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Metals, Volume 8, Issue 4 (April 2018)

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Editorial

Jump to: Research, Review

Open AccessEditorial Light-Weight Aluminum-Based Alloys—From Fundamental Science to Engineering Applications
Metals 2018, 8(4), 260; https://doi.org/10.3390/met8040260
Received: 6 April 2018 / Revised: 10 April 2018 / Accepted: 10 April 2018 / Published: 11 April 2018
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Abstract
Academia and industry alike are faced with an ever-growing demand for energy-efficiency and reduced mass [...]
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Open AccessEditorial Advances in Plastic Forming of Metals
Metals 2018, 8(4), 272; https://doi.org/10.3390/met8040272
Received: 3 April 2018 / Revised: 6 April 2018 / Accepted: 6 April 2018 / Published: 16 April 2018
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(This article belongs to the Special Issue Advances in Plastic Forming of Metals)

Research

Jump to: Editorial, Review

Open AccessArticle Study on the Size Effects of H-Shaped Fusion Zone of Fiber Laser Welded AZ31 Joint
Metals 2018, 8(4), 198; https://doi.org/10.3390/met8040198
Received: 25 January 2018 / Revised: 4 March 2018 / Accepted: 15 March 2018 / Published: 21 March 2018
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Abstract
There are two kinds of typical cross-section profiles for the fusion zone (FZ) of a laser welded thin section joint, i.e., a V-shaped cross-section and an H-shaped cross-section. Previous researches indicated that tensile strength of the V-shaped joint was lower than that of
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There are two kinds of typical cross-section profiles for the fusion zone (FZ) of a laser welded thin section joint, i.e., a V-shaped cross-section and an H-shaped cross-section. Previous researches indicated that tensile strength of the V-shaped joint was lower than that of the H-shaped one due to the greater heterogeneity of strain distribution on the V-shaped joint during tensile process. In this work, impacts of the aspect ratio of FZ on the mechanical properties of laser welded thin section joints with an H-shaped cross-section profile were investigated. Welding conditions corresponding to two typical H-shaped joints (i.e., Wnarrower with a narrower FZ, and Wwider with a wider FZ) were decided through a laser welding orthogonal experimental plan. Then, the microstructure and properties of both joints were examined and compared. The results show that the tensile strength of joint Wnarrower and joint Wwider was about 72% and 80.9% that of the base metal, respectively. Both joints fractured in the FZ during tensile processes. The low-cycle fatigue life of the base metal, the joint Wnarrower and the joint Wwider were 3377.5 cycles, 2825 cycles and 3155.3 cycles, respectively. By using high-speed imaging, it was found that the fatigue crack of joint Wnarrower initiated and propagated inside the fusion zone, while the fatigue crack of the joint Wwider initiated at the edge of the base metal and propagated for a distance within the base metal before entering into the fusion zone. This work promoted our understanding about the influence of the weld bead shape on the properties of laser welded thin section joints. Full article
(This article belongs to the Special Issue Laser Welding)
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Open AccessArticle The Effect of Low-Quantity Cr Addition on the Corrosion Behaviour of Dual-Phase High Carbon Steel
Metals 2018, 8(4), 199; https://doi.org/10.3390/met8040199
Received: 1 March 2018 / Revised: 7 March 2018 / Accepted: 19 March 2018 / Published: 21 March 2018
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Abstract
Industrial application of high carbon low alloy steel with the dual-phase structure of martensite and austenite has increased drastically in recent years. Due to its excellent compression strength and its high abrasion resistance, this grade of steel has used as a high performance
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Industrial application of high carbon low alloy steel with the dual-phase structure of martensite and austenite has increased drastically in recent years. Due to its excellent compression strength and its high abrasion resistance, this grade of steel has used as a high performance cutting tool and in press machinery applications. By increasing the usage of more corrosive media in industrial practice and increasing the demand for reducing the production cost, it is crucial to understand the effect of the small addition of Cr on the corrosion behaviour of this grade of steel. In this study, this effect was investigated using Secondary Electron Microscopy (SEM) and in-situ Atomic Force Microscopy (AFM) in the sodium chloride solution. Also, the corrosion rate was measured using the Tafel polarisation curve. It has been found that the small addition of Cr increased the stability of retained austenite, thus improving its corrosion resistance and reducing its corrosion rate. This effect has been acquired through in-situ high resolution topography images in which the samples were submerged in a corrosive solution. It has been demonstrated that the corrosion rate was reduced when the stability of austenite enhanced. Full article
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Open AccessArticle Mechanical Properties and In Vitro Behavior of Additively Manufactured and Functionally Graded Ti6Al4V Porous Scaffolds
Metals 2018, 8(4), 200; https://doi.org/10.3390/met8040200
Received: 15 February 2018 / Revised: 16 March 2018 / Accepted: 19 March 2018 / Published: 21 March 2018
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Abstract
Functionally graded lattice structures produced by additive manufacturing are promising for bone tissue engineering. Spatial variations in their porosity are reported to vary the stiffness and make it comparable to cortical or trabecular bone. However, the interplay between the mechanical properties and biological
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Functionally graded lattice structures produced by additive manufacturing are promising for bone tissue engineering. Spatial variations in their porosity are reported to vary the stiffness and make it comparable to cortical or trabecular bone. However, the interplay between the mechanical properties and biological response of functionally graded lattices is less clear. Here we show that by designing continuous gradient structures and studying their mechanical and biological properties simultaneously, orthopedic implant design can be improved and guidelines can be established. Our continuous gradient structures were generated by gradually changing the strut diameter of a body centered cubic (BCC) unit cell. This approach enables a smooth transition between unit cell layers and minimizes the effect of stress discontinuity within the scaffold. Scaffolds were fabricated using selective laser melting (SLM) and underwent mechanical and in vitro biological testing. Our results indicate that optimal gradient structures should possess small pores in their core (~900 µm) to increase their mechanical strength whilst large pores (~1100 µm) should be utilized in their outer surface to enhance cell penetration and proliferation. We suggest this approach could be widely used in the design of orthopedic implants to maximize both the mechanical and biological properties of the implant. Full article
(This article belongs to the Special Issue Titanium Alloys for Biomedical Implants and Devices)
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Open AccessArticle Effects of Grain Boundary Microconstituents on Heat-Affected Zone Cracks in a Mar-M004 Weldment
Metals 2018, 8(4), 201; https://doi.org/10.3390/met8040201
Received: 26 February 2018 / Revised: 19 March 2018 / Accepted: 19 March 2018 / Published: 21 March 2018
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Abstract
Repair-welding of a cast Mar-M004 superalloy by gas tungsten arc welding was performed. Liquation cracks of the heat-affected zone (HAZ) in a Mar-M004 weldment were closely related to the presence of low-melting constituents along the solidified boundaries in the weld. The metal carbides
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Repair-welding of a cast Mar-M004 superalloy by gas tungsten arc welding was performed. Liquation cracks of the heat-affected zone (HAZ) in a Mar-M004 weldment were closely related to the presence of low-melting constituents along the solidified boundaries in the weld. The metal carbides (MC), M3B2 and M5B3 borides, Ni7(Hf,Zr)2 intermetallic compounds, and γ-γ′colonies were found at the interdendritic boundaries. Fine boride precipitates mixed with intermetallic compounds in lamellar form were more likely to liquate during repair-welding. The melting of borides and intermetallic compounds in 1180 °C/4 h treated samples confirmed the poor weldability of the Mar-M004 superalloy due to enhanced liquation cracking. In addition to boride formation, fractographs of liquation cracks revealed strong segregation of B element in carbides and intermetallics, which might further lower the solidus temperature of the repair weld. Full article
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Open AccessArticle Influence of Alloys Position, Rolling and Welding Directions on Properties of AA2024/AA7050 Dissimilar Butt Weld Obtained by Friction Stir Welding
Metals 2018, 8(4), 202; https://doi.org/10.3390/met8040202
Received: 26 February 2018 / Revised: 14 March 2018 / Accepted: 19 March 2018 / Published: 22 March 2018
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Abstract
Friction stir welding (FSW) was carried out for the butt joining of dissimilar AA2024-T3 and AA7050-T7651 aluminium alloys with 2-mm thicknesses. A comparison between the position and orientation of different materials was performed by varying the welding speed while keeping the rotational speed
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Friction stir welding (FSW) was carried out for the butt joining of dissimilar AA2024-T3 and AA7050-T7651 aluminium alloys with 2-mm thicknesses. A comparison between the position and orientation of different materials was performed by varying the welding speed while keeping the rotational speed constant. Through an analysis of the force and torque produced during welding and a simple analytical model, the results indicate that the heat input was reduced when the AA7050 alloy was located in the advancing side (AS) of the joint. The different material positions influenced the material transportation and the interface in the centre of the stir zone (SZ). The microhardness of both materials was lower when they were in the AS of the joint. The differences in the hardness values were reduced at higher welding speeds when the heat input was decreased. The mechanical performance increased when the lower strength alloy was located in the AS. The material orientation exhibited a small influence when the AA7050 alloy was in the AS and in general on the resulting microhardness for all the cases analysed. The tensile strength values were very similar for both orientations, but an increase in the yield strength could be measured when the materials were oriented in the transverse direction. Full article
(This article belongs to the Special Issue Friction Stir Welding and Processing in Alloy Manufacturing)
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Open AccessArticle Reduction Characteristics of Carbon-Containing REE–Nb–Fe Ore Pellets
Metals 2018, 8(4), 204; https://doi.org/10.3390/met8040204
Received: 29 December 2017 / Revised: 25 February 2018 / Accepted: 19 March 2018 / Published: 23 March 2018
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Abstract
To separate and recover the valuable metals from low-grade REE (rare earth elements)–Nb–Fe ore in China, the reduction characteristics of carbon-containing REE–Nb–Fe ore pellets, including mineral phase variation, reduction degree, and reaction kinetics, were observed based on thermogravimetry experiments. The results showed that
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To separate and recover the valuable metals from low-grade REE (rare earth elements)–Nb–Fe ore in China, the reduction characteristics of carbon-containing REE–Nb–Fe ore pellets, including mineral phase variation, reduction degree, and reaction kinetics, were observed based on thermogravimetry experiments. The results showed that the reduction and separation efficiency of valuable metals in the carbon-containing pellets were superior to the ones in the previous non-compact mixture. After the reduction roasting of the pellets at 1100 °C and a subsequent magnetic separation, the iron powder with a grade of 91.7 wt % was separated, and in magnetic separation tailings the grades of Nb2O5 and (REE)O were beneficiated to approximately twice the grades in the REE–Nb–Fe ore. The reaction rate of the reduction of the carbon-containing pellets was jointly controlled by the carbon gasification reaction and the diffusion of CO in the product layer with an activation energy of 139.26–152.40 kJ·mol−1. Corresponding measures were proposed to further improve the kinetics condition. Full article
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Open AccessArticle Modeling and Experimental Study of Ore-Carbon Briquette Reduction under CO–CO2 Atmosphere
Metals 2018, 8(4), 205; https://doi.org/10.3390/met8040205
Received: 26 February 2018 / Revised: 14 March 2018 / Accepted: 21 March 2018 / Published: 23 March 2018
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Abstract
Iron ore-carbon briquette is often used as the feed material in the production of sponge iron via coal-based direct reduction processes. In this article, an experimental and simulation study on the reduction behavior of a briquette that is made by hematite and devolatilized
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Iron ore-carbon briquette is often used as the feed material in the production of sponge iron via coal-based direct reduction processes. In this article, an experimental and simulation study on the reduction behavior of a briquette that is made by hematite and devolatilized biochar fines under CO–CO2 atmosphere was carried out. The reaction model was validated against the corresponding experimental measurements and observations. Modeling predictions and experimental results indicated that the CO–CO2 atmosphere significantly influences the final reduction degree of the briquette. Increasing the reduction temperature did not increase the final reduction degree but was shown to increase the carbon that was consumed by the oxidative atmosphere. The influence of the CO–CO2 atmosphere on the briquette reduction behavior was found to be insignificant in the early stage but became considerable in the later stage; near the time of the briquette reaching its maximum reduction degree, both iron oxide reduction and metallic iron re-oxidation were able to occur. Full article
(This article belongs to the Special Issue Ironmaking and Steelmaking)
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Open AccessArticle Volatilization Behavior of β-Type Ti-Mo Alloy Manufactured by Electron Beam Melting
Metals 2018, 8(4), 206; https://doi.org/10.3390/met8040206
Received: 18 January 2018 / Revised: 14 March 2018 / Accepted: 19 March 2018 / Published: 23 March 2018
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Abstract
The effects of electron beam melting parameters on the volatilization behavior of elements and the microstructures of ingots were investigated on a β-type Ti-Mo binary alloy. The microstructures of the ingots consisted of large and columnar grains at their bottom and top sections,
