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Metals, Volume 7, Issue 7 (July 2017)

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Cover Story Structural model of the coherent interface between κ-carbide and fcc-Fe for density-functional [...] Read more.
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Editorial

Jump to: Research, Review

Open AccessEditorial Metals Challenged by Neutron and Synchrotron Radiation
Metals 2017, 7(7), 266; doi:10.3390/met7070266
Received: 28 June 2017 / Accepted: 29 June 2017 / Published: 11 July 2017
Cited by 1 | PDF Full-text (186 KB) | HTML Full-text | XML Full-text
Abstract
In the past one and a half decades, neutron and synchrotron radiation techniques have come to the forefront as an excellent set of tools for the wider investigation of material structures and properties [1,2], becoming available to a large user community.[...] Full article
(This article belongs to the Special Issue Metals Challenged by Neutron and Synchrotron Radiation)
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Research

Jump to: Editorial, Review

Open AccessArticle A New Recycling Process for Tungsten Carbide Soft Scrap That Employs a Mechanochemical Reaction with Sodium Hydroxide
Metals 2017, 7(7), 230; doi:10.3390/met7070230
Received: 2 June 2017 / Revised: 17 June 2017 / Accepted: 19 June 2017 / Published: 22 June 2017
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Abstract
WC soft scrap, including Co used as a binder, thermally oxidized at 600 °C, was subjected to grinding with NaOH in a mechanochemical reaction, followed by water leaching to establish an effective recycling process. Na2WO4 was synthesized through a mechanochemical
[...] Read more.
WC soft scrap, including Co used as a binder, thermally oxidized at 600 °C, was subjected to grinding with NaOH in a mechanochemical reaction, followed by water leaching to establish an effective recycling process. Na2WO4 was synthesized through a mechanochemical (MC) reaction with oxidized scrap, and Na2CO3 was formed when the mixing ratio of NaOH increased. These as-synthesized compounds were water-soluble. When the weight ratio of soft scrap to NaOH was 1:0.5, 99.2% W was extracted by water leaching, while the extraction yield of Co was limited to 3.57% under the same conditions. Full article
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Open AccessArticle Electrochemical Behaviour of PACVD TiN-Coated CoCrMo Medical Alloy
Metals 2017, 7(7), 231; doi:10.3390/met7070231
Received: 27 April 2017 / Revised: 14 June 2017 / Accepted: 20 June 2017 / Published: 23 June 2017
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Abstract
CoCrMo alloys have been used in hip replacements for many years, and their properties can be enhanced with hard coatings. The TiN layer can be deposited on a CoCrMo alloy to its improve corrosion properties, such as reduction of the release of potentially
[...] Read more.
CoCrMo alloys have been used in hip replacements for many years, and their properties can be enhanced with hard coatings. The TiN layer can be deposited on a CoCrMo alloy to its improve corrosion properties, such as reduction of the release of potentially harmful metal ions from CoCrMo-based surgical implants. In this work, a medical grade CoCrMo alloy was coated with TiN by means of plasma-assisted chemical deposition from the vapor phase (PACVD) technique at 500 °C for 4.5 h. The TiN/substrate interface and thickness of the TiN layer were analysed by scanning electron microscopy (SEM). Corrosion parameters Ecor, Rp, and Icor were determined via direct current (DC) and alternating current (AC) electrochemical techniques. The SEM analysis showed a highly dense and quite uniform TiN layer, with a thickness of 2 µm. The results obtained by the DC electrochemical methods show better corrosion stability of the TiN/CoCrMo samples in comparison with CoCrMo in 0.9% NaCl at (25 ± 1) °C and (36 ± 1) °C. The electrochemical impedance spectroscopy (EIS) results show that there are nuclei on the TiN coating which reduce the corrosion stability. Full article
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Open AccessArticle Effects of Q&P Processing Conditions on Austenite Carbon Enrichment Studied by In Situ High-Energy X-ray Diffraction Experiments
Metals 2017, 7(7), 232; doi:10.3390/met7070232
Received: 13 May 2017 / Revised: 10 June 2017 / Accepted: 16 June 2017 / Published: 22 June 2017
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Abstract
We report the first ultra-fast time-resolved quantitative information on the quenching and partitioning process of conventional high-strength steel by an in situ high-energy X-ray diffraction (HEXRD) experiment. The time and temperature evolutions of phase fractions, their carbon content, and internal stresses were determined
[...] Read more.
We report the first ultra-fast time-resolved quantitative information on the quenching and partitioning process of conventional high-strength steel by an in situ high-energy X-ray diffraction (HEXRD) experiment. The time and temperature evolutions of phase fractions, their carbon content, and internal stresses were determined and discussed for different process parameters. It is shown that the austenite-to-martensite transformation below the martensite start temperature Ms is followed by a stage of fast carbon enrichment in austenite during isothermal holding at both 400 and 450 °C. The analysis proposed supports the concurrent bainite transformation and carbon diffusion from martensite to austenite as the main mechanisms of this enrichment. Furthermore, we give evidence that high hydrostatic tensile stresses in austenite are produced during the final quenching, and must be taken into account for the estimation of the carbon content in austenite. Finally, a large amount of carbon is shown to be trapped in the microstructure. Full article
(This article belongs to the Special Issue Bainite and Martensite: Developments and Challenges)
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Open AccessArticle Secondary Solidification Behavior of A356 Aluminum Alloy Prepared by the Self-Inoculation Method
Metals 2017, 7(7), 233; doi:10.3390/met7070233
Received: 25 May 2017 / Revised: 17 June 2017 / Accepted: 19 June 2017 / Published: 26 June 2017
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Abstract
Semisolid slurry of A356 aluminum alloy was prepared by Self-Inoculation Method, and the secondary solidification behavior during rheo-diecasting forming process was researched. The results indicate that the component with non-dendritic and uniformly distributed microstructures can be produced by Rheo-Diecasting (RDC) process (combining Self-inoculation
[...] Read more.
Semisolid slurry of A356 aluminum alloy was prepared by Self-Inoculation Method, and the secondary solidification behavior during rheo-diecasting forming process was researched. The results indicate that the component with non-dendritic and uniformly distributed microstructures can be produced by Rheo-Diecasting (RDC) process (combining Self-inoculation Method (SIM) with High Pressure Die Casting (HPDC)). The isothermal holding time of the slurry has large effect on primary particles, but has little effect on secondary particles. Growth rate of the primary particles in the isothermal holding process conforms to the dynamic equation of Dt3 − D03 = Kt. The suitable holding time for rheo-diecasting of A356 aluminum alloy is 3 min. During filling process, the nucleation occurs throughout the entire remaining liquid, and nuclei grow stably into globular particles with the limited grain size of 6.5μm firstly, then both α1 and α2 particles appear unstable growth phenomenon due to the existence of constitutional undercooling. The average particle sizes and shape factors of both α1 and α2 are decreasing with the increase of filling distance due to different cooling rate in different positions. The growth rate of the eutectic in RDC is 4 times faster than HPDC, which is mainly due to the limitation of α2 particles in RDC process. The average eutectic spacings are decreasing with the increase of filling distance. Full article
(This article belongs to the Special Issue Microstructure and Mechanical Properties of Casting Alloys)
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Open AccessFeature PaperArticle The Nitrocarburising Response of Low Temperature Bainite Steel
Metals 2017, 7(7), 234; doi:10.3390/met7070234
Received: 31 May 2017 / Revised: 21 June 2017 / Accepted: 21 June 2017 / Published: 26 June 2017
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Abstract
The nitrocarburising response of low transformation temperature ultrafine and nanoscale bainitic steel was investigated and compared with martensite and pearlite from the same steel composition. It was found that the retained austenite content of the bainitic steel dictated the core hardness after nitrocarburising.
[...] Read more.
The nitrocarburising response of low transformation temperature ultrafine and nanoscale bainitic steel was investigated and compared with martensite and pearlite from the same steel composition. It was found that the retained austenite content of the bainitic steel dictated the core hardness after nitrocarburising. The refined bainitic structure showed improvements in the nitriding depth and hardness of the nitrocarburised layer, compared to coarser grained martensitic and pearlitic structures, possibly due to the fine structure and the distribution of nitride forming elements. Full article
(This article belongs to the Special Issue Bainite and Martensite: Developments and Challenges)
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Open AccessArticle Design of U-Geometry Parameters Using Statistical Analysis Techniques in the U-Bending Process
Metals 2017, 7(7), 235; doi:10.3390/met7070235
Received: 16 March 2017 / Revised: 9 June 2017 / Accepted: 10 June 2017 / Published: 26 June 2017
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Abstract
The various U-geometry parameters in the U-bending process result in processing difficulties in the control of the spring-back characteristic. In this study, the effects of U-geometry parameters, including channel width, bend angle, material thickness, tool radius, as well as workpiece length, and their
[...] Read more.
The various U-geometry parameters in the U-bending process result in processing difficulties in the control of the spring-back characteristic. In this study, the effects of U-geometry parameters, including channel width, bend angle, material thickness, tool radius, as well as workpiece length, and their design, were investigated using a combination of finite element method (FEM) simulation, and statistical analysis techniques. Based on stress distribution analyses, the FEM simulation results clearly identified the different bending mechanisms and effects of U-geometry parameters on the spring-back characteristic in the U-bending process, with and without pressure pads. The statistical analyses elucidated that the bend angle and channel width have a major influence in cases with and without pressure pads, respectively. The experiments were carried out to validate the FEM simulation results. Additionally, the FEM simulation results were in agreement with the experimental results, in terms of the bending forces and bending angles. Full article
(This article belongs to the Special Issue Advances in Plastic Forming of Metals)
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Open AccessFeature PaperArticle Effect of Ausforming Temperature on the Microstructure of G91 Steel
Metals 2017, 7(7), 236; doi:10.3390/met7070236
Received: 18 May 2017 / Revised: 20 June 2017 / Accepted: 23 June 2017 / Published: 27 June 2017
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Abstract
The development of thermomechanical treatments (TMT) has a high potential for improving creep-strength in 9Cr-1Mo ferritic/martensitic steel (ASTM T/P91) to operate at temperatures beyond 600 °C. To maximize the number of nanoscale MX precipitates, an ausforming procedure has been used to increase the
[...] Read more.
