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Metals, Volume 10, Issue 12 (December 2020) – 139 articles

Cover Story (view full-size image): The cell structure of aluminum foams fabricated under increased pressure is fined because high pressure reduces bubble coalescing and hinders gravity drainage. The compressive displacement–load curve of foam-filled tube is smoothed with the decrease of foam cell size, which leads to the increase of not only energy absorption but also energy absorption efficiency. This indicates that the aluminum foams fabricated by the increased pressure foaming route are an appropriate core material to improve the engineering applications of foam-filled tubes. View this paper.
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Open AccessArticle
Reuse of Grade 23 Ti6Al4V Powder during the Laser-Based Powder Bed Fusion Process
Metals 2020, 10(12), 1700; https://doi.org/10.3390/met10121700 - 21 Dec 2020
Viewed by 466
Abstract
Titanium alloy powder used for laser-based powder bed fusion (L-PBF) process is costly. One of the solutions is the inclusion of a powder recycling strategy, allowing unused or exposed powder particles to be recuperated post manufacture, replenished and used for future builds. However, [...] Read more.
Titanium alloy powder used for laser-based powder bed fusion (L-PBF) process is costly. One of the solutions is the inclusion of a powder recycling strategy, allowing unused or exposed powder particles to be recuperated post manufacture, replenished and used for future builds. However, during a L-PBF process, powder particles are exposed to high levels of concentrated energy from the laser. Particularly those in close proximity to the melt pool, leading to the formation of spatter and agglomerated particles. These particles can settle onto the powder bed, which can then influence the particle size distribution and layer uniformity. This study analysed extra-low interstitial (ELI) Ti6Al4V (Grade 23) powder when subjected to nine recycle iterations, tracking powder property variation across the successive recycling stages. Characterisation included chemical composition focusing upon O, N, and H content, particle size distribution, morphology and tapped and bulk densities. On review of the compositional analysis, the oxygen content exceeded the 0.13% limit for the ELI grade after 8 recycles, resulting in the degradation from Grade 23 level. Full article
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Open AccessArticle
Fe-6.5 wt%Si Powder Cores with Low Core Loss by Optimizing Particle Size Distribution
Metals 2020, 10(12), 1699; https://doi.org/10.3390/met10121699 - 21 Dec 2020
Viewed by 350
Abstract
The effect of different particle size distribution of Fe-6.5 wt%Si powder on the microstructure and soft magnetic properties of the corresponding soft magnetic powder cores (SMPCs) was investigated. By optimizing particle size distribution, the density of SMPCs increased and the total core loss [...] Read more.
The effect of different particle size distribution of Fe-6.5 wt%Si powder on the microstructure and soft magnetic properties of the corresponding soft magnetic powder cores (SMPCs) was investigated. By optimizing particle size distribution, the density of SMPCs increased and the total core loss significantly decreased. According to the result of loss separation, density of SMPCs is inversely proportional to hysteresis loss, while with increasing the content of the fine particles, the eddy current loss significantly decreased. It was found that with magnetic powder of particle size-grading as 10%, 10%, 60%, and 20% for particles with size between −75 to +38, −38 to +23, −23 to +13, and −13 μm, respectively, the Fe-6.5 wt%Si SMPCs exhibit optimal comprehensive magnetic performances with the effective permeability of about 60, the percent permeability at 100 Oe is up to 70%, and the lowest core loss of 553 mW/cm3. Full article
(This article belongs to the Special Issue Metal-Matrix Composites Fabricated by Powder Metallurgy)
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Open AccessArticle
Electrochemically Synthesized Nanoflowers to Nanosphere-Like NiCuSe2 Thin Films for Efficient Supercapacitor Application
Metals 2020, 10(12), 1698; https://doi.org/10.3390/met10121698 - 21 Dec 2020
Viewed by 347
Abstract
Developing efficient electrochemically active nanostructures from Earth-abundant elements has gained significant interest in recent years. Among different transition metals, nickel and copper are abundant electrocatalysts for energy-storage applications. Nickel–copper selenide (NiCuSe2) nanostructures were prepared on a stainless-steel mesh with a cost-effective, [...] Read more.
Developing efficient electrochemically active nanostructures from Earth-abundant elements has gained significant interest in recent years. Among different transition metals, nickel and copper are abundant electrocatalysts for energy-storage applications. Nickel–copper selenide (NiCuSe2) nanostructures were prepared on a stainless-steel mesh with a cost-effective, simple, and versatile electrodeposition method for supercapacitor applications. The change effect in the bath concentration of nickel and copper altered the structural and electrochemical properties of NiCuSe2 electrode. X-ray diffraction (XRD) patterns confirmed the pure phase of ternary NiCuSe2 thin films with a cubic crystal structure. The surface morphology of NiCuSe2 was tuned by nickel and copper from spherical porous nanoflowers, nanoplates, nanocubes, and nanosphere-like nanostructures deposited on the stainless-steel mesh. The electrochemical performance of the electrodeposited NiCuSe2 was investigated in alkaline 1 M KOH electrolyte. The synergetic effect of bimetallic nickel and copper with the selenide electrode showed superior specific capacity of about 42.46 mAh g−1 at 10 mV s−1 along with reasonable cycling stability. Full article
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Open AccessArticle
Control of Density and Grain Structure of a Laser Powder Bed-Fused Superelastic Ti-18Zr-14Nb Alloy: Simulation-Driven Process Mapping
Metals 2020, 10(12), 1697; https://doi.org/10.3390/met10121697 - 21 Dec 2020
Viewed by 361
Abstract
This study focuses on the control of density and grain structure of a superelastic Ti-18Zr-14Nb (at. %) alloy subjected to laser powder bed fusion. It starts with the production and characterization of a Ti-18Zr-14Nb powder feedstock and printing of a series of calibration [...] Read more.
