Next Issue
Volume 11, November
Previous Issue
Volume 11, September

Metals, Volume 11, Issue 10 (October 2021) – 166 articles

Cover Story (view full-size image): Story is coming soon. View this paper
  • Issues are regarded as officially published after their release is announced to the table of contents alert mailing list.
  • You may sign up for e-mail alerts to receive table of contents of newly released issues.
  • PDF is the official format for papers published in both, html and pdf forms. To view the papers in pdf format, click on the "PDF Full-text" link, and use the free Adobe Readerexternal link to open them.
Order results
Result details
Select all
Export citation of selected articles as:
Review
A Review on the Fabrication and Reliability of Three-Dimensional Integration Technologies for Microelectronic Packaging: Through-Si-via and Solder Bumping Process
Metals 2021, 11(10), 1664; https://doi.org/10.3390/met11101664 - 19 Oct 2021
Viewed by 312
Abstract
With the continuous miniaturization of electronic devices and the upcoming new technologies such as Artificial Intelligence (AI), Internet of Things (IoT), fifth-generation cellular networks (5G), etc., the electronics industry is achieving high-speed, high-performance, and high-density electronic packaging. Three-dimensional (3D) Si-chip stacking using through-Si-via [...] Read more.
With the continuous miniaturization of electronic devices and the upcoming new technologies such as Artificial Intelligence (AI), Internet of Things (IoT), fifth-generation cellular networks (5G), etc., the electronics industry is achieving high-speed, high-performance, and high-density electronic packaging. Three-dimensional (3D) Si-chip stacking using through-Si-via (TSV) and solder bumping processes are the key interconnection technologies that satisfy the former requirements and receive the most attention from the electronic industries. This review mainly includes two directions to get a precise understanding, such as the TSV filling and solder bumping, and explores their reliability aspects. TSV filling addresses the DRIE (deep reactive ion etching) process, including the coating of functional layers on the TSV wall such as an insulating layer, adhesion layer, and seed layer, and TSV filling with molten solder. Solder bumping processes such as electroplating, solder ball bumping, paste printing, and solder injection on a Cu pillar are discussed. In the reliability part for TSV and solder bumping, the fabrication defects, internal stresses, intermetallic compounds, and shear strength are reviewed. These studies aimed to achieve a robust 3D integration technology effectively for future high-density electronics packaging. Full article
(This article belongs to the Special Issue Reliability Aspects of Lead-Free Solder Alloys Used in Electronics)
Show Figures

Figure 1

Article
Experimental SHPB Study of Limestone Damage under Confining Pressures after Exposure to Elevated Temperatures
Metals 2021, 11(10), 1663; https://doi.org/10.3390/met11101663 - 19 Oct 2021
Viewed by 189
Abstract
Studying the dynamic performance of rocks affected by high temperatures is a crucial theoretical foundation of mining engineering design and the construction of deep metallic mineral resources. More importantly, such studies can provide technical support for the green and low-carbon mining of these [...] Read more.
Studying the dynamic performance of rocks affected by high temperatures is a crucial theoretical foundation of mining engineering design and the construction of deep metallic mineral resources. More importantly, such studies can provide technical support for the green and low-carbon mining of these resources. However, systematic studies on the dynamic mechanical properties of rocks affected by both confining pressure and temperature during the mining of deep metallic mineral resources are lacking. Therefore, systematic research was conducted on the dynamic mechanical properties of limestone under confining pressure after high-temperature treatment, and a corresponding constitutive model was established. In this study, limestones were heated to 200 °C, 400 °C, 600 °C, and 800 °C, and the Split Hopkinson Pressure Bar impact test was conducted with confining pressures of 0.0 MPa, 0.5 MPa, 1.5 MPa, and 2.5 MPa. The test results show that the temperature has a significant effect on the dynamic compressive strength of limestone, and as the temperature rises, the strength tends to first increase and then decrease, reaching the turning point at a temperature of 400 °C. The dynamic compressive strength increases as the confining pressure increases. The constitutive equation of the dynamic damage to limestone under confining pressure after high-temperature treatment is consistent with the test results. Therefore, the established constitutive model can represent the dynamic behavior of limestone, providing a reference for evaluating the dynamic performance of this material, and serving as a theoretical basis for the green and low-carbon mining of deep metallic mineral resources. Full article
(This article belongs to the Special Issue Green Low-Carbon Technology for Metalliferous Minerals)
Show Figures

Figure 1

Article
Transient Liquid Phase Sintering of PM Steel—A Matter of the Heating Rate
Metals 2021, 11(10), 1662; https://doi.org/10.3390/met11101662 - 19 Oct 2021
Viewed by 248
Abstract
Powder metallurgy (PM) offers several variants to introduce alloying elements for establishing the desired final composition. One route is the master alloy (MA) approach. The composition and the elements contained in the MA can be adjusted to obtain a liquid phase that penetrates [...] Read more.
Powder metallurgy (PM) offers several variants to introduce alloying elements for establishing the desired final composition. One route is the master alloy (MA) approach. The composition and the elements contained in the MA can be adjusted to obtain a liquid phase that penetrates through the interconnected pore network and thus enhances the distribution of the alloying elements and the homogenization of the microstructure. Such a liquid phase is often of a transient character, and therefore the amount of liquid formed and the time the liquid is present during the sintering are highly dependent on the heating rates. The heating rate has also an impact on the reaction temperatures, and therefore, by properly adjusting the heating rate, it is possible to sinter PM-steels alloyed with Fe-Cr-Si-C-MA at temperatures below 1250 °C. The present study shows the dependence of the melting regimes on the heating rate (5, 10, 20, 120 K/min) represented by “Kissinger plots”. For this purpose, liquid phase formation and distribution were monitored in quenching dilatometer experiments with defined heating up to different temperatures (1120 °C, 1180 °C, 1250 °C, 1300 °C) and subsequent quenching. Optimum sintering conditions for the materials were identified, and the concept was corroborated by C and O analysis, CCT diagrams, metallographic sections, and hardness measurements. Full article
(This article belongs to the Special Issue Sintering Behavior in Steels)
Show Figures

