. In addition, we confirm a condition that provides high activation rates of BF and show the reduction of dark signals and noise signals at the high density BSI CISs. [ABSTRACT FROM AUTHOR]

Sn whiskers are becoming a serious reliability issue in Pb-free electronic packaging applications. Among the numerous Sn whisker mitigation strategies, minor alloying additions to Sn have been proven effective. In this study, several commercial Sn and Sn-Ag baths of low-whisker formulations are evaluated to develop optimum mitigation strategies for electroplated Sn and Sn-Ag. The effects of plating variables and storage conditions, including plating thickness and current density, on Sn whisker growth are investigated for matte Sn, matte Sn-Ag, and bright Sn-Ag electroplated on a Si substrate. Two different storage conditions are applied: an ambient condition (30°C, dry air) and a high-temperature/high-humidity condition (55°C, 85% relative humidity). Scanning electron microscopy is employed to record the Sn whisker growth history of each sample up to 4000 h. Transmission electron microscopy, x-ray diffraction, and focused ion beam techniques are used to understand the microstructure, the formation of intermetallic compounds (IMCs), oxidation, the Sn whisker growth mechanism, and other features. In this study, it is found that whiskers are observed only under ambient conditions for both thin and thick samples regardless of the current density variations for matte Sn. However, whiskers are not observed on Sn-Ag-plated surfaces due to the equiaxed grains and fine AgSn IMCs located at grain boundaries. In addition, Sn whiskers can be suppressed under the high-temperature/high-humidity conditions due to the random growth of IMCs and the formation of thick oxide layers. [ABSTRACT FROM AUTHOR]

To enhance the reliability of Pb-free solders in high temperature and high humidity conditions, the minor alloying elements of Be and Co are investigated in terms of the growth of Sn whiskers and various properties of Sn-based Pb-free solders. Sn whisker growth is suppressed by adding up to 0.02 wt% Be to Sn-based solders. Adding Be and Co can effectively reduce the undercooling of Sn–1.0Ag–0.5Cu (wt%) solders. And the microstructures of Sn–1.0Ag–0.5Cu–0.02Be solders are similar to those of Sn–1.0Ag–0.5Cu. Furthermore, adding Co to solders increases the microhardness number as a result of the solid solution hardening. Adding Be causes no changes in the morphology or thickness of Cu6Sn5 at the Cu/OSP (organic solderability preservative) under bump metallurgy interface. However, the scallop-like Cu6Sn5 microstructure changes to a flat (Cu,Co)6Sn5 microstructure when 0.05 wt% of Co is added to Sn–1.0Ag–0.5Cu–0.02Be solders. [ABSTRACT FROM PUBLISHER]

The role of adjunctive corticosteroids remains controversial in meningitis by penicillin-resistant pneumococci. We determined the effect of adjunctive corticosteroids in adults with pneumococcal meningitis in a region with a high rate of penicillin resistance. A multicenter, retrospective cohort study was conducted between 1998 and 2008 in Korea. The mortality and neurological sequelae were evaluated. Among 93 patients with pneumococcal meningitis, adequate adjunctive corticosteroids were given in 45.2%. The penicillin resistance rate was 60.0%, and 42.1% were nonsusceptible to ceftriaxone. The 30-day mortality rates in the group receiving adequate corticosteroid therapy, the group in which corticosteroid was not given, and that inadequately given were 24.3, 31.6, and 27.3%, respectively, and there was no difference between the groups. The rates of development of neurological sequelae were 34.3, 33.3, and 43.5%, respectively. Multivariate analysis showed that adequate corticosteroids did not reduce mortality (HR 0.773, 95% CI 0.293-2.040) and neurologic sequelae (HR 0.604, CI 0.262-1.393). Propensity-adjusted analysis showed that adjunctive corticosteroid was not associated with time to death (HR 0.949, CI 0.374-2.408), however, a decreasing tendency was shown in neurologic sequelae in the adequate corticosteroid group (HR 0.479, CI 0.207-1.110). In conclusion, adjunctive corticosteroids did not affect mortality in adults with pneumococcal meningitis in a region with high rates of resistance to penicillin and ceftriaxone; however, the patients receiving adequate corticosteroid therapy tended to develop neurologic sequelae less frequently. [ABSTRACT FROM AUTHOR]

