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Metals, Volume 9, Issue 8 (August 2019)

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Cover Story (view full-size image) The combination of spark plasma sintering (SPS) and selective laser melting (SLM) was introduced to [...] Read more.
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Open AccessArticle
Effect of Rise and Fall Time on Dwell Fatigue Behavior of a High Strength Titanium Alloy
Metals 2019, 9(8), 914; https://doi.org/10.3390/met9080914 - 20 Aug 2019
Viewed by 464
Abstract
Frequency is an important factor influencing the fatigue behavior. Regarding to the dwell fatigue, it corresponds to the effect of rise and fall time, which is also an important issue especially for the safety evaluation of structure parts under dwell fatigue loading, such [...] Read more.
Frequency is an important factor influencing the fatigue behavior. Regarding to the dwell fatigue, it corresponds to the effect of rise and fall time, which is also an important issue especially for the safety evaluation of structure parts under dwell fatigue loading, such as the engines of aircrafts and the pressure hulls of deep-sea submersibles. In this paper, the effect of rise and fall time (2 s, 20 s, 110 s, and 200 s) on the dwell fatigue behavior is investigated for a high strength titanium alloy Ti-6Al-2Sn-2Zr-3Mo-X with basket-weave microstructure. It is shown that the dwell fatigue life decreases with increasing the rise and fall time, which could be correlated by a linear relation in log–log scale for both the specimen with circular cross section and the specimen with square cross section. The rise and fall time has no influence on the crack initiation mechanism by the scanning electron microscope observation. The cracks initiate from the specimen surface and all the fracture surfaces present multiple crack initiation sites. Moreover, the facet characteristic is observed at some crack initiation sites for both the conventional fatigue and dwell fatigue tests. The paper also indicates that the dwell period of the peak stress reduces the fatigue life and the dwell fatigue life seems to be longer for the specimen with circular cross section than that of the specimen with square cross section. Full article
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Open AccessEditorial
Fracture, Fatigue, and Structural Integrity of Metallic Materials
Metals 2019, 9(8), 913; https://doi.org/10.3390/met9080913 - 20 Aug 2019
Viewed by 512
Abstract
Fracture, fatigue, and other subcritical processes, such as creep crack growth or stress corrosion cracking, present numerous open issues from both scientific and industrial points of view [...] Full article
(This article belongs to the Special Issue Fracture, Fatigue and Structural Integrity of Metallic Materials)
Open AccessArticle
The Effects of Laser Remelting on the Microstructure and Performance of Bainitic Steel
Metals 2019, 9(8), 912; https://doi.org/10.3390/met9080912 - 20 Aug 2019
Viewed by 433
Abstract
The surface of bainitic steel was remelted by fiber laser, and the microstructure and mechanical properties of the melted layer were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), a nanoindentation instrument, and wear equipment. The study of changing the laser [...] Read more.
The surface of bainitic steel was remelted by fiber laser, and the microstructure and mechanical properties of the melted layer were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), a nanoindentation instrument, and wear equipment. The study of changing the laser scanning speed showed that the depth of the melted layer increases with decreases of the laser scanning speed. The wear-resistance property increased by 55% compared with the matrix and decreased with the reduction of laser scanning speed within a certain range. In the study of changing the laser-scanning space, the thermal effect of laser melting in the back channel on the front channel was further validated. At the same time, it was found that the solidified layer surface of hardness alternating with softness can be obtained by appropriately expanding the scanning space, which is conducive to improving the wear-resistant properties of the steel surface, and properly improving the production efficiency of the laser remelting treatment. Full article
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Open AccessArticle
Cleaner Recycling of Spent Lead-Acid Battery Paste and Co-Treatment of Pyrite Cinder via a Reductive Sulfur-Fixing Method for Valuable Metal Recovery and Sulfur Conservation
Metals 2019, 9(8), 911; https://doi.org/10.3390/met9080911 - 20 Aug 2019
Viewed by 442
Abstract
This study proposes a cleaner lead-acid battery (LAB) paste and pyrite cinder (PyC) recycling method without excessive generation of SO2. PyCs were employed as sulfur-fixing reagents to conserve sulfur as condensed sulfides, which prevented SO2 emissions. In this work, the [...] Read more.
This study proposes a cleaner lead-acid battery (LAB) paste and pyrite cinder (PyC) recycling method without excessive generation of SO2. PyCs were employed as sulfur-fixing reagents to conserve sulfur as condensed sulfides, which prevented SO2 emissions. In this work, the phase transformation mechanisms in a PbSO4-Na2CO3-Fe3O4-C reaction system were studied in detail. Furthermore, the co-treatment of spent LAB and PyCs was conducted to determine the optimal recycling conditions and to detect the influences of different processing parameters on lead recovery and sulfur fixation. In addition, a bench-scale experiment was carried out to confirm the feasibility and reliability of this novel process. The results reveal that the products were separated into three distinct layers: slag, ferrous matte, and crude lead. 98.3% of lead and 99% of silver in the feed materials were directly enriched in crude lead. Crude lead with purity of more than 98 wt.% (weight percent) was obtained by a one-step extraction. Lead contents in the produced matte and slag were below 2.7 wt.% and 0.6 wt.%, respectively. At the same time, 99.2% total sulfur was fixed and recovered. Full article
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Open AccessArticle
Parametric Study of Fixtured Vibropeening
Metals 2019, 9(8), 910; https://doi.org/10.3390/met9080910 - 19 Aug 2019
Viewed by 504
Abstract
Vibropeening is a surface treatment process, which combines the peening effect of introducing residual stress with the polishing effect of reducing surface roughness in one single process step. Vibropeening equipment induces vibrations into the media to impart residual compressive stresses in sub-surface layers, [...] Read more.