This study focuses on the control of density and grain structure of a superelastic Ti-18Zr-14Nb (at. %) alloy subjected to laser powder bed fusion. It starts with the production and characterization of a Ti-18Zr-14Nb powder feedstock and printing of a series of calibration specimens. These specimens are next subjected to chemical, structural, phase and texture analyses in order to collect experimental data needed to build simulation-driven processing maps in the laser energy density–material build rate coordinates. The results of this study prove that, once calibrated, the simulation-driven processing maps can be used to relate the main LPBF parameters (laser power, scanning speed, hatching distance and layer thickness) to the density and grain structure of the printed material, and the process productivity (build rate). Even though this demonstration is made for a specific material–system combination (TiNbZr & TruPrint 1000), such a process mapping is feasible for any material–system combination and can, therefore, be exploited for the process optimization purposes and for manufacturing of functionally graded materials or parts with intentionally seeded porosity. Full article
(This article belongs to the Special Issue Shape Memory Alloys 2020)
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Open AccessArticle
Modification of Alumina Inclusions in SWRS82B Steel by Adding Rare Earth Cerium
Metals 2020, 10(12), 1696; https://doi.org/10.3390/met10121696 - 21 Dec 2020
Viewed by 282
Abstract
The aluminum oxide inclusions in SWRS82B steel seriously affect the drawing performance of the steel strand. In this study, the influence of different additions of cerium (within the range of 0–0.034%) on the composition, morphology, size, number, and distribution of alumina inclusions was [...] Read more.
The aluminum oxide inclusions in SWRS82B steel seriously affect the drawing performance of the steel strand. In this study, the influence of different additions of cerium (within the range of 0–0.034%) on the composition, morphology, size, number, and distribution of alumina inclusions was studied by scanning electron microscope and energy spectrum analyzer. The evolution of the composition of inclusions with different cerium additions was calculated based on classical thermodynamics and Factsage software calculation. The thermodynamic calculated results were consistent with the experimental results. It indicates that the modification route of Al2O3 inclusions in SWRS82B steel by increased cerium additions is as follows: Al2O3 → Ce2S3 + CeAlO3 + Ce2O2S + Al2O3 → Ce2S3 + CeAlO3 + Ce2O2S/Ce2S3 + Ce2O2S → Ce2S3 + Ce2O2S. Besides, when the amount of cerium is in the range of 0.023% to 0.030%, CeAlO3 inclusions gradually disappear. The best characteristics of inclusions in this study were obtained in experimental samples with cerium addition of 0.023%, in which the minimum size of inclusions is in the range of 3.52–4.84 μm and mostly uniform distribution. Finally, the mechanism on the modification by cerium was discussed based on the composition evolution of inclusion during solidification with Factsage calculation and experimental results. The compositions of inclusions were also analyzed based on the inclusion evolution model. Full article
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Open AccessArticle
Constitutive Model and Microstructure Evolution Finite Element Simulation of Multidirectional Forging for GH4169 Superalloy
Metals 2020, 10(12), 1695; https://doi.org/10.3390/met10121695 - 21 Dec 2020
Viewed by 244
Abstract
This study investigates three processes of multidirectional forging (MDF), namely, closed MDF (CMDF), single-open MDF, and double-open MDF, by using a constitutive equation and a dynamic recrystallization model of hot deformation of the GH4169 superalloy. The microstructure evolution of the three processes is [...] Read more.
This study investigates three processes of multidirectional forging (MDF), namely, closed MDF (CMDF), single-open MDF, and double-open MDF, by using a constitutive equation and a dynamic recrystallization model of hot deformation of the GH4169 superalloy. The microstructure evolution of the three processes is simulated and compared. Among the three processes, the double-open MDF obtains the highest recrystallization degree, followed by the CMDF and the single-open MDF under the same reduction. The recrystallization degree of CMDF reaches 99.5% at 1000 °C and 9 passes, and the average recrystallized grain size is small, which is approximately 8.1 μm. The double-open MDF can obtain a fine grain size of forgings at 9 passes and 1000 °C, and it is easy to obtain forgings with the single-open MDF with uniform performance. The temperature is 850 °C–1000 °C, the compression rate is 0.15–0.2, and the pass is 5–9, which are the suitable parameter selection ranges for the CMDF. The temperature is 950 °C–1000 °C, the compression rate is 0.1–0.2, and the pass is 7–9, which are the suitable parameter selection ranges for single-open MDF. The temperature is 850 °C–1000 °C, the compression rate is 0.1–0.2, and the pass is 6–9, which are the suitable parameter selection ranges for the double-open MDF. Full article
(This article belongs to the Special Issue Modeling and Simulation of Metal Processing)
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Open AccessArticle
CO and CO2 Anode Gas Concentration at Lower Current Densities in Cryolite Melt
Metals 2020, 10(12), 1694; https://doi.org/10.3390/met10121694 - 20 Dec 2020
Viewed by 344
Abstract
This work aims to study the CO-CO2 gas composition at low potentials and low current densities in cryolite melt with relatively low alumina content (≤2 wt%). There is a scarcity of data in the literature regarding the low current density region and [...] Read more.
This work aims to study the CO-CO2 gas composition at low potentials and low current densities in cryolite melt with relatively low alumina content (≤2 wt%). There is a scarcity of data in the literature regarding the low current density region and also for bath low in alumina. The experimental setup was constructed to minimize the back reaction as well as the Boudouard reaction. For potentials up to 1.55 V and corresponding current densities up to 0.07 A cm−2, it was found that CO is the dominant product. Between 1.55 and 1.65 V (corresponding current density region 0.07 to 0.2 A cm−2), CO2 becomes the dominant gas product. These potential values are probably slightly large due to suspected Boudouard reaction between CO2 and carbon particles in the melt formed by disintegration of the graphite anode. The results are discussed in relation to the literature data and thermodynamic calculations. Full article
(This article belongs to the Section Extractive Metallurgy)
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Open AccessCommunication
Analysis of Nanoprecipitation Effect on Toughness Behavior in Warm Worked AA7050 Alloy
Metals 2020, 10(12), 1693; https://doi.org/10.3390/met10121693 - 20 Dec 2020
Viewed by 294
Abstract
Commonly adopted main methods aimed to improve the strength–toughness combination of high strength aluminum alloys are based on a standard process. Such a process includes alloy solution heat treatment, water-quench and reheating at controlled temperature for ageing holding times. Some alloys request an [...] Read more.