Figure 1

Article
Property Improvement of Additively Manufactured Ti64 by Heat Treatment Characterized by In Situ High Temperature EBSD and Neutron Diffraction
Metals 2021, 11(10), 1661; https://doi.org/10.3390/met11101661 - 19 Oct 2021
Viewed by 237
Abstract
Among various off-equilibrium microstructures of additively manufactured Ti-6Al-4V alloy, electron beam powder bed fusion, in which three dimensional metallic objects are fabricated by melting the ingredient powder materials layer by layer on a pre-heated bed, results in a specimen that is nearly free [...] Read more.
Among various off-equilibrium microstructures of additively manufactured Ti-6Al-4V alloy, electron beam powder bed fusion, in which three dimensional metallic objects are fabricated by melting the ingredient powder materials layer by layer on a pre-heated bed, results in a specimen that is nearly free of the preferred orientation of the α-Ti phase as well as a low beta phase fraction of ~1 wt%. However, when further heat treatment of up to 1050 °C was applied to the material in our previous study, a strong texture aligning the hexagonal basal plane of α phase with the build direction and about 6% β phase appeared at room temperature. In this study, to understand the mechanism of this heat treatment, the grain level microstructure of the additively manufactured Ti-6Al-4V was investigated using in situ high temperature EBSD up to 1000 °C, which allows the tracking of individual grains during a heat cycle. As a result, we found a random texture originating from the fine grains in the initial material and observed a significant suppression of α phase nucleation in the slow cooling after heating to 950 °C within the α and β dual phase regime but close to the the β-transus temperature at ~980 °C, which led to a coarse microstructure. Furthermore, the texture resulting from phase transformation of the additively manufactured Ti-6Al-4V assuming nucleation at the grain boundaries was modeled, using the double Burgers orientation relationship for the first time. The model successfully reproduced the measured texture, suggesting that the texture enhancement of the α phase by the additional heat treatment derives also from the variant selection during the phase transformation and nucleation on grain boundaries. Full article
Show Figures

Graphical abstract

Article
An Approach to Reduce Thermal Damages on Grinding of Bearing Steel by Controlling Cutting Fluid Temperature
Metals 2021, 11(10), 1660; https://doi.org/10.3390/met11101660 - 19 Oct 2021
Viewed by 263
Abstract
The use of cutting fluid is crucial in the grinding process due to the elevated heat generated during the process which typically flows to the workpiece and can adversely affect its integrity. Considering the conventional technique for cutting fluid application in grinding (flood), [...] Read more.
The use of cutting fluid is crucial in the grinding process due to the elevated heat generated during the process which typically flows to the workpiece and can adversely affect its integrity. Considering the conventional technique for cutting fluid application in grinding (flood), its efficiency is related to certain factors such as the type of fluid, nozzle geometry/positioning, flow rate and coolant concentration. Another parameter, one which is usually neglected, is the cutting fluid temperature. Since the heat exchange between the cutting fluid and workpiece increases with the temperature difference, controlling the cutting fluid temperature before its application could improve its cooling capability. In this context, this work aimed to analyze the surface integrity of bearing steel (hardened SAE 52100 steel) after grinding with an Al2O3 grinding wheel with the cutting fluid delivered via flood technique at different temperatures: 5 °C, 10 °C, 15 °C as well as room temperature (28 ± 1 °C). The surface integrity of the workpiece was analyzed in terms of surface roughness (Ra parameter), images of the ground surface, and the microhardness and microstructure beneath the machined surface. The results show that the surface roughness values reduced with the cutting fluid temperature. Furthermore, the application of a cutting fluid at low temperatures enabled the minimization of thermal damages regarding visible grinding burns, hardness variation, and microstructure changes. Full article
(This article belongs to the Special Issue Study of Grinding Processes for Metals and Alloys)
Show Figures

Figure 1

Article
Experimental and Numerical Analysis on TIG Arc Welding of Stainless Steel Using RSM Approach
Metals 2021, 11(10), 1659; https://doi.org/10.3390/met11101659 - 19 Oct 2021
Viewed by 197
Abstract
This study involves the validating of thermal analysis during TIG Arc welding of 1.4418 steel using finite element analyses (FEA) with experimental approaches. 3D heat transfer simulation of 1.4418 stainless steel TIG arc welding is implemented using ABAQUS software (6.14, ABAQUS Inc., Johnston, [...] Read more.
This study involves the validating of thermal analysis during TIG Arc welding of 1.4418 steel using finite element analyses (FEA) with experimental approaches. 3D heat transfer simulation of 1.4418 stainless steel TIG arc welding is implemented using ABAQUS software (6.14, ABAQUS Inc., Johnston, RI, USA), based on non-uniform Goldak’s Gaussian heat flux distribution, using additional DFLUX subroutine written in the FORTRAN (Formula Translation). The influences of the arc current and welding speed on the heat flux density, weld bead geometry, and temperature distribution at the transverse direction are analyzed by response surface methodology (RSM). Validating numerical simulation with experimental dimensions of weld bead geometry consists of width and depth of penetration with an average of 10% deviation has been performed. Results reveal that the suggested numerical model would be appropriate for the TIG arc welding process. According to the results, as the welding speed increases, the residence time of arc shortens correspondingly, bead width and depth of penetration decrease subsequently, whilst simultaneously, the current has the reverse effect. Finally, multi-objective optimization of the process is applied by Derringer’s desirability technique to achieve the proper weld. The optimum condition is obtained with 2.7 mm/s scanning speed and 120 A current to achieve full penetration weld with minimum fusion zone (FZ) and heat-affected zone (HAZ) width. Full article
Show Figures