Vibropeening is a surface treatment process, which combines the peening effect of introducing residual stress with the polishing effect of reducing surface roughness in one single process step. Vibropeening equipment induces vibrations into the media to impart residual compressive stresses in sub-surface layers, as well as polishing on the surface of the work piece. In addition to process parameters, such as vibration frequency, amplitude, and media mass, which are well known in literature, this paper will focus on the study of two additional parameters: immersion depth and process time. It was found that the lower-middle section of the vibratory trough produced the highest Almen deflection. Different continuous treatment times were also studied to explore the maximum introducible residual compressive stress state, and it was concluded that an optimal time range is required to achieve the best residual stress profile. The study demonstrates that different process parameters can influence the effectiveness of the vibropeening process, and that these can be potentially optimized for higher treatment capability. Full article
(This article belongs to the Special Issue Advanced Surface Enhancement)
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Open AccessArticle
Thermodynamic Analysis for the Magnetic-Field-Induced Precipitation Behaviours in Steels
Metals 2019, 9(8), 909; https://doi.org/10.3390/met9080909 - 19 Aug 2019
Viewed by 477
Abstract
Alloy carbide M23C6 plays a significant role in the creep strength of reduced activation steels. Experiments have proven that a magnetic field accelerates the precipitation of M23C6 at intermediate temperature. A scheme that combines first-principle calculations, Weiss [...] Read more.
Alloy carbide M23C6 plays a significant role in the creep strength of reduced activation steels. Experiments have proven that a magnetic field accelerates the precipitation of M23C6 at intermediate temperature. A scheme that combines first-principle calculations, Weiss molecular field theory and equilibrium software MTDATA is proposed to investigate the thermodynamic features of magnetic-field-induced precipitation. The calculated results reveal that the origin of the magnetic moment is the NaCl-like crystal structure. The magnetic field enhances the exchange coupling and stabilizes the ferromagnetic phase region. The external field influences the Curie temperature, thereby changing the magnitude and position of the maximum magnetic heat capacity, magnetic entropy and enthalpy. The strong magnetic field improves the stability of M23C6, and the theoretical results agree well with the previous experiment. The study provides a theoretical basis for the magnetic-field-induced precipitation behaviours in steels. Full article
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Open AccessArticle
The Zinc-Rich Corner of the Fe-Si-Sn-Zn Quaternary System at 450 °C
Metals 2019, 9(8), 908; https://doi.org/10.3390/met9080908 - 19 Aug 2019
Viewed by 423
Abstract
The 450 °C isothermal sections of the Fe-Si-Sn-Zn quaternary system with Zn composition fixed at 70 and 93 at.% were determined experimentally using optical microscopy, scanning electronic microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDS), and X-ray diffractometry (XRD). Five four-phase regions were [...] Read more.
The 450 °C isothermal sections of the Fe-Si-Sn-Zn quaternary system with Zn composition fixed at 70 and 93 at.% were determined experimentally using optical microscopy, scanning electronic microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDS), and X-ray diffractometry (XRD). Five four-phase regions were identified in the 70 at.% Zn section, whereas no four-phase region was found in the 93 at.% Zn section. The liquid phase was found to be in equilibrium with almost all phases in the two sections, including the FeSn, FeSi, FeSi2, Γ1, δ, ζ, and α-Fe phases. The solubility of Sn in the ζ, FeSi, and FeSi2 phases was rather limited; however, the maximum solubility of Si in the FeSn phase was 0.5 wt.%. No quaternary compound was found in the study. Full article
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Open AccessEditorial
Processing–Structure–Property Relationships in Metals
Metals 2019, 9(8), 907; https://doi.org/10.3390/met9080907 - 19 Aug 2019
Viewed by 506
Abstract
The increasing demand for advanced materials in construction, transportation, communications, medicine, energy production, as well as in several other fields, is the driving force for investigating the processing–structure–property relationships [...] Full article
(This article belongs to the Special Issue Processing-Structure-Property Relationships in Metals)
Open AccessArticle
Synthesis and Mechanical Testing of Calcium Aluminosilicoferrite Crystals with High Alumina Content
Metals 2019, 9(8), 906; https://doi.org/10.3390/met9080906 - 18 Aug 2019
Viewed by 540
Abstract
Due to the gradual shift to less rich iron ores, the alumina content in the raw materials used for iron-making is progressively increasing, affecting the mineralogy and the properties of iron ore sinters. In this context, the effect of Al content on the [...] Read more.
Due to the gradual shift to less rich iron ores, the alumina content in the raw materials used for iron-making is progressively increasing, affecting the mineralogy and the properties of iron ore sinters. In this context, the effect of Al content on the mechanical properties of calcium aluminosilicoferrites Ca2(Ca,Mg,Fe)6(Fe,Si,Al)6O20 (SFCA), which is the most important bonding phase in iron ore sinters, is of particular interest. In this study, high-alumina calcium aluminosilicoferrites were synthesized and their mechanical properties were determined by nanoindentation using a cube-corner indenter. For synthesis, different raw materials were taken as proxies for the adhering layer in a sinter granule. Three mixtures were prepared, high-iron, high-silica, and high-alumina and heated in an alumina crucible, which was used to simulate the high-alumina nucleus in a granule. The different raw materials used for synthesis had only minor influence on the compositions of the synthesized ferrites. All ferrites showed similar mechanical behavior during indentation, indicating that neither the chemical nor the mechanical properties were affected by the different compositions of the adhering layer, when the sinter granule is dominated by a high-alumina nucleus. The crystallographic orientation of the tested grains had only minor influence on the results of the nanoindentation experiments. Full article
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Open AccessArticle
A new Dynamic Plasticity and Failure Model for Metals
Metals 2019, 9(8), 905; https://doi.org/10.3390/met9080905 - 18 Aug 2019
Viewed by 528
Abstract
A new plasticity and failure model is developed herein for metallic materials subjected to dynamic loadings on the basis of the analysis of some available material test data and previous work. The new model consists of two parts: a strength model and a [...] Read more.
