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Metals, Volume 9, Issue 9 (September 2019)

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Cover Story (view full-size image) The wetting behavior of Ti6Al4V surfaces that were groove-structured by means of femtosecond laser [...] Read more.
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Open AccessArticle
Analysis, Validation and Optimization of the Multi-Stage Sequential Wiredrawing Process of EN AW-1370 Aluminium
Metals 2019, 9(9), 1021; https://doi.org/10.3390/met9091021 - 19 Sep 2019
Viewed by 311
Abstract
For the wiredrawing of aluminium, the initial wire rod is obtained by continuous inverted casting. The raw geometry is industrially processed in a linear multi-step wiredrawing sequence to obtain a wire that is commonly used for the manufacture of electrical conductors. In the [...] Read more.
For the wiredrawing of aluminium, the initial wire rod is obtained by continuous inverted casting. The raw geometry is industrially processed in a linear multi-step wiredrawing sequence to obtain a wire that is commonly used for the manufacture of electrical conductors. In the present work a complete study of the material has been made. The experimental procedure consisted in the realization of a sequence of section reduction stages in the laboratory, a sequence designed following the technological criteria recommended by the manufacturer of the drawing machine in which the industrial process will be implemented. From the specimens corresponding to each reduction step, it has been possible to know the evolution of the main mechanical properties when this pure aluminium is processed by wiredrawing. This information has led to establish the hardening law by which it is possible characterize the plastic behaviour of this pure metal when it is transformed by this specific sequential process of cold forming. The strain hardening law has been implemented in a numerical simulation software application and the experimental setup has been simulated for its validation. Finally, the classic analytical solution founded in the “slab method” has been applied for the design of a proposal for the optimization of the industrial wiredrawing process. Full article
(This article belongs to the Special Issue Analysis and Design of Metal-Forming Processes)
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Open AccessArticle
Light-Weight Topological Optimization for Upper Arm of an Industrial Welding Robot
Metals 2019, 9(9), 1020; https://doi.org/10.3390/met9091020 - 19 Sep 2019
Viewed by 237
Abstract
To reduce weight and improve overall performance of the industrial welding robot, light-weight design using the finite element method and structural topological optimization is presented in this paper. The work analyzed an upper arm of an industrial welding robot in the most unfavorable [...] Read more.
To reduce weight and improve overall performance of the industrial welding robot, light-weight design using the finite element method and structural topological optimization is presented in this paper. The work analyzed an upper arm of an industrial welding robot in the most unfavorable working condition, both under static and dynamic working situations, using ABAQUS and ADAMS software tools. Then the Tosca unit in ABAQUS was employed to accomplish the structural topological optimization, in order to reduce weight and improve the natural frequencies under the situation of low orders. The analyses results showed that the actual weight had been reduced to 17.9%, and the natural frequencies in low orders had increased. The maximum Mises stress, tensile stress, and elastic displacement of the gyration center had decreased. Lastly, an actual product was produced according to the model obtained from preceding analyses. The experiments of the repeatability tests showed that the overall performance of the optimized upper arm had been improved when compared to the original one. This research can present references and foundations for the kinetic analyses under the static and dynamic working conditions, and structural topological optimization designs for relative industrial welding robots. Full article
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Open AccessArticle
The Role of Microstructure on the Tensile Plastic Behaviour of Ductile Iron GJS 400 Produced through Different Cooling Rates—Part II: Tensile Modelling
Metals 2019, 9(9), 1019; https://doi.org/10.3390/met9091019 - 19 Sep 2019
Cited by 1 | Viewed by 261
Abstract
Tensile testing on ductile iron GJS 400 with different microstructures produced through four different cooling rates was performed in order to investigate the relevance of the microstructure’s parameters on its plastic behaviour. Tensile flow curve modelling was carried out with the Follansbee and [...] Read more.
Tensile testing on ductile iron GJS 400 with different microstructures produced through four different cooling rates was performed in order to investigate the relevance of the microstructure’s parameters on its plastic behaviour. Tensile flow curve modelling was carried out with the Follansbee and Estrin-Kocks-Mecking approach that allowed for an explicit correlation between plastic behaviour and some microstructure parameters. In the model, the ferritic grain size and volume fraction of pearlite and ferrite gathered in the first part of this investigation were used as inputs, while other parameters, like nodule count and interlamellar spacing in pearlite, were neglected. The model matched very well with the experimental flow curves at high strains, while some mismatch was found only at small strains, which was ascribed to the decohesion between the graphite nodules and the ferritic matrix that occurred just after yielding. It can be concluded that the plastic behaviour of GJS 400 depends mainly on the ferritic grain size and pearlitic volume fraction, and other microstructure parameters can be neglected, primarily because of their high nodularity and few defects. Full article
(This article belongs to the Special Issue Cast Irons: Properties and Applications)
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Open AccessArticle
Corrosion-Induced Damage and Residual Strength of WC-Co,Ni Cemented Carbides: Influence of Microstructure and Corrosion Medium
Metals 2019, 9(9), 1018; https://doi.org/10.3390/met9091018 - 19 Sep 2019
Viewed by 203
Abstract
The corrosion behavior of cemented carbides with binders of different chemical nature (Co and Ni) and carbides with distinct mean grain size (ultrafine and coarse) was studied. The investigation also included corrosion media (acidic and neutral solutions containing chlorides and an alkaline solution) [...] Read more.
