Metallic Region Research Articles

A Hybrid Schottky–Ohmic Drain Contact for Thermally Stressed Beta‐Gallium Oxide Field‐Effect Transistors

Degradation of ohmic contacts on β‐Ga2O3 under thermal stress conditions is a severe issue that hinders its high‐temperature applicability. Herein, a hybrid Schottky–ohmic drain contact (HSD) is demonstrated in β‐Ga2O3 field‐effect transistors (FETs). It is compared with a conventional ohmic drain contact (OD) after extended thermal annealing. Pulsed drain bias measurement is conducted to investigate the trapping process at the interface of both drain contacts with the β‐Ga2O3 channel. Even with the extended Schottky metal region, the β‐Ga2O3 FET with the HSD contact exhibits similar contact and on‐resistance. Additionally, it shows field‐effect mobility higher than that of the OD contact device. Enhanced off‐state breakdown characteristics are achieved.

Evaluation of hardness and impact toughness of drawn arc stud weldments on different structural steel grades

The drawn arc stud welding (DASW) procedure is usually qualified by visual examinations and practical destructive tests of the joint according to international standards. An assessment of the material properties in specific weld zone regions is not requested under consideration of their limited areas or the general joint dimension although the press welding process implies a complex metallurgy. Nonetheless, there is a need of knowledge regarding the heterogeneous material properties in the weld zone, especially when welding on base materials with specified strength and toughness behavior that might be significantly diminished. In this study, the local strength and toughness properties in welded joints of non-alloyed steel studs (Ø20 mm) on plates of different generic structural steel grades are investigated by hardness test and Charpy impact testing. A non-alloyed normalized structural steel (nominal yield strength 355 MPa) and a thermomechanically rolled fine grain structural steel of same strength as well as a quenched and tempered structural steel with high nominal yield strength of 690 MPa were examined. In the weld metal region, relatively similar hardness and low impact energy were determined despite of the different base plate steel grades. The base plate heat-affected zones suffer a strong embrittlement due to the DASW thermocycle.

Corrosion fatigue crack growth in A7N01S−T5 aluminum alloy MIG welded joints

This paper studies the corrosion fatigue crack growth (CFCG) in 3.5 wt% NaCl solution of the local zones of A7N01S−T5 aluminum alloy metal inert gas (MIG) welded joints cut from high−speed train underframes after service lives of 1.8 million km. The results show that the base metal (BM) region exhibits the highest rate of CFCG compared to both the heat−affected zone (HAZ) and the weld metal (WM) zone. Crack features suggest that the corrosion fatigue failure mode of the BM is hydrogen−assisted propagation and that the failure mode for both the HAZ and WM is anodic dissolution. We calculate that the multi−site adsorption and substitution of Cl− on the surface of the passivation film can make the oxygen and aluminum atoms detach from the surface of the passivation film, causing its destruction and allowing the cracks to expand further. Hydrogen is more likely to accumulate and diffuse along the grain boundaries, reducing their strength and causing them to become the most likely orientation for crack propagation. This study provides the new insight into the specific CFCG mechanisms of each zone in aluminum alloy welded joints.

The evaluation on performance of narrow- gap welding thick steel plates under the influence of main welding parameters

