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Metals, Volume 7, Issue 12 (December 2017)

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Cover Story (view full-size image) Electrical discharge machining (EDM) is a modern technology off processing difficult to machine [...] Read more.
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Open AccessArticle Effect of Shot Blasting on Fatigue Strength of Q345B Steel Plate with a Central Hole
Metals 2017, 7(12), 517; doi:10.3390/met7120517
Received: 15 October 2017 / Revised: 5 November 2017 / Accepted: 7 November 2017 / Published: 23 November 2017
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Abstract
The fatigue strength of Q345B steel plate with a central hole after shot blasting is studied herein. The improvement of fatigue strength related to the failure behavior is highlighted with due analysis of fatigue cracks initiation at the defect below the condensed surface
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The fatigue strength of Q345B steel plate with a central hole after shot blasting is studied herein. The improvement of fatigue strength related to the failure behavior is highlighted with due analysis of fatigue cracks initiation at the defect below the condensed surface induced by shot blasting. The effect of stress concentration is shown to be non-ignorable in the fatigue strength analysis. Codified fatigue categories in accordance with EN 1993-1-9 are used in drawing a comparison of studied fatigue behavior. Finally, an analytical model based on a modified reference model is proposed for the evaluation of the test fatigue strength results. It is demonstrated that the predicted results agree well with test data, since the stress ratio and the size of the defect as well as the stress concentration are appropriately considered. Full article
(This article belongs to the Special Issue Fatigue and Wear for Steels)
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Open AccessArticle Hexagonal Boron Nitride Impregnated Silane Composite Coating for Corrosion Resistance of Magnesium Alloys for Temporary Bioimplant Applications
Metals 2017, 7(12), 518; doi:10.3390/met7120518
Received: 27 September 2017 / Revised: 7 November 2017 / Accepted: 7 November 2017 / Published: 23 November 2017
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Abstract
Magnesium and its alloys are attractive potential materials for construction of biodegradable temporary implant devices. However, their rapid degradation in human body fluid before the desired service life is reached necessitate the application of suitable coatings. To this end, WZ21 magnesium alloy surface
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Magnesium and its alloys are attractive potential materials for construction of biodegradable temporary implant devices. However, their rapid degradation in human body fluid before the desired service life is reached necessitate the application of suitable coatings. To this end, WZ21 magnesium alloy surface was modified by hexagonal boron nitride (hBN)-impregnated silane coating. The coating was chemically characterised by Raman spectroscopy. Potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS) of the coated alloy in Hanks’ solution showed a five-fold improvement in the corrosion resistance of the alloy due to the composite coating. Post-corrosion analyses corroborated the electrochemical data and provided a mechanistic insight of the improvement provided by the composite coating. Full article
(This article belongs to the Special Issue Corrosion of Magnesium Alloys)
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Open AccessArticle Effect of Weld Current on the Microstructure and Mechanical Properties of a Resistance Spot-Welded TWIP Steel Sheet
Metals 2017, 7(12), 519; doi:10.3390/met7120519
Received: 30 September 2017 / Revised: 1 November 2017 / Accepted: 14 November 2017 / Published: 23 November 2017
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Abstract
In this study the effect of the weld current on the microstructure and mechanical properties of a resistance spot-welded twinning-induced plasticity (TWIP) steel sheet was investigated using optical microscopy, scanning electron microscopy–electron back-scattered diffraction (SEM–EBSD), microhardness measurements, a tensile shear test and fractography.
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In this study the effect of the weld current on the microstructure and mechanical properties of a resistance spot-welded twinning-induced plasticity (TWIP) steel sheet was investigated using optical microscopy, scanning electron microscopy–electron back-scattered diffraction (SEM–EBSD), microhardness measurements, a tensile shear test and fractography. Higher weld currents promoted the formation of a macro expulsion cavity in the fusion zone. Additionally, higher weld currents led to a higher indentation depth, a wider heat-affected zone (HAZ), coarser grain structure and thicker annealing twins in the HAZ, and a relatively equiaxed dendritic structure in the centre of the fusion zone. The hardness values in the weld zone were lower than that of the base metal. The lowest hardness values were observed in the HAZ. No strong relationship was observed between the hardness values in the weld zone and the weld current. A higher joint strength, tensile deformation and failure energy absorption capacity were obtained with a weld current of 12 kA, a welding time of 300 ms and an electrode force of 3 kN. A complex fracture surface with both brittle and limited ductile manner was observed in the joints, while the base metal exhibited a ductile fracture. Joints with a higher tensile shear load (TSL) commonly exhibited more brittle fracture characteristics. Full article
(This article belongs to the Special Issue Alloy Steels)
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Open AccessArticle Study in Wire Feedability-Related Properties of Al-5Mg Solid Wire Electrodes Bearing Zr for High-Speed Train
Metals 2017, 7(12), 520; doi:10.3390/met7120520
Received: 24 September 2017 / Revised: 19 November 2017 / Accepted: 20 November 2017 / Published: 23 November 2017
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Abstract
This work offers an analysis of the wire feedability-related properties of Al-5Mg solid wire electrodes bearing Zr. Effects of Zr content on microstructures and mechanical properties of the Al-5Mg alloys were studied. Experimental results have demonstrated that α-Al dendrites of the as-cast Al-5Mg
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This work offers an analysis of the wire feedability-related properties of Al-5Mg solid wire electrodes bearing Zr. Effects of Zr content on microstructures and mechanical properties of the Al-5Mg alloys were studied. Experimental results have demonstrated that α-Al dendrites of the as-cast Al-5Mg alloy are refined, and the tensile strength, microhardness and roughness of the 1.2 mm wire electrode are improved with an appropriate addition of Zr. In addition, the tensile strength and elongation of the welded joints welded using Al-5Mg wire electrodes bearing Zr reach the maximum value when 0.12% Zr is added into the wire alloy. However, when excess Zr is added, α-Al phases of the wire alloy and welded joint are coarsened, and the mechanical properties are deteriorated. Moreover, the structure and principle of a novel apparatus, which can enhance the feedability of the wire electrode, are introduced and the apparatus can achieve the rough and fine adjustments of cast and helix of the wire electrode. Full article
(This article belongs to the Special Issue Light Weight Alloys: Processing, Properties and Their Applications)
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Open AccessArticle Permeability Study of Austenitic Stainless Steel Surfaces Produced by Selective Laser Melting
Metals 2017, 7(12), 521; doi:10.3390/met7120521
Received: 20 October 2017 / Revised: 6 November 2017 / Accepted: 17 November 2017 / Published: 24 November 2017
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Abstract
Selective laser melting (SLM) is emerging as a versatile process for fabricating different metal components with acceptable mechanical properties and geometrical accuracy. The process has been used in the manufacturing of several parts (e.g., aerospace or biomedical components), and offers the capability to
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Selective laser melting (SLM) is emerging as a versatile process for fabricating different metal components with acceptable mechanical properties and geometrical accuracy. The process has been used in the manufacturing of several parts (e.g., aerospace or biomedical components), and offers the capability to tailor the performance of several surface and mechanical properties. In this work, permeability properties and surface roughness of stainless steel (SS316L) surfaces were evaluated through experimentation with three different laser scanning patterns (chessboard, meander, and stripe), and different sloping angles between the fabricated surface and the laser beam incident on the process. Results showed that for each scanning pattern, the roughness decreased as the sloping angle increased consistently in all experimental trials. Furthermore, in the case of the permeability evaluation, the manufactured surfaces showed changes in properties for each series of experiments performed with different scanning patterns. The chessboard pattern showed a change of 67° to 107° in contact angle, while the meander and stripe patterns showed a variation in contact angle in a range of 65° to 85°. The different scanning strategies in the SLM process resulted in an alternative method for surface enhancement with different hydrophobicity properties, valuable for designing the most appropriate permeability characteristics for specific applications. Full article
(This article belongs to the Special Issue Metallic Additive Manufacturing: Design, Process and Post-processing)
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Open AccessArticle Thermal Growth Cu1.2Mn1.8O4 Spinel Coatings on Metal Interconnects for Solid Oxide Fuel Cell Applications
Metals 2017, 7(12), 522; doi:10.3390/met7120522
Received: 24 October 2017 / Revised: 15 November 2017 / Accepted: 20 November 2017 / Published: 24 November 2017
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Abstract
A novel cobalt-free Cu1.2Mn1.8O4 spinel coating is prepared and evaluated for the metal interconnect of solid oxide fuel cell. Mn-35Cu and Co-35Mn alloy coatings are deposited on 430 SS substrate and then in-situ oxidized in air at 750
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A novel cobalt-free Cu1.2Mn1.8O4 spinel coating is prepared and evaluated for the metal interconnect of solid oxide fuel cell. Mn-35Cu and Co-35Mn alloy coatings are deposited on 430 SS substrate and then in-situ oxidized in air at 750 °C for 100 h. XRD results confirm that Cu1.2Mn1.8O4 spinel with some Mn2O3 is formed, and the average thickness of the coating is 70–80 μm according to cross section image. Spinel oxide coating is compact and has good adherence to the substrate, and very low Cr and Fe contents are detected in the coating. A small area specific resistance of 8.7 mΩ cm2 is achieved at 800 °C for the composited Cu1.2Mn1.8O4 spinel coating, which is much less than that of the composited (Co,Mn)3O4 spinel coating. The research indicates that the Cu1.2Mn1.8O4 coating evolved by the high-energy micro-arc alloying process is a promising coating material for the metallic interconnects. Full article
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Open AccessArticle Effects of Phase Evolution on Mechanical Properties of Laser-Welded Ferritic Fe-Al-Mn-C Steel
Metals 2017, 7(12), 523; doi:10.3390/met7120523
Received: 30 September 2017 / Revised: 22 November 2017 / Accepted: 22 November 2017 / Published: 24 November 2017
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Abstract
In the present study, the evolution of microstructure in laser-welded joints of ferrite-based dual-phase Fe-Al-Mn-C steel sheets was analyzed and its effect on the mechanical properties of the joints was investigated. Laser welding was performed using different powers and welding speeds to attain
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In the present study, the evolution of microstructure in laser-welded joints of ferrite-based dual-phase Fe-Al-Mn-C steel sheets was analyzed and its effect on the mechanical properties of the joints was investigated. Laser welding was performed using different powers and welding speeds to attain different heat inputs. Electron backscatter diffraction (EBSD) examinations and hardness measurements were used to characterize the microstructure of the welds. The tensile properties were found to depend on the heat input, but joint strength exceeding that of the base metal (BM) were obtained at low heat inputs. However, the fracture location shifted from the base metal to the heat-affected zone (HAZ) as the heat input was increased. The HAZ consisted of a mixture of austenite, ferrite and martensite, and its width increased with increasing the heat input. It was supposed that the incompatibility between the ferrite, austenite and martensite phases led to early void formation and fracturing of the phase interfaces in the wide HAZ. Full article
(This article belongs to the Special Issue Medium-Mn Steels, a Promising Type of the 3rd Generation Steels)
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Open AccessArticle Hot-Dip Aluminizing on AISI F55–UNS S32760 Super Duplex Stainless Steel Properties: Effect of Thermal Treatments
Metals 2017, 7(12), 525; doi:10.3390/met7120525
Received: 21 October 2017 / Revised: 13 November 2017 / Accepted: 22 November 2017 / Published: 29 November 2017
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Abstract
The behavior of super duplex stainless steels AISI F55-UNS S32760 in hot-dip aluminizing process has been studied, investigating the influence of cold working and of different initial microstructures obtained through a preliminary thermal treatment. The microstructural features examined are the secondary austenite precipitation,