A new plasticity and failure model is developed herein for metallic materials subjected to dynamic loadings on the basis of the analysis of some available material test data and previous work. The new model consists of two parts: a strength model and a failure criterion. The strength model takes into consideration both tension and shear stress-strain relationships, as well as the effect of Lode angle, while the failure criterion takes into account both the effects of stress triaxiality and Lode angle. Furthermore, the effects of strain rate and temperature are also catered for in the model. In particular, new non-linear functions are suggested for the effects of strain rate and temperature in the strength model in order to describe accurately the mechanical behavior of metallic materials at very high loading rates and temperature. The new model is compared with available material test data for 2024-T351 aluminum alloy, 6061-T6 aluminum alloy, oxygen free high conductivity (OFHC) copper, 4340 steel, Ti-6Al-4V alloys, and Q235 mild steel in terms of stress–strain curves in both tension and shear, strain rate effect, temperature effect and fracture under different loading conditions. The new model is also compared with the JC constitutive model with the respective JC and BW fracture criteria by conducting numerical simulations of quasi-static smooth and notched bar tensile tests and ballistic perforation tests on 2024-T351 aluminum alloy in terms of cup and cone failure pattern, ballistic limit, residual velocity and failure mode. It transpires that the new plasticity and failure model can be used to predict the response and failure of metallic materials and structures under different loading conditions. It also transpires that the new model is advantageous over the existing models. Full article
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Open AccessArticle
Influence of Heat Treatment on the Workability of Modified 9Cr-2W Steel with Higher B Content
Metals 2019, 9(8), 904; https://doi.org/10.3390/met9080904 - 18 Aug 2019
Viewed by 571
Abstract
In this study, the effect of heat treatment on the fracture behavior of alloy B steel with boron (B) contents as high as 130 ppm was investigated. The Alloy B are derived from Gr.92 steel with outstanding creep characteristics. The amounts of minor [...] Read more.
In this study, the effect of heat treatment on the fracture behavior of alloy B steel with boron (B) contents as high as 130 ppm was investigated. The Alloy B are derived from Gr.92 steel with outstanding creep characteristics. The amounts of minor alloying elements such as B, N, Nb, Ta, and C were optimized to achieve better mechanical properties at high temperatures. Hence, workability of the alloy B and Gr.92 were compared. An increase in the B content affected the phase transformation temperature and texture of the steel. The development of the {111}<uvw> components in γ-fibers depended on the austenite fraction of the steel after the phase transformation. An increase in the B content of the steel increased its α-to-γ phase transformation temperature, thus preventing the occurrence of sufficient transformation under the normalizing condition. Cracks occurred at the point of the elastic-to-plastic deformation transition in the normal direction during the rolling process, thereby resulting in failure. Therefore, it is necessary to avoid intermediate heat treatment conditions, in which γ-fibers do not fully develop, i.e., to avoid an imperfect normalization. Full article
(This article belongs to the Special Issue Forming Processes of Modern Metallic Materials)
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Open AccessArticle
Development of an Analytical Model for the Extraction of Manganese from Marine Nodules
Metals 2019, 9(8), 903; https://doi.org/10.3390/met9080903 - 17 Aug 2019
Viewed by 619
Abstract
Multivariable analytical models provide a descriptive (albeit approximate) mathematical relationship between a set of independent variables and one or more dependent variables. The current work develops an analytical model that extends a design of experiments for the leaching of manganese from marine nodules, [...] Read more.
Multivariable analytical models provide a descriptive (albeit approximate) mathematical relationship between a set of independent variables and one or more dependent variables. The current work develops an analytical model that extends a design of experiments for the leaching of manganese from marine nodules, using sulfuric acid (H2SO4) in the presence of iron-containing tailings, which are both by-products of conventional copper extraction. The experiments are configured to address the effect of time, particle size, acid concentration, Fe2O3/MnO2 ratio, stirring speed and temperature, under typical industrial conditions. The recovery of manganese has been modeled using a first order differential equation that accurately fits experimental results, noting that Fe2O3/MnO2 and temperature are the most critical independent variables, while the particle size is the least influential (under typical conditions). This study obtains representative fitting parameters, that can be used to explore the incorporation of Mn recovery from marine nodules, as part of the extended value chain of copper sulfide processing. Full article
(This article belongs to the Special Issue Advanced Simulation Technologies of Metallurgical Processing)
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Open AccessArticle
Enhancing Corrosion Resistance of High-Carbon Steel by Formation of Surface Layers Using Wastes as Input
Metals 2019, 9(8), 902; https://doi.org/10.3390/met9080902 - 16 Aug 2019
Viewed by 602
Abstract
Series of super-hard ceramic layers have been successfully developed on high carbon steels, with a significant improvement of corrosion resistance and hardness, without changing the original properties, which were derived from mixtures of slag (electric arc furnace), waste glass (bottles), and automotive shredder [...] Read more.
