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Metals, Volume 9, Issue 12 (December 2019) – 120 articles

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Cover Story (view full-size image) Refractory high entropy alloys (HEAs) are considered to be a candidate as structure materials for [...] Read more.
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Open AccessArticle
Power Spinning of the Curved Head with Tailor Welded Aluminum Alloy Blank: Deformation, Microstructure, and Property
Metals 2019, 9(12), 1359; https://doi.org/10.3390/met9121359 - 17 Dec 2019
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Abstract
The power spinning of tailor-welded blank (TWB) provides a feasible way to form the large-scale curved heads of aluminum alloy. However, the inhomogeneous material property of TWB produces different and more complex spinning behaviors compared with the traditional spinning of an integral homogenous [...] Read more.
The power spinning of tailor-welded blank (TWB) provides a feasible way to form the large-scale curved heads of aluminum alloy. However, the inhomogeneous material property of TWB produces different and more complex spinning behaviors compared with the traditional spinning of an integral homogenous blank. In this research, the deformation characteristics, microstructure, and the properties of the power spun curved head with aluminum alloy TWB were studied. A finite element model considering the inhomogeneous material property of welded blank is developed for the analysis of the power spinning process. To conduct accurate and efficient simulation, an effective meshing method is proposed according to the feature of TWB. The simulation and experimental results show that the weld zone (WZ) presents the larger equivalent stress but smaller equivalent strain than base material zone (BMZ) in power spinning due to its larger deformation resistance. Under the combined effects of the spiral local loading path and inhomogeneous deformability of TWB, the equivalent strain near the weld zone has an asymmetric V-shaped distribution. Strain inhomogeneity gradually increases with deformation and leads to an increase of the flange swing degree. In addition, the circumferential thickness distribution is relatively uniform, which is little affected by the existence of the weld line. However, the circumferential unfitability distribution becomes non-uniform and the roundness is worsened due to the existence of the weld line. Compared to the initial blank, the microstructure in WZ and BMZ are both elongated after spinning. The tensile strength is improved but plasticity reduced after power spinning based on the circumferential and radial tests of WZ and BMZ. The results are of theoretical and technical guidance for the power spinning of the curved head component with TWB. Full article
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Open AccessEditorial
Metals Powders: Synthesis and Processing
Metals 2019, 9(12), 1358; https://doi.org/10.3390/met9121358 - 17 Dec 2019
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Abstract
Metallic parts can be obtained by a wide variety of techniques [...] Full article
(This article belongs to the Special Issue Metals Powders: Synthesis and Processing)
Open AccessArticle
Investigation of the Effect of Short Exposure in the Temperature Range of 750–950 °C on the Ductility of Haynes® 282® by Advanced Microstructural Characterization
Metals 2019, 9(12), 1357; https://doi.org/10.3390/met9121357 - 17 Dec 2019
Viewed by 666
Abstract
A Gleeble-based test method has been developed to study the change in the ductility signature of Haynes® 282® during isothermal exposure from 5 s to 1800 s. A temperature range of 750 to 950 °C has been used to investigate the [...] Read more.
A Gleeble-based test method has been developed to study the change in the ductility signature of Haynes® 282® during isothermal exposure from 5 s to 1800 s. A temperature range of 750 to 950 °C has been used to investigate the effect of age-hardening reactions. Microstructural constituents have been analyzed and quantified using scanning and transmission electron microscopy. Carbides present in the material are identified as primary MC-type TiC carbides, Mo-rich M6C secondary carbides, and Cr-rich M23C6 secondary carbides. Gamma prime (γ′) precipitates are present in all the material conditions with particle sizes ranging from 2.5 nm to 58 nm. Isothermal exposure causes the growth of γ′ and development of a grain boundary carbide network. A ductility minimum is observed at 800–850 °C. The fracture mode is found to be dependent on the stroke rate, where a transition toward intergranular fracture is observed for stroke rates below 0.055 mm/s. Intergranular fracture is characterized by microvoids present on grain facets, while ductility did not change during ongoing age-hardening reactions for intergranularly fractured Haynes® 282®. Full article
(This article belongs to the Special Issue Welding Metallurgy and Weldability of Superalloys)
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Open AccessEditorial
Modelling and Simulation of Sheet Metal Forming Processes
Metals 2019, 9(12), 1356; https://doi.org/10.3390/met9121356 - 17 Dec 2019
Viewed by 281
Abstract
Numerical simulation of sheet metal forming processes has become an indispensable tool for the design of components and their forming process, in industries ranging from the automotive, to the aeronautics, packing and household appliances [...] Full article
(This article belongs to the Special Issue Modelling and Simulation of Sheet Metal Forming Processes)
Open AccessArticle
Multiparametric Investigation of Welding Techniques on Toe Radius of High Strength Steel at Low-Temperature Levels Using 3D-Scanning Techniques
Metals 2019, 9(12), 1355; https://doi.org/10.3390/met9121355 - 17 Dec 2019
Viewed by 334
Abstract
To avoid the occurrence of surface cracks at the welds, it is important to lower the stress concentration in the zone of the weld face by an appropriate choice of parameters. A plethora of experiments was conducted varying four welding techniques. The welded [...] Read more.
To avoid the occurrence of surface cracks at the welds, it is important to lower the stress concentration in the zone of the weld face by an appropriate choice of parameters. A plethora of experiments was conducted varying four welding techniques. The welded samples were scanned with 3D scanners and the toe radius was measured on each sample. The significance of the obtained results was analyzed using Pareto diagrams. The experiment results analysis shows that the length of the electrode stick-out has a significant influence on the toe radius, while the shielding gas has a great effect on the toe radius. Moreover, with the analysis of results obtained by experiments it was proved that the interaction of the torch angle and the number of cover passes, as well as that of the torch angle and the shielding gas, has a significant influence on the toe radius. Full article
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Open AccessArticle
Removal of Phosphorus from High-Phosphorus Manganese Ores by Ammonia-Ammonium Carbonate Leaching Method
Metals 2019, 9(12), 1354; https://doi.org/10.3390/met9121354 - 16 Dec 2019
Viewed by 364
Abstract
High-phosphorus manganese ores provide an important source of manganese, which is regarded as an irreplaceable material in the steel industry. The ammonia-ammonium carbonate leaching method was proposed for the removal of phosphorus and extracting manganese from high-phosphorus manganese ore, both effectively and environmentally. [...] Read more.