The corrosion behavior of cemented carbides with binders of different chemical nature (Co and Ni) and carbides with distinct mean grain size (ultrafine and coarse) was studied. The investigation also included corrosion media (acidic and neutral solutions containing chlorides and an alkaline solution) as experimental variables. Immersion tests were performed to induce corrosion damage in a controlled way. Electrochemical parameters were measured together with a detailed inspection of the corroded surfaces. Microstructural influence on the tolerance to corrosion damage was evaluated in terms of residual strength. Results pointed out that corrosion rates were lower in the alkaline solution. In contrast, acidic media led to higher corrosion rates, especially for cemented carbides with Co regardless the influence of carbide mean grain size. Corrosion damage resulted in strength degradation due to the formation of surface corrosion pits in acidic solution. In neutral and alkaline solutions, much less pronounced effects were determined. Focused Ion Beam (FIB)/ Field Emission Scanning Electron Microscopy (FESEM) results revealed differences in corrosion-induced damage scenario. In acidic solution, corrosion starts at binder pool centers and evolves towards binder/WC interfaces. Meanwhile, corrosion in alkaline solution is initially located at binder/WC interfaces, and subsequently expands into the ceramic particles, developing a microcrack network inside this phase. Full article
(This article belongs to the Special Issue Design of Cemented Carbides and Cermet)
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Open AccessArticle
Spectral Characterization of Copper and Iron Sulfide Combustion: A Multivariate Data Analysis Approach for Mineral Identification on the Blend
Metals 2019, 9(9), 1017; https://doi.org/10.3390/met9091017 - 19 Sep 2019
Viewed by 296
Abstract
The pyrometallurgical processes for primary copper production have only off-line and time-demanding analytical techniques to characterize the in and out streams of the smelting and converting steps. Since these processes are highly exothermic, relevant process information could potentially be obtained from the visible [...] Read more.
The pyrometallurgical processes for primary copper production have only off-line and time-demanding analytical techniques to characterize the in and out streams of the smelting and converting steps. Since these processes are highly exothermic, relevant process information could potentially be obtained from the visible and near-infrared radiation emitted to the environment. In this work, we apply spectral sensing and multivariate data analysis methodologies to identify and classify copper and iron sulfide minerals present in the blend from spectra measured during their combustion in a laboratory drop-tube setup, in which chemical reactions that take place in flash smelting furnaces can be reproduced. Controlled combustion experiments were conducted with two industrial concentrates and with high-grade mineral species as well, with a focus on pyrite and chalcopyrite. Exploratory analysis by means of Principal Component Analysis (PCA) applied on the spectral data depicted high correlation features among species with similar elemental compositions. Classification algorithms were tested on the spectral data, and a classification accuracy of 95.3% with a support vector machine (SVM) algorithm with a Gaussian kernel was achieved. The results obtained by the described procedures are shown to be very promising as a first step in the development of a predictive and analytical tool in search of fitting the current need for real-time control of pyrometallurgical processes. Full article
(This article belongs to the Special Issue Advances in Pyrometallurgy)
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Open AccessArticle
Prediction of Bake Hardening Behavior of Selected Advanced High Strength Automotive Steels and Hailstone Failure Discussion
Metals 2019, 9(9), 1016; https://doi.org/10.3390/met9091016 - 18 Sep 2019
Viewed by 217
Abstract
The purpose of the present study is three-fold. Firstly, it attempts to describe the bake hardening (BH) behavior of selected interstitial free (IF) and dual phase (DP) steels. Secondly, it predicts the BH behavior of the IF DX 51D and DP 500 HCT [...] Read more.
The purpose of the present study is three-fold. Firstly, it attempts to describe the bake hardening (BH) behavior of selected interstitial free (IF) and dual phase (DP) steels. Secondly, it predicts the BH behavior of the IF DX 51D and DP 500 HCT 590X plates of steel, and thirdly studies material failure prevention in scholarly sources. The research is aimed at investigating the increasing steel strength during the BH of these two high-strength sheets of steel used for outer vehicle body parts. Samples of steel were pre-strained to 1%, 2%, and 5% and then baked at 140–220 °C for 10 to 30 min. The BH effect was determined from three factors: pre-strain, baking temperature, and baking time. Research has shown that increasing the yield strength by the BH effect is predictable. Therefore, the number of experiments could be reduced for the investigation of BH effect for other kinds of IF and DP steels. The literature study of the hailstone failure reveals that the knowledge of BH steels behavior helps to calculate the steel supplier´s failure mode effect analysis (FMEA) risk priority number. Full article
(This article belongs to the Special Issue Failure Mechanisms in Alloys)
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Open AccessArticle
Oxidative Leaching of Zinc and Alkalis from Iron Blast Furnace Sludge
Metals 2019, 9(9), 1015; https://doi.org/10.3390/met9091015 - 18 Sep 2019
Viewed by 226
Abstract
The sludge from a wet-off gas cleaning system of the iron blast furnace (BF) contains significant amounts of iron; however, they cannot be recycled due to their high content of zinc and alkalis. These compounds are detrimental to the optimal performance of iron [...] Read more.
The sludge from a wet-off gas cleaning system of the iron blast furnace (BF) contains significant amounts of iron; however, they cannot be recycled due to their high content of zinc and alkalis. These compounds are detrimental to the optimal performance of iron and steelmaking furnaces. In this work, a comparative laboratory study to reduce zinc and alkali contained in the blast furnace sludge (BFS) is presented. The effect of leaching parameters such as oxidant (i.e., ferric ion, oxygen or ozone), aqueous solution media (i.e., 0.2 M NH4Cl, 0.2 M HCl and 0.1 M H2SO4) and temperature (i.e., 27 and 80 °C) on Zn and alkalis (Na2O and K2O) removal were studied by applying an experimental design. The results obtained show that Zn and K2O removal of 85% and 75% were achieved under the following conditions: Ozone as an oxidant agent and 0.1 M H2SO4 as an aqueous medium, temperature had no significant effect. The results are supported by thermodynamic diagrams and the possible chemical reactions are mentioned. Although the results also indicate that leaching under the above conditions dissolves up to 9% of iron, this loss is much less than leaching without the oxidizing conditions generated by the ozone. The BFS obtained from this treatment could be recirculated to the iron or steelmaking processes to recover iron values. Full article
(This article belongs to the Special Issue Advances in Mineral Processing and Hydrometallurgy)
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Open AccessArticle
Online Tool Wear Monitoring by the Analysis of Cutting Forces in Transient State for Dry Machining of Ti6Al4V Alloy
Metals 2019, 9(9), 1014; https://doi.org/10.3390/met9091014 - 17 Sep 2019
Viewed by 290
Abstract
In this work, the analysis of the cutting speed and feed rate influence on tool wear and cutting forces in Ti6Al4V alloy dry machining is presented. The study has been focused on the machining in a transient state. The tool wear mechanisms, tool [...] Read more.