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The effects of electron beam melting parameters on the volatilization behavior of elements and the microstructures of ingots were investigated on a β-type Ti-Mo binary alloy. The microstructures of the ingots consisted of large and columnar grains at their bottom and top sections, respectively, and they were similar at different melting powers, from 10.5 kW to 15.0 kW, and the melting time ranging from 10 min to 40 min, without apparent metallurgical defects. Mass losses of ingots exhibited an increasing tendency, with increases of both melting power and melting time. Combined with a theoretical calculation and X-ray fluorescence results, Ti was identified as the main volatilization element due to its much higher vapor pressure than that of the Mo element. The considerable compensation method of the volatile Ti element was established in terms of theoretical and experimental results, which could provide a guidance for fabricating composition-controllable Ti-Mo binary alloys via electron beam melting technology. Full article
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Open AccessArticle Mechanical Property Testing of Hydrogenated Zirconium Irradiated with Electrons
Metals 2018, 8(4), 207; https://doi.org/10.3390/met8040207
Received: 22 February 2018 / Revised: 17 March 2018 / Accepted: 20 March 2018 / Published: 23 March 2018
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Abstract
The mechanical properties of the hydrogenated zirconium alloy Zr-1Nb are studied under different conditions for hydrogen removal by an electron beam and thermal heating. The mechanical testing of zirconium samples is analyzed during hydrogenation and irradiation with a low energy electron beam. The
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The mechanical properties of the hydrogenated zirconium alloy Zr-1Nb are studied under different conditions for hydrogen removal by an electron beam and thermal heating. The mechanical testing of zirconium samples is analyzed during hydrogenation and irradiation with a low energy electron beam. The plasticity of the samples is shown to be increased during the radiation stimulation of hydrogen removal from zirconium by even a weak electron beam. In this case, the tensile strength (ultimate strength) is practically not changed. Full article
(This article belongs to the Special Issue Radiation Effects in Metals)
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Open AccessArticle Friction Stir Welding of Non-Heat-Treatable High-Strength Alloy 5083-O
Metals 2018, 8(4), 208; https://doi.org/10.3390/met8040208
Received: 28 February 2018 / Revised: 20 March 2018 / Accepted: 20 March 2018 / Published: 23 March 2018
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Abstract
5083 aluminum alloy is increasingly used because of its excellent corrosion resistance, high work-hardening rate, and strength. In order to improve its weldability and feasibility, material behavior, material flow, and defects induced while friction stir welding 5083 should be studied. In this study,
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5083 aluminum alloy is increasingly used because of its excellent corrosion resistance, high work-hardening rate, and strength. In order to improve its weldability and feasibility, material behavior, material flow, and defects induced while friction stir welding 5083 should be studied. In this study, they were investigated by thermo-structural analysis. The flow stress of 5083-O has a high rate of sensitivity among high temperatures and wide strain rate ranges. Therefore, the details of the mechanical properties of 5083-O at high temperatures and wide strain rate ranges were investigated to obtain reasonable analysis results using a precise flow stress model. The tool/workpiece interface temperature during FSW is critical for accurate analysis results. This study used special equipment to measure tool temperature in order to investigate the interface temperatures precisely, and then the obtained data were used for optimization and verification of the thermal boundary conditions for analysis modeling. Using the developed model, the material behavior and material flow during FSW of 5083-O were analyzed. The tool and workpiece interface temperatures, flow stresses, strain rates, and velocities were investigated with the cylinder and threaded probes in detail. One of the analysis results indicated that the material flow rate on the rear side of a probe directly affected defect generation while joining. Full article
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Open AccessArticle Effect of Segregation and Surface Condition on Corrosion of Rheo-HPDC Al–Si Alloys
Metals 2018, 8(4), 209; https://doi.org/10.3390/met8040209
Received: 22 February 2018 / Revised: 21 March 2018 / Accepted: 23 March 2018 / Published: 24 March 2018
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Abstract
Corrosion properties of two Al–Si alloys processed by Rheo-high pressure die cast (HPDC) method were examined using polarization and electrochemical impedance spectroscopy (EIS) techniques on as-cast and ground surfaces. The effects of the silicon content, transverse and longitudinal macrosegregation on the corrosion resistance
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Corrosion properties of two Al–Si alloys processed by Rheo-high pressure die cast (HPDC) method were examined using polarization and electrochemical impedance spectroscopy (EIS) techniques on as-cast and ground surfaces. The effects of the silicon content, transverse and longitudinal macrosegregation on the corrosion resistance of the alloys were determined. Microstructural studies revealed that samples from different positions contain different fractions of solid and liquid parts of the initial slurry. Electrochemical behavior of as-cast, ground surface, and bulk material was shown to be different due to the presence of a segregated skin layer and surface quality. Full article
(This article belongs to the Special Issue Semi-solid Processing of Alloys and Composites)
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Open AccessArticle Rotating Bending Fatigue Microscopic Fracture Characteristics and Life Prediction of 7075-T7351 Al Alloy
Metals 2018, 8(4), 210; https://doi.org/10.3390/met8040210
Received: 3 February 2018 / Revised: 16 March 2018 / Accepted: 18 March 2018 / Published: 25 March 2018
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Abstract
Rotating bending fatigue tests were carried out by using the 7075-T7351 Al alloy with a microarc oxidation (MAO) coating (h = 10 μm) and with no coating. Tests were conducted in air and 5.0% NaCl aqueous solution conditions. The fatigue microscopic fracture
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Rotating bending fatigue tests were carried out by using the 7075-T7351 Al alloy with a microarc oxidation (MAO) coating (h = 10 μm) and with no coating. Tests were conducted in air and 5.0% NaCl aqueous solution conditions. The fatigue microscopic fracture behavior of the metals was investigated by using scanning electron microscope and three-dimensional digital microscope technologies. The empirical formulas between the stress intensity factor ΔK and the fatigue life Nf in the different conditions were obtained. In addition, the reason for data scattering in the fatigue lives of uncoated 7075-T7351 samples under the same stress amplitude in air was analyzed. Furthermore, the fatigue characteristic life of 7075-T7351 alloy was predicted by the three-parameter Weibull distribution model. Full article
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Open AccessArticle Experimental Investigation of Laser Ablation Characteristics on Nickel-Coated Beryllium Copper
Metals 2018, 8(4), 211; https://doi.org/10.3390/met8040211
Received: 26 February 2018 / Revised: 16 March 2018 / Accepted: 22 March 2018 / Published: 25 March 2018
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Abstract
As electronic products are miniaturized, the components of the spring contact probe are made very fine. Current mechanical processing may make it difficult to perform micro-machining with a high degree of precision. A laser is often used for the high precision micro-machining due
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As electronic products are miniaturized, the components of the spring contact probe are made very fine. Current mechanical processing may make it difficult to perform micro-machining with a high degree of precision. A laser is often used for the high precision micro-machining due to its advantages such as a contact-free process, high energy concentration, fast processing time, and applicability to almost every material. The production of micro-electronics using nickel-coated copper is rapidly increasing and laser material processing is becoming a key processing technology owing to high precision requirements. Before applying laser material processing, it is necessary to understand the ablation characteristics of the materials. Therefore, this study systematically investigates the ablation characteristics of nickel-coated beryllium copper. Key laser parameters are pulse duration (4~200 ns) and the total accumulated energy (1~1000 mJ). The processed workpiece is evaluated by analyzing the heat affected zone (HAZ), material removal zone (MRZ), and roundness. Moreover, the surface characteristics such as a burr, spatter, and roundness shapes are analyzed using scanning electron microscope (SEM). Full article
(This article belongs to the Special Issue Metallic Materials and Manufacturing)
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Open AccessArticle Mean Stress Effect on the Axial Fatigue Strength of DIN 34CrNiMo6 Quenched and Tempered Steel
Metals 2018, 8(4), 213; https://doi.org/10.3390/met8040213
Received: 19 February 2018 / Revised: 19 March 2018 / Accepted: 22 March 2018 / Published: 26 March 2018
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Abstract
The present study consists of a theoretical and experimental investigation of the effect of axial mean stresses on the high cycle fatigue behaviour of DIN 34CrNiMo6 high strength steel in quenched and tempered conditions. The axial S-N curves under 4 different
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The present study consists of a theoretical and experimental investigation of the effect of axial mean stresses on the high cycle fatigue behaviour of DIN 34CrNiMo6 high strength steel in quenched and tempered conditions. The axial S-N curves under 4 different stresses ratios were obtained. Experimental results show that increasing the value of the tension mean stresses gradually reduces the axial stress amplitude the material can withstand without failure. Moreover, the compressive mean stresses show a beneficial effect in terms of the axial fatigue strength, resulting in a non-symmetrical Haigh diagram. A historic review of the axial mean stress effect is presented, showing the shape of the Haigh diagrams for ductile metals and presenting the most-known empirical and physical theories. The results for this steel are compared with the physical theories of Findley based on the critical plane; the Froustey’s and Marin’s methods, based on energetic theories; and the Crossland invariants method based on the Gough’s theory of fatigue damage. Taking into account the experimental results, a physical fatigue function based on energetic considerations is proposed. Its application to the fatigue case with mean stresses can be interpreted in terms of a balance of elastic energies of distortion and volume change. Macro-analyses of specimen fracture appearance were conducted in order to obtain the fracture characteristics for different mean stress values. Full article
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Open AccessArticle Numerical Analysis of Stress Gradient and Traps Effects on Carbon Diffusion in AISI 316L during Low Temperature Gas Phase Carburization
Metals 2018, 8(4), 214; https://doi.org/10.3390/met8040214
Received: 14 March 2018 / Revised: 15 March 2018 / Accepted: 21 March 2018 / Published: 26 March 2018
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Abstract
In order to elucidate the roles of the composition-induced stress gradient and the traps formed by chromium atoms in carbon diffusion in AISI 316L austenitic stainless steel during low temperature gas phase carburization, the carbon concentration-depth profiles were analyzed by a diffusion model
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In order to elucidate the roles of the composition-induced stress gradient and the traps formed by chromium atoms in carbon diffusion in AISI 316L austenitic stainless steel during low temperature gas phase carburization, the carbon concentration-depth profiles were analyzed by a diffusion model considering the composition-induced stress gradient and the trapping effect. The results show that the carbon concentration-depth profiles calculated by this model show good agreement with the experimental results. The composition-induced compressive stress gradient can enhance the carbon diffusion but reduce the surface carbon concentration; these effects are not pronounced. Carbon atoms prefer to occupy the trap sites, and the detrapping activation energy (Qt = 33 kJ·mol−1) was deduced from fitting the experimental carbon concentration-depth profile. Furthermore, this applied diffusion model can be used to interpret the enhanced carbon diffusion in low temperature carburized AISI 316L. Full article
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Open AccessArticle Hybrid Reinforced Magnesium Matrix Composites (Mg/Sic/GNPs): Drilling Investigation
Metals 2018, 8(4), 215; https://doi.org/10.3390/met8040215
Received: 6 January 2018 / Revised: 19 March 2018 / Accepted: 23 March 2018 / Published: 27 March 2018
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Abstract
The machinability of graphene-reinforced magnesium-based hybrid nanocomposites produced through the application of powder metallurgy method has not been completely reported. This article presents an experimental investigation on the thrust force, the surface roughness (Ra), and drilled surfaces characteristics in the drilling
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The machinability of graphene-reinforced magnesium-based hybrid nanocomposites produced through the application of powder metallurgy method has not been completely reported. This article presents an experimental investigation on the thrust force, the surface roughness (Ra), and drilled surfaces characteristics in the drilling process of a Mg/SiC/GNPs (magnesium matrix based silicon carbide and graphene nanoplatelets) hybrid magnesium matrix composite. The hybrid composite material was produced through the application of a powder metallurgy method. The experiments were carried out with uncoated, PVD (Physical Vapor Deposition), and CVD (Chemical Vapor Deposition) coated tungsten carbide drill bits at three levels of cutting speeds (30, 40, and 50 m/min), and three different levels of feed rate (0.10, 0.15, and 0.20 mm/rev) under dry machining conditions. Taguchi’s L27 (33) orthogonal array and S/N ratio were used to optimize the optimal parameters for thrust force and surface roughness. The experimental results indicated that the thrust force and the surface roughness were extremely dependent on a particular type of drill bits, feed rate, and cutting speed. The feed rate parameter is known to have a significant influence on the surface finish. Full article
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Open AccessArticle Hot Deformation Behavior and Processing Map of Mg-3Sn-2Ca-0.4Al-0.4Zn Alloy
Metals 2018, 8(4), 216; https://doi.org/10.3390/met8040216
Received: 11 January 2018 / Revised: 20 March 2018 / Accepted: 21 March 2018 / Published: 27 March 2018
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Abstract
Among newly developed TX (Mg-Sn-Ca) alloys, TX32 alloy strikes a good balance between ductility, corrosion, and creep properties. This study reports the influence of aluminum and zinc additions (0.4 wt % each) to TX32 alloy on its strength and deformation behavior. Uniaxial compression
[...] Read more.