Figure 1

Article
Effect of Temperature on Corrosion Resistance of Layered Double Hydroxides Conversion Coatings on Magnesium Alloys Based on a Closed-Cycle System
Metals 2021, 11(10), 1658; https://doi.org/10.3390/met11101658 - 19 Oct 2021
Viewed by 192
Abstract
The effect of temperature on the corrosion resistance of layered double hydroxide (LDH) conversion coatings on AZ91D magnesium alloy, based on a closed-cycle system, was investigated. Scanning electron microscopy (SEM), photoelectron spectroscopy (XPS), and X-ray diffractometry (GAXRD) were used to study the surface [...] Read more.
The effect of temperature on the corrosion resistance of layered double hydroxide (LDH) conversion coatings on AZ91D magnesium alloy, based on a closed-cycle system, was investigated. Scanning electron microscopy (SEM), photoelectron spectroscopy (XPS), and X-ray diffractometry (GAXRD) were used to study the surface morphology, chemical composition, and phase composition of the conversion coating. The corrosion resistance of the LDH conversion coating was determined through electropotentiometric polarisation curve and hydrogen evolution and immersion tests. The results showed that the conversion coating has the highest density and a more uniform, complete, and effective corrosion resistance at 50 °C. The chemical composition of the LDH conversion coating mainly comprises C, O, Mg, and Al, and the main phase is Mg6Al2(OH)16CO3·4H2O. Full article
Show Figures

Figure 1

Article
Phase Composition, Nanohardness and Young’s Modulus in Ti-Fe Alloys after Heat Treatment and High Pressure Torsion
Metals 2021, 11(10), 1657; https://doi.org/10.3390/met11101657 - 19 Oct 2021
Viewed by 258
Abstract
Four titanium-iron binary alloys were studied. They were preliminarily annealed in the (α + β) and (α + TiFe) regions of the Ti-Fe phase diagram. The changes in the phase composition, nanohardness, and Young’s modulus of the annealed alloys before and after high [...] Read more.
Four titanium-iron binary alloys were studied. They were preliminarily annealed in the (α + β) and (α + TiFe) regions of the Ti-Fe phase diagram. The changes in the phase composition, nanohardness, and Young’s modulus of the annealed alloys before and after high pressure torsion (HPT) were investigated. Alloys with high iron content after HPT contain a large fraction of the ω phase. The nanohardness of the material in the middle of the radius of the HPT samples varies in the same range of values between 4.4 and 5.8 GPa, regardless of the preliminary annealing. Young’s modulus is a parameter sensitive to structural and phase changes in the material. After HPT, it increases by a factor of 1.5 after preliminary annealing in the (α + β) region in comparison with that in (α + TiFe) region. Full article
Show Figures

Figure 1

Article
Fatigue Crack Growth Behaviour and Role of Roughness-Induced Crack Closure in CP Ti: Stress Amplitude Dependence
Metals 2021, 11(10), 1656; https://doi.org/10.3390/met11101656 - 19 Oct 2021
Viewed by 266
Abstract
This paper investigated the fatigue crack propagation mechanism of CP Ti at various stress amplitudes (175, 200, 227 MPa). One single crack at 175 MPa and three main cracks via sub-crack coalescence at 227 MPa were found to be responsible for fatigue failure. [...] Read more.
This paper investigated the fatigue crack propagation mechanism of CP Ti at various stress amplitudes (175, 200, 227 MPa). One single crack at 175 MPa and three main cracks via sub-crack coalescence at 227 MPa were found to be responsible for fatigue failure. Crack deflection and crack branching that cause roughness-induced crack closure (RICC) appeared at all studied stress amplitudes; hence, RICC at various stages of crack propagation (100, 300 and 500 µm) could be quantitatively calculated. Noticeably, a lower RICC at higher stress amplitudes (227 MPa) for fatigue cracks longer than 100 µm was found than for those at 175 MPa. This caused the variation in crack growth rates in the studied conditions. Full article
(This article belongs to the Special Issue Fracture Mechanics and Fatigue Design in Metallic Materials)
Show Figures

