Open AccessArticle
First-Principles Investigation of Structural, Electronic and Elastic Properties of HfX (X = Os, Ir and Pt) Compounds
Metals 2017, 7(8), 317; doi:10.3390/met7080317 (registering DOI) -
Abstract
The structural, electronic and elastic properties of B2 structure Hafnium compounds were investigated by means of first-principles calculations based on the density functional theory within generalized gradient approximation (GGA) and local density approximation (LDA) methods. Both GGA and LDA methods can make acceptable
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The structural, electronic and elastic properties of B2 structure Hafnium compounds were investigated by means of first-principles calculations based on the density functional theory within generalized gradient approximation (GGA) and local density approximation (LDA) methods. Both GGA and LDA methods can make acceptable optimized lattice parameters in comparison with experimental parameters. Therefore, both GGA and LDA methods are used to predict the electronic and elastic properties of B2 HfX (X = Os, Ir and Pt) compounds. Initially, the calculated formation enthalpies have confirmed the order of thermodynamic stability as HfPt > HfIr > HfOs. Secondly, the electronic structures are analyzed to explain the bonding characters and stabilities in these compounds. Furthermore, the calculated elastic properties and elastic anisotropic behaviors are ordered and analyzed in these compounds. The calculated bulk moduli are in the reduced order of HfOs > HfIr > HfPt, which has exhibited the linear relationship with electron densities. Finally, the anisotropy of acoustic velocities, Debye temperatures and thermal conductivities are obtained and discussed. Full article
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Open AccessArticle
Influence of Build Orientation, Heat Treatment, and Laser Power on the Hardness of Ti6Al4V Manufactured Using the DMLS Process
Metals 2017, 7(8), 318; doi:10.3390/met7080318 (registering DOI) -
Abstract
This contribution is focused on the influence of build orientation on hardness of materials sintered using direct metal laser sintering (DMLS) technology. It builds on the current research works that has monitored the influence of build orientation on a fatigue life, mechanical properties,
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This contribution is focused on the influence of build orientation on hardness of materials sintered using direct metal laser sintering (DMLS) technology. It builds on the current research works that has monitored the influence of build orientation on a fatigue life, mechanical properties, roughness after machining, etc. In the mentioned work, a slight influence of build orientation on the above properties was shown. The hardness was measured on a Ti6Al4V alloy which was made of powder by DMLS technology. The individual materials were sintered at different laser powers, then annealed to remove internal stresses. Part of the experiment examined the metallographic analysis of materials in the direction perpendicular to the sintered layers and parallel with the sintered layers. Microhardness was measured on metallographic cross-sections and the results were statistically processed. The influence of laser power on a respective material hardness was assessed by one-way analysis of variance (ANOVA), a comparison of the hardness between sintered and sintered-annealed samples, as well as the comparison of hardness in the two considered directions was performed by t-test and F-test. A statistically significant difference in the hardness of the materials prepared at different laser powers was found. The influence of heat treatment, as well as the direction of material building also showed a statistically significant difference. Full article
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Open AccessArticle
Study on Microstructure and Properties of Bimodal Structured Ultrafine-Grained Ferrite Steel
Metals 2017, 7(8), 316; doi:10.3390/met7080316 (registering DOI) -
Abstract
The objective of the study research was to obtain bimodal structured ultrafine-grained ferrite steel with outstanding mechanical properties and excellent corrosion resistance. The bimodal microstructure was fabricated by the cold rolling and annealing process of a dual-phase steel. The influences of the annealing
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The objective of the study research was to obtain bimodal structured ultrafine-grained ferrite steel with outstanding mechanical properties and excellent corrosion resistance. The bimodal microstructure was fabricated by the cold rolling and annealing process of a dual-phase steel. The influences of the annealing process on microstructure evolution and the mechanical properties of the cold-rolled dual-phase steel were investigated. The effect of bimodal microstructure on corrosion resistance was also studied. The results showed that the bimodal characteristic of ferrite steel was most apparent in cold-rolled samples annealed at 650 °C for 40 min. More importantly, due to the coordinated action of fine-grained strengthening, back-stress strengthening, and precipitation strengthening, the yield strength (517 MPa) of the bimodal microstructure improved significantly, while the total elongation remained at a high level of 26%. The results of corrosion experiments showed that the corrosion resistance of bimodal ferrite steel was better than that of dual-phase steel with the same composition. This was mainly because the Volta potential difference of bimodal ferrite steel was smaller than that of dual-phase steel, which was conducive to forming a protective rust layer. Full article