To synthesize low-cost, highly conductive metal nanoparticles for inkjet printing materials, we synthesized Sn-Ag bimetallic nanoparticles using a polyol process with poly(vinyl pyrrolidone). Because a surface oxidation layer forms on Sn nanoparticles, various compositions of Sn- xAg [ x = 0, 20, 40, 60, 80, 100 (wt%)] nanoparticles were synthesized and characterized for the purpose of removing the β-Sn phase. The results of XPS, TEM, and XRD analyses confirm that the formation of a bimetallic phase, such as AgSn or AgSn, hinders the β-Sn phase and, consequently, leads to the removal of the surface oxidation layer. To measure the sheet resistance of various compositions of Sn-Ag nanoparticles, we made the ink that contains Sn-Ag by dispersing 10 wt% of Sn-Ag nanoparticles in methanol. The sheet resistance is decreased by the conductive Sn-Ag phases, such as the fcc, AgSn, and AgSn phases, but sharply increased by the low-conductive Sn nanoparticles and the surface oxidation layer on the Sn nanoparticles. The sheet resistance results confirm that 80Ag20Sn and 60Ag40Sn bimetallic nanoparticles are suitable candidates for inkjet printing materials. [ABSTRACT FROM AUTHOR]

Various-sized Ag nanoparticles capped with oleylamine were synthesized by means of a thermal decomposition process for low-temperature electronic devices. The Ag nanoparticles, which had diameter of 5.1 nm to 12.2 nm, were synthesized in incubation and ripening stages related to nucleation and growth. After the Ag nanoparticles were made into ink with a proper solvent, inkjet printing and thermal sintering methods were used to form a metal thin film with thickness of 100 nm. A type of thermal sintering related to percolation transformation and surface sintering was conducted at a temperature much lower than the melting point of bulk Ag. The electrical resistivity was examined with the aid of a four-point probe system and compared with the resistivity of bulk Ag, showing that the Ag film had much higher resistivity than bulk Ag. To improve the electrical stability and properties, we applied hexamethyldisilazane (HMDS) surface treatment to the substrate and dipped the as-deposited films into methanol. Both treatments helped to diminish and stabilize the resistivity of the printed conductive films. [ABSTRACT FROM AUTHOR]

In the electronic packaging field, the Sn-Zn alloy system has been recommended as a high-temperature Pb-free solder. There is a need for thermodynamic data on the Sn-Ni-Zn ternary system. Such data would serve as a basis for understanding the interfacial reaction between Sn-Zn high-temperature solder and Ni substrates and for thermodynamically evaluating the proper composition level of Ni and Zn in Sn-based solder. This study has investigated the phase equilibria of the Sn-Ni-Zn ternary system at 800°C, 500°C, and 200°C (for Ni composition of less than 60 at.%). Scanning electron microscopy (SEM), x-ray diffraction (XRD), and electron probe microanalysis (EPMA) were used to identify the equilibrium phases. On the basis of the experimental data and thermodynamic parameters, the isothermal sections of the Sn-Ni-Zn ternary system have been described, considering the ternary solubility in the binary phases and newfound ternary phases τ1 (SnNiZn) and τ2 (SnNiZn). [ABSTRACT FROM AUTHOR]

The electromigration (EM) performance of Pb-free solder joints is investigated in terms of solder composition (Sn-0.5Cu vs. Sn-1.8Ag) and joining path to Cu vs. Ni(P) under bump metallization (UBM). In the double-sided joints of Ni(P)/solder/Cu, the micro-structure of solder joints and the interfacial intermetallic compound (IMC) layers are significantly affected by solder composition and joining path. The as-reflowed microstructure of Sn-0.5Cu joints consists of small columnar grains with thin IMC layers at both UBM interfaces, independent of the joining path, while Sn-1.8Ag joints have a few large grains of low-angle grain boundaries with thick IMC layers when joined first to Ni(P) UBM, but a few 60° twins with thin IMC layers when joined first to Cu UBM. The EM stressing under high current densities at 150°C reveals that Sn-1.8Ag joints have a superior lifetime compared to Sn-0.5Cu joints. In addition, the EM lifetime of Sn-1.8Ag joints reflowed first on Ni(P) UBM is the longest among four groups of the solder joints examined. [ABSTRACT FROM AUTHOR]

For enhanced wetting properties of Zn-doped solder alloys, this paper proposes Cu5Zn8-bearing solders. A mechanical alloying process with controlled milling time and rotational speed was used to successfully fabricate Cu5Zn8-bearing powders with a diameter of 50 μm to 70 μm. Their composition was identified by inductively coupled plasma atomic emission spectroscopy. After the powders were made into a paste with a rosin-activated type of flux, the wetting angles of the Cu5Zn8-bearing paste solders on a Cu substrate were compared with the wetting angles of bulk solder alloys with the same amount of Cu and Zn alloying elements. The reason for the enhanced wetting properties of Cu5Zn8-bearing solders is explained by thermodynamic calculations and differential scanning calorimetry experiments. In addition, the interfacial reactions and the shear strength with Cu substrates are also discussed. [ABSTRACT FROM AUTHOR]

