Metals

Open AccessArticle

Surface Integrity of Cryogenically Finished Additively Manufactured and Conventional Ti-6Al-4V Alloy

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Pankaj Kumar Singh

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Santosh Kumar

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Pramod Kumar Jain

Metals 2023, 13(4), 693; https://doi.org/10.3390/met13040693 (registering DOI) - 31 Mar 2023

Abstract

Additive manufacturing (AM) is used for the fabrication of solid components of complex geometries for customized applications. However, AM-fabricated components frequently require finishing operations such as abrasive grinding, which causes a different surface characteristic compared to the conventionally manufactured components. Thus, it is [...] Read more.

Additive manufacturing (AM) is used for the fabrication of solid components of complex geometries for customized applications. However, AM-fabricated components frequently require finishing operations such as abrasive grinding, which causes a different surface characteristic compared to the conventionally manufactured components. Thus, it is essential to study the effect of process parameters and the heat treatment on surface quality of the AM components because these may behave differently to the conventional manufactured components. In this study, surface characteristics of AM samples of Ti-6Al-4V with a cryogenically cooled finishing operation is compared with that of conventionally processed samples. The samples under investigation were fabricated by two different methods, namely, Direct Metal Laser Sintering (DMLS) and conventional processing. The effect of the two processes on surface characteristics, such as microhardness, surface roughness, X-ray diffraction (XRD), and mechanical properties has been studied. The average surface roughness from cryogenic grinding was reduced by 27.25% and 23.15% for the AM, and 30.08% and 29.13% for conventional samples, as compared to dry and moist conditions, respectively. The finished DMLS and conventional samples showed increase of microhardness by 14.07%, 14.27%, 17.54% and 17.48%, 8.06%, 38.68%, in dry, moist, and cryogenic conditions, respectively. In cryogenic conditions, as the DOC and table feed increased, a greater increase in peak broadening was observed. The peak broadening in XRD of finished DMLS components indicates that a significant level of plastic deformation occurred compared to the finished conventionally manufactured Ti-6Al-4V samples, which suggests that the DMLS samples are more sensitive to the finishing process. Compared to dry and moist grinding, cryogenic grinding was found to have the smallest grains in the layer just below the surface. The impact of cryogenic cooling on surface properties of AM Ti-6Al-4V samples is higher as compared to that on conventionally processed Ti-6Al-4V samples. Full article

(This article belongs to the Special Issue Additive Manufacturing of Metallic Materials: Characterization, Properties, and Modeling)

Open AccessArticle

Dynamic Recrystallization Kinetics of As-Cast Fe-Cr-Al-La Stainless Steel during Hot Deformation

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Metals 2023, 13(4), 692; https://doi.org/10.3390/met13040692 (registering DOI) - 31 Mar 2023

Abstract

To investigate the dynamic recrystallization (DRX) behavior of as-cast Fe-20Cr-5.5Al-0.64La stainless steel, a series of compression tests were carried out on a Gleeble-3500 thermal simulator in the temperature range of 1000~1150 °C and the strain rate range of 0.001~1 s⁻¹. The [...] Read more.

To investigate the dynamic recrystallization (DRX) behavior of as-cast Fe-20Cr-5.5Al-0.64La stainless steel, a series of compression tests were carried out on a Gleeble-3500 thermal simulator in the temperature range of 1000~1150 °C and the strain rate range of 0.001~1 s⁻¹. The true stress-true strain curves were obtained and their characteristics were analyzed. Using regression analysis, the apparent activation energy for the Fe-20Cr-5.5Al-0.64La stainless steel was estimated to be 300.19 kJ/mol, and the constitutive equation was developed successfully with a hyperbolic sine equation as: . The critical strain, the peak strain and the strain for the maximum softening rate were identified based on the work hardening rate curves and expressed as a function of the Zener−Hollomon parameter. The kinetic model of DRX was established using the stress−strain data. According to the analysis of the kinetics model and microstructure evolution, the evolution of DRX volume could be described as follows: the volume fraction of DRX grains increased with an increase in strain; at a fixed deformation temperature, the DRX volume fraction was larger at a lower strain rate for the same strain; and the size of DRX grains increased with an increase in temperature or a decrease in strain rate. Full article