Among newly developed TX (Mg-Sn-Ca) alloys, TX32 alloy strikes a good balance between ductility, corrosion, and creep properties. This study reports the influence of aluminum and zinc additions (0.4 wt % each) to TX32 alloy on its strength and deformation behavior. Uniaxial compression tests were performed under various strain rates and temperature conditions in the ranges of 0.0003–10 s−1 and 300–500 °C, respectively. A processing map was developed for TXAZ3200 alloy, and it exhibits three domains that enable good hot workability in the ranges (1) 300–340 °C/0.0003–0.001 s−1; (2) 400–480 °C/0.01–1 s−1; and (3) 350–500 °C/0.0003–0.01 s−1. The occurrence of dynamic recrystallization in these domains was confirmed from the microstructural observations. The estimated apparent activation energy in Domains 2 and 3 (219 and 245 kJ/mole) is higher than the value of self-diffusion in magnesium. This is due to the formation of intermetallic phases in the matrix that generates back stress. The strength of TXAZ3200 alloy improved up to 150 °C as compared to TX32 alloy, suggesting solid solution strengthening due to Al and Zn. Also, the hot deformation behavior of TXAZ3200 alloy was compared in the form of processing maps with TX32, TX32-0.4Al, TX32-0.4Zn, and TX32-1Al-1Zn alloys. Full article
(This article belongs to the Special Issue Metallic Materials and Manufacturing)
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Open AccessArticle Influence of Heat Treatment on Microstructures and Mechanical Properties of NiCuCrMoTiAlNb Nickel-Based Alloy
Metals 2018, 8(4), 217; https://doi.org/10.3390/met8040217
Received: 18 January 2018 / Revised: 16 March 2018 / Accepted: 20 March 2018 / Published: 27 March 2018
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Abstract
As-cast NiCuCrMoTiAlNb nickel-based alloys were subjected to two-stage heat treatment, including solution treatment and subsequent aging treatment. Furthermore, the influence of heat treatment on microstructures and mechanical properties of NiCuCrMoTiAlNb nickel-based alloys was further investigated. The as-cast NiCuCrMoTiAlNb Ni-based alloys are able to
[...] Read more.
As-cast NiCuCrMoTiAlNb nickel-based alloys were subjected to two-stage heat treatment, including solution treatment and subsequent aging treatment. Furthermore, the influence of heat treatment on microstructures and mechanical properties of NiCuCrMoTiAlNb nickel-based alloys was further investigated. The as-cast NiCuCrMoTiAlNb Ni-based alloys are able to experience large plastic deformation at room temperature, where nanocrystalline phases are induced. In the case of heat-treated NiCuCrMoTiAlNb nickel-based alloys, with increasing Nb content, plenty of Ni3(Al, Ti) precipitates (γ′ phases) are distributed in the γ matrix and they are able to become the obstacles to impede the movement of dislocations, which is responsible for increasing the yield strength of NiCuCrMoTiAlNb nickel-based alloys. Pile-up of dislocations in the vicinity of γ′ precipitates adversely influences plasticity of NiCuCrMoTiAlNb nickel-based alloys. Full article
(This article belongs to the Special Issue Non-Ferrous Metallic Materials)
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Open AccessArticle Surface Analysis of Uncoated and PVD Coated Punch at the Hole-Flanging Process
Metals 2018, 8(4), 218; https://doi.org/10.3390/met8040218
Received: 19 February 2018 / Revised: 23 March 2018 / Accepted: 26 March 2018 / Published: 27 March 2018
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Abstract
This paper researches the surface condition and wear on the hole-flanging punch when producing a flanged Ø7 mm hole in a steel strip S355J2 + N (1.0577) with a thickness of 3 mm. The hole was flanged by a punch with a defined
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This paper researches the surface condition and wear on the hole-flanging punch when producing a flanged Ø7 mm hole in a steel strip S355J2 + N (1.0577) with a thickness of 3 mm. The hole was flanged by a punch with a defined geometry known as a tangent ogive and described via a caliber radius head (CRH) ratio. During the process, wear of the punch made of hardened tool steel 1.3343 appeared after 20,000 strokes. Thus, a multipurpose coating TiCN-MP deposited via Lateral Rotating Arc-Cathode technology was applied on the punch to extend the punch lifetime. The coated punch was polished to remove droplets after deposition process. By applying TiCN-MP coating, 120,000 strokes were applied to reach the same wear as for the uncoated tool steel. The surface of the punch made of the hardened tool steel for uncoated and PVD coated conditions was researched by scanning electron microscopy after wear, and an energy dispersive X-ray (EDX) analysis was done to identify components of bonded material. In addition, the normal pressure on the punch active surface was studied via a numerical simulation of the hole-flanging process. The position of the high normal pressure is well correlated to the position of the adhesive wear for the uncoated and coated punches. Full article
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Open AccessArticle Linking Ab Initio Data on Hydrogen and Carbon in Steel to Statistical and Continuum Descriptions
Metals 2018, 8(4), 219; https://doi.org/10.3390/met8040219
Received: 28 February 2018 / Revised: 23 March 2018 / Accepted: 23 March 2018 / Published: 27 March 2018
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Abstract
We present a selection of scale transfer approaches from the electronic to the continuum regime for topics relevant to hydrogen embrittlement. With a focus on grain boundary related hydrogen embrittlement, we discuss the scale transfer for the dependence of the carbon solution behavior
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We present a selection of scale transfer approaches from the electronic to the continuum regime for topics relevant to hydrogen embrittlement. With a focus on grain boundary related hydrogen embrittlement, we discuss the scale transfer for the dependence of the carbon solution behavior in steel on elastic effects and the hydrogen solution in austenitic bulk regions depending on Al content. We introduce an approximative scheme to estimate grain boundary energies for varying carbon and hydrogen population. We employ this approach for a discussion of the suppressing influence of Al on the substitution of carbon with hydrogen at grain boundaries, which is an assumed mechanism for grain boundary hydrogen embrittlement. Finally, we discuss the dependence of hydride formation on the grain boundary stiffness. Full article
(This article belongs to the Special Issue First-Principles Approaches to Metals, Alloys, and Metallic Compounds)
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Open AccessArticle An Investigation of the Microstructure and Fatigue Behavior of Additively Manufactured AISI 316L Stainless Steel with Regard to the Influence of Heat Treatment
Metals 2018, 8(4), 220; https://doi.org/10.3390/met8040220
Received: 23 February 2018 / Revised: 22 March 2018 / Accepted: 23 March 2018 / Published: 28 March 2018
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Abstract
To exploit the whole potential of Additive Manufacturing, it is essential to investigate the complex relationships between Additive Manufacturing processes, the resulting microstructure, and mechanical properties of the materials and components. In the present work, Selective Laser Melted (SLM) (process category: powder bed
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To exploit the whole potential of Additive Manufacturing, it is essential to investigate the complex relationships between Additive Manufacturing processes, the resulting microstructure, and mechanical properties of the materials and components. In the present work, Selective Laser Melted (SLM) (process category: powder bed fusion), Laser Deposition Welded (LDW) (process category: direct energy deposition) and, for comparison, Continuous Casted and then hot and cold drawn (CC) austenitic stainless steel AISI 316L blanks were investigated with regard to their microstructure and mechanical properties. To exclude the influence of surface topography and focus the investigation on the volume microstructure, the blanks were turned into final geometry of specimens. The additively manufactured (AM-) blanks were manufactured in both the horizontal and vertical building directions. In the horizontally built specimens, the layer planes are perpendicular and in vertical building direction, they are parallel to the load axis of the specimens. The materials from different manufacturing processes exhibit different chemical composition and hence, austenite stability. Additionally, all types of blanks were heat treated (2 h, 1070 °C, H2O) and the influence of the heat treatment on the properties of differently manufactured materials were investigated. From the cyclic deformation curves obtained in the load increase tests, the anisotropic fatigue behavior of the AM-specimens could be detected with only one specimen in each building direction for the different Additive Manufacturing processes, which could be confirmed by constant amplitude tests. The results showed higher fatigue strength for horizontally built specimens compared to the vertical building direction. Furthermore, the constant amplitude tests show that the austenite stability influences the fatigue behavior of differently manufactured 316L. Using load increase tests as an efficient rating method of the anisotropic fatigue behavior, the influence of the heat treatment on anisotropy could be determined with a small number of specimens. These investigations showed no significant influence of the heat treatment on the anisotropic behavior of the AM-specimens. Full article
(This article belongs to the Special Issue Additive Manufacturing of Ferrous Materials)
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Open AccessArticle Correlation between Fatigue Crack Growth Behavior and Fracture Surface Roughness on Cold-Rolled Austenitic Stainless Steels in Gaseous Hydrogen
Metals 2018, 8(4), 221; https://doi.org/10.3390/met8040221
Received: 6 March 2018 / Revised: 26 March 2018 / Accepted: 26 March 2018 / Published: 28 March 2018
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Abstract
Austenitic stainless steels are often considered candidate materials for use in hydrogen-containing environments because of their low hydrogen embrittlement susceptibility. In this study, the fatigue crack growth behavior of the solution-annealed and cold-rolled 301, 304L, and 310S austenitic stainless steels was characterized in
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Austenitic stainless steels are often considered candidate materials for use in hydrogen-containing environments because of their low hydrogen embrittlement susceptibility. In this study, the fatigue crack growth behavior of the solution-annealed and cold-rolled 301, 304L, and 310S austenitic stainless steels was characterized in 0.2 MPa gaseous hydrogen to evaluate the hydrogen-assisted fatigue crack growth and correlate the fatigue crack growth rates with the fracture feature or fracture surface roughness. Regardless of the testing conditions, higher fracture surface roughness could be obtained in a higher stress intensity factor (∆K) range and for the counterpart cold-rolled specimen in hydrogen. The accelerated fatigue crack growth of 301 and 304L in hydrogen was accompanied by high fracture surface roughness and was associated with strain-induced martensitic transformation in the plastic zone ahead of the fatigue crack tip. Full article
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Open AccessArticle Study of Semi-Solid Magnesium Alloys (With RE Elements) as a Non-Newtonian Fluid Described by Rheological Models
Metals 2018, 8(4), 222; https://doi.org/10.3390/met8040222
Received: 28 December 2017 / Revised: 15 March 2018 / Accepted: 23 March 2018 / Published: 28 March 2018
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Abstract
This paper includes the results of high-temperature rheological experiments on semi-solid magnesium alloys and the verification of different models describing the rheological behaviour of semi-solid magnesium alloys. Such information is key from the point of view of designing alloy forming processes in their