The effects of the addition of Zn to Sn-0.7Cu solders are investigated. The study is focused on the interfacial reactions, microstructures, and mechanical properties after reaction with Ni-P under bump metallurgies (UBMs). The Zn contents in Sn-0.7Cu- xZn are varied as 0.2, 0.4, and 0.8 (in wt.% unless otherwise specified). In the reaction with Ni-P UBM during thermal aging at 150°C for 1000 h, (Cu,Ni)6Sn5 intermetallic compounds (IMCs) are formed at the Sn-0.7Cu/UBM interface, whereas Zn is incorporated into IMCs to form (Cu,Ni,Zn)6Sn5 in the Zn-doped solders. As the Zn content increases, the interfacial IMC thickness is reduced. A total reduction of about 40% in IMC thickness was observed for the 0.8% Zn-doped Sn-Cu. The same IMC particles are also observed in the matrix of each solder. In Sn-0.7Cu, (Cu,Ni)6Sn5 particles are coarsened during aging, while (Cu,Ni,Zn)6Sn5 particles in the Zn-added solders are less coarsened and remain much smaller than (Cu,Ni)6Sn5. The growth rate of (Cu,Ni)6Sn5 during thermal aging is significantly suppressed by the addition of Zn. Consequently, after reaction with Ni-P UBM, the Zn-doped solders exhibit a thermally stable microstructure as measured by hardness and shear strength. [ABSTRACT FROM AUTHOR]

The effects of Co addition on the undercooling, microstructure, and microhardness of Sn-3.5Ag solder (all in wt.% unless specified otherwise) and interfacial reactions with Ni-P under bump metallurgy (UBM) are investigated when the Co content varies from 0.01 wt.% to 0.7 wt.%. When more than 0.02 wt.% Co was added to Sn-3.5Ag solder, the undercooling of the Sn-3.5Ag solder was significantly reduced and the microstructures coarsened with the increased eutectic region. In addition, the hardness value increased as the Co content in Sn-3.5Ag increased. In the interfacial reactions with Ni-P UBM, a spalling phenomenon of intermetallic compounds (IMCs) during reflow was prevented in the Sn-3.5Ag- xCo ( x ≥ 0.02 wt.%). However, when more than 0.05 wt.% Co was added to Sn-3.5Ag, the IMC morphology changed from a bulky shape to a plate-like shape. The bulky IMCs were Ni3Sn4 and the plate-like IMCs were Sn-Ni-Co ternary compounds. The main issues discussed include the relations between the morphological changes and the IMC phases, the effects of Co addition on the prevention of IMC spalling, and the optimum level of Co addition. [ABSTRACT FROM AUTHOR]

The transition in morphology of Ni3Sn4 grains that formed at the interface between liquid Sn-3.5Ag (numbers are in wt.% unless specified otherwise) solder and Ni substrate has been observed at 250–650°C. The morphological transition of Ni3Sn4 is due to the decrease of entropy of formation of the Ni3Sn4 phase and has been explained well by the change of Jackson’s parameter with temperature. According to the variation of solder joint strength with temperature, it decreased rapidly between 350°C and 450°C, where the thickness of the Ni3Sn4 intermetallic compound (IMC) layer was around 6.5 µm. However, the solder joint strength decreased slowly with an increase of soldering time without a significant drop, although the thickness of the IMC was larger than 6.5 µm. The notable drop of solder joint strength and the fracture mode transition with increase of soldering temperature appears to come from excessive lateral growth of IMC grains between 350°C and 450°C. [ABSTRACT FROM AUTHOR]

Molecular dynamics (MD) simulation was used to investigate the closing mechanism of zigzag single-walled carbon nanotubes (SWCNT) at an experimental are-discharge temperature of 3000 K. The closing mechanism was studied with a variation in the diameter and length of the SWCNT. The (10,0) SWCNT with a diameter of 0.78 nm and a length of 2.13 nm showed a saddle-shaped cap that was caused by a heptagon-octagon pair and a nonagon. When its length was increased three times in, the closing process was observed faster and the closed structure maintained a similar saddle shape, while this resulted from double heptagon-octagon pairs. In the case of (18,0) SWCNT with a diameter of 1.404 nm, a zipper-like closing mechanism was found and a flat cap was attained. It was also revealed that the longer the length of the (18,0) SWCNT, the slower is the closing process, contrary to the case of (10,0) SWCNT. [ABSTRACT FROM AUTHOR]