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The behavior of super duplex stainless steels AISI F55-UNS S32760 in hot-dip aluminizing process has been studied, investigating the influence of cold working and of different initial microstructures obtained through a preliminary thermal treatment. The microstructural features examined are the secondary austenite precipitation, the static recovery of ferrite and the thermal dissolution of austenite within ferritic matrix. The hot-dip aluminizing temperature has been optimized through sessile drop tests. The treatment has been performed at 1100 °C for 300 s, 900 s and 2700 s. A strong chemical interaction occurs, generating intermetallic compounds at the interface. Molten aluminum interacts exclusively with the ferritic phase due to its much higher diffusivity in this phase coupled with its marked ferrite-stabilizer behavior. Thus, the influence of cold working is not remarkable, since the strains are mainly allocated by austenitic phase. The diffusivity of aluminum increases due to lattice defects thermally generated and, mainly, to influence given by grain boundaries, multiplied by secondary austenite precipitation, which act as short-circuit diffusion paths. Ni and Cr contents in the ferritic matrix have an influence but not highly relevant. Then, the best starting condition of the super duplex stainless steel substrates, to obtain a thick interfacial layer, are the thermal annealing at 1080 °C for 360 s/mm after a solution thermal treatment at 1300 °C for 60 s/mm. Full article
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Open AccessArticle Ultrasonic Pulse-Echo Signal Analysis for Damage Evaluation of Metallic Slit-Plate Hysteretic Dampers
Metals 2017, 7(12), 526; doi:10.3390/met7120526
Received: 9 November 2017 / Revised: 20 November 2017 / Accepted: 23 November 2017 / Published: 26 November 2017
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Abstract
This paper proposes a pulse-echo Ultrasonic Testing (UT) methodology to quantify the damage of hysteretic dampers subjected to cyclic loadings. Energy dissipation is known as an innovative strategy for the protection of buildings against earthquakes. It consists of installing special devices called dampers
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This paper proposes a pulse-echo Ultrasonic Testing (UT) methodology to quantify the damage of hysteretic dampers subjected to cyclic loadings. Energy dissipation is known as an innovative strategy for the protection of buildings against earthquakes. It consists of installing special devices called dampers in the construction, which are entrusted to dissipate most of the energy input by the earthquake, thus keeping the main structure basically undamaged. In particular, the hysteretic dampers dissipate the input energy through plastic deformations in their metallic parts. Several moderate ground motions would not exhaust the capacity of the dampers, but they cause damage—plastic deformations in the device. Therefore, continuous or periodic inspections of the damper are required in order to decide upon its eventual replacement. In this particular work, several hysteretic dampers made of stainless steel were subjected to different patterns of low-frequency cyclic loads that caused diverse levels of damage. Each damper underwent pulse-echo UT before and after the cyclic loading. Spectral energy of the echo signals was properly calculated at each damage level in order to define a reliable damage index. The new index has been compared with a well-established mechanical damage index, ID, previously proposed by the authors. A successful correlation was observed, making the pulse-echo UT technique promising for this particular application. Full article
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Open AccessArticle Effects of Strain Rate and Measuring Temperature on the Elastocaloric Cooling in a Columnar-Grained Cu71Al17.5Mn11.5 Shape Memory Alloy
Metals 2017, 7(12), 527; doi:10.3390/met7120527
Received: 22 October 2017 / Revised: 16 November 2017 / Accepted: 18 November 2017 / Published: 27 November 2017
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Abstract
Solid-state refrigeration technology based on elastocaloric effects (eCEs) is attracting more and more attention from scientists and engineers. The response speed of the elastocaloric materials, which relates to the sensitivity to the strain rate and measuring temperature, is a significant parameter to evaluate
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Solid-state refrigeration technology based on elastocaloric effects (eCEs) is attracting more and more attention from scientists and engineers. The response speed of the elastocaloric materials, which relates to the sensitivity to the strain rate and measuring temperature, is a significant parameter to evaluate the development of the elastocaloric material in device applications. Because the Cu-Al-Mn shape memory alloy (SMA) possesses a good eCE and a wide temperature window, it has been reported to be the most promising elastocaloric cooling material. In the present paper, the temperature changes (ΔT) induced by reversible martensitic transformation in a columnar-grained Cu71Al17.5Mn11.5 SMA fabricated by directional solidification were directly measured over the strain rate range of 0.005–0.19 s−1 and the measuring temperature range of 291–420 K. The maximum adiabatic ΔT of 16.5 K and a lower strain-rate sensitivity compared to TiNi-based SMAs were observed. With increasing strain rate, the ΔT value and the corresponding coefficient of performance (COP) of the alloy first increased, then achieved saturation when the strain rate reached 0.05 s−1. When the measuring temperature rose, the ΔT value increased linearly while the COP decreased linearly. The results of our work provide theoretical reference for the design of elastocaloric cooling devices made of this alloy. Full article
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Open AccessArticle Radial Basis Functional Model of Multi-Point Dieless Forming Process for Springback Reduction and Compensation
Metals 2017, 7(12), 528; doi:10.3390/met7120528
Received: 29 September 2017 / Revised: 30 October 2017 / Accepted: 23 November 2017 / Published: 27 November 2017
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Abstract
Springback in multi-point dieless forming (MDF) is a common problem because of the small deformation and blank holder free boundary condition. Numerical simulations are widely used in sheet metal forming to predict the springback. However, the computational time in using the numerical tools
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Springback in multi-point dieless forming (MDF) is a common problem because of the small deformation and blank holder free boundary condition. Numerical simulations are widely used in sheet metal forming to predict the springback. However, the computational time in using the numerical tools is time costly to find the optimal process parameters value. This study proposes radial basis function (RBF) to replace the numerical simulation model by using statistical analyses that are based on a design of experiment (DOE). Punch holding time, blank thickness, and curvature radius are chosen as effective process parameters for determining the springback. The Latin hypercube DOE method facilitates statistical analyses and the extraction of a prediction model in the experimental process parameter domain. Finite element (FE) simulation model is conducted in the ABAQUS commercial software to generate the springback responses of the training and testing samples. The genetic algorithm is applied to find the optimal value for reducing and compensating the induced springback for the different blank thicknesses using the developed RBF prediction model. Finally, the RBF numerical result is verified by comparing with the FE simulation result of the optimal process parameters and both results show that the springback is almost negligible from the target shape. Full article
(This article belongs to the Special Issue Advances in Plastic Forming of Metals)
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Open AccessArticle Microstructure of Multi-Pass Friction-Stir-Processed Al-Zn-Mg-Cu Alloys Reinforced by Nano-Sized TiB2 Particles and the Effect of T6 Heat Treatment
Metals 2017, 7(12), 530; doi:10.3390/met7120530
Received: 23 October 2017 / Revised: 8 November 2017 / Accepted: 14 November 2017 / Published: 27 November 2017
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Abstract
In this work, a fine-grained structure with a uniform distribution of TiB2 particles and precipitates was achieved in TiB2 particle-reinforced (PR) Al-Zn-Mg-Cu alloys by friction stir processing (FSP). The effects of multi-pass FSP on the microstructure, and TiB2 particle distribution,
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In this work, a fine-grained structure with a uniform distribution of TiB2 particles and precipitates was achieved in TiB2 particle-reinforced (PR) Al-Zn-Mg-Cu alloys by friction stir processing (FSP). The effects of multi-pass FSP on the microstructure, and TiB2 particle distribution, as well as the microstructural evolution in the following T6 treatment, were investigated by X-ray diffraction, scanning electron microscopy and associated electron backscattered diffraction. The results showed that the distribution of TiB2 particles and alloy precipitates was further improved with an increase in the FSP passes. Moreover, compared with alloy segregation in the as-cast PR alloys during T6 treatment, a complete solution of the precipitates was achieved in the FSP-treated PR alloys. The fine-grained structure of the FSP-treated PR alloys was thermally stable without any abnormal growth at the high temperature of T6 treatment due to the pinning effect of dispersed TiB2 particles. The strength and ductility of the PR alloys were simultaneously improved by the combination of FSP and T6 treatment. Full article
(This article belongs to the Special Issue Heat Treatment of Aluminum Alloys)
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Open AccessArticle Revisiting Formability and Failure of AISI304 Sheets in SPIF: Experimental Approach and Numerical Validation
Metals 2017, 7(12), 531; doi:10.3390/met7120531
Received: 11 October 2017 / Revised: 22 November 2017 / Accepted: 24 November 2017 / Published: 28 November 2017
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Abstract
Single Point Incremental Forming (SPIF) is a flexible and economic manufacturing process with a strong potential for manufacturing small and medium batches of highly customized parts. Formability and failure in SPIF have been intensively discussed in recent years, especially because this process allows
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Single Point Incremental Forming (SPIF) is a flexible and economic manufacturing process with a strong potential for manufacturing small and medium batches of highly customized parts. Formability and failure in SPIF have been intensively discussed in recent years, especially because this process allows stable plastic deformation well above the conventional forming limits, as this enhanced formability is only achievable within a certain range of process parameters depending on the material type. This paper analyzes formability and failure of AISI304-H111 sheets deformed by SPIF compared to conventional testing conditions (including Nakazima and stretch-bending tests). With this purpose, experimental tests in SPIF and stretch-bending were carried out and a numerical model of SPIF is performed. The results allow the authors to establish the following contributions regarding SPIF: (i) the setting of the limits of the formability enhancement when small tool diameters are used, (ii) the evolution of the crack when failure is attained and (iii) the determination of the conditions upon which necking is suppressed, leading directly to ductile fracture in SPIF. Full article
(This article belongs to the Special Issue Advances in Plastic Forming of Metals)
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Open AccessArticle Effect of Different Welding Processes on Electrochemical and Corrosion Behavior of Pure Nickel in 1 M NaCl Solution
Metals 2017, 7(12), 532; doi:10.3390/met7120532
Received: 28 September 2017 / Revised: 19 November 2017 / Accepted: 27 November 2017 / Published: 29 November 2017
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Abstract
A plasma arc welding (PAW)-tungsten inert gas (TIG) hybrid welding process is proposed to weld pure nickel. In PAW-TIG welding, the arc of the PAW was first to be ignited, then TIG was ignited, while in PAW welding, only the PAW arc was
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A plasma arc welding (PAW)-tungsten inert gas (TIG) hybrid welding process is proposed to weld pure nickel. In PAW-TIG welding, the arc of the PAW was first to be ignited, then TIG was ignited, while in PAW welding, only the PAW arc was launched. This paper investigated the effect of different welding processes on electrochemical and corrosion performance of between a pure nickel joint and a base metal in an aerated 1 M NaCl solution, respectively. The average grain size of the joint fabricated by PAW welding (denoted as JP joint) is 463.57 μm, the joint fabricated by PAW-TIG welding(denoted as JP-T joint) is 547.32 μm, and the base metal (BM) is 47.32 μm. In this work, the passivity behaviors of samples were characterized for two welding processes by electrochemical impedance spectroscopy (EIS), open circuit potential versus immersion time (OCP-t), and the potentiodynamic polarization plots. EIS spectra, attained with different immersion times, were analyzed and fitted by an equivalent electrical circuit. Photomicrographs of BM, JP, and JP-T were also taken with a scanning electron microscope (SEM) to reveal the morphological structure of the pit surfaces. Electrochemical tests show that the sequence of the corrosion resistance is BM > JP > JP-T. The size and quantity of the hemispherical corrosion pits of all samples are different. The corrosion morphology observations found a consistency with the consequence of the electrochemical measurements. The results show that an increase of the grain dimensions due to different heat treatments decreased the pure nickel stability to pitting corrosion. Full article
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Open AccessArticle Electropolymerisation of Aniline on AZ91 Magnesium Alloy: The Effect of Coating Electrolyte Corrosiveness
Metals 2017, 7(12), 533; doi:10.3390/met7120533
Received: 22 September 2017 / Revised: 23 November 2017 / Accepted: 27 November 2017 / Published: 29 November 2017
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Abstract
In this study, polyaniline was coated on AZ91 magnesium alloy using an electropolymerisation technique, and the effect of corrosiveness of the coating electrolytes on the polymerisation and the coating performance were evaluated. Two electrolytes, i.e., aniline + sodium salicylate (PASS) and aniline +
