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Metals, Volume 9, Issue 1 (January 2019)

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Cover Story (view full-size image) A finite element based model incorporating an enhanced friction model to consider the effect of [...] Read more.
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Open AccessArticle Forming Process, Microstructure, and Mechanical Properties of Thin-Walled 316L Stainless Steel Using Speed-Cold-Welding Additive Manufacturing
Metals 2019, 9(1), 109; https://doi.org/10.3390/met9010109
Received: 22 November 2018 / Revised: 28 December 2018 / Accepted: 17 January 2019 / Published: 21 January 2019
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Abstract
Wire and arc additive manufacturing (WAAM) produces thin-walled parts superior to other additive manufacturing methods, because of its high efficiency, good compactability, and low cost. However, the WAAM accuracy is limited by its large heat input. Here, 0.8 mm 316L stainless steel welding [...] Read more.
Wire and arc additive manufacturing (WAAM) produces thin-walled parts superior to other additive manufacturing methods, because of its high efficiency, good compactability, and low cost. However, the WAAM accuracy is limited by its large heat input. Here, 0.8 mm 316L stainless steel welding wire is deposited via speed cold welding to form 30-layered thin-walled samples, with 2 mm thickness, and up to 65 mm height. The effects of three process parameters (the bottom current mode, scanning speed, and cooling time) on the deposition process stability, macro morphology, structure, and mechanical properties are studied. In the experiment, the probability density curves of electrical parameters of sample #GRBC-30 cm/min-10 s on the third and tenth layers were narrower than other samples, which implied a more stable process. The three process parameters mainly affect the deposition morphology and have a minor performance effect. The hardness and tensile properties mainly depend on the deposition direction. Gradual, layer-by-layer current reduction improves the bottom molding and performance, and the deposition efficiency, and stabilizes the process. Scanning speed enhancement or cooling time reduction destabilizes the end formation, reduces the effective deposition rate, and slightly degrades the performance. All deposited samples are distinctly anisotropic, but satisfy the industrial standard. Overall, deposition in speed cold welding mode, with 10 s cooling time, 30 cm/min scanning speed, and gradually reduced bottom current exhibits good stability, and the molding efficiency and mechanical properties are optimal. Full article
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Open AccessArticle Effects of Yb Addition on the Microstructure and Mechanical Properties of As-Cast ADC12 Alloy
Metals 2019, 9(1), 108; https://doi.org/10.3390/met9010108
Received: 27 November 2018 / Revised: 13 January 2019 / Accepted: 17 January 2019 / Published: 21 January 2019
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Abstract
The effects of addition of different amounts of rare earth ytterbium (Yb) on the microstructure and mechanical properties of the casting ADC12 alloy were investigated by mechanical properties testing and microstructure observation. The results indicate that Yb modification had a big influence on [...] Read more.
The effects of addition of different amounts of rare earth ytterbium (Yb) on the microstructure and mechanical properties of the casting ADC12 alloy were investigated by mechanical properties testing and microstructure observation. The results indicate that Yb modification had a big influence on the microstructure and properties of the as-cast alloy. The optimum level of Yb content was 0.8 wt %. The coarse dendritic primary α-Al phases were fully refined, leading to the decreasing of the secondary dendrite arm spacing. The morphology of eutectic silicon phases changed from acicular into short rod-like and even granular. There was a structural transformation of β-Fe phases from massive to small rod-shaped morphology. Additionally, the tensile strength, elongation, and microhardness were 267.9 MPa, 4.2%, and 107.3 HV, respectively, increases of 55.4, 121.1, and 41.4%, respectively, compared with the matrix alloy. Fractographic examinations reveal that mainly ductile fracture for Yb addition of 0.8 wt %. The fracture appearances matched the tendency of the tensile properties. Furthermore, the addition of Yb can generate a rare earth phase consisting of the three elements of Al, Si, Yb, with some small iron-rich phases attached around the rare earth phase. Full article
(This article belongs to the Special Issue Solidification Processes of Light Metal Alloys)
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Open AccessArticle Stochastic Material Point Method for Analysis in Non-Linear Dynamics of Metals
Metals 2019, 9(1), 107; https://doi.org/10.3390/met9010107
Received: 20 December 2018 / Revised: 9 January 2019 / Accepted: 18 January 2019 / Published: 21 January 2019
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Abstract
A stochastic material point method is proposed for stochastic analysis in non-linear dynamics of metals with varying random material properties. The basic random variables are parameters of equation of state and those of constitutive equation. In conjunction with the material point method, the [...] Read more.
A stochastic material point method is proposed for stochastic analysis in non-linear dynamics of metals with varying random material properties. The basic random variables are parameters of equation of state and those of constitutive equation. In conjunction with the material point method, the Taylor series expansion is employed to predict first- and second-moment characteristics of structural response. Unlike the traditional grid methods, the stochastic material point method does not require structured mesh; instead, only a scattered cluster of nodes is required in the computational domain. In addition, there is no need for fixed connectivity between nodes. Hence, the stochastic material point method is more suitable than the stochastic method based on grids, when solving dynamics problems of metals involving large deformations and strong nonlinearity. Numerical examples show good agreement between the results of the stochastic material point method and Monte Carlo simulation. This study examines the accuracy and convergence of the stochastic material point method. The stochastic material point method offers a new option when solving stochastic dynamics problems of metals involving large deformation and strong nonlinearity, since the method is convenient and efficient. Full article
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Open AccessFeature PaperReview Repair and Reinforcement of Historic Timber Structures with Stainless Steel—A Review
Metals 2019, 9(1), 106; https://doi.org/10.3390/met9010106
Received: 20 December 2018 / Revised: 11 January 2019 / Accepted: 17 January 2019 / Published: 21 January 2019
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Abstract
Recent trends in the use of stainless steel profiles for repair and reinforcement of historic timber structures, after degradation due to biotic and non-biotic attacks, are discussed in this paper. These structural challenges can vary from inadequate load carrying capacity to complexities involved [...] Read more.