High-phosphorus manganese ores provide an important source of manganese, which is regarded as an irreplaceable material in the steel industry. The ammonia-ammonium carbonate leaching method was proposed for the removal of phosphorus and extracting manganese from high-phosphorus manganese ore, both effectively and environmentally. To explore the dissolution behavior of phosphorus and manganese in the ammonia-ammonium carbonate solution, the effect of the ammonia-to-ammonium carbonate concentration ratio, the leaching temperature, and the liquid-to-solid ratio on manganese extraction and dephosphorization rate were investigated. In addition, the composition of precipitated manganiferous sample, which was obtained from high-phosphorus manganese ores by ammonia-ammonium carbonate leaching process, was also studied. The results indicated that more than 99.2% phosphorus was removed and more than 83.5% of manganese was extracted by ammonia-ammonium carbonate leaching under the following conditions: ammonia to ammonium carbonate concentrations: 14:2 mol/L; liquid/solid ratio: 5:1 mL/g; leaching temperature: 25 °C; The precipitated manganiferous sample has little impurities, Mn% is 44.12%, P% is 0.02%, P/Mn = 0.00045. Full article
(This article belongs to the Special Issue Separation and Leaching for Metals Recovery)
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Open AccessArticle
Corrosion Study of Pipeline Steel under Stress at Different Cathodic Potentials by EIS
Metals 2019, 9(12), 1353; https://doi.org/10.3390/met9121353 - 16 Dec 2019
Viewed by 324
Abstract
The effect of different cathodic potentials applied to the X70 pipeline steel immersed in acidified and aerated synthetic soil solution under stress using a slow strain rate test (SSRT) and electrochemical impedance spectroscopy (EIS) was studied. According to SSRT results and the fracture [...] Read more.
The effect of different cathodic potentials applied to the X70 pipeline steel immersed in acidified and aerated synthetic soil solution under stress using a slow strain rate test (SSRT) and electrochemical impedance spectroscopy (EIS) was studied. According to SSRT results and the fracture surface analysis by scanning electron microscopy (SEM), the steel susceptibility to stress corrosion cracking (SCC) increased as the cathodic polarization increased (Ecp). This behavior is attributed to the anodic dissolution at the tip of the crack and the increment of the cathodic reaction (hydrogen evolution) producing hydrogen embrittlement. Nevertheless, when the Ecp was subjected to the maximum cathodic potential applied (−970 mV), the susceptibility decreased; this behavior is attributed to the fact that the anodic dissolution was suppressed and the process of the SCC was dominated only by hydrogen embrittlement (HE). The EIS results showed that the cathodic process was influenced by the mass transport (hydrogen diffusion) due to the steel undergoing so many changes in the metallic surface as a result of the applied strain that it generated active sites at the surface. Full article
(This article belongs to the Special Issue Corrosion and Protection of Metals)
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Open AccessArticle
Influence of Crystal Structure of Nitride Compound Layer on Torsion Fatigue Strength of Alloy Steel
Metals 2019, 9(12), 1352; https://doi.org/10.3390/met9121352 - 16 Dec 2019
Viewed by 308
Abstract
The demand for high-strength components for commercial vehicles has recently increased. Conventional gas nitrocarburizing has been used to increase strength and productivity of the crankshaft. A potential-controlled nitriding process was recently developed to control the crystal structure of the nitride compound layer. It [...] Read more.
The demand for high-strength components for commercial vehicles has recently increased. Conventional gas nitrocarburizing has been used to increase strength and productivity of the crankshaft. A potential-controlled nitriding process was recently developed to control the crystal structure of the nitride compound layer. It has been found that this treatment improves the bending fatigue strength compared with conventional treatment, and has the potential to cope with the increase in crankshaft strength. However, the effect of torsional fatigue strength has not been studied. Therefore, in this study, the influence of the crystal structure of the nitride compound layer on torsional fatigue strength was investigated. Two kinds of test specimens with different crystal structures of the compound layer were prepared using gas nitriding treatment with controlled nitriding potential for an alloy steel bar (JIS-SCM435). Torsional fatigue tests were carried out using these test specimens. Although the compound layer of these test specimens had different crystal structures, the hardness distribution and residual stress distribution on the diffusion layer were almost the same. The relationship between stress amplitude and number of cycles to failure (S-N curve) showed that the torsional fatigue limits of the specimens were almost the same. This indicates that the crystal structure of the nitride compound layer did not affect the torsional fatigue limits, because the origin of the torsional fatigue failure is inside the specimen. Full article
(This article belongs to the Special Issue Advanced Surface Enhancement)
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Open AccessArticle
Laser Beam Welding of a Low Density Refractory High Entropy Alloy
Metals 2019, 9(12), 1351; https://doi.org/10.3390/met9121351 - 16 Dec 2019
Viewed by 335
Abstract
The effect of laser beam welding on the structure and properties of a Ti1.89NbCrV0.56 refractory high entropy alloy was studied. In particular, the effect of different pre-heating temperatures was examined. Due to the low ductility of the material, laser beam [...] Read more.