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In this study, polyaniline was coated on AZ91 magnesium alloy using an electropolymerisation technique, and the effect of corrosiveness of the coating electrolytes on the polymerisation and the coating performance were evaluated. Two electrolytes, i.e., aniline + sodium salicylate (PASS) and aniline + potassium hydroxide (PAPH), with different corrosiveness, were used for polyaniline coating on AZ91 magnesium alloy. Potentiodynamic polarisation results suggested that salicylic acid (C7H5NaO3) was more corrosive for the alloy than potassium hydroxide (KOH), which can be attributed to the difference in the pH of the electrolytes. The PASS electrolyte coating formed on the alloy was relatively thick (~9 µm) and exhibited scattered pore-like morphology, whereas the PAPH electrolyte coating was thin (~3 µm) and uniform. Fourier Transform Infrared (FTIR) spectroscopy analysis revealed that the PASS electrolyte coating corresponds to polyaniline, whereas the PAPH electrolyte coating showed weak polyaniline bands. The corrosion protection performance of the coatings was evaluated in chloride-containing solution. The potentiodynamic polarisation results suggested that the corrosion rate of the alloy decreased significantly with the PASS electrolyte coating, whereas the PAPH electrolyte coating was detrimental. The degree of protection (DP) provided by the PASS electrolyte coating was ~83%. Post-corrosion analysis revealed higher corrosion attack in the PAPH electrolyte-coated alloy in comparison with the PASS electrolyte coated alloy. Thus, it can be concluded that the corrosiveness of the PASS coating electrolyte did not adversely affect the formation/performance of polyaniline on AZ91 magnesium alloy. Full article
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Open AccessArticle Effects of Welding Parameters on Strength and Corrosion Behavior of Dissimilar Galvanized Q&P and TRIP Spot Welds
Metals 2017, 7(12), 534; doi:10.3390/met7120534
Received: 7 November 2017 / Revised: 22 November 2017 / Accepted: 24 November 2017 / Published: 1 December 2017
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Abstract
This study investigates the effects of the main welding parameters on mechanical strength and corrosion behavior of galvanized quenching and partitioning and transformation induced plasticity spot welds, which are proposed to assemble advanced structural car elements for the automotive industry. Steel sheets have
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This study investigates the effects of the main welding parameters on mechanical strength and corrosion behavior of galvanized quenching and partitioning and transformation induced plasticity spot welds, which are proposed to assemble advanced structural car elements for the automotive industry. Steel sheets have been welded with different current, clamping force, and welding time settings. The quality of the spot welds has been assessed through lap-shear and salt spray corrosion tests, also evaluating the effects of metal expulsion on strength and corrosion resistance of the joints. An energy dispersive spectrometry elemental mapping has been used to assess the damage of the galvanized zinc coating and the nature of the corrosive products. Welding current and time have the strongest influence on the shear strength of the spot welds, whereas clamping force is of minor importance. However, clamping force has the primary effect on avoiding expulsion of molten metal from the nugget during the joining process. Furthermore, clamping force has a beneficial influence on the corrosion resistance because it mainly hinders the permeation of the corrosive environment towards the spot welds. Although the welded samples can exhibit high shear strength also when a metal expulsion occurs, this phenomenon should be avoided because it enhances the damage and vaporization of the protective zinc coating. Full article
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Open AccessArticle Experimental and Numerical Investigation of an Overheated Aluminum Droplet Wetting a Zinc-Coated Steel Surface
Metals 2017, 7(12), 535; doi:10.3390/met7120535
Received: 3 November 2017 / Revised: 22 November 2017 / Accepted: 28 November 2017 / Published: 1 December 2017
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Abstract
Wetting steel surfaces with liquid aluminum without the use of flux can be enabled by the presence of a zinc-coating. The mechanisms behind this effect are not yet fully understood. Research results on single aluminum droplets falling on commercial galvanized steel substrates revealed
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Wetting steel surfaces with liquid aluminum without the use of flux can be enabled by the presence of a zinc-coating. The mechanisms behind this effect are not yet fully understood. Research results on single aluminum droplets falling on commercial galvanized steel substrates revealed the good wetting capability of zinc coatings independently from the coating type. The final wetting angle and length are apparently linked to the time where zinc is liquefied during its contact with the overheated aluminum melt. This led to the assumption that the interaction is basically a fluid dynamic effect of liquid aluminum getting locally alloyed by zinc. A numerical model was developed to describe the transient behavior of droplet movement and mixing with the liquefied zinc layer to understand the spreading dynamics. The simulations reveal a displacement of the molten zinc after the impact of the droplet, which ultimately leads to an accumulation of zinc in the outer weld toe after solidification. The simulation approach neglects the effect of evaporating zinc, resulting in a slight overestimation of the final droplet width. However, in terms of spreading initiation during the first milliseconds, the simulation is in good correlation with experimental observations and demonstrates the reason for the good wetting in the presence of zinc coatings. Full article
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Open AccessArticle New Nanocomposite Materials with Improved Mechanical Strength and Tailored Coefficient of Thermal Expansion for Electro-Packaging Applications
Metals 2017, 7(12), 536; doi:10.3390/met7120536
Received: 31 October 2017 / Revised: 27 November 2017 / Accepted: 28 November 2017 / Published: 1 December 2017
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Abstract
In this research, copper nanocomposites reinforced by graphene nanoplatelets (GNPs) were fabricated using a wet mixing method followed by a classical powder metallurgy route. In order to find the best dispersion technique, ball milling and wet mixing were chosen. Qualitative evaluation of the
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In this research, copper nanocomposites reinforced by graphene nanoplatelets (GNPs) were fabricated using a wet mixing method followed by a classical powder metallurgy route. In order to find the best dispersion technique, ball milling and wet mixing were chosen. Qualitative evaluation of the structure of the graphene after mixing indicated that the wet mixing is an appropriate technique to disperse the GNPs. Thereafter, the influence of graphene content on microstructure, density, hardness, elastic modulus, and thermal expansion coefficient of composites was investigated. It was shown that by increasing the graphene content the aggregation of graphene is more obvious and, thus, these agglomerates affect the final properties adversely. In comparison with the unreinforced Cu, Cu–GNP composites were lighter, and their hardness and Young’s modulus were higher as a consequence of graphene addition. According to the microstructural observation of pure copper and its composites after sintering, it was concluded that grain refinement is the main mechanism of strengthening in this research. Apart from the mechanical characteristics, the coefficient of thermal expansion of composites decreased remarkably and the combination of this feature with appropriate mechanical properties can make them a promising candidate for use in electronic packaging applications. Full article
(This article belongs to the Special Issue Metal Matrix Composites)
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Open AccessArticle The Effect of Two-Step Heat Treatment Parameters on Microstructure and Mechanical Properties of 42SiMn Steel
Metals 2017, 7(12), 537; doi:10.3390/met7120537
Received: 30 October 2017 / Revised: 27 November 2017 / Accepted: 27 November 2017 / Published: 1 December 2017
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Abstract
Medium-carbon steel 42SiMn (0.4C-0.6Mn-2Si-0.03Nb) was used for a two-step heat treatment consisting of a soaking hold and an annealing hold at bainite transformation temperature. Various heating temperatures, cooling rates, and bainitic hold temperatures were applied to the steel to obtain microstructures typical for
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Medium-carbon steel 42SiMn (0.4C-0.6Mn-2Si-0.03Nb) was used for a two-step heat treatment consisting of a soaking hold and an annealing hold at bainite transformation temperature. Various heating temperatures, cooling rates, and bainitic hold temperatures were applied to the steel to obtain microstructures typical for TRIP (Transformation Induced Plasticity) steels. TRIP steels utilize the positive effects of a multiphase microstructure with retained austenite, creating a good combination of strength and total elongation and an excellent deep-drawing ability. Typical microstructures consist of ferrite, bainite, and 10–15% of retained austenite. In this work, tensile strengths in the region of 887–1063 MPa were achieved with total elongation A5mm of 26–47%, and the final microstructures contained 4–16% of retained austenite. The most suitable microstructure and the best combination of high strength and total elongation were achieved for the processing with intercritical heating temperature of 850 °C and cooling at 30 °C/s to the bainitic hold of 400 °C. Very fine pearlite persisted in the microstructures, even after applying a cooling rate of 50 °C/s, however these small areas with extremely fine laths did not prevent the retention of up to 16% of retained austenite, and high total elongation A5mm above 40% was still reached for these microstructures. Full article
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Open AccessArticle Microstructural, Mechanical, and Electrochemical Analysis of Duplex and Superduplex Stainless Steels Welded with the Autogenous TIG Process Using Different Heat Input
Metals 2017, 7(12), 538; doi:10.3390/met7120538
Received: 1 November 2017 / Revised: 23 November 2017 / Accepted: 27 November 2017 / Published: 1 December 2017
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Abstract
Duplex Stainless Steels (DSS) and Superduplex Stainless Steels (SDSS) have a strong appeal in the petrochemical industry. These steels have excellent properties, such as corrosion resistance and good toughness besides good weldability. Welding techniques take into account the loss of alloying elements during
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Duplex Stainless Steels (DSS) and Superduplex Stainless Steels (SDSS) have a strong appeal in the petrochemical industry. These steels have excellent properties, such as corrosion resistance and good toughness besides good weldability. Welding techniques take into account the loss of alloying elements during the process, so this loss is usually compensated by the addition of a filler metal rich in alloying elements. A possible problem would be during the welding of these materials in adverse conditions in service, where the operator could have difficulties in welding with the filler metal. Therefore, in this work, two DSS and one SDSS were welded, by autogenous Tungsten Inert Gas (TIG), i.e., without addition of a filler metal, by three different heat inputs. After welding, microstructural, mechanical, and electrochemical analysis was performed. The microstructures were characterized for each welding condition, with the aid of optical microscopy (OM). Vickers hardness, Charpy-V, and cyclic polarization tests were also performed. After the electrochemical tests, the samples were analyzed by scanning electron microscopy (SEM). The SDSS welded with high heat input kept the balance of the austenite and ferrite, and toughness above the limit value. The hardness values remain constant in the weld regions and SDSS is the most resistant to corrosion. Full article
(This article belongs to the Special Issue Physical Metallurgy of High Performance Steels)
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Open AccessArticle Mechanism of Dynamic Recrystallization and Evolution of Texture in the Hot Working Domains of the Processing Map for Mg-4Al-2Ba-2Ca Alloy
Metals 2017, 7(12), 539; doi:10.3390/met7120539
Received: 21 October 2017 / Revised: 14 November 2017 / Accepted: 22 November 2017 / Published: 2 December 2017
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Abstract
The occurrence of dynamic recrystallization (DRX) and its effect on the evolution of texture during uniaxial compression of a creep-resistant cast Mg-4Al-2Ba-2Ca alloy in the temperature range of 260–500 °C and strain rate range of 0.0003–10 s−1 has been studied using transmission
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The occurrence of dynamic recrystallization (DRX) and its effect on the evolution of texture during uniaxial compression of a creep-resistant cast Mg-4Al-2Ba-2Ca alloy in the temperature range of 260–500 °C and strain rate range of 0.0003–10 s−1 has been studied using transmission electron microscopy and electron backscatter diffraction techniques with a view to understand its mechanism. For this purpose, a processing map has been developed for this alloy, which revealed two domains of DRX in the temperature and strain rate ranges of: (1) 300–390 °C/0.0003–0.001 s−1 and (2) 400–500 °C/0.0003–0.5 s−1. In Domain 1, DRX occurs by basal slip and recovery by dislocation climb, as indicated by the presence of planar slip bands and high dislocation density leading to tilt boundary formation and a low-intensity basal texture. On the other hand, DRX in Domain 2 occurs by second order pyramidal slip and recovery by cross-slip since the microstructure revealed tangled dislocation structure with twist boundaries and randomized texture. The high volume content of intermetallic phases Mg21Al3Ba2 and (Al,Mg)2Ca eutectic phase is considered to be responsible for the observed hot deformation behavior. Full article
(This article belongs to the Special Issue Dynamic Recrystallization Behavior of Metallic Materials)