Series of super-hard ceramic layers have been successfully developed on high carbon steels, with a significant improvement of corrosion resistance and hardness, without changing the original properties, which were derived from mixtures of slag (electric arc furnace), waste glass (bottles), and automotive shredder residue (ASR) plastics (polypropylene) via the single step surface modification technique. Microstructural analysis by laser scanning confocal microscopy (LSCM), crystallography analysis by X-ray diffraction (XRD), micro-level chemical analysis by scanning electron microscopy and energy dispersive spectroscopy (SEM and EDS), and depth profile surface analysis with three-dimensional chemical mapping by time-of-flight secondary ion mass spectrometry (TOF-SIMS), followed by electrochemical corrosion test by the Tafel method and hardness test—Vickers hardness measurement. Three areas have been classified, modified surface, interface, and main substrate areas as the synthesis of ceramic layers into surface of the steels that thermodynamically formed during the heat treatment process. Chemical composition analyses have revealed that generated layers consisting of chromium (Cr)- and magnesium (Mg)-based compound have shown an improved corrosion resistance to 52% and hardness to 70% without modifying the initial volume fraction of constituent phases–martensite and retained austenite. These findings have substantially highlighted to the potential use of waste-integrated inputs as raw materials for production in cost-effective way, concurrently decreasing the demand on new resource for coating, alleviating the disadvantageous impact to the environment from waste disposal in landfills. Full article
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Open AccessArticle
Elasto-Plastic Behaviour of Transversely Isotropic Cellular Materials with Inner Gas Pressure
Metals 2019, 9(8), 901; https://doi.org/10.3390/met9080901 - 16 Aug 2019
Viewed by 568
Abstract
The fabrication process of cellular materials, such as foaming, usually leads to cells elongated in one direction, but equiaxed in a plane normal to that direction. This study is aimed at understanding the elasto-plastic behaviour of transversely isotropic cellular materials with inner gas [...] Read more.
The fabrication process of cellular materials, such as foaming, usually leads to cells elongated in one direction, but equiaxed in a plane normal to that direction. This study is aimed at understanding the elasto-plastic behaviour of transversely isotropic cellular materials with inner gas pressure. An idealised ellipsoidal-cell face-centred-cubic foam that is filled with gas was generated and modelled to obtain the uniaxial stress–strain relationship, Poisson’s ratio and multiaxial yield surface. The effects of the elongation ratio and gas pressure on the elasto-plastic properties for a relative density of 0.5 were investigated. It was found that an increase in the elongation ratio caused increases in both the elastic modulus and yield stress for uniaxial loading along the cell elongation direction, and led to a tilted multiaxial yield surface in the mean stress and Mises equivalent stress plane. Compared to isotropic spheroidal-cell foams, the size of the yield surface of the ellipsoidal-cell foam is smaller for high-stress triaxiality, but larger for low-stress triaxiality, and the yield surface rotates counter-clockwise with the Lode angle increasing. The gas pressure caused asymmetry of the uniaxial stress–strain curve (e.g., reduced tensile yield stress), and it increased the nominal plastic Poisson’s ratio for compression, but had the opposite effect for tension. Furthermore, the gas pressure shifted the yield surface towards the negative mean stress axis with a distance equal to the gas pressure. The combined effects of the elongation ratio and gas pressure are complicated, particularly for the elasto-plastic properties in the plane in which the cells are equiaxed. Full article
(This article belongs to the Special Issue Cellular Metals: Fabrication, Properties and Applications)
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Open AccessArticle
Thermodynamics and Agglomeration Behavior on Spinel Inclusion in Al-Deoxidized Steel Coupling with Mg Treatment
Metals 2019, 9(8), 900; https://doi.org/10.3390/met9080900 - 16 Aug 2019
Viewed by 512
Abstract
There are many types of non-metallic MgAl2O4 inclusions observed in Al-deoxidized steel coupling with Mg treatment, including single-particle MgAl2O4, agglomerated MgAl2O4, and MgAl2O4-MnS. Thermodynamic calculation shows that MgAl [...] Read more.
There are many types of non-metallic MgAl2O4 inclusions observed in Al-deoxidized steel coupling with Mg treatment, including single-particle MgAl2O4, agglomerated MgAl2O4, and MgAl2O4-MnS. Thermodynamic calculation shows that MgAl2O4 precipitates in the liquid phase. The phase transformation follows liquid + Al2O3 + MgAl2O4 → liquid + MgAl2O4 → liquid + MgO + MgAl2O4 → liquid + MgO with the Mg content increasing when the Al content is a constant in molten steel, and it is in agreement with the experimental results for the formation of MgAl2O4 in molten steel. The calculation results of various attractive forces between two particles show that the cavity bridge force plays a dominant role in the agglomeration process and results in the agglomerated MgAl2O4. The lattice mismatch calculation result shows that MgAl2O4 can provide effective sites for MnS nucleating in steel. Full article
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Open AccessFeature PaperArticle
Selective Milling and Elemental Assay of Printed Circuit Board Particles for Their Recycling Purpose
Metals 2019, 9(8), 899; https://doi.org/10.3390/met9080899 - 16 Aug 2019
Viewed by 564
Abstract
Selective/preferential milling of printed circuit board (PCB) particles followed by non-destructive characterization of the mill products was performed in order to understand the effects of different feed masses into a hammer mill and different milling time on the metal recovery and enrichment ratio. [...] Read more.