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This paper includes the results of high-temperature rheological experiments on semi-solid magnesium alloys and the verification of different models describing the rheological behaviour of semi-solid magnesium alloys. Such information is key from the point of view of designing alloy forming processes in their semi-solid states. Magnesium alloys are a very attractive material, due to their light weight and good plastic properties; on the other hand, this material is very reactive in a liquid (semi-solid) state, which is challenging from a testing and forming perspective. Formulating/finding models for an accurate description of the rheological behaviour of semi-solid magnesium alloys seems to be key from the standpoint of developing and optimising forming processes for semi-solid magnesium alloys. Full article
(This article belongs to the Special Issue Semi-solid Processing of Alloys and Composites)
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Open AccessFeature PaperArticle Effect of Cold Rolling on the Mechanical Properties and Formability of FSWed Sheets in AA5754-H114
Metals 2018, 8(4), 223; https://doi.org/10.3390/met8040223
Received: 27 February 2018 / Revised: 23 March 2018 / Accepted: 25 March 2018 / Published: 28 March 2018
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Abstract
The effect of cold rolling, performed after friction stir welding (FSW), on the mechanical properties and formability of joints in AA5754-H114 aluminium alloy was investigated. Friction stir welding was carried out on 2.5 mm thick sheets with constant values of rotational and welding
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The effect of cold rolling, performed after friction stir welding (FSW), on the mechanical properties and formability of joints in AA5754-H114 aluminium alloy was investigated. Friction stir welding was carried out on 2.5 mm thick sheets with constant values of rotational and welding speeds of 1200 rpm and 100 mm/min, respectively. Then, FSWed workpieces were cold rolled, with the rolling direction perpendicular to the welding line, in order to obtain height reductions ranging from 0.1 to 0.5 mm. Cold rolling with the same height reductions was also carried out on the base material in the as-received condition. The mechanical properties and formability of both friction stir welded joints and base material, before and after cold rolling, were evaluated by means of the uniaxial tensile and hemispherical punch tests. The nominal stress vs. nominal strain and punch force vs. punch stroke curves were analysed in detail. Finally, the scanning electron microscope fractography was used to evaluate the fractured surface of tensile samples. Full article
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Open AccessArticle Room Temperature Mechanical Properties of A356 Alloy with Ni Additions from 0.5 Wt to 2 Wt %
Metals 2018, 8(4), 224; https://doi.org/10.3390/met8040224
Received: 6 February 2018 / Revised: 6 March 2018 / Accepted: 26 March 2018 / Published: 29 March 2018
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Abstract
In recent years, the influence of Ni on high-temperature mechanical properties of casting Al alloys has been extensively examined in the literature. In the present study, room temperature mechanical properties of an A356 alloy with Ni additions from 0.5 to 2 wt %
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In recent years, the influence of Ni on high-temperature mechanical properties of casting Al alloys has been extensively examined in the literature. In the present study, room temperature mechanical properties of an A356 alloy with Ni additions from 0.5 to 2 wt % were investigated. The role of Ni-based compounds and eutectic Si particles in reinforcing the Al matrix was studied with image analysis and was then related to tensile properties and microhardness. In the as-cast condition, the formation of the 3D network is not sufficient to determine an increase of mechanical properties of the alloys since fracture propagates by cleavage through eutectic Si particles and Ni aluminides or by the debonding of brittle phases from the aluminum matrix. After T6 heat treatment the increasing amount of Ni aluminides, due to further addition of Ni to the alloy, together with their brittle behavior, leads to a decrease of yield strength, ultimate tensile strength, and Vickers microhardness. Despite the fact that Ni addition up to 2 wt % hinders spheroidization of eutectic Si particles during T6 heat treatment, it also promotes the formation of a higher number of brittle Ni-based compounds that easily promote fracture propagation. Full article
(This article belongs to the Special Issue Microstructure and Mechanical Properties of Casting Alloys)
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Open AccessArticle Influence of Scandium Addition on Stress Corrosion Cracking Susceptibility of Al-Zn-Mg Alloy in Different Corrosive Environments
Metals 2018, 8(4), 225; https://doi.org/10.3390/met8040225
Received: 14 February 2018 / Revised: 22 March 2018 / Accepted: 28 March 2018 / Published: 29 March 2018
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Abstract
Stress corrosion cracking (SCC) susceptibilities of Al-Zn-Mg alloys without and with Scandium addition were evaluated in 3.5% NaCl solution at different pH and different strain rate, using slow strain rate test technique. The results indicate that Sc addition reduces grain size and width
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Stress corrosion cracking (SCC) susceptibilities of Al-Zn-Mg alloys without and with Scandium addition were evaluated in 3.5% NaCl solution at different pH and different strain rate, using slow strain rate test technique. The results indicate that Sc addition reduces grain size and width of precipitation free zones, and transforms grain boundary precipitates from continuous distribution into interrupted distribution by inhibiting recrystallization. In solution at pH 1, pH 3 and pH 7, Sc addition reduces the degree of localized corrosion of alloy surface and SCC susceptibility of Al-Zn-Mg alloy. However, in solution at pH 10 and pH 12, grain refinement significantly promotes the diffusion of hydrogen atoms into matrix, thus Sc addition increases SCC susceptibility of Al-Zn-Mg alloy. Under different strain rate conditions, Sc addition can all reduce SCC susceptibility of Al-Zn-Mg alloy in solution at pH 1, pH 3 and pH 7, and can all increase SCC susceptibility of Al-Zn-Mg alloy in solution at pH 10 and pH 12. As a result, Sc modified Al-Zn-Mg alloy in practical applications should be avoided in alkaline environments. Full article
(This article belongs to the Special Issue Environmentally Assisted Cracking in Advanced High Strength Alloys)
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Open AccessArticle The Effects of Nitrogen Gas on Microstructural and Mechanical Properties of TIG Welded S32205 Duplex Stainless Steel
Metals 2018, 8(4), 226; https://doi.org/10.3390/met8040226
Received: 26 January 2018 / Revised: 19 March 2018 / Accepted: 28 March 2018 / Published: 1 April 2018
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Abstract
Duplex stainless steels are gaining greater interest due to their increasing amounts of application fields. Accordingly, there is a need for awareness of problems associated with improper microstructural distributions such as δ-ferrite (delta-ferrite), austenite and other important intermetallic phases that may form in
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Duplex stainless steels are gaining greater interest due to their increasing amounts of application fields. Accordingly, there is a need for awareness of problems associated with improper microstructural distributions such as δ-ferrite (delta-ferrite), austenite and other important intermetallic phases that may form in these steel weldments. Since δ-ferrite versus austenite ratio profoundly influences corrosion and mechanical properties, optimum δ-ferrite ratios must be kept approximately within 35–65 vol % and balance austenite to maintain satisfactory corrosion and mechanical properties on welding of these steels. Cooling rates of welds and alloying elements in base metal are the major factors that determine the final microstructure of these steels. In this work, 3 mm thickness of 2205 duplex stainless-steel plates were TIG (Tungsten Inert Gas) welded with various amounts of nitrogen gas added to argon shielding gas. Specimens were joined within the same welding parameters and cooling conditions. As nitrogen is a potential austenite stabilizer and an interstitial solid solution hardener, the effects of nitrogen on mechanical properties such as hardness profiles, grain sizes and microstructural modifications are investigated thoroughly by changing the welding shielding gas compositions. Increasing the nitrogen content in argon shielding gas also increases the amount of austenitic phase while δ-ferrite ratios decreases. Nitrogen spherodized the grains of austenitic structure much more than observed in δ-ferrite. The strength values of specimens that welded with the addition of nitrogen gas into the argon shielding gas are increased more in both austenitic and delta-ferritic structure as compared to specimens that welded with plain argon shielding gas. The addition of 1 vol % of nitrogen gas into argon shielding gas provided the optimum phase balance of austenite and δ-ferrite in S32205 duplex stainless-steel TIG-welded specimens. Full article
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Open AccessArticle Precipitation, Recrystallization, and Evolution of Annealing Twins in a Cu-Cr-Zr Alloy
Metals 2018, 8(4), 227; https://doi.org/10.3390/met8040227
Received: 14 February 2018 / Revised: 26 March 2018 / Accepted: 27 March 2018 / Published: 1 April 2018
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Abstract
In this paper, the precipitation, recrystallization, and evolution of twins in Cu-Cr-Zr alloy strips were investigated. Tensile specimens were aged at three different temperatures for various times so as to bring the strips into every possible aging condition. The results show that the
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In this paper, the precipitation, recrystallization, and evolution of twins in Cu-Cr-Zr alloy strips were investigated. Tensile specimens were aged at three different temperatures for various times so as to bring the strips into every possible aging condition. The results show that the appropriate aging parameter for the 70% reduced cold-rolled alloy strips is 723 K for 240 min, with a tensile strength of 536 MPa and an electrical conductivity of 85.3% International Annealed Copper Standards (IACS) at the peak aged condition. The formation of fcc (face-centered cubic) ordered Cr-rich precipitates (β′) is an important factor influencing the significant improvement of properties near the peak aged condition. In terms of crystallographic orientation relationships, there are basically two types of β′ precipitates in the alloy. Beyond the Cr-rich precipitates (β′(I)) formed during the early aging stages, which mimic a cube-on-cube orientation relationship (OR) with the matrix, another Cr-rich precipitate (β′(II)) is observed in the peak aged condition. β′(II) is coherent with the matrix, with the following ORs: [111]β′(II)//[100]Cu, {02-2}β′(II)//{02-2}Cu and [011]β′(II)//[211]Cu, {200}β′(II)//{-111}Cu. These precipitates have a strong dislocation and grain boundary pinning effect, which hinder the dislocation movement and crystal boundary migration, and eventually delay recrystallization and enhance the recrystallization resistance of the peak aged strips. During the subsequent annealing process, the transition phase β′ gradually loses the coherence mismatch and grows into a larger equilibrium phase of chromium with a bcc (body-centered cubic) structure (β), resulting in the reduction of the pinning effect to dislocations and sub-grains, so that recrystallization occurs. Annealing twins are formed during the recrystallization process to release the deformation energy and to reduce the drive force for interface migration, eventually hindering grain growth. Full article
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Open AccessArticle Fabrication of Superhydrophobic Metallic Surface by Wire Electrical Discharge Machining for Seamless Roll-to-Roll Printing
Metals 2018, 8(4), 228; https://doi.org/10.3390/met8040228
Received: 25 February 2018 / Revised: 28 March 2018 / Accepted: 30 March 2018 / Published: 2 April 2018
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Abstract
