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Metals, Volume 11, Issue 9 (September 2021) – 167 articles

Cover Story (view full-size image): The heat losses in the submerged entry nozzle (SEN) region were investigated using a novel numerical approach by coupling the convection and heat transfer in the liquid slag and melt pool. It was revealed that the parasitic solidification occurred inside an SEN bore with partially or completely absent insulation. SEN clogging was found to promote the solidification of the entrapped melt. The accelerated flow and the impaired superheat inside the mold cavity were detected due to the combined effect of the clogging and parasitic solidification. This study aims to assist in the development of clog-free and energy-saving SEN designs. View this paper
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Article
Recovery of Rare Earth Oxides from Flotation Concentrates of Bastnaesite Ore by Ultra-Fine Centrifugal Concentration
Metals 2021, 11(9), 1498; https://doi.org/10.3390/met11091498 - 21 Sep 2021
Cited by 1 | Viewed by 658
Abstract
Historically, the ability to effectively separate carbonate gangue from bastnaesite via flotation has frequently proven to be challenging without sacrificing significant rare earth oxide (REO) grade or recovery. However, in light of the fact that the rare earth bearing minerals often exhibit higher [...] Read more.
Historically, the ability to effectively separate carbonate gangue from bastnaesite via flotation has frequently proven to be challenging without sacrificing significant rare earth oxide (REO) grade or recovery. However, in light of the fact that the rare earth bearing minerals often exhibit higher specific gravities than the carbonate gangue, the possibility exists that the use of gravity separation could be used to achieve such a selective separation. This however is complicated by the fact that, in cases such as this study when the liberation size is finer than 50 microns, most traditional gravity separation methods become increasingly challenging. The aim of this study is to determine the applicability of centrifugal concentrators to beneficiate ultra-fine (UF) bastnaesite and calcite bearing flotation concentrates. By using a UF Falcon, it was possible to achieve initial gravity REO recoveries exceeding 90% while rejecting on the order of 25% to 35% of the total calcium from an assortment of rougher and cleaner flotation concentrates. Additionally, when additional stages of cleaner UF Falcon gravity separation were operated in an open circuit configuration, it was possible, from an original fine feed of 35 microns containing 50.5% REO and 5.5% Ca, to upgrade up to approximately 59% REO and 2.0% calcium. While not the goal of this study, these results also support previous limited data to suggest that UF Falcons are potentially capable of treating a wider range of materials than they were originally designed for, including feeds rich in heavy mineral content. Full article
(This article belongs to the Special Issue Advances in Mineral Processing and Hydrometallurgy II)
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Article
Deformation Mechanism Investigation on Low Density 18Mn Steels under Different Solid Solution Treatments
Metals 2021, 11(9), 1497; https://doi.org/10.3390/met11091497 - 21 Sep 2021
Cited by 1 | Viewed by 654
Abstract
To meet the demand of the 10% weight reduction goal for automotive steel, the microstructure and mechanical properties of Fe-18Mn-Al-C steel with different carbon and aluminum contents were investigated under different solid solution treatments, and the deformation mechanisms of the experimental steels were [...] Read more.
To meet the demand of the 10% weight reduction goal for automotive steel, the microstructure and mechanical properties of Fe-18Mn-Al-C steel with different carbon and aluminum contents were investigated under different solid solution treatments, and the deformation mechanisms of the experimental steels were elucidated. Aided by thermodynamic calculation, transmission electron microscopy (TEM) and in situ scanning electron microscope (SEM) analysis, it was shown that for the 18Mn-1.5Al experimental steel with about 20 mJ/m2 stacking fault energy (SFE), the twinning-induced plasticity (TWIP) effect always dominated in this steel after different solid solution treatments under tensile deformation. With the 7 wt% aluminum addition, the SFE of austenite was affected by temperature and the range of SFE was between 60 and 65 mJ/m2. The existence of δ-ferrite obviously inhibited the TWIP effect. With the increase in the solution treatment temperature, δ-ferrite gradually transformed into the austenite, and the n-value remained low and stable in a large strain range, which were caused by the local hardening during the tensile deformation. Due to the difference in the deformability of the austenite and δ-ferrite structure as well as the inconsistent extension of the slip band, the micro-cracks were easily initiated in the 18Mn-7Al experimental steel; then, it exhibited lower plasticity. Full article
(This article belongs to the Special Issue Strengthening Mechanisms of Metals and Alloys)
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Article
Study on Adding Ammonium Hydrogen Fluoride to Improve Manganese Leaching Efficiency of Ammonia Leaching Low-Grade Rhodochrosite
Metals 2021, 11(9), 1496; https://doi.org/10.3390/met11091496 - 21 Sep 2021
Viewed by 494
Abstract
The ammonia leaching method for treating low-grade rhodochrosite has the advantages of a good impurity removal effect and low environmental pollution. In this paper, aiming at the low leaching efficiency of low-grade rhodochrosite treated by the ammonia leaching method, studies on enhancing the [...] Read more.
The ammonia leaching method for treating low-grade rhodochrosite has the advantages of a good impurity removal effect and low environmental pollution. In this paper, aiming at the low leaching efficiency of low-grade rhodochrosite treated by the ammonia leaching method, studies on enhancing the leaching efficiency of manganese by using ammonium hydrogen fluoride as an additive are carried out. The effects of different ammonia concentrations, leaching temperatures, leaching times, liquid-solid ratios, stirring rates, and the addition of ammonium hydrogen fluoride on the leaching efficiency of manganese with and without ammonium hydrogen fluoride as an additive were comparatively studied, and the parameters of ammonia concentration, ammonia leaching temperature, and ammonium hydrogen fluoride dosage were optimized in the experimental study. The results indicated that ammonium hydrogen fluoride as an additive in the treatment of low-grade rhodochrosite by the ammonia leaching method could effectively increase the leaching efficiency of manganese, and the optimal process parameters were obtained. Meanwhile, the addition of ammonium hydrogen fluoride didn’t affect the quality of the steamed ammonia product. Full article
(This article belongs to the Special Issue Separation and Leaching for Metals Recovery 2021)
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Article
Interface Formation and Bonding Mechanisms of Laser Welding of PMMA Plastic and 304 Austenitic Stainless Steel
Metals 2021, 11(9), 1495; https://doi.org/10.3390/met11091495 - 21 Sep 2021
Cited by 1 | Viewed by 833
Abstract
Laser welding experiments involving amorphous thermoplastic polymer (PMMA) and 304 austenitic stainless steel plates were conducted to explore the influence of laser welding process parameters on plastic–metal joints. A high-speed camera was applied to record the dynamics of the molten pool and the [...] Read more.