The development of thermomechanical treatments (TMT) has a high potential for improving creep-strength in 9Cr-1Mo ferritic/martensitic steel (ASTM T/P91) to operate at temperatures beyond 600 °C. To maximize the number of nanoscale MX precipitates, an ausforming procedure has been used to increase the number of nucleation sites for precipitation inside the martensite lath. Relative to standard heat treatments (consisting of austenitization at about 1040 °C followed by tempering at about 730 °C) this processing concept has enabled achieving a microstructure containing approximately three orders of magnitude higher number density of MX precipitates having a size around four times smaller in ASTM T/P91 steel. On the other hand; this TMT has little effect on the size and number density of M23C6 particles. The optimized microstructure produced by this TMT route proposed is expected to improve the creep strength of this steel. Full article
(This article belongs to the Special Issue Bainite and Martensite: Developments and Challenges)
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Open AccessArticle Leaching Kinetics of Hemimorphite in Ammonium Chloride Solution
Metals 2017, 7(7), 237; doi:10.3390/met7070237
Received: 11 May 2017 / Revised: 21 June 2017 / Accepted: 22 June 2017 / Published: 28 June 2017
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Abstract
The leaching kinetics of hemimorphite (Zn4Si2O7(OH)2·H2O) in ammonium chloride solution was presented in detail. Effects of stirring speed (150–350 rpm), leaching temperature (75–108 °C), particle size of hemimorphite (45–150 μm), and the concentration
[...] Read more.
The leaching kinetics of hemimorphite (Zn4Si2O7(OH)2·H2O) in ammonium chloride solution was presented in detail. Effects of stirring speed (150–350 rpm), leaching temperature (75–108 °C), particle size of hemimorphite (45–150 μm), and the concentration of ammonium chloride (3.5–5.5 mol/L) on the zinc extraction rate were studied. The zinc extraction rate enhanced slightly with the increase in stirring speed, but increased significantly with an increase in the leaching temperature and ammonium chloride concentration. Zinc extraction was enhanced significantly in the first 60 min with decreasing particle size, but had little effect on the leaching process after 60 min. Scanning electron microscopy (SEM) analysis showed that some silica gel formed in the leaching process was not separated from the hemimorphite surface, but covered some of the active particle surface. The Elovich equation successfully described the leaching kinetics of hemimorphite in ammonium chloride solution with an apparent activation energy of 405.14 kJ/mol at temperatures of 75–90 °C and 239.61 kJ/mol at temperatures of 95–108 °C, which is characteristic for a chemically-controlled process. Silica gel is generated at temperatures of 75–90 °C and decomposed into silica at temperatures of 95–108 °C. Full article
(This article belongs to the Special Issue Valuable Metal Recycling)
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Open AccessArticle Morphology and Crystallography of Ausferrite in Austempered Ductile Iron
Metals 2017, 7(7), 238; doi:10.3390/met7070238
Received: 27 May 2017 / Revised: 18 June 2017 / Accepted: 26 June 2017 / Published: 29 June 2017
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Abstract
The microstructure of austempered ductile iron was investigated by electron backscatter diffraction technique. The results show that the orientation relationship between acicular bainitic ferrite and austenite is Greninger–Troiano relationship. A single austenite grain is divided into four packets and each packet contains six
[...] Read more.
The microstructure of austempered ductile iron was investigated by electron backscatter diffraction technique. The results show that the orientation relationship between acicular bainitic ferrite and austenite is Greninger–Troiano relationship. A single austenite grain is divided into four packets and each packet contains six variants that share a {011}α (i.e., {111}γ) plane. When two γ grains are twinned, the twins share a {111}γ plane and have seven packets. The adjacent acicular bainitic ferrite plates (or laths) sharing a 001 γ axis have small misorientation of about 5.7°. The adjacent acicular bainitic ferrite plates (or laths) not sharing a 001 γ axis have two high misorientation angles of ~54.3° and ~60.0°. Further, the low angle boundary to high angle boundary ratio is far less than the ratio of the variant pairs with small misorientation to the ones with large misorientation. This work is available for structures obtained as a consequence of the heat treatment of austempering. Full article
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Open AccessArticle The Influence of Laser Welding on the Mechanical Properties of Dual Phase and Trip Steels
Metals 2017, 7(7), 239; doi:10.3390/met7070239
Received: 6 June 2017 / Revised: 23 June 2017 / Accepted: 26 June 2017 / Published: 29 June 2017
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Abstract
Nowadays, a wide range of materials is used for car body structures in order to improve both the passengers’ safety and fuel consumption. These are joined by laser welding and solid state fiber lasers being used more and more in present. The article
[...] Read more.
Nowadays, a wide range of materials is used for car body structures in order to improve both the passengers’ safety and fuel consumption. These are joined by laser welding and solid state fiber lasers being used more and more in present. The article is focused on the research of laser welding influence on the mechanical and deformation properties, microstructure and microhardness of advanced high-strength steels: high-strength low-alloyed steel HC340LA, dual phase steel HCT600X and multi-phase residual austenite steel RAK40/70. The proper welding parameters have been found based on weld quality evaluation. The specimens for tensile test with longitudinal laser weld were used to measure mechanical and deformation properties. Microstructure and microhardness of laser welds were evaluated in the base metal, heat affected zone and fusion zone. The higher values of strength and lower ones for deformation properties of laser-welded materials have been found for dual and multi-phase steel. The microhardness strongly depends on the carbon equivalent of steel. Deformation properties are more sensitive than strength properties to the change of microstructure in the fusion zone and heat affected zone. Full article
(This article belongs to the Special Issue Laser Welding)
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Open AccessArticle Separation and Pre-Concentration of Pb and Cd in Water Samples Using 3-(2-hydroxyphenyl)-1H-1,2,4-triazole-5(4H)-thione (HTT) and Their Determination by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES)
Metals 2017, 7(7), 240; doi:10.3390/met7070240
Received: 3 April 2017 / Revised: 15 June 2017 / Accepted: 22 June 2017 / Published: 29 June 2017
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Abstract
A new method for the separation, pre-concentration and accurate determination of trace amounts of Pb and Cd in water samples using Amberlite XAD-16 resin functionalized with a new chelating ligand, 3-(2-hydroxyphenyl)-1H-1,2,4-triazole-5(4H)-thione (HTT), Amberlite XAD-16-HTT and inductively coupled plasma atomic
[...] Read more.
A new method for the separation, pre-concentration and accurate determination of trace amounts of Pb and Cd in water samples using Amberlite XAD-16 resin functionalized with a new chelating ligand, 3-(2-hydroxyphenyl)-1H-1,2,4-triazole-5(4H)-thione (HTT), Amberlite XAD-16-HTT and inductively coupled plasma atomic emission spectrometry (ICP-AES) is reported in the present study. Fourier transform infrared (FTIR) spectroscopy was used to characterize the chelating resin. The effects of analytical parameters such as the pH of the medium, amount of adsorbent, type and volume of eluent, flow rate of the sample solution, volume of the sample solution, and matrix interference on the retention of metal ions were investigated. Also, 1 M HNO3 was used for the elution of the sorbed metals, and ICP-AES was used for the analysis of elutes offline. The results indicate that pH 5 is the optimum pH for the sorption of Pb and Cd ions. The limit of detection was found to be 0.16 and 0.22 μg/L for Pb and Cd, respectively, by applying a pre-concentration factor of 50. The method was validated using the international water reference material (NIST 1643e). The developed enrichment method has a high selectivity, sensitivity, and reproducibility; this method was successfully applied for the determination of Pb and Cd in surface water samples collected in Nellore District, Penner River belt as well as Bay of Bengal, Andhra Pradesh, India. Full article
(This article belongs to the Special Issue Heavy Metal Determination and Removal)
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Open AccessFeature PaperArticle Cumulative Effect of Strength Enhancer—Lanthanum and Ductility Enhancer—Cerium on Mechanical Response of Magnesium
Metals 2017, 7(7), 241; doi:10.3390/met7070241
Received: 2 June 2017 / Revised: 22 June 2017 / Accepted: 26 June 2017 / Published: 29 June 2017
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Abstract
In the present work, the cumulative effect of strength enhancer Lanthanum (La) and ductility enhancer Cerium (Ce) on the mechanical response of pure Mg was investigated. A ternary Mg-4La-0.4Ce alloy was developed using a disintegrated melt deposition method followed by hot extrusion. The
[...] Read more.
In the present work, the cumulative effect of strength enhancer Lanthanum (La) and ductility enhancer Cerium (Ce) on the mechanical response of pure Mg was investigated. A ternary Mg-4La-0.4Ce alloy was developed using a disintegrated melt deposition method followed by hot extrusion. The mechanical characterization revealed that the ternary alloy exhibited superior hardness and tensile and compressive strengths when compared to Mg and Mg-0.4Ce binary alloy, thereby validating the role of La as a strength enhancer. Furthermore, the ductility of the chosen alloy was also enhanced as compared to Mg and other La rich Mg alloys, indicating that the ductility enhancement is primarily due to Ce. The microstructural characterization revealed that the cumulative addition of La and Ce refined the grain size and led to the formation of a large volume of secondary phases which affected the mechanical properties. The effect of fine grains and the presence of secondary phases on the deformation behavior of the alloy were conclusively ascertained with the aid of deformation and fracture studies. Full article
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Open AccessArticle Acoustic Emission Signatures of Fatigue Damage in Idealized Bevel Gear Spline for Localized Sensing
Metals 2017, 7(7), 242; doi:10.3390/met7070242
Received: 30 May 2017 / Revised: 26 June 2017 / Accepted: 26 June 2017 / Published: 30 June 2017
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Abstract
In many rotating machinery applications, such as helicopters, the splines of an externally-splined steel shaft that emerges from the gearbox engage with the reverse geometry of an internally splined driven shaft for the delivery of power. The splined section of the shaft is
[...] Read more.