Figure 1

Article
Investigation of Primary Recrystallization and Decarbonization with Different Heating Rates of Intermediate Annealing Using Nb-Containing Grain-Oriented Silicon Steel
Metals 2021, 11(10), 1655; https://doi.org/10.3390/met11101655 - 19 Oct 2021
Viewed by 197
Abstract
An Nb-containing grain-oriented silicon steel was produced through double-stage cold rolling in order to investigate the effect of the heating rate during intermediate annealing on primary recrystallization and decarburization behavior. The microstructure and texture were observed and analyzed by an optical microscope and [...] Read more.
An Nb-containing grain-oriented silicon steel was produced through double-stage cold rolling in order to investigate the effect of the heating rate during intermediate annealing on primary recrystallization and decarburization behavior. The microstructure and texture were observed and analyzed by an optical microscope and an electron backscatter diffraction system. A transmission electron microscope was used to observe the precipitation behavior of inhibitors. The decarburization effect during intermediate annealing was also calculated and discussed. The results show that primary recrystallization takes place after intermediate annealing. As the heating rate increases, the average grain size decreases gradually. The textures of {411}<148> and {111}<112> were found to be the strongest along the thickness direction in all of the annealed specimens and are mainly surrounded by HEGB and HAGB (>45°). A large number of inhibitors with the size of 14~20 nm precipitate are distributed evenly in the matrix. The above results indicate that the higher heating rate during intermediate annealing contributes to both an excellent microstructure and magnetic properties. From the calculation, as the heating rate increases, decarbonization tends to proceed in the insulation stage, and the total amount of carbonization declines. Full article
Show Figures

Figure 1

Review
Challenges and Outlines of Steelmaking toward the Year 2030 and Beyond—Indian Perspective
Metals 2021, 11(10), 1654; https://doi.org/10.3390/met11101654 - 19 Oct 2021
Viewed by 317
Abstract
In FY-20, India’s steel production was 109 MT, and it is the second-largest steel producer on the planet, after China. India’s per capita consumption of steel was around 75 kg, which has risen from 59 kg in FY-14. Despite the increase in consumption, [...] Read more.
In FY-20, India’s steel production was 109 MT, and it is the second-largest steel producer on the planet, after China. India’s per capita consumption of steel was around 75 kg, which has risen from 59 kg in FY-14. Despite the increase in consumption, it is much lower than the average global consumption of 230 kg. The per capita consumption of steel is one of the strongest indicators of economic development across the nation. Thus, India has an ambitious plan of increasing steel production to around 250 MT and per capita consumption to around 160 kg by the year 2030. Steel manufacturers in India can be classified based on production routes as (a) oxygen route (BF/BOF route) and (b) electric route (electric arc furnace and induction furnace). One of the major issues for manufacturers of both routes is the availability of raw materials such as iron ore, direct reduced iron (DRI), and scrap. To achieve the level of 250 MT, steel manufacturers have to focus on improving the current process and product scenario as well as on research and development activities. The challenge to stop global warming has forced the global steel industry to strongly cut its CO2 emissions. In the case of India, this target will be extremely difficult by ruling in the production duplication planned by the year 2030. This work focuses on the recent developments of various processes and challenges associated with them. Possibilities and opportunities for improving the current processes such as top gas recycling, increasing pulverized coal injection, and hydrogenation as well as the implementation of new processes such as HIsarna and other CO2-lean iron production technologies are discussed. In addition, the eventual transition to hydrogen ironmaking and “green” electricity in smelting are considered. By fast-acting improvements in current facilities and brave investments in new carbon-lean technologies, the CO2 emissions of the Indian steel industry can peak and turn downward toward carbon-neutral production. Full article
(This article belongs to the Special Issue Challenges and Prospects of Steelmaking Towards the Year 2050)
Show Figures

Figure 1

Article
Texture Memory in Hexagonal Metals and Its Mechanism
Metals 2021, 11(10), 1653; https://doi.org/10.3390/met11101653 - 18 Oct 2021
Viewed by 329
Abstract
Texture memory is a phenomenon in which retention of initial textures occurs after a complete cycle of forward and backward transformations, and it occurs in various phase-transforming materials including cubic and hexagonal metals such as steels and Ti and Zr alloys. Texture memory [...] Read more.
Texture memory is a phenomenon in which retention of initial textures occurs after a complete cycle of forward and backward transformations, and it occurs in various phase-transforming materials including cubic and hexagonal metals such as steels and Ti and Zr alloys. Texture memory is known to be caused by the phenomena called variant selection, in which some of the allowed child orientations in an orientation relationship between the parent and child phases are preferentially selected. Without such variant selection, the phase transformations would randomize preferred orientations. In this article, the methods of prediction of texture memory and mechanisms of variant selections in hexagonal metals are explored. The prediction method using harmonic expansion of orientation distribution functions with the variant selection in which the Burgers orientation relationship, {110}β//{0001}α-hex <11¯1>β//21¯1¯0α-hex, is held with two or more adjacent parent grains at the same time, called “double Burgers orientation relation (DBOR)”, is introduced. This method is shown to be a powerful tool by which to analyze texture memory and ultimately provide predictive capabilities for texture changes during phase transformations. Variation in nucleation and growth rates on special boundaries and an extensive growth of selected variants are also described. Analysis of textures of commercially pure Ti observed in situ by pulsed neutron diffraction reveals that the texture memory in CP-Ti is indeed quite well predicted by consideration of the mechanism of DBOR. The analysis also suggests that the nucleation and growth rates on the special boundary of 90° rotation about 21¯1¯0α-hex should be about three times larger than those of the other special boundaries, and the selected variants should grow extensively into not only one parent grain but also other grains in α-hex(hexagonal)→β(bcc) transformation. The model calculations of texture development during two consecutive cycles of α-hexβα-hex transformation in CP-Ti and Zr are also shown. Full article
Show Figures