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Open AccessArticle
Broadband Dual-Phase Plasmons through Metallization of Polymeric Heterojunctions
Metals 2017, 7(8), 314; doi:10.3390/met7080314 -
Abstract
Large-area dual-phase plasmonic gold nanostructures were produced using the phase-separation pattern of a polymer blend film, where two typical light-emitting polymeric semiconductors of poly (9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) and poly (9,9-dioctylfluorene-co-bis-N,N′-(4-butylphenyl)-bis-N,N′-phenyl-1,4 phenylenediamine) (PFB)
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Large-area dual-phase plasmonic gold nanostructures were produced using the phase-separation pattern of a polymer blend film, where two typical light-emitting polymeric semiconductors of poly (9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) and poly (9,9-dioctylfluorene-co-bis-N,N′-(4-butylphenyl)-bis-N,N′-phenyl-1,4 phenylenediamine) (PFB) have been employed to construct the heterojunction patterns. The laser-induced selective cross-linking of F8BT molecules and the subsequent rinsing process using the good solvent of chloroform for PFB supplies a stable template for a further metallization process. When colloidal gold nanoparticles were spin-coated onto the surface of the template, a majority of the gold nanoparticles were confined into the “holes” of originally PFB-rich phase, while a minor portion stays on the “ridges” of F8BT-rich phase. After the annealing process, larger gold nanoparticles were produced inside the holes and smaller ones on the ridges, which induced localized surface plasmon resonance in the near infrared and in the visible, respectively. The structural parameters of the gold plasmonic pattern can be tuned by different surface modification and annealing processes, which can tune the spectroscopic response in the spectral position and in the spectral intensity. The produced nanostructures with broadband plasmon resonance can be used as a template for random lasers with strong optical scattering at both the pump and emission wavelengths and for photovoltaic devices with strong absorption in the visible and near infrared. Full article
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Open AccessArticle
Preparing Ferro-Nickel Alloy from Low-Grade Laterite Nickel Ore Based on Metallized Reduction–Magnetic Separation
Metals 2017, 7(8), 313; doi:10.3390/met7080313 -
Abstract
Nickel, a valued metal, mainly exists as nickel oxide in laterite nickel ore. Furthermore, a large part of the laterite nickel ore is low-grade saprolitic ore. In this paper, a research on preparing ferro-nickel alloy from low-grade saprolitic laterite nickel ore using metallized
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Nickel, a valued metal, mainly exists as nickel oxide in laterite nickel ore. Furthermore, a large part of the laterite nickel ore is low-grade saprolitic ore. In this paper, a research on preparing ferro-nickel alloy from low-grade saprolitic laterite nickel ore using metallized reduction-magnetic separation was studied. In the research, the carbothermic reductions of iron oxide and nickel oxide were analyzed in terms of thermodynamics. The influences of reduction temperature, reduction time, carbon ratio, and CaO addition on the recoveries and grades of iron and nickel were experimentally investigated. To analyze and clarify the related mechanism, the microstructure of ferro-nickel alloy was observed by optical microscope (OM) and scanning electron microscope/energy dispersive spectrometer (SEM/EDS). Accordingly, the results showed that, increasing reduction temperature can improve the grades and recoveries of nickel and iron; appropriate reduction time, carbon ratio and CaO addition can favor aggregation and growing up of the ferro-nickel particles, improving the grades and recoveries of nickel and iron. The optimal process parameters obtained were a reduction temperature of 1350 °C, reduction time of 2 h, carbon ratio of 1.2, and CaO addition of 10%. In this case, the ferro-nickel alloy with nickel grade 7.90% and iron grade 77.32% was prepared successfully from the low-grade saprolitic ore with nickel content 1.82%. The nickel and iron recoveries were 89.36% and 95.87% respectively, which achieved the highly efficient recovery and utilization of iron and nickel of low-grade laterite nickel ore. Full article