In many rotating machinery applications, such as helicopters, the splines of an externally-splined steel shaft that emerges from the gearbox engage with the reverse geometry of an internally splined driven shaft for the delivery of power. The splined section of the shaft is a critical and non-redundant element which is prone to cracking due to complex loading conditions. Thus, early detection of flaws is required to prevent catastrophic failures. The acoustic emission (AE) method is a direct way of detecting such active flaws, but its application to detect flaws in a splined shaft in a gearbox is difficult due to the interference of background noise and uncertainty about the effects of the wave propagation path on the received AE signature. Here, to model how AE may detect fault propagation in a hollow cylindrical splined shaft, the splined section is essentially unrolled into a metal plate of the same thickness as the cylinder wall. Spline ridges are cut into this plate, a through-notch is cut perpendicular to the spline to model fatigue crack initiation, and tensile cyclic loading is applied parallel to the spline to propagate the crack. In this paper, the new piezoelectric sensor array is introduced with the purpose of placing them within the gearbox to minimize the wave propagation path. The fatigue crack growth of a notched and flattened gearbox spline component is monitored using a new piezoelectric sensor array and conventional sensors in a laboratory environment with the purpose of developing source models and testing the new sensor performance. The AE data is continuously collected together with strain gauges strategically positioned on the structure. A significant amount of continuous emission due to the plastic deformation accompanied with the crack growth is observed. The frequency spectra of continuous emissions and burst emissions are compared to understand the differences of plastic deformation and sudden crack jump. The correlation of the cumulative AE events at the notch tip and the strain data is used to predict crack growth. The performance of the new sensor array is compared with the conventional AE sensors in terms of signal to noise ratio and the ability to detect fatigue cracking. Full article
(This article belongs to the Special Issue Advanced Non-Destructive Testing in Steels)
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Open AccessArticle Effect of Anode Pulse-Width on the Microstructure and Wear Resistance of Microarc Oxidation Coatings
Metals 2017, 7(7), 243; doi:10.3390/met7070243
Received: 3 May 2017 / Revised: 27 June 2017 / Accepted: 27 June 2017 / Published: 30 June 2017
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Abstract
Microarc oxidation (MAO) coatings were prepared on 2024-T4 aluminum alloys using a pulsed bipolar power supply at different anode pulse-widths. After the MAO coatings were formed, the micropores and microcracks on the surface of the MAO coatings were filled with Fluorinated ethylene propylene
[...] Read more.
Microarc oxidation (MAO) coatings were prepared on 2024-T4 aluminum alloys using a pulsed bipolar power supply at different anode pulse-widths. After the MAO coatings were formed, the micropores and microcracks on the surface of the MAO coatings were filled with Fluorinated ethylene propylene (FEP) dispersion for preparing MAO self-lubricating composite coatings containing FEP. The effect of the anode pulse-width on the microstructure and wear resistance of the microarc oxidation coatings was investigated. The wear resistance of the microarc oxidation self-lubricating composite coatings was analyzed. The results revealed that the MAO self-lubricating composite coatings integrated the advantages of wear resistance of the MAO ceramic coatings and a low friction coefficient of FEP. Compared to the MAO coatings, the microarc oxidation self-lubricating composite coatings exhibited a lower friction coefficient and lower wear rates. Full article
(This article belongs to the Special Issue Light Weight Alloys: Processing, Properties and Their Applications)
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Open AccessArticle Investigation of Dendrite Coarsening in Complex Shaped Lamellar Graphite Iron Castings
Metals 2017, 7(7), 244; doi:10.3390/met7070244
Received: 31 May 2017 / Revised: 28 June 2017 / Accepted: 29 June 2017 / Published: 1 July 2017
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Abstract
Shrinkage porosity and metal expansion penetration are two casting defects that appear frequently during the production of complex-shaped lamellar graphite iron components. These casting defects are formed during the solidification and usually form in the part of the casting which solidifies last. The
[...] Read more.
Shrinkage porosity and metal expansion penetration are two casting defects that appear frequently during the production of complex-shaped lamellar graphite iron components. These casting defects are formed during the solidification and usually form in the part of the casting which solidifies last. The position of the area that solidifies last is dependent on the thermal conditions. Test castings with thermal conditions like those existing in a complex-shaped casting were successfully applied to provoke a shrinkage porosity defect and a metal expansion penetration defect. The investigation of the primary dendrite morphology in the defected positions indicates a maximum intradendritic space, where the shrinkage porosity and metal expansion penetration defects appear. Moving away from the defect formation area, the intradendritic space decreases. A comparison of the intradendritic space with the simulated local solidification times indicates a strong relationship, which can be explained by the dynamic coarsening process. More specifically, long local solidification times facilitates the formation of a locally coarsened austenite morphology. This, in turn, enables the formation of a shrinkage porosity or a metal expansion penetration. Full article
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Open AccessArticle Enhanced Surface Precipitates on Ultrafine-Grained Titanium in Physiological Solution
Metals 2017, 7(7), 245; doi:10.3390/met7070245
Received: 17 May 2017 / Revised: 15 June 2017 / Accepted: 27 June 2017 / Published: 1 July 2017
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Abstract
Enhanced cell adherence to the surface of nanocrystallized commercially pure titanium (CP–Ti) was observed by several authors. However, the understanding of the surface modification of Ti in a physiological solution due to nanocrystallized grain size has not been reached. In this work, equal
[...] Read more.
Enhanced cell adherence to the surface of nanocrystallized commercially pure titanium (CP–Ti) was observed by several authors. However, the understanding of the surface modification of Ti in a physiological solution due to nanocrystallized grain size has not been reached. In this work, equal channel angular pressing (ECAP) was applied to manufacturing ultrafine grained CP–Ti. Martensite and Widmanstatten microstructures were also obtained for comparison. The CP–Ti pieces with different microstructures were subjected to soaking tests in a simulated body fluid. Electrochemical impedance spectroscopy (EIS) measurements, X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM), energy dispersive spectrometer (EDS) were used to characterize the surfaces. The results show the surface precipitates mainly contain Ti, O, Ca and P. The quantity of precipitates on ECAPed CP–Ti is the largest among different specimens corresponded to the observation of the thickest layer formation on ECAPed CP–Ti found by EIS. EDS results show more CaPO and less Ti are included on ECAPed Ti comparing to the deposits on other two types of specimens. Smaller numbers of precipitates and denser film are produced on the surface of the water-quenched CP–Ti. The regeneration kinetics of the CaP precipitates evaluated by Gibbs free energy is introduced to interpret the precipitating behaviors on different CP–Ti specimens. Full article
(This article belongs to the Special Issue Synthesis and Properties of Bulk Nanostructured Metallic Materials)
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Open AccessArticle Analysis of Relaxation Processes in HNS Due to Interstitial-Substitutional Pairs
Metals 2017, 7(7), 246; doi:10.3390/met7070246
Received: 8 June 2017 / Revised: 28 June 2017 / Accepted: 29 June 2017 / Published: 2 July 2017
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Abstract
Mechanical Spectroscopy (MS) tests have been performed on a high nitrogen (0.8 wt %) austenitic steel (HNS) with resonance frequencies in the range of kHz. Two sets of samples have been examined: the first set in an as-prepared condition, the second one submitted
[...] Read more.
Mechanical Spectroscopy (MS) tests have been performed on a high nitrogen (0.8 wt %) austenitic steel (HNS) with resonance frequencies in the range of kHz. Two sets of samples have been examined: the first set in an as-prepared condition, the second one submitted to a heat treatment of 2 h at 800 °C, which induces a discontinuous precipitation of Cr2N phase. In both sets, the damping spectrum shows a broad peak whose position and shape is changed by the precipitation of Cr2N phase. The results are explained by considering interstitial-substitutional (i-s) interactions.
Full article
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Open AccessArticle Interfacial Microstructure and Shear Strength of Brazed Cu-Cr-Zr Alloy Cylinder and Cylindrical Hole by Au Based Solder
Metals 2017, 7(7), 247; doi:10.3390/met7070247
Received: 6 May 2017 / Revised: 26 June 2017 / Accepted: 27 June 2017 / Published: 3 July 2017
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Abstract
Au-Ge-Ni solder was chosen for brazing of the Cu-Cr-Zr alloy cylinder and a part with a cylindrical hole (sleeve) below 550 °C. The Au based solder was first sintered on the surface of the cylinder and then brazed to the inner surface of
[...] Read more.