This work presents the experimental results of narrow gap butt welding of steel plates with large thickness by using the Metal Active Gas (MAG) welding method.The typical defects are accompanied with this process such as the infusion in the side wall and the porosity due to the narrow gap which affect on the melting process. Thus, some publications noted the results of welding for the thickness up to 20−30 mm and the chamfer angle about 30° using GMAW/MIG, GTAW/TIG, SMAW and new development such as laser – arc hybrid, laser multi- pass technique, super -TIG welding etc. But the production requires the solution to save the costs by the reduction of time, labour and investment keeping the standard quality. That is the aim of this study. In order to improve the quality of weld joint and increase the productivity of the process, is it suggested to develop the innovative welding process, in which the welding voltage – Uw, the translational velocity of the tip – Vt, and rotational velocity of the tip – Vr, are changing. This helped to increase the thickness of steel plates up to 50 mm and the chamfer angle decreased at 15°, providing the satisfied quality of the weld. The micrography study serve as the preliminary proof of this hypothesis.
 The microstructures in 4 regions, such as the weld center zone, heat-affected zone (HAZ), parent metal region, and the boundary between the weld metal and the HAZ were examined. The microstructures of 13 positions from different experiments are investigated using the optical microscope (Axiovert 25).These experiments covered all specific points (node) locating accordingly to three layers from bottom to top of the weld joint . The findings proved the welding quality is similar in case of narrow gap but the chamfer angle is twice lower and the thickness is increased. The result of the study enhances the productivity due to saving the labour cost and the welding materials. It is recommended to consider the effect of other factors (such as cooling conditions, dwell time when the arc approaching the side walls) to optimize the weld quality. There is the huge volume of the heavy steel constructions with the thick steel construction and specific narrow gap in industry. The results of this study with the optimization and more deeper evaluation the influence of main parameters of welding process to eliminate the typical defects will be the valuable reco mmendation for the managers and engineers in the production of metallic constructions

Hybrid Silicon Substrate FinFET-Metal Insulator Metal (MIM) Memristor Based Sense Amplifier Design for the Non-Volatile SRAM Cell

Maintaining power consumption has become a critical hurdle in the manufacturing process as CMOS technologies continue to be downscaled. The longevity of portable gadgets is reduced as power usage increases. As a result, less-cost, high-density, less-power, and better-performance memory devices are in great demand in the electronics industry for a wide range of applications, including Internet of Things (IoT) and electronic devices like laptops and smartphones. All of the specifications for designing a non-volatile memory will benefit from the use of memristors. In addition to being non-volatile, memristive devices are also characterized by the high switching frequency, low wattage requirement, and compact size. Traditional transistors can be replaced by silicon substrate-based FinFETs, which are substantially more efficient in terms of area and power, to improve the design. As a result, the design of non-volatile SRAM cell in conjunction with silicon substrate-based FinFET and Metal Insulator Metal (MIM) based Memristor is proposed and compared to traditional SRAMs. The power consumption of the proposed hybrid design has outperformed the standard Silicon substrate FinFET design by 91.8% better. It has also been reported that the delay for the suggested design is actually quite a bit shorter, coming in at approximately 1.989 ps. The proposed architecture has been made significantly more practical for use as a low-power and high-speed memory system because of the incorporation of high-K insulation at the interface of metal regions. In addition, Monte Carlo (MC) simulations have been run for the reported 6T-SRAM designs in order to have a better understanding of the device stability.

Ultrasonic testing of butt joints in electrotechnical steel plates using Lamb waves

Using Lamb waves, the influence of the welding quality of thin steel sheets on the physical and mechanical properties of electrical steel has been studied. It is shown that Lamb waves excited in the zero symmetric mode are an effective source of information about the state of the material both in the welded joint of plates and in the region of the base metal not affected by thermal effects. Markers of quality of welded joints are determined. It has been established that the most informative parameters are the phase velocity of the Lamb wave and its amplitude. On the basis of velocity measurements, a macroscopic anisotropy of the acoustic properties of the material was found. It is assumed that the origin of this anisotropy is due to residual stresses that arise in the technological process of processing steel sheets. The results obtained are of interest for specialized quality control of butt welds in thin steel sheets.

Unexpected higher corrosion in the gas phase region of metals caused by calcium and magnesium ions compared to sodium ions.

In the marine environment, Na+ ions have been the focus of attention owing to their high content, which is one of the important factors causing marine corrosion. With reference to the content of macro ions in seawater, circular iron samples were semi-immersed in 0.04 M MgCl2 and 0.6 M NaCl solutions containing different proportions of ethanol. Unexpectedly, we observed more severe corrosion effects in the gas phase region and at the gas-liquid interface of metal samples semi-immersed in the MgCl2 solution. Although the concentration of the MgCl2 solution was only 1/15 of that of the NaCl solution, the iron corrosion induced by MgCl2 was significantly more severe than that caused by NaCl when the ethanol content was increased. Mg2+ ions outperform Na+ ions in metal gas phase corrosion. Especially in the oxygen content of the gas phase corrosion product, MgCl2 caused an increase by up to 52.7%, while NaCl only resulted in a 10.3% increase. Ethanol is normally regarded as a corrosion inhibitor and exists in the liquid phase. Interestingly, in the gas phase and at the gas-liquid interface, ethanol aggravated rather than reducing iron corrosion, particularly in the presence of Mg2+ ions. In addition, we observed that Ca2+ ions produced more severe corrosion effects.