To design and develop high-temperature solder alloys, the thermodynamic calculations of phase equilibria have been performed on the binary Au-Sb and ternary Au-Sb-Sn systems over the entire composition range. The Gibbs free energy of individual phases has been approximated using a subregular-solution model, and the thermodynamic parameters for each phase have been evaluated using available experimental information on phase boundaries and other related thermodynamic properties. The calculated phase diagrams and thermodynamic quantities of the Au-Sb binary system show good agreement with experimental data, and the liquidus projection and the vertical sections in the Au-Sb-Sn ternary system are well reproduced using assessed thermodynamic parameters derived in this work. [ABSTRACT FROM AUTHOR]

The formation and the growth of the intermetallic compound (IMC, hereafter) at the interface between the Sn-3.5Ag (numbers are all in wt.% unless otherwise specified) solder alloy and the Cu substrate were investigated. Solder joints were prepared by changing the soldering time at 250°C from 30 sec to 10 h and the morphological change of IMCs with soldering time was observed. It resulted from the competition between the growth of IMC and the dissolution of Cu from the substrate and IMCs. They were further aged at 130°C up to 800 h. During aging, the columnar morphology of IMCs changed to a more planar type while the scallop morphology remained unchanged. It was observed that the growth behavior of IMCs was closely related with the initial soldering condition. [ABSTRACT FROM AUTHOR]

Good interfacial bonding between the matrix and the second phase is very important and may be guaranteed by the low lattice mismatch between them. In this study, trialuminide intermetallics such as tetragonal D022 and DO23 with A13M (M=Ti, V, Zr) or cubic Ll2 with Al66Mn9(Ti, Zr)25 were chosen as second phases to be dispersed on the basis of MEAM (Modified Embedded Atom Method) simulations. Specific compositions were determined based on thermodynamic calculations. Alloys were mechanically alloyed using Al powders and intermetallic powders that were separately fabricated. Hot pressed samples under vacuum were analyzed in terms of phase formation during heat treatment and were tested in compression at room temperature and 693K. Specimens showed enhanced strength with a yield strength of 800-920MPa at room temperature and 190-260MPa at 693K. Observation of no phase change during heat treatment indicated high thermal stability of the microstructure. [ABSTRACT FROM AUTHOR]

The binary eutectic Sn-3.5wt.%Ag alloy was soldered on the Ni/Cu plate at 250°C, the thickness of the Ni layer changing from 0 through 2 and 4 µm to infinity, and soldering time changing from 30 to 120 s at intervals of 30 s. The infinite thickness was equivalent to the bare Ni plate. The morphology, composition and phase identification of the intermetallic compound (IMC, hereafter) formed at the interface were examined. Depending on the initial Ni thickness, different IMC phases were observed at 30 s: Cu6Sn5 on bare Cu, metastable NiSn3 + Ni3Sn4 on Ni(2 µm)/Cu, Ni3Sn4 on Ni(4 µm)/Cu, and Ni3Sn + Ni3Sn4 on bare Ni. With increased soldering time, a Cu-Sn-based η-(Cu6Sn5)1−xNix phase formed under the pre-formed Ni-Sn IMC layer both at 60 s in the Ni(2 µm)/Cu plate and at 90 s in the Ni(4 µm)/Cu plate. The two-layer IMC pattern remained thereafter. The wetting behavior of each joint was different and it may have resulted from the type of IMC formed on each plate. The thickness of the protective Ni layer over the Cu plate was found to be an important factor in determining the interfacial reaction and the wetting behavior. [ABSTRACT FROM AUTHOR]

A thermodynamic method to predict the intermetallic compound which forms first at the substrate/solder interface during the soldering process has been suggested through calculations of metastable phase equilibria between the substrate and the liquid solder and by comparison of the driving forces of formation of individual intermetallic compound phases. It has been applied to the interfacial reaction between Cu substrate and Sn-Ag, Sn-Zn eutectic solders. The prediction from thermodynamic calculations was in good agreement with observed experimental results. The solid-state growth behavior of compound phases formed at the interface of Cu/Sn-Zn and Cu/Sn-Ag eutectic solder joints was explained and a schematic diffusion path suggested through calculated ternary phase diagrams. [ABSTRACT FROM AUTHOR]