Recent trends in the use of stainless steel profiles for repair and reinforcement of historic timber structures, after degradation due to biotic and non-biotic attacks, are discussed in this paper. These structural challenges can vary from inadequate load carrying capacity to complexities involved with choice of repair materials and techniques. Given the recurring requirements of conservation authorities in terms of reversibility of interventions and compatibility between historic and new materials, an increase in the use of non-invasive reinforcement materials and reversible techniques was observed. Subsequently, engineers and researchers have increasingly employed stainless steel alloys in retrofitting historic timber structures. This paper therefore presents the state of the art in the use of stainless steel profiles in retrofitting timber structural elements within historic structures. It includes a review of the development of the retrofitting methods and existing experimental studies on the mechanical behavior of timber structures reinforced with stainless steel. Finally, it presents a number of case studies and draws conclusions on current trends and practices based on reported studies. Full article
(This article belongs to the Special Issue Manufacturing and Application of Stainless Steels)
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Open AccessArticle Precipitation Strengthening in Ni–Cu Alloys Fabricated Using Wire Arc Additive Manufacturing Technology
Metals 2019, 9(1), 105; https://doi.org/10.3390/met9010105
Received: 18 December 2018 / Revised: 18 January 2019 / Accepted: 18 January 2019 / Published: 21 January 2019
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Abstract
Two Ni–Cu alloys, Monel K500 and FM60, with various contents of Ti, Mn, Al, Fe and C were deposited in the form of plates on a metal base plate using wire arc additive manufacturing technology. Three deposition speeds have been applied: 300, 400 [...] Read more.
Two Ni–Cu alloys, Monel K500 and FM60, with various contents of Ti, Mn, Al, Fe and C were deposited in the form of plates on a metal base plate using wire arc additive manufacturing technology. Three deposition speeds have been applied: 300, 400 and 500 mm/min. To modify the as-welded microstructure and properties, the deposited walls/plates have been subjected to two heat treatment procedures: annealing at 1100 °C for 15 min, slow cooling to 610 °C, ageing at this temperature for 8 h and either (i) air cooling to room temperature or (ii) slow cooling to 480 °C, ageing at this temperature for 8 h and air cooling to room temperature. The microstructure characterisation and mechanical properties testing have been conducted for each of the 18 chemistry/processing conditions. The dependences of the precipitate’s parameters (size, number density and chemistry), mechanical properties and wear resistance on the alloy composition, deposition speed and heat treatment have been obtained. In Monel K500, the precipitates were mainly of the TiC/TiCN type, and in FM60, they were of the MnS and TiAlMgO types. Monel K500 has shown higher hardness, strength, toughness and wear resistance in all studied conditions. Ageing at 610 °C improved properties in both alloys following the precipitation of new particles. Ageing at 480 °C could result in a properties loss if the particle coarsening (decrease in number density) took place. Full article
(This article belongs to the Special Issue Strengthening Mechanisms in Metallic Materials)
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Open AccessArticle Influence of Al on Evolution of the Inclusions in Ti-Bearing Steel with Ca Treatment
Metals 2019, 9(1), 104; https://doi.org/10.3390/met9010104
Received: 29 December 2018 / Revised: 17 January 2019 / Accepted: 18 January 2019 / Published: 21 January 2019
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Abstract
Experimental simulations of steelmaking with different amounts of aluminum were achieved in the tube furnace at 1873 K and field scanning electron microscopy and energy dispersive X-ray spectroscopy (FE-SEM and EDX) were employed to explore the characteristics of the inclusions in Ti-bearing steel [...] Read more.
Experimental simulations of steelmaking with different amounts of aluminum were achieved in the tube furnace at 1873 K and field scanning electron microscopy and energy dispersive X-ray spectroscopy (FE-SEM and EDX) were employed to explore the characteristics of the inclusions in Ti-bearing steel during the calcium treatment process. It was found that morphologies, chemical compositions, and the size distribution of the inclusions were obviously different before and after calcium treatment. The calcium addition need be carefully considered regarding the mass fraction of aluminum with the purpose of modifying the solid inclusions to liquid phases. The thermodynamic analysis of inclusion formation in the Al–Ti–Ca–O system at 1873 K was conducted, as well as transformation behaviors of inclusions including all types of solid inclusions and liquid phases during solidification. The thermodynamic equilibrium calculations are in good agreement with experimental data, which can be used to estimate inclusion formation in Ti-bearing steel. Full article
(This article belongs to the Special Issue Refining and Casting of Steel)
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Open AccessArticle Ultrasonic Peening Treatment Used to Improve Stress Corrosion Resistance of AlSi10Mg Components Fabricated Using Selective Laser Melting
Metals 2019, 9(1), 103; https://doi.org/10.3390/met9010103
Received: 25 December 2018 / Revised: 11 January 2019 / Accepted: 17 January 2019 / Published: 19 January 2019
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Abstract
As a rapidly evolving advanced digital manufacturing technology, additive manufacturing (AM) has its advantages including short manufacturing cycle, material saving, and complexity for free. It has great potential for application in marine and offshore engineering. However, stress corrosion damage will be a big [...] Read more.
As a rapidly evolving advanced digital manufacturing technology, additive manufacturing (AM) has its advantages including short manufacturing cycle, material saving, and complexity for free. It has great potential for application in marine and offshore engineering. However, stress corrosion damage will be a big threat for the additively manufactured metal parts in the ocean environment due to large residual stresses generated in the building process. This paper focuses on the effect of ultrasonic peening treatment (UPT) on stress corrosion resistance of AlSi10Mg components fabricated using Selective Laser Melting (SLM). Firstly, AlSi10Mg specimens were prepared using an SLM machine, and UPT was conducted on the specimen’s top surface. Then, a series of measurements and analyses were carried out for the specimens before and after the UPT process. The residual stresses and hardness of the specimens were measured, and the surface morphology was observed using a scanning electron microscope (SEM). The resistance of stress corrosion was evaluated by the electrochemical corrosion test. The experimental results show that UPT can significantly improve stress corrosion resistance of SLM-fabricated specimens. Full article
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Open AccessArticle Low Cycle Fatigue and Relaxation Performance of Ferritic–Martensitic Grade P92 Steel
Metals 2019, 9(1), 99; https://doi.org/10.3390/met9010099
Received: 12 December 2018 / Revised: 9 January 2019 / Accepted: 10 January 2019 / Published: 18 January 2019
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Abstract
Due to their excellent creep resistance and good oxidation resistance, 9–12% Cr ferritic–martensitic stainless steels are widely used as high temperature construction materials in power plants. However, the mutual combination of different loadings (e.g., creep and fatigue), due to a “flexible” operation of [...] Read more.