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Open AccessArticle The Effect of Eutectic Structure on the Creep Properties of Sn-3.0Ag-0.5Cu and Sn-8.0Sb-3.0Ag Solders
Metals 2017, 7(12), 540; doi:10.3390/met7120540
Received: 9 November 2017 / Revised: 26 November 2017 / Accepted: 28 November 2017 / Published: 3 December 2017
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Abstract
Solder joints are the main weak points of power modules used in harsh environments. For the power module of electric vehicles, the maximum operating temperature of a chip can reach 175 °C under driving conditions. Therefore, it is necessary to study the high-temperature
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Solder joints are the main weak points of power modules used in harsh environments. For the power module of electric vehicles, the maximum operating temperature of a chip can reach 175 °C under driving conditions. Therefore, it is necessary to study the high-temperature reliability of solder joints. This study investigated the creep properties of Sn-3.0Ag-0.5Cu (SAC305) and Sn-8.0Sb-3.0Ag (SSA8030) solder joints. The creep test was conducted at 175 and 190 °C with the application of 2.45 MPa. The SAC305 solder had superior creep properties to those of SSA8030 solder at 175 °C and at largely the same homologous temperature ( T H ~0.91 for SAC305 and T H ~0.92 for SSA8030). Both solders had primary β-Sn and a eutectic mixture of β-Sn and Ag3Sn. Compared to SSA8030, the SAC305 solder contained ~10% more eutectic structure and contained Ag3Sn that was 3 times smaller and more round in shape. Furthermore, the SSA8030 solder precipitated SnSb in an elongated fiber shape (1–50 μm in size) after the creep test. Coarse and elongated Ag3Sn and SnSb of the SSA8030 solder negatively affected crack propagation in the dislocation creep region and decreased the creep resistance. Full article
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Open AccessArticle Extraction of Palladium(II) from Hydrochloric Acid Solutions by Solvent Extraction with Mixtures Containing Either Cyanex 301 or LIX 63
Metals 2017, 7(12), 541; doi:10.3390/met7120541
Received: 14 October 2017 / Revised: 23 November 2017 / Accepted: 28 November 2017 / Published: 4 December 2017
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Abstract
Cyanex 301 and 5,8-diethyl-7-hydroxyldodecane-6-oxime (LIX 63) can selectively extract Pd(II) over Pt(IV) from concentrated hydrochloric acid solutions. Therefore, solvent extraction experiments have been performed by extractant mixtures containing either Cyanex 301 or LIX 63, and the extraction behavior of Pd(II) was compared. Among
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Cyanex 301 and 5,8-diethyl-7-hydroxyldodecane-6-oxime (LIX 63) can selectively extract Pd(II) over Pt(IV) from concentrated hydrochloric acid solutions. Therefore, solvent extraction experiments have been performed by extractant mixtures containing either Cyanex 301 or LIX 63, and the extraction behavior of Pd(II) was compared. Among the mixtures of Cyanex 301, the highest synergistic enhancement coefficient was achieved by mixing Cyanex 301 and trioctylphosphine oxide (TOPO). However, it was very difficult to strip the Pd(II) from the loaded mixture phase. Among the mixtures of LIX 63, the mixture of LIX 63 and alamine 336/TOPO enhanced the extraction of Pd(II). Although the synergistic coefficient by Cyanex 301 + TOPO was higher than that by LIX 63 + Alamine 336, the Pd(II) in the loaded mixture phase of LIX 63 and alamine 336 was easily stripped by thiourea. Full article
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Open AccessArticle Microstructure and Mechanical Properties of Al/Steel Friction Stir Lap Weld
Metals 2017, 7(12), 542; doi:10.3390/met7120542
Received: 6 November 2017 / Revised: 29 November 2017 / Accepted: 30 November 2017 / Published: 5 December 2017
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Abstract
The friction stir welding tool with convex pin tip was designed to realize the lap joining of 6082-T6 aluminum alloy and Q235A steel. With decreasing welding speed and increasing rotation speed, the basic constitutions of mixed stir zone changed from α-Fe fine grains,
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The friction stir welding tool with convex pin tip was designed to realize the lap joining of 6082-T6 aluminum alloy and Q235A steel. With decreasing welding speed and increasing rotation speed, the basic constitutions of mixed stir zone changed from α-Fe fine grains, thin intermetallic compound (IMC) and Al/Fe composite structure to hook-like and chaotic mixed layered structure, resulting in joint deterioration. The maximum shear load can reach 7500 N and is predominately affected by the morphology of the IMC layers, which in turn depend on rotation speed, welding speed and other parameters. Nano-hardness decreases from about 3.9 GPa in the upper steel surface layer to about 1.3 GPa in the steel base material. Microhardness profile reveals that the maximum hardness occurs at the interface zone. The morphology of layered structure, FeAl3 IMC thickness and steel grain size can be controlled by choosing suitable welding parameters and tool shape. Full article
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Open AccessArticle AISI 304 Welding Fracture Resistance by a Charpy Impact Test with a High Speed Sampling Rate
Metals 2017, 7(12), 543; doi:10.3390/met7120543
Received: 24 October 2017 / Revised: 27 November 2017 / Accepted: 29 November 2017 / Published: 5 December 2017
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Abstract
The purpose of this study was to evaluate fracture resistance in AISI 304. The J-R curve was constructed from data, which resulted from an impact test by Charpy Impact machine equipped with high-speed sampling rate data acquisition equipment. The critical values of fracture
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The purpose of this study was to evaluate fracture resistance in AISI 304. The J-R curve was constructed from data, which resulted from an impact test by Charpy Impact machine equipped with high-speed sampling rate data acquisition equipment. The critical values of fracture resistance in fusion zones (FZ), high temperature heat affected zones (HTHAZ), low temperature heat affected zones (LTHAZ) and unaffected base metals (UBM) were obtained by calculation methods using some formulas and by graphical methods. Laboratory experiments demonstrated the relationships among the values of energy absorption along the impact test with the obstruction of dislocation movement due to the presence of chromium interstitial solute in all zones and chromium rich carbide precipitates in fusion zones and heat affected zones. Full article
(This article belongs to the Special Issue Mechanical Behavior of High-Strength Low-Alloy Steels)
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Open AccessArticle Influence of Combined Helical and Pass Rolling on Structure and Residual Porosity of an AA6082-0.2 wt % Al2O3 Composite Produced by Casting with Ultrasonic Processing
Metals 2017, 7(12), 544; doi:10.3390/met7120544
Received: 25 October 2017 / Revised: 29 November 2017 / Accepted: 30 November 2017 / Published: 5 December 2017
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Abstract
The influence of combined (helical and pass) rolling on the structure, residual porosity, and microhardness of an AA6082-0.2 wt % Al2O3 composite produced by casting with ultrasonic processing was evaluated in comparison with the matrix alloy. The nanosized alumina particles
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The influence of combined (helical and pass) rolling on the structure, residual porosity, and microhardness of an AA6082-0.2 wt % Al2O3 composite produced by casting with ultrasonic processing was evaluated in comparison with the matrix alloy. The nanosized alumina particles resulted in a more homogeneous and fine-grained structure of the composite after deformation with higher microhardness in comparison with the matrix alloy. However, the residual porosity of the AA6082-0.2 wt % Al2O3 composite was retained even after combined rolling on the level typical of alloys produced by the method, which may be a result of relatively low stresses and strains introduced during deformation. Full article
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Open AccessArticle Temperature and Stress Simulation of 4H-SiC during Laser-Induced Silicidation for Ohmic Contact Generation
Metals 2017, 7(12), 545; doi:10.3390/met7120545
Received: 4 October 2017 / Revised: 13 November 2017 / Accepted: 28 November 2017 / Published: 5 December 2017
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Abstract
We report here on the simulation of temperature and stress evolution of 4H-SiC during laser-induced silicidation to locally generate ohmic contacts between the semiconductor and nickel metallization. The simulation is based on optical free carrier absorption, thermal conduction, and thermal radiation. Our results
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We report here on the simulation of temperature and stress evolution of 4H-SiC during laser-induced silicidation to locally generate ohmic contacts between the semiconductor and nickel metallization. The simulation is based on optical free carrier absorption, thermal conduction, and thermal radiation. Our results show that, during laser irradiation, similar temperatures and correspondingly similar contact resistances, as compared to conventional oven-driven annealing processes, are achievable, yet with the advantageous potential to limit the temperature treatment spatially to the desired regions for electrical contacts and without the necessity of heating complete wafers. However, due to temperature gradients during local laser silicidation, thermal induced stress appears, which may damage the SiC wafer. Based on the simulated results for temperature and stress increase, we identify an optimized regime for laser-induced local silicidation and compare it to experimental data and observations. Full article
(This article belongs to the Special Issue Metallization of Non-Conductive Substrates)
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Open AccessArticle Fiber Laser Welding of Dissimilar 2205/304 Stainless Steel Plates
Metals 2017, 7(12), 546; doi:10.3390/met7120546
Received: 27 September 2017 / Revised: 13 November 2017 / Accepted: 27 November 2017 / Published: 6 December 2017
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Abstract
In this study, an attempt on pulsed-fiber laser welding on an austenitic-duplex stainless steel butt joint configuration was investigated. The influence of various welding parameters, such as beam diameter, peak power, pulse repetition rate, and pulse width on the weld beads geometry was
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In this study, an attempt on pulsed-fiber laser welding on an austenitic-duplex stainless steel butt joint configuration was investigated. The influence of various welding parameters, such as beam diameter, peak power, pulse repetition rate, and pulse width on the weld beads geometry was studied by checking the width and depth of the welds after each round of welding parameters combination. The weld bead dimensions and microstructural progression of the weld joints were observed microscopically. Finally, the full penetration specimens were subjected to tensile tests, which were coupled with the analysis of the fracture surfaces. From the results, combination of the selected weld parameters resulted in robust weldments with similar features to those of duplex and austenitic weld metals. The weld depth and width were found to increase proportionally to the laser power. Furthermore, the weld bead geometry was found to be positively affected by the pulse width. Microstructural studies revealed the presence of dendritic and fine grain structures within the weld zone at low peak power, while ferritic microstructures were found on the sides of the weld metal near the SS 304 and austenitic-ferritic microstructure beside the duplex 2205 boundary. Regarding the micro-hardness tests, there was an improvement when compared to the hardness of duplex and austenitic stainless steels base metals. Additionally, the tensile strength of the fiber laser welded joints was found to be higher when compared to the tensile strength of the base metals (duplex and austenitic) in all of the joints. Full article
(This article belongs to the Special Issue Laser Welding)
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Open AccessFeature PaperArticle Detection of Capillary-Mediated Energy Fields on a Grain Boundary Groove: Solid–Liquid Interface Perturbations
Metals 2017, 7(12), 547; doi:10.3390/met7120547
Received: 29 September 2017 / Revised: 28 November 2017 / Accepted: 29 November 2017 / Published: 6 December 2017
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Abstract
Grain boundary grooves are common features on polycrystalline solid–liquid interfaces. Their local microstructure can be closely approximated as a “variational” groove, the theoretical profile for which is analyzed here for its Gibbs–Thomson thermo-potential distribution. The distribution of thermo-potentials for a variational groove exhibits
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Grain boundary grooves are common features on polycrystalline solid–liquid interfaces. Their local microstructure can be closely approximated as a “variational” groove, the theoretical profile for which is analyzed here for its Gibbs–Thomson thermo-potential distribution. The distribution of thermo-potentials for a variational groove exhibits gradients tangential to the solid–liquid interface. Energy fluxes stimulated by capillary-mediated tangential gradients are divergent and thus capable of redistributing energy on real or simulated grain boundary grooves. Moreover, the importance of such capillary-mediated energy fields on interfaces is their influence on stability and pattern formation dynamics. The capillary-mediated field expected to be present on a stationary grain boundary groove is verified quantitatively using the multiphase-field approach. Simulation and post-processing measurements fully corroborate the presence and intensity distribution of interfacial cooling, proving that thermodynamically-consistent numerical models already support, without any modification, capillary perturbation fields, the existence of which is currently overlooked in formulations of sharp interface dynamic models. Full article
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Open AccessArticle Rhodium and Hafnium Influence on the Microstructure, Phase Composition, and Oxidation Resistance of Aluminide Coatings