The effect of laser beam welding on the structure and properties of a Ti1.89NbCrV0.56 refractory high entropy alloy was studied. In particular, the effect of different pre-heating temperatures was examined. Due to the low ductility of the material, laser beam welding at room temperature resulted in the formations of hot cracks. Sound butt joints without cracks were produced using pre-heating to T ≥ 600 °C. In the initial as-cast condition, the alloy consisted of coarse bcc grains with a small amount of lens-shaped C15 Laves phase particles. A columnar microstructure was formed in the welds; the thickness of the grains increased with the temperature of pre-heating before welding. The Laves phase particles were formed in the seams after welding at 600 °C or 800 °C, however, these particles were not observed after welding at room temperature or at 400 °C. Soaking at elevated temperatures did not change the microstructure of the base material considerably, however, “additional” small Laves particles formed at 600 °C or 800 °C. Tensile test of welded specimens performed at 750 °C resulted in the fracture of the base material because of the higher hardness of the welds. The latter can be associated with the bcc grains refinement in the seams. Full article
(This article belongs to the Special Issue High Entropy Alloys: Challenges and Prospects)
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Open AccessArticle
Blast-Induced Compression of a Thin-Walled Aluminum Honeycomb Structure—Experiment and Modeling
Metals 2019, 9(12), 1350; https://doi.org/10.3390/met9121350 - 15 Dec 2019
Viewed by 392
Abstract
The presented discussion concerns the behavior of a thin-walled hexagonal aluminum honeycomb structure subjected to blast loading. The shock wave affecting the structure is generated by detonation of the C4 charge in an explosive-driven shock tube (EDST). The EDST set-up is an instrumented [...] Read more.
The presented discussion concerns the behavior of a thin-walled hexagonal aluminum honeycomb structure subjected to blast loading. The shock wave affecting the structure is generated by detonation of the C4 charge in an explosive-driven shock tube (EDST). The EDST set-up is an instrumented device that makes it possible to study blast effects in more stable and repeatable conditions than those obtained in a free-air detonation. The formation of folds characteristic of a honeycomb deformation in the axial compression distributes the initial loading over a time period, which is considered as an efficient method of energy dissipation. The test configuration is modeled in the Ls-Dyna explicit code, which enables analysis of the mechanisms of energy absorption that accompanies structural deformation under a blast loading. The conclusions reached in the performed experimental and numerical investigation can be applied to the modeling and optimization of cellular structures used to mitigate blast loadings. Full article
(This article belongs to the Special Issue Metallic Materials under Dynamic Loading)
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Open AccessFeature PaperArticle
Directed Irradiation Synthesis as an Advanced Plasma Technology for Surface Modification to Activate Porous and “as-received” Titanium Surfaces
Metals 2019, 9(12), 1349; https://doi.org/10.3390/met9121349 - 15 Dec 2019
Viewed by 370
Abstract
For the design of smart titanium implants, it is essential to balance the surface properties without any detrimental effect on the bulk properties of the material. Therefore, in this study, an irradiation-driven surface modification called directed irradiation synthesis (DIS) has been developed to [...] Read more.
For the design of smart titanium implants, it is essential to balance the surface properties without any detrimental effect on the bulk properties of the material. Therefore, in this study, an irradiation-driven surface modification called directed irradiation synthesis (DIS) has been developed to nanopattern porous and “as-received” c.p. Ti surfaces with the aim of improving cellular viability. Nanofeatures were developed using singly-charged argon ions at 0.5 and 1.0 keV energies, incident angles from 0° to 75° degrees, and fluences up to 5.0 × 1017 cm−2. Irradiated surfaces were evaluated by scanning electron microscopy, atomic force microscopy and contact angle, observing an increased hydrophilicity (a contact angle reduction of 73.4% and 49.3%) and a higher roughness on both surfaces except for higher incident angles, which showed the smoothest surface. In-vitro studies demonstrated the biocompatibility of directed irradiation synthesis (DIS) reaching 84% and 87% cell viability levels at 1 and 7 days respectively, and a lower percentage of damaged DNA in tail compared to the control c.p. Ti. All these results confirm the potential of the DIS technique to modify complex surfaces at the nanoscale level promoting their biological performance. Full article
(This article belongs to the Special Issue Tailor-Made Porous Biomaterials for Hard and Soft Tissues)
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Open AccessArticle
Evaluation of Microstructures and Mechanical Properties of Sn-10Sb-Ni Lead-Free Solder Alloys with Small Amount of Ni Using Miniature Size Specimens
Metals 2019, 9(12), 1348; https://doi.org/10.3390/met9121348 - 14 Dec 2019
Viewed by 371
Abstract
Sn-Sb-Ni solder alloy is expected to be used as a die-attach material for a next-generation power semiconductors in power module. The aim of this paper is to investigate the effects of the Ni content on microstructures, tensile, and fatigue properties of Sn-10Sb-xNi (x [...] Read more.
Sn-Sb-Ni solder alloy is expected to be used as a die-attach material for a next-generation power semiconductors in power module. The aim of this paper is to investigate the effects of the Ni content on microstructures, tensile, and fatigue properties of Sn-10Sb-xNi (x = 0.05, 0.10, 0.25, 0.50) (mass%) lead-free solder alloys using miniature size specimens. The Sn-10Sb-Ni solder alloys have the microstructure in which Sb-Sn and Ni-Sb compounds are dispersed in the β-Sn matrix. As the Sb and Ni content increases, Sb-Sn and Ni-Sb compounds are coarsened, respectively. The effect of the Ni content on tensile properties of the alloy is slight at 25 °C. At 150 °C and 200 °C, 0.1% proof stress and tensile strength increase gradually with the Ni content increases, and saturate at the Ni amount over 0.25 mass%. According to the fatigue test at 200 °C, the fatigue properties of Sn-10Sb-Ni with 0.10–0.25 mass% Ni are better than that of the Sn-10Sb. From the experimental results, Sn-10Sb-Ni with 0.10–0.25 mass% Ni have superior mechanical properties. Full article
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Open AccessArticle
Nickel, Graphene, and Yttria-Stabilized Zirconia (YSZ)-Added Mg by Grinding in Hydrogen Atmosphere for Hydrogen Storage
Metals 2019, 9(12), 1347; https://doi.org/10.3390/met9121347 - 14 Dec 2019
Viewed by 370
Abstract
Magnesium (Mg) has good hydrogen storage features except for its slow reaction kinetics with hydrogen and high hydride decomposition temperature. Yttria (Y2O3)-stabilized zirconia (ZrO2) (YSZ), nickel (Ni), and graphene were picked as additives to Mg to solve [...] Read more.