Laser welding experiments involving amorphous thermoplastic polymer (PMMA) and 304 austenitic stainless steel plates were conducted to explore the influence of laser welding process parameters on plastic–metal joints. A high-speed camera was applied to record the dynamics of the molten pool and the formation of bubbles to reveal the bonding mechanisms of the hybrid joints. The influence of process parameters on the joints was analyzed using temperature measurements performed with thermocouples. The microstructure morphology of joints was observed using SEM. The mechanical characterization of the hybrid joints was carried out to understand the effect of the welding conditions on the weld morphology, flaws and shear stress. Different interface temperatures resulted in two types of bubbles and led to different weld morphology characteristics. A stable hybrid joint with the best shear stress was produced with a laser line energy of 20.16 J/mm2, a temperature of 305 °C and small bubbles. The shear stress of the effective joint under the maximum mechanical resistance was 4.17 MPa. The chemical bonds (M-O, M-C) and mechanical anchoring that formed on the steel’s surface contributed to the joint bonding. Range analysis provided guidance for identifying the impact of individual factors in the shear stress for the laser welding of plastic–metal. Full article
(This article belongs to the Special Issue Laser Welding Technology)
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Article
Electrochemical Study of Nd and Pr Co-Deposition onto Mo and W from Molten Oxyfluorides
Metals 2021, 11(9), 1494; https://doi.org/10.3390/met11091494 - 21 Sep 2021
Viewed by 600
Abstract
Electrodeposition processes of neodymium and praseodymium in molten NdF3 + PrF3 + LiF + 1 wt.%Pr6O11 + 1 wt.%Nd2O3 and NdF3 + PrF3 + LiF + 2 wt.%Pr6O11 + 2 [...] Read more.
Electrodeposition processes of neodymium and praseodymium in molten NdF3 + PrF3 + LiF + 1 wt.%Pr6O11 + 1 wt.%Nd2O3 and NdF3 + PrF3 + LiF + 2 wt.%Pr6O11 + 2 wt.%Nd2O3 electrolytes at 1323 K were investigated. Cyclic voltammetry, square wave voltammetry, and open circuit potentiometry were applied to study the electrochemical reduction of Nd(III) and Pr(III) ions on Mo and W cathodes. It was established that a critical condition for Nd and Pr co-deposition in oxyfluoride electrolytes was a constant praseodymium deposition overpotential of ≈−0.100 V, which was shown to result in co-deposition current densities approaching 6 mAcm−2. Analysis of the results obtained by applied electrochemical techniques showed that praseodymium deposition proceeds as a one-step process involving exchange of three electrons (Pr(III)→Pr(0)) and that neodymium deposition is a two-step process: the first involves one electron exchange (Nd(III)→Nd(II)), and the second involves an exchange of two electrons (Nd(II)→Nd(0)). X-ray diffraction analyses confirmed the formation of metallic Nd and Pr on the working substrate. Keeping the anodic potential to the glassy carbon working anode low results in very low levels of carbon oxides, fluorine and fluorocarbon gas emissions, which should qualify the studied system as an environmentally friendly option for rare earth metal deposition. The newly reported data for Nd and Pr metals co-deposition provide valuable information for the recycling of neodymium-iron-boron magnets. Full article
(This article belongs to the Special Issue Advances in Understanding Metal Electrolysis Processes)
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Article
Effects of Process Control Agent Amount, Milling Time, and Annealing Heat Treatment on the Microstructure of AlCrCuFeNi High-Entropy Alloy Synthesized through Mechanical Alloying
Metals 2021, 11(9), 1493; https://doi.org/10.3390/met11091493 - 20 Sep 2021
Cited by 4 | Viewed by 803
Abstract
This study was conducted to investigate the characteristics of the AlCrCuFeNi high-entropy alloy (HEA) synthesized through mechanical alloying (MA). In addition, effects of Process Control Agent (PCA) amount and milling time were investigated using X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), and [...] Read more.
This study was conducted to investigate the characteristics of the AlCrCuFeNi high-entropy alloy (HEA) synthesized through mechanical alloying (MA). In addition, effects of Process Control Agent (PCA) amount and milling time were investigated using X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). The results indicated that the synthesized AlCrCuFeNi alloy is a dual phase (FCC + BCC) HEA and the formation of the phases is strongly affected by the PCA amount. A high amount of PCA postponed the alloying process and prevented solid solution formation. Furthermore, with an increase in the PCA amount, lattice strain decreased, crystallite size increased, and the morphology of the mechanically alloyed particles changed from spherical to a plate-like shape. Additionally, investigation of thermal properties and annealing behavior at different temperatures revealed no phase transformation up to 400 °C; however, the amount of the phases changed. By increasing the temperature to 600 °C, a sigma phase (σ) and a B2-ordered solid solution formed; moreover, at 800 °C, the FCC phase decomposed into two different FCC phases. Full article
(This article belongs to the Special Issue Spark Plasma Sintering on Metals and Alloys)
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Article
Investigating Nanoindentation Creep Behavior of Pulsed-TIG Welded Inconel 718 and Commercially Pure Titanium Using a Vanadium Interlayer
Metals 2021, 11(9), 1492; https://doi.org/10.3390/met11091492 - 20 Sep 2021
Viewed by 779
Abstract
In a dissimilar welded joint between Ni base alloys and titanium, creep failure is a potential concern as it could threaten to undermine the integrity of the joint. In this research, the mechanical heterogeneity of a Pulsed TIG welded joint between commercially pure [...] Read more.