Parametric study for the induced electric current of an electromagnetically driven flow

In this work, the electric scalar and the magnetic vector potential magnetohydrodynamic formulations are implemented in the COMSOL Multiphysics software for the simulation of an electrovortex flow in a cuboid vessel. The flow is generated by a Lorentz force produced by the interaction of a direct electric current, which is injected through two solid electrodes located on the top and bottom of the vessel and an external magnetic field generated by one or a pair of permanent magnets. A good comparison between numerical and experimental velocity profiles reported by the workgroup is observed. The induced electric current fields obtained from Ohm's and Ampere's laws are explored in the solid electrodes and liquid metal regions. A parametric study for the interaction parameter in the range of 1 ≤ N ≤ 50 is presented. For both formulations, the same induced electric current distributions were obtained. Interestingly, for a pair of magnets, the induced electric current distribution is symmetric and the penetration of its main component into the solid electrodes increases with N, whereas for one single magnet, the induced current is non-symmetric and its penetration is small. Results also indicate that depending on the MF there are zones, where the induced electric current is small and the velocity is high. For a pair of magnets, this behavior is observed close to the interface of the LM-solid electrodes. Tables 2, Figs 10, Refs 43.

Spatiotemporal dynamics of voltage-induced resistance transition in the double-exchange model

We present multi-scale dynamical simulations of voltage-induced insulator-to-metal transition in the double exchange model, a canonical example of itinerant magnet and correlated electron systems. By combining nonequilibrium Green's function method with large-scale Landau-Lifshitz-Gilbert dynamics, we show that the transition from an antiferromagnetic insulator to the low-resistance state is initiated by the nucleation of a thin ferromagnetic conducting layer at the anode. The metal-insulator interface separating the two phases is then driven toward the opposite electrode by the voltage stress, giving rise to a growing metallic region. We further show that the initial transformation kinetics is well described by the Kolmogorov-Avrami-Ishibashi model with an effective spatial-dimension that depends on the applied voltage. Implications of our findings for the resistive switching in colossal magnetoresistant materials are also discussed.

3D-TCAD benchmark of two-gate dual-doped Reconfigurable FETs on FDSOI28 technology

Through 3D-TCAD simulations this work aims to demonstrate the benefits of Reconfigurable FETs based on dual doping with respect to the Schottky junctions counterparts using the 28 nm FDSOI platform. These devices feature both N and P dopant species at source and drain to allow for electron and hole symmetrical currents instead of using mid-gap metallic regions. Quasi-static results reveals much larger currents thanks to the enhanced carrier injection with analogous capacitances, leading to faster logic circuits in mixed-mode simulations. Dynamic results also show lower energy-delay products making these devices more efficient and appealing to implement reprogrammable logic.

Heat Treatment of Multi-Material Additively Manufactured Maraging Steel and Co-Cr-Mo Alloy

The prospect of converting an entire assembly of parts with challenging geometry to a single part with sectional variation of properties has stimulated a growing interest in multi-material Additive Manufacturing (AM). Accordingly, the present work utilized a dual-metal Laser Powder Bed Fusion (LPBF) technique to manufacture a multi-material component, consisting of Co-Cr-Mo alloy (MP1) and maraging steel (MS1) in a single manufacturing process. The research also attempted to establish a heat treatment strategy compatible with these alloys. The resulting heat treatment effects on the microstructure, texture, and microhardness were investigated. Diffusion calculation results suggested an overall diffusion depth of 120 μm in the interface after heat treatment, which can increase the resulting joint strength if intermetallic precipitation is avoided. Electron Backscatter Diffraction (EBSD) analysis of the heat-treated samples showed that both the base metal regions retained the dominant fiber textures after printing, which is the <110> || building direction (BD) fiber texture for the MP1 region and the <111> || BD and <100> || BD fiber textures for the MS1 region. Nanoindentation tests also revealed a considerably higher hardness in the MS1 region and a slight reduction of hardness in the MP1 region after heat treatment, which can be early evidence of the successful application of the heat treatment strategy to both base metals. Future work will investigate the mechanical properties of the as-printed and heat-treated samples and verify if any precipitates formed in the MS1-MP1 interface.