In this work, the analysis of the cutting speed and feed rate influence on tool wear and cutting forces in Ti6Al4V alloy dry machining is presented. The study has been focused on the machining in a transient state. The tool wear mechanisms, tool wear intensity and cutting forces evolution have been analyzed as a function of the cutting parameters. Experimental results show that the main cutting force amplitude exhibits a general trend to increase with both cutting parameters. Crater wear was more evident at high cutting speeds, whereas flank wear was present on the whole interval of the cutting parameters analyzed. Furthermore, the cutting speed shows a slightly higher influence on crater wear and the feed rate shows a higher influence on flank wear. Finally, several experimental parametric models have been obtained. These models allow predicting the evolution of crater and flank tool wear, as well as the cutting forces, as a function of the cutting parameters. Additionally, a model that allows monitoring the tool wear on the machining transient state as a function of the main cutting force amplitude has been developed. Full article
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Open AccessArticle
Dynamic Mechanical Relaxation in LaCe-Based Metallic Glasses: Influence of the Chemical Composition
Metals 2019, 9(9), 1013; https://doi.org/10.3390/met9091013 - 17 Sep 2019
Viewed by 256
Abstract
The mechanical relaxation behavior of the (La0.5Ce0.5)65Al10(CoxCu1−x)25 at% (x = 0, 0.2, 0.4, 0.6, and 0.8) metallic glasses was probed by dynamic mechanical analysis. The intensity of the secondary β [...] Read more.
The mechanical relaxation behavior of the (La0.5Ce0.5)65Al10(CoxCu1−x)25 at% (x = 0, 0.2, 0.4, 0.6, and 0.8) metallic glasses was probed by dynamic mechanical analysis. The intensity of the secondary β relaxation increases along with the Co/Cu ratio, as has been reported in metallic glasses where the enthalpy of mixing for all pairs of atoms is negative. Furthermore, the intensity of the secondary β relaxation decreases after physical aging below the glass transition temperature, which is probably due to the reduction of the atomic mobility induced by physical aging. Full article
(This article belongs to the Special Issue Recent Advancements in Metallic Glasses)
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Open AccessArticle
The Microstructure, Mechanical Properties, and Corrosion Resistance of UNS S32707 Hyper-Duplex Stainless Steel Processed by Selective Laser Melting
Metals 2019, 9(9), 1012; https://doi.org/10.3390/met9091012 - 17 Sep 2019
Viewed by 249
Abstract
UNS S32707 hyper-duplex stainless steel (HDSS) parts with complex shapes for ocean engineering were prepared by selective laser melting (SLM) process. In the process of SLM, the balance between austenite and ferrite was undermined due to the high melting temperature and rapid cooling [...] Read more.
UNS S32707 hyper-duplex stainless steel (HDSS) parts with complex shapes for ocean engineering were prepared by selective laser melting (SLM) process. In the process of SLM, the balance between austenite and ferrite was undermined due to the high melting temperature and rapid cooling rate, resulting in poor ductility and toughness. The solution annealing was carried out with various temperatures (1050–1200 °C) for one hour at a time. The evolution of microstructures, mechanical properties, and corrosion resistance of UNS S32707 samples prepared by SLM was comprehensively investigated. The results indicate that a decrease in nitrogen content during the SLM process reduced the content of austenite, and a nearly balanced microstructure was obtained after appropriate solution annealing. The ratio between ferrite and austenite was approximately 59.5:40.5. The samples with solution treated at 1150 °C and 1100 °C exhibited better comprehensive mechanical properties and pitting resistance, respectively. Full article
(This article belongs to the Special Issue Additive Manufacturing of Metals)
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Open AccessArticle
Improved LSPR Properties of Ag–Pt and Pt Nanoparticles: A Systematic Study on Various Configurations and Compositions of NPs via the Solid-State Dewetting of Ag–Pt Bilayers
Metals 2019, 9(9), 1011; https://doi.org/10.3390/met9091011 - 16 Sep 2019
Viewed by 288
Abstract
The localized surface plasmon resonance (LSPR) of noble metal nanoparticles (NPs) has become an important research topic in various fields and can be systematically tuned to obtain the desired device performance through the appropriate structural and elemental modifications. In this research, the improved [...] Read more.
The localized surface plasmon resonance (LSPR) of noble metal nanoparticles (NPs) has become an important research topic in various fields and can be systematically tuned to obtain the desired device performance through the appropriate structural and elemental modifications. In this research, the improved LSPR properties of Pt NPs and diverse configurations and compositions of Ag–Pt bimetallic alloy NPs were demonstrated on sapphire (0001) via the solid-state dewetting (SSD) of Ag–Pt bilayers. A strong and dynamic LSPR response in the ultraviolet (UV) and visible (VIS) regions was demonstrated depending on the elemental composition and surface morphology of the NPs, which is discussed along with finite difference time domain (FDTD) simulations. In comparison, the Ag–Pt NPs exhibited stronger LSPR excitation, whereas the Pt NPs showed a relatively weaker and broader response. Meanwhile, the Pt NPs fabricated in this study still demonstrated a much-enhanced LSPR response compared to previous studies on the solid-state dewetting of pure Pt films due to improvements in configuration, uniformity, and interparticle gaps. Various surface morphologies of NPs, such as connected nanoclusters, elongated NPs, and isolated spherical NPs, were obtained on the basis of alloying, diffusion, Rayleigh instability, and a surface minimization mechanism, which were different from those of pure Ag and Pt NPs in similar growth conditions. Particularly, one-step annealing of an Ag–Pt bilayer yielded Ag–Pt alloy NPs below 600 °C, which subsequently transformed into pure Pt NPs above 650 °C, in which the high diffusivity and high vapor pressure of Ag atoms significantly facilitated the overall growth process of the NPs. Full article
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Open AccessArticle
Modelling of Mass and Thermal Balance and Simulation of Iron Sintering Process with Biomass
Metals 2019, 9(9), 1010; https://doi.org/10.3390/met9091010 - 16 Sep 2019
Viewed by 616
Abstract
This paper specifies the mathematical and physical modelling of the iron sintering process in laboratory conditions. The aim is to get the simplest approach (using thermodynamic software “HSC Chemistry”, version 9, Outokumpu Research Oy, Pori, Finland) that allows one to predict the output [...] Read more.