Commonly adopted main methods aimed to improve the strength–toughness combination of high strength aluminum alloys are based on a standard process. Such a process includes alloy solution heat treatment, water-quench and reheating at controlled temperature for ageing holding times. Some alloys request an intermediate cold working hardening step before ageing for an optimum strength result. Recently a warm working step has been proposed and applied. This replaces the cold working after solution treatment and quenching and before the final ageing treatment. Such an alternative process proved to be very effective in improving strength–toughness behavior of 7XXX aluminum alloys. In this paper the precipitation state following this promising process is analyzed and compared to that of the standard route. The results put in evidence the differences in nanoprecipitation densities that are claimed to be responsible for strength and toughness improved properties. Full article
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Open AccessArticle
Effect of Cooling Path on Microstructures and Hardness of Hot-Stamped Steel
Metals 2020, 10(12), 1692; https://doi.org/10.3390/met10121692 - 18 Dec 2020
Viewed by 461
Abstract
The final mechanical properties of hot-stamped steel are determined by the microstructures which are greatly influenced by the cooling process after hot stamping. This research studied the effect of the cooling path on the microstructures and hardness of 22MnB5 hot-stamped steel. The cooling [...] Read more.
The final mechanical properties of hot-stamped steel are determined by the microstructures which are greatly influenced by the cooling process after hot stamping. This research studied the effect of the cooling path on the microstructures and hardness of 22MnB5 hot-stamped steel. The cooling path was divided into continuous and discontinuous (primary and secondary) processes. After cooling, the Vickers hardness along the thickness of the specimens was measured. The results indicate that, for a continuous cooling process, there was a critical cooling rate of 25 °C/s to obtain fully martensitic microstructure. For the discontinuous cooling process, the slower was the cooling rate, the higher was the degree of auto-tempering that occurred, and the greater was the amount of carbides that formed, regardless of the primary or secondary cooling rate. When the cooling rate was lower than the critical value, a higher primary cooling rate suppressed the auto-tempering of lath martensite and increased the quenched hardness. By contrast, the hardness was not sensitive to the cooling rate when it exceeded the critical value. Full article
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Open AccessArticle
Effects of High Temperature Aging Treatment on the Microstructure and Impact Toughness of Z2CND18-12N Austenitic Stainless Steel
Metals 2020, 10(12), 1691; https://doi.org/10.3390/met10121691 - 18 Dec 2020
Viewed by 327
Abstract
During the casting cooling process or the forging process, austenitic stainless steel will remain at around 800 °C for some time. During this period, precipitate particle behaviors in austenitic stainless steel (containing ferrite) will cause a reduction in ductility, which can lead to [...] Read more.
During the casting cooling process or the forging process, austenitic stainless steel will remain at around 800 °C for some time. During this period, precipitate particle behaviors in austenitic stainless steel (containing ferrite) will cause a reduction in ductility, which can lead to material cracking. In this study, the effects of aging at 800 °C on the microstructure, impact toughness and microhardness of Z2CND18-12N austenitic stainless steel were systematically investigated. The precipitation processes of the χ and σ phases were characterized by color metallography and back scattered electron (BSE) signals. The toughness was investigated by the Charpy impact test. After the aging treatment, the χ and σ phases precipitated successively in the ferrite, and as the aging duration increased, the χ-phase dissolved and the σ-phase precipitated along the austenite grain boundaries. These all lead to a decrease in toughness and an increase in microhardness. Finally, the relationship between fracture morphology and aging time is discussed herein, and a crack mechanism is given. Full article
(This article belongs to the Special Issue Inclusion/Precipitate Engineering in Steels)
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Open AccessReview
A Compact Review of Laser Welding Technologies for Amorphous Alloys
Metals 2020, 10(12), 1690; https://doi.org/10.3390/met10121690 - 18 Dec 2020
Viewed by 284
Abstract
Amorphous alloys have emerged as important materials for precision machinery, energy conversion, information processing, and aerospace components. This is due to their unique structure and excellent properties, including superior strength, high elasticity, and excellent corrosion resistance, which have attracted the attention of many [...] Read more.
Amorphous alloys have emerged as important materials for precision machinery, energy conversion, information processing, and aerospace components. This is due to their unique structure and excellent properties, including superior strength, high elasticity, and excellent corrosion resistance, which have attracted the attention of many researchers. However, the size of the amorphous alloy components remains limited, which affects industrial applications. Significant developments in connection with this technology are urgently needed. Laser welding represents an efficient welding method that uses a laser beam with high energy-density for heating. Laser welding has gradually become a research hotspot as a joining method for amorphous alloys due to its fast heating and cooling rates. In this compact review, the current status of research into amorphous-alloy laser welding technology is discussed, the influence of technological parameters and other welding conditions on welding quality is analyzed, and an outlook on future research and development is provided. This paper can serve as a useful reference for both fundamental research and engineering applications in this field. Full article
(This article belongs to the Special Issue Technology of Welding and Joining)
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Open AccessArticle
Rapid Joining of Commercial-Purity Ti to 304 Stainless Steel Using Joule Heating Diffusion Bonding: Interfacial Microstructure and Strength of the Dissimilar Joint
Metals 2020, 10(12), 1689; https://doi.org/10.3390/met10121689 - 18 Dec 2020
Viewed by 269
Abstract
A new solid-state bonding technique, Joule heating diffusion bonding, was used for the dissimilar bonding of commercial-purity Ti to 304 stainless steel within a short time without macroscopic deformation of the workpieces. The tensile strengths of the joints produced at various bonding parameters [...] Read more.