In a dissimilar welded joint between Ni base alloys and titanium, creep failure is a potential concern as it could threaten to undermine the integrity of the joint. In this research, the mechanical heterogeneity of a Pulsed TIG welded joint between commercially pure titanium (CpTi) and Inconel 718 (IN718) with a vanadium (V) interlayer was studied through a nanoindentation technique with respect to hardness, elastic modulus, and ambient temperature creep deformation across all regions (fusion zones and interfaces, mainly composed of a dendritic morphology). According to the experimental results, a nanohardness of approximately 10 GPa was observed at the V/IN718 interface, which was almost 70% higher than that at the V/CpTi interface. This happened due to the formation of intermetallic compounds (IMCs) (e.g., Ti2Ni, NiV3, NiTi) and a (Ti, V) solid solution at the V/IN718 and V/CpTi interfaces, respectively. In addition, nanohardness at the V/IN718 interface was inhomogeneous as compared to that at the V/CpTi interface. Creep deformation behavior at the IN718 side was relatively higher than that at different regions on the CpTi side. The decreased plastic deformation or creep effect of the IMCs could be attributed to their higher hardness value. Compared to the base metals (CpTi and IN718), the IMCs exhibited a strain hardening effect. The calculated values of the creep stress exponent were found in the range of 1.51–3.52 and 2.52–4.15 in the V/CpTi and V/IN718 interfaces, respectively. Furthermore, the results indicated that the creep mechanism could have been due to diffusional creep and dislocation climb. Full article
(This article belongs to the Special Issue High-Productivity Welding of Metals and Alloys)
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Article
Preparation of Ag0 Nanoparticles by EDM Method as Catalysts for Oxygen Reduction
Metals 2021, 11(9), 1491; https://doi.org/10.3390/met11091491 - 20 Sep 2021
Cited by 1 | Viewed by 674
Abstract
At present, platinum-based catalysts are the best cathode catalysts, but due to their high prices, they are difficult to use widely. Under alkaline conditions, silver is a better low-cost substitute. Here, a physical preparation method—electrical discharge machining (EDM)—is used to prepare Ag0 [...] Read more.
At present, platinum-based catalysts are the best cathode catalysts, but due to their high prices, they are difficult to use widely. Under alkaline conditions, silver is a better low-cost substitute. Here, a physical preparation method—electrical discharge machining (EDM)—is used to prepare Ag0 nanoparticles. The method is simple and has a high yield. The diameter of prepared nanoparticles is about 30 nm and the nanoparticle surface is rich in defects. These defects enhance the adsorption of O2. In addition, defects can cause tensile strain on the silver catalyst, causing the d-band center of silver to move upward. The defects and the upward shift of the d-band center jointly improve the adsorption energy and catalytic performance of Ag0. This work provides a new method for the engineering construction of surface defects and the preparation of metal catalysts. Full article
(This article belongs to the Special Issue Research on Metal Nanoparticles)
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Article
Preparation of Battery-Grade Lithium Carbonate with Lithium-Containing Desorption Solution
Metals 2021, 11(9), 1490; https://doi.org/10.3390/met11091490 - 19 Sep 2021
Viewed by 676
Abstract
In this study, a process for preparing battery-grade lithium carbonate with lithium-rich solution obtained from the low lithium leaching solution of fly ash by adsorption method was proposed. A carbonization-decomposition process was carried out to remove impurities such as iron and aluminum. First, [...] Read more.
In this study, a process for preparing battery-grade lithium carbonate with lithium-rich solution obtained from the low lithium leaching solution of fly ash by adsorption method was proposed. A carbonization-decomposition process was carried out to remove impurities such as iron and aluminum. First, primary Li2CO3 was treated by CO2 to get the more soluble bicarbonates. The decomposition of LiHCO3 produced insoluble Li2CO3 at 90 °C And Li2CO3 was smashed by air stream pulverization. The final precipitation yielded a high purity (99.6%) and homogeneous Li2CO3. Some factors affecting production efficiency were investigated. The results showed that a liquid-solid ratio of 25:1, a carbonization temperature of 25 °C, an air velocity of 2 L/min, and a stirring speed of 400 rpm; a decomposition temperature of 90 °C and a stirring speed of 400 rpm, a molar ratio of EDTA to Ca 2:1; an air pressure of 0.3 MPa and hot water washing precipitate (L/S mass ratio 2:1) promoted ions removal. Full article
(This article belongs to the Special Issue Recent Advances in Leaching and Extractive Metallurgy)
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Article
Dynamic Mechanical Properties of Ti–Al3Ti–Al Laminated Composites: Experimental and Numerical Investigation
Metals 2021, 11(9), 1489; https://doi.org/10.3390/met11091489 - 19 Sep 2021
Viewed by 673
Abstract
The Ti–Al3Ti–Al laminated composites with different Al contents were prepared by vacuum hot pressing sintering technology. The effects of Al content on the dynamic mechanical properties of the composites were studied using the combination of Split Hopkinson Pressure Bar experiment and finite element [...] Read more.
The Ti–Al3Ti–Al laminated composites with different Al contents were prepared by vacuum hot pressing sintering technology. The effects of Al content on the dynamic mechanical properties of the composites were studied using the combination of Split Hopkinson Pressure Bar experiment and finite element analysis. The results showed that different Al content changes the fracture mode of the composites. The laminated composites without Al have higher brittleness and lower fracture strain. The Ti–Al3Ti–Al laminated composites containing 10–15%Al have better dynamic mechanical properties than those without Al, but the subsequent increase of Al content is not conducive to the improvement of strength. However, when the Al content in the specimen reaches 30%, the dynamic mechanical properties of the composites decrease, multi-crack phenomenon and relatively large strain occur, and the Al extruded from the layers fills the crack. Full article
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Article
Effect of the Thermomechanical Treatment on the Corrosion of UNSM Processed Inconel 718: An Electrochemical Study
Metals 2021, 11(9), 1488; https://doi.org/10.3390/met11091488 - 18 Sep 2021
Viewed by 548
Abstract
In this work, the influence of thermal (TT), mechanical, and thermomechanical (TMT) treatments using the ultrasonic nanocrystal surface modification (UNSM) on the corrosion protection properties of Inconel 718 was studied, correlating the changes in the electrochemical properties with the promoted microstructure. The UNSM [...] Read more.