(This article belongs to the Special Issue Deformation of Metals and Alloys: Theory, Simulations and Experiments)

Open AccessArticle

Effect of Power on Structural and Mechanical Properties of DC Magnetron Sputtered Cr Coatings

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Metals 2023, 13(4), 691; https://doi.org/10.3390/met13040691 (registering DOI) - 31 Mar 2023

Abstract

Cr coatings were deposited on the surface of PCrNi1MoA steel by DC magnetron sputtering. The effects of power (100~250 W) on the structure and mechanical properties of the coating were systematically studied. The results show that all Cr coatings have strong (110) preferred [...] Read more.

Cr coatings were deposited on the surface of PCrNi1MoA steel by DC magnetron sputtering. The effects of power (100~250 W) on the structure and mechanical properties of the coating were systematically studied. The results show that all Cr coatings have strong (110) preferred orientation and anisotropic surface morphology, and the cross sections are columnar structures. With the increase in power, the deposition rate increases linearly, the surface roughness and grain size increase gradually, and the nanomechanical properties decrease first and then increase slightly. At 100 W, the columnar grain of the coating is compact and continuous, and the wear resistance and plastic deformation resistance are the best, with the highest binding force of 27.04 N. At 200 W, due to grain growth and tensile stress, internal defects increase, and mechanical properties are poor. The combination of coating and substrates is not tight enough, and it is easy to fall off and fail under the action of external force. When the power reaches 250 W, the higher bombardment rate helps the coating release stress, and reduce porosity. Full article

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Open AccessArticle

Hall–Petch Description of the Necking Point Stress

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Alexey Vinogradov

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Yuri Estrin

Metals 2023, 13(4), 690; https://doi.org/10.3390/met13040690 (registering DOI) - 31 Mar 2023

Abstract

We posited that the grain size dependence of the tensile necking stress, as determined by the Considère criterion for plastic instability, is a more meaningful characteristic of the Hall–Petch (H–P) effect than that of the yield stress or the 0.2% proof stress. An [...] Read more.

We posited that the grain size dependence of the tensile necking stress, as determined by the Considère criterion for plastic instability, is a more meaningful characteristic of the Hall–Petch (H–P) effect than that of the yield stress or the 0.2% proof stress. An inverse square-root dependence of the necking stress on the grain size was derived from a dislocation dynamics-based constitutive model. In this model, the grain size effect enters the stress indirectly via the evolution of the dislocation density. Model predictions were confirmed by the experimental data for nickel and titanium. Full article

(This article belongs to the Special Issue Editorial Board Members’ Collection Series: Metal Crystal/Polycrystal Plastic Strain Hardening)

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Open AccessArticle

Q&P Response of a Medium Carbon Low Alloy Steel

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Metals 2023, 13(4), 689; https://doi.org/10.3390/met13040689 - 31 Mar 2023

Abstract

An Fe-0.44%C-1.8%Si-1.3%Mn-0.82%Cr-0.28%Mo steel was subjected to quenching followed by low-temperature tempering (Q&T) and quenching and partitioning (Q&P) processing after full austenitization. The Q&P treatment led to an increase in the volume fraction of retained austenite (RA) by factors ranging from 30 to 40 [...] Read more.

An Fe-0.44%C-1.8%Si-1.3%Mn-0.82%Cr-0.28%Mo steel was subjected to quenching followed by low-temperature tempering (Q&T) and quenching and partitioning (Q&P) processing after full austenitization. The Q&P treatment led to an increase in the volume fraction of retained austenite (RA) by factors ranging from 30 to 40 depending on the quenching temperature, T_q, and an additional precipitation of transition η-carbides in the martensitic matrix. The Q&P processing provided a decrease in the yield stress (YS) from 1730 to 1350 MPa and an increase in the ductility by a factor of 3; the product of strength and elongation (PSE) increased from 13.7 to 32 GPa·%. The novelty of the work lies in establishing the origin of the good ductility and high YS of Q&P steel. Blocky-type RA plays a vital role in the effect of Q&P processing on mechanical properties. The main feature of RA is a very high dislocation density proving the strength of ~1000 MPa of this structural component. The strength of RA controls the YS of the steel if its volume fraction is ≥25%. Ductility is provided by the almost full transformation of RA into strain-induced martensite under tension. The localization of plastic deformation in the form of deformation bands is associated with the γ→α′ transformation. Medium carbon Q&P steel with a high volume fraction of RA meets the requirements for advanced high-strength steel (AHSS) belonging to the third generation of AHSS due to the combination of the YS > 1050 MPa with the PSE > 30 GPa·%. Full article