This paper presents a proposal of a direct one-step method to fabricate a multi-scale superhydrophobic metallic seamless roll mold. The mold was fabricated using the wire electrical discharge machining (WEDM) technique for a roll-to-roll imprinting application to produce a large superhydrophobic surface. Taking
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This paper presents a proposal of a direct one-step method to fabricate a multi-scale superhydrophobic metallic seamless roll mold. The mold was fabricated using the wire electrical discharge machining (WEDM) technique for a roll-to-roll imprinting application to produce a large superhydrophobic surface. Taking advantage of the exfoliating characteristic of the metallic surface, nano-sized surface roughness was spontaneously formed while manufacturing the micro-sized structure: that is, a dual-scale hierarchical structure was easily produced in a simple one-step fabrication with a large area on the aluminum metal surface. This hierarchical structure showed superhydrophobicity without chemical coating. A roll-type seamless mold for the roll-to-roll process was fabricated through engraving the patterns on the cylindrical substrate, thereby enabling to make a continuous film with superhydrophobicity. Full article
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Open AccessArticle Microstructure and Mechanical Properties of Ultrasonic Spot Welded Mg/Al Alloy Dissimilar Joints
Metals 2018, 8(4), 229; https://doi.org/10.3390/met8040229
Received: 17 February 2018 / Revised: 30 March 2018 / Accepted: 30 March 2018 / Published: 2 April 2018
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Abstract
Lightweight structural applications of magnesium and aluminum alloys inevitably necessitate welding and joining, especially dissimilar welding between these alloys. The objective of this study was to examine the feasibility of joining ZEK100 Mg alloy to Al6022 alloy via ultrasonic spot welding, focusing on
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Lightweight structural applications of magnesium and aluminum alloys inevitably necessitate welding and joining, especially dissimilar welding between these alloys. The objective of this study was to examine the feasibility of joining ZEK100 Mg alloy to Al6022 alloy via ultrasonic spot welding, focusing on effects of welding energy. An interface diffusion layer consisting of α-Mg and Al12Mg17 eutectic structure was observed to form, with its thickness increased from ~0.5 µm to ~30 µm with increasing welding energy from 500 J to 2000 J. The tensile lap shear peak load or strength and critical stress intensity of the welded joints first increased and then decreased with increasing welding energy, with their peak values achieved at 750 J. Fatigue life of the joints made at 750 J and 2000 J was equivalent at the lower cyclic loading levels, while it was longer for the joints made at 750 J at the higher cyclic loading levels. Fatigue fracture mode changed from interfacial failure to mainly transverse-through-thickness crack growth with decreasing cyclic loading level, which corresponded well to the bi-linear characteristic of S-N curves. Crack initiation basically occurred at the weld nugget border and at the interface between the two sheets, which can be understood via a theoretical stress analysis. Full article
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Open AccessArticle Using Genetic Algorithms with Multi-Objective Optimization to Adjust Finite Element Models of Welded Joints
Metals 2018, 8(4), 230; https://doi.org/10.3390/met8040230
Received: 9 January 2018 / Revised: 26 March 2018 / Accepted: 28 March 2018 / Published: 2 April 2018
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Abstract
To ensure realistic results when modeling welded joints using the finite element method (FEM), it is essential to appropriately characterize the thermo-mechanical behavior of the elastic-plastic Finite Element (FE) models. This task is complex. Any small differences between the actual welded joints and
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To ensure realistic results when modeling welded joints using the finite element method (FEM), it is essential to appropriately characterize the thermo-mechanical behavior of the elastic-plastic Finite Element (FE) models. This task is complex. Any small differences between the actual welded joints and the welded joints based on FEM can be amplified enormously in the presence of nonlinearities. Due to the intense concentration of heat on a small area to create such joints, the regions near the weld line undergo severe thermal cycles. These generate significant angular distortion due mainly to the residual stresses. This paper proposes a method to determine the parameters that are most appropriate for modeling the Butt joint single V-groove welded joint FE models’ thermo-mechanical behavior that were created by the one-pass Gas Metal Arc Welding (GMAW). The method is based on experimental data, as well as genetic algorithms (GA) with multi-objective functions. As a practical example, the proposed methodology is validated with three different welded joints specimens that are manufactured by different voltages and currents (26 volts and 140 amps, 28 volts and 210 amps, and 35 volts and 260 amps). The electrode orientation, shielding gas flow rate, distance between nozzle and plate, and welding speed were considered to be constant for all of the specimens that were studied, and their values were 80°, 20.0 L/min, 4.0 mm, and 6 mm/s, respectively. The base material was EN 235JR low carbon steel, whereas the weld bead was ER70S-6 for the three specimens that were welded. An agreement between the temperature field and the angular distortion that was obtained by the adjusted FE models and those that were obtained experimentally demonstrates that the proposed methodology may be valid for automatically determining the most appropriate parameters. Full article
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Open AccessArticle Experimental Investigations of the In-Die Quenching Efficiency and Die Surface Temperature of Hot Stamping Aluminium Alloys
Metals 2018, 8(4), 231; https://doi.org/10.3390/met8040231
Received: 28 February 2018 / Revised: 24 March 2018 / Accepted: 27 March 2018 / Published: 2 April 2018
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Abstract
The in-die quenching is a key stage in the hot stamping volume production chain which determines the post-formed strength of lightweight alloy components, tool life, and hot stamping productivity. In this paper, the performance of in-die quenching, reflected by the quenching efficiency (the
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The in-die quenching is a key stage in the hot stamping volume production chain which determines the post-formed strength of lightweight alloy components, tool life, and hot stamping productivity. In this paper, the performance of in-die quenching, reflected by the quenching efficiency (the time of work-piece held within stamping dies) and die surface temperature during the simulated hot stamping process of AA6082, was experimentally and analytically investigated. A range of in-die quenching experiments were performed for different initial work-piece and die temperatures, quenching pressures, work-piece thickness, and die clearances, under hot stamping conditions. In addition, a one-dimensional (1D) closed-form heat transfer model was used to calculate the die surface temperature evolution that is difficult to obtain during practical manufacture situations. The results have shown that the in-die quenching efficiency can be significantly increased by decreasing the initial work-piece and die temperatures. Die clearances are required to be designed precisely to obtain sufficiently high quenching rates and satisfying post-formed strength for hot-stamped panel components. This study systematically considered an extensive variety of influencing factors on the in-die quenching performance, which can provide practical guides for stamping tool designers and manufacture systems for hot-stamping volume production. Full article
(This article belongs to the Special Issue Material and Process Design for Lightweight Structures)
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Open AccessArticle Effect of Tempering Temperature on the Low Temperature Impact Toughness of 42CrMo4-V Steel
Metals 2018, 8(4), 232; https://doi.org/10.3390/met8040232
Received: 7 March 2018 / Revised: 28 March 2018 / Accepted: 29 March 2018 / Published: 2 April 2018
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Abstract
Effects of tempering temperature on the microstructures and low temperature impact toughness of 42CrMo4-V steel were investigated. Microstructures of 42CrMo4-V steel after tempering at 570–720 °C for 3 h were experimentally investigated using scanning electron microscopy (SEM), electron back-scattered diffraction (EBSD), transmission electron
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Effects of tempering temperature on the microstructures and low temperature impact toughness of 42CrMo4-V steel were investigated. Microstructures of 42CrMo4-V steel after tempering at 570–720 °C for 3 h were experimentally investigated using scanning electron microscopy (SEM), electron back-scattered diffraction (EBSD), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The results showed that the carbide precipitation sequence of 42CrMo4-V steel is M8C7 → M3C and the absorbed energies of 42CrMo4-V steel increase greatly from 21.7 J to 132.3 J with increasing tempering temperature from 570 °C to 720 °C. The changes of impact toughness with increasing tempering temperature were attributed to the softening of matrix, the evolution of carbide precipitates and grain structures. Full article
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Open AccessArticle Preparation and Performance Analysis of Nb Matrix Composites Reinforced by Reactants of Nb and SiC
Metals 2018, 8(4), 233; https://doi.org/10.3390/met8040233
Received: 5 February 2018 / Revised: 22 March 2018 / Accepted: 27 March 2018 / Published: 3 April 2018
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Abstract
In this paper, one kind of new composite material formed with Nb and SiC was prepared by hot pressing sintering. The influence of the addition of SiC particles on the mechanical properties at room and high temperature was analyzed. The composite material consists
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In this paper, one kind of new composite material formed with Nb and SiC was prepared by hot pressing sintering. The influence of the addition of SiC particles on the mechanical properties at room and high temperature was analyzed. The composite material consists of three phases: Nb2C, Nb3Si, and Nb solid solution (Nbss). The fraction of SiC particles added in the Nb matrix was 3%, 5%, and 7%, respectively. Flexural strength, Vickers hardness, and compressive strength at room temperature were improved with the increasing of SiC content. Among them, compressive strength and fracture toughness were higher than those of Nb/Nb5Si3 composites. The compressive strength at high temperature of the new composites was higher than that of Nb-Si alloys, which improved with the increasing of SiC content. Full article
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Open AccessArticle Value Recovery from Waste Liquid Crystal Display Glass Cullet through Leaching: Understanding the Correlation between Indium Leaching Behavior and Cullet Piece Size
Metals 2018, 8(4), 235; https://doi.org/10.3390/met8040235
Received: 22 March 2018 / Revised: 29 March 2018 / Accepted: 30 March 2018 / Published: 3 April 2018
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Abstract
For hydrometallurgical recovery of indium from glass cullet after dismantling a waste liquid crystal display (LCD), leaching is the rudimentary stage. Though size reduction of the cullet pieces adds convenience for recycling, from an efficiency and cost-effectiveness perspective regarding leaching process development, determining