Thermomechanical and Material Flow Analysis during Friction Stir Welding of Marine Grade Aluminum Alloy 5083

_ This research aims to depict the thermal history, residual stress distribution, axial force applied, and material flow behavior on aluminum alloy 5083 (AA5083) plates, during the friction stir welding (FSW) process. This alloy finds most its use in shipbuilding industries and for marine constructions. It has been developed using an explicit, fully coupled thermomechanical nonlinear finite element (FE) analysis approach. The analysis was performed to simulate the effect of three stages, namely plunging, dwelling, and welding, of the FSW process. The ABAQUS/Explicit program was used for the computational modeling. To build a reliable and computationally efficient FE model, features such as arbitrary Lagrangian-Eulerian (ALE) formulation, adaptive meshing/ remeshing approach, mesh sensitivity analysis, and mass scaling have been introduced. The interaction between the tool bottom surface and the plate top surface was defined using a finite sliding and a sticking property. A Coulomb friction model with a temperature-dependent coefficient of friction (COF) was used to describe the tool-workpiece interaction. In addition, a small experiment was done with the following process parameters; a rotating tool speed of 875 rpm, a traverse speed of 60 mm/min, and a tool tilt angle of 0° to produce a defect-free butt joint to validate the numerically generated thermal profiles. The temperature was found slightly higher on the advancing side (AS). Residual stress distribution created over the whole width of the plates was also investigated. Introduction The introduction of friction stir welding (FSW) process by The Welding Institute in 1991 (Thomas 1991) drew much attention. During fusion welding of 5 mm AA5083 plates, the heat input should be very high. Because of this high input, a higher thermal gradient is produced, which leads to the formation of several intermetallic compounds (IMCs). Because of this IMC formation, the strength of the welded joint is reduced. However, the steep thermal gradient produced leads to the formation of finer microstructure near the weld bead and coarser along the base metal region. These results in the heterogeneity of the weld bead microstructure leading to less efficiency and accuracy of the weldment.

Effects of microstructure heterogeneity on tensile properties and failure mechanism of GTAW joint of as-cast Ti2531

In this study, as-cast dual-phase titanium alloy Ti2531 was welded by Gas Tungsten Arc Welding, and the effects of microstructure heterogeneity on tensile properties and failure mechanism was analyzed. Tensile test results showed that the specimens fractured in the base metal region, and the tensile strength R m of the welded plate was 855 MPa ~ 859 MPa, which was almost the same as that of the base metal. It was found that, compared with the base metal region, the fine and basketweave phase in the weld zone and heat-affected zone resulted in higher hardness and yield strength. Therefore, plastic strain concentration occurred in the base metal region and a large number of kink bands were found, which accounts for the relatively good plasticity with the fracture strain of 0.073–0.09. In addition, by means of intergranular orientation analysis, it was demonstrated that [0001] α and [101] β were the rotation axes of kink bands in the α and β phases, respectively. Furthermore, by observing the high-resolution electron microscopy, it was found that these kink bands were formed by the arrangement of edge dislocations. As a consequence, when the lattice distortion was severe, the unstable expansion of kink bands occurred and cracks were formed in widmanstätten colonies, inducing the failure of the specimen in the base metal region and great tensile strength equivalent to that of base material. • The weld joint of Ti2531 had good tensile strength close to that of base material. • Plastic deformation was concentrated in base metal region rather than other regions. • Kink bands were formed to coordinate severe plastic deformation in base metal region. • The instable expansion of kink bands resulted in the fracture of the welded specimen.