This paper specifies the mathematical and physical modelling of the iron sintering process in laboratory conditions. The aim is to get the simplest approach (using thermodynamic software “HSC Chemistry”, version 9, Outokumpu Research Oy, Pori, Finland) that allows one to predict the output parameters based on the initial composition analysis. As a part of the application of mathematical modelling, a mass and thermal balance of combustion of carbonaceous fuels (including biomass) and a mass and thermal balance of high-temperature sintering of an agglomeration charge were determined. The objective of the paper was to point out the advantages of modelling using thermodynamic software and apply the results into a simulation of the sintering process. The outcome of mathematical modelling correlates to the outcome of physical modelling for fuel combustion and the agglomerate production in a laboratory sintering pan. The energy required to reach the desired sintering temperatures and acquire the standard quality of agglomerate was calculated using 4.97% of coke breeze. In a real experiment with the laboratory sintering pan, 4.35% of coke was used. When a biomass fuel with a lower calorific value (lignin) is used in the agglomeration charge, the amount of fuel has to be increased to 5.52% (with 20% substitution of coke). This paper also aimed at predicting methodological tools and defining thermodynamic conditions for creating an interactive simulation. In addition, kinetics should be considered to improve the predicting capabilities of the current model and therefore in further research it will be required to optimise the computational program pursuant to the results of the kinetics experiments. Full article
(This article belongs to the Special Issue Mathematical Modeling and Simulation in Ironmaking and Steelmaking)
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Open AccessArticle
Process and Parameter Optimization of the Double-Pulsed GMAW Process
Metals 2019, 9(9), 1009; https://doi.org/10.3390/met9091009 - 15 Sep 2019
Viewed by 326
Abstract
The double pulsed gas metal arc welding (DP-GMAW) process has been effectively employed to realize joining of steel plates and obtain weld bead surfaces with high quality fish scale ripples. In this work, a DP-GMAW process based on robot operation using the latest [...] Read more.
The double pulsed gas metal arc welding (DP-GMAW) process has been effectively employed to realize joining of steel plates and obtain weld bead surfaces with high quality fish scale ripples. In this work, a DP-GMAW process based on robot operation using the latest twinpulse XT DP control technology was employed to join the stainless-steel base plates. Four key operational parameters, which were robot welding speed, twin pulse frequency, twin pulse relation and twin pulse current change in percent, were selected to be input elements of orthogonal experimental design, which included nine experiments with three levels. To accurately understand the performance and process of weld bead obtained from DP-GMAW operation based on robot operation, the appearance observation and key shape parameters measurement, microstructure analysis, tensile and hardness testing, as well as stability analysis of the electrical signals, were conducted. Correlation analysis showed that the grain size was significantly correlative to the toughness and hardness. Then, to obtain quantitative evaluation results, fuzzy comprehensive evaluation (FCE) was employed to provide quality evaluation of weld beads from the above experiments. The influential levels of the key operational parameters on the appearance, grain size and FCE scores, and corresponding physical analyses, were respectively presented. In addition, optimal parameters combinations for obtaining weld beads with optimal appearance, grain size, and the highest FCE scores of weld bead quality were respectively provided according to the range analysis of the results from orthogonal experimental design. This work can provide an effective analysis method of influential levels of key operational parameters on the performance of the weld bead, optimal operational parameters combination seeking method, and quantitative quality evaluation method for the DP-GMAW process, which can improve the process optimization and increase the production efficiency, both in academic research and actual industrial production. Full article
(This article belongs to the Special Issue Advanced Welding Technology in Metals)
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Open AccessArticle
Development of a High Strength Mg-9Li Alloy via Multi-Pass ECAP and Post-Rolling
Metals 2019, 9(9), 1008; https://doi.org/10.3390/met9091008 - 14 Sep 2019
Viewed by 320
Abstract
In this study, a high-strength Mg-9Li alloy was developed via multi-pass equal-channel-angular-pressing (ECAP) and post rolling, of which the yield tensile stress (YTS) and ultimate tensile stress (UTS) were 166 MPa and 174 MPa representing about 219% and 70% increase in YTS and [...] Read more.
In this study, a high-strength Mg-9Li alloy was developed via multi-pass equal-channel-angular-pressing (ECAP) and post rolling, of which the yield tensile stress (YTS) and ultimate tensile stress (UTS) were 166 MPa and 174 MPa representing about 219% and 70% increase in YTS and UTS respectively, compared to the cast alloy. The cast alloy was ECAP processed at 200 °C for 4, 8, and 16 passes, followed by room-temperature rolling to a total thickness reduction of 50%. The 8-passes ECAPed (E8) alloy presented the best strength of all the ECAPed alloys, and the post rolling endowed the alloy (E8R) further strengthening and the best strength of all the alloys. Grain-boundary strengthening and dislocation strengthening were the two major factors for the high strength of the processed alloys. The α-Mg phase grains were greatly refined to about 2 μm after 8-passes ECAP, and was further refined to about 800 nm ~1.5 μm after rolling. Significant grain refinement endowed the alloy with sufficient grain-boundary strengthening. Profuse intragranular dislocation accumulated in the deformed matrix, leading to the significant dislocation hardening of the alloy. Rolling-induced strong basal texture of the α-Mg phase also enhanced the further strengthening of the E8R alloy. Full article
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Open AccessArticle
Determination of Hydrogen Transport Behaviour in Boron-Manganese Steels Using Different Methods and Boundary Conditions
Metals 2019, 9(9), 1007; https://doi.org/10.3390/met9091007 - 12 Sep 2019
Viewed by 313
Abstract
Within the framework of the project "ELOBEV" (research of electrolytic coating systems for joining elements made of high-strength materials) funded by the Federal Ministry of Education and Research, a test methodology for the assessment of the danger of hydrogen-assisted and liquid metal-induced cracking [...] Read more.