In this work, the influence of thermal (TT), mechanical, and thermomechanical (TMT) treatments using the ultrasonic nanocrystal surface modification (UNSM) on the corrosion protection properties of Inconel 718 was studied, correlating the changes in the electrochemical properties with the promoted microstructure. The UNSM treatment had a grain refinement effect on the top surface, reducing the grain size from 11.5 to 7.4 µm for the first 10 µm in depth. The high grain boundary density, due to the grain refinement, enabled a faster growth of the passive film. The impedance showed a decrease in the charge transfer resistance by three orders of magnitude, from 106 to 103 Ω cm2 for as-received to 1000 °C, as the TT temperature crossed the solvus of the γ′/γ″ and approached the solvus of the δ-phase. The UNSM treatment lowered the pitting corrosion susceptibility, increasing the charge transfer resistance and decreasing the effective capacitance of the double layer, leading to the thickest passive film with 6.8 nm. Full article
(This article belongs to the Special Issue Corrosion and Inhibition Processes)
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Article
Manipulation of Microstructure and Mechanical Properties in N-Doped CoCrFeMnNi High-Entropy Alloys
Metals 2021, 11(9), 1487; https://doi.org/10.3390/met11091487 - 18 Sep 2021
Cited by 1 | Viewed by 709
Abstract
Herein, we carefully investigate the effect of nitrogen doping in the equiatomic CoCrFeMnNi high-entropy alloy (HEA) on the microstructure evolution and mechanical properties. After homogenization (1100 °C for 20 h), cold-rolling (reduction ratio of 60%) and subsequent annealing (800 °C for 1 h), [...] Read more.
Herein, we carefully investigate the effect of nitrogen doping in the equiatomic CoCrFeMnNi high-entropy alloy (HEA) on the microstructure evolution and mechanical properties. After homogenization (1100 °C for 20 h), cold-rolling (reduction ratio of 60%) and subsequent annealing (800 °C for 1 h), a unique complex heterogeneous microstructure consisting of fine recrystallized grains, large non-recrystallized grains, and nanoscale Cr2N precipitates, were obtained in nitrogen-doped (0.3 wt.%) CoCrFeMnNi HEA. The yield strength and ultimate tensile strength can be significantly improved in nitrogen-doped (0.3 wt.%) CoCrFeMnNi HEA with a complex heterogeneous microstructure, which shows more than two times higher than those compared to CoCrFeMnNi HEA under the identical process condition. It is achieved by the simultaneous operation of various strengthening mechanisms from the complex heterogeneous microstructure. Although it still has not solved the problem of ductility reduction, as the strength increases because the microstructure optimization is not yet complete, it is expected that precise control of the unique complex heterogeneous structure in nitrogen-doped CoCrFeMnNi HEA can open a new era in overcoming the strength–ductility trade-off, one of the oldest dilemmas of structural materials. Full article
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Review
Dissimilar Non-Ferrous Metal Welding: An Insight on Experimental and Numerical Analysis
Metals 2021, 11(9), 1486; https://doi.org/10.3390/met11091486 - 18 Sep 2021
Cited by 5 | Viewed by 1029
Abstract
In recent years Gas Metal Arc Welding (GMAW) technology has expanded its functionalities in various areas which have further motivated its usage in several emerging manufacturing industries. There are several issues and challenges associated with this technology, especially in dissimilar metal welding (DMW). [...] Read more.
In recent years Gas Metal Arc Welding (GMAW) technology has expanded its functionalities in various areas which have further motivated its usage in several emerging manufacturing industries. There are several issues and challenges associated with this technology, especially in dissimilar metal welding (DMW). One of the predominant challenges is selecting appropriate welding parameters which influence the efficiency of this technology. To explore several modern advancements in this expertise, this paper has done an exclusive survey on various standards of GMAW and its variants for selecting suitable parameters for welding dissimilar nonferrous metals. This review summarizes various experimental and numerical results along with related illustrations to highlight the feasibility of welding dissimilar nonferrous metals using traditional GMAW and investigations on advanced GMAW processes such as cold metal transfer (CMT) and pulsed GMAW (P-GMAW). Simulation and modeling of nonferrous DMW have identified several research gaps and modeling problems. Researchers and manufacturers can use this review as a guideline to choose appropriate welding parameters to implement GMAW and its variants for non-ferrous dissimilar welding. It found that by controlling the heat input and effective post-heat treatments, adequate joint properties can be achieved. Automated large -scale manufacturing will widen the utilization scope of GMAW and avoid some costly methods such as laser welding, ultrasonic welding, and friction stir welding etc. Full article
(This article belongs to the Special Issue Numerical Simulation of Metals Welding Process)
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Article
Natural Aging Effect of Al-20Zn-3Cu Alloy on Mechanical Properties and Its Relation to Microstructural Change
Metals 2021, 11(9), 1485; https://doi.org/10.3390/met11091485 - 18 Sep 2021
Viewed by 455
Abstract
We investigate the effect of the natural age-hardening response of the Al-20Zn-3Cu alloy with natural aging times up to 12 months. The ultimate tensile strength of the Al-20Zn-3Cu alloy is drastically enhanced from 308 to 320 MPa after 2 months and from 320 [...] Read more.