A new solid-state bonding technique, Joule heating diffusion bonding, was used for the dissimilar bonding of commercial-purity Ti to 304 stainless steel within a short time without macroscopic deformation of the workpieces. The tensile strengths of the joints produced at various bonding parameters were examined at room temperature, and the microstructures of the joints and the fracture surfaces were analyzed to clarify the effect of the microstructural factors on the tensile strength of the joints. The tensile strength of the joints increased with the increase in the fraction of the sufficiently bonded interface. In the joints with the well-bonded interface, the tensile strength decreased with the increase in the thickness of the brittle Fe-Ti-type intermetallic compound layers at the joint interface. This study suggested that the high tensile strength could be achieved in the Joule heating diffusion bonded joints with the well-bonded interface where the thickness of the Fe-Ti-type intermetallic compound layers was thinner than 0.5 µm. Full article
(This article belongs to the Special Issue Dissimilar Material Welding and Joining)
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Open AccessArticle
Phase Transformation-Induced Improvement in Hardness and High-Temperature Wear Resistance of Plasma-Sprayed and Remelted NiCrBSi/WC Coatings
Metals 2020, 10(12), 1688; https://doi.org/10.3390/met10121688 - 17 Dec 2020
Viewed by 309
Abstract
The remelting method is introduced to improve the properties of the as-sprayed NiCrBSi coatings. In this work, tungsten carbide (WC) was selected as reinforcement and the as-sprayed and remelted NiCrBSi/WC composite coatings were investigated by X-ray diffraction, scanning electron microscopy, hardness test and [...] Read more.
The remelting method is introduced to improve the properties of the as-sprayed NiCrBSi coatings. In this work, tungsten carbide (WC) was selected as reinforcement and the as-sprayed and remelted NiCrBSi/WC composite coatings were investigated by X-ray diffraction, scanning electron microscopy, hardness test and tribology test. After spraying, WC particles are evenly distributed in the coating. The remelting process induced the decarburizing reaction of WC, resulting in the formation of dispersed W2C. The dispersed W2C particles play an important role in the dispersion strengthening. Meanwhile, the pores and lamellar structures are eliminated in the remelted NiCrBSi/WC composite coating. Due to these two advantages, the hardness and the high-temperature wear resistance of the remelted NiCrBSi/WC composite coating are significantly improved compared with those with an as-sprayed NiCrBSi coating; the as-sprayed NiCrBSi coating, as-sprayed NiCrBSi/WC composite coating and remelted NiCrBSi/WC composite coating have average hardness of 673.82, 785.14, 1061.23 HV, and their friction coefficients are 0.3418, 0.3261, 0.2431, respectively. The wear volume of the remelted NiCrBSi/WC composite coating is only one-third of that of the as-sprayed NiCrBSi coating. Full article
(This article belongs to the Special Issue Plasma Treatment on Alloys' Surface)
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Open AccessArticle
Kinetics of Dry-Batch Grinding in a Laboratory-Scale Ball Mill of Sn–Ta–Nb Minerals from the Penouta Mine (Spain)
Metals 2020, 10(12), 1687; https://doi.org/10.3390/met10121687 - 17 Dec 2020
Viewed by 282
Abstract
The optimization of processing plants is one of the main concerns in the mining industry, since the comminution stage, a fundamental operation, accounts for up to 70% of total energy consumption. The aim of this study was to determine the effects that ball [...] Read more.
The optimization of processing plants is one of the main concerns in the mining industry, since the comminution stage, a fundamental operation, accounts for up to 70% of total energy consumption. The aim of this study was to determine the effects that ball size and mill speed exert on the milling kinetics over a wide range of particle sizes. This was done through dry milling and batch grinding tests performed on two samples from the Penouta Sn–Ta–Nb mine (Galicia, Spain), and following Austin methodology. In addition, the relationships amongst Sn, Ta and Nb content, as metals of interest, the specific rate of breakage Si, the kinetic parameters, and the operational conditions were studied through X-Ray fluorescence (XRF) techniques. The results show that, overall, the specific rate of breakage Si decreases with decreasing feed particle size and increasing ball size for most of the tested conditions. A selection function, αT, was formulated on the basis of the ball size for both Penouta mine samples. Finally, it was found that there does exist a direct relationship amongst Sn, Ta and Nb content, as metals of interest, in the milling product, the specific rate of breakage Si and the operational–mineralogical variables of ball size, mill speed and feed particle size. Full article
(This article belongs to the Special Issue Grinding and Concentration Technology of Critical Metals)
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Open AccessArticle
Numerical Research of Fracture Toughness of Aged Ferritic-Martensitic Steel
Metals 2020, 10(12), 1686; https://doi.org/10.3390/met10121686 - 17 Dec 2020
Viewed by 278
Abstract
Generally, material properties such as the modulus of elasticity, yield strength or fracture toughness are determined by conducting an experiment. Sometimes experimental determination cannot be done due to specific experimental conditions, lack of testing material and so on. Also, experiments are time consuming [...] Read more.
Generally, material properties such as the modulus of elasticity, yield strength or fracture toughness are determined by conducting an experiment. Sometimes experimental determination cannot be done due to specific experimental conditions, lack of testing material and so on. Also, experiments are time consuming and costly. Therefore, there arises the need for alternative determination methods. A numerical method for the fracture toughness determination of steel P91 is suggested in this paper. For this purpose, the universal finite element software ABAQUS was used. The numerical simulation of the C(T) specimen tension test was carried out using non-linear simulation for a conditional load PQ determination, and linear simulation for fracture toughness value KQ determination. The suggested method is validated by comparing numerical and experimental tests results. The secondary aim of the paper is the evaluation of the ageing effect on the fracture toughness of steel P91. Thermal ageing of the steel was carried out in an electric furnace at 650 °C up to 11,000 h. As the numerical results had a good coincidence with experimental data at room temperature, the prediction of fracture toughness at elevated temperature, i.e., 550 °C, using numerical method was carried out. Full article
(This article belongs to the Special Issue Fracture and Damage Mechanics of Metals, Steels and Alloys)
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Open AccessArticle
Grouping Methods of Cluster Dynamics Model for Precipitation Kinetics
Metals 2020, 10(12), 1685; https://doi.org/10.3390/met10121685 - 16 Dec 2020
Viewed by 361
Abstract
Due to its simplicity and efficiency, cluster dynamics modeling has been widely used to simulate microstructure evolution in materials, such as defect formation in metals. However, its computation cost becomes prohibitive when the clusters grow too large, so a particle-size-grouping method is often [...] Read more.