Magnesium (Mg) has good hydrogen storage features except for its slow reaction kinetics with hydrogen and high hydride decomposition temperature. Yttria (Y2O3)-stabilized zirconia (ZrO2) (YSZ), nickel (Ni), and graphene were picked as additives to Mg to solve these problems. Samples with a composition of 92.5 wt% Mg + 2.5 wt% YSZ + 2.5 wt% Ni + 2.5 wt% graphene (designated as Mg + YSZ + Ni + graphene) were prepared by grinding in hydrogen atmosphere. The activation of Mg + YSZ + Ni + graphene was finished at the third cycle (n = 3). Mg + YSZ + Ni + graphene had an efficient hydrogen storage capacity (the amount of hydrogen absorbed for 60 min) over 7 wt% (7.11 wt%) at n = 1. Mg + YSZ + Ni + graphene contained Mg2Ni phase after cycling. The addition of Ni and Ni + YSZ greatly increased the initial hydride formation and decomposition rates, and the amount of hydrogen absorbed and released for 60 min, Ha (60 min) and Hd (60 min), respectively, of a 95 wt% Mg + 5 wt% graphene sample (Mg + graphene). Rapid nucleation of the Mg2Ni-H solid solution in Ni-containing samples is believed to have led to higher initial decomposition rates than Mg + graphene and Mg. The addition of YSZ also enhanced the initial decomposition rate and Hd (60 min) compared to a sample with a composition of 95 wt% Mg + 2.5 wt% Ni + 2.5 wt% graphene (Mg + Ni + graphene). Full article
(This article belongs to the Special Issue Advanced Hydrogen Storage Metallic Materials/Nanomaterials)
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Open AccessFeature PaperArticle
Understanding the Interdependence of Penetration Depth and Deformation on Nanoindentation of Nanoporous Silver
Metals 2019, 9(12), 1346; https://doi.org/10.3390/met9121346 - 14 Dec 2019
Viewed by 367
Abstract
A silver-based nanoporous material was produced by dealloying (selective chemical etching) of an Ag38.75Cu38.75Si22.5 crystalline alloy. Composed of connected ligaments, this material was imaged using a scanning electron microscope (SEM) and focused ion-beam (FIB) scanning electron microscope tomography. [...] Read more.
A silver-based nanoporous material was produced by dealloying (selective chemical etching) of an Ag38.75Cu38.75Si22.5 crystalline alloy. Composed of connected ligaments, this material was imaged using a scanning electron microscope (SEM) and focused ion-beam (FIB) scanning electron microscope tomography. Its mechanical behavior was evaluated using nanoindentation and found to be heterogeneous, with density variation over a length scale of a few tens of nanometers, similar to the indent size. This technique proved relevant to the investigation of a material’s mechanical strength, as well as to how its behavior related to the material’s microstructure. The hardness is recorded as a function of the indent depth and a phenomenological description based on strain gradient and densification kinetic was proposed to describe the resultant depth dependence. Full article
(This article belongs to the Special Issue Trends in Plasticity of Metals and Alloys)
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Open AccessFeature PaperArticle
Power Law Breakdown in the Creep in Single-Phase Metals
Metals 2019, 9(12), 1345; https://doi.org/10.3390/met9121345 - 14 Dec 2019
Viewed by 324
Abstract
New analysis provides insight into the basis of power-law breakdown (PLB) in the steady-state creep of metals and alloys. A variety of theories has been presented in the past but this new examination suggests that there is evidence that a dramatic supersaturation of [...] Read more.
New analysis provides insight into the basis of power-law breakdown (PLB) in the steady-state creep of metals and alloys. A variety of theories has been presented in the past but this new examination suggests that there is evidence that a dramatic supersaturation of vacancies leading to very high diffusion rates and enhanced dislocation climb is associated with the rate-controlling process for creep in PLB. The effect of vacancy supersaturation may be enhanced by dislocation short circuit diffusion paths at lower temperatures due to the dramatic increase in dislocation density. Full article
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Open AccessArticle
On the Use of Functionally Graded Materials to Differentiate the Effects of Surface Severe Plastic Deformation, Roughness and Chemical Composition on Cell Proliferation
Metals 2019, 9(12), 1344; https://doi.org/10.3390/met9121344 - 13 Dec 2019
Viewed by 304
Abstract
Additive manufacturing allows the manufacture of parts made of functionally graded materials (FGM) with a chemical gradient. This research work underlines that the use of FGM makes it possible to study mechanical, microstructural or biological characteristics while minimizing the number of required samples. [...] Read more.