Selective/preferential milling of printed circuit board (PCB) particles followed by non-destructive characterization of the mill products was performed in order to understand the effects of different feed masses into a hammer mill and different milling time on the metal recovery and enrichment ratio. Those are important variables affecting and determining the process performance and capacity. The milling tests and elemental assay characterization were conducted by using a hammer mill and a portable X-ray fluorescence analysis (XRF), respectively. The results showed the preferential metal concentration/enrichment was achieved for several elements and their degree was varied depending on the parameters. Using the experimental data, predictive models of metal recovery were developed and the global trend of metal recoveries was observed under different mill feed and milling time and discussed. Full article
(This article belongs to the Special Issue Advances in Characterization of Heterogeneous Metals/Alloys)
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Open AccessArticle
Microstructural Changes and Impact Toughness of Fill Pass in X80 Steel Weld Metal
Metals 2019, 9(8), 898; https://doi.org/10.3390/met9080898 - 16 Aug 2019
Viewed by 479
Abstract
Multi-pass welding is used in high-pressure and thick-walled pipes in natural gas and oil pipelines. When a welding layer of a welded joint is subjected to different welding thermal cycles, its microstructure and properties change, thereby affecting the overall welding performance. In this [...] Read more.
Multi-pass welding is used in high-pressure and thick-walled pipes in natural gas and oil pipelines. When a welding layer of a welded joint is subjected to different welding thermal cycles, its microstructure and properties change, thereby affecting the overall welding performance. In this study, the temperature and microstructural variations of the fill pass 2 (FP2) in the entire welding process were investigated by combining the thermal cycle with the cascade welding method. The original FP2 and FP2 after double thermal cycles had the worse deformation ability by tensile test. The toughness of FP2 improved after a single thermal cycle, decreased after double thermal cycles, and improved again after triple thermal cycles. The content of martensite–austenite (M–A) constituents and the average grain size of FP2 in the cascade samples were inversely proportional to FP2 toughness. Massive M–A constituents and their unique distribution at the inter-critical temperature were harmful to weld metal toughness. Controlling the size and fraction of M–A constituents can improve weld metal toughness. Full article
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Open AccessArticle
Tensile Behavior and Deformation Mechanism of Fe-Mn-Al-C Low Density Steel with High Strength and High Plasticity
Metals 2019, 9(8), 897; https://doi.org/10.3390/met9080897 - 16 Aug 2019
Viewed by 467
Abstract
Tensile behavior and plastic deformation mechanisms of Fe-22.8Mn-8.48Al-0.86C low-density steel were studied in this thesis. After solution treatment 1100 °C for 1 h; the steels obtained an excellent combination in mechanical properties; with tensile strength of 757.4 MPa and total elongation of 68%; [...] Read more.
Tensile behavior and plastic deformation mechanisms of Fe-22.8Mn-8.48Al-0.86C low-density steel were studied in this thesis. After solution treatment 1100 °C for 1 h; the steels obtained an excellent combination in mechanical properties; with tensile strength of 757.4 MPa and total elongation of 68%; which were attributed to the existence of annealing twins in austenite. The present steel presented a multiple stage strain hardening behavior which was associated with the changes of such dislocation substructures. With the increase of strain, the gradual transition from tangled dislocations to dense dislocation walls and microbands was found in (the transmission electron microscopy) TEM microstructures. Due to the influence of the evolution of the microstructure during the deformation process, the work hardening behavior of the experimental steel shows three distinct stages. Full article
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Open AccessArticle
Development on a Prediction Model for Experimental Condition of Flexibly Reconfigurable Roll Forming Process
Metals 2019, 9(8), 896; https://doi.org/10.3390/met9080896 - 15 Aug 2019
Viewed by 543
Abstract
Flexibly-reconfigurable roll forming (FRRF) is a novel sheet metal forming technology by which sheet metal is shaped into a desired curvature using reconfigurable rollers and gaps. FRRF is conducive to producing multi-curvature surfaces by controlling the longitudinal strain distribution. However, it is difficult [...] Read more.
Flexibly-reconfigurable roll forming (FRRF) is a novel sheet metal forming technology by which sheet metal is shaped into a desired curvature using reconfigurable rollers and gaps. FRRF is conducive to producing multi-curvature surfaces by controlling the longitudinal strain distribution. However, it is difficult to predict the forming results since FRRF technology forms a secondary surface from the primary curvature. This study investigates the use of regression analysis as a basis for a model that can predict the longitudinal curvature of sheet metal. The following variables were considered as input parameters: Maximum compression value, radius of curvature in the transverse direction, and initial blank width. Regression model samples are obtained by performing experiments using FRRF equipment whilst the experimental design was generated by a three-level, three-factor full factorial design. The experimental surfaces are of a convex and of a saddle-type shape, with a total sample size of 54. Through regression analysis it has been shown that the longitudinal curvature can be expressed by means of a quadratic equation. The matching quadratic function was verified with R-squared values and root-mean-square errors, whilst the normality of the sample data was also verified. To apply the model to the actual forming process, the regression model was converted to deduce the compression characteristics for forming the target surface. Throughout the study, the proposed analytical procedure was validated, and a statistical formula for estimating the longitudinal curvature produced by the FRRF apparatus established. Full article
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Open AccessArticle
Influence of Preaging Treatment on Bake-Hardening Response and Electrochemical Corrosion Behavior of High Strength Al-Zn-Mg-Cu-Zr Alloy
Metals 2019, 9(8), 895; https://doi.org/10.3390/met9080895 - 15 Aug 2019
Viewed by 589
Abstract
The influence of preaging (PA) treatments on the bake hardening (BH) response of a AlZnMgCuZr aluminum alloy which served as automotive body structures were studied in this paper. A novel two-step PA treatment was particularly designed and further employed. The mechanical properties of [...] Read more.