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Open AccessErratum
Erratum: Structure, Texture and Phases in 3D Printed IN718 Alloy Subjected to Homogenization and HIP Treatments. Metals 2017, 7, 196
Metals 2017, 7(8), 315; doi:10.3390/met7080315 -
Abstract
The authors wish to make the following corrections to the main text in the published paper [1]. In this paper, the weight of CuCl2 should be changed from 5 mg to 5 g to provide accurate recipe for the IN718 etchant.[...] Full article
Open AccessArticle
Statistical Analysis and Fatigue Life Estimations for Quenched and Tempered Steel at Different Tempering Temperatures
Metals 2017, 7(8), 312; doi:10.3390/met7080312 -
Abstract
In this paper, the statistical properties and fatigue life estimations of 0.44% carbon steel at different tempering temperatures are presented. The specimens were austenized at 900 °C for 10 min, quenched in water, tempered at different temperatures, and then machined to the design
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In this paper, the statistical properties and fatigue life estimations of 0.44% carbon steel at different tempering temperatures are presented. The specimens were austenized at 900 °C for 10 min, quenched in water, tempered at different temperatures, and then machined to the design geometry and average surface roughness of Ra = 0.4 μm. The effect of tempering temperature on the fatigue life of 0.44% carbon steel was investigated using 75 fatigue tests, divided into three groups at temperatures 500 °C, 600 °C, and 700 °C. S–N and P–S–N curves were established. Two methods of estimating the mean fatigue life are presented. One is based on dislocation dipole accumulation and Paris’ law; another is based on the kriging model. Six more fatigue tests were carried out to validate the presented methods. Test results showed that the first method is superior to the second in terms of estimating accuracy from the validation datum. However, the second method could estimate the mean fatigue life of quenched and tempered 0.44% carbon steel with an average surface roughness of Ra = 0.4 μm when the tempering temperature was set to a value other than 500 °C, 600 °C, or 700 °C, with no additional fatigue test needed. Full article
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Open AccessArticle
An Algorithm for Surface Defect Identification of Steel Plates Based on Genetic Algorithm and Extreme Learning Machine
Metals 2017, 7(8), 311; doi:10.3390/met7080311 -
Abstract
Defects on the surface of steel plates are one of the most important factors affecting the quality of steel plates. It is of great importance to detect such defects through online surface inspection systems, whose ability of defect identification comes from self-learning through
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Defects on the surface of steel plates are one of the most important factors affecting the quality of steel plates. It is of great importance to detect such defects through online surface inspection systems, whose ability of defect identification comes from self-learning through training samples. Extreme Learning Machine (ELM) is a fast machine learning algorithm with a high accuracy of identification. ELM is implemented by a hidden matrix generated with random initialization parameters, while different parameters usually result in different performances. To solve this problem, an improved ELM algorithm combined with a Genetic Algorithm was proposed and applied for the surface defect identification of hot rolled steel plates. The output matrix of the ELM’s hidden layers was treated as a chromosome, and some novel iteration rules were added. The algorithm was tested with 1675 samples of hot rolled steel plates, including pockmarks, chaps, scars, longitudinal cracks, longitudinal scratches, scales, transverse cracks, transverse scratches, and roll marks. The results showed that the highest identification accuracies for the training and the testing set obtained by the G-ELM (Genetic Extreme Learning Machine) algorithm were 98.46% and 94.30%, respectively, which were about 5% higher than those obtained by the ELM algorithm. Full article
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Open AccessArticle
Microstructure and Strengthening-Toughening Mechanism of Nitrogen-Alloyed 4Cr5Mo2V Hot-Working Die Steel
Metals 2017, 7(8), 310; doi:10.3390/met7080310 -
Abstract
The microstructure and strengthening-toughening mechanism of a modified 4Cr5Mo2V hot-working die steel with nitrogen (0.08% N) were investigated using hardness and toughness measurements, optical microscopy, scanning electron microscopy, X-ray diffraction experiments, transmission electron microscopy, and dilatometry. The results showed that the nitrogen addition