Additive manufacturing allows the manufacture of parts made of functionally graded materials (FGM) with a chemical gradient. This research work underlines that the use of FGM makes it possible to study mechanical, microstructural or biological characteristics while minimizing the number of required samples. The application of severe plastic deformation (SPD) by surface mechanical attrition treatment (SMAT) on FGM brings new insights on a major question in this field: which is the most important parameter between roughness, chemistry and microstructure modification on biocompatibility? Our study demonstrates that roughness has a large impact on adhesion while microstructure refinement plays a key role during the early stage of proliferation. After several days, chemistry is the main parameter that holds sway in the proliferation stage. With this respect, we also show that niobium has a much better biocompatibility than molybdenum when alloyed with titanium. Full article
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Open AccessArticle
Comparison of Charge Storage Properties of Prussian Blue Analogues Containing Cobalt and Copper
Metals 2019, 9(12), 1343; https://doi.org/10.3390/met9121343 - 13 Dec 2019
Viewed by 348
Abstract
Prussian blue analogues are of great interest as alternative battery materials because of their long life cycle and potential use of earth-abundant elements. In this work, thin film mixed-metal hexacyanoferrates (HCFs) based on NiCo and NiCu alloys were fabricated in an all electrochemical [...] Read more.
Prussian blue analogues are of great interest as alternative battery materials because of their long life cycle and potential use of earth-abundant elements. In this work, thin film mixed-metal hexacyanoferrates (HCFs) based on NiCo and NiCu alloys were fabricated in an all electrochemical process. The structure and composition of the samples were characterized, along with the charge storage capacity and kinetics of the charge transfer reaction. For both NiCo-HCF and NiCu-HCF samples, the total charge capacity increased with the substitution of Ni with more Co or Cu, and the increase was larger for Cu samples than for Co samples. On the other hand, the charge storage kinetics had only a modest change with substituted metal, and these effects were independent of the amount of that substitution. Thus, the mixed-metal HCFs have promise for increasing overall storage capacity without negatively influencing the rate capability when used in battery applications. Full article
(This article belongs to the Special Issue Metals and Alloys for Energy Conversion and Storage Applications)
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Open AccessArticle
Particle Size-Dependent Microstructure, Hardness and Electrochemical Corrosion Behavior of Atmospheric Plasma Sprayed NiCrBSi Coatings
Metals 2019, 9(12), 1342; https://doi.org/10.3390/met9121342 - 12 Dec 2019
Viewed by 333
Abstract
Particle size is a critical consideration for many powder coating-related industries since it significantly influences the properties of the produced materials. However, the effect of particle size on the characteristics of plasma sprayed NiCrBSi coatings is not well understood. This work investigates the [...] Read more.
Particle size is a critical consideration for many powder coating-related industries since it significantly influences the properties of the produced materials. However, the effect of particle size on the characteristics of plasma sprayed NiCrBSi coatings is not well understood. This work investigates the microstructures, hardness and electrochemical corrosion behavior of plasma sprayed NiCrBSi coatings synthesized using different-sized powders. All coatings mainly consist of Ni, N3B, CrB, Cr7C3 and Cr3C2 phases. The coatings produced by small particles (50–75 μm) exhibit lower porosity (2.0 ± 0.8%). Such coatings show a higher fraction (15.5 vol.%) of the amorphous phase and lower hardness (700 HV0.5) than the counterparts (8.7 vol.% and 760 HV0.5, respectively) produced by large particles (75–100 μm) with higher porosity (3.0 ± 1.6%). Meanwhile, the coatings produced from smaller particles possess a larger number of non-bonded boundaries, leading to the easier penetration of corrosive medium, as well as a higher corrosion current density (0.254 ± 0.062 μA/cm2) and a lower charge transfer resistance (0.37 ± 0.07 MΩ cm2). These distinctions are attributed to particle size-induced different melting degrees and stackings of in-flight particles during deposition. Full article
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Open AccessArticle
Investigation on Contact Heating of Aluminum Alloy Sheets in Hot Stamping Process
Metals 2019, 9(12), 1341; https://doi.org/10.3390/met9121341 - 12 Dec 2019
Viewed by 336
Abstract
Application of the hot stamping process on heat-treatable aluminum alloys effectively solves the problems of large springback and poor ductility during forming at room temperature, which expands the range of applications of aluminum alloys in the transportation industry. Sheet heating plays an important [...] Read more.
Application of the hot stamping process on heat-treatable aluminum alloys effectively solves the problems of large springback and poor ductility during forming at room temperature, which expands the range of applications of aluminum alloys in the transportation industry. Sheet heating plays an important role in the hot stamping process, and increasing the heating rate can improve the hot stamping efficiency to some extent. In this paper, the feasibility of applying contact heating techniques with higher heating rates in the hot stamping process was studied. A contact heating device was designed, and the temperature distribution of the device contact surface was observed. Furthermore, the heating characteristics of 7075 aluminum alloy sheets during the contact heating process were explored by experiments and finite element simulation. Finally, the rapid solution treatment of aluminum alloy was carried out with a contact heating device, which was compared with the furnace heating solution treatment. The experimental and simulation results indicate that the device contact surface has a relatively uniform temperature distribution, and the aluminum alloy sheets can be heated to close to the set temperature in 15 s using contact heating techniques. Meanwhile, the rapid solution treatment of aluminum alloy sheets can be achieved within 15–20 s by contact heating techniques, obtaining superior mechanical properties. This suggests that the contact heating process can be used for rapid heating and rapid solution treatment of aluminum alloy sheets in hot stamping process. Full article
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Open AccessArticle
Production of Ferronickel Concentrate from Low-Grade Nickel Laterite Ore by Non-Melting Reduction Magnetic Separation Process
Metals 2019, 9(12), 1340; https://doi.org/10.3390/met9121340 - 12 Dec 2019
Viewed by 348
Abstract
The production of ferronickel concentrate from low-grade nickel laterite ore containing 1.31% nickel (Ni) was studied by the non-melting reduction magnetic separation process. The sodium chloride was used as additive and coal as a reductant. The effects of roasting temperature, roasting duration, reductant [...] Read more.