Due to its simplicity and efficiency, cluster dynamics modeling has been widely used to simulate microstructure evolution in materials, such as defect formation in metals. However, its computation cost becomes prohibitive when the clusters grow too large, so a particle-size-grouping method is often required. In this paper, three different size-grouping methods are compared with the exact solution of the ungrouped cluster dynamics model for Al3Sc precipitation in an Al-0.18 at.% Sc alloy. A new assumption of logarithmically-linear distribution of cluster number densities inside each size group is shown to be the most efficient way to match with all results of the ungrouped model. Finally, the calculated results are compared with the measured sizes and distributions of Al3Sc precipitates at different aging temperatures. The new size-grouping method is shown to have better accuracy for the chosen discretization and time-stepping method evaluated. This will enable significant computational savings, and the extension of time scales and cluster sizes to the ranges of realistic metallurgical systems, while preserving reasonable accuracy. Full article
(This article belongs to the Special Issue Advanced Computational Modeling of Metal Transformation Processes)
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Open AccessArticle
Complete Extraction of Amorphous Aluminosilicate from Coal Fly Ash by Alkali Leaching under Atmospheric Pressure
Metals 2020, 10(12), 1684; https://doi.org/10.3390/met10121684 - 16 Dec 2020
Viewed by 370
Abstract
One of the potential sources of alumina and mesoporous silica is the coal-fired thermal plants waste known as the coal fly ash (CFA). The studies of the alumina extraction from CFA are often focused on the preliminary desilication, but the efficiency of the [...] Read more.
One of the potential sources of alumina and mesoporous silica is the coal-fired thermal plants waste known as the coal fly ash (CFA). The studies of the alumina extraction from CFA are often focused on the preliminary desilication, but the efficiency of the alkali desilication is low due to formation of the desilication product—Na6[Al6Si6O24]·Na2X (DSP). This research is focused on the possibility of CFA desilication without formation of DSP using a leaching process with higher liquid to solid ratios (L/S) and alkali concentrations. The experimental data were analyzed using an artificial neural network (ANN) machine learning method and a shrinking core model (SCM). The investigation of the CFA morphology, chemical and phase composition before and after leaching were carried out by scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX), inductively coupled plasma optical emission spectrometry (ICP-OES) and X-ray diffraction (XRD). The present work shows that it is possible to avoid formation of DSP if using the L/S ratio >20 and concentration of Na2O—400 g/L during CFA leaching. The kinetics analysis by SCM showed that the process is limited by the surface chemical reaction at T <100 °C, and by diffusion through the product layer at T >100 °C, respectively. The SEM images of the solid residue after NaOH leaching under conditions that prevent the DSP formation show mullite particles with an acicular structure. Full article
(This article belongs to the Special Issue Separation and Leaching for Metals Recovery)
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Open AccessArticle
Characterization of High-Strength Packaging Steels: Obtaining Material Data for Precise Finite Element Process Modelling
Metals 2020, 10(12), 1683; https://doi.org/10.3390/met10121683 - 16 Dec 2020
Viewed by 301
Abstract
The steadily increasing demand for downgauging to reduce costs in packaging steel applications requires the development of high-strength packaging steel grades to meet strength requirements. At the same time, the demand for a simulative, computer-aided layout of industrial forming processes is growing to [...] Read more.
The steadily increasing demand for downgauging to reduce costs in packaging steel applications requires the development of high-strength packaging steel grades to meet strength requirements. At the same time, the demand for a simulative, computer-aided layout of industrial forming processes is growing to reduce costs in tool constructions for downgauging manners. As part of this work, different high-strength packaging steels were characterized for use in a finite element based process layout and validated using application-oriented experiments. Due to a low hardening rate and the occurrence of Lüders bands, high-strength packaging steels show a low amount of elongation in tensile tests, while for other stress states higher degrees of deformation are possible. Thus, common extrapolation methods fail to reproduce the flow curve of high-strength packaging steels. Therefore, a new approach to extrapolate the flow curve of high-strength packaging steels is presented using the tensile test and bulge test data together with a combined Swift–Voce hardening law. Furthermore, it is shown that the use of complex anisotropic yield locus models such as Yld2000-2d is necessary for high-strength packaging steels in order to be able to precisely simulate application-oriented loads in between plane strain and biaxial tension in validation experiments. Finally, the benefit of a material selection process for packaging steel applications guided by finite element simulations based on precisely characterized material behaviour is demonstrated. Full article
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Open AccessArticle
Dislocation Breakaway Damping in AA7050 Alloy
Metals 2020, 10(12), 1682; https://doi.org/10.3390/met10121682 - 16 Dec 2020
Viewed by 293
Abstract
The AA7050 alloy prepared through the standard industrial hot-forging cycle has been investigated by means of isothermal mechanical spectroscopy (MS) from room temperature up to 185 °C. Each MS test consisted of a cycle with two stages, at increasing and decreasing strain. After [...] Read more.
The AA7050 alloy prepared through the standard industrial hot-forging cycle has been investigated by means of isothermal mechanical spectroscopy (MS) from room temperature up to 185 °C. Each MS test consisted of a cycle with two stages, at increasing and decreasing strain. After each cycle the damping value resulted to be higher than the original one indicating the occurrence of an irreversible transformation. Such phenomenon, observed for all the test temperatures, becomes more relevant for T ≥ 150 °C. The irreversible transformation has been discussed and explained by considering the evolution of the mean dislocation link length between pinning points represented by nanometric MgZn2 precipitates. The breakaway of dislocation segments from pinning points occurs in the stage at increasing strain and is not fully recovered during the second stage at decreasing strain thus the mean link length increases in a MS test cycle. The onset of thermal activated dislocation cross-slip at about 150 °C favors the dislocation breakaway and consequently enhances the effect on damping. Full article
(This article belongs to the Special Issue Lightweight Alloys for Aerospace Applications)
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Open AccessArticle
Effects of Ti6Al4V Surfaces Manufactured through Precision Centrifugal Casting and Modified by Calcium and Phosphorus Ion Implantation on Human Osteoblasts
Metals 2020, 10(12), 1681; https://doi.org/10.3390/met10121681 - 16 Dec 2020
Viewed by 320
Abstract
(1) In order to enable a more widespread use of uncemented titanium-based endoprostheses to replace cobalt-containing cemented endoprostheses for joint replacement, it is essential to achieve optimal osseointegrative properties and develop economic fabrication processes while retaining the highest biomedical quality of titanium materials. [...] Read more.