Au-Ge-Ni solder was chosen for brazing of the Cu-Cr-Zr alloy cylinder and a part with a cylindrical hole (sleeve) below 550 °C. The Au based solder was first sintered on the surface of the cylinder and then brazed to the inner surface of the sleeve. The effects of the heating process, the temperature and the holding time at the temperature on the microstructure of the sintered layer on the surface of the cylinder, the brazed interfacial microstructure, and the brazed shear strength between the cylinder and the sleeve were investigated by scanning electron microscope, energy dispersive X-ray spectroscopy analysis, and tensile shear tests. By approach of side solder melt feeding and brazing under proper parameters, the voids and micro cracks due to a lack of enough solder melt feeding are greatly lessened and the brazed shear strength of 100 MPa is ensured even with large clearances around 0.01 mm. Full article
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Open AccessFeature PaperArticle Simultaneous Removal of Hg(II) and Phenol Using Functionalized Activated Carbon Derived from Areca Nut Waste
Metals 2017, 7(7), 248; doi:10.3390/met7070248
Received: 30 April 2017 / Revised: 26 June 2017 / Accepted: 28 June 2017 / Published: 3 July 2017
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Abstract
Areca nut waste was utilized to obtain high surface area activated carbon (AC), and it was further functionalized with succinic anhydride under microwave irradiation. The surface morphology and surface functional groups of the materials were discussed with the help of scanning electron microscope(SEM)
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Areca nut waste was utilized to obtain high surface area activated carbon (AC), and it was further functionalized with succinic anhydride under microwave irradiation. The surface morphology and surface functional groups of the materials were discussed with the help of scanning electron microscope(SEM) images and fourier transform infra-red (FT-IR) analysis. The specific surface area of the AC and functionalized-AC was obtained by the Brunauer-Emmett-Teller (BET) method, and found to be 367.303 and 308.032 m2/g, respectively. Batch experiments showed that higher pH favoured the removal of Hg(II), whereas the phenol removal was slightly affected by the changes in the solution pH. The kinetic data followed pseudo-first order kinetic model, and intra-particle diffusion played a significant role in the removal of both pollutants. The maximum sorption capacity of Hg(II) and phenol were evaluated using Langmuir adsorption isotherms, and found to be 11.23 and 5.37 mg/g, respectively. The removal of Hg(II) was significantly suppressed in the presence of chloride ions due to the formation of a HgCl2 species. The phenol was specifically adsorbed, forming the donor–acceptor complexes or π–π electron interactions at the surface of the solid. Further, a fixed-bed column study was conducted for both Hg(II) and phenol. The loading capacity of the column was estimated using the nonlinear Thomas equation, and found to be 2.49 and 2.70 mg/g, respectively. Therefore, the study showed that functionalized AC obtained from areca nut waste could be employed as a sustainable adsorbent for the simultaneous removal of Hg(II) and phenol from polluted water. Full article
(This article belongs to the Special Issue Heavy Metal Determination and Removal)
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Open AccessArticle Comparative Investigation of Tungsten Fibre Nets Reinforced Tungsten Composite Fabricated by Three Different Methods
Metals 2017, 7(7), 249; doi:10.3390/met7070249
Received: 1 March 2017 / Revised: 17 June 2017 / Accepted: 20 June 2017 / Published: 4 July 2017
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Abstract
Tungsten fibre nets reinforced tungsten composites (Wf/W) containing four net layers were fabricated by spark plasma sintering (SPS), hot pressing (HP) and cold rolling after HP (HPCR), with the weight fraction of fibres being 17.4%, 10.5% and 10.5%, respectively. The relative
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Tungsten fibre nets reinforced tungsten composites (Wf/W) containing four net layers were fabricated by spark plasma sintering (SPS), hot pressing (HP) and cold rolling after HP (HPCR), with the weight fraction of fibres being 17.4%, 10.5% and 10.5%, respectively. The relative density of the HPCRed samples is the highest (99.8%) while that of the HPed composites is the lowest (95.1%). Optical and scanning electron microscopy and electron back scattering diffraction were exploited to characterize the microstructure, while tensile and hardness tests were used to evaluate the mechanical properties of the samples. It was found that partial recrystallization of fibres occurred after the sintering at 1800 °C. The SPSed and HPed Wf/W composites begin to exhibit plastic deformation at 600 °C with tensile strength (TS) of 536 and 425 MPa and total elongation at break (TE) of 11.6% and 23.0%, respectively, while the HPCRed Wf/W composites exhibit plastic deformation at around 400 °C. The TS and TE of the HPCRed Wf/W composites at 400 °C are 784 MPa and 8.4%, respectively. The enhanced mechanical performance of the Wf/W composites over the pure tungsten can be attributed to the necking, cracking, and debonding of the tungsten fibres. Full article
(This article belongs to the Special Issue Metal Matrix Composites)
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Open AccessArticle Effect of Hybrid Reinforcements on the Microstructure and Mechanical Properties of Ti-5Al-5Mo-5V-Fe-Cr Titanium Alloy
Metals 2017, 7(7), 250; doi:10.3390/met7070250
Received: 27 May 2017 / Revised: 27 June 2017 / Accepted: 27 June 2017 / Published: 5 July 2017
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Abstract
In order to investigate the different effects of trace TiB and TiC on the microstructure and the mechanical properties of Ti-5Al-5Mo-5V-1Fe-1Cr Ti alloy, two different modified Ti-5Al-5Mo-5V-1Fe-1Cr Ti alloys are fabricated via a consumable vacuum arc-remelting furnace in this work. Though the volume
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In order to investigate the different effects of trace TiB and TiC on the microstructure and the mechanical properties of Ti-5Al-5Mo-5V-1Fe-1Cr Ti alloy, two different modified Ti-5Al-5Mo-5V-1Fe-1Cr Ti alloys are fabricated via a consumable vacuum arc-remelting furnace in this work. Though the volume fractions of the reinforcements are the same in the two alloys, the molar ratio of short fibers to particles is different. The materials are subjected to thermomechanical processing and heat treatment. The effects of TiB short fibers and TiC particles on the spheroidization of α phase or the refinement of β phase have no obvious difference during heat treatment. Subsequently, the room temperature tensile test is carried out. The area covered by the σ-ε curve of the tensile test is used to compare toughness. It is revealed that the refinement of the β phase and the load bearing of TiB play key roles in promoting the toughness of the alloys. TiB tends to parallel the external load during tensile tests. The distribution of TiB also changes during isothermal compression test. Owing to the competition of dynamic softening with dynamic hardening, the length direction of TiB tends to parallel to the direction of maximum shear stress during the compression, which makes TiB play the role of load bearing better. Full article
(This article belongs to the Special Issue Titanium Alloys 2017)
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Open AccessArticle Dissolution of Grain Boundary Carbides by the Effect of Solution Annealing Heat Treatment and Aging Treatment on Heat-Resistant Cast Steel HK30
Metals 2017, 7(7), 251; doi:10.3390/met7070251
Received: 29 May 2017 / Revised: 18 June 2017 / Accepted: 26 June 2017 / Published: 5 July 2017
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Abstract
Decreasing the weight of heavy-duty vehicles is an ongoing concern. However, the need to deal with high temperatures in components such as manifolds imposes, by itself, some restrictions regarding material selection, being further limited when other required properties (e.g., functional, manufacturing or cost
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Decreasing the weight of heavy-duty vehicles is an ongoing concern. However, the need to deal with high temperatures in components such as manifolds imposes, by itself, some restrictions regarding material selection, being further limited when other required properties (e.g., functional, manufacturing or cost requirements) are taken into account. Cast austenitic stainless steels may represent a good choice in this context but the existence of concentrated chromium carbides can generate undesirable results. A good combination of heat treatments can be applied to cast heat-resistant austenitic stainless steels, in an effort to achieve the dispersion of fine carbides, consequently improving their microstructure, mechanical properties and creep resistance. In this work, an austenitic stainless steel usually used in high temperature applications was characterized and subjected to solution annealing and aging heat treatments. The material analyzed was the austenitic cast stainless steel HK30 and the goals of the work were to evaluate the effects of solution annealing heat treatments on the dissolution of grain boundary chromium carbides and the effects of aging treatments on creep resistance. The results show that the elimination of grain boundary chromium carbides is possible by applying a solution annealing heat treatment. Additionally, the precipitation of fine dispersed carbides is obtained after the aging treatment with an increase of hardness and, consequently, an expected improvement of creep resistance. Thus, the novelty presented by this work consists of selecting the best heat treatment combination in order to promote dispersion of carbides, thus avoiding further crack nucleation phenomena when parts are cyclically subjected to load and unload; this work also found the most adequate mechanical properties and achieved corrosion resistance regarding the application in heavy-duty vehicle components subjected to mechanical and thermal fatigue. By discovering methods of improving the properties of cast materials, large savings can be made both in terms of production costs as well as in the overall weight of the components. Full article
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Open AccessFeature PaperArticle High-Temperature Tempered Martensite Embrittlement in Quenched-and-Tempered Offshore Steels
Metals 2017, 7(7), 253; doi:10.3390/met7070253
Received: 31 May 2017 / Revised: 23 June 2017 / Accepted: 3 July 2017 / Published: 6 July 2017
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Abstract
Embrittlement induced by high-temperature tempering was investigated in two quenched-and-tempered offshore steels. Electron backscattering diffraction and analysis of Kernel average misorientation were applied to study the coalescence of martensite; transmission Kikuchi diffraction coupled with compositional mapping was used to characterize the martensite/austenite (M/A)
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Embrittlement induced by high-temperature tempering was investigated in two quenched-and-tempered offshore steels. Electron backscattering diffraction and analysis of Kernel average misorientation were applied to study the coalescence of martensite; transmission Kikuchi diffraction coupled with compositional mapping was used to characterize the martensite/austenite (M/A) phases. It is suggested that the formation of lenticular martensite along prior austenite grain boundaries or packet boundaries primarily explains the embrittlement in conventional S690Q steel, which has a higher carbon content. This embrittlement can be cured by additional heat treatment to decompose martensite into ferrite and cementite. In a newly designed NiCu steel with reduced carbon content, new lath martensite formed along interlath or inter-block boundaries of prior martensite. This microstructure is less detrimental to the impact toughness of the steel. Full article
(This article belongs to the Special Issue Bainite and Martensite: Developments and Challenges)
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Open AccessArticle On the Short Surface Fatigue Crack Growth Behavior in a Fine-Grained WC-Co Cemented Carbide
Metals 2017, 7(7), 254; doi:10.3390/met7070254
Received: 28 May 2017 / Revised: 28 June 2017 / Accepted: 3 July 2017 / Published: 6 July 2017