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For hydrometallurgical recovery of indium from glass cullet after dismantling a waste liquid crystal display (LCD), leaching is the rudimentary stage. Though size reduction of the cullet pieces adds convenience for recycling, from an efficiency and cost-effectiveness perspective regarding leaching process development, determining the proper cullet piece size is essential. Hence, in this study, leaching efficiency of indium as a function of cullet piece size was investigated, wherein the proper mechanical classification of crushed glass cullet could be addressed. The optimum conditions of 5 M mineral acid as the lixiviant, pulp density of 500 g/L, temperature of 75 °C, agitation speed of 500 rpm, 2 h process time were kept constant for the leaching studies. It was concluded that the size of the waste LCD cullet inversely affected the leaching efficiency of indium. For efficient leaching, a smaller cullet size is recommended; hence, waste LCD should be crushed to pieces 1 mm or smaller. Indium leaching behavior comparison using HCl, HNO3, H2SO4 revealed that all three mineral acids had similar leaching efficiencies. The reported process provides the missing link between physical dismantling and chemical processing for indium recovery via techno-economical-sustainable process development. Full article
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Open AccessArticle Mechanical Behavior of Two Ferrite–Martensite Dual-Phase Steels over a Broad Range of Strain Rates
Metals 2018, 8(4), 236; https://doi.org/10.3390/met8040236
Received: 27 February 2018 / Revised: 22 March 2018 / Accepted: 26 March 2018 / Published: 3 April 2018
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Abstract
The present study concerns the deformation and fracture behavior of two ferrite–martensite dual phase steels (FMDP660 and FMDP780) with different phase fractions subjected to different strain rate (0.001 s−1 to 1000 s−1) tensile testing. For both steels, the yield strength
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The present study concerns the deformation and fracture behavior of two ferrite–martensite dual phase steels (FMDP660 and FMDP780) with different phase fractions subjected to different strain rate (0.001 s−1 to 1000 s−1) tensile testing. For both steels, the yield strength (YS) monotonically increased with strain rates, whereas the values of ultimate tensile strength (UTS), uniform elongation (UE) and post-uniform elongation (PUE) were maintained stable at the low strain rate range (0.001–0.1 s−1), followed by a significant increase with strain rate at high strain rate levels (0.1–1000 s−1). The FMDP780 steel with a higher fraction of martensite possessed a stronger strain rate sensitivity of tensile strength and elongation (UE and PUE) values at the high strain rate stage, compared with the FMDP660 sample. The change of UTS and UE with different strain rates and phase fractions was highly related to the strain hardening behavior, which was controlled by the dislocation multiplication in ferrite, as validated by transmission electron microscopy (TEM). The fracture surface of the two steels was characterized by dimpled-type fracture associated with microvoid formation at the ferrite–martensite interfaces, regardless of the strain rates. The change of the dimple size and PUE value of the two steels with strain rates was attributed to the effect of adiabatic heating during tensile testing. Full article
(This article belongs to the Special Issue Mechanical Behavior of High-Strength Low-Alloy Steels)
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Open AccessArticle Stress-Corrosion Cracking Behaviour of Lean-Duplex Stainless Steels in Chloride/Thiosulphate Environments
Metals 2018, 8(4), 237; https://doi.org/10.3390/met8040237
Received: 1 March 2018 / Revised: 24 March 2018 / Accepted: 2 April 2018 / Published: 4 April 2018
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Abstract
The stress-corrosion cracking (SCC) behaviour of two lean-duplex stainless steels (DSS 2304 and LDSS 2404) was studied by slow strain-rate tests (SSRT) in 20% NaCl solution at 80 °C (pH about 6) and in NACE TM-0177 solution at 25 °C (pH 2.7), both
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The stress-corrosion cracking (SCC) behaviour of two lean-duplex stainless steels (DSS 2304 and LDSS 2404) was studied by slow strain-rate tests (SSRT) in 20% NaCl solution at 80 °C (pH about 6) and in NACE TM-0177 solution at 25 °C (pH 2.7), both in the absence and in the presence of thiosulphate ions (S2O32−). The SCC susceptibility of the two alloys was compared to that of LDSS 2101 investigated in a previous study. LDSS 2404 was always immune to SCC, while DSS 2304 (and LDSS 2101) suffered this corrosion form at specific concentrations. The high SCC resistance of DSS 2404 in both environments was connected to its high Mo content, while the significant SCC susceptibility of LDSS 2101 in NACE TM-0177 solution was likely due to the high Mn content of the alloy. Full article
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Open AccessFeature PaperArticle Characterization of the Micro-Arc Coatings Containing β-Tricalcium Phosphate Particles on Mg-0.8Ca Alloy
Metals 2018, 8(4), 238; https://doi.org/10.3390/met8040238
Received: 4 March 2018 / Revised: 2 April 2018 / Accepted: 3 April 2018 / Published: 4 April 2018
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Abstract
The characterization of the microstructure, morphology, topography, composition, and physical and chemical properties of the coatings containing β-tricalcium phosphate (β-TCP) particles deposited by the micro-arc oxidation (MAO) method on biodegradable Mg-0.8Ca alloy has been performed. The electrolyte for the MAO process included the
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The characterization of the microstructure, morphology, topography, composition, and physical and chemical properties of the coatings containing β-tricalcium phosphate (β-TCP) particles deposited by the micro-arc oxidation (MAO) method on biodegradable Mg-0.8Ca alloy has been performed. The electrolyte for the MAO process included the following components: Na2HPO4·12H2O, NaOH, NaF, and β-Ca3(PO4)2 (β-TCP). The coating morphology, microstructure, and compositions have been studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). With increasing of the MAO voltage from 350 to 500 V, the coating thickness and surface average roughness of the coatings increased linearly from 6 to 150 µm and from 2 to 8 µm, respectively. The coating deposited at 350 V had more homogeneous porous morphology with numerous pores similar by sizes (2–3 µm) than the coatings formed at 450–500 V. The β-TCP isometric particles were included in the coating surface. The XRD recognized the amorphous-crystalline structure in the coatings with incorporation of the following phases: β-TCP, α-TCP, MgO (periclase) and hydroxyapatite (HA). The corrosion experiments showed that the biodegradation rate of the Mg-0.8Ca alloy coated by calcium phosphates is almost 10 times less than that of uncoated alloy. Full article
(This article belongs to the Special Issue Plasma Electrolytic Oxidation)
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Open AccessArticle Enhancement of the Young’s Modulus through Infrared Heat Treatment: A Study of the Microstructure and the Mass Effect of Real Body 6082 Aluminum Forgings
Metals 2018, 8(4), 239; https://doi.org/10.3390/met8040239
Received: 9 March 2018 / Revised: 30 March 2018 / Accepted: 4 April 2018 / Published: 4 April 2018
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Abstract
To avoid the phenomenon of abnormal grain coarsening, and increase the Young’s modulus of forgings, an infrared heat treatment was used on different mass forgings and compared with the results of an air furnace heat treatment. This work focused on the effects of
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To avoid the phenomenon of abnormal grain coarsening, and increase the Young’s modulus of forgings, an infrared heat treatment was used on different mass forgings and compared with the results of an air furnace heat treatment. This work focused on the effects of microstructural evolution and the mechanical properties of two different mass 6082 real forgings. The experimental results show that infrared heat treatment can effectively reduce the mass effect after heat treatment, inhibit the coarse grains formed, and keep the non-equiaxed grains along the metal flows, thus significantly improving the ductility of the material. In addition, the rapid heating characteristic of infrared can effectively shorten the duration of heat treatment and greatly enhance the Young’s modulus and the vibration resistance of 6082 entity forgings. Full article
(This article belongs to the Special Issue Heat Treatment of Aluminum Alloys)
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Open AccessArticle Study on the Control of Rare Earth Metals and Their Behaviors in the Industrial Practical Production of Q420q Structural Bridge Steel Plate
Metals 2018, 8(4), 240; https://doi.org/10.3390/met8040240
Received: 24 February 2018 / Revised: 29 March 2018 / Accepted: 31 March 2018 / Published: 5 April 2018
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Abstract
Rare earth (RE) addition can refine and change the shape/distribution of inclusions in steel to improve its strength and toughness. In this paper, the control of RE, specifically Ce and La, and their behaviors in the practical industrial production of high-strength structural steel
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Rare earth (RE) addition can refine and change the shape/distribution of inclusions in steel to improve its strength and toughness. In this paper, the control of RE, specifically Ce and La, and their behaviors in the practical industrial production of high-strength structural steel with 420 MPa yield strength were studied. In particular, the interactions between RE and Al, Nb, S, O were investigated, with the aim of improving the steel toughness and welding performance. The impact energy of the plate with RE is approximately 50 J higher than the regular plate without RE. The toughness of the plate from ladle furnace (LF) refining with RE addition is better than the one from Ruhrstahl and Hereaeus (RH) refining. The RE inclusions could induce the intragranular ferrite and refine the grain size to the preferred size. After welding at the heat input of 200 kJ/cm, the grain size at the heat affected zone was found to be the finest in the plate from the LF process with RE addition. Notably, the microstructure of ferrite was quasi-polygonal. Full article
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Open AccessArticle Effect of Porosity on the Fatigue Behavior of Gas Metal Arc Welding Lap Fillet Joint in GA 590 MPa Steel Sheets
Metals 2018, 8(4), 241; https://doi.org/10.3390/met8040241
Received: 26 February 2018 / Revised: 27 March 2018 / Accepted: 4 April 2018 / Published: 5 April 2018
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Abstract
Weld defects such as blowholes and surface pores occur due to zinc vaporization during the gas metal arc welding of lap fillet joints of Zn-coated steel. In this study, the effect of porosity on fatigue behavior was investigated. A Zn-coated steel sheet with
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Weld defects such as blowholes and surface pores occur due to zinc vaporization during the gas metal arc welding of lap fillet joints of Zn-coated steel. In this study, the effect of porosity on fatigue behavior was investigated. A Zn-coated steel sheet with the strength of 590 MPa and a thickness of 2.3 mm was used as the base material. Three kinds of specimens with weld pore defects, such as blowholes and surface pores, were prepared and the tensile shear strength, hardness and fatigue behavior were investigated. The pore defects in the welds reduced the tensile shear strength. In the fatigue test, at higher load stresses between 122 and 366 MPa, pore defects reduced the fatigue life of the weld. However, the pore defects in the welds did not significantly affect the fatigue life of the welds at stresses below 92 MPa. Full article
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Open AccessArticle The Prediction of the Mechanical Properties for Dual-Phase High Strength Steel Grades Based on Microstructure Characteristics
Metals 2018, 8(4), 242; https://doi.org/10.3390/met8040242
Received: 28 February 2018 / Revised: 29 March 2018 / Accepted: 3 April 2018 / Published: 5 April 2018
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Abstract
The decrease of emissions from vehicle operation is connected mainly to the reduction of the car’s body weight. The high strength and good formability of the dual phase steel grades predetermine these to be used in the structural parts of the car’s body