(1) In order to enable a more widespread use of uncemented titanium-based endoprostheses to replace cobalt-containing cemented endoprostheses for joint replacement, it is essential to achieve optimal osseointegrative properties and develop economic fabrication processes while retaining the highest biomedical quality of titanium materials. One approach is the usage of an optimized form of Ti6Al4V-precision casting for manufacturing. Besides the chemical and physical properties, it is necessary to investigate possible biological influences in order to test whether the new manufacturing process is equivalent to conventional methods. (2) Methods: Primary human osteoblasts were seeded on discs, which were produced by a novel Ti6Al4V centrifugal-casting process in comparison with standard machined discs of the same titanium alloy. In a second step, the surfaces were modified by calcium or phosphorus ion beam implantation. In vitro, we analyzed the effects on proliferation, differentiation, and apoptotic processes. (3) Results: SEM analysis of cells seeded on the surfaces showed no obvious differences between the reference material and the cast material with or without ion implantation. The MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) proliferation assay also did not reveal any significant differences. Additionally, the osteogenic differentiation process tested by quantitative polymerase chain reactions (PCR), Alizarin red S assay, and C-terminal collagen type I propeptide (CICP) Elisa was not significantly modified. No signs of induced apoptosis were observed. (4) Conclusions: In this study, we could show that the newly developed process of centrifugal casting generated a material with comparable surface features to standard machined Ti6Al4V material. In terms of biological impact on primary human osteoblasts, no significant differences were recognized. Additional Ca- or P-ion implantation did not improve or impair these characteristics in the dosages applied. These findings indicate that spin casting of Ti6Al4V may represent an interesting alternative to the production of geometrically complex orthopedic implants. Full article
(This article belongs to the Special Issue Titanium and Its Alloys for Biomedical Applications)
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Open AccessArticle
Plasma-Assisted Chemical Vapor Deposition of TiBN Coatings on Nanostructured Cemented WC-Co
Metals 2020, 10(12), 1680; https://doi.org/10.3390/met10121680 - 16 Dec 2020
Viewed by 266
Abstract
The plasma-assisted chemical vapor deposition (PACVD) technique has shown many advantages in applications, where thin coatings with superior wear properties are demanded, especially for geometrically complex parts. In this study, multilayered gradient TiBN coatings that were deposited on nanostructured cemented carbides by the [...] Read more.
The plasma-assisted chemical vapor deposition (PACVD) technique has shown many advantages in applications, where thin coatings with superior wear properties are demanded, especially for geometrically complex parts. In this study, multilayered gradient TiBN coatings that were deposited on nanostructured cemented carbides by the PACVD method were investigated. Nanostructured samples of cemented carbides with the addition of 5 and 15 wt.% Co were sintered by the hot isostatic pressing, sinter-HIP technique. Surface preparation was conducted on samples in order to enable maximum coating adhesion. Tests that were conducted on produced samples aimed to investigate the mechanical and physical properties of coated samples. These tests included nanoindentation, surface layer characterization, and coating adhesion evaluation while using the Rockwell and scratch test. The obtained results confirmed that the PACVD process can be utilized for applying thin hard coatings to nanostructured cemented carbides that are produced by the sinter HIP process, resulting in a base material/ coating system that exhibits excellent physical and mechanical properties. The results presented in this paper give a valuable contribution to the research of TiBN coating systems and their potential for application under heavy wear conditions. Full article
(This article belongs to the Special Issue Advanced Hard Materials)
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Open AccessArticle
Effects of Sn and Sb on the Hot Ductility of Nb+Ti Microalloyed Steels
Metals 2020, 10(12), 1679; https://doi.org/10.3390/met10121679 - 16 Dec 2020
Viewed by 326
Abstract
Referencing the composition of a typical Nb+Ti microalloyed steel (Q345B), two kinds of steels, one microalloyed with Sn and Sb, and the other one only microalloyed with Sb were designed to study the effects of Sn and Sb on the hot ductility of [...] Read more.
Referencing the composition of a typical Nb+Ti microalloyed steel (Q345B), two kinds of steels, one microalloyed with Sn and Sb, and the other one only microalloyed with Sb were designed to study the effects of Sn and Sb on the hot ductility of Nb+Ti microalloyed steels. The Gleeble-3500 tester was adopted to determine the high-temperature mechanical properties of the two test steels. Fracture morphologies, microstructures and interior precipitation status were analyzed by SEM, CLSM (Confocal laser scanning microscope) and EDS, respectively. Results revealed that within the range of 950–650 °C, there existed the ductility trough for the two steels, which were mainly attributed to the precipitation of TiN and Nb (C, N). Additionally, precipitation of Sn and Sb were not observed in this research and the hot ductility was not affected by the addition of Sn and Sb, as compared with the Nb+Ti microalloyed steel. Therefore, addition of a small amount of Sn and Sb (≤0.05 wt.%) to the Nb+Ti microalloyed steel is favorable due to the improvement on corrosion resistance. Full article
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Open AccessArticle
Comparison of Extraction Ability between a Mixture of Alamine 336/Aliquat 336 and D2EHPA and Ionic Liquid ALi-D2 from Weak Hydrochloric Acid Solution
Metals 2020, 10(12), 1678; https://doi.org/10.3390/met10121678 - 15 Dec 2020
Viewed by 285
Abstract
The development of extraction systems to improve the extraction efficiency of metals using commercial extractants and ionic liquids is of importance. The extraction behavior of Co(II) between mixture of Alamine 336/Aliquat 336 and D2EHPA and synthesized ionic liquid ALi-D2 was compared in this [...] Read more.