Metals 2017, 7(12), 548; doi:10.3390/met7120548
Received: 12 October 2017 / Revised: 28 November 2017 / Accepted: 29 November 2017 / Published: 7 December 2017
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Abstract
A 0.5 μm thick layer of rhodium was deposited on the CMSX 4 superalloy by the electroplating method. The rhodium-coated superalloy was hafnized and aluminized or only aluminized using the Chemical vapour deposition method. A comparison was made of the microstructure, phase composition,
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A 0.5 μm thick layer of rhodium was deposited on the CMSX 4 superalloy by the electroplating method. The rhodium-coated superalloy was hafnized and aluminized or only aluminized using the Chemical vapour deposition method. A comparison was made of the microstructure, phase composition, and oxidation resistance of three aluminide coatings: nonmodified (a), rhodium-modified (b), and rhodium- and hafnium-modified (c). All three coatings consisted of two layers: the additive layer and the interdiffusion layer. Rhodium-doped (rhodium- and hafnium-doped) β-NiAl phase was found in the additive layer of the rhodium-modified (rhodium- and hafnium-modified) aluminide coating. Topologically Closed-Pack (μ and σ) phases precipitated in the matrix of the interdiffusion layer. Rhodium also dissolved in the β-NiAl phase between the additive and interdiffusion layers, whereas Hf-rich particles precipitated in the (Ni,Rh)Al phase at the additive/interdiffusion layer interface in the rhodium- and hafnium-modified coating (c). The rhodium-modified aluminide coating (b) has better oxidation resistance than the nonmodified one (a), whereas the rhodium- and hafnium-modified aluminide coating (c) has better oxidation resistance than the rhodium-modified (b) and nonmodified (a) ones. Full article
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Open AccessArticle Modeling and Simulation of the Gray-to-White Transition during Solidification of a Hypereutectic Gray Cast Iron: Application to a Stub-to-Carbon Connection Used in Smelting Processes
Metals 2017, 7(12), 549; doi:10.3390/met7120549
Received: 22 September 2017 / Revised: 25 November 2017 / Accepted: 1 December 2017 / Published: 7 December 2017
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Abstract
This work reports on experimental and numerical results of the gray-to-white transition (GWT) during solidification of a hypereutectic gray cast iron (GCI) in a casting test using a stub-to-carbon (STC) connection assembly. Since in this process non-uniform cooling rates are produced, the mechanical
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This work reports on experimental and numerical results of the gray-to-white transition (GWT) during solidification of a hypereutectic gray cast iron (GCI) in a casting test using a stub-to-carbon (STC) connection assembly. Since in this process non-uniform cooling rates are produced, the mechanical properties are expected to spatially vary due to the development of different microstructures along the thimble. The twin aims of this work were to (1) experimentally validate the GWT prediction capabilities of the microstructural model proposed earlier by the authors in the rodding process of a hypereutectic GCI-STC, and (2) estimate, from the numerically obtained microstructure and ultimate tensile strength (UTS), the local hardness of the alloy after the numerical predictions of the microstructure were experimentally validated. To this end, the final microstructure at different points of the thimble and the hardness profile along its radial direction were measured for validation purposes. Moreover, this rodding process was simulated using an extension of a thermal microstructural model previously developed by the authors and the GWT was superimposed on that simulation. The computed results encompass cooling curves, the evolution of gray and white fractions, eutectic radii and densities and, in addition, the hardness profile. A detailed discussion of the experimental and numerical results is presented. Finally, the computed GWT was found to adequately reproduce the experimental data. Full article
(This article belongs to the Special Issue Microstructure and Mechanical Properties of Casting Alloys)
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Open AccessArticle Experimental Investigation of Surface Layer Properties of High Thermal Conductivity Tool Steel after Electrical Discharge Machining
Metals 2017, 7(12), 550; doi:10.3390/met7120550
Received: 20 September 2017 / Revised: 19 November 2017 / Accepted: 1 December 2017 / Published: 7 December 2017
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Abstract
New materials require the use of advanced technology in manufacturing complex shape parts. One of the modern materials widely used in the tool industry for injection molds or hot stamping dies is high conductivity tool steel (HTCS) 150. Due to its hardness (55
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New materials require the use of advanced technology in manufacturing complex shape parts. One of the modern materials widely used in the tool industry for injection molds or hot stamping dies is high conductivity tool steel (HTCS) 150. Due to its hardness (55 HRC) and thermal conductivity at 66 W/mK, this material is difficult to machine by conventional treatment and is being increasingly manufactured by nonconventional technology such as electrical discharge machining (EDM). In the EDM process, material is removed from the workpiece by a series of electrical discharges that cause changes to the surface layers properties. The final state of the surface layer directly influences the durability of the produced elements. This paper presents the influence of EDM process parameters: discharge current Ic and the pulse time ton on surface layer properties. The experimental investigation was carried out with an experimental methodology design. Surface layers properties including roughness 3D parameters, the thickness of the white layer, heat affected zone, tempered layer and occurring micro cracks were investigated and described. The influence of the response surface methodology (RSM) of discharge current Ic and the pulse time ton on the thickness of the white layer and roughness parameters Sa, Sds and Ssc were described and established. Full article
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Open AccessArticle Effect of Cobalt on Microstructure and Wear Resistance of Ni-Based Alloy Coating Fabricated by Laser Cladding
Metals 2017, 7(12), 551; doi:10.3390/met7120551
Received: 5 November 2017 / Revised: 29 November 2017 / Accepted: 4 December 2017 / Published: 7 December 2017
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Abstract
Ni-based alloy powders with different contents of cobalt (Co) have been deposited on a 42CrMo steel substrate surface using a fiber laser. The effects of Co content on the microstructure, composition, hardness, and wear properties of the claddings were studied by scanning electron
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Ni-based alloy powders with different contents of cobalt (Co) have been deposited on a 42CrMo steel substrate surface using a fiber laser. The effects of Co content on the microstructure, composition, hardness, and wear properties of the claddings were studied by scanning electron microscopy (SEM), an electron probe microanalyzer (EPMA), X-ray diffraction (XRD), a hardness tester, and a wear tester. The results show that the phases in the cladding layers are mainly γ, M7(C, B)3, M23(C, B)6, and M2B. With the increase in Co content, the amounts of M7(C, B)3, M23(C, B)6, and M2B gradually decrease, and the width of the eutectic structure in the cladding layer also gradually decreases. The microhardness decreases but the wear resistance of the cladding layer gradually improves with the increase of Co content. The wear resistance of the NiCo30 cladding layer is 3.6 times that of the NiCo00 cladding layer. With the increase of Co content, the wear mechanism of the cladding layer is changed from abrasive wear to adhesive wear. Full article
(This article belongs to the Special Issue Laser Welding of Industrial Metal Alloys)
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Open AccessArticle A Numerical Study on the Excitation of Guided Waves in Rectangular Plates Using Multiple Point Sources
Metals 2017, 7(12), 552; doi:10.3390/met7120552
Received: 10 October 2017 / Revised: 27 November 2017 / Accepted: 29 November 2017 / Published: 8 December 2017
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Abstract
Ultrasonic guided waves are widely used to inspect and monitor the structural integrity of plates and plate-like structures, such as ship hulls and large storage-tank floors. Recently, ultrasonic guided waves have also been used to remove ice and fouling from ship hulls, wind-turbine
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Ultrasonic guided waves are widely used to inspect and monitor the structural integrity of plates and plate-like structures, such as ship hulls and large storage-tank floors. Recently, ultrasonic guided waves have also been used to remove ice and fouling from ship hulls, wind-turbine blades and aeroplane wings. In these applications, the strength of the sound source must be high for scanning a large area, or to break the bond between ice, fouling and plate substrate. More than one transducer may be used to achieve maximum sound power output. However, multiple sources can interact with each other, and form a sound field in the structure with local constructive and destructive regions. Destructive regions are weak regions and shall be avoided. When multiple transducers are used it is important that they are arranged in a particular way so that the desired wave modes can be excited to cover the whole structure. The objective of this paper is to provide a theoretical basis for generating particular wave mode patterns in finite-width rectangular plates whose length is assumed to be infinitely long with respect to its width and thickness. The wave modes have displacements in both width and thickness directions, and are thus different from the classical Lamb-type wave modes. A two-dimensional semi-analytical finite element (SAFE) method was used to study dispersion characteristics and mode shapes in the plate up to ultrasonic frequencies. The modal analysis provided information on the generation of modes suitable for a particular application. The number of point sources and direction of loading for the excitation of a few representative modes was investigated. Based on the SAFE analysis, a standard finite element modelling package, Abaqus, was used to excite the designed modes in a three-dimensional plate. The generated wave patterns in Abaqus were then compared with mode shapes predicted in the SAFE model. Good agreement was observed between the intended modes calculated in SAFE and the actual, excited modes in Abaqus. Full article
(This article belongs to the Special Issue Advanced Non-Destructive Testing in Steels)
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Open AccessArticle Experimental and Numerical Studies of Sheet Metal Forming with Damage Using Gas Detonation Process
Metals 2017, 7(12), 556; doi:10.3390/met7120556
Received: 9 November 2017 / Revised: 29 November 2017 / Accepted: 6 December 2017 / Published: 10 December 2017
Cited by 1 | PDF Full-text (4004 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Gas detonation forming is a high-speed forming method, which has the potential to form complex geometries, including sharp angles and undercuts, in a very short process time. Despite many efforts being made to develop detonation forming, many important aspects remain unclear and have
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Gas detonation forming is a high-speed forming method, which has the potential to form complex geometries, including sharp angles and undercuts, in a very short process time. Despite many efforts being made to develop detonation forming, many important aspects remain unclear and have not been studied experimentally, nor numerically in detail, e.g., the ability to produce sharp corners, the effect of peak load on deformation and damage location and its propagation in the workpiece. In the present work, DC04 steel cups were formed using gas detonation forming, and finite element method (FEM) simulations of the cup forming process were performed. The simulations on 3D computational models were carried out with explicit dynamic analysis using the Johnson–Cook material model. The results obtained in the simulations were in good agreement with the experimental observations, e.g., deformed shape and thickness distribution. Moreover, the proposed computational model was capable of predicting the damage initiation and evolution correctly, which was mainly due to the high-pressure magnitude or an initial offset of the workpiece in the experiments. Full article
(This article belongs to the Special Issue Modelling and Simulation of Sheet Metal Forming Processes)
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Open AccessArticle Concentration and Separation of Scandium from Ni Laterite Ore Processing Streams
Metals 2017, 7(12), 557; doi:10.3390/met7120557
Received: 7 November 2017 / Revised: 8 December 2017 / Accepted: 8 December 2017 / Published: 12 December 2017
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Abstract
The presence of a considerable amount of scandium in lateritic nickel-cobalt ores necessitates the investigation of possible processing alternatives to recover scandium as a byproduct during nickel and cobalt production. Therefore, in this study, rather than interfering with the main nickel-cobalt production circuit,
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The presence of a considerable amount of scandium in lateritic nickel-cobalt ores necessitates the investigation of possible processing alternatives to recover scandium as a byproduct during nickel and cobalt production. Therefore, in this study, rather than interfering with the main nickel-cobalt production circuit, the precipitation-separation behavior of scandium during a pH-controlled precipitation process from a synthetically prepared solution was investigated to adopt the Sc recovery circuit into an already existing hydrometallurgical nickel-cobalt hydroxide processing plant. The composition of the synthetic solution was determined according to the hydrometallurgical nickel laterite ore processing streams obtained from a HPAL (high-pressure sulphuric acid leaching) process. In order to selectively precipitate and concentrate scandium with minimum nickel and cobalt co-precipitation, the pH of the solution was adjusted by CaCO3, MgO, Na2CO3, and NaOH. It was found that precipitation with MgO or Na2CO3 is more advantageous to obtain a precipitate containing higher amounts of scandium with minimum mass when compared to the CaCO3 route, which makes further processing more viable. As a result of this study, it is proposed that by a simple pH-controlled precipitation process, scandium can be separated from the nickel and cobalt containing process solutions as a byproduct without affecting the conventional nickel-cobalt hydroxide production. By further processing this scandium-enriched residue by means of leaching, SX (solvent extraction), and precipitation, an intermediate (NH4)2NaScF6 product can be obtained. Full article