The influence of preaging (PA) treatments on the bake hardening (BH) response of a AlZnMgCuZr aluminum alloy which served as automotive body structures were studied in this paper. A novel two-step PA treatment was particularly designed and further employed. The mechanical properties of the alloy were tested in detail. The microstructure was characterized by optical microscope (OM), transmission electron microscopy (TEM) and 3D measuring laser microscope (3D–MLM). Meanwhile, the corrosion behavior was investigated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. The results indicated that the PA treatment was beneficial for the improvement of BH response after baking at 180 °C immediately after the solution treatment and the micro-hardness reached the peak value (194 HV) after 10 h holding, which had a percentage improvement of 110.87% compared to the hardness under the solution condition. The PA treatments decreased natural aging (NA) adverse effects, while it had the lowest NA effect and optimal BH response under 120 °C/20 min. Such a novel two-step PA treatment was revealed further to decrease the NA effect and increase the BH response compared to the optimal PA treatment, in particular, the BH value could reach 168 MPa and was 21.7% higher than that of optimal PA + NA treatment. The optimal corrosion resistance has been shown up by the combined characterizations of potentiodynamic polarization curves, EIS Nyquist plots, and 3D–MLM images. Full article
(This article belongs to the Special Issue Phase Transformations in Aluminium Alloys)
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Open AccessArticle
Effect of Tool Rotational Speed on the Microstructure and Mechanical Properties of Bobbin Tool Friction Stir Welded 6082-T6 Aluminum Alloy
Metals 2019, 9(8), 894; https://doi.org/10.3390/met9080894 - 15 Aug 2019
Viewed by 514
Abstract
Samples of 6082-T6 aluminum alloy were welded by bobbin tool friction stir welding at different rotational speeds. The thermal cycles, microstructure, microhardness, and tensile properties of the specimens were investigated. The results show that the maximum temperature at the joint increases first and [...] Read more.
Samples of 6082-T6 aluminum alloy were welded by bobbin tool friction stir welding at different rotational speeds. The thermal cycles, microstructure, microhardness, and tensile properties of the specimens were investigated. The results show that the maximum temperature at the joint increases first and then decreases with increasing rotational speed, and the maximum temperature is 509 °C at 1000 r/min. The macromorphology of the cross-section of the joint is rectangular, and an ‘’S” line and gray-white texture can be observed. The stirred zone had much smaller equiaxed recrystallized grains. With increasing welding speed, the average grain size in the stirred zone region decreases. The microhardness distribution of the cross-section of all joints is W-shaped. When the rotational speed increases, the hardness of the heat-affected zone decreases gradually, and the hardness of the stirred zone increases. At 600 r/min, the strength is the lowest. The fracture location is between the stirred zone and the thermomechanically affected zone. When the rotational speed is increased, the fracture location is entirely located in the heat affected zone, and the fracture surface is dimple-like; the strength significantly increases and reaches a maximum at 800 r/min. Full article
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Open AccessArticle
Evaluation of Volume Fraction of Austenite in Austempering Process of Austempered Ductile Iron
Metals 2019, 9(8), 893; https://doi.org/10.3390/met9080893 - 15 Aug 2019
Viewed by 479
Abstract
In the present work, an evaluation of the volume fraction of austenite in austempered ductile iron (ADI) is presented by means of three different methods. Experimental tests were conducted on ADI samples after different austempering conditions and contained different volume fractions of the [...] Read more.
In the present work, an evaluation of the volume fraction of austenite in austempered ductile iron (ADI) is presented by means of three different methods. Experimental tests were conducted on ADI samples after different austempering conditions and contained different volume fractions of the phase components in the metallic matrix (ferrite plates + austenite). A comparison of the volume fraction of austenite was carried out by metallographic magnetic methods using a variable field, as well as X-ray quantitative phase analysis. The main purpose of this work is to show the effectiveness of the proposed magnetic method for estimating the volume fraction of austenite in ADI cast iron. It is evident that the new method in which variable magnetic fields are used to quantify the phase composition exhibits very high accuracy within the second stage of the austempering transformation, in which the metallic matrix consists of ferrite plates and high-carbon austenite. Finally, this research shows that within the first and third stages the estimation of the volume fraction of the austenite is hampered by errors resulting from the presence of martensite (first stage) and carbide phases (third stage). Full article
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Open AccessArticle
Investigation on Springback Behavior of Cu/Ni Clad Foils during Flexible Die Micro V-Bending Process
Metals 2019, 9(8), 892; https://doi.org/10.3390/met9080892 - 15 Aug 2019
Viewed by 478
Abstract
With the increasing demand for micro parts using metal laminates in modern production, the manufacturing processes of thin sheet parts have been elevated. However, it is difficult to predict the deformation behavior with miniaturization because of size effects in micro-scale. In this study, [...] Read more.