(This article belongs to the Special Issue Creep and Deformation of Metals and Alloys at Elevated Temperatures II)

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Open AccessArticle

Microstructure Characteristics and Mechanical Properties of Flash Butt Welded 590 MPa V-N Microalloyed Heavy-Duty Truck Wheel Steel

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Metals 2023, 13(4), 688; https://doi.org/10.3390/met13040688 - 30 Mar 2023

Abstract

This study reports the welded joint of a novel 590 MPa V-N microalloyed wheel steel on microstructure and mechanical properties after flash butt welding. The welding parameters were flash current 48°/582.0 A, upsetting current 44°/516.6 A, and workpiece clearance 1.5 mm. The evolution [...] Read more.

This study reports the welded joint of a novel 590 MPa V-N microalloyed wheel steel on microstructure and mechanical properties after flash butt welding. The welding parameters were flash current 48°/582.0 A, upsetting current 44°/516.6 A, and workpiece clearance 1.5 mm. The evolution of microstructure in the welded joint occurred as follows: welding seam (ferrite side plate + acicular ferrite +martensite)→coarse-grained zone (acicular ferrite + granular bainite)→fine-grained zone (fine-grained ferrite + M/A island)→base metal (equiaxed ferrite + pearlite). The standard impact energy value of welding seam, coarse grain zone, fine grain zone, and base metal at −40 °C was 116, 128, 144, and 88 J, respectively. The mechanical property of the joint was excellent. The microstructure, the number of grain boundaries, and the dislocation density directly affected the strength and hardness of the joint. The increase of large angle grain boundaries and the decrease of effective grain size were beneficial to the improvement of toughness. The hot-rolled 590 MPa V-N microalloyed wheel steel had superior weldability. Full article

(This article belongs to the Special Issue Metal Catalysts for Heterogeneous Catalytic Reactions)

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Open AccessCommunication

Eutectic MoNbTa(WC)_x Composites with Excellent Elevated Temperature Strength

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Metals 2023, 13(4), 687; https://doi.org/10.3390/met13040687 - 30 Mar 2023

Abstract

To develop materials with a promising utilization future in the extreme environments of aerospace, the MoNbTa(WC)_x composites were prepared by vacuum arc melting, of which the crystal structure, microstructure, and compression properties at elevated temperature were investigated. The MoNbTa(WC)_x composites had [...] Read more.

To develop materials with a promising utilization future in the extreme environments of aerospace, the MoNbTa(WC)_x composites were prepared by vacuum arc melting, of which the crystal structure, microstructure, and compression properties at elevated temperature were investigated. The MoNbTa(WC)_x composites had eutectic structures that consisted of body-centered cubic (BCC) phase and eutectoid structures. The lamellar fine eutectoid structures were composed of BCC-structured high entropy alloy (HEA) Mo-Nb-Ta-W and FCC-structured carbide Mo-Nb-Ta-W-C. It was demonstrated that the ductility and elevated temperature strength was enhanced simultaneously combined with the effect of eutectic structures and WC addition. The optimal true yield strength and true fracture strain reached 1205 MPa and 29.2% in MoNbTa(WC)_0.9 at 1200 °C, meanwhile, the fracture strain at ambient temperature was 13.96%. Distinct strain hardening was observed at the initial deformation stage of MoNbTa(WC)_0.9 at 1200 °C. The compression performances of MoNbTa(WC)_x were superior in comparison with most refractory high entropy alloys. Full article

(This article belongs to the Special Issue Deformation Behavior and Mechanical Properties of High Entropy Alloys)

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Open AccessCommunication

In-Situ Observation of Steel/Slag/Inclusion Interaction by Means of High-Temperature Confocal Scanning Laser Microscopy

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Julian Cejka

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Susanne Katharina Michelic

Metals 2023, 13(4), 686; https://doi.org/10.3390/met13040686 - 30 Mar 2023

Abstract

Non-metallic inclusions (NMIs) in steels have been the focus of various experimental studies due to their detrimental character. While isolated processes, such as agglomeration or dissolution, have been well investigated, holistic in-situ views with high-temperature confocal scanning laser microscopy (HT-CSLM) have been rare. [...] Read more.