Superconductivity enhancement in polar metal regions of Sr0.95Ba0.05TiO3 and Sr0.985Ca0.015TiO3 revealed by systematic Nb doping

Two different ferroelectric materials, Sr0.95Ba0.05TiO3 and Sr0.985Ca0.015TiO3, can be turned into polar metals with broken centrosymmetry via electron doping. Systematic substitution of Nb5+ for Ti4+ has revealed that these polar metals both commonly show a simple superconducting dome with a single convex shape. Interestingly, the superconducting transition temperature Tc is enhanced more strongly in these polar metals when compared with the nonpolar matrix Sr(Ti, Nb)O3. The maximum Tc reaches 0.75 K, which is the highest reported value among the SrTiO3-based families to date. However, the Tc enhancement is unexpectedly lower within the vicinity of the putative ferroelectric quantum critical point. The enhancement then becomes much more prominent at locations further inside the dilute carrier-density region, where the screening is less effective. These results suggest that centrosymmetry breaking, i.e., the ferroelectric nature, does not kill the superconductivity. Instead, it enhances the superconductivity directly, despite the absence of strong quantum fluctuations.

Joints properties in rotary friction welding of AA5083-H112 aluminium alloy

Rotary friction welded joints of AA5083-H112 aluminium alloy rods with diameter of 15 mm and length of 50 mm were produced at various rotational speeds. The current research is aimed to understand the static and fatigue properties of welding joints. Several experiments were carried out including macrostructure and microstructure observations, hardness measurements, tensile testing, residual stress measurements by neutron diffraction, rotary bending fatigue tests and fractography. The results showed that the static fracture occurred at the base metal away from the weld metal region for all weld joints under study with the average ultimate tensile strength of 272.7 MPa. In this condition, the joint efficiency was higher than 100%. It was found that the high strength of the weld joints was associated with fine-grained microstructure. On the other hand, fatigue property of the weld was influenced by both welding microstructure and residual stress. This argument was supported by the facts that the initial crack occurred at HAZ at which the residual stress was tensile and then followed by fatigue crack growth from HAZ towards TMAZ.

Characterization of weld joints produced by continuous wave and double pulse gas metal arc welding in naval grade high-strength low-alloy steel

The current research examines gas metal arc welding (GMAW) joints generated in naval grade high-strength low-alloy (HSLA) steel using both continuous wave GMAW (CW-GMAW) and double pulse GMAW (DP-GMAW). The joint was created in four passes with DP-GMAW, whereas CW-GMAW required eight passes. Weld joints were characterized using various techniques, including optical microscopy (OM), scanning electron microscopy (SEM), residual stress analysis, and mechanical evaluation. The mechanical evaluation consisted of microhardness, impact, and tensile tests. The Charpy V-notch (CVN) impact test was performed at room temperature and −60°C. For both CW-GMAW and DP-GMAW, the heat-affected zone and the fusion zone were harder than the base metal. The fracture occurred in the base metal region in all the tensile test specimens containing the weld joints. The DP-GMAW joints showed higher impact toughness at both room temperature and −60°C. In comparison to the fusion zone of the CW-GMAW joint, the fusion zone of the DP-GMAW joint had a greater volume fraction of acicular ferrite, a finer grain size, and a higher percentage of high-angle grain boundaries. These factors have contributed, it is believed, to the higher impact toughness of the DP-GMAW joint.

Effects of Bi substitution on electroresistance behaviours in La0.8-xBixNa0.2MnO3 manganites

The observation of the electroresistance (ER) effect related to the reduction of resistivity under increased applied current indicates the potential of manganite material for next-generation spintronic-based devices. The observed behaviour was attributed to the presence of magnetic inhomogeneity. However, such relation is still not well understood, hence the current-induced effect on the resistivity in monovalent-doped La0.8-xBixNa0.2MnO3 (x = 0–0.20) manganite prepared via solid-state method is reported. All samples exhibited low resistivity in the temperature ranges of 30 K–300 K under a higher applied current of 5 mA compared with 1 mA, leading to the observation of the ER effect. The reduction of resistivity in the metallic region was due to the enhancement of DE itinerant hopping and the decrease in the scattering effect of conduction electrons, whereas in the insulating region, resistivity reduction is suggested to be related to the weakening of the electron–lattice attraction, as indicated by the reduction in activation energy (Ea) of charge carriers. Both x = 0.15 and x = 0.20 samples respectively exhibited large ER effects of 158% and 171% at 300 K amongst the studied samples. The enhancement of ER with Bi substitution is suggested due to the presence of magnetic inhomogeneities induced by MnO6 distortion which favours the formation of filamentary conduction paths under the presence of high applied current. The findings indicate that Bi substitution in La0.8-xBixNa0.2MnO3 (x = 0–0.20) manganites enhanced the sensitivity to the changes in electric field which shows that the investigated samples could be potentially used for non-volatile memory devices.