We investigate the effect of the natural age-hardening response of the Al-20Zn-3Cu alloy with natural aging times up to 12 months. The ultimate tensile strength of the Al-20Zn-3Cu alloy is drastically enhanced from 308 to 320 MPa after 2 months and from 320 to 346 MPa after 9 months. Then, natural age hardening becomes saturated after 9 months. A microstructural investigation reveals that the natural age-hardening mechanism is mainly induced by the diffusion of the Zn element. First, a rapid decrease in the volume fraction of the eutectoid lamellae (α-Al+η-Zn) is observed at the early stage of natural aging, leading to an increase in the tensile strength. This originates from the relatively high diffusivity of Zn due to its low melting temperature. Then, the diffusion of Zn into the Al matrix induces clusters of solute atoms that enhance the growth rate of the nanoprecipitates formed in the Al matrix. As a consequence, the tensile strength of the natural-aged Al-20Zn-3Cu alloy increases drastically after 9 months, whereas the ductility is significantly degraded. Full article
(This article belongs to the Special Issue High-Strength Alloys)
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Article
Systematic Development of Eutectic High Entropy Alloys by Thermodynamic Modeling and Experimentation: An Example of the CoCrFeNi-Mo System
Metals 2021, 11(9), 1484; https://doi.org/10.3390/met11091484 - 18 Sep 2021
Cited by 2 | Viewed by 668
Abstract
Face centered cubic (FCC) high-entropy alloys (HEA) exhibit excellent ductility while body centered cubic (BCC) HEAs are characterized by high strength. Development of fine two-phase eutectic microstructure (consisting of a tough phase such as fcc and a hard phase such as bcc/intermetallic) can [...] Read more.
Face centered cubic (FCC) high-entropy alloys (HEA) exhibit excellent ductility while body centered cubic (BCC) HEAs are characterized by high strength. Development of fine two-phase eutectic microstructure (consisting of a tough phase such as fcc and a hard phase such as bcc/intermetallic) can help in obtaining an extraordinary combination of strength and ductility in HEAs. Designing eutectic high entropy alloys is an extremely difficult task for which different empirical and non-empirical methods have been previously tried. In the present study, the possibility of developing a eutectic microstructure by the addition of Mo to CoCrFeNi was evaluated by calculation of the pseudo-binary phase diagram. Experimental results validated the presence of eutectic reaction in the calculated phase diagrams; however, small changes in the calculated phase diagrams were proposed. It has been shown that calculated pseudo-binary phase diagrams can provide a very good starting point for the development of eutectic HEAs and help in exponentially reducing the amount of experimental effort that may be required otherwise. Eutectic mixture consisting of FCC (A2) phase and intermetallic phases (σ and μ) was successfully obtained by the addition of Mo to the CoCrFeNi system. The development of the eutectic microstructure showed a profound effect on the mechanical properties. Hardness of the samples increased from 150 HV for CoCrFeNiMo0.1 to 425.5 HV for CoCrFeNiMo1.0, whereas yield strength increased from around 218 MPa for CoCrFeNiMo0.1 to around 1100 MPa for CoCrFeNiMo1.0. Full article
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Article
Study on the Relationship between High Temperature Mechanical Properties and Precipitates Evolution of 7085 Al Alloy after Long Time Thermal Exposures
Metals 2021, 11(9), 1483; https://doi.org/10.3390/met11091483 - 18 Sep 2021
Cited by 2 | Viewed by 586
Abstract
The requirement for 7085 Al alloy as large airframe parts has been increasing due to its low quenching sensitivity and high strength. However, the relationship between high temperature mechanical properties and the evolution of precipitates in hot environments is still unclear. In this [...] Read more.
The requirement for 7085 Al alloy as large airframe parts has been increasing due to its low quenching sensitivity and high strength. However, the relationship between high temperature mechanical properties and the evolution of precipitates in hot environments is still unclear. In this work, thermal exposure followed by tensile tests were conducted on the 7085 Al alloy at various temperatures (100 °C, 125 °C, 150 °C and 175 °C). Variations of hardness, electrical conductivity and tensile properties were investigated. The evolution of the nano scale precipitates was also quantitatively characterized by transmission electron microscopy (TEM). The results show that the hardness and electrical conductivity of the alloy are more sensitive to the temperature than to the time. The strength decreases continuously with the increase of temperature due to the transformation from η′ to η phase during the process. Furthermore, the main η phase in the alloy transformed from V3 and V4 to V1 and V2 variants when the temperature was 125 °C. Additionally, with increasing the temperature, the average precipitate radius increased, meanwhile the volume fraction and number density of the precipitates decreased. The strengthening effect of nano scale precipitates on tensile properties of the alloy was calculated and analyzed. Full article
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Article
Toward a Simplified Arc Impingement Model in a Direct-Current Electric Arc Furnace
Metals 2021, 11(9), 1482; https://doi.org/10.3390/met11091482 - 17 Sep 2021
Viewed by 849
Abstract
A 2D axisymmetric two-phase model was developed to study the effect of an arc impingement on the liquid metal inside an electric arc furnace. In addition to the arc flow dynamics, the model covered the heat transfer and magneto hydrodynamics of the arc [...] Read more.
A 2D axisymmetric two-phase model was developed to study the effect of an arc impingement on the liquid metal inside an electric arc furnace. In addition to the arc flow dynamics, the model covered the heat transfer and magneto hydrodynamics of the arc and the liquid metal. Through a parametric study, three different parameters were considered to predict the most important factors affecting the arc and overall behaviour of the process: the arc gap, the density of the gas, and the total electric current. Understanding the effect of these parameters can show the key factors altering the arc dynamics. The study showed that the total applied current was the most important parameter that influenced the impingement depth and mixing of the liquid metal. The depth of the impingement and strength of the mixing of the liquid bath were directly proportional to the current applied in the furnace. The initial arc gap distance was found to be crucial for sustaining a continuous and stable arc. The value of the gas density was very important for the velocity profile; however, it had no significant effect on the impingement depth. This showed that a constant density could be used instead of a varying gas density with temperature to increase the computational efficiency. The study assessed the effects of the aforementioned factors on the arc impingement depth, velocity magnitude, and arc stability. The conclusions acquired and challenges are also presented. Full article
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Article
Tube Expansion by Single Point Incremental Forming: An Experimental and Numerical Investigation
Metals 2021, 11(9), 1481; https://doi.org/10.3390/met11091481 - 17 Sep 2021
Cited by 1 | Viewed by 653
Abstract
In this paper, we revisit the formability of tube expansion by single point incremental forming to account for the material strain hardening and the non-proportional loading paths that were not taken into consideration in a previously published analytical model of the process built [...] Read more.