The development of extraction systems to improve the extraction efficiency of metals using commercial extractants and ionic liquids is of importance. The extraction behavior of Co(II) between mixture of Alamine 336/Aliquat 336 and D2EHPA and synthesized ionic liquid ALi-D2 was compared in this work. Some factors, such as equilibrium pH, properties of the extractants, and concentration of components in the mixture had a remarkable effect on the extraction of Co(II). The interactions occurring in the mixtures as well as the change in solution pH were analyzed. Co(II) was completely extracted by ionic liquid when equilibrium pH was higher than 6.5, while it was difficult to extract Co(II) by employing the mixture of D2EHPA and Alamine 336/Aliquat 336. The formation of ionic liquid in the mixture of D2EHPA and Aliquat 336 was verified through FT-IR spectra. In addition, the competition extraction of hydrogen ion and Co(II) by ionic liquid ALi-D2 was explained. Among the three kinds of extractants, the ionic liquid showed the best extraction efficiency for Co(II) and pH control from weak acidic solutions. The present study provides valuable information on the extraction behavior of metal ion by the mixtures of commercial extractants, and thus can give some light on the development of metal extraction systems. Full article
(This article belongs to the Special Issue Solvent Extraction of Transition Metals)
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Open AccessReview
Structural and Biomedical Properties of Common Additively Manufactured Biomaterials: A Concise Review
Metals 2020, 10(12), 1677; https://doi.org/10.3390/met10121677 - 15 Dec 2020
Viewed by 312
Abstract
Biomaterials are in high demand due to the increasing geriatric population and a high prevalence of cardiovascular and orthopedic disorders. The combination of additive manufacturing (AM) and biomaterials is promising, especially towards patient-specific applications. With AM, unique and complex structures can be manufactured. [...] Read more.
Biomaterials are in high demand due to the increasing geriatric population and a high prevalence of cardiovascular and orthopedic disorders. The combination of additive manufacturing (AM) and biomaterials is promising, especially towards patient-specific applications. With AM, unique and complex structures can be manufactured. Furthermore, the direct link to computer-aided design and digital scans allows for a direct replicable product. However, the appropriate selection of biomaterials and corresponding AM methods can be challenging but is a key factor for success. This article provides a concise material selection guide for the AM biomedical field. After providing a general description of biomaterial classes—biotolerant, bioinert, bioactive, and biodegradable—we give an overview of common ceramic, polymeric, and metallic biomaterials that can be produced by AM and review their biomedical and mechanical properties. As the field of load-bearing metallic implants experiences rapid growth, we dedicate a large portion of this review to this field and portray interesting future research directions. This article provides a general overview of the field, but it also provides possibilities for deepening the knowledge in specific aspects as it comprises comprehensive tables including materials, applications, AM techniques, and references. Full article
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Open AccessArticle
On the Simultaneous Improving of Strength and Elongation in Dual Phase Steels via Cold Rolling
Metals 2020, 10(12), 1676; https://doi.org/10.3390/met10121676 - 15 Dec 2020
Viewed by 332
Abstract
The ferrite-pearlite microstructure was cold-rolled to form dual phase (DP) steels, the percentage reduction of which varied. To do so, the steels were annealed in two steps and then the workpiece underwent water quenching. Accordingly, a decrease was observed in the average size [...] Read more.
The ferrite-pearlite microstructure was cold-rolled to form dual phase (DP) steels, the percentage reduction of which varied. To do so, the steels were annealed in two steps and then the workpiece underwent water quenching. Accordingly, a decrease was observed in the average size of the ferrite grains, from above 15 µm to below 2 µm, subsequent to the thermomechanical processing. By an increase in the reduction percentage, the volume fraction of martensite grew. The balance between strength and elongation also improved nearly 3 times, equivalent to approximately 37,297 MPa% in DP in comparison to 11,501 MPa% in the ferrite-pearlite microstructure, even after 50% cold-rolling. Based on Hollomon and differential Crussard-Jaoul (DC–J) analyses, the DP steels under investigation deformed in two and three stages, respectively. The modified C–J (MC–J) analysis, however, revealed that the deformation process took place in four stages. The rate of strain hardening at the onset of the deformation process was rather high in all DP steels. The given rate increased once the size of the ferrite grains reduced; an increase in the volume fraction of martensite due to larger percentage of reduction also contributed to the higher rate of strain hardening. The observation of the fractured surfaces of the tensile specimens indicated ductile fracture of the studied DP steels. Full article
(This article belongs to the Special Issue Microstructural Engineering in Metallic Materials)
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Open AccessArticle
High Velocity Oxygen Liquid-Fuel (HVOLF) Spraying of WC-Based Coatings for Transport Industrial Applications
Metals 2020, 10(12), 1675; https://doi.org/10.3390/met10121675 - 14 Dec 2020
Viewed by 364
Abstract
In this article, we analyse five types of coatings, in terms of their microstructure, hardness, porosity, and wear resistance, in the as-sprayed state. The coatings are WC-based (WC-FeCrAl, WC-WB-Co, and WC-NiMoCrFeCo), alloy-based (Co-MoCrSi), or nanoWC coating-based (nanoWC-CoCr). Two tests were applied to assess [...] Read more.
In this article, we analyse five types of coatings, in terms of their microstructure, hardness, porosity, and wear resistance, in the as-sprayed state. The coatings are WC-based (WC-FeCrAl, WC-WB-Co, and WC-NiMoCrFeCo), alloy-based (Co-MoCrSi), or nanoWC coating-based (nanoWC-CoCr). Two tests were applied to assess the wear resistance of the coatings: a dry-pot wear test with two impact angles and an abrasive test using an abrasive cloth with two grit sizes. Porosity was determined by image analysis. Vickers impression was performed on cross-sections of the coatings, in order to determine their indentation fracture toughness. The highest hardness of the tested coatings was recorded for the nanoWC coating, followed by the rest of the WC-based coatings; meanwhile, the lowest hardness was recorded for the alloy coating. Minimal porosity was achieved by the alloy coating, due to its different nature and the absence of hard particles with a higher melting point. The NanoWC coating and other WC-based coatings had a higher porosity; however, porosity did not exceed 1% for each coating. The best wear resistance was achieved by the nanoWC coating, followed by the other WC-based coatings, with the lowest obtained by the alloy coating. The same tendency was recorded when determining the indentation fracture toughness. From a microscopic point of view, the structure of the evaluated coatings is not compact; nevertheless, their properties are excellent, and they act as compact coatings under load. Full article
(This article belongs to the Special Issue Application of Alloys in Transport)
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Open AccessArticle
Effect of Pre-Treatment with Sodium Chloride/Sulfuric Acid on the Bornite Concentrate Leaching in Chloride Medium
Metals 2020, 10(12), 1674; https://doi.org/10.3390/met10121674 - 14 Dec 2020
Viewed by 301
Abstract
In this work, the effect of the pre-treatment of bornite concentrate with a sodium chloride–sulfuric acid mixture prior to leaching with chloride solutions was evaluated. The influence of the dosage of NaCl and the resting time in the copper solution was evaluated. The [...] Read more.