Due to their excellent creep resistance and good oxidation resistance, 9–12% Cr ferritic–martensitic stainless steels are widely used as high temperature construction materials in power plants. However, the mutual combination of different loadings (e.g., creep and fatigue), due to a “flexible” operation of power plants, may seriously reduce the lifetimes of the respective components. In the present study, low cycle fatigue (LCF) and relaxation fatigue (RF) tests performed on grade P92 helped to understand the behavior of ferritic–martensitic steels under a combined loading. The softening and lifetime behavior strongly depend on the temperature and total strain range. Especially at small strain amplitudes, the lifetime is seriously reduced when adding a hold time which indicates the importance of considering technically relevant small strains. Full article
(This article belongs to the Special Issue Creep and High Temperature Deformation of Metals and Alloys)
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Open AccessArticle Dissimilar Metals Laser Welding between DP1000 Steel and Aluminum Alloy 1050
Metals 2019, 9(1), 102; https://doi.org/10.3390/met9010102
Received: 16 December 2018 / Revised: 11 January 2019 / Accepted: 14 January 2019 / Published: 18 January 2019
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Abstract
The welding of dissimilar metals was carried out using a pulsed Nd: YAG laser to join DP1000 steel and an aluminum alloy 1050 H111. Two sheets of each metal, with 30 × 14 × 1 mm3, were lap welded, since butt [...] Read more.
The welding of dissimilar metals was carried out using a pulsed Nd: YAG laser to join DP1000 steel and an aluminum alloy 1050 H111. Two sheets of each metal, with 30 × 14 × 1 mm3, were lap welded, since butt welding proved to be nearly impossible due to the huge thermal conductivity differences and melting temperature differences of these materials. The aim of this research was to find the optimal laser welding parameters based on the mechanical and microstructure investigations. Thus, the welded samples were then subjected to tensile testing to evaluate the quality of the joining operation. The best set of welding parameters was replicated, and the welding joint obtained using these proper parameters was carefully analyzed using optical and scanning electron microscopes. Despite the predicted difficulties of welding two distinct metals, good quality welded joints were achieved. Additionally, some samples performed satisfactorily well in the mechanical tests, reaching tensile strengths close to the original 1050 aluminum alloy. Full article
(This article belongs to the Special Issue Dissimilar Metal Welding)
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Open AccessArticle Experimental Determinations of Mixing Times in the IronArc Pilot Plant Process
Metals 2019, 9(1), 101; https://doi.org/10.3390/met9010101
Received: 28 November 2018 / Revised: 6 January 2019 / Accepted: 8 January 2019 / Published: 18 January 2019
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Abstract
IronArc is a newly developed technology and an emerging future process for pig iron production. The long-term goal with this technology is to reduce the CO2 emissions and energy consumption compared to existing technologies. The production rate of this process is dependent [...] Read more.
IronArc is a newly developed technology and an emerging future process for pig iron production. The long-term goal with this technology is to reduce the CO2 emissions and energy consumption compared to existing technologies. The production rate of this process is dependent on the stirring, which was investigated in the pilot plant process by measuring the mixing time in the slag bath. Moreover, slag investigations were done both based on light optical microscope studies as well as by Thermo-Calc calculations in order to determine the phases of the slag during operation. This was done because the viscosity (which is another important parameter) is dependent on the liquid and solid fractions of the slag. The overall results show that it was possible to determine the mixing time by means of the addition of a tracer (MnO2 powder) to the slag. The mixing time for the trials showed that the slag was homogenized after seconds. For two of the trials, homogenization had already been reached in the second sample after tracer addition, which means ≤8 s. The phase analysis from the slag indicated that the slag is in a liquid state during the operation of the process. Full article
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Open AccessReview Laser Hybrid Butt Welding of Large Thickness Naval Steel
Metals 2019, 9(1), 100; https://doi.org/10.3390/met9010100
Received: 27 November 2018 / Revised: 10 January 2019 / Accepted: 14 January 2019 / Published: 18 January 2019
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Abstract
Plates joining is one of the first stage at large vessels manufacturing line, process conditioning the whole shipbuilding production. Laser Arc Hybrid Welding (LAHW) process is nowadays providing promising results for large thickness naval steel, being primarily used for welding plates with thicknesses [...] Read more.
Plates joining is one of the first stage at large vessels manufacturing line, process conditioning the whole shipbuilding production. Laser Arc Hybrid Welding (LAHW) process is nowadays providing promising results for large thickness naval steel, being primarily used for welding plates with thicknesses between 6 to 15 mm, reaching up to 51 mm. In addition to this high penetration ability, LAHW allows increasing the production rates. Therefore, this technology is proposed as an alternative to conventional welding processes in shipbuilding, as it integrates the advantages of laser and arc welding, providing high process stability, high welding speed and penetration, narrow weld beads with a low heat input and good metallurgical properties. The present review reports the most representative investigation regarding the use of this technology to join large thickness flat panels of naval steel. It includes a summary of the most influential process variables, equipment characteristics, material properties, naval regulations, as well as microstructural characterisation and mechanical properties of joints. This review is thought to help readers from different backgrounds, covering from non-expert on welding or on naval sector, to industrial LAHW applicators and researchers. The industrial need of performing one single pass procedure to assure high quality welds of high thickness is suggested as one of the key aspects for future investigations. Full article
(This article belongs to the Special Issue Laser Welding of Industrial Metal Alloys)
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Open AccessArticle Combustion Synthesis of Chromium Nitrides
Metals 2019, 9(1), 98; https://doi.org/10.3390/met9010098
Received: 11 December 2018 / Revised: 6 January 2019 / Accepted: 16 January 2019 / Published: 17 January 2019
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This paper explores different modes of synthesis by combustion of chromium-nitrogen and ferrochromium-nitrogen alloys. The SH-synthesis of chromium nitrides and ferrochromium nitrides was performed. Regular patterns in layer-by-layer and surface modes of Cr combustion in nitrogen were investigated. The mechanism of non-stationary combustion [...] Read more.