Non-metallic inclusions (NMIs) in steels have been the focus of various experimental studies due to their detrimental character. While isolated processes, such as agglomeration or dissolution, have been well investigated, holistic in-situ views with high-temperature confocal scanning laser microscopy (HT-CSLM) have been rare. In this work a novel and suitable method is presented to simultaneously observe agglomeration, movement, detachment, and dissolution of non-metallic inclusions by combined the melting of steel and slag with a dual-crucible approach. Therefore, different steel/slag combinations were tested. It is shown that, with transparent that does not become tarnished by the ions stemming from the steel, the steel’s surface and non-metallic inclusions are observable. Furthermore, technological limitations are discussed, including restrictions regarding the melting point of steels and certain steel/slag combinations. Full article

(This article belongs to the Special Issue Advanced Tundish Metallurgy and Clean Steel Technology)

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Open AccessArticle

Development of the Al₁₂SiCuFe Alloy Foam Composites with ZrSiO₄ Reinforcements at Different Foaming Temperatures

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Udayagiri Chandrasekhar

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João Paulo Davim

Metals 2023, 13(4), 685; https://doi.org/10.3390/met13040685 - 30 Mar 2023

Abstract

Lightweight aluminum composite is a class of foam material that finds many applications. These properties make it suitable for many industries, such as the transportation, aerospace and sports industries. In the present work, closed-cell foams of an Al-Si12CuFe alloy and its composite are [...] Read more.

Lightweight aluminum composite is a class of foam material that finds many applications. These properties make it suitable for many industries, such as the transportation, aerospace and sports industries. In the present work, closed-cell foams of an Al-Si12CuFe alloy and its composite are developed by a stir casting process. The optimization of the foaming temperature for the alloy and composite foams was conducted in terms of the ligament and node size of the alloy and also the volatility of the zircon with the melt, to provide strength to the cell walls. CaCO₃ as a blowing agent was homogeneously distributed in the molten metal without adding any thickener to develop the metal foam. The decomposition rate of CaCO₃ is temperature-dependent, which is attributed to the formation of gas bubbles in the molten alloy. Cell structure, such as cell size and cell wall thickness, is controlled by manufacturing process parameters, and both the physical and mechanical properties are dependent on the foam cell structure, with cell size being the major variable. The results show that the increase in cell wall thickness with higher temperature leads to a decrease in cell size. By adding the zircon to the melt, the cell size of the composite foam first increases, and then the thickening of the wall occurs as the temperature is increased. The uniform distribution of the blowing agent in molten metal helps in the formation of a uniform cell structure. In this work, a comparative structural study of alloy foam and composite foam is presented regarding cell size, cell shape and foam stability at different temperatures. Full article

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Open AccessArticle

Wear Behavior Phenomena of TiN/TiAlN HiPIMS PVD-Coated Tools on Milling Inconel 718

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Vitor F. C. Sousa

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Filipe Fernandes

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Francisco J. G. Silva

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Rúben D. F. S. Costa

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Naiara Sebbe

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Rita C. M. Sales-Contini

Metals 2023, 13(4), 684; https://doi.org/10.3390/met13040684 - 30 Mar 2023

Abstract

Due to Inconel 718’s high mechanical properties, even at higher temperatures, tendency to work-harden, and low thermal conductivity, this alloy is considered hard to machine. The machining of this alloy causes high amounts of tool wear, leading to its premature failure. There seems [...] Read more.