The production of ferronickel concentrate from low-grade nickel laterite ore containing 1.31% nickel (Ni) was studied by the non-melting reduction magnetic separation process. The sodium chloride was used as additive and coal as a reductant. The effects of roasting temperature, roasting duration, reductant dosage, additive dosage, and grinding time on the grade and recovery were investigated. The optimal reduction conditions are a roasting temperature of 1250 °C, roasting duration of 80 min, reductant dosage of 10%, additive dosage of 5%, and a grinding time of 12 min. The grades of nickel and iron are improved from 2.13% and 51.12% to 8.15% and 64.28%, and the recovery of nickel is improved from 75.40% to 97.76%. The research results show that the additive in favor of the phase changes from lizardite phase to forsterite phase. The additive promotes agglomeration and separation of nickel and iron. Full article
(This article belongs to the Special Issue Advances in Pyrometallurgy)
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Open AccessArticle
Copper Extraction from Black Copper Ores through Modification of the Solution Potential in the Irrigation Solution
Metals 2019, 9(12), 1339; https://doi.org/10.3390/met9121339 - 11 Dec 2019
Viewed by 406
Abstract
This article presented the behavior of ores containing black copper under acid leaching. The solution potential was modified by adding agents, and five leaching conditions were evaluated, one as a control based on sulfuric acid leaching (conventional), and the others by changing the [...] Read more.
This article presented the behavior of ores containing black copper under acid leaching. The solution potential was modified by adding agents, and five leaching conditions were evaluated, one as a control based on sulfuric acid leaching (conventional), and the others by changing the solution potential with: ferrous sulfate (FeSO4), white metal (Cu2S), sulfur dioxide (SO2), and ozone (O3). Leaching behavior was evaluated with laboratory bottle (ISO-pH) and column leaching tests. Two ores samples from the Lomas Bayas mine were used. The samples, identified as low (LG) and high grade (HG), were characterized as 0.13–0.25% Cu and 0.15–0.38% Mn, respectively. The mineralogical analysis indicated that black copper represented around 20% of total Cu (0.05% Cu). The results of the bottle tests indicated that the solution potential decreased with the addition of reducing agents, while the copper extraction rate with the HG sample increased to 83.7%, which exceeded the extraction rate obtained by conventional acid leaching by 25%. Ozone did not favor the extraction of Mn and Cu extraction when the solution potential increased. Cu and Mn extraction were directly related. The results of the column leaching tests showed that it was possible to maintain the solution potential at values below 600 mV (SHE) with the addition of white metal and sulfur dioxide while obtaining the highest copper extraction rate of approximately 60%, which was 18% higher than the rate obtained with conventional leaching. Sulfuric acid consumption was 11 kg/t over 45 days of leaching. Full article
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Open AccessArticle
Investigation of AlCrN-Coated Inserts on Cryogenic Turning of Ti-6Al-4V Alloy
Metals 2019, 9(12), 1338; https://doi.org/10.3390/met9121338 - 11 Dec 2019
Viewed by 405
Abstract
Over the past decade, the focus of the metal cutting industry has been on the improvement of tool life for achieving higher productivity and better finish. Researchers are attempting to reduce tool failure in several ways such as modified coating characteristics of a [...] Read more.
Over the past decade, the focus of the metal cutting industry has been on the improvement of tool life for achieving higher productivity and better finish. Researchers are attempting to reduce tool failure in several ways such as modified coating characteristics of a cutting tool, conventional coolant, cryogenic coolant, and cryogenic treated insert. In this study, a single layer coating was made on cutting carbide inserts with newly determined thickness. Coating thickness, presence of coating materials, and coated insert hardness were observed. This investigation also dealt with the effect of machining parameters on the cutting force, surface finish, and tool wear when turning Ti-6Al-4V alloy without coating and Physical Vapor Deposition (PVD)-AlCrN coated carbide cutting inserts under cryogenic conditions. The experimental results showed that AlCrN-based coated tools with cryogenic conditions developed reduced tool wear and surface roughness on the machined surface, and cutting force reductions were observed when a comparison was made with the uncoated carbide insert. The best optimal parameters of a cutting speed (Vc) of 215 m/min, feed rate (f) of 0.102 mm/rev, and depth of cut (doc) of 0.5 mm are recommended for turning titanium alloy using the multi-response TOPSIS technique. Full article
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Open AccessArticle
Microstructure and Tensile Properties of AlSi10Mg Alloy Manufactured by Multi-Laser Beam Selective Laser Melting (SLM)
Metals 2019, 9(12), 1337; https://doi.org/10.3390/met9121337 - 11 Dec 2019
Cited by 1 | Viewed by 338
Abstract
The multi-beam selective laser forming system is a new type of powder bed laser forming equipment that is different from single-laser selective laser melting (SLM) printers. It is a new generation for a metal powder material moulding process that has high efficiency, large [...] Read more.
The multi-beam selective laser forming system is a new type of powder bed laser forming equipment that is different from single-laser selective laser melting (SLM) printers. It is a new generation for a metal powder material moulding process that has high efficiency, large size and batch manufacturing. It is a new development of a powder bed laser forming process trend. In this paper, the microstructure and tensile properties of both the multi-laser-formed AlSi10Mg isolated and overlap areas are studied to ensure that the parts can achieve perfect seamless splicing and to identify whether the parts in different regions have the same performance. It was discovered that as the number of scans increases, the depth and width of the melt pool and microscopic grain structure in the overlap zone increase. The preferential crystallite growth orientation reaches the (200) plane. A small amount of smooth surface appeared at the fracture of the overlap area of the two scans, the dimples were reduced and the structure became larger, resulting in a decrease in tensile properties. Full article
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Open AccessArticle
Synergistic Effect of Nd and Ga on the Microstructure and Mechanical Properties of ER4047 Alloy Wires
Metals 2019, 9(12), 1336; https://doi.org/10.3390/met9121336 - 11 Dec 2019
Viewed by 324
Abstract
The synergistic effects of Nd and Ga on the microstructure and mechanical properties of ER4047 alloy wires and the resulting MIG(Melt inert-gas welding) joints were investigated. Experimental results show that the hydrogen content in the liquid and solid alloy decreases rapidly and then [...] Read more.