Figure 1

Article
Wear Dry Behavior of the Al-6061-Al2O3 Composite Synthesized by Mechanical Alloying
Metals 2021, 11(10), 1652; https://doi.org/10.3390/met11101652 - 18 Oct 2021
Viewed by 314
Abstract
The present research deals with the comparative wear behavior of a mechanically milled Al-6061 alloy and the same alloy reinforced with 5 wt.% of Al2O3 nanoparticles (Al-6061-Al2O3) under different dry sliding conditions. For this purpose, an [...] Read more.
The present research deals with the comparative wear behavior of a mechanically milled Al-6061 alloy and the same alloy reinforced with 5 wt.% of Al2O3 nanoparticles (Al-6061-Al2O3) under different dry sliding conditions. For this purpose, an aluminum-silicon-based material was synthesized by high-energy mechanical alloying, cold consolidated, and sintered under pressureless and vacuum conditions. The mechanical behavior was evaluated by sliding wear and microhardness tests. The structural characterization was carried out by X-ray diffraction and scanning electron microscopy. Results showed a clear wear resistance improvement in the aluminum matrix composite (Al-6061-Al2O3) in comparison with the Al-6061 alloy since nanoparticles act as a third hard body against wear. This behavior is attributed to the significant increment in hardness on the reinforced material, whose strengthening mechanisms mainly lie in a nanometric size and homogeneous dispersion of particles offering an effective load transfer from the matrix to the reinforcement. Discussion of the wear performance was in terms of a protective thin film oxide formation, where protective behavior decreases as a function of the sliding speed. Full article
Show Figures

Figure 1

Article
Carbonitriding of Forging Dies
Metals 2021, 11(10), 1651; https://doi.org/10.3390/met11101651 - 18 Oct 2021
Viewed by 186
Abstract
Forging dies have to resist high mechanical and thermal loads. Therefore, they are usually nitrided. Former investigations showed that the abrasive wear at the critical parts of the dies is much higher than the nitriding hardness depth. Carbonitriding offers the possibility to increase [...] Read more.
Forging dies have to resist high mechanical and thermal loads. Therefore, they are usually nitrided. Former investigations showed that the abrasive wear at the critical parts of the dies is much higher than the nitriding hardness depth. Carbonitriding offers the possibility to increase the hardness depth in shorter treatment times because of the higher treatment temperature. The (carbo-)nitrided surface region obtains a better hardness at elevated temperatures and a better wear resistance than the untreated steel. In order to create a wear- and corrosion-resistant compound layer at the surface, a nitriding process step can be conducted after carbonitriding. The present work deals with developing a carbonitriding treatment for forging dies and investigations on the wear resistance of the created surface zones in model wear tests and tool life time experiments under industrial conditions. The aim of this work was to produce heat- and wear-resistant precipitation layers in hot working tool steels in economical treatment durations. Full article
(This article belongs to the Special Issue Heat Treatment and Mechanical Properties of Metals and Alloys)
Show Figures

Figure 1

Article
Database Clustering after Automatic Feature Analysis of Nonmetallic Inclusions in Steel
Metals 2021, 11(10), 1650; https://doi.org/10.3390/met11101650 - 18 Oct 2021
Viewed by 238
Abstract
Non-metallic inclusions (NMIs) in steel have a negative impact on the properties of steel, so the problem of producing clean steels is actual. The existing metallographic methods for evaluating and analyzing nonmetallic inclusions make it possible to determine the composition and type of [...] Read more.
Non-metallic inclusions (NMIs) in steel have a negative impact on the properties of steel, so the problem of producing clean steels is actual. The existing metallographic methods for evaluating and analyzing nonmetallic inclusions make it possible to determine the composition and type of NMIs, but do not determine their real composition. The analysis of single NMIs using scanning electron microscope (SEM), fractional gas analysis (FGA), or electrolytic extraction (EE) of NMIs is too complicated. Therefore, in this work, a technique based on the automatic feature analysis (AFA) of a large number of particles by SEM was used. This method allows to obtain statistically reliable information about the amount, composition, and size of NMIs. To analyze the obtained databases of compositions and sizes of NMIs, clustering was carried out by the hierarchical method by constructing tree diagrams, as well as by the k-means method. This made it possible to identify the groups of NMIs of similar chemical composition (clusters) in the steel and to compare them with specific stages of the steelmaking process. Using this method, samples of steels produced at different steel plants and using different technologies were studied. The analysis of the features of melting of each steel is carried out and the features of the formation of NMIs in each considered case are revealed. It is shown that in all the studied samples of different steels, produced at different steel plants, similar clusters of NMIs were found. Due to this, the proposed method can become the basis for creating a modern universal classification of NMIs, which adequately describes the current state of steelmaking. Full article
Show Figures

Figure 1

Article
Numerical Analysis of Friction Effects on Temperature and Phases within Forged Ti-6Al-4V Alloy Aeroengine Drum
Metals 2021, 11(10), 1649; https://doi.org/10.3390/met11101649 - 18 Oct 2021
Viewed by 186
Abstract
Friction conditions significantly impact the temperature and phases of titanium forged parts, further directly affecting the microstructures and mechanical properties of final parts. In this paper, a 2D simplified finite element (FE) model combined with phase transition equations is developed to simulate a [...] Read more.
Friction conditions significantly impact the temperature and phases of titanium forged parts, further directly affecting the microstructures and mechanical properties of final parts. In this paper, a 2D simplified finite element (FE) model combined with phase transition equations is developed to simulate a Ti-6Al-4V drum forging procedure. Then, friction effects on the temperature and phases of the forged drum are numerically analyzed and verified by experiments. The simulated results indicate that a reasonable range of friction factor is needed to obtain a relatively homogenous temperature distribution within the forged drum. Moreover, unlike its small influence on the α + β phase, improving friction obviously decreases the general levels of temperature and β phase and increases the homogeneities of α and β phases within the forged drum, which are associated with cooling rates and the heating effects of friction and deformation. Full article
(This article belongs to the Special Issue Lightweight Metals: Process, Microstructure, and Properties)
Show Figures