Within the framework of the project "ELOBEV" (research of electrolytic coating systems for joining elements made of high-strength materials) funded by the Federal Ministry of Education and Research, a test methodology for the assessment of the danger of hydrogen-assisted and liquid metal-induced cracking for auxiliary joining elements is being developed. One working point of the project is the determination of the hydrogen transport behaviour in high-strength boron-manganese steels and their coating concepts. Permeation measurements under different boundary conditions are used to characterize the hydrogen transport in 22MnB5 and 37MnB4. The results are validated by thermal desorption analyses with a constant heating rate and an isothermal temperature control. Several methods for the determination of the diffusion velocity are investigated and the determined values are compared with each other. Full article
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Open AccessArticle
Influence of Arc Brazing Parameters on Microstructure and Joint Properties of Electro-Galvanized Steel
Metals 2019, 9(9), 1006; https://doi.org/10.3390/met9091006 - 12 Sep 2019
Viewed by 273
Abstract
Arc brazing of zinc-coated steel (EG, Electro-galvanized steel) using Cu-3 wt%Si filler metal was performed. The influence of arc current and brazing speed on the bonding properties of the joint, such as bead characteristics, arc penetration, joint hardness, and tensile shear strength were [...] Read more.
Arc brazing of zinc-coated steel (EG, Electro-galvanized steel) using Cu-3 wt%Si filler metal was performed. The influence of arc current and brazing speed on the bonding properties of the joint, such as bead characteristics, arc penetration, joint hardness, and tensile shear strength were evaluated. The microstructural characteristics of the joint were examined by scanning electron microscopy (SEM) and the compositional information was revealed by energy dispersive spectroscopy (EDS). The throat thickness varies inversely with the brazing speed. The EG joint shows the formation of Fe2Si phases, which result in higher microhardness than the base metal. The tensile samples were fractured in base metal, while minor bead cracks developed in the samples brazed at 80 cm/min-80 A, 60 cm/min-70 A, 70 cm/min-70 A. Full article
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Open AccessArticle
Effects of Hardening Model and Variation of Elastic Modulus on Springback Prediction in Roll Forming
Metals 2019, 9(9), 1005; https://doi.org/10.3390/met9091005 - 12 Sep 2019
Viewed by 302
Abstract
In this paper, the uniaxial loading–unloading–reloading (LUR) tensile test was conducted to determine the elastic modulus depending on the plastic pre-strain. To obtain the material parameters and parameter of Yoshida-Uemori’s kinematic hardening models, tension–compression experiments were carried out. The experimental results of the [...] Read more.
In this paper, the uniaxial loading–unloading–reloading (LUR) tensile test was conducted to determine the elastic modulus depending on the plastic pre-strain. To obtain the material parameters and parameter of Yoshida-Uemori’s kinematic hardening models, tension–compression experiments were carried out. The experimental results of the cyclic loading tests together with the numerically predicted response of the plastic behavior were utilized to determine the parameters using the Ls-opt optimization tool. The springback phenomenon is a critical issue in industrial sheet metal forming processes, which could affect the quality of the product. Therefore, it is necessary to represent a method to predict the springback. To achieve this aim, the calibrated plasticity models based on appropriate tests (cyclic loading) were implemented in commercial finite element (FE) code Ls-dyna to predict the springback in the roll forming process. Moreover, appropriate experimental tests were performed to validate the numerical results, which were obtained by the proposed model. The results showed that the hardening models and the variation of elastic modulus have significant impact on springback accuracy. The Yoshida-Uemori’s hardening represents more accurate prediction of the springback during the roll forming process when compared to isotropic hardening. Using the chord modulus to determine the reduction in elastic modulus gave more accurate results to predict springback when compared with the unloading and loading modulus to both hardening models. Full article
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Open AccessReview
Additive Manufacturing of Customized Metallic Orthopedic Implants: Materials, Structures, and Surface Modifications
Metals 2019, 9(9), 1004; https://doi.org/10.3390/met9091004 - 12 Sep 2019
Viewed by 325
Abstract
Metals have been used for orthopedic implants for a long time due to their excellent mechanical properties. With the rapid development of additive manufacturing (AM) technology, studying customized implants with complex microstructures for patients has become a trend of various bone defect repair. [...] Read more.
Metals have been used for orthopedic implants for a long time due to their excellent mechanical properties. With the rapid development of additive manufacturing (AM) technology, studying customized implants with complex microstructures for patients has become a trend of various bone defect repair. A superior customized implant should have good biocompatibility and mechanical properties matching the defect bone. To meet the performance requirements of implants, this paper introduces the biomedical metallic materials currently applied to orthopedic implants from the design to manufacture, elaborates the structure design and surface modification of the orthopedic implant. By selecting the appropriate implant material and processing method, optimizing the implant structure and modifying the surface can ensure the performance requirements of the implant. Finally, this paper discusses the future development trend of the orthopedic implant. Full article
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Open AccessArticle
Model-Based Analysis of Factors Affecting the Burden Layer Structure in the Blast Furnace Shaft
Metals 2019, 9(9), 1003; https://doi.org/10.3390/met9091003 - 12 Sep 2019
Viewed by 225
Abstract
The distribution of burden layers in an ironmaking blast furnace strongly influences the conditions in the upper part of the process. The bed permeability largely depends on the distribution of ore and coke in the lumpy zone, which affects the radial gas flow [...] Read more.