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The microstructure and strengthening-toughening mechanism of a modified 4Cr5Mo2V hot-working die steel with nitrogen (0.08% N) were investigated using hardness and toughness measurements, optical microscopy, scanning electron microscopy, X-ray diffraction experiments, transmission electron microscopy, and dilatometry. The results showed that the nitrogen addition could increase the hardness and temperability of 4Cr5Mo2V steel without toughness loss with a suitable heat treatment procedure. The fair match of high strength and toughness of the nitrogen-alloyed 4Cr5Mo2V steel is associated with the refinement of the prior austenite grain, the solution hardening of nitrogen atoms, and the increase of retained austenite. Before quenching, nitrogen tends to precipitate in the form of a large amount of undissolved finer V(C, N), imposing a stronger effect on restricting the growth of prior austenitic grains and increasing the grain refining efficiency of VC by 6.8 times according to an estimate. During the quenching process, the nitrogen decreases the MS of the martensitic transformation, increasing retained austenite, which is a benefit for toughness. During the tempering process, some of the N atoms in M(C, N) were dissolved in the matrix, causing crystal lattice distortions, thus boosting the solution reinforcing effect. Meanwhile, the solid-dissolved nitrogen inhibits the diffusion of carbon, decreasing the growth rate of the carbides and increasing tempering resistance. Full article
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Open AccessArticle
Surface Characterization and Corrosion Resistance of 36Cr-Ni-Mo4 Steel Coated by WC-Co Cermet Electrode Using Micro-Electro Welding
Metals 2017, 7(8), 308; doi:10.3390/met7080308 -
Abstract
In this paper the influence of spark energy on corrosion resistance, hardness, surface roughness and morphology of WC-Co coated 36Cr-Ni-Mo4 steel by Micro-Electro Welding (MEW) was investigated. Frequencies of 5, 8 and 11 kHz, currents of 15, 25 and 35 A and duty
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In this paper the influence of spark energy on corrosion resistance, hardness, surface roughness and morphology of WC-Co coated 36Cr-Ni-Mo4 steel by Micro-Electro Welding (MEW) was investigated. Frequencies of 5, 8 and 11 kHz, currents of 15, 25 and 35 A and duty cycles of 10, 30 and 50 % were applied for coating of the samples using a WC-Co cermet electrode. The results indicate that increasing the current, Duty cycle and frequency of the process increases spark energy. As spark energy increases, efficiency of coating increases to 80% and then decreases. X-ray diffraction (XRD) analysis was used to identify the phases. The results indicated that other than the peaks obtained for the metallic Iron with BCC (Body Centered Cubic) structure, Tungsten Carbide, Cr7C3 and Titanium Carbide phases were also seen on the surface. Vickers micro hardness method was used for hardness measurement of the samples. Surface hardness increases to 817.33 HV0.05 with spark energy increasing up to 1.03 mJ, and then reducing. Optical Microscopy (OM) and scanning electron microscopy (SEM) to study Microstructural and atomic force microscopy (AFM) to study the topography, morphology and roughness were used. Polarization technique in 3.5 wt % NaCl solution was used to evaluate the corrosion properties. The results of the energy dispersive X-ray spectroscopy (EDS) analysis indicate that with increasing spark energy, the amount of Tungsten in surface increases to 41.95 wt % and then decreases. As spark energy increases up to 2.17 mJ, thickness of coating increases to 8.31 μm and then decreases. As spark energy increases, surface roughness is also increased. Corrosion test results indicated that the lowest corrosion rate (2.6 × 10−8 mpy) is related to the sample with the highest level of efficiency. Full article
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Open AccessArticle
Microstructure, Mechanical Property, and Phase Transformation of Quaternary NiTiFeNb and NiTiFeTa Shape Memory Alloys
Metals 2017, 7(8), 309; doi:10.3390/met7080309 -
Abstract
Based on ternary Ni45Ti51.8Fe3.2 (at %) shape memory alloy (SMA), Nb and Ta elements are added to an NiTiFe SMA by replacing Ni element, and consequently quaternary Ni44Ti51.8Fe3.2Nb1 and Ni44
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Based on ternary Ni45Ti51.8Fe3.2 (at %) shape memory alloy (SMA), Nb and Ta elements are added to an NiTiFe SMA by replacing Ni element, and consequently quaternary Ni44Ti51.8Fe3.2Nb1 and Ni44Ti51.8Fe3.2Ta1 (at %) SMAs are fabricated. The microstructure, mechanical property, and phase transformation of NiTiFeNb and NiTiFeTa SMAs are further investigated. Ti2Ni and β-Nb phases can be observed in NiTiFeNb SMA, whereas Ti2Ni and Ni3Ti phases can be captured in NiTiFeTa SMA. As compared to NiTiFe SMA, quaternary NiTiFeNb and NiTiFeTa SMAs possess the higher strength, since solution strengthening plays a considerable role. NiTiFeNb and NiTiFeTa SMAs exhibit a one-step transformation from B2 austenite to B19’ martensite during cooling, but they experience a two-step transformation of B19’-R-B2 during heating. Full article
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Open AccessArticle
FEM Simulation of Dissimilar Aluminum Titanium Fiber Laser Welding Using 2D and 3D Gaussian Heat Sources