In this paper, we revisit the formability of tube expansion by single point incremental forming to account for the material strain hardening and the non-proportional loading paths that were not taken into consideration in a previously published analytical model of the process built upon a rigid perfectly plastic material. The objective is to provide a new insight on the reason why the critical strains at failure of tube expansion by single point incremental forming are far superior to those of conventional tube expansion by rigid tapered conical punches. For this purpose, we replaced the stress triaxiality ratio that is responsible for the accumulation of damage and cracking by tension in monotonic, proportional loading paths, by integral forms of the stress triaxiality ratio that are more adequate for the non-proportional paths resulting from the loading and unloading cycles of incremental tube expansion. Experimental and numerical simulation results plotted in the effective strain vs. stress triaxiality space confirm the validity of the new damage accumulation approach for handling the non-proportional loading paths that oscillate cyclically from shearing to biaxial stretching, as the single point hemispherical tool approaches, contacts and moves away from a specific location of the incrementally expanded tube surface. Full article
(This article belongs to the Special Issue Tube and Sheet Metal Forming Processes and Applications)
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Article
Effect of the Basicity on Mineralogical Phases and Micro-Structure of Dephosphorization Slag in the New Double Slag Converter Steelmaking Process
Metals 2021, 11(9), 1480; https://doi.org/10.3390/met11091480 - 17 Sep 2021
Viewed by 576
Abstract
In the present work, the effect of the basicity at the lower range from 0.98 to 2.13 on dephosphorization of hot metal at 1623 K was studied through high-temperature laboratorial experiments. With the increase of the basicity from 0.98 to 2.13, the P [...] Read more.
In the present work, the effect of the basicity at the lower range from 0.98 to 2.13 on dephosphorization of hot metal at 1623 K was studied through high-temperature laboratorial experiments. With the increase of the basicity from 0.98 to 2.13, the P and C contents in hot metal rapidly decrease and increase at first, and then gradually decrease and increase, respectively. From the scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) and X-ray diffraction (XRD) results, with the increase of the basicity, the phase containing the high P content changes from the matrix phase into the phosphorus (P)-rich phase. Under the present experimental conditions, the P-rich phase can only be precipitated from the liquid slag when the basicity is higher than 1.55, which is a benefit to the dephosphorization. As the Raman intensity of the P-O-Ca structure unit in the P-rich phase is significantly higher than that of the P-O-Si structure unit, most of the phosphorus in the P-rich phase exists in the P-O-Ca structure unit and a small amount of phosphorus exists in the P-O-Si structure unit. With the increase of the basicity of the dephosphorization slag, the activity coefficient of P2O5, γ(P2O5) , in the liquid phase decreases, while the basicity in the liquid phase increases. Full article
(This article belongs to the Special Issue Oxygen Steelmaking Process)
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Article
Prediction of Cracking Susceptibility of Commercial Aluminum Alloys during Solidification
Metals 2021, 11(9), 1479; https://doi.org/10.3390/met11091479 - 17 Sep 2021
Viewed by 857
Abstract
Cracking during solidification is a complex phenomenon which has been investigated from various angles for decades using both experimental and theoretical methods. In this paper, cracking susceptibility was investigated by a simulation method for three series of aluminum alloys: AA2xxx, AA6xxx, and AA7xxx [...] Read more.
Cracking during solidification is a complex phenomenon which has been investigated from various angles for decades using both experimental and theoretical methods. In this paper, cracking susceptibility was investigated by a simulation method for three series of aluminum alloys: AA2xxx, AA6xxx, and AA7xxx alloys. The simulation tool was developed using the CALPHAD method and is readily applicable to multicomponent alloy systems. For each series of alloys, cracking susceptible index values were calculated for more than 1000 alloy compositions by high-throughput calculation. Cracking susceptible maps were then constructed for these three series of aluminum alloys using the simulated results. The effects of major and minor alloying elements were clearly demonstrated by these index maps. The cooling rate effect was also studied, and it was concluded that back diffusion in the solid can significantly improve the cracking susceptibility. Full article
(This article belongs to the Special Issue Calphad Tools for the Metallurgy of Solidification)
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Article
Excellent Wear Resistance of a High-Speed Train Brake Disc Steel with High Hardening Ratcheting Strain Zone
Metals 2021, 11(9), 1478; https://doi.org/10.3390/met11091478 - 17 Sep 2021
Viewed by 664
Abstract
Wear resistance of brake discs has a significant effect on the safety of high-speed trains. In this work, the rolling–sliding wear resistance of a low-carbon martensitic brake disc steel was investigated. The microstructure evolution and mechanical properties from the worn surface to the [...] Read more.
Wear resistance of brake discs has a significant effect on the safety of high-speed trains. In this work, the rolling–sliding wear resistance of a low-carbon martensitic brake disc steel was investigated. The microstructure evolution and mechanical properties from the worn surface to the matrix were analyzed to promote parameters for the application of this steel. The results indicated that a ratcheting strain zone was formed at the surface of the brake disc steel under asymmetric cycling load and presented the morphology of the plastic flow line. An equation between the shear strain and the depth from the surface was established, which reflected the gradient distribution of the shear strain. The martensite lath refined into the nano/sub-micron grain and strip on the topmost surface. The micron scratch test results exhibited that the hardening rate and fracture toughness of the ratcheting strain zone varied continually along with depth, and the highest hardening rate occurred on the worn surface due to the increase of dislocation density and grain refinement. Additionally, the brake disc steel obtained better wear resistance than that of other wear-resistant materials used for railways due to steel having the highest hardening rate in the ratcheting strain zone. Full article
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Article
Microstructure and Mechanical Properties of the ((CoCrFeNi)95Nb5)100−xMox High-Entropy Alloy Coating Fabricated under Different Laser Power
Metals 2021, 11(9), 1477; https://doi.org/10.3390/met11091477 - 17 Sep 2021
Cited by 2 | Viewed by 599
Abstract
In this paper, the ((CoCrFeNi)95Nb5)100−xMox (x = 1, 1.5 and 2) high-entropy alloy (HEA) coatings were fabricated on the substrate of 45# steel by laser cladding process under different laser beam power. The influence [...] Read more.