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Abstract
In the present study, the fatigue crack growth (FCG) behavior of short surface cracks in a fine-grained cemented carbide with a length of less than 1 mm was investigated. The rotating bending and the four-point bending fatigue tests were carried out at stress
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In the present study, the fatigue crack growth (FCG) behavior of short surface cracks in a fine-grained cemented carbide with a length of less than 1 mm was investigated. The rotating bending and the four-point bending fatigue tests were carried out at stress ratios of R = −1 and R = 0.1 (R = maximum stress/minimum stress). It was found that a short surface crack had a longer stable fatigue crack growth area than a long through-thickness crack; the FCG behaviors of the two types of crack are clearly different. Furthermore, the FCG path of short surface cracks was investigated in detail to study the interaction between fatigue cracks and microstructures of the cemented carbide such as WC grains and the Co phase. At a low Kmax (Kmax = the maximum stress intensity factor), it was found that fatigue crack growth within WC grains is difficult because of a small driving force; instead, crack growth is along the brittle WC/WC interface. On the other hand, at a high Kmax, WC grain breakage often occurs, since the driving force of FCG is large, and the fatigue crack grows linearly. Full article
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Open AccessFeature PaperArticle Failure Assessment of Steel/CFRP Double Strap Joints
Metals 2017, 7(7), 255; doi:10.3390/met7070255
Received: 8 June 2017 / Revised: 25 June 2017 / Accepted: 1 July 2017 / Published: 6 July 2017
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Abstract
In the current study, the failure behavior of retrofitted steel structures was studied experimentally and theoretically with steel/carbon fiber reinforced polymer (CFRP) double strap joints (DSJs) under quasi-static tensile loading. A series of DSJs with different bonding lengths are also considered and examined
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In the current study, the failure behavior of retrofitted steel structures was studied experimentally and theoretically with steel/carbon fiber reinforced polymer (CFRP) double strap joints (DSJs) under quasi-static tensile loading. A series of DSJs with different bonding lengths are also considered and examined to experimentally assess the effective bond length. To predict the failure load values of the tested specimens, a new stress-based method, namely the point stress (PS) method is proposed. Although some theoretical predictive modelling for the strength between steel/CFRP joints under various loading conditions has been presented, in this work by using the new proposed approach, one can calculate rapidly and conveniently the failure loads of the steel/CFRP specimens. Furthermore, to assess the validity of the new proposed method, further experimental data on steel/CFRP DSJs available in the open literature are predicted using the PS method. Finally, it was found that a good agreement exists between the experimental results and the theoretical predictions based on the PS method. Full article
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Open AccessArticle A Finite Element Model to Simulate Defect Formation during Friction Stir Welding
Metals 2017, 7(7), 256; doi:10.3390/met7070256
Received: 16 June 2017 / Revised: 27 June 2017 / Accepted: 28 June 2017 / Published: 7 July 2017
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Abstract
In this study, a 3D coupled thermo-mechanical finite element model is developed to predict and analyze the defect formation during friction stir welding based on coupled Eulerian Lagrangian method. The model is validated by comparing the estimated welding temperature, processed zone shape and
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In this study, a 3D coupled thermo-mechanical finite element model is developed to predict and analyze the defect formation during friction stir welding based on coupled Eulerian Lagrangian method. The model is validated by comparing the estimated welding temperature, processed zone shape and void size with those obtained experimentally. The results compared indicate that the simulated temperature and the data measured are in good agreement with each other. In addition, the model can predict the plasticized zone shape and the presence of a void in the weld quite accurately. However, the void size is overestimated. The effects of welding parameters and tool pin profile are also analyzed. The results reveal that welding at low welding speed or high tool rotational speed could produce a smaller void. Moreover, compared to a smooth tool pin, a featured tool pin can enhance plastic flow in the weld and achieve defect-free weldment. The results are helpful for the optimization of the welding process and the design of welding tools. Full article
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Open AccessArticle Localization Phenomena in Disordered Tantalum Films
Metals 2017, 7(7), 257; doi:10.3390/met7070257
Received: 1 May 2017 / Revised: 29 June 2017 / Accepted: 30 June 2017 / Published: 7 July 2017
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Abstract
Using dc transport and wide-band spectroscopic ellipsometry techniques we study localization phenomena in highly disordered metallic β-Ta films grown by rf sputtering deposition. The dc transport study implies non-metallic behavior (dρ/dT < 0), with negative temperature coefficient of resistivity
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Using dc transport and wide-band spectroscopic ellipsometry techniques we study localization phenomena in highly disordered metallic β -Ta films grown by rf sputtering deposition. The dc transport study implies non-metallic behavior (d ρ /dT < 0), with negative temperature coefficient of resistivity (TCR). We found that as the absolute TCR value increased, specifying an elevated degree of disorder, the free charge carrier Drude response decreases, indicating the enhanced charge carrier localization. Moreover, we found that the pronounced changes occur at the extended spectral range, involving not only the Drude resonance, but also the higher-energy Lorentz bands, in evidence of the attendant electronic correlations. We propose that the charge carrier localization, or delocalization, is accompanied by the pronounced electronic band structure reconstruction due to many-body effects, which may be the key feature for understanding the physics of highly disordered metals. Full article
(This article belongs to the Special Issue Bulk Metallic Glasses)
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Open AccessArticle Effect of Austempering Time on the Microstructure and Carbon Partitioning of Ultrahigh Strength Steel 56NiCrMoV7
Metals 2017, 7(7), 258; doi:10.3390/met7070258
Received: 23 May 2017 / Revised: 26 June 2017 / Accepted: 3 July 2017 / Published: 7 July 2017
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Abstract
Ultrahigh strength steel 56NiCrMoV7 was austempered at 270 °C for different durations in order to investigate the microstructure evolution, carbon partitioning behaviour and hardness property. Detailed microstructure has been characterised using optical microscopy and field emission gun scanning electron microscopy. A newly developed
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Ultrahigh strength steel 56NiCrMoV7 was austempered at 270 °C for different durations in order to investigate the microstructure evolution, carbon partitioning behaviour and hardness property. Detailed microstructure has been characterised using optical microscopy and field emission gun scanning electron microscopy. A newly developed X-ray diffraction method has been employed to dissolve the bainitic/martensitic ferrite phase as two sub-phases of different tetragonal ratios, which provides quantitative analyses of the carbon partitioning between the resultant ferrites and the retained austenite. The results show that, a short-term austempering treatment was in the incubation period of the bainite transformation, which resulted in maximum hardness being equivalent to the oil-quenching treatment. The associated microstructure comprises fine carbide-free martensitic and bainitic ferrites of supersaturated carbon contents as well as carbon-rich retained austenite. In particular, the short-term austempering treatment helped prevent the formation of lengthy martensitic laths as those being found in the microstructure of oil-quenched sample. When the austempering time was increased from 20 to 80 min, progressive decrease of the hardness was associated with the evolution of the microstructure, including progressive coarsening of bainitic ferrite, carbide precipitating inside high-carbon bainitic ferrite and its subsequent decarbonisation. Full article
(This article belongs to the Special Issue Bainite and Martensite: Developments and Challenges)
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Open AccessArticle Metallization of Extruded Briquettes (BREX) in Midrex Process
Metals 2017, 7(7), 259; doi:10.3390/met7070259
Received: 12 February 2017 / Revised: 3 July 2017 / Accepted: 4 July 2017 / Published: 7 July 2017
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Abstract
The results of the full-scale testing of the Extruded Briquettes (BREX) as the charge components of the industrial Midrex reactor are discussed. The influence of the type of binder on the degree of metallization of BREX is analyzed. Magnesium sulfate-based binder helps to
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The results of the full-scale testing of the Extruded Briquettes (BREX) as the charge components of the industrial Midrex reactor are discussed. The influence of the type of binder on the degree of metallization of BREX is analyzed. Magnesium sulfate-based binder helps to reach highest metallization degree of BREX. Mineralogical study shows the difference in the iron-silicate phase’s development as well as in the porosity change during metallization depending on the binder used. Full article
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Open AccessArticle On the Invariance of Hardness at Vickers Indentation of Pre-Stressed Materials
Metals 2017, 7(7), 260; doi:10.3390/met7070260
Received: 18 June 2017 / Revised: 30 June 2017 / Accepted: 6 July 2017 / Published: 7 July 2017
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Abstract
The influence from residual surface stresses on global indentation properties, i.e., hardness and size of the contact area, have been studied quite frequently in recent years. A fundamental assumption when evaluating such tests is that the material hardness is independent of any residual
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The influence from residual surface stresses on global indentation properties, i.e., hardness and size of the contact area, have been studied quite frequently in recent years. A fundamental assumption when evaluating such tests is that the material hardness is independent of any residual stresses. This assumption has been verified in the case of cone indentation of classical Mises elastoplastic materials. However, a detailed investigation of this feature in the case of three-dimensional indentation, i.e., Vickers and Berkovic indentation, has not been presented previously. It is therefore the aim of the present study to remedy this shortcoming using finite element methods. The numerical results pertinent to Vickers indentation clearly show that the material hardness is independent of residual (or applied) stresses (also in case of three-dimensional indentation problems). The limitations of the validity of hardness invariance are also discussed in some detail. Full article
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Open AccessArticle Characteristics of the Dynamic Recrystallization Behavior of Ti-45Al-8.5Nb-0.2W-0.2B-0.3Y Alloy during High Temperature Deformation
Metals 2017, 7(7), 261; doi:10.3390/met7070261
Received: 7 June 2017 / Revised: 30 June 2017 / Accepted: 4 July 2017 / Published: 8 July 2017
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Abstract
The dynamic recrystallization (DRX) behavior of Ti-45Al-8.5Nb-0.2W-0.2B-0.3Y (at %) alloy has been investigated through hot compression tests. The tests were executed at a temperature range of 1000–1200 °C and a strain rate range of 0.001–1 s−1 under a true strain of 0.9.