Effect of the notch location on the Charpy-V toughness results for robotic flux-cored arc welded multipass joints

Abstract In this study, the effect of the notch locations on the Charpy-V toughness values of the all-welded joint obtained using robotic flux-cored arc welding was investigated with respect to microstructures at the notch locations. Charpy impact tests were performed through the thickness with notch location at the centerline as well as off-set regions of the weld metal in addition to the microhardness measurements conducted. The detailed weld metal characterization was conducted using a stereo microscope, optical microscope, and scanning electron microscope at the same location where the Charpy tests and microhardness tests were performed. The sub-zero impact toughness test results indicated that the columnar weld metal regions exhibited low toughness values while the centerline microstructure consisting of mainly reheated regions displayed much higher toughness values even at the test temperature of −60 °C, satisfying the toughness requirement of the requested 47 J value. It is concluded that a small variation of the through-thickness notch position may result in different toughness values for the same weld metal. On this basis, the notching procedure of the Charpy-V samples for the multi-pass weld metal should be conducted with care and obtained results should be explained with respective notch position and microstructure.

Positioning Tank-Wall Magnetic Shunts of a Three-Phase Power Transformer Considering Thermal Effects

This article presents an investigation of the optimal positioning of tank-wall magnetic shunts in power transformers. Magnetic shunts are made of grain-oriented magnetic silicon steel laminations and are used to avoid hot spots in metallic regions inside the power transformer. The magnetodynamic equations are solved in terms of the electric vector potential and the magnetic scalar potential. Thermal effects are calculated using heat transfer coefficients. This article proposes and solves an optimization problem where the objective is to position several shunts near the tank wall. Several design variables, temperature, and geometrical constraints are considered. As the finite-element (FE) model to be solved is in 3-D, the computing resources must be efficiently used. A multi-threading method was developed and numerically tested where the 3-D FE model, temperature calculation, and the particle swarm optimizer (PSO) are executed in a multicore computer in a parallel scheme.

Structural, Magnetic, and Electrical Properties and Magnetoresistance of Monovalent K-Substituted La0.7Ba0.3−xKxMnO3 (x = 0 and 0.04) Manganite

The effects of K+ substitution at the Ba-site on the structural, magnetic, and electrical properties and magnetoresistance (MR) of La0.7Ba0.3−xKxMnO3 (x = 0 and 0.04) manganites prepared via the solid-state method were investigated. Rietveld refinement of X-ray diffraction data confirmed that both samples were crystallized in the rhombohedral structure with the R3c¯ space group. In addition, the unit cell volume, V, and the average grain size also increased with K+ ions. Magnetization versus applied field (M–H) measurement was carried out, and the saturation magnetization (Ms) was found to increase from 1.81 μB/f.u. (x = 0) to 4.11 μB /f.u. (x = 0.04), implying that K+ ions strengthened the ferromagnetic (FM) interaction. Furthermore, the metal–insulator transition temperature, TMI, increased from 257 K (x = 0) to 271 K (x = 0.04). The observed behaviour may be related to the enhancement of double-exchange (DE) interaction due to the increase in Mn-O-Mn bond angle and electronic bandwidth (W), favouring the increasing rate of the eg electron hopping process. The fitting of the electrical resistivity data in the metallic region describes the significance of residual resistivity, electron–electron and electron–magnon scattering processes to elucidate the electronic transport properties. Within the insulating region, variable range hopping (VRH) and small polaron hopping (SPH) models are proposed to describe the conduction mechanism.