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Open AccessArticle In Situ Observations of Blistering of a Metal Irradiated with 2-MeV Protons
Metals 2017, 7(12), 558; doi:10.3390/met7120558
Received: 24 October 2017 / Revised: 30 November 2017 / Accepted: 1 December 2017 / Published: 12 December 2017
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Abstract
A vacuum-insulated tandem accelerator was used to observe in situ blistering during 2-MeV proton irradiation of metallic samples to a fluence of up to 6.7 × 1020 cm−2. Samples consisting of copper of different purity, tantalum and tantalum-copper compounds were
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A vacuum-insulated tandem accelerator was used to observe in situ blistering during 2-MeV proton irradiation of metallic samples to a fluence of up to 6.7 × 1020 cm−2. Samples consisting of copper of different purity, tantalum and tantalum-copper compounds were placed on the proton beam path and forced to cool. The surface state of the samples was observed using a charge-coupled device camera with a remote microscope. Thermistors, a pyrometer and an infrared camera were applied to measure the temperature of the samples during irradiation. After irradiation, the samples were analyzed on an X-ray diffractometer, laser and electron microscopes. The present study describes the experiment, presents the results obtained and notes their relevance and significance in the development of a lithium target for an accelerator-based neutron source, for use in boron neutron capture therapy of cancer. Full article
(This article belongs to the Special Issue Radiation Effects in Metals)
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Open AccessArticle Electromagnetic Forming Rules of a Stiffened Panel with Grid Ribs
Metals 2017, 7(12), 559; doi:10.3390/met7120559
Received: 11 October 2017 / Revised: 15 November 2017 / Accepted: 7 December 2017 / Published: 12 December 2017
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Abstract
Electromagnetic forming (EMF), a technology with advantages of contact-free force and high energy density, generally aims at forming parts by using a fixed coil and one-time discharge. In this study, multi-stage EMF is introduced to form a panel with stiffened grid ribs. The
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Electromagnetic forming (EMF), a technology with advantages of contact-free force and high energy density, generally aims at forming parts by using a fixed coil and one-time discharge. In this study, multi-stage EMF is introduced to form a panel with stiffened grid ribs. The forming rules of the stiffened panel is revealed via analyzing the distribution and evolution of the simulated stress and strain in the ribs and web, where the grid-rib panels were decomposed as the flat panel and two panels with uni-directional ribs (ribs only in X direction or Y direction). It is shown that the forming depth is mainly attributed to the forces on the web, although electromagnetic force is applied on both the ribs and the web, especially, large force on the ribs. The ribs are subjected to uniaxial stress parallel to their directions, and the web is subjected to plane stress in the deformation region. Furthermore, the change of the uniaxial stress characteristic in the X-direction ribs is influenced by the electromagnetic force, reverse bend and inertial effect. The plastic deformation mainly occurs in the Y-direction ribs of the deformation region under a three-direction strain state. Full article
(This article belongs to the Special Issue Modern Aerospace Materials)
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Open AccessArticle Fracture Resistance of 14Cr ODS Steel Exposed to a High Temperature Gas
Metals 2017, 7(12), 560; doi:10.3390/met7120560
Received: 31 October 2017 / Revised: 4 December 2017 / Accepted: 8 December 2017 / Published: 12 December 2017
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Abstract
This paper studies the impact fracture behavior of the 14%Cr Oxide Dispersion Strengthened (ODS) steel (ODM401) after high temperature exposures in helium and air in comparison to the as-received state. A steel bar was produced by mechanical alloying and hot-extrusion at 1150 °C.
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This paper studies the impact fracture behavior of the 14%Cr Oxide Dispersion Strengthened (ODS) steel (ODM401) after high temperature exposures in helium and air in comparison to the as-received state. A steel bar was produced by mechanical alloying and hot-extrusion at 1150 °C. Further, it was cut into small specimens, which were consequently exposed to air or 99.9% helium in a furnace at 720 °C for 500 h. Impact energy transition curves are shifted towards higher temperatures after the gas exposures. The transition temperatures of the exposed states significantly increase in comparison to the as-received steel by about 40 °C in He and 60 °C in the air. Differences are discussed in terms of microstructure, surface and subsurface Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) observations. The embrittlement was explained as temperature and environmental effects resulting in a decrease of dislocation level, slight change of the particle composition and interface/grain boundary segregations, which consequently affected the nucleation of voids leading to the ductile fracture. Full article
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Open AccessArticle Thermo-Viscoplastic Behavior of Ni-Based Superalloy Haynes 282 and Its Application to Machining Simulation
Metals 2017, 7(12), 561; doi:10.3390/met7120561
Received: 4 November 2017 / Revised: 10 December 2017 / Accepted: 11 December 2017 / Published: 13 December 2017
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Abstract
Ni-based superalloys are extensively used in high-responsibility applications in components of aerospace engines and gas turbines with high temperature service lives. The wrought, γ’-strengthened superalloy Haynes 282 has been recently developed for applications similar to other common superalloys, such as Waspaloy or
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Ni-based superalloys are extensively used in high-responsibility applications in components of aerospace engines and gas turbines with high temperature service lives. The wrought, γ’-strengthened superalloy Haynes 282 has been recently developed for applications similar to other common superalloys, such as Waspaloy or Inconel 718, with improved creep behavior, thermal stability, and fabrication ability. Despite the potential of Haynes 282, there are still important gaps in the knowledge of the mechanical behavior of this alloy. In fact, it was not possible to find information concerning the mechanical behavior of the alloy under impulsive loading. This paper focuses on the mechanical characterization of the Haynes 282 at strain rates ranging from 0.1 to 2800 s−1 and high temperatures ranging from 293 to 523 K using Hopkinson bar compression tests. The experimental results from the thermo-mechanical characterization allowed for calibration of the Johnson–Cook model widely used in modeling metallic alloy’s responses under dynamic loading. Moreover, the behavior of Haynes 282 was compared to that reported for Inconel 718, and the results were used to successfully model the orthogonal cutting of Haynes 282, being a typical case of dynamic loading requiring previous characterization of the alloy. Full article
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Open AccessArticle Improved Plasticity of Ti-Based Bulk Metallic Glass at Room Temperature by Electroless Thin Nickel Coating
Metals 2017, 7(12), 562; doi:10.3390/met7120562
Received: 4 November 2017 / Revised: 5 December 2017 / Accepted: 6 December 2017 / Published: 14 December 2017
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Abstract
By restricting the dilated deformation, surface modification can stimulate multiple shear banding and improve the plasticity of bulk metallic glasses (BMGs). Aimed at modifying the surface of BMGs by thin layers, a crystalline Ni coating with ultrafine grains was coated on the surface
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By restricting the dilated deformation, surface modification can stimulate multiple shear banding and improve the plasticity of bulk metallic glasses (BMGs). Aimed at modifying the surface of BMGs by thin layers, a crystalline Ni coating with ultrafine grains was coated on the surface of a Ti-based BMG by electroless plating. With a thickness of about 10 μm, the prepared thin coating could effectively limit the fast propagation of primary shear bands and stimulate the nucleation of multiple shear bands. As a result, the compression plasticity of the coated Ti-based BMG was improved to about 3.7% from near 0% of the non-coated BMG. Except for a small amount of Ni coating was adhered to the BMG substrate after fracture, most of the coatings were peeled off from the surface. It can be attributed to the abnormal growth of some coarse grains/particles in local region of the coating, which induces a large tensile stress at the interface between the coating and the BMG substrate. It is suggested that, for electroless nickel plating, improving the adhesive bonding strength between the coating and the substrate has a better geometric restriction effect than simply increasing the thickness of the coating. Full article
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Open AccessArticle Fabrication of an Ultra-Fine Grained Pure Titanium with High Strength and Good Ductility via ECAP plus Cold Rolling
Metals 2017, 7(12), 563; doi:10.3390/met7120563
Received: 6 November 2017 / Revised: 29 November 2017 / Accepted: 8 December 2017 / Published: 14 December 2017
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Abstract
Microstructure evolutions and mechanical properties of a commercially pure titanium (CP-Ti, grade 2) during multi-pass rotary-die equal-channel angular pressing (RD-ECAP) and cold rolling (CR) were systematically investigated in this work, to achieve comprehensive property for faster industrial applications. The obtained results showed that
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Microstructure evolutions and mechanical properties of a commercially pure titanium (CP-Ti, grade 2) during multi-pass rotary-die equal-channel angular pressing (RD-ECAP) and cold rolling (CR) were systematically investigated in this work, to achieve comprehensive property for faster industrial applications. The obtained results showed that the grain size of CP-Ti decreased from 80 μm of as-received stage to 500 nm and 310 nm after four passes and eight passes of ECAP, respectively. Moreover, abundant dislocations were observed in ECAP samples. After subsequent cold rolling, the grain size of ECAPed CP-Ti was further refined to 120 nm and 90 nm, suggesting a good refining effect by combination of ECAP and CR. XRD (X-ray diffractometer) analysis and TEM (transmission electron microscope) observations indicated that the dislocation density increased remarkably after subsequent CR processing. Room temperature tensile tests showed that CP-Ti after ECAP + CR exhibited the best combination of strength and ductility, with ultimate tensile strength and fracture strain reaching 920 MPa and 20%. The high strength of this deformed CP-Ti originated mainly from refined grains and high density of dislocations, while the good ductility could be attributed to the improved homogeneity of UFG (ultra-fine grained) microstructure. Thus, a high strength and ductility ultra-fine grained CP-Ti was successfully prepared via ECAP plus CR. 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 Pulse Laser Welding Parameters and Filler Metal on Microstructure and Mechanical Properties of Al-4.7Mg-0.32Mn-0.21Sc-0.1Zr Alloy
Metals 2017, 7(12), 564; doi:10.3390/met7120564
Received: 13 November 2017 / Revised: 6 December 2017 / Accepted: 12 December 2017 / Published: 14 December 2017
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Abstract
The effect of pulse laser welding parameters and filler metal on microstructure and mechanical properties of the new heat-treatable, wieldable, cryogenic Al-4.7Mg-0.32Mn-0.21Sc-0.1Zr alloy were investigated. The optimum parameters of pulsed laser welding were found. They were 330–340 V in voltage, 0.2–0.25 mm in
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The effect of pulse laser welding parameters and filler metal on microstructure and mechanical properties of the new heat-treatable, wieldable, cryogenic Al-4.7Mg-0.32Mn-0.21Sc-0.1Zr alloy were investigated. The optimum parameters of pulsed laser welding were found. They were 330–340 V in voltage, 0.2–0.25 mm in pulse overlap with 12 ms duration, and 2 mm/s speed and ramp-down pulse shape. Pulsed laser welding without and with Al-5Mg filler metal led to the formation of duplex (columnar and fine grains) as-cast structures with hot cracks and gas porosity as defects in the weld zone. Using Al-5Ti-1B filler metal for welding led to the formation of the fine grain structure with an average grain size of 4 ± 0.2 µm and without any weld defects. The average concentration of Mg is 2.8%; Mn, 0.2%; Zr, 0.1%; Sc, 0.15%; and Ti, 2.1% were formed in the weld. The ultimate tensile strength (UTS) of the welded alloy with AlTiB was 260 MPa, which was equal to the base metal in the as-cast condition. The UTS was increased by 60 MPa after annealing at 370 °C for 6 h that was 85% of UTS of the base alloy. Full article
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Open AccessArticle Friction Stir Welding of near α and α + β Titanium Alloys: Metallurgical and Mechanical Characterization
Metals 2017, 7(12), 565; doi:10.3390/met7120565
Received: 19 October 2017 / Revised: 11 December 2017 / Accepted: 11 December 2017 / Published: 14 December 2017
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Abstract