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The dynamic recrystallization (DRX) behavior of Ti-45Al-8.5Nb-0.2W-0.2B-0.3Y (at %) alloy has been investigated through hot compression tests. The tests were executed at a temperature range of 1000–1200 °C and a strain rate range of 0.001–1 s−1 under a true strain of 0.9. It was found that the α2 phase which is produced during heat treatment is reduced during hot compression due to thermo-mechanical coupling. The value of the activation energy is 506.38 KJ/mol. With the increase in deformation temperature and the decrease in strain rate, DRX is more likely to occur, as a result of sufficient time and energy for the DRX process. Furthermore, the volume fraction of high angle grain boundaries increases to 89.01% at a temperature of 1200 °C and the strain rate of 0.001 s−1, meaning completely dynamic recrystallization. In addition, DRX is related to the formation of twin boundaries. The volume fraction of twin boundaries rises to 16.93% at the same condition of completely dynamic recrystallization. Full article
(This article belongs to the Special Issue Light Weight Alloys: Processing, Properties and Their Applications)
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Open AccessArticle Effect of Fe-Content on the Mechanical Properties of Recycled Al Alloys during Hot Compression
Metals 2017, 7(7), 262; doi:10.3390/met7070262
Received: 10 June 2017 / Revised: 28 June 2017 / Accepted: 7 July 2017 / Published: 10 July 2017
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Abstract
It is unavoidable that Fe impurities will be mixed into Al alloys during recycling of automotive aluminum parts, and the Fe content has a significant effect on the mechanical properties of the recycled Al alloys. In this work, hot compression tests of two
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It is unavoidable that Fe impurities will be mixed into Al alloys during recycling of automotive aluminum parts, and the Fe content has a significant effect on the mechanical properties of the recycled Al alloys. In this work, hot compression tests of two Fe-containing Al alloys were carried out at elevated temperatures within a wide strain rate range from 0.01 s−1 to 10 s−1. The effect of Fe content on the peak stress of the stress vs. strain curves, strain rate sensitivity and activation energy for dynamic recrystallization are analyzed. Results show that the recycled Al alloy containing 0.5 wt % Fe exhibits higher peak stresses and larger activation energy than the recycled Al alloy containing 0.1 wt % Fe, which results from the fact that there are more dispersed AlMgFeSi and/or AlFeSi precipitates in the recycled Al alloy containing 0.5 wt % Fe as confirmed by SEM observation and energy spectrum analysis. It is also shown that the Fe content has little effect on the strain rate sensitivity of the recycled Al alloys. Full article
(This article belongs to the Special Issue Light Weight Alloys: Processing, Properties and Their Applications)
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Open AccessArticle Bainitic Transformation and Properties of Low Carbon Carbide-Free Bainitic Steels with Cr Addition
Metals 2017, 7(7), 263; doi:10.3390/met7070263
Received: 28 June 2017 / Revised: 4 July 2017 / Accepted: 6 July 2017 / Published: 10 July 2017
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Abstract
Two low carbon carbide-free bainitic steels (with and without Cr addition) were designed, and each steel was treated by two kinds of heat treatment procedure (austempering and continuous cooling). The effects of Cr addition on bainitic transformation, microstructure, and properties of low carbon
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Two low carbon carbide-free bainitic steels (with and without Cr addition) were designed, and each steel was treated by two kinds of heat treatment procedure (austempering and continuous cooling). The effects of Cr addition on bainitic transformation, microstructure, and properties of low carbon bainitic steels were investigated by dilatometry, metallography, X-ray diffraction, and a tensile test. The results show that Cr addition hinders the isothermal bainitic transformation, and this effect is more significant at higher transformation temperatures. In addition, Cr addition increases the tensile strength and elongation simultaneously for austempering treatment at a lower temperature. However, when the austempering temperature is higher, the strength increases and the elongation obviously decreases by Cr addition, resulting in the decrease in the product of tensile strength and elongation. Meanwhile, the austempering temperature should be lower in Cr-added steel than that in Cr-free steel in order to obtain better comprehensive properties. Moreover, for the continuous cooling treatment in the present study, the product of tensile strength and elongation significantly decreases with Cr addition due to more amounts of martensite. Full article
(This article belongs to the Special Issue Alloy Steels)
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Open AccessFeature PaperArticle The Role of κ-Carbides as Hydrogen Traps in High-Mn Steels
Metals 2017, 7(7), 264; doi:10.3390/met7070264
Received: 13 June 2017 / Revised: 30 June 2017 / Accepted: 3 July 2017 / Published: 11 July 2017
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Abstract
Since the addition of Al to high-Mn steels is known to reduce their sensitivity to hydrogen-induced delayed fracture, we investigate possible trapping effects connected to the presence of Al in the grain interior employing density-functional theory (DFT). The role of Al-based precipitates is
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Since the addition of Al to high-Mn steels is known to reduce their sensitivity to hydrogen-induced delayed fracture, we investigate possible trapping effects connected to the presence of Al in the grain interior employing density-functional theory (DFT). The role of Al-based precipitates is also investigated to understand the relevance of short-range ordering effects. So-called E21-Fe3AlC κ-carbides are frequently observed in Fe-Mn-Al-C alloys. Since H tends to occupy the same positions as C in these precipitates, the interaction and competition between both interstitials is also investigated via DFT-based simulations. While the individual H–H/C–H chemical interactions are generally repulsive, the tendency of interstitials to increase the lattice parameter can yield a net increase of the trapping capability. An increased Mn content is shown to enhance H trapping due to attractive short-range interactions. Favorable short-range ordering is expected to occur at the interface between an Fe matrix and the E21-Fe3AlC κ-carbides, which is identified as a particularly attractive trapping site for H. At the same time, accumulation of H at sites of this type is observed to yield decohesion of this interface, thereby promoting fracture formation. The interplay of these effects, evident in the trapping energies at various locations and dependent on the H concentration, can be expressed mathematically, resulting in a term that describes the hydrogen embrittlement. Full article
(This article belongs to the Special Issue First-Principles Approaches to Metals, Alloys, and Metallic Compounds)
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Open AccessArticle Low Cycle Fatigue Behaviour of DP Steels: Micromechanical Modelling vs. Validation
Metals 2017, 7(7), 265; doi:10.3390/met7070265
Received: 22 June 2017 / Revised: 5 July 2017 / Accepted: 6 July 2017 / Published: 11 July 2017
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Abstract
This study aims to simulate the stabilised stress-strain hysteresis loop of dual phase (DP) steel using micromechanical modelling. For this purpose, the investigation was conducted both experimentally and numerically. In the experimental part, the microstructure characterisation, monotonic tensile tests and low cycle fatigue
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This study aims to simulate the stabilised stress-strain hysteresis loop of dual phase (DP) steel using micromechanical modelling. For this purpose, the investigation was conducted both experimentally and numerically. In the experimental part, the microstructure characterisation, monotonic tensile tests and low cycle fatigue tests were performed. In the numerical part, the representative volume element (RVE) was employed to study the effect of the DP steel microstructure of the low cycle fatigue behavior of DP steel. A dislocation-density based model was utilised to identify the tensile behavior of ferrite and martensite. Then, by establishing a correlation between the monotonic and cyclic behavior of ferrite and martensite phases, the cyclic deformation properties of single phases were estimated. Accordingly, Chaboche kinematic hardening parameters were identified from the predicted cyclic curve of individual phases in DP steel. Finally, the predicted hysteresis loop from low cycle fatigue modelling was in very good agreement with the experimental one. The stabilised hysteresis loop of DP steel can be successfully predicted using the developed approach. Full article
(This article belongs to the Special Issue Microstructure based Modeling of Metallic Materials)
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Open AccessArticle Microstructure and Mechanical Properties of Ti6Al4V Alloy Modified and Reinforced by In Situ Ti5Si3/Ti Composite Ribbon Inoculants
Metals 2017, 7(7), 267; doi:10.3390/met7070267
Received: 6 May 2017 / Revised: 30 June 2017 / Accepted: 7 July 2017 / Published: 12 July 2017
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Abstract
This paper deals with a novel fabrication method (a vacuum rapid solidification technique) to prepare in situ Ti5Si3/Ti composite ribbon as inoculants to modify Ti6Al4V alloy to obtain titanium matrix composites (TMCs). Microstructure and morphology observations showed that the
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This paper deals with a novel fabrication method (a vacuum rapid solidification technique) to prepare in situ Ti5Si3/Ti composite ribbon as inoculants to modify Ti6Al4V alloy to obtain titanium matrix composites (TMCs). Microstructure and morphology observations showed that the grain size of the TMCs was refined as the volume fraction of inoculants increased. The grain size of the TMCs can be refined from a grade of 650 μm to about 110 μm with a very small refiner adding ratio of 0.6% in weight. Thereafter, the mechanical properties of the TMCs, including their tensile strength, microhardness, impact properties, and resistant properties were improved obviously by adding the ribbon inoculants. The excellent grain refining and reinforcement effect can be attributed to the nano-sized Ti5Si3 refiner particles distributed homogeneously in the matrix, the well-banded particle/matrix interface, and the good wettability between the Ti5Si3 particles in inoculants and the Ti6Al4V alloy melt, which are benefit for the heterogeneous nucleation of the TMCs during solidification. Full article
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Open AccessArticle Investigation on Deformation Mechanisms of NiTi Shape Memory Alloy Tube under Radial Loading
Metals 2017, 7(7), 268; doi:10.3390/met7070268
Received: 9 June 2017 / Revised: 2 July 2017 / Accepted: 11 July 2017 / Published: 13 July 2017
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Abstract
NiTi shape memory alloy (SMA) tube was coupled with mild steel cylinder in order to investigate deformation mechanisms of NiTi SMA tubes undergoing radial loading. NiTi SMA tubes of interest deal with two kinds of nominal compositions; namely, Ni-50 at % Ti and
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NiTi shape memory alloy (SMA) tube was coupled with mild steel cylinder in order to investigate deformation mechanisms of NiTi SMA tubes undergoing radial loading. NiTi SMA tubes of interest deal with two kinds of nominal compositions; namely, Ni-50 at % Ti and Ni-49.1 at % Ti, where at room temperature, B19′ martensite is dominant in the former, and B2 austensite is complete in the latter. The mechanics of the NiTi SMA tube during radial loading were analyzed based on elastic mechanics and plastic yield theory, where effective stress and effective strain are determined as two important variables that investigate deformation mechanisms of the NiTi SMA tube during radial loading. As for the NiTi SMA tube with austenite structure, stress-induced martensite (SIM) transformation as well as plastic deformation of SIM occur with the continuous increase of effective stress. As for NiTi SMA tube which possesses martensite structure, reorientation and detwinning of twinned martensite as well as plastic deformation of reoriented and detwinned martensite occur with the continuous increase in the effective stress. Plastic deformation for dislocation slip has a negative impact on superelasticity and shape memory effect of NiTi SMA tube. Full article
(This article belongs to the Special Issue Shape Memory Alloys 2017)
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Open AccessFeature PaperArticle Microstructure and Mechanical Properties of Ti5553 Butt Welds Performed by LBW under Conduction Regime
Metals 2017, 7(7), 269; doi:10.3390/met7070269
Received: 20 June 2017 / Revised: 7 July 2017 / Accepted: 10 July 2017 / Published: 13 July 2017
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Abstract