Figure 1

Article
Effects of Ce-Rich Misch Metal on the Microstructures and Tensile Properties of as-Cast Mg-7Al-3Sn-1Zn Alloys
Metals 2021, 11(10), 1648; https://doi.org/10.3390/met11101648 - 18 Oct 2021
Viewed by 183
Abstract
The effects of small amounts of Ce-rich misch metal (Mm: 0.5, 1.0 and 2.0 wt.%) addition on the microstructure and tensile properties of as-cast Mg-7Al-3Sn-1Zn wt.% (ATZ731) alloy have been investigated. The addition of Mm restricts the formation of the Mg17Al [...] Read more.
The effects of small amounts of Ce-rich misch metal (Mm: 0.5, 1.0 and 2.0 wt.%) addition on the microstructure and tensile properties of as-cast Mg-7Al-3Sn-1Zn wt.% (ATZ731) alloy have been investigated. The addition of Mm restricts the formation of the Mg17Al12 phase but greatly promotes the Al4Mm phase. The proper Mm addition enhances the strength and ductility of ATZ731 alloys at both room temperature (RT) and 175 °C. ATZ731 alloys with 1.0 wt.% Mm addition exhibit an advantageous combination strength and ductility, with the ultimate tensile strength (UTS), 0.2% yield strength (YS) and elongation to failure (Ef) at 175 °C of ~148 MPa, ~102 MPa and ~28%, improved by ~14.7%, ~24.3% and ~53.8%, respectively, compared to those of ATZ731 alloy. This enhancement is primarily owing to the refined microstructures and the high thermal stability of Al4Mm at the elevated temperature in contrast with that of the Mg17Al12 phase. The fracture modes are also discussed. Full article
(This article belongs to the Section Metal Casting, Forming and Heat Treatment)
Show Figures

Figure 1

Article
Thermoactivated Dislocation Motion in Rolled and Extruded Magnesium: Data of the Low-Temperature Acoustic Experiment
Metals 2021, 11(10), 1647; https://doi.org/10.3390/met11101647 - 18 Oct 2021
Viewed by 194
Abstract
Acoustic properties (logarithmic decrement and dynamic Young’s modulus) of commercial grade magnesium have been measured in the temperature range 51–310 K. Two types of magnesium samples have been studied: polycrystalline magnesium rolled at room temperature and subjected to hot extrusion. It is shown [...] Read more.
Acoustic properties (logarithmic decrement and dynamic Young’s modulus) of commercial grade magnesium have been measured in the temperature range 51–310 K. Two types of magnesium samples have been studied: polycrystalline magnesium rolled at room temperature and subjected to hot extrusion. It is shown that the amplitude dependences of the acoustic properties are due to the thermally activated breakaway of dislocations from weak pinning centers. Within the framework of the Indenbom-Chernov theory of thermally activated dislocation hysteresis, the binding energy of the interaction between dislocations and defects was estimated. Furthermore, dependences of the activation energy and activation volume on the applied stress were obtained in the microplastic region. The temperature dependences of the dynamic Young’s modulus are obtained in the amplitude independent region in the temperature range of 51–310 K. Functional form of the Young’s modulus temperature dependences corresponds to the classical concepts of the effect of thermal excitation of electrons and phonons on the elastic properties of crystals. Full article
Show Figures

Figure 1

Article
Microstructural Evolution as a Function of Increasing Aluminum Content in Novel Lightweight Cast Irons
Metals 2021, 11(10), 1646; https://doi.org/10.3390/met11101646 - 18 Oct 2021
Viewed by 252
Abstract
In the context of the development of new lightweight materials, Al-alloyed cast irons have a great potential for reducing the weight of the different part of the vehicles in the transport industry. The correlation of the amount of Al and its effect in [...] Read more.
In the context of the development of new lightweight materials, Al-alloyed cast irons have a great potential for reducing the weight of the different part of the vehicles in the transport industry. The correlation of the amount of Al and its effect in the microstructure of cast irons is not completely well established as it is affected by many factors such as chemical composition, cooling rate, etc. In this work, four novel lightweight cast irons were developed with different amounts of Al (from 0 wt. % to 15 wt. %). The alloys were manufactured by an easily scalable and affordable gravity casting process in an induction furnace, and casted in a resin-bonded sand mold. The microstructural evolution as a function of increasing Al content by different microstructural characterization techniques was studied. The hardness of the cast irons was measured by the Vickers indentation test and correlated with the previously characterized microstructures. In general, the microstructural evolution shows that the perlite content decrease with the increment of wt. % of Al. The opposite occurs with the ferrite content. In the case of graphite, a slight increment occurs with 2 wt. % of Al, but a great decrease occurs until 15 wt. % of Al. The addition of Al promotes the stabilization of ferrite in the studied alloys. The hardness obtained varied from 235 HV and 363 HV in function of the Al content. The addition of Al increases the hardness of the studied cast irons, but not gradually. The alloy with the highest hardness is the alloy containing 7 wt. % Al, which is correlated with the formation of kappa-carbides and finer perlite. Full article
(This article belongs to the Special Issue Recent Advances in Cast Irons)
Show Figures