The distribution of burden layers in an ironmaking blast furnace strongly influences the conditions in the upper part of the process. The bed permeability largely depends on the distribution of ore and coke in the lumpy zone, which affects the radial gas flow distribution in the shaft. Along with the continuous advancement of technology, more information about the internal conditions of the blast furnace can be obtained through advanced measurement equipment, including 2D profiles and 3D surface maps of the top burden surface. However, the change of layer structure along with the burden descent cannot be directly measured. A mathematical model predicting the burden distribution and the internal layer structure during the descending process is established in this paper. The accuracy of the burden distribution model is verified by a comparison with experimental results. A sensitivity study was undertaken to clarify the role of some factors on the arising layer distribution, including the descent-rate distribution, the initial burden surface profile, and the charging direction through the charging matrix. The findings can be used as a theoretical basis to guide plant operations for optimizing the charging. Full article
(This article belongs to the Special Issue Advanced Simulation Technologies of Metallurgical Processing)
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Open AccessArticle
Double Reinforcement of Al–Fe Intermetallic Composites Fabricated by Friction Stir Processing
Metals 2019, 9(9), 1002; https://doi.org/10.3390/met9091002 - 12 Sep 2019
Viewed by 193
Abstract
A double reinforced layer on an aluminum alloy surface was produced using friction stir processing (FSP) by adding 34CrNiMo6 powder into Al (AA2024) substrate for better wear resistance and gradient transitions. The microstructures of the composites were analyzed using scanning electron microscopy (SEM) [...] Read more.
A double reinforced layer on an aluminum alloy surface was produced using friction stir processing (FSP) by adding 34CrNiMo6 powder into Al (AA2024) substrate for better wear resistance and gradient transitions. The microstructures of the composites were analyzed using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The phase composition was examined by X-ray diffraction (XRD). The results show that the double reinforced layer of the Al13Fe4 intermetallic compound could be successfully fabricated via FSP. The volume fraction of Al13Fe4 in the double reinforced layer was higher than in the single reinforced layer due to adding 34CrNiMo6 powder and reinforced twice, and the Al13Fe4 particles were dispersed more homogeneously in the double reinforced layer. The interfaces between the double and single reinforced layer had a good metallurgical bond. The microhardness of the double reinforcement layer was significantly increased. Compared with the AA2024 substrate, the microhardness of the double and single reinforced layers increased five- (576 HV) and two-fold (254 HV), respectively. Full article
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Open AccessArticle
Effect of Nonmetallic Inclusions on Fatigue Properties of Superelastic Ti-Ni Fine Wire
Metals 2019, 9(9), 999; https://doi.org/10.3390/met9090999 - 11 Sep 2019
Viewed by 286
Abstract
This study investigated the effects of the types and length of nonmetallic inclusions on fatigue properties in rotating bending fatigue testing of Ti-Ni alloy fine wire. It was fabricated to include titanium carbides Ti(C,O) and titanium oxides Ti4Ni2Ox [...] Read more.
This study investigated the effects of the types and length of nonmetallic inclusions on fatigue properties in rotating bending fatigue testing of Ti-Ni alloy fine wire. It was fabricated to include titanium carbides Ti(C,O) and titanium oxides Ti4Ni2Ox as either single phases or a mixture of both phases as nonmetallic inclusions in Ti-Ni alloy. The fatigue strength of Ti-Ni alloy depended on the number of nonmetallic inclusions of a length of ≥2 μm. Compared with Ti(C,O), Ti4Ni2Ox is coarse. It also exhibited a trend of readily forming particles and void assemblies, which are a defect morphology that originates from nonmetallic inclusions and readily act as crack origins of fatigue fractures. Full article
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Open AccessArticle
Microstructure and Mechanical Performance of the DD98M-DD98M Single Crystal Superalloy Joints Brazed Using a Pd-Si Composite Filler
Metals 2019, 9(9), 1001; https://doi.org/10.3390/met9091001 - 11 Sep 2019
Viewed by 198
Abstract
In this work, the DD98M single crystal superalloys were brazed to themselves using a Pd-Si composite filler. The effect of brazing temperature and soaking time on the microstructure and mechanical behavior of the joints was studied. The microstructure and phase constitution in the [...] Read more.
In this work, the DD98M single crystal superalloys were brazed to themselves using a Pd-Si composite filler. The effect of brazing temperature and soaking time on the microstructure and mechanical behavior of the joints was studied. The microstructure and phase constitution in the joint were identified by the SEM and EDS analysis. The results indicated that the joint obtained was constituted by DD98M/zone 2/zone 1/zone 2/DD98M. The zone 1 was primarily made up of the Ni (Pd, Cr, Co) (s.s), Pd4Si, Pd (Ni, Ti, Al) (s.s) and Pd-rich Ni (Pd, Cr, Co) (s.s), while the zone 2 consisted of the Ni (Pd, Cr, Co) (s.s) and Al2Pd5. During the brazing process, increasing the brazing temperature strengthened the fluidity of the liquid filler, which was favorable to eliminating the solidified pores in the brazing seam. Furthermore, a higher brazing temperature would cause the phases in the zones 1 and 2 to be coarsened remarkably. When setting the brazing temperature to 1060 °C, extending the soaking time made the amount of Pd (Ni, Ti, Al) (s.s) decrease, whereas the amount of Pd4Si increased, because the peritectic reaction between the Pd (Ni, Ti, Al) (s.s) and remnant liquid filler was enhanced. Among the brazing process parameters under investigation, the maximum joint average shear strength obtained reached 338 MPa when the joint was brazed at 1060 °C for 30 min. A ductile fracture mode happened during the shear tests under a joining condition. The work performed can provide valuable data to design the single crystal superalloy brazed joint. Full article
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Open AccessFeature PaperArticle
Development of Novel AlSi10Mg Based Nanocomposites: Microstructure, Thermal and Mechanical Properties
Metals 2019, 9(9), 1000; https://doi.org/10.3390/met9091000 - 11 Sep 2019
Viewed by 227
Abstract
Al matrix nanocomposites are interestingly employed in the automotive, military, aerospace and electronics packaging industries. In this study, Graphene Nanoplatelets (GNPs) reinforced AlSi10Mg nanocomposites were produced via powder metallurgy. The effect of GNPs content on density, microstructure and mechanical characteristics of the AlSi10Mg/GNPs [...] Read more.