Ti-5Al-5V-5Mo-3Cr (Ti5553) is a metastable β titanium alloy with a high potential use in the aeronautic industry due to its high strength, excellent hardenability, fracture toughness and high fatigue resistance. However, recent research shows this alloy has a limited weldability. Different welding technologies
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Ti-5Al-5V-5Mo-3Cr (Ti5553) is a metastable β titanium alloy with a high potential use in the aeronautic industry due to its high strength, excellent hardenability, fracture toughness and high fatigue resistance. However, recent research shows this alloy has a limited weldability. Different welding technologies have been applied in the literature to weld this alloy, such as electron beam welding (EBW), gas tungsten arc welding (GTAW) or laser beam welding (LBW) under keyhole regime. Thus, in tensile tests, joints normally break at the weld zones, the strength of the welds being always lower than that of the base metal. In the present work, a novel approach, based on the application of LBW under conduction regime (with a High-Power Diode Laser, HPDL), has been employed for the first time to weld this alloy. Microstructure, microhardness and strength of obtained welds were analyzed and reported in this paper. LBW under conduction regime (LBW-CR) leads to welds with slightly higher values of Ultimate Tensile Strength (UTS) than those previously obtained with other joining processes, probably due to the higher hardness of the fusion zone and to lower porosity of the weld. Full article
(This article belongs to the Special Issue Laser Welding)
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Open AccessArticle Effects of Welding Speed on Microstructure and Mechanical Property of Fiber Laser Welded Dissimilar Butt Joints between AISI316L and EH36
Metals 2017, 7(7), 270; doi:10.3390/met7070270
Received: 5 May 2017 / Revised: 6 July 2017 / Accepted: 7 July 2017 / Published: 13 July 2017
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Abstract
Fiber laser welding of dissimilar materials between AISI316L austenitic stainless steel and EH36 ship steels were conducted. Then the effects of welding speed on microstructure and mechanical characterization of the welded joint were investigated. Optical microscopy, Scanning Electron Microscopy (SEM), and X-ray Diffraction
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Fiber laser welding of dissimilar materials between AISI316L austenitic stainless steel and EH36 ship steels were conducted. Then the effects of welding speed on microstructure and mechanical characterization of the welded joint were investigated. Optical microscopy, Scanning Electron Microscopy (SEM), and X-ray Diffraction (XRD) were used to analyze the microstructure. Microhardness testing, transverse tensile strength, and impact tests at the temperature of −40 °C were performed to study the mechanical properties. The martensite phase formed due to the rapid cooling rate during laser welding and low Creq/Nieq ratio. The coarse martensite grains in the center seam are transformed to finer martensite grains as the welding speed increases resulting in the higher cooling rate. The microhardness of joints was about 350 HV0.3, which was twice that of the base metal because of the formation of the martensite phase. When the welding speed was 0.6 m/min, fewer defects were found, and tensile testing indicated overmatching of the weld metal relative to the base metal. In addition, the joints also exhibited better ductility and impact toughness. Full article
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Open AccessArticle In-Situ Investigation of Strain-Induced Martensitic Transformation Kinetics in an Austenitic Stainless Steel by Inductive Measurements
Metals 2017, 7(7), 271; doi:10.3390/met7070271
Received: 31 May 2017 / Revised: 10 July 2017 / Accepted: 12 July 2017 / Published: 13 July 2017
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Abstract
An inductive sensor developed by Philips ATC has been used to study in-situ the austenite (γ) to martensite (α′) phase transformation kinetics during tensile testing in an AISI 301 austenitic stainless steel. A correlation between the sensor output signal and the volume fraction
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An inductive sensor developed by Philips ATC has been used to study in-situ the austenite (γ) to martensite (α′) phase transformation kinetics during tensile testing in an AISI 301 austenitic stainless steel. A correlation between the sensor output signal and the volume fraction of α′-martensite has been found by comparing the results to the ex-situ characterization by magnetization measurements, light optical microscopy, and X-ray diffraction. The sensor has allowed for the observation of the stepwise transformation behavior, a not-well-understood phenomena that takes place in large regions of the bulk material and that so far had only been observed by synchrotron X-ray diffraction. Full article
(This article belongs to the Special Issue Bainite and Martensite: Developments and Challenges)
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Open AccessArticle An Efficient Approach for Lithium and Aluminum Recovery from Coal Fly Ash by Pre-Desilication and Intensified Acid Leaching Processes
Metals 2017, 7(7), 272; doi:10.3390/met7070272
Received: 26 June 2017 / Revised: 10 July 2017 / Accepted: 11 July 2017 / Published: 14 July 2017
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Abstract
A novel technique was developed for the recovery of lithium and aluminum from coal fly ash using a combination of pre-desilication and an intensified acid leaching process. The main components of the high-aluminum fly ash were found to be Al2O3
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A novel technique was developed for the recovery of lithium and aluminum from coal fly ash using a combination of pre-desilication and an intensified acid leaching process. The main components of the high-aluminum fly ash were found to be Al2O3 and SiO2, and the Al/Si ratio increased from 1.0 to 1.5 after desiliconization. The lithium content of the coal fly ash met national recycling standards. The optimal acid leaching conditions, under which the leaching efficiencies of lithium and aluminum were 82.23% and 76.72%, respectively, were as follows: 6 mol/L HCl, 1:20 solid to liquid ratio, 120 °C and 4 h. During the hydrochloric acid pressure leaching process, spherical particles of desilicated fly ash were decomposed into flakes. Part of the mullite phase was dissolved, and most of the glass phase leached into the liquor. The generation of the silicates hindered lithium transport, which decreased the leaching rate of lithium. This work suggests that the preprocessing is a promising option for effective recovery of high-aluminum and fly ash-associated lithium. Full article
(This article belongs to the Special Issue Valuable Metal Recycling)
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Open AccessArticle Excellent Performance of Fe78Si9B13 Metallic Glass for Activating Peroxymonosulfate in Degradation of Naphthol Green B
Metals 2017, 7(7), 273; doi:10.3390/met7070273
Received: 19 June 2017 / Revised: 12 July 2017 / Accepted: 13 July 2017 / Published: 17 July 2017
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Abstract
The functional application of metallic glasses in the catalytic field has widely attracted research attention due to its unique atomic structure compared to crystalline materials. It has been reported that metallic glasses can effectively activate H2O2 and persulfate, yet the
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The functional application of metallic glasses in the catalytic field has widely attracted research attention due to its unique atomic structure compared to crystalline materials. It has been reported that metallic glasses can effectively activate H2O2 and persulfate, yet the activation of peroxymonosulfate by metallic glasses is not studied well. In this work, the metallic glass with atomic composition of Fe78Si9B13 was applied for investigating the peroxymonosulfate (PMS) activation on degradation of naphthol green B (NGB) dye. The change of surface morphology indicated the important role of oxide films during the dye degradation. The effects and first-order kinetics model of various reaction parameters were evaluated systematically, including PMS concentration, catalyst dosage, irradiation intensity, and dye concentration. The results showed that about 98% of the dye removal rate could be achieved only within 10 min under rational conditions. The reaction kinetics k of 0.1339 min−1 without ribbons was sharply improved to 0.3140 min−1 by adding 0.5 g/L ribbons, indicating the superior activation ability of Fe78Si9B13 metallic glass. The recycling experiment revealed that the Fe78Si9B13 ribbons exhibited the excellent surface stability and catalytic reusability for activating PMS even after reused for 10th run. Full article
(This article belongs to the Special Issue Bulk Metallic Glasses)
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Open AccessArticle Investigation of Service Life Prediction Models for Metallic Organic Coatings Using Full-Range Frequency EIS Data
Metals 2017, 7(7), 274; doi:10.3390/met7070274
Received: 17 June 2017 / Revised: 13 July 2017 / Accepted: 13 July 2017 / Published: 17 July 2017
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Abstract
Various service life prediction models of organic coatings were analyzed based on the acquirement of the measurement of Electrochemical Impedance Spectroscopy (EIS) from indoor accelerated tests. First, some theoretical formulas on corrosion lifetime predictions of coatings were introduced, followed by the comparative assessment
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Various service life prediction models of organic coatings were analyzed based on the acquirement of the measurement of Electrochemical Impedance Spectroscopy (EIS) from indoor accelerated tests. First, some theoretical formulas on corrosion lifetime predictions of coatings were introduced, followed by the comparative assessment of four practical prediction models in view of prediction accuracy in application. The prediction from impedance data at single low frequency |Z| 0.1 Hz, the classical degradation kinetics, and proposed improved degradation kinetics model, as well as a self-organized neural network prediction based on sample detection, were focused in this paper. The standard AF1410 plates employed as the metallic substrates were coated with sprayed zinc layer, epoxy-ester primer and polyurethane enamel layer. The accelerated experiments which mimicked coastal areas of China were carried out with the specimens after surface treatment. The assessment of results showed that the proposed improved degradation kinetics model and neural network classification model based on the full range of frequency data obviously have higher prediction accuracies than the traditional degradation kinetics model, and the prediction precision of the sample detection-based neural network classification was the highest among these models. The study gives some insights for coating degradation lifetime prediction which may be useful and supportive for practical applications. Full article
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Open AccessArticle Feature Size Effect on Formability of Multilayer Metal Composite Sheets under Microscale Laser Flexible Forming
Metals 2017, 7(7), 275; doi:10.3390/met7070275
Received: 14 June 2017 / Revised: 12 July 2017 / Accepted: 15 July 2017 / Published: 18 July 2017
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Abstract
Multilayer metal composite sheets possess superior properties to monolithic metal sheets, and formability is different from monolithic metal sheets. In this research, the feature size effect on formability of multilayer metal composite sheets under microscale laser flexible forming was studied by experiment. Two-layer
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Multilayer metal composite sheets possess superior properties to monolithic metal sheets, and formability is different from monolithic metal sheets. In this research, the feature size effect on formability of multilayer metal composite sheets under microscale laser flexible forming was studied by experiment. Two-layer copper/nickel composite sheets were selected as experimental materials. Five types of micro molds with different diameters were utilized. The formability of materials was evaluated by forming depth, thickness thinning, surface quality, and micro-hardness distribution. The research results showed that the formability of two-layer copper/nickel composite sheets was strongly influenced by feature size. With feature size increasing, the effect of layer stacking sequence on forming depth, thickness thinning ratio, and surface roughness became increasingly larger. However, the normalized forming depth, thickness thinning ratio, surface roughness, and micro-hardness of the formed components under the same layer stacking sequence first increased and then decreased with increasing feature size. The deformation behavior of copper/nickel composite sheets was determined by the external layer. The deformation extent was larger when the copper layer was set as the external layer. Full article
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Open AccessArticle Infrared Dissimilar Joining of Ti50Ni50 and 316L Stainless Steel with Copper Barrier Layer in between Two Silver-Based Fillers
Metals 2017, 7(7), 276; doi:10.3390/met7070276
Received: 1 July 2017 / Revised: 16 July 2017 / Accepted: 17 July 2017 / Published: 18 July 2017
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Abstract