This paper explores different modes of synthesis by combustion of chromium-nitrogen and ferrochromium-nitrogen alloys. The SH-synthesis of chromium nitrides and ferrochromium nitrides was performed. Regular patterns in layer-by-layer and surface modes of Cr combustion in nitrogen were investigated. The mechanism of non-stationary combustion during the synthesis of chromium was investigated. Regular patterns of chromium and ferrochromium combustion in the cocurrent filtration mode were analyzed, and the possibility to intensify the SHS process using the pressure filtration principle was assessed. The process of chromium powder combustion in the cocurrent flow of nitrogen-containing gas in the range of specific flow rates from 20 cm3/s·cm2 was investigated. Pressure filtration intensifies the process of combustion wave propagation in the Cr–N2 system. Here, the combustion rate increases while the degree of nitridation decreases. We discovered superadiabatic heating modes when the reaction zone was blown with pure nitrogen and a nitrogen-argon mixture. The tempering mode that was realized during pressure filtration allows for the uptake of high-temperature single-phase non-stoichiometric phases of Cr2N. Full article
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Open AccessArticle Investigation on the High-Temperature Oxidation Resistance of Ni-(3~10) Ta and Ni-(3~10) Y Alloys
Metals 2019, 9(1), 97; https://doi.org/10.3390/met9010097
Received: 27 November 2018 / Revised: 15 January 2019 / Accepted: 15 January 2019 / Published: 17 January 2019
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Abstract
Ni-(3~10) Ta and Ni-(3~10) Y alloys were fabricated by vacuum arc melting. The oxidation resistance of the alloys was studied by cyclic and isothermal oxidation tests at 800 °C in static air. The present work focused on the investigation of the effects of [...] Read more.
Ni-(3~10) Ta and Ni-(3~10) Y alloys were fabricated by vacuum arc melting. The oxidation resistance of the alloys was studied by cyclic and isothermal oxidation tests at 800 °C in static air. The present work focused on the investigation of the effects of the alloying elements (Ta and Y) on the oxidation behavior of Ni-based alloys. The oxidation behavior of alloys was evaluated by mass gain, composition, as well as the microstructure of oxidized products. The experimental results indicated that Ta at a low content (3 wt %) had a positive role in enhancing oxidation resistance by decreasing the oxygen vacancy concentration of the oxide layer to prevent the inward diffusion of oxygen during oxidation, and the mass gain decreased from 2.9 mg·cm−2 to 1.7 mg·cm−2 (800 °C/200 h), while Y (3~10 wt %) degraded the oxidation resistance. However, it is worth mentioning that the pinning effect of Y2O3 increased the adhesion between the substrate and oxide layer by changing the growing patterns of the oxide layer from a plane growth to fibrous growth. Among the results, the bonding of the substrate and oxide layer was best in the Ni-3Y alloys. Full article
(This article belongs to the Special Issue High-Temperature Corrosion and Oxidation of Metals)
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Open AccessArticle Fe–Si–Al Coatings with Stable Wear Resistance Prepared by Laser Cladding Industrial Wastes
Metals 2019, 9(1), 96; https://doi.org/10.3390/met9010096
Received: 17 December 2018 / Revised: 10 January 2019 / Accepted: 14 January 2019 / Published: 17 January 2019
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Because wear is one of the most common reasons for the failure of metals, the development of a low-cost coating with enhanced wear resistance is of great importance. In the present study, Fe–Si–Al coatings with superior and stable wear resistance were prepared by [...] Read more.
Because wear is one of the most common reasons for the failure of metals, the development of a low-cost coating with enhanced wear resistance is of great importance. In the present study, Fe–Si–Al coatings with superior and stable wear resistance were prepared by laser cladding Fe–Si–Al industrial waste onto 1045 carbon steel. The microstructure, as well as the wear mechanism of the Fe–Si–Al coatings, was investigated. The Fe–Si–Al coatings consist of a (Al, Fe, Si) solid solution phase in both columnar grain form and equiaxed grain form. The Fe–Si–Al coatings possess enhanced microhardness of 494 ± 15 HV0.3 and low mass loss of 5 × 10−5 mg·(N·m)−1. The wear resistance is ten times higher than that of the 1045 carbon steel matrix. The wear of the Fe–Si–Al coatings is mainly dominated by abrasive wear and adhesive wear. This work provides important insight into the preparation of low-cost, wear-resistant coatings, as well as stable, superior wear resistance. Full article
(This article belongs to the Special Issue Additive Layer Manufacturing using Metal Deposition)
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Open AccessArticle Kinetic Studies on Gas-Based Reduction of Vanadium Titano-Magnetite Pellet
Metals 2019, 9(1), 95; https://doi.org/10.3390/met9010095
Received: 5 January 2019 / Revised: 13 January 2019 / Accepted: 14 January 2019 / Published: 16 January 2019
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Vanadium titano-magnetite (VTM) is a significant resource in China—analysis shows that China possesses approximately 10 billion tons of VTM. In this study, we characterize VTM’s isothermal reduction mechanisms in the mixture of H2, CO, and N2 where the variables considered [...] Read more.