In this work, the effect of the pre-treatment of bornite concentrate with a sodium chloride–sulfuric acid mixture prior to leaching with chloride solutions was evaluated. The influence of the dosage of NaCl and the resting time in the copper solution was evaluated. The solid residues of the pre-treatment were characterized by XRD to evaluate the changes that took place in the bornite. The experimental results show that as the sitting time and the amount of sodium chloride added are increased, the dissolution of the sulfide species also increased. The pre-treatment affects Cu preferentially because it has greater mobility than iron in the bornite crystal lattice. The pre-treatment promotes the formation of soluble Cu and Fe species. The efficiency of the pre-treatment depends largely on the formation of hydrochloric acid in the mixture at the particle level, due to the ease with which it diffuses through the bornite particles, achieving greater penetration of the pre-treatment. Full article
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Open AccessArticle
Effect of La Addition on Solidification Behavior and Phase Composition of Cast Al-Mg-Si Alloy
Metals 2020, 10(12), 1673; https://doi.org/10.3390/met10121673 - 14 Dec 2020
Viewed by 389
Abstract
The current study focusses on the phase composition, solidification path, and microstructure evaluation of gravity cast Al-4Mg-0.5Si-xLa aluminum alloy, where x = 0, 0.1, 0.25, 0.5, 0.75, and 1 wt.% La. A computational CalPhaD approach implemented in Thermo-Calc software and scanning [...] Read more.
The current study focusses on the phase composition, solidification path, and microstructure evaluation of gravity cast Al-4Mg-0.5Si-xLa aluminum alloy, where x = 0, 0.1, 0.25, 0.5, 0.75, and 1 wt.% La. A computational CalPhaD approach implemented in Thermo-Calc software and scanning electron microscopy technique equipped with electron microprobe analysis (EMPA) was employed to assess its above-mentioned characteristics. The thermodynamic analysis showed that the equilibrium solidification path of La-containing Al-Mg-Si alloys consists of only binary phases LaSi2 and Mg2Si precipitation along with α-Al from the liquid and further solid-state transformation of this mixture into α-Al + Al11La3 + Mg2Si + Al3Mg2 composition. Scheil–Gulliver simulation showed a similar solidification pathway but was accompanied by an increase in the solidification range (from ~55 °C to 210 °C). Furthermore, microstructural observations were congruent with the calculated fraction of phases at 560 °C and related to α-Al + LaSi2 + Mg2Si three-phase region in terms of formation of La-rich phase having both eliminating effect on the eutectic Mg2Si phase. Quantitative EMPA analysis and elemental mapping revealed that the La-rich phase included Al, La, and Si and may be described as Al2LaSi2 phase. This phase shows a visible modifying effect on the eutectic Mg2Si phase, likely due to absorbing on the liquid/solid interface. Full article
(This article belongs to the Special Issue Physical Metallurgy of Light Alloys and Composite Materials)
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Open AccessArticle
Effects of Post Heat Treatment on the Mechanical Properties of Cold-Rolled Ti/Cu Clad Sheet
Metals 2020, 10(12), 1672; https://doi.org/10.3390/met10121672 - 14 Dec 2020
Viewed by 261
Abstract
Titanium and titanium alloys have excellent corrosion and heat resistance, but weak electric and thermal conductivity. The weak conductivity of titanium can be overcome by cladding with copper, which has high conductivity. Although titanium is expensive, it is selected as a material suitable [...] Read more.
Titanium and titanium alloys have excellent corrosion and heat resistance, but weak electric and thermal conductivity. The weak conductivity of titanium can be overcome by cladding with copper, which has high conductivity. Although titanium is expensive, it is selected as a material suitable for applications requiring corrosion resistance such as in heat exchangers. This study was to investigate the effect of post heat treatment on the mechanical properties of the Ti/Cu cold-rolled clad plate by using the interfacial diffusion bonding. A titanium clad by cold rolling should be heat-treated after the rolling process to improve the bonding properties through the diffusion of metals and removal of residual stress due to work hardening, despite the easy formation of intermetallic compounds of Ti and Cu. As a result post-treatment, the elongation was improved by more than two times from 21% to max. 53% by the Ti-Cu interface diffusion phenomenon and the average tensile strength of the 450 °C heat-treated specimens was 353 MPa. By securing high elongation while maintaining excellent tensile and yield strength through post-treatment, the formability of Ti-Cu clad plate can be greatly improved. Full article
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Open AccessArticle
Prediction of Surface Integrity Parameters in Roller Burnishing of Ti6Al4V
Metals 2020, 10(12), 1671; https://doi.org/10.3390/met10121671 - 14 Dec 2020
Viewed by 295
Abstract
Burnishing is considered a super finishing process able to drastically increase surface quality in terms of hardness and roughness of the manufactured parts. Consequently, it is considered appealing for the performance enhancement of products where the surface quality plays a crucial role. However, [...] Read more.
Burnishing is considered a super finishing process able to drastically increase surface quality in terms of hardness and roughness of the manufactured parts. Consequently, it is considered appealing for the performance enhancement of products where the surface quality plays a crucial role. However, when burnishing grade 5 titanium alloy, a quantitative relationship between process parameters and surface integrity is still missing. This work provides a deep analysis of the burnishing parameters and their influence on the surface integrity of Ti-6Al-4V. In particular, starting from a large experimental campaign, statistical analysis of the results is performed and models able to describe the surface integrity response based on different burnishing parameters are presented. The overall results allow us to clearly define the relationship within the input and output variables identifying, by the proposed models, different operational windows for surface integrity improvement. Full article
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