Al matrix nanocomposites are interestingly employed in the automotive, military, aerospace and electronics packaging industries. In this study, Graphene Nanoplatelets (GNPs) reinforced AlSi10Mg nanocomposites were produced via powder metallurgy. The effect of GNPs content on density, microstructure and mechanical characteristics of the AlSi10Mg/GNPs nanocomposites was investigated systematically. To this aim, AlSi10Mg/GNPs nanocomposites reinforced with 0.5, 1.0 and 2.0 wt.% of GNPs were produced by wet mixing method following by hot compaction at 600 °C. To evaluate the effect of GNPs on mechanical properties of the as-fabricated nanocomposite, Vickers hardness and tensile properties of composites analyzed at room temperature. According to the results, it was found that the fabrication of AlSi10Mg/GNPs nanocomposites is faced with several challenges such as agglomeration and non-uniform dispersion of GNPs that should be addressed to achieve the desirable thermal and mechanical properties. For instance, surprisingly, it is revealed that the mechanical and thermal properties of nanocomposites were deteriorated in the presence of a high quantity of GNPs (>1.0 wt.%), which can be attributed to the GNPs agglomeration and accordingly introduction of internal porosity in the nanocomposite. The relatively low fraction of GNPs can uniformly be dispersed in the matrix and improve the performance of the nanocomposite. Full article
(This article belongs to the Special Issue Graphene Reinforced Metal Matrix Nanocomposites)
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Open AccessArticle
Kinetics of MgO Reduction in CaO-Al2O3-MgO Slag by Al in Liquid Fe
Metals 2019, 9(9), 998; https://doi.org/10.3390/met9090998 - 10 Sep 2019
Viewed by 249
Abstract
Kinetics analysis without fully taking into account the effect of mass transport in slag phase on MgO reduction by Al in liquid steel would lead to overestimation of Mg pickup by steel and driving force of the reaction. Two rate models considering mass [...] Read more.
Kinetics analysis without fully taking into account the effect of mass transport in slag phase on MgO reduction by Al in liquid steel would lead to overestimation of Mg pickup by steel and driving force of the reaction. Two rate models considering mass transport in (a) steel melt phase only (single control model) and (b) steel and slag melt phases (mixed control model) were developed for evaluating the thermodynamic equilibria between CaO-Al2O3-MgO slags and Al-killed steels. Calculated results from the two models were compared and then validated by equilibrium experiments between a CaO-Al2O3-MgO slag (Al2O3-saturated) and Al-killed steels with different Al levels at 1873 K (1600 °C). Results showed that the calculated reaction rate in the mixed control model was always lower than that in the single control model due to the slow mass transport in the slag phase. The mass transfer coefficient of [Mg] in the steel was computed to be 6.2 × 10−5 m/s from the equilibrium experiment results between an Fe-1.0 mass% Al steel and 51 mass% CaO-39 mass% Al2O3-10 mass% MgO slag at 1873 K (1600 °C), with which the mixed control model was validated at different initial Al levels in the steels. Full article
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Open AccessArticle
On the Grain Growth Kinetics of a Low Density Steel
Metals 2019, 9(9), 997; https://doi.org/10.3390/met9090997 - 10 Sep 2019
Viewed by 281
Abstract
The grain growth kinetics of an age-hardenable Fe-Mn-Al-C steel were investigated. Kinetics of grain growth were determined between 1173 and 1348 K (900–1075 °C) to obtain a range of grain sizes from 30 to 475 μm. It was found that grain growth was [...] Read more.
The grain growth kinetics of an age-hardenable Fe-Mn-Al-C steel were investigated. Kinetics of grain growth were determined between 1173 and 1348 K (900–1075 °C) to obtain a range of grain sizes from 30 to 475 μm. It was found that grain growth was negligible at 1173 K (900 °C) for times up to 15 h. The activation energy for grain growth was found to be 467 kJ/mol. The hardness and mean linear intercept (L3) were correlated to follow a traditional Hall-Petch relationship. Tensile properties of the alloy were determined after various solution treatments performed for 2 h followed by water quenching. Tensile strength increased from 810 to 960 MPa and ductility was reduced from 80 to 60% as the grain size decreased from 200 μm to 30 μm as grain coarsening was mitigated by lowering the solution treatment temperature. Full article
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Open AccessEditorial
Diversity of Nanoporous Metals
Metals 2019, 9(9), 996; https://doi.org/10.3390/met9090996 - 10 Sep 2019
Viewed by 251
Abstract
Nanoporous metals have been attracting considerable research and industrial attention because of the structural uniqueness of their bicontinuous metallic structure [...] Full article
(This article belongs to the Special Issue Nanoporous Metals)
Open AccessArticle
Porous Titanium Surfaces to Control Bacteria Growth: Mechanical Properties and Sulfonated Polyetheretherketone Coatings as Antibiofouling Approaches
Metals 2019, 9(9), 995; https://doi.org/10.3390/met9090995 - 10 Sep 2019
Viewed by 278
Abstract
Here, titanium porous substrates were fabricated by a space holder technique. The relationship between microstructural characteristics (pore equivalent diameter, mean free-path between pores, roughness and contact surface), mechanical properties (Young’s modulus, yield strength and dynamic micro-hardness) and bacterial behavior are discussed. The bacterial [...] Read more.