In this paper, the ((CoCrFeNi)95Nb5)100−xMox (x = 1, 1.5 and 2) high-entropy alloy (HEA) coatings were fabricated on the substrate of 45# steel by laser cladding process under different laser beam power. The influence of laser beam power and molybdenum element content on the microstructure and microhardness of the HEA coatings was investigated. Results show that the HEA coatings were composed of face-centered cubic (FCC) phase and Laves phase, had low porosity, and bonded well to the substrate. The Mo1 coating is composed of cellular dendritic structures and columnar dendritic structures. With the increase of molybdenum element content, the columnar dendritic structures disappeared, the grains are refined, and the arrangement of grains is more compact. The volume fraction of the interdendritic phase under the laser beam power of 800 W was small and irregular. After the laser beam power was increased to 1000 W, the volume fraction of the interdendritic phase was increased. Under the laser beam power of 1200 W, the volume fraction of the interdendritic phase was small again. Therefore, the coatings fabricated under the laser beam power of 1000 W had a larger volume fraction of the interdendritic phase and higher microhardness. With the increase in molybdenum content, the grain changed from columnar dendrite to cellular dendrite, and the microhardness of the coating increased. The characteristics of the laser cladding process, the formation of Laves phase, and the fine grain strengthening lead to high microhardness of the coatings. Full article
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Article
A Comparison of Laboratory Coal Testing with the Blast Furnace Process and Coal Injection
Metals 2021, 11(9), 1476; https://doi.org/10.3390/met11091476 - 17 Sep 2021
Cited by 1 | Viewed by 531 | Correction
Abstract
The injection of coal through tuyeres into a blast furnace is widely adopted throughout the industry to reduce the amount of coke used and to improve the efficiency of the iron making process. Coals are selected depending on their availability, cost, and the [...] Read more.
The injection of coal through tuyeres into a blast furnace is widely adopted throughout the industry to reduce the amount of coke used and to improve the efficiency of the iron making process. Coals are selected depending on their availability, cost, and the physical and chemical properties determined by tests, such as the volatile matter content, fixed carbon, and ash content. This paper describes research comparing the laboratory measured properties of injection coals that were used over a two-month production period compared to the process variables and measurements of the blast furnace during that study period. In addition to the standard tests, a drop tube furnace (DTF) was used to compare the burnout of coals and the char properties against the production data using a range of statistical techniques. Linear regression modelling indicated that the coal type was the most important predictor of the coal rate but that the properties measured using laboratory tests of those coals were a minor feature in the model. However, comparisons of the Spearman’s correlations between different variables indicated that the reverse Boudouard reactivity of the chars, prepared in the DTF from the coals, did appear to be related to some extent to the coal and coke rates on production. It appears that the constant process adjustments made by the process control systems on the furnace make it difficult to identify strong correlations with the laboratory data and that the frequency of coal sampling and the coal blend variability are likely to contribute to this difficulty. Full article
(This article belongs to the Special Issue Advances in Ironmaking and Steelmaking Processes)
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Article
Thermoelectric Power in Ce Systems with Unstable Valence
Metals 2021, 11(9), 1475; https://doi.org/10.3390/met11091475 - 17 Sep 2021
Viewed by 435
Abstract
In this paper, we report on a few exemplary tests of the applicability of analysis based on the interconfiguration fluctuation model (ICF) for a description of the temperature dependence of the thermoelectric power, S(T). The examples include a series of [...] Read more.
In this paper, we report on a few exemplary tests of the applicability of analysis based on the interconfiguration fluctuation model (ICF) for a description of the temperature dependence of the thermoelectric power, S(T). The examples include a series of alloys: CeNi2(Si1−yGey)2, Ce(Ni1−xCux)2Si2, and the fluctuating valence (FV) compound CeNi4Ga. The two series develop from CeNi2Si2 being the FV system, where the f states occupation increases progressively with the Ge or Cu substitution. We find here that the ICF model parameters are of similar magnitude both for the analysis of the temperature dependence of the magnetic susceptibility and thermoelectric power. The ICF-type model appears to be a powerful tool for the analysis of S(T) dependences in Ce-based FV compounds and alloys. Full article
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Article
Experimental Investigation of Material Properties in FSW Dissimilar Aluminum-Steel Lap Joints
Metals 2021, 11(9), 1474; https://doi.org/10.3390/met11091474 - 16 Sep 2021
Cited by 3 | Viewed by 548
Abstract
The friction stir lap welding of AA5083 H111 aluminum alloy and S355J2 grade DH36 structural steel was investigated. A polycrystalline cubic boron nitride with tungsten and rhenium additives tool was used. According to visual inspection, radiographic examination, and tensile test, it was observed [...] Read more.
The friction stir lap welding of AA5083 H111 aluminum alloy and S355J2 grade DH36 structural steel was investigated. A polycrystalline cubic boron nitride with tungsten and rhenium additives tool was used. According to visual inspection, radiographic examination, and tensile test, it was observed that the best results were obtained for rotation speeds of about 700–800 rpm, with a feed speed ranging between 1.3 and 1.9 mm/s. From the fatigue tests, it is possible to state that there was a preferential propagation of cracks in the part of the aluminum alloy base material. Furthermore, a different response to fatigue stress for samples extracted from the same weld at different positions was observed, which introduces an overall variability in weld behavior along the welding direction. The specimens obtained in the second part of the weld endured a larger number of cycles before reaching failure, which can be related to progressively varying thermal conditions, dissipation behavior, and better metal coupling as the tool travels along the welding line. Full article
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Article
Minimizing the Negative Effects of Coolant Channels on the Torsional and Torsional-Axial Stiffness of Drills
Metals 2021, 11(9), 1473; https://doi.org/10.3390/met11091473 - 16 Sep 2021
Cited by 1 | Viewed by 520
Abstract
Coolant channels allow internal coolant delivery to the cutting region and significantly improve drilling, but these channels also reduce the torsional and torsional-axial stiffness of the drills. Such a reduction in stiffness can degrade the quality of the drilled holes. The evacuation of [...] Read more.