Vanadium titano-magnetite (VTM) is a significant resource in China—analysis shows that China possesses approximately 10 billion tons of VTM. In this study, we characterize VTM’s isothermal reduction mechanisms in the mixture of H2, CO, and N2 where the variables considered include reduction time, reduction temperature, gas composition, and pellet size. The kinetics of the reduction process were studied following a shrinking core model. The results indicate that the reduction degree of oxidized VTM pellets increases with increases of reduction time and reduction temperature but decreases with increasing pellet size. Moreover, we found that an increase of H2/(H2 + CO) ratio induced an increase of the reduction degree. We discuss the transformation of main Ti-bearing mineral phases, and we consider the most probable reaction mechanism. For the entire reduction process, the kinetic results confirm the existence of an early and later stages that are controlled by interface chemical reaction and diffusion, respectively. Furthermore, the results show that the diffusion-control step can be observably shortened via decreased pellet size because a thinner product layer is formed during the reduction process. Our study thus provides a valuable technical basis for industrial applications of VTM. Full article
(This article belongs to the Special Issue Ironmaking and Steelmaking)
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Open AccessArticle Investigation of Test Parameters on EBSD Analysis of Retained Austenite in TRIP and Pipeline Steels
Metals 2019, 9(1), 94; https://doi.org/10.3390/met9010094
Received: 22 December 2018 / Revised: 11 January 2019 / Accepted: 14 January 2019 / Published: 16 January 2019
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In this article we discuss the effect of different test parameters on the analysis of retained austenite in TRIP590, TRIP780 and X90 steels, by means of Electron Backscattered Diffraction (EBSD) and X-ray Diffraction (XRD), respectively. By analyzing the measuring retained austenite content under [...] Read more.
In this article we discuss the effect of different test parameters on the analysis of retained austenite in TRIP590, TRIP780 and X90 steels, by means of Electron Backscattered Diffraction (EBSD) and X-ray Diffraction (XRD), respectively. By analyzing the measuring retained austenite content under different conditions, the optimal test parameters were obtained. The retained austenite content measured both by the EBSD and XRD methods were also compared. The results showed that the test parameters had a great influence on the measured results of retained austenite content in steel by the EBSD method. The higher the indexing rate, the better the precision of the measured results. The step size used for EBSD analysis should not exceed 1/5 of the average grain size of retained austenite. The scanning area for EBSD retained austenite analysis in TRIP and pipeline steels should be no less than 0.068 mm2, which is recommended to be performed by multiple small fields. Full article
(This article belongs to the Special Issue Advances in Microstructural Characterization of Metallic Materials)
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Open AccessArticle Structure of Solidified Films of CaO-SiO2-Na2O Based Low-Fluorine Mold Flux
Metals 2019, 9(1), 93; https://doi.org/10.3390/met9010093
Received: 4 December 2018 / Revised: 8 January 2019 / Accepted: 11 January 2019 / Published: 16 January 2019
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As an essential synthetic material used in the continuous casting of steels, mold fluxes improve the surface quality of steel slabs. In this study, a CaO-SiO2-Na2O-based low-fluorine mold flux was solidified by an improved water-cooled copper probe with different [...] Read more.
As an essential synthetic material used in the continuous casting of steels, mold fluxes improve the surface quality of steel slabs. In this study, a CaO-SiO2-Na2O-based low-fluorine mold flux was solidified by an improved water-cooled copper probe with different temperatures of molten flux and different probe immersion times. The heat flux through solid films and the film structures were calculated and inspected, respectively. Internal cracks (formed in the glassy layer of films during solidification) were observed. The formation and evolution of those cracks contributed to the unstable heat flux density. The roughness of the surface in contact with the water-cooled copper probe formed as films were still glassy and the roughness had no causal relationship with crystallization or devitrification. Combeite with columnar and faceted dendritic shapes were the main crystal in the film. Full article
(This article belongs to the Special Issue Ironmaking and Steelmaking)
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Open AccessArticle A-242 Aluminium Alloy Foams Manufacture from the Recycling of Beverage Cans
Metals 2019, 9(1), 92; https://doi.org/10.3390/met9010092
Received: 5 December 2018 / Revised: 7 January 2019 / Accepted: 11 January 2019 / Published: 16 January 2019
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This paper presents and discusses a methodology implemented to study the process of the preparation of aluminium alloy foams using the alloy A-242, beginning from the recycling of secondary aluminium obtained from beverage cans. The foams are prepared by a melting process by [...] Read more.
This paper presents and discusses a methodology implemented to study the process of the preparation of aluminium alloy foams using the alloy A-242, beginning from the recycling of secondary aluminium obtained from beverage cans. The foams are prepared by a melting process by adding 0.50 wt.% calcium to the A-242 aluminium alloy with the aim to change its viscosity in the molten state. To obtain the foam, titanium hydride is added in different concentrations (0.50 wt.%, 0.75 wt.%, and 1.00 wt.%) and at different temperatures (923, 948 K, and 973 K) while the foaming time is kept constant at 30 s. For a set of experimental parameter values, aluminium alloy foams with the average relative density of 0.12 were obtained and had an 88.22% average porosity. In this way, it is possible to state that the preparation of aluminium alloy foams A-242 processed from the recycling of cans is possible, with characteristics and properties similar to those obtained using commercial-purity metals. Full article
(This article belongs to the Special Issue Cellular Metals: Fabrication, Properties and Applications)
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Open AccessArticle Mechanical and Microstructural Investigations of the Laser Welding of Different Zinc-Coated Steels
Metals 2019, 9(1), 91; https://doi.org/10.3390/met9010091
Received: 9 December 2018 / Revised: 5 January 2019 / Accepted: 11 January 2019 / Published: 16 January 2019
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Abstract
Tailor welded blanks (TWB) represent an anisotropic and non-homogenous material. The knowledge of the mechanical properties and microstructure of the fusion zone and heat-affected zone (HAZ) obtained with laser welding is essential to ensure the reliability of the process. In this paper, laser-welded [...] Read more.