This article presents an investigation of the phase equilibria in the Sn-Bi-In ternary alloy system, performed both by theoretical and experimental methods. Following the regular solution model and a standard thermochemical calculation, a theoretical evaluation of the phase equilibrium in the entire ternary system is conducted. The thermodynamic parameters required for the calculation are initially obtained by fitting the model to existing data available from prior studies. The theoretical results are then validated and further improved by experimental work in which alloys with several critical compositions were chosen and examined. In the experimental work, differential scanning calorimetry (DSC), X-ray diffraction (XRD), and energy-dispersive X-ray (EDX) spectroscopy were jointly used to identify the transition temperatures and the phases in the microstructure. The resulting phase diagram agrees well both with the existing data and with the data from the current experiments. However, different from previous findings, this study finds a nonbinary nature of the Sn-BiIn and Sn-BiIn2 quasi-binaries and nine invariant reactions, one eutectic, six peritectic and two peritectoid. The phase-reaction scheme (Scheil diagram), the liquidus projection, and the phase diagram, covering entire compositional ranges, are established. [ABSTRACT FROM AUTHOR]

A model for the coarsening resistance of multicomponent carbides was used to study the effect of Mo and Cr on the coarsening kinetics of MC carbides in commercial AF1410 and experimental alloy steels. Experimental studies of coarsening behavior of the carbides in these steels have been made by using transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The measured coarsening rate constant agrees with model predictions within a factor of 2 to 3. The coarsening kinetics of MC carbides in these alloys is found to be controlled by the volume diffusion of alloying element M. A Cr-Mo alloy steel with the predicted optimum composition showed the slowest coarsening kinetics and highest hardness at long tempering times. [ABSTRACT FROM AUTHOR]

In high Co-Ni steels containing the strong carbide-forming elements Mo, Cr, and W, secondary hardening is accomplished by the precipitation of fine-scale MC alloy carbides. Thermodynamic stability and coarsening resistance of these carbides depend on the alloy content of these elements. A model for the MC coarsening kinetics in multicomponent alloys has been used to identify the optimum alloying addition for maximum coarsening resistance and as a basis for selection of four experimental alloy steels. Necessary information pertaining to the equilibrium in these steels was obtained using the Thermo-Calc software and database developed at the Royal Institute of Technology, Stockholm, Sweden. [ABSTRACT FROM AUTHOR]

The development of very high-strength levels in many alloy steels is achieved by a secondary hardening reaction. In high Co-Ni steels containing the strong carbide-forming elements Mo, Cr, and W, secondary hardening is accomplished by the precipitation of fine-scale MC alloy carbides. Coarsening resistance of the MC precipitates depends on the alloy content of these elements, and there should be an addition to the alloy of these carbide-forming elements which optimizes the MC coarsening resistance. Current Lifshitz-Slyozov-Wagner (LSW) theory cannot properly be used to describe, the coarsening behavior of multicomponent carbides, which involves concentrations and diffusivities of two or more solutes and nonspherical carbide morphologies. A model is introduced for the coarsening resistance of multicomponent carbides. This model treats the coarsening of shape-preserving particle and is applicable to rodlike particles. [ABSTRACT FROM AUTHOR]

Aging works of two melt-spun Al-2 at pct (Ti,V,Zr) alloys showed that metastable L1 Al(Ti,V,Zr) precipitates were dominant and did not transform to stable D0 ones: the average radius was 3 to 4 nm and the interparticle spacing was 10 to 30 nm at 698 K up to 400 hours. Coarsening kinetics was found to be very sluggish and was coincident with the low lattice mismatch. Due to the low coarsening rate and the high thermal stability of the precipitated phase, rapidly so-lidified Al-Ti-V-Zr systems show promise as base of high-strength Al alloys for high-temperature applications. [ABSTRACT FROM AUTHOR]

Manipulation of grain boundaries in polycrystalline perovskite is an essential consideration for both the optoelectronic properties and environmental stability of solar cells as the solution-processing of perovskite films inevitably introduces many defects at grain boundaries. Though small molecule-based additives have proven to be effective defect passivating agents, their high volatility and diffusivity cannot render perovskite films robust enough against harsh environments. Here we suggest design rules for effective molecules by considering their molecular structure. From these, we introduce a strategy to form macromolecular intermediate phases using long chain polymers, which leads to the formation of a polymer-perovskite composite cross-linker. The cross-linker functions to bridge the perovskite grains, minimizing grain-to-grain electrical decoupling and yielding excellent environmental stability against moisture, light, and heat, which has not been attainable with small molecule defect passivating agents. Consequently, all photovoltaic parameters are significantly enhanced in the solar cells and the devices also show excellent stability. Defective grain boundaries of polycrystalline perovskite films are one of the major causes of the instability of the solar cell devices. Here Han et al. choose a polymer with proper molecular structure to crosslink the perovskite grains to greatly improve the device stability. [ABSTRACT FROM AUTHOR]