The synergistic effects of Nd and Ga on the microstructure and mechanical properties of ER4047 alloy wires and the resulting MIG(Melt inert-gas welding) joints were investigated. Experimental results show that the hydrogen content in the liquid and solid alloy decreases rapidly and then increases slowly with the addition of Nd in the range of 0–0.8 wt.%. Under the same conditions, the hydrogen content ratio in the solid and liquid is between 1.9 and 2.1. After adding 0.08–0.2 wt.% Nd, the α-Al dendrites and eutectic Si phases in the ER4047 alloys are refined and modified, respectively; the quality index of the cast rod increases and the weld percent porosity of the MIG joint significantly decreases. However, when 0.8 wt.% Nd is added, although the size of the eutectic Si phase reaches a minimum value, a large number of coarse needle-like Nd-rich phases precipitate in the structure. Moreover, Ga inhibits the precipitation of the Nd-rich phases, thus improving the mechanical properties, especially the elongation of the cast rod. When 0.2 wt.% Nd and 0.05 wt.% Ga are added into the alloy wire, the porosity of the MIG joint reaches the lowest value herein, and the tensile strength and face/back bending angles reach their maximum values. Full article
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Open AccessArticle
Study of Inconel 718 Welded by Bead-On-Plate Laser Welding under High-Frequency Micro-Vibration Condition
Metals 2019, 9(12), 1335; https://doi.org/10.3390/met9121335 - 11 Dec 2019
Viewed by 336
Abstract
Inconel 718 alloy laser-welded joints have poor mechanical properties due to the presence of Laves phases and liquation cracks. This paper intends to solve the above problems by high-frequency micro-vibration-coupled bead-on-plate laser welding. According to the shape of the weld beam, the upper [...] Read more.
Inconel 718 alloy laser-welded joints have poor mechanical properties due to the presence of Laves phases and liquation cracks. This paper intends to solve the above problems by high-frequency micro-vibration-coupled bead-on-plate laser welding. According to the shape of the weld beam, the upper part of the weld is defined as the nail head, and the lower part is the nail body. The results showed that high-frequency micro-vibration can achieve grain refinement. The micro-vibration could break the primary dendrite arm to form secondary dendrite and reduce epitaxial growth of the cellular crystal region. Micro-vibration exacerbated the flow of Niobium (Nb) elements surrounded by dendrites and reduced dendritic segregation, which decreased the formation of Laves phases. The combination of interdendritic Nickel (Ni), Titanium (Ti), and Nb and the precipitation of strengthening phases γ′ and γ″ were promoted. When the vibration acceleration was 50.10 m/s2, it could inhibit the formation of Laves phases among dendrites and the size of the bulk Laves phase was effectively reduced. The cracks generated in the Inconel 718 alloy were distributed at three locations including the nail-head, the nail-body, and the junction of nail-head and nail-body. When the vibration frequency was 919 Hz, the length of the liquation crack reduced from 180 to 110 μm. While under 1331 Hz, the expansion of the liquation crack was extended, with the length of 200 μm. Full article
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Open AccessArticle
Process Optimization on Multilayer Morphology During 316L Double-wire CMT+P Deposition Process
Metals 2019, 9(12), 1334; https://doi.org/10.3390/met9121334 - 11 Dec 2019
Viewed by 265
Abstract
Cold metal transfer (CMT) has been widely used in metal additive manufacturing for its low heat input, less splashing and high efficiency. Wire feeding speed and travelling speed are important processes that affect morphology in CMT deposition. This study optimized the forming process [...] Read more.
Cold metal transfer (CMT) has been widely used in metal additive manufacturing for its low heat input, less splashing and high efficiency. Wire feeding speed and travelling speed are important processes that affect morphology in CMT deposition. This study optimized the forming process of 30-layer stainless-steel part deposited by double-wire and double-arc CMT plus pulse (CMT+P) process, and investigated the effect of the ratio of wire feeding speed to travelling speed on deposition morphology. The results show that asynchronous arc striking and extinguishing can improve the forming. Moreover, the deposition molding is affected by the interaction of heat input and heat accumulation. With the similar ratio of wire feeding speed to travelling speed and the similar heat input, increasing the wire feeding speed can increase the heat accumulation and the width of sample, and decrease the height. The optimum process interval of wire feeding speed to travelling speed ratio and heat input is 3.9–4.2 and 70–74.8 J/mm, respectively. Although the increasing heat accumulation makes grain coarse and slight decreases mechanical property, the highest deposition rate can be up to 5.4 kg/h, when wire feeding speed and travelling speed are 5 m/min and 120 cm/min, respectively, and the tensile strength and elongation rate of which can reach the basic standard requirements for stainless-steel forgings. Full article
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Open AccessArticle
Grain Refinement of AZ91 Magnesium Alloy Induced by Al-V-B Master Alloy
Metals 2019, 9(12), 1333; https://doi.org/10.3390/met9121333 - 10 Dec 2019
Viewed by 400
Abstract
It has long been recognized that grain refinement of Mg-Al alloys is difficult, although various methods have been tried. In the present paper, a novel grain refiner, Al-3.4V-1B master alloy, has been developed to refine the as-cast AZ91 alloy. A comparative study on [...] Read more.