With the increasing demand for micro parts using metal laminates in modern production, the manufacturing processes of thin sheet parts have been elevated. However, it is difficult to predict the deformation behavior with miniaturization because of size effects in micro-scale. In this study, the flexible die micro V-bending behavior of Cu/Ni clad foils was investigated. The bending experiments with three different punch angles and Cu/Ni clad foils under different annealed temperatures were performed. The results show that the springback angle increases with the increase of bending angle and annealing temperature. The placement of Cu/Ni clad foils induced compressive stress results in the more obvious thinning of thickness and decreasing of springback angle. The interactive effects of the distribution of deformation zones and compressive stress induced by the interface layer result in the springback behavior of Cu/Ni clad foils during the flexible die micro V-bending process. Full article
(This article belongs to the Special Issue Clad Metals: Fabrication, Properties and Applications)
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Open AccessArticle
Initial β Grain Size Effect on High-Temperature Flow Behavior of Tb8 Titanium Alloys in Single β Phase Field
Metals 2019, 9(8), 891; https://doi.org/10.3390/met9080891 - 15 Aug 2019
Viewed by 456
Abstract
The high-temperature flow behavior of TB8 titanium alloys with two different grain sizes was investigated in this present work. Results show that a significant characteristic of stress drop is visible at the start stage of the hot deformation process when the strain rates [...] Read more.
The high-temperature flow behavior of TB8 titanium alloys with two different grain sizes was investigated in this present work. Results show that a significant characteristic of stress drop is visible at the start stage of the hot deformation process when the strain rates are 100 and 10−1 s−1. With the further increasing of strain, the flow stress initially rises to a maximum value and subsequently attains a plateau for the strain rates of 100 s−1 and a slight decrease for the strain rates of 10−1 s−1. Only dynamic recovery occurs under these deformation conditions. When the strain rates drop to 10−3 s−1, the dynamic recrystallization takes place during hot deformation. The values of deformation activation energy and materials constants at different strains were calculated. The processing maps at different strains were established for the fine- and coarse-grained alloys. The optimal processing parameter for hot processing was attained to be 900 °C/10−3 s−1 for fine-grained alloys and 950 °C/10−3 s−1 for coarse-grained alloys, respectively. Full article
(This article belongs to the Special Issue Titanium Alloys: Processing and Properties)
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Open AccessArticle
Influence of Nickel Powders on Corrosion Resistance of Cold Sprayed Coatings on Al7075 Substrate
Metals 2019, 9(8), 890; https://doi.org/10.3390/met9080890 - 15 Aug 2019
Viewed by 445
Abstract
The influence of the size and structure of nickel powder grains on the corrosion resistance of nickel coatings on an Al7075 substrate in an acidic chloride solution was investigated. The Ni coating was produced by the cold spraying (CS) method. The surface and [...] Read more.
The influence of the size and structure of nickel powder grains on the corrosion resistance of nickel coatings on an Al7075 substrate in an acidic chloride solution was investigated. The Ni coating was produced by the cold spraying (CS) method. The surface and microstructure of specimens were observed by a scanning electron microscope (SEM). The corrosion test of the materials was carried out by using the electrochemical method. It has been found that the size of Ni powders has a significant effect on the corrosion resistance of nickel coatings. The porosity of nickel coatings on the Al7075 alloy increases with the increasing size of nickel powders. The corrosion rate of nickel coatings in the chloride environment decreases as the diameter of the nickel powders decreases. On the other hand, the highest corrosion resistance of nickel coatings was obtained using the Ni powders of the irregular spherical or dendritic structure. Moreover, the large particles of nickel powder cause strong residual stress (compared to small grains) in the depth of the nickel coatings. Full article
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Open AccessArticle
Analytical Modeling of the Mixed-Mode Growth and Dissolution of Precipitates in a Finite System
Metals 2019, 9(8), 889; https://doi.org/10.3390/met9080889 - 14 Aug 2019
Viewed by 552
Abstract
In this paper, a novel analytical modeling of the growth and dissolution of precipitates in substitutional alloys is presented. This model uses an existing solution for the shape-preserved growth of ellipsoidal precipitates in the mixed-mode regime, which takes into account the interfacial mobility [...] Read more.
In this paper, a novel analytical modeling of the growth and dissolution of precipitates in substitutional alloys is presented. This model uses an existing solution for the shape-preserved growth of ellipsoidal precipitates in the mixed-mode regime, which takes into account the interfacial mobility of the precipitate. The dissolution model is developed by neglecting the transient term in the mass conservation equation, keeping the convective term. It is shown that such an approach yields the so-called reversed-growth approximation. A time discretization procedure is proposed to take into account the evolution of the solute concentration in the matrix as the phase transformation progresses. The model is applied to calculate the evolution of the radius of spherical θ-Al2Cu precipitates in an Al rich matrix at two different temperatures, for which growth or dissolution occurs. A comparison of the model is made, with the results obtained using the numerical solver DICTRA. The very good agreement obtained for cases where the interfacial mobility is very high indicates that the time discretization procedure is accurate. Full article
(This article belongs to the Special Issue Phase Transformations in Aluminium Alloys)
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Open AccessArticle
Environmental Behavior of Low Carbon Steel Produced by a Wire Arc Additive Manufacturing Process
Metals 2019, 9(8), 888; https://doi.org/10.3390/met9080888 - 14 Aug 2019
Viewed by 537
Abstract
Current additive manufacturing (AM) processes are mainly focused on powder bed technologies, such as electron beam melting (EBM) and selective laser melting (SLM). However, the main disadvantages of such techniques are related to the high cost of metal powder, the degree of energy [...] Read more.