Here, titanium porous substrates were fabricated by a space holder technique. The relationship between microstructural characteristics (pore equivalent diameter, mean free-path between pores, roughness and contact surface), mechanical properties (Young’s modulus, yield strength and dynamic micro-hardness) and bacterial behavior are discussed. The bacterial strains evaluated are often found on dental implants: Methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa. The colony-forming units increased with the size of the spacer for both types of studied strains. An antibiofouling synthetic coating based on a sulfonated polyetheretherketone polymer revealed an effective chemical surface modification for inhibiting MRSA adhesion and growth. These findings collectively suggest that porous titanium implants designed with a pore size of 100–200 µm can be considered most suitable, assuring the best biomechanical and bifunctional anti-bacterial properties. Full article
(This article belongs to the Special Issue Powder Metallurgy of Titanium Alloys)
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Open AccessArticle
Effects of Solid Content and Substrate Concentration on Bioleaching of Heavy Metals from Sewage Sludge Using Aspergillus niger
Metals 2019, 9(9), 994; https://doi.org/10.3390/met9090994 - 09 Sep 2019
Viewed by 268
Abstract
The presence of heavy metals in sewage sludge not only affects the performance of sludge anaerobic digestion process but also restricts the land application of treated sewage sludge. Therefore, a fungi-mediated bioleaching process for simultaneous metal leaching and sludge digestion by Aspergillus niger [...] Read more.
The presence of heavy metals in sewage sludge not only affects the performance of sludge anaerobic digestion process but also restricts the land application of treated sewage sludge. Therefore, a fungi-mediated bioleaching process for simultaneous metal leaching and sludge digestion by Aspergillus niger was developed to treat the sewage sludge containing heavy metals in this study. The effects of two important parameters, sludge solid content and substrate (sucrose) concentration, on the performance of fungal bioleaching were investigated in this study. The results showed that the rate of pH reduction increased with increasing sludge solid contents and sucrose concentrations. In this study, the efficiency of metal removal decreases in the order of Mn > Zn > Ni > Pb. The efficiencies of metal leaching and solid degradation (SS and VSS) were found to be decreased with an increase of sludge solid content and a decrease of sucrose concentration. At 2 days of reaction time, the maximum efficiency of metal solubilization was 95, 56, 21 and 13% for Mn, Zn, Ni and Pb, respectively. Full article
(This article belongs to the Special Issue Separation and Leaching for Metals Recovery)
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Open AccessArticle
Acquiring High-Quality Oil Casing Steel 26CrMoVTiB under Optimal Continuous Casting Process Conditions
Metals 2019, 9(9), 993; https://doi.org/10.3390/met9090993 - 09 Sep 2019
Viewed by 248
Abstract
While the solidification macrostructure of continuous cast billets is an important factor influencing the final performance and rolling yield of oil casing steel, the continuous casting process parameters have a direct influence on the solidification structure. This study simulated the solidification process of [...] Read more.
While the solidification macrostructure of continuous cast billets is an important factor influencing the final performance and rolling yield of oil casing steel, the continuous casting process parameters have a direct influence on the solidification structure. This study simulated the solidification process of the continuous casting round billets of oil casing steel using a cellular automaton–finite element (CAFE) model. According to the simulation results, at a superheat degree of 20–35 K, a casting speed of 1.9–2.1 m/min, and a secondary cooling specific water flow of 0.34–0.45 L/Kg, the solidification structure had a relatively high equiaxed crystal ratio and small average grain radius. Guided by the simulation results, this paper establishes optimal process schemes for producing 26CrMoVTiB steel round billets, comparatively analyzes the equiaxed crystal ratio and central shrinkage of round billets produced according to these schemes, and defines the optimal continuous casting process conditions, which are: superheat degree = 25 K, casting speed = 2.1 m/min, and specific water flow = 0.35 L/Kg. When adopting these process parameters, the 26CrMoVTiB steel round billets demonstrate a tiny central shrinkage and an equiaxed crystal ratio of 45.2%. Full article
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Open AccessArticle
Tungsten Matrix Composite Reinforced with CoCrFeMnNi High-Entropy Alloy: Impact of Processing Routes on Microstructure and Mechanical Properties
Metals 2019, 9(9), 992; https://doi.org/10.3390/met9090992 - 09 Sep 2019
Viewed by 313
Abstract
Tungsten heavy alloy composite was developed by using novel CoCrFeMnNi high-entropy alloy as the binder/reinforcement phase. Elemental tungsten (W) powder and mechanically alloyed CoCrFeMnNi high-entropy alloy were mixed gently in high energy ball mill and consolidated using different sintering process with varying heating [...] Read more.
Tungsten heavy alloy composite was developed by using novel CoCrFeMnNi high-entropy alloy as the binder/reinforcement phase. Elemental tungsten (W) powder and mechanically alloyed CoCrFeMnNi high-entropy alloy were mixed gently in high energy ball mill and consolidated using different sintering process with varying heating rate (in trend of conventional sintering < microwave sintering < spark plasma sintering). Mechanically alloyed CoCrFeMnNi high-entropy alloy have shown a predominant face-centered cubic (fcc) phase with minor Cr-rich σ-phase. Consolidated tungsten heavy high-entropy alloys (WHHEA) composites reveal the presence of Cr–Mn-rich oxide phase in addition to W-grains and high-entropy alloys (HEA) phase. An increase in heating rate restricts the tungsten grain growth with reduces the volume fraction of the Cr–Mn-rich phase. Finally, spark plasma sintering with a higher heating rate and shorter sintering time has revealed higher compressive strength (~2041 MPa) than the other two competitors (microwave sintering: ~1962 MPa and conventional sintering: ~1758 MPa), which may be attributed to finer W-grains and reduced fraction of Cr–Mn rich oxide phase. Full article
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