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The decrease of emissions from vehicle operation is connected mainly to the reduction of the car’s body weight. The high strength and good formability of the dual phase steel grades predetermine these to be used in the structural parts of the car’s body safety zones. The plastic properties of dual phase steel grades are determined by the ferrite matrix while the strength properties are improved by the volume and distribution of martensite. The aim of this paper is to describe the relationship between the mechanical properties and the parameters of structure and substructure. The heat treatment of low carbon steel X60, low alloyed steel S460MC, and dual phase steel DP600 allowed for them to reach states with a wide range of volume fractions of secondary phases and grain size. The mechanical properties were identified by a tensile test, volume fraction of secondary phases, and grain size were measured by image analysis. It was found that by increasing the annealing temperature, the volume fraction of the secondary phase increased, and the ferrite grains were refined. Regression analysis was used to find out the equations for predicting mechanical properties based on the volume fraction of the secondary phase and grain size, following the annealing temperature. The hardening mechanism of the dual phase steel grades for the states they reached was described by the relationship between the strain-hardening exponent and the density of dislocations. This allows for the designing of dual phase steel grades that are “tailored” to the needs of the automotive industry customers. Full article
(This article belongs to the Special Issue Mechanical Behavior of High-Strength Low-Alloy Steels)
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Open AccessArticle Physically-Based Modeling and Characterization of Hot Flow Behavior in an Interphase-Precipitated Ti-Mo Microalloyed Steel
Metals 2018, 8(4), 243; https://doi.org/10.3390/met8040243
Received: 21 March 2018 / Revised: 1 April 2018 / Accepted: 3 April 2018 / Published: 6 April 2018
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Abstract
In this contribution, a series of hot compression tests was conducted on a typical interphase-precipitated Ti-Mo steel at relatively higher strain rates of 0.1~10 s−1 and temperatures of 900~1150 °C using a Gleeble-2000 thermo-mechanical simulator. A combination of Bergstrom and Kolmogorov–Johnson–Mehl–Avrami models
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In this contribution, a series of hot compression tests was conducted on a typical interphase-precipitated Ti-Mo steel at relatively higher strain rates of 0.1~10 s−1 and temperatures of 900~1150 °C using a Gleeble-2000 thermo-mechanical simulator. A combination of Bergstrom and Kolmogorov–Johnson–Mehl–Avrami models was first used to accurately predict the whole flow behaviors of Ti-Mo steel involving dynamic recrystallization, under various hot deformation conditions. By comparing the characteristic stresses and material parameters, especially at the higher strain rates studied, the dependence of hot flow behavior on strain rate and deformation temperature was further clarified. The hardening parameter U and peak density ρp exhibited an approximately positive linear relationship with the Zener–Hollomon (Z) parameter, while the softening parameter Ω dropped with increasing Z value. The Avrami exponent nA varied between 1.2 and 2.1 with lnZ, implying two diverse nucleation mechanisms of dynamic recrystallization. The experimental verification was performed as well based on the microstructural evolution and mechanism analysis upon straining. The proposed constitutive models may provide a powerful tool for optimizing the hot working processes of high performance Ti-Mo microalloyed steels with interphase precipitation. Full article
(This article belongs to the Special Issue Advances in Microalloyed Steels)
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Open AccessArticle Study of Localized Corrosion of AISI 430 and AISI 304 Batches Having Different Roughness
Metals 2018, 8(4), 244; https://doi.org/10.3390/met8040244
Received: 25 February 2018 / Revised: 30 March 2018 / Accepted: 4 April 2018 / Published: 6 April 2018
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Abstract
In this work, the localized corrosion resistance of different batches of AISI 430 and AISI 304 stainless steels, having Scotch-Brite surface finishing, was investigated as a function of their roughness (in terms of Rz) and chemical composition. The study was performed by recording
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In this work, the localized corrosion resistance of different batches of AISI 430 and AISI 304 stainless steels, having Scotch-Brite surface finishing, was investigated as a function of their roughness (in terms of Rz) and chemical composition. The study was performed by recording anodic cyclic potentiodynamic polarization curves at room temperature in two NaCl solutions (0.35 and 1.75 wt %). From the anodic curves, corrosion potential (Ecorr), protection potential (Eprot), and pitting potential (Epit) were obtained. In general, the results indicate that AISI 304 has better localized corrosion resistance than AISI 430, both in terms of pitting initiation and repassivation ability, independently from roughness. In particular, an increase of roughness determined a decrease of Epit only in the case of AISI 304 in the less concentrated NaCl solution. This result was related to the higher variability of the corresponding Rz values compared to those of AISI 430. Finally, from the analysis of the loop hysteresis of the anodic curves, in relation to Epit−Eprot values, durability information on the tested stainless steels were obtained: AISI 304 shows higher corrosion performances with respect to AISI 430, thanks to the higher chromium content of the former compared to the latter. Full article
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Open AccessArticle The Influence of Thermal History on the Multistage Transformation of NiTi Shape-Memory Alloys
Metals 2018, 8(4), 246; https://doi.org/10.3390/met8040246
Received: 12 March 2018 / Revised: 29 March 2018 / Accepted: 3 April 2018 / Published: 7 April 2018
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Abstract
The multistage martensitic phase transformation of a polycrystalline NiTi shape-memory alloy (50.3 at. %Ni–49.7 at. % Ti) has been studied by means of calorimetric measurements. After a conventional thermal treatment followed by successive thermal cycles, the initial two-step forward transformation splits into four-overlapping
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The multistage martensitic phase transformation of a polycrystalline NiTi shape-memory alloy (50.3 at. %Ni–49.7 at. % Ti) has been studied by means of calorimetric measurements. After a conventional thermal treatment followed by successive thermal cycles, the initial two-step forward transformation splits into four-overlapping stages. However, the reverse martensitic transformation maintains the initial two-step sequence, usually assigned to the B19′→R→B2 transformation. The correlation between the forward and reverse steps has been established by means of selected thermal cycles together with an estimation of their enthalpy and thermal hysteresis. These results have also provided information about the storage of the elastic strain energy and the frictional works associated with the variants’ nucleation. Moreover, the study around the forward transformation temperature range by means of uncompleted thermal cycles undoubtedly shows the presence of temperature memory effects in both stages. Full article
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Open AccessArticle The Role of a MDP/VBATDT-Primer Composition on Resin Bonding to Zirconia
Metals 2018, 8(4), 247; https://doi.org/10.3390/met8040247
Received: 26 February 2018 / Revised: 3 April 2018 / Accepted: 4 April 2018 / Published: 7 April 2018
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Abstract
Yttria-tetragonal zirconia polycrystal (Y-TZP) is a difficult substrate to bond to due to the absence of a glass phase and the material’s chemical inertness. This study evaluated the effect of two monomers for metal, MDP (10-methacryloyloxydecyl dihydrogen phosphate) and VBATDT (6-(4-vinylbenzyl-n-propyl)amino-1,3,5-trizaine-2,4-dithiol) on bond
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Yttria-tetragonal zirconia polycrystal (Y-TZP) is a difficult substrate to bond to due to the absence of a glass phase and the material’s chemical inertness. This study evaluated the effect of two monomers for metal, MDP (10-methacryloyloxydecyl dihydrogen phosphate) and VBATDT (6-(4-vinylbenzyl-n-propyl)amino-1,3,5-trizaine-2,4-dithiol) on bond strength to Y-TZP. Seven combinations with different concentrations of MDP and VBATDT-monomers (0.0, 0.1, 0.5, or 1.0 wt %) in acetone solution were developed and applied to the surface of Y-TZP slabs, which were bonded to composite resin substrates using a resin cement under standard loading. Non-primed samples were used as controls. Bonded specimens were cut for microtensile testing and tested after either 48 h or 180 days in water storage at room temperature. All samples from control group (no primer) and MV5 group (0% MDP/0.5% VBATDT) debonded spontaneously. Two-way ANOVA showed that the primer had a significant effect (p < 0.001) on bond strength to zirconia, whilst storage time did not (p = 0.203). Tukey HSD (honest significant difference) test indicated that groups with at least 0.5% of each monomer resulted in higher initial bond strength values. Although chemical bonding to zirconia is credited to MDP, a correct balance between MDP and VBATDT may imply in better bond strength results. The minimum concentration of each monomer should not be lower than 0.5 wt %. Full article
(This article belongs to the Special Issue Science, Characterization and Technology of Joining and Welding)
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Open AccessArticle The Effect of Cerium Ions on the Structure, Porosity and Electrochemical Properties of Si/Zr-Based Hybrid Sol-Gel Coatings Deposited on Aluminum
Metals 2018, 8(4), 248; https://doi.org/10.3390/met8040248
Received: 12 February 2018 / Revised: 26 March 2018 / Accepted: 3 April 2018 / Published: 7 April 2018
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Abstract
This study was focused on the synthesis and characterization of Si/Zr-based hybrid sol-gel coatings with and without the addition of cerium(III) ions. The coatings were deposited on aluminum aiming to act as an effective and ecologically harmless alternative to toxic chromate coatings. The
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This study was focused on the synthesis and characterization of Si/Zr-based hybrid sol-gel coatings with and without the addition of cerium(III) ions. The coatings were deposited on aluminum aiming to act as an effective and ecologically harmless alternative to toxic chromate coatings. The chemical composition, structure, thermal properties and porosity of the non-doped and Ce-doped coatings containing various Zr contents were examined by Raman spectroscopy and photothermal beam deflection spectroscopy. The corrosion properties of the coated aluminum substrates were studied using AC and DC electrochemical methods in 0.1 M NaCl electrolyte solution. Barrier and protecting properties of the coatings were monitored upon long-term immersion in chloride solution using electrochemical impedance spectroscopy. The effect of cerium ions was two-fold: on the formation of a more condensed Si−O−Zr network structure and on the formation of Ce-based deposits, which diminish the rate of cathodic reaction at the coating/metal interface. These effects acted synergistically and resulted in the creation of the coatings with effective barrier and active corrosion protection. Full article
(This article belongs to the Special Issue Corrosion Inhibition)
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Open AccessArticle Machinability of Eco-Friendly Lead-Free Brass Alloys: Cutting-Force and Surface-Roughness Optimization
Metals 2018, 8(4), 250; https://doi.org/10.3390/met8040250
Received: 22 March 2018 / Revised: 3 April 2018 / Accepted: 4 April 2018 / Published: 8 April 2018
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Abstract
The machinability in turning mode of three lead-free brass alloys, CuZn42 (CW510L), CuZn38As (CW511L) and CuZn36 (C27450) was evaluated in comparison with a reference free-cutting leaded brass CuZn39Pb3 (CW614N), as far as the quality characteristics, i.e., cutting force and surface roughness, were concerned.