Current additive manufacturing (AM) processes are mainly focused on powder bed technologies, such as electron beam melting (EBM) and selective laser melting (SLM). However, the main disadvantages of such techniques are related to the high cost of metal powder, the degree of energy consumption, and the sizes of the components, that are limited by the size of the printing cell. The aim of the present study was to evaluate the environmental behavior of low carbon steel (ER70S-6) produced by a relatively inexpensive AM process using wire feed arc welding. The mechanical properties were examined by tension testing and hardness measurements, while microstructure was assessed by scanning electron microscopy and X-ray diffraction analysis. General corrosion performance was evaluated by salt spray testing, immersion testing, potentiodynamic polarization analysis, and electrochemical impedance spectroscopy. Stress corrosion performance was characterized in terms of slow strain rate testing (SSRT). All corrosion tests were carried out in 3.5% NaCl solution at room temperature. The results indicated that the general corrosion resistance of wire arc additive manufacturing (WAAM) samples were quite similar to those of the counterpart ST-37 steel and the stress corrosion resistance of both alloys was adequate. Altogether, it was clearly evident that the WAAM process did not encounter any deterioration in corrosion performance compared to its conventional wrought alloy counterpart. Full article
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Open AccessArticle
Microstructure and Mechanical Properties of Nb and V Microalloyed TRIP-Assisted Steels
Metals 2019, 9(8), 887; https://doi.org/10.3390/met9080887 - 14 Aug 2019
Viewed by 562
Abstract
The intercritical annealing and isothermal bainitic processing response was studied for three Nb and V microalloyed Transformation-Induced Plasticity (TRIP)-assisted 980 MPa grade steels. Their mechanical and microstructural properties were compared to industrially produced TRIP 800 steel. Depending on the isothermal holding temperature and [...] Read more.
The intercritical annealing and isothermal bainitic processing response was studied for three Nb and V microalloyed Transformation-Induced Plasticity (TRIP)-assisted 980 MPa grade steels. Their mechanical and microstructural properties were compared to industrially produced TRIP 800 steel. Depending on the isothermal holding temperature and microalloying, the experimental steels reached properties comparable to the reference steel. The retained austenite content did not show direct correlation to elongation properties. Niobium was found to be more effective microalloying element than vanadium in increasing the elongation properties, which were investigated by measuring true fracture strain from tensile test specimens. Full article
(This article belongs to the Special Issue TRIP Steels)
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Open AccessArticle
Mixing Phenomenon and Flow Field in Ladle of RH Process
Metals 2019, 9(8), 886; https://doi.org/10.3390/met9080886 - 14 Aug 2019
Viewed by 481
Abstract
Particle image velocimetry (PIV) system was adopted to investigate the relationship between the mixing phenomenon and the flow field of a 210 t RH degasser by a 1:4 scale water model. The results of mixing simulation experiments indicated that the mixing time decreased [...] Read more.
Particle image velocimetry (PIV) system was adopted to investigate the relationship between the mixing phenomenon and the flow field of a 210 t RH degasser by a 1:4 scale water model. The results of mixing simulation experiments indicated that the mixing time decreased with the increase of gas blowing rate. However, with the increase of Snorkel immersion depth (SID), the mixing time presented a decreasing rend firstly and then increased. The measurement of flow fields of RH ladle by PIV system can explain the phenomenon above. According to the characteristics of the flow field in RH ladle, the flow field can be divided into the mixing layer, the transition layer, and the inactive layer. On the one hand, the stirring power in RH ladle and vacuum chamber both increases with more gas blowing rate, leading to the decrease of mixing time. On the other hand, with SID increases from 400 mm to 480 mm, the gas blowing depth increase results in the mixing power increases, and the mixing time decreases at the beginning. Because of too much-molten steel in the vacuum chamber and the expanding of the inactive layer in RH ladle, however, the utilization rate of the gas driving force begins to decrease. Therefore, the mixing time started to increases with the increase of SID. Full article
(This article belongs to the Special Issue Refining and Casting of Steel)
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Open AccessArticle
Failure and Control of PCBN Tools in the Process of Milling Hardened Steel
Metals 2019, 9(8), 885; https://doi.org/10.3390/met9080885 - 14 Aug 2019
Viewed by 498
Abstract
The polycrystalline cubic boron nitride (PCBN) milling tool can be used in the mold industry to replace cemented carbide tools to improve machining efficiency and quality. It is necessary to study the tool wear and failure mechanism to increase machining efficiency and extend [...] Read more.
The polycrystalline cubic boron nitride (PCBN) milling tool can be used in the mold industry to replace cemented carbide tools to improve machining efficiency and quality. It is necessary to study the tool wear and failure mechanism to increase machining efficiency and extend tool life. Cr12MoV is used to analyze the failure form of PCBN tools in the interrupted cutting of hardened steels at low and high speed conditions in milling experiments. Experimental results show that the failure forms of PCBN tools include chipping and flank wear at low speed, and the failure modes at high speed are flank wear, the surface spalling of the rake face, and the fatigue failure on the flank face. The failure mechanism of different failure forms is analyzed by observing the surface morphology of the tool and using the theory of fracture mechanics. The results show that a high cutting speed should be selected to avoid the early damage of low speed and achieve better application of PCBN tools. At high cutting speed, tool failure is mainly caused by mechanical wear, diffusion wear, and oxidation wear. Moreover, a fatigue crack will occur at the cutting edge on the chamfered tool under thermal–mechanical coupling because of the intergranular fracture of the CBN grain and binder. A large area of accumulated fatigue damage may appear due to the influence of alternating mechanical stress and thermal stress. Finally, the control method to avoid tool failure is presented. Full article
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