It has long been recognized that grain refinement of Mg-Al alloys is difficult, although various methods have been tried. In the present paper, a novel grain refiner, Al-3.4V-1B master alloy, has been developed to refine the as-cast AZ91 alloy. A comparative study on grain refinement effects of Al-3.4V-1B, Al-5V, and Al-3Ti-1B master alloys was performed under the same solidification conditions. It is shown that Al-3.4V-1B master alloy not only has significant grain refinement ability, but also keeps stable anti-fading capacity with holding time up to 2 h. Based on the analysis of grain refinement, VB2 particles introduced by Al-3.4V-1B master alloy are the heterogeneous nuclei for AZ91 alloy. Full article
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Open AccessFeature PaperArticle
Animal Origin Bioactive Hydroxyapatite Thin Films Synthesized by RF-Magnetron Sputtering on 3D Printed Cranial Implants
Metals 2019, 9(12), 1332; https://doi.org/10.3390/met9121332 - 10 Dec 2019
Viewed by 453
Abstract
Ti6Al4V cranial prostheses in the form of patterned meshes were 3D printed by selective laser melting in an argon environment; using a CO2 laser source and micron-sized Ti6Al4V powder as the starting material. The size and shape of prostheses were chosen based [...] Read more.
Ti6Al4V cranial prostheses in the form of patterned meshes were 3D printed by selective laser melting in an argon environment; using a CO2 laser source and micron-sized Ti6Al4V powder as the starting material. The size and shape of prostheses were chosen based on actual computer tomography images of patient skull fractures supplied in the framework of a collaboration with a neurosurgery clinic. After optimizations of scanning speed and laser parameters, the printed material was defect-free (as shown by metallographic analyses) and chemically homogeneous, without elemental segregation or depletion. The prostheses were coated by radio-frequency magnetron sputtering (RF-MS) with a bioactive thin layer of hydroxyapatite using a bioceramic powder derived from biogenic resources (Bio-HA). Initially amorphous, the films were converted to fully-crystalline form by applying a post-deposition thermal-treatment at 500 °C/1 h in air. The X-ray diffraction structural investigations indicated the phase purity of the deposited films composed solely of a hexagonal hydroxyapatite-like compound. On the other hand, the Fourier transform infrared spectroscopic investigations revealed that the biological carbonatation of the bone mineral phase was well-replicated in the case of crystallized Bio-HA RF-MS implant coatings. The in vitro acellular assays, performed in both the fully inorganic Kokubo’s simulated body fluid and the biomimetic organic–inorganic McCoy’s 5A cell culture medium up to 21 days, emphasized both the good resistance to degradation and the biomineralization capacity of the films. Further in vitro tests conducted in SaOs-2 osteoblast-like cells showed a positive proliferation rate on the Bio-HA RF-MS coating along with a good adhesion developed on the biomaterial surface by elongated membrane protrusions. Full article
(This article belongs to the Special Issue Metal Additive Manufacturing – State of the Art 2020)
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Open AccessArticle
Effect of B2O3 on the Crystallization Behavior of CaF2-Based Slag for Electroslag Remelting 9CrMoCoB Steel
Metals 2019, 9(12), 1331; https://doi.org/10.3390/met9121331 - 10 Dec 2019
Viewed by 348
Abstract
The non-isothermal crystallization characteristics of the electroslag remelting (ESR)-type slag with varied B2O3 contents were investigated by non-isothermal differential scanning calorimetry (DSC), field emission scanning electron microscopy (SEM-EDS), and X-ray diffraction (XRD). The crystallization mechanism of the B2O [...] Read more.
The non-isothermal crystallization characteristics of the electroslag remelting (ESR)-type slag with varied B2O3 contents were investigated by non-isothermal differential scanning calorimetry (DSC), field emission scanning electron microscopy (SEM-EDS), and X-ray diffraction (XRD). The crystallization mechanism of the B2O3-bearing slag was also identified based on kinetics analysis. The results showed that the primary crystalline phase was CaF2, there was no change in the type of the primary crystal as B2O3 content increased, and the morphology of the CaF2 crystal was mainly dendritic. The sequence of crystal precipitation during the cooling process was CaF2 to Ca12Al14O32F2 and MgO/MgAl2O4, followed by Ca3B2O6. The activation energy of CaF2 crystallization increased firstly, then decreased and reached stability, while the activation energy of Ca3B2O6 crystallization increased continuously with the increasing B2O3 content. The crystallization behavior of CaF2 was three-dimensional growth with a constant nucleation rate. The proper B2O3 content added into the CaF2-based ESR slag should be around 1.0% to limit the precipitation of the CaF2 crystal to attain good surface ingot quality and stable ESR operation. Full article
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Open AccessArticle
Microstructure, Micro-Indentation, and Scratch Behavior of Cr Films Prepared on Al alloys by Using Magnetron Sputtering
Metals 2019, 9(12), 1330; https://doi.org/10.3390/met9121330 - 09 Dec 2019
Viewed by 403
Abstract
In this study, closed-field unbalanced magnetron sputtering (CFUMS) was employed to deposit pure Cr films on soft substrate of 2024 Al alloy. The effects of deposition powers and biases on the microstructures and mechanical performance of Cr films were systematically investigated by using [...] Read more.
In this study, closed-field unbalanced magnetron sputtering (CFUMS) was employed to deposit pure Cr films on soft substrate of 2024 Al alloy. The effects of deposition powers and biases on the microstructures and mechanical performance of Cr films were systematically investigated by using X-ray diffraction (XRD), scanning electron microscope (SEM), micro-indentation and scratch test. Results showed that all the Cr films had a strong (110) preferred orientation and anisotropic surface morphology with columnar structures. The size of Cr particles was in the range of 50–350 nm, increasing with larger target power and higher biases. The hardness of Cr films was between 3.3 and 4.8 GPa, which was much higher than the Al alloy substrate (1.44 GPa). The Young’s modulus of Cr film could reach a maximum value of 169 GPa at 2.0 kW/70 V. The critical load increased when increasing the power but decreased with higher bias, achieving a maximum value of 53.83 N at 2.0 kW/10 V. The adhesive failure mechanism of Cr film was mainly attributed to the plastic deformation of softer Al substrate. Full article
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