Butt welds of friction stir welded dissimilar titanium alloys (near α: Ti-6242 standard grain (SG) and α+β; Ti-54M) were produced for varying processing parameters (rotation speed: rpm and traverse speed; mm·min−1). Microstructures, microhardness, and fractured surfaces were analyzed
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Butt welds of friction stir welded dissimilar titanium alloys (near α: Ti-6242 standard grain (SG) and α + β ; Ti-54M) were produced for varying processing parameters (rotation speed: rpm and traverse speed; mm·min−1). Microstructures, microhardness, and fractured surfaces were analyzed for three different rpms and mm·min−1 with Ti-6242 SG and Ti-54M kept on the advancing and retreating side, respectively. While constant traverse speed (varying rotation speed) has no significant effect on micrographic patterns in weld nugget, constant rotation speed (with increasing traverse speed) results in an increasing number of streaks with specified spacing (advances per revolution) (consisting of material migrating from retreating side) on the advancing side. Although, hardness variation within streaks (due to lower values of v ω ; where v   and   ω are traverse and rotation speed) were challenging to evaluate, yet hardness maps imitated the micrographic morphology of the weld nugget. For varying rotation (225–325 rpm) and traverse speed (100–150 mm·min−1), corresponding microstructure evolutions on the advancing and retreating side were related, with variations in evolving temperatures for corresponding welding parameters. Fractured surfaces revealed an appearance of a combination of transcrystalline and intercrystalline fracture for all the processing parameters. Nature of solid state joining has been shown with a distinct boundary between Ti-6242 SG and Ti-54M, demonstrating the interlocking between streaks of different aspect ratios of these two alloys. Full article
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Open AccessArticle Antibacterial Properties and Corrosion Resistance of the Newly Developed Biomaterial, Ti–12Nb–1Ag Alloy
Metals 2017, 7(12), 566; doi:10.3390/met7120566
Received: 3 October 2017 / Revised: 30 November 2017 / Accepted: 11 December 2017 / Published: 15 December 2017
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Abstract
Currently, the development of biomaterials has focused on having a low Young’s modulus, biocompatibility, corrosion resistance, and antibacterial properties. Ti–Nb alloys have higher research value due to their excellent corrosion resistance and low Young’s modulus. In recent years, the antibacterial properties of materials
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Currently, the development of biomaterials has focused on having a low Young’s modulus, biocompatibility, corrosion resistance, and antibacterial properties. Ti–Nb alloys have higher research value due to their excellent corrosion resistance and low Young’s modulus. In recent years, the antibacterial properties of materials have been enhanced by the addition of Ag and Cu. Therefore, the corrosion resistance and antibacterial properties of the Ti–12Nb–1Ag alloy formulated in the current study were investigated and compared to those of commonly used Ti alloys, G2 pure Ti (ASTM B348 CP Grade 2), and Ti–6Al–4V, via electrochemical and E. coli antibacterial tests. Meanwhile, we also carried out a microstructural analysis to investigate the composition of the alloy. The results were as follows: (1) The electrochemical test demonstrated that Ti–12Nb–1Ag had a higher corrosion resistance than Ti–6Al–4V, which is similar to the properties of pure Ti. (2) The E. coli antibacterial test demonstrated that the sterilization rate of Ti–12Nb–1Ag was higher than that of the Ti–6Al–4V alloy and pure Ti. (3) The microstructural analysis revealed that Ti–12Nb–1Ag had an acicular martensite structure, with nano-Ag precipitates observed. Based on the results of the E. coli antibacterial test and the principles of sterilization of nano-precipitates and Ag, we inferred that the nano-Ag precipitates of Ti–12Nb–1Ag enhanced the antibacterial properties of the newly developed biomaterial, which is, namely, the Ti–12Nb–1Ag alloy. Full article
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Open AccessArticle Microstructure Analysis of Neutron Absorber Al/B4C Metal Matrix Composites
Metals 2017, 7(12), 567; doi:10.3390/met7120567
Received: 4 November 2017 / Revised: 2 December 2017 / Accepted: 13 December 2017 / Published: 15 December 2017
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Abstract
The microstructure of Al/B4C metal matrix composites (MMCs) used as neutron absorbers in both dry storage casks and wet storage pools of spent nuclear fuel was analyzed by SEM and TEM. A polishing method of a focused Ga+ ion beam
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The microstructure of Al/B4C metal matrix composites (MMCs) used as neutron absorbers in both dry storage casks and wet storage pools of spent nuclear fuel was analyzed by SEM and TEM. A polishing method of a focused Ga+ ion beam was used to obtain an ideal sample surface with very low roughness, which was used to statistically analyze the distribution characteristics and size factor of B4C particles in the aluminum matrix. The area of B4C particles mainly ranged from 0 to 0.5 μm2, which was the proportion of 64.29%, 86.99% and 76.86% of total statistical results for the Al-15%B4C, Al-25%B4C and Al-30%B4C MMCs, respectively. The average area of B4C particles in the Al-15%B4C, Al-25%B4C and Al-30%B4C MMCs were about 1.396, 0.528 and 1.183 μm2, respectively. The nanoscale precipitates were analyzed by the element mappings in scanning transmission electron microscopy (STEM) mode and electron energy loss spectroscopy (EELS) mode, which included elliptic alloy precipitates with elemental Cu, Cr, Fe and Si, except for Al, and B4C nanoparticles with polygonal shape. The interface characteristics showed that the (021) crystal plane of B4C particle and (111) crystal plane of aluminum matrix grew together. The lattice misfit was about 1.68% for (111)Al//(021)B4C. The corrosion properties and corresponding mechanism of Al/B4C MMCs were investigated in an aqueous solution with 5000 ppm boric acid at 100 °C and atmospheric pressure, which showed that the mass increment rate was first decreased with increasing corrosion time and then increased. Full article
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Open AccessArticle Modelling of the Superplastic Deformation of the Near-α Titanium Alloy (Ti-2.5Al-1.8Mn) Using Arrhenius-Type Constitutive Model and Artificial Neural Network
Metals 2017, 7(12), 568; doi:10.3390/met7120568
Received: 10 November 2017 / Revised: 8 December 2017 / Accepted: 11 December 2017 / Published: 15 December 2017
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Abstract
The paper focuses on developing constitutive models for superplastic deformation behaviour of near-α titanium alloy (Ti-2.5Al-1.8Mn) at elevated temperatures in a range from 840 to 890 °C and in a strain rate range from 2 × 10−4 to 8 × 10
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The paper focuses on developing constitutive models for superplastic deformation behaviour of near-α titanium alloy (Ti-2.5Al-1.8Mn) at elevated temperatures in a range from 840 to 890 °C and in a strain rate range from 2 × 10−4 to 8 × 10−4 s−1. Stress–strain experimental tensile tests data were used to develop the mathematical models. Both, hyperbolic sine Arrhenius-type constitutive model and artificial neural-network model were constructed. A comparative study on the competence of the developed models to predict the superplastic deformation behaviour of this alloy was made. The fitting results suggest that the artificial neural-network model has higher accuracy and is more efficient in fitting the superplastic deformation flow behaviour of near-α Titanium alloy (Ti-2.5Al-1.8Mn) at superplastic forming than the Arrhenius-type constitutive model. However, the tested results revealed that the error for the artificial neural-network is higher than the case of Arrhenius-type constitutive model for predicting the unmodelled conditions. Full article
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Open AccessFeature PaperArticle An Experimental Evaluation of Electron Beam Welded Thixoformed 7075 Aluminum Alloy Plate Material
Metals 2017, 7(12), 569; doi:10.3390/met7120569
Received: 8 November 2017 / Revised: 12 December 2017 / Accepted: 13 December 2017 / Published: 15 December 2017
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Abstract
Two plates of thixoformed 7075 aluminum alloy were joined using Electron Beam Welding (EBW). A post-welding-heat treatment (PWHT) was performed within the semi-solid temperature range of this alloy at three temperatures, 610, 617 and 628 °C, for 3 min. The microstructural evolution and
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Two plates of thixoformed 7075 aluminum alloy were joined using Electron Beam Welding (EBW). A post-welding-heat treatment (PWHT) was performed within the semi-solid temperature range of this alloy at three temperatures, 610, 617 and 628 °C, for 3 min. The microstructural evolution and mechanical properties of EB welded plates, as well as the heat-treated specimens, were investigated in the Base Metal (BM), Heat Affected Zone (HAZ), and Fusion Zone (FZ), using optical microscopy, Scanning Electron Microscopy (SEM), EDX (Energy Dispersive X-ray Analysis), and Vickers hardness test. Results indicated that after EBW, the grain size substantially decreased from 67 µm in both BM and HAZ to 7 µm in the FZ, and a hardness increment was observed in the FZ as compared to the BM and HAZ. Furthermore, the PWHT led to grain coarsening throughout the material, along with a further increase in hardness in the FZ. Full article
(This article belongs to the Special Issue Semi-solid Processing of Alloys and Composites)
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Open AccessArticle Mechanical Alloying as an Effective Way to Achieve Superior Properties of Fe–Co–Ni Binder Alloy
Metals 2017, 7(12), 570; doi:10.3390/met7120570
Received: 22 November 2017 / Revised: 8 December 2017 / Accepted: 11 December 2017 / Published: 17 December 2017
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Abstract
This study addresses the fabrication of nanocrystalline Fe–Co–Ni alloy using two operations: mechanical alloying (MA) of elemental powders and hot pressing (HP). The evolution of the phase composition and structure of the powder particles after MA was investigated. Ball milling with rotation speed
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This study addresses the fabrication of nanocrystalline Fe–Co–Ni alloy using two operations: mechanical alloying (MA) of elemental powders and hot pressing (HP). The evolution of the phase composition and structure of the powder particles after MA was investigated. Ball milling with rotation speed 700 rpm for 15–20 min allows the production of a bcc Fe-based supersaturated solid solution. During the HP of this powder, this solution decomposes into a bcc (Fe) solid solution and fcc Fe3Ni precipitates, which act as a recrystallization barrier at elevated temperatures. This factor, along with the solid solution strengthening of the (α–Fe) matrix and high concentration of lattice defects (dislocations and twins), provides high mechanical properties (ultimate bending strength of 2000 MPa and hardness of 108 HRB) and wear resistance of the alloy. The developed Fe–Co–Ni alloy is promising for use as a binder in diamond tools designed for machining abrasive materials. Full article
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Open AccessFeature PaperArticle Microstructure and Mechanical Properties of a High-Mn TWIP Steel Subjected to Cold Rolling and Annealing
Metals 2017, 7(12), 571; doi:10.3390/met7120571
Received: 20 November 2017 / Revised: 13 December 2017 / Accepted: 14 December 2017 / Published: 18 December 2017
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Abstract
The structure–property relationship was studied in an Fe-18Mn-0.6C-1.5Al steel subjected to cold rolling to various total reductions from 20% to 80% and subsequent annealing for 30 min at temperatures of 673 to 973 K. The cold rolling resulted in significant strengthening of the
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The structure–property relationship was studied in an Fe-18Mn-0.6C-1.5Al steel subjected to cold rolling to various total reductions from 20% to 80% and subsequent annealing for 30 min at temperatures of 673 to 973 K. The cold rolling resulted in significant strengthening of the steel. The hardness increased from 1900 to almost 6000 MPa after rolling reduction of 80%. Recovery of cold worked microstructure developed during annealing at temperatures of 673 and 773 K, resulting in slight softening, which did not exceed 0.2. On the other hand, static recrystallization readily developed in the cold rolled samples with total reductions above 20% during annealing at 873 and 973 K, leading to fractional softening of about 0.8. The recrystallized grain size depended on annealing temperature and rolling reduction; namely, it decreased with a decrease in the temperature and an increase in the rolling reduction. The mean recrystallized grain size from approximately 1 to 8 μm could be developed depending on the rolling/annealing conditions. The recovered and fine grained recrystallized steel samples were characterized by improved strength properties. The yield strength of the recovered, recrystallized, and partially recrystallized steel samples could be expressed by a unique relationship taking into account the fractional contributions from dislocation and grain size strengthening into overall strength. Full article
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Open AccessArticle Guidelines for Selecting Plugs Used in Thin-Walled Tube Drawing Processes of Metallic Alloys
Metals 2017, 7(12), 572; doi:10.3390/met7120572
Received: 18 November 2017 / Revised: 11 December 2017 / Accepted: 13 December 2017 / Published: 18 December 2017
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Abstract
In this paper, some practical guidelines to select the plug or set of plugs more adequate to carry out drawing processes of thin-walled tubes carried out with fixed conical inner plug are presented. For this purpose, the most relevant input parameters have been