Figure 1

Article
Characterization of AlSi10Mg-CP-Ti Metal/Metal Composite Materials Produced by Electro-Sinter-Forging
Metals 2021, 11(10), 1645; https://doi.org/10.3390/met11101645 - 17 Oct 2021
Viewed by 226
Abstract
Metal–metal composites represent a particular class of materials showing innovative mechanical and electrical properties. Conventionally, such materials are produced by severely plastically deforming two ductile phases via rolling or extruding, swaging, and wire drawing. This study presents the feasibility of producing metal–metal composites [...] Read more.
Metal–metal composites represent a particular class of materials showing innovative mechanical and electrical properties. Conventionally, such materials are produced by severely plastically deforming two ductile phases via rolling or extruding, swaging, and wire drawing. This study presents the feasibility of producing metal–metal composites via a capacitive discharge-assisted sintering process named electro-sinter-forging. Two different metal–metal composites with CP-Ti/AlSi10Mg ratios (20/80 and 80/20 vol.%) are evaluated, and the effects of the starting compositions on the microstructural and compositional properties of the materials are presented. Bi-phasic metal–metal composites constituted by isolated α-Ti and AlSi10Mg domains with a microhardness of 113 ± 13 HV0.025 for the Ti20-AlSi and 244 ± 35 HV0.025 for the Ti80-AlSi are produced. The effect of the applied current is crucial to obtain high theoretical density, but too high currents may result in Ti dissolution in the Ti80-AlSi composite. Massive phase transformations due to the formation of AlTiSi-based intermetallic compounds are observed through thermal analysis and confirmed by morphological and compositional observation. Finally, a possible explanation for the mechanisms regulating densification is proposed accounting for current and pressure synergistic effects. Full article
Show Figures

Figure 1

Review
Microstructure Design and Its Effect on Mechanical Properties in Gamma Titanium Aluminides
Metals 2021, 11(10), 1644; https://doi.org/10.3390/met11101644 - 16 Oct 2021
Viewed by 281
Abstract
Intermetallic gamma titanium aluminides display attractive engineering properties at high temperatures of up to 750 °C. To date, they have been used in low-pressure turbine blades and turbocharger rotors in advanced aircraft and automotive engines. This review summarizes the fundamental information of the [...] Read more.
Intermetallic gamma titanium aluminides display attractive engineering properties at high temperatures of up to 750 °C. To date, they have been used in low-pressure turbine blades and turbocharger rotors in advanced aircraft and automotive engines. This review summarizes the fundamental information of the Ti–Al system. After providing the development of γ TiAl alloys, typical phases, microstructures and their characteristics in TiAl alloys, the paper focuses on the effects of alloying elements on the phase boundary shifting, stabilizing effects and strengthening mechanism. The relationships between chemical additions, microstructure evolution and mechanical properties of the alloy are discussed. In parallel, the processing technologies and the common heat treatment methods are described in detail, both of which are applied to optimize the mechanical properties via adjusting microstructures. On this basis, the effects from chemical composition, processing technologies and heat treatments on microstructure, which controls the mechanical properties, can be obtained. It has a certain guiding significance for tailoring the microstructures to gain desired mechanical properties. Full article
(This article belongs to the Special Issue Microstructure and Properties of High Temperature Intermetallic)
Show Figures

Figure 1

Editorial
High Entropy Materials: Challenges and Prospects
Metals 2021, 11(10), 1643; https://doi.org/10.3390/met11101643 - 15 Oct 2021
Viewed by 116
Abstract
Entropy is an important concept in thermodynamics, measuring the disorder in a system or, more precisely, the number of possible microscopic configurations of individual atoms or molecules of a system, i.e., microstates [...] Full article
(This article belongs to the Special Issue High Entropy Materials: Challenges and Prospects)
Article
A Novel Multi-Objective Process Parameter Interval Optimization Method for Steel Production
Metals 2021, 11(10), 1642; https://doi.org/10.3390/met11101642 - 15 Oct 2021
Viewed by 96
Abstract
Customized small batch orders and sustainable development requirements pose challenges for product quality control and manufacturing process optimization for steel production. Building a multi-quality objective process parameter optimization method that converts the original single target optimization into multi-objective interval capability optimization has become [...] Read more.
Customized small batch orders and sustainable development requirements pose challenges for product quality control and manufacturing process optimization for steel production. Building a multi-quality objective process parameter optimization method that converts the original single target optimization into multi-objective interval capability optimization has become a new method to ensure product quality qualification rate and reduce production costs. Aiming at the multi-quality objective control problem of plate products, we proposed a novel multi-objective process parameter interval optimization model (MPPIO) with equipment process control capability and parameter sensitive analysis. The multi-output support vector regression method was used to establish a multi-quality objective prediction model, which was settled as a verification model for the process parameter optimization results based on the particle swarm optimization algorithm (PSO). The process control capability functions of key parameters were fitted based on the real data in production. With these functions, each optimized particle of the classical PSO was converted into the particle beam of the MIPPO. The iteration process was weight controlled by calculating the Morris sensitivity between each input parameter and output index in the multi-quality objective prediction model, and finally the processing control window of each key parameter was determined according to the process parameter optimization results. The experimental results show that the MPPIO model can obtain the optimal parameter optimization results with the maximum processing capacity and meet the customized processing range requirements. The MPPIO model can reduce the difficulty of control and save production costs while ensuring the product properties is qualified. Full article
Show Figures