Due to Inconel 718’s high mechanical properties, even at higher temperatures, tendency to work-harden, and low thermal conductivity, this alloy is considered hard to machine. The machining of this alloy causes high amounts of tool wear, leading to its premature failure. There seems to be a gap in the literature, particularly regarding milling and finishing operations applied to Inconel 718 parts. In the present study, the wear behavior of multilayered PVD HiPIMS (High-power impulse magnetron sputtering)-coated TiN/TiAlN end-mills used for finishing operations on Inconel 718 is evaluated, aiming to establish/expand the understanding of the wear behavior of coated tools when machining these alloys. Different machining parameters, such as cutting speed, cutting length, and feed per tooth, are tested, evaluating the influence of these parameters’ variations on tool wear. The sustained wear was evaluated using SEM (Scanning electron microscope) analysis, characterizing the tools’ wear and identifying the predominant wear mechanisms. The machined surface was also evaluated after each machining test, establishing a relationship between the tools’ wear and production quality. It was noticed that the feed rate parameter exerted the most influence on the tools’ production quality, while the cutting speed mostly impacted the tools’ wear. The main wear mechanisms identified were abrasion, material adhesion, cratering, and adhesive wear. The findings of this study might prove useful for future research conducted on this topic, either optimization studies or studies on the simulation of the milling of Inconel alloys, such as the one presented here. Full article

(This article belongs to the Special Issue Machining: State-of-the-Art 2022)

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Open AccessReview

Influence of Parameters and Regimes of the Electrodeposition on Hardness of Copper Coatings

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Ivana O. Mladenović

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Nebojša D. Nikolić

Metals 2023, 13(4), 683; https://doi.org/10.3390/met13040683 - 30 Mar 2023

Abstract

Correlation among morphological, structural and hardness characteristics of electrodeposited copper coatings is presented in this review paper. Cu coatings were produced applying constant galvanostatic (DC) and pulsating current (PC) regimes on hard silicon (Si(111)) and brass substrates. The parameters of the electrochemical deposition [...] Read more.

Correlation among morphological, structural and hardness characteristics of electrodeposited copper coatings is presented in this review paper. Cu coatings were produced applying constant galvanostatic (DC) and pulsating current (PC) regimes on hard silicon (Si(111)) and brass substrates. The parameters of the electrochemical deposition which include the kinds of electrolyte and cathode, the coating thickness and the electrolyte stirring, as well as the parameters defining PC regime, such as the average current density and the current density amplitude, were analyzed. Morphology and structure of Cu coatings were examined by scanning electron microscope (SEM), atomic force microscope (AFM) and by X-ray diffraction (XRD), while hardness was examined by Vickers microindentation. The coatings of Cu on both Si(111) and brass cathodes belong to “soft film (coating) on hard substrate” composite hardness system, and the Chicot–Lesage (C–L) composite hardness model was applied to estimate a hardness of the Cu coatings. Analyzing the examined parameters and regimes of electrodeposition, the critical relative indentation depth (RID)_c of 0.14 has been defined by the C–L model. Based on done analyses, it is shown that this RID value, separating a zone where measured hardness corresponds to the coating hardness and a zone where it is necessary to apply the C–L model to determine an absolute hardness of the Cu coatings, has an universal character for the electrolytically produced Cu coatings on Si(111) and brass substrates. Full article

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Open AccessArticle

Active and Passive Thermal Management in Wire Arc Additive Manufacturing

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Vishwanath Nagallapati

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Vivek Kumar Khare

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Abhay Sharma

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Suryakumar Simhambhatla

Metals 2023, 13(4), 682; https://doi.org/10.3390/met13040682 - 30 Mar 2023

Abstract

This article presents innovative approaches for managing residual stresses and distortion in additive manufacturing (AM) of metal components (baseplate material: EN8; filler wire material: ER70S-6). The experiments are conducted with two approaches for thermal management—passive and active. The passive approach of experiments is [...] Read more.