Tailor welded blanks (TWB) represent an anisotropic and non-homogenous material. The knowledge of the mechanical properties and microstructure of the fusion zone and heat-affected zone (HAZ) obtained with laser welding is essential to ensure the reliability of the process. In this paper, laser-welded hot-dip Zn-coated low carbon microalloyed steels with different thickness and mechanical properties were used. The mechanical properties of the laser-welded blanks were determined by tensile tests and formability by Erichsen cupping tests. In addition, the pore formation during the laser welding process was analyzed. The microstructural analysis confirmed the formation of the favorable structure of the weld metal and the heat-affected zone without the presence of martensite. The obtained results showed that it is possible to produce TWBs with suitable mechanical properties by laser welding. Full article
(This article belongs to the Special Issue Science, Characterization and Technology of Joining and Welding)
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Open AccessArticle Dislocations Help Initiate the αγ Phase Transformation in Iron—An Atomistic Study
Metals 2019, 9(1), 90; https://doi.org/10.3390/met9010090
Received: 21 December 2018 / Revised: 12 January 2019 / Accepted: 14 January 2019 / Published: 16 January 2019
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Abstract
Using molecular dynamics simulation, we studied the influence of pre-existing dislocations on the austenitic and the martensitic phase transformations in pure iron. The simulations were performed in a thin-film geometry with (100) surfaces. We found that dislocations alleviate the transformation by lowering the [...] Read more.
Using molecular dynamics simulation, we studied the influence of pre-existing dislocations on the austenitic and the martensitic phase transformations in pure iron. The simulations were performed in a thin-film geometry with (100) surfaces. We found that dislocations alleviate the transformation by lowering the austenitic transformation temperature and increasing the martensitic transformation temperature. In all cases, the new phase nucleates at the dislocations. The orientation relationships governing the nucleation process are dominated by the Burgers, Kurdjumov–Sachs, and Nishiyama–Wassermann pathways. However, upon growth and coalescence of the transformed material, the final microstructure consists of only few twinned variants separated by twin boundaries; this simple structure is dictated by the free surfaces which tend to form conserved planes under the transformation. After transformation, the material also contains abundant dislocations. Full article
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Open AccessArticle Variation of Magnetic Memory Signals in Fatigue Crack Initiation and Propagation Behavior
Metals 2019, 9(1), 89; https://doi.org/10.3390/met9010089
Received: 13 December 2018 / Revised: 9 January 2019 / Accepted: 11 January 2019 / Published: 16 January 2019
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Abstract
To monitor fatigue crack initiation and propagation, and to judge the fatigue damage status of ferromagnetic material, fatigue bending tests of four-point single edge notch bend (SENB4) specimens were carried out. Metal magnetic memory signals were measured during the whole fatigue process. The [...] Read more.
To monitor fatigue crack initiation and propagation, and to judge the fatigue damage status of ferromagnetic material, fatigue bending tests of four-point single edge notch bend (SENB4) specimens were carried out. Metal magnetic memory signals were measured during the whole fatigue process. The results showed that the fatigue process could be divided into four stages by observing the morphology of the fracture surface. With the increase of fatigue loading cycles, the tangential component of the magnetic field (Hx) and the normal component of the magnetic field (Hy) increased. At the notch Hx presented a “trough” shape and had a maximum value at the midpoint, while Hy at the notch rotated clockwise around the midpoint. Compared with the tangential characteristic parameters, the variation of normal characteristic parameters (i.e., maximum gradient value of Hy (Ky-max) and the variation range of Hy at the notch (∆Hyn), with the fatigue loading cycles are more similar to the variation of fatigue crack length with loading cycles), both Ky-max and ∆Hyn had a good linear relationship with fatigue crack length. Plastic deformation accumulated on both sides of the fatigue crack, and metal magnetic memory (MMM) signals measured from the specimens were able to indicate the location of the fatigue crack and the variation of the fatigue crack length. Furthermore, the distribution of magnetic signals was analyzed according to the theories of stress magnetization and magnetic flux leakage. Full article
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Open AccessArticle Effect of Primary Crystals on Pore Morphology during Semi-Solid Foaming of A2024 Alloys
Metals 2019, 9(1), 88; https://doi.org/10.3390/met9010088
Received: 23 November 2018 / Revised: 27 December 2018 / Accepted: 9 January 2019 / Published: 16 January 2019
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Abstract
We investigated pore formation in aluminum foams by controlling primary crystal morphology using three master alloys. The first one was a direct chill cast A2024 (Al-Cu-Mg) alloy (DC-cast alloy). The others were A2024 alloys prepared to possess fine spherical primary crystals. The second [...] Read more.
We investigated pore formation in aluminum foams by controlling primary crystal morphology using three master alloys. The first one was a direct chill cast A2024 (Al-Cu-Mg) alloy (DC-cast alloy). The others were A2024 alloys prepared to possess fine spherical primary crystals. The second alloy was made by applying compressive strain through a Strain-Induced Melt-Activated process alloy (SIMA alloy). The third one was a slope-cast A2024 alloy (slope-cast alloy). Each alloy was heated to either 635 °C (fraction of solid fs = 20%) or 630 °C (fs = 40%). TiH2 powder was added to the alloys as a foaming agent upon heating them to a semi-solid state and they were stirred while being held in the furnace. Subsequently, A2024 alloy foams were obtained via water-cooling. The primary crystals of the DC-cast alloy were coarse and irregular before foaming. After foaming, the size of the primary crystals remained irregular, but also became spherical. The SIMA and slope-cast alloys possessed fine spherical primary crystals before and after foaming. In addition to average-sized pores (macro-pores), small pores were observed inside the cell walls (micro-pores) of each alloy. The formation of macro-pores did not depend on the formation of the primary crystals. Only in the DC-cast alloy did fine micro-pores exist within the primary crystals. The number of micro-pores in the SIMA and slope-cast alloys was one third of that in the DC-cast alloy. Full article
(This article belongs to the Special Issue Cellular Metals: Fabrication, Properties and Applications)
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Open AccessArticle Influence of Vibration Treatment and Modification of A356 Aluminum Alloy on Its Structure and Mechanical Properties
Metals 2019, 9(1), 87; https://doi.org/10.3390/met9010087
Received: 13 December 2018 / Revised: 28 December 2018 / Accepted: 12 January 2019 / Published: 15 January 2019
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Abstract
A series of casting experiments was conducted with A356 aluminum alloys by applying vibration treatment and using Al-TiB2 composite master alloys. The main vibration effects include the promotion of nucleation and a reduction in as-cast grain size. Using composite master alloys with [...] Read more.