Coolant channels allow internal coolant delivery to the cutting region and significantly improve drilling, but these channels also reduce the torsional and torsional-axial stiffness of the drills. Such a reduction in stiffness can degrade the quality of the drilled holes. The evacuation of cutting chips and the delivery of the cutting fluid put strict geometrical restrictions on the cross-section design of the drill. This necessitates careful selection and optimization of features such as the geometry of the coolant channels. This paper presents a new method that uses Prandtl’s stress function to predict the torsional and torsional-axial stiffness values. Using this method drills with one central channel are compared to those with two eccentric coolant channels, which shows that with the same cross-section area, the reduction of axial and torsional-axial stiffness is notably smaller for the design with two eccentric channels compared to a single central channel. The stress function method is further used to select the appropriate location of the eccentric coolant channels to minimize the loss of torsional and torsional-axial stiffness. These results are verified by comparison to the results of three-dimensional finite element analyses. Full article
(This article belongs to the Special Issue Modeling and Simulation of Metal Processing)
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Article
Role of Heat Treatment on Atomic Order and Ordering Domains in Ni45Co5Mn36.6In13.4 Ribbons
Metals 2021, 11(9), 1472; https://doi.org/10.3390/met11091472 - 16 Sep 2021
Viewed by 452
Abstract
The effects of cooling rate and annealed temperature on the state of atomic order and microstructure of L21 domains of Ni45Co5Mn36.6In13.4 ribbons are investigated comprehensively. The state of atomic order is quantitatively studied by in [...] Read more.
The effects of cooling rate and annealed temperature on the state of atomic order and microstructure of L21 domains of Ni45Co5Mn36.6In13.4 ribbons are investigated comprehensively. The state of atomic order is quantitatively studied by in situ X-ray diffraction (XRD), and the microstructure of ordered domains is revealed by transmission electron microscopy (TEM). As-spun ribbons show B2 structure of low atomic order, exhibiting the dispersive L21 domains’ morphology. By applying heat treatment around the order–disorder transition temperature followed by furnace cooling or quenching into water, respectively, we found the strong dependence of ordered domains on cooling rates. Furnace cooling samples show L21 domains with small sized antiphase boundary, revealing a high degree of atomic order, while quenching hinders the formation of ordered domains. Annealing above the order–disorder transition temperature followed by quenching preserves the disordered atomic state with the mixture of L21 structure in B2 matrix. Full article
(This article belongs to the Special Issue Magnetic Shape Memory Alloys)
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Article
Corrosion Behavior of AlFeCrCoNiZrx High-Entropy Alloys in 0.5 M Sulfuric Acid Solution
Metals 2021, 11(9), 1471; https://doi.org/10.3390/met11091471 - 16 Sep 2021
Cited by 3 | Viewed by 797
Abstract
AlCoCrFeNiZrx (x = 0, 0.1, 0.2, 0.3, and 0.5) high-entropy alloys (HEAs) were prepared by a non-consumable vacuum arc melting technology, and the microstructure and corrosion behavior were investigated by XRD, SEM, immersion tests, and electrochemical measurements. The results indicate that [...] Read more.
AlCoCrFeNiZrx (x = 0, 0.1, 0.2, 0.3, and 0.5) high-entropy alloys (HEAs) were prepared by a non-consumable vacuum arc melting technology, and the microstructure and corrosion behavior were investigated by XRD, SEM, immersion tests, and electrochemical measurements. The results indicate that galvanic corrosion of the AlCoCrFeNiZrx alloys occurred in 0.5 M H2SO4 solution, and only 0.1 mol of the added Zr could greatly improve the corrosion resistance of the alloys. The corrosion properties of the AlCoCrFeNiZrx HEAs had similar change tendencies with the increase in the Zr content in the immersion tests, potentiodynamic polarization measurements, and electrochemical impedance analysis, that is, the corrosion resistance of the AlCoCrFeNiZrx alloys in a 0.5 M H2SO4 solution first increased and then decreased with the increase in the Zr content. The Zr0.1 alloys were found to have the best selective corrosion and general corrosion resistance with the smallest corrosion rate, whereas the Zr0.3 alloys presented the worst selective corrosion and general corrosion resistance with the highest corrosion rate from both the immersion tests and the potentiodynamic polarization measurements. Full article
(This article belongs to the Special Issue Wear and Corrosion Behavior of High-Entropy Alloy)
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Article
Investigation of the Possibility of Tailoring the Chemical Com-Position of the NiTi Alloy by Selective Laser Melting
Metals 2021, 11(9), 1470; https://doi.org/10.3390/met11091470 - 16 Sep 2021
Cited by 2 | Viewed by 615
Abstract
In this work a study of the selective laser melting process of two NiTi alloys of equiatomic, and rich Ni composition were conducted. A study of the influence of the technological parameters on the alloy density was carried out. Values of technological parameters [...] Read more.
In this work a study of the selective laser melting process of two NiTi alloys of equiatomic, and rich Ni composition were conducted. A study of the influence of the technological parameters on the alloy density was carried out. Values of technological parameters were obtained to ensure production of samples with the lowest number of defects. When using process parameters with the same energy density but different values of the constituent technological parameters, the amount of nickel carried away by evaporation changed insignificantly. An increase in the energy density led to an increase in the amount of nickel carried away, causing final samples with lower Ni content. When using multiple laser processing in the low-energy parameter set, it was possible to achieve a decrease in the nickel content in the alloy, similar to that with single high-energy processing. DSC studies showed a significant increase in transformation temperatures upon repeated laser processing due to the higher evaporation of nickel. The use of double laser treatment gave a decrease in the final density of the sample compared to a single treatment, but its value is still higher than when using a single treatment with a higher energy density. Full article
(This article belongs to the Special Issue Advanced Manufacturing of Novel Materials)
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Editorial
Sustainable Steel Industry: Energy and Resource Efficiency, Low-Emissions and Carbon-Lean Production
Metals 2021, 11(9), 1469; https://doi.org/10.3390/met11091469 - 16 Sep 2021
Viewed by 663
Abstract
The three pillars of sustainability represented by the environment, economy and society in the steel manufacturing industry are directly connected to the efficient and effective management of resources, such as energy, raw materials, by-products and water [...] Full article
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