This article presents innovative approaches for managing residual stresses and distortion in additive manufacturing (AM) of metal components (baseplate material: EN8; filler wire material: ER70S-6). The experiments are conducted with two approaches for thermal management—passive and active. The passive approach of experiments is performed by varying the selected process parameters to study their effect on residual stresses and distortion. The chosen parameters are current, torch speed, geometry, continuous or a delay in the deposition, and cooling arrangement. Based on the understanding gained from the passive approach, the active approach of thermal management was implemented by insulating the substrate with and without adaptive current and heating the substrate. The experimental results were corroborated with the simulation to understand the process better. A comparative study for hardness was made based on the T8/5 extracted from the simulation. These experiments and simulations endorse passive and active thermal management as effective tools that can alter the distortion and residual stress pattern and the mechanical properties of an AM component. The investigation concludes that the process parameters that lead to higher heat input vis-à-vis an increase in current or a decrease in speed increase the distortion. On the other hand, the parameters that affect the rate of heat distribution vis-à-vis torch speed and geometry affect the residual stresses. When current, traverse speed and a/b ratio were kept the same, active thermal management with a heated base reduced distortion from 1.226 mm to 0.431 mm, a 65% reduction compared to passive thermal management. Additionally, the maximum residual stress was reduced from 492.31 MPa to 250.68 MPa, with residual stresses decreasing from 418.57 MPa to 372 MPa. Overall, active thermal management resulted in a 63% reduction in distortion, lowering it from 1.35 mm to 0.50 mm using external heating. The components that are difficult to complete because of the in-process distortion are expected to be manufactured with thermal management, e.g., heating the substrate is an effective measure to manage the in-process distortion. Thermal management techniques depend on geometry; for instance, a concave surface, because of self-heating, reduces the cooling rate and has relatively less variation in hardness. Full article

(This article belongs to the Special Issue Wire Arc Additive Manufacturing of Metal and Alloys)

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Open AccessFeature PaperArticle

Investigation of the Porosity Gradient in Thickness Direction Formed by Cold Rolling in Porous Aluminum

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Jörn Tychsen

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Joachim Rösler

Metals 2023, 13(4), 681; https://doi.org/10.3390/met13040681 - 30 Mar 2023

Abstract

To adapt porous material for its application as low noise trailing edge, a special rolling process, using a time-varied rolling gap, was used in previous research to produce a porosity gradient in the direction of rolling. Investigations suggest that a gradient in porosity [...] Read more.

To adapt porous material for its application as low noise trailing edge, a special rolling process, using a time-varied rolling gap, was used in previous research to produce a porosity gradient in the direction of rolling. Investigations suggest that a gradient in porosity may also be produced in the thickness direction of the material, i.e., in the rolling gap direction, without using a specialized rolling mill. Such a gradient may help to further increase acoustic efficiency of porous materials. The aim of this study was to analyze the dependency of such a gradient on the rolling parameters, and to clarify which stress components are significantly responsible for an increased near-surface compaction. Experiments using different relative compressed lengths were performed to analyze shear-dominated and friction-dominated rolling. The material was characterized using compression tests, computed tomography and flow resistance measurements. It is shown that the compressed length is an important parameter for adjusting a porosity gradient. Rolling with small values of compressed length during all rolling passes leads to increased compaction of near-surface regions, compared to interior ones. The difference in porosity achieved was up to 15%. Furthermore, the results suggested that a gradient in hydrostatic stress is responsible for the porosity gradient. Validation of the results by FE simulation is forthcoming, but not part of this publication. Full article

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Open AccessEditorial

Numerical Modeling of Materials under Extreme Conditions

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Yao Shen

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Ning Gao

Metals 2023, 13(4), 680; https://doi.org/10.3390/met13040680 - 30 Mar 2023

Abstract

Materials used under extreme conditions are important in various industrial and defense fields [...] Full article

(This article belongs to the Special Issue Numerical Modeling of Materials under Extreme Conditions)

Open AccessArticle

Strengthening Granulating and Sintering Performance of Refractory Iron Concentrate by Pre-Pelletizing

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Metals 2023, 13(4), 679; https://doi.org/10.3390/met13040679 - 30 Mar 2023

Abstract

May Concentrate Iron ore, as a refractory iron concentrate, deteriorates the permeability of the sintered layer during the sintering process due to its fine particle size and poor granulating performance. Therefore, it cannot be widely used in iron ore sintering. In this study, [...] Read more.