A series of casting experiments was conducted with A356 aluminum alloys by applying vibration treatment and using Al-TiB2 composite master alloys. The main vibration effects include the promotion of nucleation and a reduction in as-cast grain size. Using composite master alloys with titanium diboride microparticles allows further reduction in the average grain size to 140 µm. The reasons for this behavior are discussed in terms of the complex effect on the melt, considering the destruction of dendrites, and the presence of additional crystallization centers. Tensile tests were performed on the samples obtained during the vibration treatment and with titanium diboride particles. The tensile strength increased from 182 to 227 MPa after the vibration treatment for the alloys containing titanium diboride. Full article
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Open AccessArticle A Comprehensive Study of Steel Powders (316L, H13, P20 and 18Ni300) for Their Selective Laser Melting Additive Manufacturing
Metals 2019, 9(1), 86; https://doi.org/10.3390/met9010086
Received: 2 December 2018 / Revised: 10 January 2019 / Accepted: 11 January 2019 / Published: 15 January 2019
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Abstract
The determination of microstructural details for powder materials is vital for facilitating their selective laser melting (SLM) process. Four widely used steels (316L, H13, P20 and 18Ni300) have been investigated to detail their powders’ microstructures as well as laser absorptivity to understand their [...] Read more.
The determination of microstructural details for powder materials is vital for facilitating their selective laser melting (SLM) process. Four widely used steels (316L, H13, P20 and 18Ni300) have been investigated to detail their powders’ microstructures as well as laser absorptivity to understand their SLM processing from raw material perspective. Phase components of these four steel powders were characterized by X-ray diffraction (XRD), synchrotron radiation X-ray diffraction (SR-XRD) and scanning electron microscopy (SEM). X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) were utilized to reveal the surface structure of these four steel powders. It is found that phase components of H13, P20 and 18Ni300 are mainly composed of martensite and a small amount of austenite due to the high cooling rate during gas atomization processing, while 316L is characterized by austenite. XPS results show that the four steel powders all possess a layered surface structure, consisting of a thin iron oxide layer at the outmost surface and metal matrix at the inner surface. It is found that the presence of such oxide layer can improve the absorptivity of steel powders and is beneficial for their SLM process. Full article
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Open AccessReview Refining Principles and Technical Methodologies to Produce Ultra-Pure Magnesium for High-Tech Applications
Metals 2019, 9(1), 85; https://doi.org/10.3390/met9010085
Received: 23 November 2018 / Revised: 9 January 2019 / Accepted: 10 January 2019 / Published: 15 January 2019
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Abstract
During the last decade, magnesium-based medical implants have become the focal point of a large number of scientific studies due to their perceived favorable properties. Implants manufactured from magnesium alloys are not only biocompatible and biodegradable, but they are also the answer to [...] Read more.
During the last decade, magnesium-based medical implants have become the focal point of a large number of scientific studies due to their perceived favorable properties. Implants manufactured from magnesium alloys are not only biocompatible and biodegradable, but they are also the answer to problems associated with other materials like stress shielding (Ti alloys) and low mechanical stability (polymers). Magnesium has also been a metal of interest in another field. By offering superior technical and economic features in comparison to lithium, it has received significant attention in recent years as a potential battery anode alternative. Natural abundancy, low cost, environmental friendliness, large volumetric capacity, and enhanced operational safety are among the reasons that magnesium anodes are the next breakthrough in battery development. Unfortunately, commercial production of such implants and primary and secondary cells has been hindered due to magnesium’s low corrosion resistance. Corrosion investigations have shown that this inferior quality is a direct result of the presence of certain impurities in metallic magnesium such as iron, copper, cobalt, and nickel, even at the lowest levels of concentration. Magnesium’s sensitivity to corrosion is an obstacle for its usage not only in biomedical implants and batteries, but also in the automotive/aerospace industries. Therefore, investigations focusing on magnesium refinement with the goal of producing high and ultra-high purity magnesium suitable for such demanding applications are imperative. In this paper, vacuum distillation fundamentals and techniques are thoroughly reviewed as the main refining principles for magnesium. Full article
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Open AccessFeature PaperArticle Effect of Temperature and Texture on Hall–Petch Strengthening by Grain and Annealing Twin Boundaries in the MnFeNi Medium-Entropy Alloy
Metals 2019, 9(1), 84; https://doi.org/10.3390/met9010084
Received: 21 December 2018 / Revised: 8 January 2019 / Accepted: 11 January 2019 / Published: 15 January 2019
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Abstract
Among equiatomic alloys of the Cr-Mn-Fe-Co-Ni system, MnFeNi was shown to exhibit a strong anti-invar behavior but little is known regarding its mechanical properties. The objective of the present study is to investigate Hall–Petch strengthening by grain and annealing twin boundaries in MnFeNi. [...] Read more.
Among equiatomic alloys of the Cr-Mn-Fe-Co-Ni system, MnFeNi was shown to exhibit a strong anti-invar behavior but little is known regarding its mechanical properties. The objective of the present study is to investigate Hall–Petch strengthening by grain and annealing twin boundaries in MnFeNi. For this purpose, seven different grain sizes between 17 and 216 µm were produced. Mean grain sizes (excluding annealing twin boundaries) and crystallite sizes (including them) were determined using the linear intercept method. Overall, 25% of the boundaries were found to be annealing twin boundaries regardless of the grain size. In some cases, two twin boundaries can be present in one grain forming an annealing twin, which thickness represents one quarter of the mean grain size. Based on a comparison of the mean twin thickness of different alloys with different stacking fault energy (SFE), we estimated an SFE of 80 ± 20 mJ/m2 for MnFeNi. Compression tests of MnFeNi with different grain sizes were performed between 77 and 873 K and revealed a parallel shift of the Hall–Petch lines with temperature. The interaction between dislocations and boundaries was investigated by scanning transmission electron microscopy (STEM) in a deformed specimen. It was found that a large number of dislocations are piling up against grain boundaries while the pile-ups at annealing twin boundaries contain much fewer dislocations. This indicates that annealing twin boundaries in this alloy are less effective obstacles to dislocation motion than grain boundaries. Full article
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Open AccessArticle Hydrometallurgical Process for Zinc Recovery from C.Z.O. Generated by the Steelmaking Industry with Ammonia–Ammonium Chloride Solution
Metals 2019, 9(1), 83; https://doi.org/10.3390/met9010083
Received: 7 December 2018 / Revised: 23 December 2018 / Accepted: 7 January 2019 / Published: 14 January 2019
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Abstract
In this research, some experimental steps were investigated to recover zinc contained in crude zinc oxide (C.Z.O.). In the first stage, the C.Z.O. was treated in NH3–NH4Cl–H2O solution to dissolve the metals. The optimized leaching conditions in [...] Read more.