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In this paper, some practical guidelines to select the plug or set of plugs more adequate to carry out drawing processes of thin-walled tubes carried out with fixed conical inner plug are presented. For this purpose, the most relevant input parameters have been considered in this study: the tube material, the most important geometrical parameters of the process (die semiangle, α , and cross-sectional area reduction, r ) and the friction conditions (Coulomb friction coefficients, μ 1 , between the die and the tube outer surface, and μ 2 , between the plug and the tube inner surface). Three work-hardening materials are analyzed: the annealed copper UNS C11000, the aluminum UNS A91100, and the stainless steel UNS S34000. The analysis is realized by means of the upper bound method (UBM), modelling the plastic deformation zone by triangular rigid zones (TRZ), under the validated assumption that the process occurs under plane strain conditions. The obtained results allow establishing, for each material, a group of geometrical parameters, friction conditions, a set of plugs that make possible to carry out the process under good conditions, and the optimum plug to carry out the process using the minimum amount of energy. The proposed model is validated by means of an own finite element analysis (FEA) carried out under different conditions and, in addition, by other finite element method (FEM) simulations and real experiments taken from other researchers found in the literature (called literature simulations and literature experimental results, respectively). As a main conclusion, it is possible to affirm that the plug that allows carrying out the process with minimum quantity of energy is cylindrical in most cases. Full article
(This article belongs to the Special Issue Metallic Materials and Manufacturing)
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Open AccessFeature PaperArticle Effect of Tungsten on Creep Behavior of 9%Cr–3%Co Martensitic Steels
Metals 2017, 7(12), 573; doi:10.3390/met7120573
Received: 20 November 2017 / Revised: 8 December 2017 / Accepted: 11 December 2017 / Published: 18 December 2017
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Abstract
The effect of increasing tungsten content from 2 to 3 wt % on the creep rupture strength of a 3 wt % Co-modified P92-type steel was studied. Creep tests were carried out at a temperature of 650 °C under applied stresses ranging from
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The effect of increasing tungsten content from 2 to 3 wt % on the creep rupture strength of a 3 wt % Co-modified P92-type steel was studied. Creep tests were carried out at a temperature of 650 °C under applied stresses ranging from 100 to 220 MPa with a step of 20 MPa. It was found that an increase in W content from 2 to 3 wt % resulted in a +15% and +14% increase in the creep rupture strength in the short-term region (up to 103 h) and long-term one (up to 104 h), respectively. On the other hand, in the long-term creep region, the effect of W on creep strength diminished with increasing rupture time, up to complete disappearance at 105 h, because of depletion of excess W from the solid solution in the form of precipitation of the Laves phase particles. An increase in W content led to the increased amount of Laves phase and rapid coarsening of these particles under long-term creep. The contribution of W to the enhancement of creep resistance has short-term character. Full article
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Open AccessFeature PaperArticle Coating of Tungsten Wire with Ni/Al Multilayers for Self-Healing Applications
Metals 2017, 7(12), 574; doi:10.3390/met7120574
Received: 3 October 2017 / Revised: 14 December 2017 / Accepted: 14 December 2017 / Published: 19 December 2017
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Abstract
Self-healing materials are able to partially or completely reverse the damage inflicted on them. The possibility of self-healing mechanical and chemical failures that occur during service will improve the lifetime and reliability of structural materials. For this purpose, two main steps must be
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Self-healing materials are able to partially or completely reverse the damage inflicted on them. The possibility of self-healing mechanical and chemical failures that occur during service will improve the lifetime and reliability of structural materials. For this purpose, two main steps must be considered: (i) detection, and (ii) repairing (healing) of cracks. The exothermic character of reactive multilayers has potential for self-healing applications, namely in the healing step. In this context, Ni(V)/Al multilayer thin films were deposited onto tungsten wires by magnetron sputtering from two targets. A detailed microstructural characterization was carried out by scanning and transmission electron microscopy after deposition, as well as after ignition by applying an electrical discharge. The as-deposited films presented an irregular layered structure with local defects not observed for flat substrates, although Ni- and Al-rich nanolayers could be distinguished. The as-reacted films were constituted by Al3Ni2 grains with Al3V phase at the grain boundaries. In order to use reactive multilayers for self-healing purposes, the heat released must be maximised by improving the microstructure of the nanolayered films. Nevertheless, after ignition, the Ni(V)/Al multilayer films deposited onto W wire underwent a self-sustained reaction, releasing heat. Full article
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Open AccessReview Collagen-Nanoparticles Composites for Wound Healing and Infection Control
Metals 2017, 7(12), 516; doi:10.3390/met7120516
Received: 7 October 2017 / Revised: 9 November 2017 / Accepted: 15 November 2017 / Published: 23 November 2017
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Abstract
Nowadays, the world is facing a serious crisis represented by the rapid emergence of resistant bacteria, which jeopardizes the efficacy of antibiotics. This crisis has been attributed to the overuse and misuse of antibiotics, as well as the cessation of new drug production
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Nowadays, the world is facing a serious crisis represented by the rapid emergence of resistant bacteria, which jeopardizes the efficacy of antibiotics. This crisis has been attributed to the overuse and misuse of antibiotics, as well as the cessation of new drug production by the pharmaceutical industry. Therefore, bacterial strains with resistance to multiple antibiotic classes have appeared, such as Staphylococcus aureus, Acinetobacter spp. and Pseudomonas aeruginosa. This review aims to provide an updated summary of the current approach to the treatment of infections due to resistant microorganisms, with a focus on the application of the antimicrobial effects of inorganic nanoparticles in combination with collagen to promote wound healing. In addition, the paper describes the current approaches in the field of functionalized collagen hydrogels capable of wound healing and inhibiting microbial biofilm production. Full article
(This article belongs to the Special Issue Metallic and Metal Oxide Nanoparticles: Novel Approaches)
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Open AccessReview A Review: Effect of Friction Stir Welding on Microstructure and Mechanical Properties of Magnesium Alloys
Metals 2017, 7(12), 524; doi:10.3390/met7120524
Received: 13 October 2017 / Revised: 25 November 2017 / Accepted: 22 November 2017 / Published: 25 November 2017
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Abstract
Friction stir welding (FSW) is well recognized as a very practical technology for joining magnesium alloys. Although, a large amount of progress have been made on the FSW of magnesium alloys, it should be emphasized that many challenges still remain in joining magnesium
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Friction stir welding (FSW) is well recognized as a very practical technology for joining magnesium alloys. Although, a large amount of progress have been made on the FSW of magnesium alloys, it should be emphasized that many challenges still remain in joining magnesium using FSW. In this article, we briefly review the background of friction stir welding of magnesium alloys, and then focus on the effects of the friction stir welding on the macrostructure, microstructure evolution, texture distribution, and the mechanical properties of the welding joints. The macro-defects in welds and their relationship to the welding parameters such as welding speed, rotation speed, and axial force were also discussed. The review concluded with some suggested methods improvement and future challenges related to FSW of magnesium alloys. The purpose of the present review paper is to fully understand the relationships between the microstructure and the properties, and then establish a global, state-of-the-art FSW of magnesium alloys. Full article
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Open AccessFeature PaperReview Magnetic Adsorbents for the Recovery of Precious Metals from Leach Solutions and Wastewater
Metals 2017, 7(12), 529; doi:10.3390/met7120529
Received: 15 September 2017 / Revised: 24 October 2017 / Accepted: 14 November 2017 / Published: 27 November 2017
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Abstract
Precious metals which include the platinum group, gold, and silver, play indispensable roles in high technology industries of the modern world due to their outstanding physical and chemical properties. As a result of diminishing availability of mineral sources, increasing demand, and environmental concerns,
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Precious metals which include the platinum group, gold, and silver, play indispensable roles in high technology industries of the modern world due to their outstanding physical and chemical properties. As a result of diminishing availability of mineral sources, increasing demand, and environmental concerns, the recovery of precious metals from both leaching and industrial waste solutions is becoming a very important technology. Magnetic solid phase extraction (MSPE) is a technique that has received substantial consideration in the separation and recovery of precious metals because of the many advantages it offers compared to conventional methods. This technique is based on the extraction of different analytes from solutions using solid adsorbents with magnetic properties. This review focuses on different types of magnetic adsorbents, the main procedures used for synthesis, characterization and their application in precious metals recovery based on recently published literatures. Full article
(This article belongs to the Special Issue Valuable Metal Recycling)
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Open AccessFeature PaperReview Predicting the Performance of Organic Corrosion Inhibitors
Metals 2017, 7(12), 553; doi:10.3390/met7120553
Received: 20 November 2017 / Revised: 4 December 2017 / Accepted: 5 December 2017 / Published: 8 December 2017
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Abstract
The withdrawal of effective but toxic corrosion inhibitors has provided an impetus for the discovery of new, benign organic compounds to fill that role. Concurrently, developments in the high-throughput synthesis of organic compounds, the establishment of large libraries of available chemicals, accelerated corrosion
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The withdrawal of effective but toxic corrosion inhibitors has provided an impetus for the discovery of new, benign organic compounds to fill that role. Concurrently, developments in the high-throughput synthesis of organic compounds, the establishment of large libraries of available chemicals, accelerated corrosion inhibition testing technologies, and the increased capability of machine learning methods have made discovery of new corrosion inhibitors much faster and cheaper than it used to be. We summarize these technical developments in the corrosion inhibition field and describe how data-driven machine learning methods can generate models linking molecular properties to corrosion inhibition that can be used to predict the performance of materials not yet synthesized or tested. We briefly summarize the literature on quantitative structure–property relationships models of small organic molecule corrosion inhibitors. The success of these models provides a paradigm for rapid discovery of novel, effective corrosion inhibitors for a range of metals and alloys in diverse environments. Full article
(This article belongs to the Special Issue Corrosion Inhibition)
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Open AccessReview Recovery of Gold from Pregnant Thiosulfate Solutions by the Resin Adsorption Technique
Metals 2017, 7(12), 555; doi:10.3390/met7120555
Received: 14 November 2017 / Revised: 4 December 2017 / Accepted: 6 December 2017 / Published: 12 December 2017
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Abstract
This review is devoted to an integrated evaluation of the current use and future development of the resin adsorption technique in gold recovery from pregnant thiosulfate solutions. Comparisons are firstly made with other recovery techniques, including precipitation, activated carbon adsorption, solvent extraction, electrowinning
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This review is devoted to an integrated evaluation of the current use and future development of the resin adsorption technique in gold recovery from pregnant thiosulfate solutions. Comparisons are firstly made with other recovery techniques, including precipitation, activated carbon adsorption, solvent extraction, electrowinning and mesoporous silica adsorption. A detailed discussion about the recent advances of the technique in gold recovery from pregnant thiosulfate solutions is then presented from the aspects of gold adsorption on the resins and gold-loaded resin elution, respectively. On the basis of summarizing the present research, the major limitations of the resin adsorption technique are eventually pointed out and future development will also be prospected. Full article
(This article belongs to the Special Issue Advances in Hydrometallurgy)
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Open AccessCorrection Correction: Škugor Rončević, I.; et al. Effective and Environmentally Friendly Nickel Coating on the Magnesium Alloy. Metals 2016, 6, 316
Metals 2017, 7(12), 554; doi:10.3390/met7120554
Received: 29 November 2017 / Revised: 29 November 2017 / Accepted: 30 November 2017 / Published: 8 December 2017
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Abstract
The following changes have been made to the published manuscript “Effective and Environmentally Friendly Nickel Coating on the Magnesium Alloy [...]
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