Metals 2017, 7(8), 307; doi:10.3390/met7080307 -
Abstract
For a dissimilar laser weld, the model of the heat source is a paramount boundary condition for the prediction of the thermal phenomena, which occur during the welding cycle. In this paper, both two-dimensional (2D) and three-dimensional (3D) Gaussian heat sources were studied
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For a dissimilar laser weld, the model of the heat source is a paramount boundary condition for the prediction of the thermal phenomena, which occur during the welding cycle. In this paper, both two-dimensional (2D) and three-dimensional (3D) Gaussian heat sources were studied for the thermal analysis of the fiber laser welding of titanium and aluminum dissimilar butt joint. The models were calibrated comparing the fusion zone of the experiment with that of the numerical model. The actual temperature during the welding cycle was registered by a thermocouple and used for validation of the numerical model. When it came to calculate the fusion zone dimensions in the transversal section, the 2D heat source showed more accurate results. The 3D heat source provided better results for the simulated weld pool and cooling rate. Full article
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Open AccessArticle
Microstructural, Mechanical, Texture and Residual Stress Characterizations of X52 Pipeline Steel
Metals 2017, 7(8), 306; doi:10.3390/met7080306 -
Abstract
In this paper, the microstructural and mechanical properties of a high-strength low-alloy (HSLA) API 5L X52 steel, which is widely utilized in the construction of gas pipelines, were characterized with optical microscopy, electron backscatter diffraction, and standard mechanical tests. The outcomes of these
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In this paper, the microstructural and mechanical properties of a high-strength low-alloy (HSLA) API 5L X52 steel, which is widely utilized in the construction of gas pipelines, were characterized with optical microscopy, electron backscatter diffraction, and standard mechanical tests. The outcomes of these characterizations were used to evaluate the strengthening contributions of the solid solution, grain size, dislocations, and precipitates to the overall strength of the steel. In addition, texture and residual stresses were determined with neutron diffraction. The residual stresses were found to be low in comparison with the expected stresses due to the operating pressure. However, these stresses could contribute to the initiation and propagation of stress corrosion cracking at the outer surface of the pipe. Neutron diffraction results also suggested that the outer surface of the pipe had a texture that is expected to have a low resistance to high pH stress corrosion cracking. Both conclusions were found to be consistent with field observations. Full article
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Open AccessFeature PaperReview
Neutron Reflectometry for Studying Corrosion and Corrosion Inhibition
Metals 2017, 7(8), 304; doi:10.3390/met7080304 -
Abstract
Neutron reflectometry is an extremely powerful technique to monitor chemical and morphological changes at interfaces at the angstrom-level. Its ability to characterise metal, oxide and organic layers simultaneously or separately and in situ makes it an excellent tool for fundamental studies of corrosion
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Neutron reflectometry is an extremely powerful technique to monitor chemical and morphological changes at interfaces at the angstrom-level. Its ability to characterise metal, oxide and organic layers simultaneously or separately and in situ makes it an excellent tool for fundamental studies of corrosion and particularly adsorbed corrosion inhibitors. However, apart from a small body of key studies, it has yet to be fully exploited in this area. We present here an outline of the experimental method with particular focus on its application to the study of corrosive systems. This is illustrated with recent examples from the literature addressing corrosion, inhibition and related phenomena. Full article
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Open AccessArticle
Inspection of Prebaked Carbon Anodes Using Multi-Spectral Acousto-Ultrasonic Excitation
Metals 2017, 7(8), 305; doi:10.3390/met7080305 -
Abstract
Reduction cell operation in primary aluminum production is strongly influenced by the properties of baked anodes. Producing consistent anode quality is more challenging nowadays due to the increasing variability of raw materials. Taking timely corrective actions to attenuate the impact of raw material