May Concentrate Iron ore, as a refractory iron concentrate, deteriorates the permeability of the sintered layer during the sintering process due to its fine particle size and poor granulating performance. Therefore, it cannot be widely used in iron ore sintering. In this study, the strengthening granulation of May Concentrate Iron ore using pre-pelletizing to expand its utilization ratio was proposed. The experiments of conventional granulation, pre-pelletizing granulation and sinter pot test were carried out. Increasing May Concentrate Iron ore (a refractory iron concentrate) proportion was detrimental to conventional granulation, reducing the quasi-particle particle size and strength. May Concentrate Iron granulating and sintering performances were improved by pre-pelletizing. The quasi-particle average size at 36% May Concentrate Iron proportion jumped to 4.92 mm of pre-pelletizing granulation from 3.22 mm of conventional granulation. Meanwhile, the permeability index rose to 0.33 from 0.11, while the falling and drying pulverization ratio fell to 7.05% and 6.11% from 22.59% and 15.88%, respectively. The consolidation mode of matrix materials was liquid phase consolidation, while that of May Concentrate Iron pellets was solid phase consolidation, forming the structure of the pellets embedded in the matrix materials. Furthermore, the partial alkalinity of the matrix materials was increased because of the separation of May Concentrate Iron, generating a large amount of acicular calcium ferrite with better consolidation strength than conventional granulation sintering. Full article

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Open AccessArticle

The Effect of Size and Strain on Micro Stripe Magnetic Domain Structure of CoFeB Thin Films

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Metals 2023, 13(4), 678; https://doi.org/10.3390/met13040678 - 30 Mar 2023

Abstract

The prerequisite for flexible magnetic electronic devices is the knowledge of the preparation technology of flexible magnetic films and the evolution of the film properties under strain. In this work, CoFeB amorphous ferromagnetic films with stripe domains were prepared on flexible polyimide (PI) [...] Read more.

The prerequisite for flexible magnetic electronic devices is the knowledge of the preparation technology of flexible magnetic films and the evolution of the film properties under strain. In this work, CoFeB amorphous ferromagnetic films with stripe domains were prepared on flexible polyimide (PI) substrates by oblique sputtering. The results show that oblique sputtering induces the formation of columnar crystal structure in CoFeB films, which increases the perpendicular magnetic anisotropy of the films, thus leading to the appearance of stripe magnetic domain structures. On this basis, the CoFeB films with stripe domains were processed on a microscopic scale to investigate the size effect and strain regulation on the microscopic domain structure of the magnetic films. The characterization of the magnetic domain structure shows that the stripe domain contrast is reduced by the striped structure prepared by lithography. The triangular, circular and ring patterns deflect the alignment of the stripe domain to different degrees. The experimental results show that the deflection of the stripe domains is caused by the anisotropy of the shapes produced by the different patterns and that the size of the microstructure needs to be close to the period of the stripe domains for the size effect to be significant. In addition, the strain-induced magnetoelastic anisotropy effectively rotates the orientation of the stripe domains, and the variation in domain contrast demonstrates that tensile/compressive strains vary the magnitude of the out-of-plane stray field of the film. Our results provide some insight into the modulation of the physical properties of flexible magnetic films. Full article

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Open AccessArticle

Preparation of Porous Composite Phase Na Super Ionic Conductor Adsorbent by In Situ Process for Ultrafast and Efficient Strontium Adsorption from Wastewater

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Metals 2023, 13(4), 677; https://doi.org/10.3390/met13040677 - 29 Mar 2023

Abstract

Strontium, the main component of radioactive nuclear wastewater, is characterized by a high fission yield and an extended half-life. It is easily absorbed by the human body, thus greatly threatening the environment and the human body. In this study, a mesoporous composite phase [...] Read more.