Infrared dissimilar joining Ti50Ni50 and 316L stainless steel using Cu foil in between Cusil-ABA and BAg-8 filler metals has been studied. The Cu foil serves as a barrier layer with thicknesses of 70 μm and 50 μm, and it successfully
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Infrared dissimilar joining Ti50Ni50 and 316L stainless steel using Cu foil in between Cusil-ABA and BAg-8 filler metals has been studied. The Cu foil serves as a barrier layer with thicknesses of 70 μm and 50 μm, and it successfully isolates the interfacial reaction between Ti and Fe at the 316L SS (stainless steel) substrate side. In contrast, the Cu foil with 25 μm in thickness is completely dissolved into the braze melt during brazing and fails to be a barrier layer. A layer of (CuxNi1−x)2Ti intermetallic is formed at the Ti50Ni50 substrate side, and the Cu interlayer is dissolved into the Cusil-ABA melt to from a few proeutectic Cu particles for all specimens. For the 316L SS substrate side, no interfacial layer is observed and (Ag, Cu) eutectic dominates the brazed joint for 70 μm/50 μm Cu foil. The average shear strength of the bond with Cu barrier layer is greatly increased compared with that without Cu. The brazed joints with a 50 μm Cu layer demonstrate the highest average shear strengths of 354 MPa and 349 MPa for samples joined at 820 °C and 850 °C, respectively. Cracks are initiated/propagated in (Ag, Cu) eutectic next to the 316L substrate side featured with ductile dimple fracture. It shows great potential for industrial application. Full article
(This article belongs to the Special Issue Shape Memory Alloys 2017)
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Open AccessArticle Transition of the Interface between Iron and Carbide Precipitate From Coherent to Semi-Coherent
Metals 2017, 7(7), 277; doi:10.3390/met7070277
Received: 5 May 2017 / Revised: 10 July 2017 / Accepted: 14 July 2017 / Published: 19 July 2017
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Abstract
There are some precipitates that undergo transition from a coherent to semi-coherent state during growth. An example of such a precipitate in steel is carbide with a NaCl-type structure, such as TiC and NbC. The interface energy between carbide precipitate and iron is
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There are some precipitates that undergo transition from a coherent to semi-coherent state during growth. An example of such a precipitate in steel is carbide with a NaCl-type structure, such as TiC and NbC. The interface energy between carbide precipitate and iron is obtained via large-scale first-principles electronic structure calculation. The strain energy is estimated by structure optimization of the iron matrix with virtual carbide precipitate using the empirical potential. The transition of the interface from a coherent to semi-coherent state was examined by comparing the interface and strain energies between the coherent and semi-coherent interfaces. The sizes where both the precipitates undergo this transition are smaller than those of the interfaces with minimum misfit. The estimated transition diameter of TiC is in agreement with the experimentally obtained value. Full article
(This article belongs to the Special Issue First-Principles Approaches to Metals, Alloys, and Metallic Compounds)
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Open AccessArticle Effect of Pyrite on Thiosulfate Leaching of Gold and the Role of Ammonium Alcohol Polyvinyl Phosphate (AAPP)
Metals 2017, 7(7), 278; doi:10.3390/met7070278
Received: 18 June 2017 / Revised: 13 July 2017 / Accepted: 14 July 2017 / Published: 19 July 2017
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Abstract
The effect of pyrite and the role of ammonium alcohol polyvinyl phosphate (AAPP) during gold leaching in ammoniacal thiosulfate solutions were investigated using pure gold foils. The results showed that pyrite catalyzed the decomposition and also significantly increased the consumption of thiosulfate. This
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The effect of pyrite and the role of ammonium alcohol polyvinyl phosphate (AAPP) during gold leaching in ammoniacal thiosulfate solutions were investigated using pure gold foils. The results showed that pyrite catalyzed the decomposition and also significantly increased the consumption of thiosulfate. This detrimental effect became more severe with increasing pyrite content. Further, the presence of pyrite also substantially slowed the gold leaching kinetics and reduced the overall gold dissolution. The reduction in gold dissolution was found to be caused primarily by the surface passivation of the gold. The negative effects of pyrite, however, can be alleviated by the addition of AAPP. Comparison of zeta potentials of pyrite with and without AAPP suggests that AAPP had adsorbed on the surface of the pyrite and weakened the catalytic effect of pyrite on the thiosulfate decomposition by blocking the contact between the pyrite and thiosulfate anions. AAPP also competed with thiosulfate anions to complex with the cupric ion at the axial coordinate sites, and thus abated the oxidation of thiosulfate by cupric ions. Moreover, the indiscriminate adsorption of AAPP on the surfaces of gold and passivation species prevented the passivation of the gold surface by surface charge and electrostatic repulsion. Therefore, AAPP effectively stabilized the thiosulfate in the solution and facilitated the gold leaching in the presence of pyrite. Full article
(This article belongs to the Special Issue Valuable Metal Recycling)
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Open AccessArticle Aluminum and Nickel Matrix Composites Reinforced by CNTs: Dispersion/Mixture by Ultrasonication
Metals 2017, 7(7), 279; doi:10.3390/met7070279
Received: 21 June 2017 / Revised: 12 July 2017 / Accepted: 18 July 2017 / Published: 22 July 2017
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Abstract
The main challenge in the production of metal matrix composites reinforced by carbon nanotubes (CNTs) is the development of a manufacturing process ensuring the dispersion of nanoparticles without damaging them, and the formation of a strong bond with the metallic matrix to achieve
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The main challenge in the production of metal matrix composites reinforced by carbon nanotubes (CNTs) is the development of a manufacturing process ensuring the dispersion of nanoparticles without damaging them, and the formation of a strong bond with the metallic matrix to achieve an effective load transfer, so that the maximum reinforcement effect of CNTs will be accomplished. This research focuses on the production by powder metallurgy of aluminum and nickel matrix composites reinforced by CNTs, using ultrasonication as the dispersion and mixture process. Microstructural characterization of nanocomposites was performed by optical microscopy (OM), scanning and transmission electron microscopy (SEM and TEM), electron backscattered diffraction (EBSD) and high-resolution transmission electron microscopy (HRTEM). Microstructural characterization revealed that the use of ultrasonication as the dispersion and mixture process in the production of Al/CNT and Ni/CNT nanocomposites promoted the dispersion and embedding of individual CNT in the metallic matrices. CNT clusters at grain boundary junctions were also observed. The strengthening effect of the CNTs is shown by the increase in hardness for all nanocomposites. The highest hardness values were observed for Al/CNT and Ni/CNT nanocomposites, with a 1.00 vol % CNTs. Full article
(This article belongs to the Special Issue Metal Matrix Composites)
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Open AccessArticle Effect of Structural Heterogeneity of 17Mn1Si Steel on the Temperature Dependence of Impact Deformation and Fracture
Metals 2017, 7(7), 280; doi:10.3390/met7070280
Received: 7 June 2017 / Revised: 12 July 2017 / Accepted: 14 July 2017 / Published: 22 July 2017
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Abstract
The paper deals with a theoretical and experimental study of the relationship between the microstructural parameters, mechanical properties, and impact deformation and fracture of steels using the example of 17Mn1Si pipe steel. A model for the behavior of a polycrystalline grain conglomerate under
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The paper deals with a theoretical and experimental study of the relationship between the microstructural parameters, mechanical properties, and impact deformation and fracture of steels using the example of 17Mn1Si pipe steel. A model for the behavior of a polycrystalline grain conglomerate under impact loading at different temperatures was proposed within a cellular automata framework. It was shown that the intensity of dissipation processes explicitly depends on temperature and these processes play an important role in stress relaxation at the boundaries of structural elements. The Experimental study reveals the relationship between pendulum impact test temperature and the deformation/fracture energy of the steel. The impact toughness was shown to decrease almost linearly with the decreasing test temperature, which agrees with the fractographic analysis data confirming the increase in the fraction of brittle fracture in this case. It was shown with the aid of the proposed model and numerical simulations that the use of the excitable cellular automata method and an explicit account of test temperature through the possibility of energy release at internal interfaces help to explain the experimentally observed features of impact failure at different temperatures. Full article
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Open AccessArticle The Microstructures and Tensile Properties of As-Extruded Mg–4Sm–xZn–0.5Zr (x = 0, 1, 2, 3, 4 wt %) Alloys
Metals 2017, 7(7), 281; doi:10.3390/met7070281
Received: 19 June 2017 / Revised: 17 July 2017 / Accepted: 19 July 2017 / Published: 24 July 2017
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Abstract
The microstructures and tensile properties of as-cast and as-extruded Mg–4Sm–xZn–0.5Zr (x = 0, 1, 2, 3, 4 wt %) alloys were systematically investigated by optical microscope, X-ray diffractometer (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). Numerous nanoscale
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The microstructures and tensile properties of as-cast and as-extruded Mg–4Sm–xZn–0.5Zr (x = 0, 1, 2, 3, 4 wt %) alloys were systematically investigated by optical microscope, X-ray diffractometer (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). Numerous nanoscale dynamic precipitates could be observed in the as-extruded alloys containing high content of Zn, and the nanoscale particles were termed as (Mg,Zn)3Sm phase. Some basal disc-like precipitates were observed in as-extruded Mg–4Sm–4Zn–0.5Zr alloy, which were proposed to have a hexagonal structure with a = 0.556 nm. The dynamic precipitates effectively pinned the motions of DRXed (dynamic recrystallized) grain boundaries leading to an obvious reduction of DRXed grain size, and the tensile yield strength of as-extruded alloy was improved. The as-extruded Mg–4Sm–4Zn–0.5Zr alloy exhibits the best comprehensive mechanical properties at room temperature among all the alloys, and the yield strength, ultimate tensile strength and elongation are about 246 MPa, 273 MPa and 21% respectively. Full article
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Open AccessReview Mg and Its Alloys for Biomedical Applications: Exploring Corrosion and Its Interplay with Mechanical Failure
Metals 2017, 7(7), 252; doi:10.3390/met7070252
Received: 6 June 2017 / Revised: 25 June 2017 / Accepted: 25 June 2017 / Published: 5 July 2017
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Abstract
The future of biomaterial design will rely on temporary implant materials that degrade while tissues grow, releasing no toxic species during degradation and no residue after full regeneration of the targeted anatomic site. In this aspect, Mg and its alloys are receiving increasing
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The future of biomaterial design will rely on temporary implant materials that degrade while tissues grow, releasing no toxic species during degradation and no residue after full regeneration of the targeted anatomic site. In this aspect, Mg and its alloys are receiving increasing attention because they allow both mechanical strength and biodegradability. Yet their use as biomedical implants is limited due to their poor corrosion resistance and the consequential mechanical integrity problems leading to corrosion assisted cracking. This review provides the reader with an overview of current biomaterials, their stringent mechanical and chemical requirements and the potential of Mg alloys to fulfil them. We provide insight into corrosion mechanisms of Mg and its alloys, the fundamentals and established models behind stress corrosion cracking and corrosion fatigue. We explain Mgs unique negative differential effect and approaches to describe it. Finally, we go into depth on corrosion improvements, reviewing literature on high purity Mg, on the effect of alloying elements and their tolerance levels, as well as research on surface treatments that allow to tune degradation kinetics. Bridging fundamentals aspects with current research activities in the field, this review intends to give a substantial overview for all interested readers; potential and current researchers and practitioners of the future not yet familiar with this promising material. Full article
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