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Reduction cell operation in primary aluminum production is strongly influenced by the properties of baked anodes. Producing consistent anode quality is more challenging nowadays due to the increasing variability of raw materials. Taking timely corrective actions to attenuate the impact of raw material fluctuations on anode quality is also difficult based on the core sampling and characterization scheme currently used by most anode manufacturers, because it is applied on a very small proportion of the anode production (about 1%), and long-time delays are required for lab characterization. The objective of this work is to develop rapid and non-destructive methods for the inspection of baked anodes. Previous work has established that sequential excitation of smaller parts collected from an industrial sized anode using acousto-ultrasonic signals at different frequencies allowed detecting and discriminating anode defects (pores and cracks). This was validated qualitatively using X-ray computed tomography. This work improves the method by using frequency-modulated excitation and building quantitative relationships between the acousto-ultrasonic signals and defects extracted from tomography images using Wavelet Transforms and Partial Least Squares (PLS) regression. The new excitation approach was found to provide similar or better inspection performance compared with sequential excitation, while requiring a shorter cycle time. Full article
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Open AccessArticle
High-Yield One-Pot Recovery and Characterization of Nanostructured Cobalt Oxalate from Spent Lithium-Ion Batteries and Successive Re-Synthesis of LiCoO2
Metals 2017, 7(8), 303; doi:10.3390/met7080303 -
Abstract
A complete recycling process for the cathode material of spent lithium-ion batteries is demonstrated with a simple two-step process comprised of one-pot cobalt recovery to nanostructured materials and single step synthesis of LiCoO2. For the facile and efficient recovery of cobalt,
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A complete recycling process for the cathode material of spent lithium-ion batteries is demonstrated with a simple two-step process comprised of one-pot cobalt recovery to nanostructured materials and single step synthesis of LiCoO2. For the facile and efficient recovery of cobalt, we employ malic acid as a leaching agent and oxalic acid as a precipitating agent, resulting in nanostructured cobalt oxalate. X-ray diffraction and Fourier transform infrared spectroscopy (FT-IR) analysis clearly show that cobalt species are simultaneously leached and precipitated as cobalt oxalate with a high yield of 99.28%, and this material can then be used as a reactant for the synthesis of LiCoO2 for use as a cathode material. In addition to its advantages in simplifying the process, the proposed method allows for not only enhancing the efficiency of cobalt recovery, but also enabling reaction without a reducing agent, H2O2. Through successive single-step reaction of the obtained cobalt oxalate without any purification process, LiCoO2 is also successfully synthesized. The effect of the annealing temperature during synthesis on the nanostructure and charge–discharge properties is also investigated. Half-cell tests with recycled LiCoO2 exhibit a high discharge capacity (131 mA·h·g−1) and 93% charge–discharge efficiency. Full article
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Open AccessArticle
X-ray Tomography Characterisation of Lattice Structures Processed by Selective Electron Beam Melting
Metals 2017, 7(8), 300; doi:10.3390/met7080300 -
Abstract
Metallic lattice structures intentionally contain open porosity; however, they can also contain unwanted closed porosity within the structural members. The entrained porosity and defects within three different geometries of Ti-6Al-4V lattices, fabricated by Selective Electron Beam Melting (SEBM), is assessed from X-ray computed
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Metallic lattice structures intentionally contain open porosity; however, they can also contain unwanted closed porosity within the structural members. The entrained porosity and defects within three different geometries of Ti-6Al-4V lattices, fabricated by Selective Electron Beam Melting (SEBM), is assessed from X-ray computed tomography (CT) scans. The results suggest that horizontal struts that are built upon loose powder show particularly high (~20 × 10−3 vol %) levels of pores, as do nodes at which many (in our case 24) struts meet. On the other hand, for struts more closely aligned (0° to 54°) to the build direction, the fraction of porosity appears to be much lower (~0.17 × 10−3%) arising mainly from pores contained within the original atomised powder particles. Full article
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Open AccessArticle
Effects of Vacuum-Carburizing Conditions on Surface-Hardened Layer Properties of Transformation-Induced Plasticity-Aided Martensitic Steel
Metals 2017, 7(8), 301; doi:10.3390/met7080301 -
Abstract
The effects of carbon potential in vacuum-carburization on the surface-hardened layer properties of the 0.2%C-1.5%Si-1.5%Mn-1.0%Cr-0.05%Nb transformation-induced plasticity-aided martensitic steel were investigated for the fabrication of precision gears. The volume fraction of retained austenite and hardness in the surface hardened layer of the steel