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The machinability in turning mode of three lead-free brass alloys, CuZn42 (CW510L), CuZn38As (CW511L) and CuZn36 (C27450) was evaluated in comparison with a reference free-cutting leaded brass CuZn39Pb3 (CW614N), as far as the quality characteristics, i.e., cutting force and surface roughness, were concerned. A design of experiments (DOE) technique, according to the Taguchi L16 orthogonal array (OA) methodology, as well as analysis of variance (ANOVA) were employed in order to identify the critical-to-machinability parameters and to obtain their optimum values for high-performance machining. The experimental design consisted of four factors (cutting speed, depth of cut, feed rate and alloy) with four levels for each factor using the “smaller-the-better” criterion for quality characteristics’ optimization. The data means and signal-to-noise (S/N) responses indicated that the depth of cut and the feed rate were the most influential factors for the cutting force and surface roughness, respectively. The optimized machining parameters for cutting force (34.59 N) and surface roughness (1.22 μm) minimization were determined. Confirmation experiments (cutting force: 39.37 N and surface roughness: 1.71 μm) seem to show that they are in close agreement to the main conclusions, thereby validating the findings of the statistical evaluation performed. Full article
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Open AccessArticle Study on the Interfacial Reactions between an Fe–Mn–Si Alloy and Complex Oxides Containing FeO during Isothermal Heating
Metals 2018, 8(4), 251; https://doi.org/10.3390/met8040251
Received: 16 March 2018 / Revised: 3 April 2018 / Accepted: 5 April 2018 / Published: 9 April 2018
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Abstract
To precisely control the characteristics of complex oxides by heat treatment, the effect of FeO on the interfacial reactions that occur between an Fe–Mn–Si alloy and CaO–SiO2–Al2O3–MgO–MnO–FeO oxide was studied and clarified. Eight types of diffusion couples
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To precisely control the characteristics of complex oxides by heat treatment, the effect of FeO on the interfacial reactions that occur between an Fe–Mn–Si alloy and CaO–SiO2–Al2O3–MgO–MnO–FeO oxide was studied and clarified. Eight types of diffusion couples with different compositions of oxides were produced using a confocal scanning laser microscope (CSLM). The morphologies of the alloy–oxide interfaces and the changes in their chemical compositions with isothermal heating at 1273 and 1473 K for 10 h were investigated. A modified dynamic calculation model was established and verified to achieve better understanding on the interfacial reaction mechanism between the Fe–Mn–Si alloy and the multicomponent oxide with different FeO content during isothermal heating. The results showed that during isothermal heating at 1273 and 1473 K, “solid–solid” and “solid–liquid” alloy–oxide reactions occurred in the A-1-x and A-2-x diffusion couples, respectively. The interfacial alloy–oxide reactions were enhanced by increasing the initial FeO content in the oxide and the heating temperature. The particle precipitation zone (PPZ), Mn-depleted zone (MDZ) and Si-depleted zone (SDZ) widths in the A-1-x and A-2-x diffusion couples after heating also showed a positive correlation with the increase in the initial FeO content in the oxide, as well as the size and number of MnO·SiO2 inclusions. The diffused oxygen from the oxide reacting with elemental Mn and Si in the alloy plays a dominant role in the A-1-x diffusion couple during heating, whereas for A-2-x, the dominant reaction is between elemental Si in the alloy and MnO in the oxide. Full article
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Open AccessArticle Chemical Dealloying Synthesis of CuS Nanowire-on-Nanoplate Network as Anode Materials for Li-Ion Batteries
Metals 2018, 8(4), 252; https://doi.org/10.3390/met8040252
Received: 7 March 2018 / Revised: 3 April 2018 / Accepted: 4 April 2018 / Published: 9 April 2018
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Abstract
CuS is a metal sulfide anode material used in constructing lithium ion batteries (LIBs) with great promise. However, its practical application is limited by rapid capacity decline, poor cycling, and rate performance. In this work, the CuS nanowire-on-nanoplate network is synthesized through an
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CuS is a metal sulfide anode material used in constructing lithium ion batteries (LIBs) with great promise. However, its practical application is limited by rapid capacity decline, poor cycling, and rate performance. In this work, the CuS nanowire-on-nanoplate network is synthesized through an improved dealloying method under two contrasting reaction temperatures. When used as an LIB anode, the as-obtained CuS network exhibits superior cycling performance (420 mAh·g−1 retained after 100 cycles at 0.2 C). When at 3 C, it still delivers a capacity of around 350 mAh·g−1. The improved electrochemical performances of the CuS anode should be attributed to the well-designed nanowire-on-nanoplate network structure in which the introduction of nanowires improves Li storage sites, shortens Li-ion diffusion distance, enhances the conductivity of active materials, and offers multiscale spaces for buffering the volume variation. The fabrication route adopted in this paper has an important significance for developing the dealloying technique and designing more suitable anode structures for LIBs. Full article
(This article belongs to the Special Issue Nanoporous Metals)
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Open AccessArticle Microstructure and Mechanical Properties of Al–SiC Nanocomposites Synthesized by Surface-Modified Aluminium Powder
Metals 2018, 8(4), 253; https://doi.org/10.3390/met8040253
Received: 5 March 2018 / Revised: 27 March 2018 / Accepted: 3 April 2018 / Published: 9 April 2018
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Abstract
Ceramic nanoparticle-reinforced aluminium metal matrix composites (AMMCs) have superior mechanical properties compared with matrix alloys, exhibiting great potential in structural applications in industries such as the aerospace and automotive sectors. This research proposes a new method for distributing SiC nanoparticles in an aluminium
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Ceramic nanoparticle-reinforced aluminium metal matrix composites (AMMCs) have superior mechanical properties compared with matrix alloys, exhibiting great potential in structural applications in industries such as the aerospace and automotive sectors. This research proposes a new method for distributing SiC nanoparticles in an aluminium matrix alloy by powder metallurgy. The mixing of aluminium powder and SiC nanoparticles was processed by a two-step procedure, which included ultrasound-assisted stirring and planetary agitation. After that, the mixing powder was subjected to compaction, sintering and extrusion. A blank sample and three composite sheets containing 1, 2 and 3 wt % SiC nanoparticles were prepared and the mechanical properties were investigated by micro-hardness and tensile tests. A scanning electron microscope (SEM) and electron back-scattered diffraction (EBSD) were used for microstructural analysis of the composite. Experimental results revealed that by adding 1, 2, 3 wt % SiC nanoparticles, hardness was increased by 26%, 34.5%, 40.0% and tensile strength was increased by 22.3%, 28.6% and 29.3%, respectively. The grain size of the aluminium matrix decreased with the addition of SiC nanoparticles. Moreover, a decrease of elongation was observed with the increasing weight fraction of SiC. Full article
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Open AccessArticle Abnormal Grain Growth in the Heat Affected Zone of Friction Stir Welded Joint of 32Mn-7Cr-1Mo-0.3N Steel during Post-Weld Heat Treatment
Metals 2018, 8(4), 254; https://doi.org/10.3390/met8040254
Received: 12 March 2018 / Revised: 3 April 2018 / Accepted: 5 April 2018 / Published: 9 April 2018
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Abstract
The abnormal grain growth in the heat affected zone of the friction stir welded joint of 32Mn-7Cr-1Mo-0.3N steel after post-weld heat treatment was confirmed by physical simulation experiments. The microstructural stability of the heat affected zone can be weakened by the welding thermal
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The abnormal grain growth in the heat affected zone of the friction stir welded joint of 32Mn-7Cr-1Mo-0.3N steel after post-weld heat treatment was confirmed by physical simulation experiments. The microstructural stability of the heat affected zone can be weakened by the welding thermal cycle. It was speculated to be due to the variation of the non-equilibrium segregation state of solute atoms at the grain boundaries. In addition, the pressure stress in the welding process can promote abnormal grain growth in the post-weld heat treatment. Full article
(This article belongs to the Special Issue Friction Stir Welding and Processing in Alloy Manufacturing)
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Open AccessArticle Internal Friction Angle of Metal Powders
Metals 2018, 8(4), 255; https://doi.org/10.3390/met8040255
Received: 25 January 2018 / Revised: 6 April 2018 / Accepted: 6 April 2018 / Published: 10 April 2018
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Abstract
Metal powders are components with multidisciplinary usage as their application is very broad. Their consistent characterization across all disciplines is important for ensuring repeatable and trouble-free processes. Ten metal powders were tested in the study. In all cases, the particle size distribution and
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Metal powders are components with multidisciplinary usage as their application is very broad. Their consistent characterization across all disciplines is important for ensuring repeatable and trouble-free processes. Ten metal powders were tested in the study. In all cases, the particle size distribution and morphology (scanning electron microscope—SEM photos) were determined. The aim of this work was to inspect the flow behavior of metal powders through another measured characteristic, namely the angle of internal friction. The measured values of the effective internal friction angle in the range 28.6–32.9°, together with the spherical particle shape and the particle size distribution, revealed the likely dominant mode of the metal particle transfer mechanism for stainless steel 316L, zinc and aluminum powder. This third piston flow mechanism is described and illustrated in detail. The angle of internal friction is mentioned as another suitable parameter for the characterization of metal powders, not only for the relative simplicity of the determination but also for gaining insight into the method of the movement of individual particles during the flow. Full article
(This article belongs to the Special Issue Powder Synthesis and Processing)
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Open AccessArticle Correction of Flow Curves and Constitutive Modelling of a Ti-6Al-4V Alloy
Metals 2018, 8(4), 256; https://doi.org/10.3390/met8040256
Received: 9 March 2018 / Revised: 29 March 2018 / Accepted: 5 April 2018 / Published: 10 April 2018
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Abstract
Isothermal uniaxial compressions of a Ti-6Al-4V alloy were carried out in the temperature range of 800–1050 °C and strain rate range of 0.001–1 s−1. The effects of friction between the specimen and anvils as well as the increase in temperature caused
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Isothermal uniaxial compressions of a Ti-6Al-4V alloy were carried out in the temperature range of 800–1050 °C and strain rate range of 0.001–1 s−1. The effects of friction between the specimen and anvils as well as the increase in temperature caused by the high strain rate deformation were considered, and flow curves were corrected as a result. Constitutive models were discussed based on the corrected flow curves. The correlation coefficient and average absolute relative error for the strain compensated Arrhenius-type constitutive model are 0.986 and 9.168%, respectively, while the values for a modified Johnson-Cook constitutive model are 0.924 and 22.673%, respectively. Therefore, the strain compensated Arrhenius-type constitutive model has a better prediction capability than a modified Johnson-Cook constitutive model. Full article
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Open AccessArticle A Springback Prediction Model for Warm Forming of Aluminum Alloy Sheets Using Tangential Stresses on a Cross-Section of Sheet
Metals 2018, 8(4), 257; https://doi.org/10.3390/met8040257
Received: 22 February 2018 / Revised: 4 April 2018 / Accepted: 5 April 2018 / Published: 10 April 2018
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Abstract
Warm U-draw bending tests were performed on a 5182 aluminum alloy under isothermal and non-isothermal conditions, and the amounts of springback under the corresponding conditions were measured. Finite element method analyses were then conducted to calculate the tangential stress distribution on the cross-section
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Warm U-draw bending tests were performed on a 5182 aluminum alloy under isothermal and non-isothermal conditions, and the amounts of springback under the corresponding conditions were measured. Finite element method analyses were then conducted to calculate the tangential stress distribution on the cross-section of the sheet during the warm forming process. It was found that the experimentally measured springback values were proportionally related to the differences in the amounts of tangential stresses at the top and bottom layers of the sheet section. A functional model that can account for the correlation between the amount of springback and the difference in tangential stresses at the top and bottom layers of the sheet section was derived based on an Euler beam and a nonlinear flow stress model with temperature and strain rate dependencies. The developed model, which can predict springback behavior using only results of forming analyses of warm formed aluminum alloy sheets, is anticipated to provide for advancements in the understanding of springback behavior at warm temperatures and improve the efficiency of design and analysis processes used to fabricate parts with complicated shapes by saving considerable time and costs for the analysis of springback. Full article
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