Strontium, the main component of radioactive nuclear wastewater, is characterized by a high fission yield and an extended half-life. It is easily absorbed by the human body, thus greatly threatening the environment and the human body. In this study, a mesoporous composite phase sodium superionic conductor (NVP@NMP) was synthesized by the droplet template method, and the rapid capture of Sr²⁺ from wastewater was achieved by constructing a nano-heterogeneous interface to increase the ion diffusion rate. NVP@NMP showed efficient and rapid removal of strontium ions in adsorption kinetics, isothermal adsorption, solution pH, and interfering ions concentration tests. Especially the equilibrium time of 2 min for strontium absorption by NVP@NMP and a maximum theoretical adsorption capacity of 361.36 mg/g. The adsorption process was spontaneous, endothermic, and feasible. At higher concentrations of other competing ions (Na, K, Ca, Mg, and Cs), the adsorbent exhibited higher selectivity towards Sr²⁺.TEM, XPS, and XRD analyses revealed that ion exchange was the main mechanism for the NVP@NMP ultrafast adsorption of Sr²⁺. In this research, we investigated the feasibility of ultrafast strontium capture by sodium superionic conductor structured phosphates and explained the ultrafast strontium adsorption mechanism of NASICON materials through XPS. Full article

(This article belongs to the Special Issue Separation and Recovery of Rare and Precious Metals from Secondary Resources)

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Open AccessReview

Future Research and Developments on Reuse and Recycling of Steelmaking By-Products

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Valentina Colla

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Teresa Annunziata Branca

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Roland Pietruck

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Simon Wölfelschneider

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Metals 2023, 13(4), 676; https://doi.org/10.3390/met13040676 - 29 Mar 2023

Abstract

In the steel sector, sustainable management of by-products is a key challenge to preserve natural resources and achieve the zero waste goal. In this paper, the main trends of future research and development on reuse and recycling of by-products of the steel industry [...] Read more.

In the steel sector, sustainable management of by-products is a key challenge to preserve natural resources and achieve the zero waste goal. In this paper, the main trends of future research and development on reuse and recycling of by-products of the steel industry are presented in the form of a roadmap, which is the outcome of a dissemination project funded by the European Union based on the analysis of the most relevant and recent European projects concerning reuse and recycling of by-products from the steel production cycle. In particular, the developed roadmap highlights the most important topics of future research activities and challenges related to reuse and recycling of by-products from the existing or alternative steelmaking routes. A time horizon of 10 years has been considered, taking into account the European Commission targets to achieve carbon neutrality in a circular economy context. In addition, current technological trends derived from past and ongoing research projects are analysed. Research needs are based on the main categories of by-products and residual materials. Due to the different pathways to reduce CO₂ emissions, each category is divided into subcategories considering both current and novel process routes targeting decarbonization of steel production. This work identifies the most urgent and demanding research directions for the coming years based on a survey targeting the steel companies, services providers of the steel industry and research organizations active in the field. Full article

(This article belongs to the Special Issue Reuse and Recycling of By-Products in the Steel Sector)

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Open AccessArticle

Magnesium Alloy Scrap Vacuum Gasification—Directional Condensation to Purify Magnesium

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Metals 2023, 13(4), 675; https://doi.org/10.3390/met13040675 - 29 Mar 2023

Abstract

Magnesium alloys, known as a “21st-century green engineering material”, are widely used in many fields, including during the production and consumption of magnesium alloys die-casting products such as AZ91D, AM50, and AM60B. In addition, a large amount of waste is generated, which not [...] Read more.

Magnesium alloys, known as a “21st-century green engineering material”, are widely used in many fields, including during the production and consumption of magnesium alloys die-casting products such as AZ91D, AM50, and AM60B. In addition, a large amount of waste is generated, which not only pollutes the environment but also wastes secondary resources. Hereby, we reported the vacuum gasification—directional condensation method, calculated the vapor pressure separation coefficient parameters, and drew the gas-liquid phase equilibrium diagram depending on the distillation temperature, condensation temperature, and system pressure for the magnesium volatilization process. The results showed that under the following conditions (distillation temperature: 1073 K, system pressure: 100 Pa, condensation temperature: 873 K, and condensation duration: 30 min), the magnesium volatilization yield could approach 93.76%, and the purity of magnesium could reach 99.98%. This research is a good theoretical and practical basis for the recovery of magnesium alloy waste using the vacuum gasification method. Full article

(This article belongs to the Special Issue Recovery and Extraction of Valuable Metal)

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