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The effects of carbon potential in vacuum-carburization on the surface-hardened layer properties of the 0.2%C-1.5%Si-1.5%Mn-1.0%Cr-0.05%Nb transformation-induced plasticity-aided martensitic steel were investigated for the fabrication of precision gears. The volume fraction of retained austenite and hardness in the surface hardened layer of the steel increased with increasing carbon potential. Subsequent fine-particle peening enhanced the hardness and the compressive residual stress via severe plastic deformation and strain-induced martensite transformation, especially under a high carbon potential. The severe plastic deformation mainly contributed to increased hardness and compressive residual stress and the contribution of the strain-induced martensitic transformation was relatively small. Full article
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Open AccessArticle
Reaction Mechanism and Distribution Behavior of Arsenic in the Bottom Blown Copper Smelting Process
Metals 2017, 7(8), 302; doi:10.3390/met7080302 -
Abstract
The control of arsenic, a toxic and carcinogenic element, is an important issue for all copper smelters. In this work, the reaction mechanism and distribution behavior of arsenic in the bottom blown copper smelting process (SKS process) were investigated and compared to the
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The control of arsenic, a toxic and carcinogenic element, is an important issue for all copper smelters. In this work, the reaction mechanism and distribution behavior of arsenic in the bottom blown copper smelting process (SKS process) were investigated and compared to the flash smelting process. There are obvious differences of arsenic distribution in the SKS process and flash process, resulting from the differences of oxygen potentials, volatilizations, smelting temperatures, reaction intensities, and mass transfer processes. Under stable production conditions, the distributions of arsenic among matte, slag, and gas phases are 6%, 12%, and 82%, respectively. Less arsenic is reported in the gas phase with the flash process than with the SKS process. The main arsenic species in gas phase are AsS (g), AsO (g), and As2 (g). Arsenic exists in the slag predominantly as As2O3 (l), and in matte as As (l). High matte grade is harmful to the elimination of arsenic to gas. The changing of Fe/SiO2 has slight effects on the distributions of arsenic. In order to enhance the removal of arsenic from the SKS smelting system to the gas phase, low oxygen concentration, low ratios of oxygen/ore, and low matte grade should be chosen. In the SKS smelting process, no dust is recycled, and almost all dust is collected and further treated to eliminate arsenic and recover valuable metals by other process streams. Full article
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Open AccessArticle
Hot Deformation Behavior of a Spray-Deposited Al-8.31Zn-2.07Mg-2.46Cu-0.12Zr Alloy
Metals 2017, 7(8), 299; doi:10.3390/met7080299 -
Abstract
Metallic materials have a significant number of applications, among which Al alloys have drawn people’s attention due to their low density and high strength. High-strength Al-based alloys, such as 7XXX Al alloys, contain many alloying elements and with high concentration, whose microstructures present
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Metallic materials have a significant number of applications, among which Al alloys have drawn people’s attention due to their low density and high strength. High-strength Al-based alloys, such as 7XXX Al alloys, contain many alloying elements and with high concentration, whose microstructures present casting voids, segregation, dendrites, etc. In this work, a spray deposition method was employed to fabricate an Al-8.31Zn-2.07Mg-2.46Cu-0.12Zr (wt %) alloy with fine structure. The hot deformation behavior of the studied alloy was investigated using a Gleeble 1500 thermal simulator and electron microscopes. The microstructure evolution, variation in the properties, and precipitation behavior were systematically investigated to explore a short process producing an alloy with high property values. The results revealed that the MgZn2 particles were detected from inside the grain and grain boundary, while some Al3Zr particles were inside the grain. An Arrhenius equation was employed to describe the relationship between the flow stress and the strain rate, and the established constitutive equation was that: ε˙=[sinh(0.017σ)]4.049exp[19.14(129.9/RT)]. An appropriate hot extrusion temperature was determined to be 460 °C. Hot deformation (460 °C by 60%) + age treatment (120 °C) was optimized to shorten the processing method for the as-spray-deposited alloy, after which considerable properties were approached. The high strength was mainly attributed to the grain boundary strengthening and the precipitation strengthening from the nanoscale MgZn2 and Al3Zr precipitates. Full article
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