In this research, some experimental steps were investigated to recover zinc contained in crude zinc oxide (C.Z.O.). In the first stage, the C.Z.O. was treated in NH3–NH4Cl–H2O solution to dissolve the metals. The optimized leaching conditions in batch experiments were obtained: agitation speed 250 rpm, concentration of ammonia and ammonium chloride 2.5 mol/L and 5 mol/L, respectively, time 30min, temperature 40 °C, and L/S = 6 mL/g. The extraction percentage of zinc was over 81% under the optimized leaching conditions. The kinetic study indicates that zinc extraction from the C.Z.O particles was very rapid. In the second stage, the solution from the leaching process was purified by adding zinc dust to the solution. The Cu, Cd, Pb, Sb, and As could be reduced to levels of 0.03, 0.09, 0.87, 0.22, and 0.12 mg/L after the purification process. Finally, the electrowinning process was used to recover dissolved Zn from the final solution. The zinc content in the electrowon zinc was more than 99.99%. Full article
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Open AccessArticle Microstructure and Properties of Porous Titanium Prepared by Spark Plasma Sintering
Metals 2019, 9(1), 82; https://doi.org/10.3390/met9010082
Received: 24 December 2018 / Revised: 9 January 2019 / Accepted: 11 January 2019 / Published: 14 January 2019
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Abstract
Porous titanium samples with a porosity of 1.34~15.54% were prepared by a spark plasma sintering (SPS) process at sintering temperatures of 800 °C, 850 °C and 900 °C, and a sintering pressure of 10 MPa. The microstructures and fracture morphology of the samples [...] Read more.
Porous titanium samples with a porosity of 1.34~15.54% were prepared by a spark plasma sintering (SPS) process at sintering temperatures of 800 °C, 850 °C and 900 °C, and a sintering pressure of 10 MPa. The microstructures and fracture morphology of the samples were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses. The compressive strength and elastic modulus were likewise measured. The results showed that no new phase occurred after the samples were sintered, and the main phases were α phase of hcp structure. The porosity of the samples decreased significantly with the increase of sintering temperature. At 800 °C, the sample phase was dominated by equiaxed α. There were more irregular coarse pores in the samples. At 850 °C, the microstructure was mainly zigzag α, and the pores were finely and relatively uniform in distribution. At 900 °C, the sample’s structure transformed into a dense sheet-like α. The sample’s densities increased and the pores disappeared. The room temperature compression test showed that the porous titanium sintered by SPS had excellent compressive strength. The yield strength, compressive strength, compressive strain and elastic modulus were 81.85~122.36 MPa, 161.65~498.86 MPa, 36.75~59.97% and 2.79~4.22 GPa, respectively. Full article
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Open AccessArticle Bioleaching for Copper Extraction of Marginal Ores from the Brazilian Amazon Region
Metals 2019, 9(1), 81; https://doi.org/10.3390/met9010081
Received: 5 December 2018 / Revised: 8 January 2019 / Accepted: 8 January 2019 / Published: 14 January 2019
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Abstract
The use of biotechnology to explore low-grade ore deposits and mining tailings is one of the most promising alternatives to reduce environmental impacts and costs of copper extraction. However, such technology still depends on improvements to be fully applied in Brazil under industrial [...] Read more.
The use of biotechnology to explore low-grade ore deposits and mining tailings is one of the most promising alternatives to reduce environmental impacts and costs of copper extraction. However, such technology still depends on improvements to be fully applied in Brazil under industrial scale. In this way, the bioleaching, by Acidithiobacillus ferrooxidans, in columns and stirred reactors were evaluated regarding to copper extraction of a mineral sulfide and a weathered ore from the Brazilian Amazon region. Samples (granulometry of 2.0/4.75 mm) were characterized by X-ray diffraction (XRD), energy dispersive X-ray fluorescence (EDXRF) spectrometry and scanning electrons microscopy (SEM). The pH and Oxidation-reduction potential (Eh) were daily monitored and leachate samples were collected for copper extraction determination by EDXRF. After 47 days, the columns bioleaching efficiency was 1% (1298 mg Cu·L−1) and 0.95% (985 mg Cu·L−1) for 2.00/4.75 mm sulfide ore, respectively, whereas the stirred reactors bioleaching resulted in 4% (348 mg Cu·L−1) for the mineral sulfide and 47% (295.5 mg Cu·L−1) for the weathered ore. Full article
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Open AccessArticle Modification of Mechanical Properties of High-Strength Titanium Alloys VT23 and VT23M Due to Impact-Oscillatory Loading
Metals 2019, 9(1), 80; https://doi.org/10.3390/met9010080
Received: 30 November 2018 / Revised: 9 January 2019 / Accepted: 10 January 2019 / Published: 14 January 2019
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Abstract
A simple technological method is proposed and tested experimentally, which allows for the improvement of mechanical properties in sheet two-phase high-strength titanium alloys VT23 and VT23M on the finished product (rolled metal), due to impact-oscillatory loading. Under impact-oscillatory loading and dynamic non-equilibrium processes [...] Read more.
A simple technological method is proposed and tested experimentally, which allows for the improvement of mechanical properties in sheet two-phase high-strength titanium alloys VT23 and VT23M on the finished product (rolled metal), due to impact-oscillatory loading. Under impact-oscillatory loading and dynamic non-equilibrium processes (DNP) are realized in titanium alloys, leading to the self-organization of the structure. As a result, the mechanical properties of titanium alloys vary significantly with subsequent loading after the realization of DNP. In this study, the test modes are found, which can be used in the production conditions. Full article
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