Figure 1

Article
Thermodynamic Analysis and Experimental Investigation of Al and F Removal from Sulfuric Acid Leachate of Spent LiFePO4 Battery Powder
Metals 2021, 11(10), 1641; https://doi.org/10.3390/met11101641 - 15 Oct 2021
Viewed by 127
Abstract
The co-precipitation thermodynamics of the Li+–Fe2+/Fe3+–Al3+–F–SO42−–PO43−–H2O system at 298 K is studied, aiming to understand the precipitation characteristics. Based on the principle of simultaneous equilibrium [...] Read more.
The co-precipitation thermodynamics of the Li+–Fe2+/Fe3+–Al3+–F–SO42−–PO43−–H2O system at 298 K is studied, aiming to understand the precipitation characteristics. Based on the principle of simultaneous equilibrium and the mass action law, the missing Ksp values of AlF3 and FeF3 were estimated. The results of thermodynamic calculation demonstrate that Al3+ and F in the sulfuric acid leachate could be preferentially precipitated in the form of AlPO4 and FeF3 by the precise adjustment of the final pH value. Only a small amount of P and Fe was lost by the precipitation of Fe3(PO4)2·8H2O, FePO4, and Fe(OH)3 during the purification process. Controlling the oxidation of ferrous ions effectively is of critical significance for the loss reduction of P and Fe. Precipitation experiments at different pH value indicated that the concentration of Al3+ and F in the leachate decreased as the final pH value rose from 3.05 to 3.90. When the final pH value was around 3.75, aluminum and fluoride ion impurities could be deeply purified, and the loss rate of phosphate ions and iron ions could be reduced as much as possible. Relevant research results can provide theoretical guidance for the purification of leachate in the wet recycling process of lithium-ion batteries. Full article
(This article belongs to the Special Issue Thermodynamic Modeling of Metallurgical Processes)
Show Figures

Figure 1

Article
Manufacturing of Tool Steels by PBF-EB
Metals 2021, 11(10), 1640; https://doi.org/10.3390/met11101640 - 14 Oct 2021
Viewed by 284
Abstract
Additive manufacturing (AM) of metals is stimulating the tool making industry. Moreover, besides the production of lost forms, AM processes are now being used to directly generate tools, molds or parts, leading to massive time savings. In the case of material development for [...] Read more.
Additive manufacturing (AM) of metals is stimulating the tool making industry. Moreover, besides the production of lost forms, AM processes are now being used to directly generate tools, molds or parts, leading to massive time savings. In the case of material development for AM, the challenge is to operate with carbon-containing iron-based materials distinguished by high strength and hardness, as well as high corrosion resistance and thermal conductivity. Often, those materials are susceptible to crack formation during processing. Using Electron Beam Powder Bed Fusion (PBF-EB), the challenge of crack formation can be overcome by using high process temperatures in the range 800–900 °C. In this paper, results on the processing of a cold-working tool steel (X65MoCrWV3-2) and a hot-working steel (X37CrMoV5-1) will be presented. These include the processing window, processing strategies to minimize the density of cracks and properties with respect to microstructure and hardness. Full article
(This article belongs to the Special Issue Advances in Powder Metallurgy)
Show Figures

Figure 1

Article
Wear Behaviour of N Ion Implanted Ti-6Al-4V Alloy Processed by Selective Laser Melting
Metals 2021, 11(10), 1639; https://doi.org/10.3390/met11101639 - 14 Oct 2021
Viewed by 199
Abstract
Selective laser melting (SLM) is a laser-based powder bed fusion additive manufacturing technique extensively used in industry. One of the most commonly used alloys in SLM process is Ti-6Al-4V. However, its tribological properties when coated with N ion implantation is not well understood. [...] Read more.
Selective laser melting (SLM) is a laser-based powder bed fusion additive manufacturing technique extensively used in industry. One of the most commonly used alloys in SLM process is Ti-6Al-4V. However, its tribological properties when coated with N ion implantation is not well understood. In the ion implantation process used in this study, N2+ and N+ are accelerated to the energy of 60 keV and implanted to a fluence of 6 × 1017 at.cm−2. The effect of N ion implanted layer in terms of hardness values and how this implanted layer may affect wear process and wear rate is investigated in this paper. Sliding wear tests were conducted on SLM and conventionally processed samples implanted with N ions, followed by examining the wear tracks and coefficient of friction in order to explain the wear rate data obtained. The results showed that N+ implantation increased hardness within the depth of ~200 nm and reduced wear rate in SLM samples, while N2+ was not beneficial. Full article
(This article belongs to the Special Issue Tribological Behavior of Surface-Modified Metallic Components)
Show Figures

Figure 1

Article
Structural-Phase State, Mechanical Properties, Acoustic and Magnetic Characteristics in the Sustainable Deformation Localization Zones of Power Equipment Made of Structural and Heat Resistant Steels
Metals 2021, 11(10), 1638; https://doi.org/10.3390/met11101638 - 14 Oct 2021
Viewed by 203
Abstract
The paper presents the results of the analysis of the microstructure, mechanical properties, acoustic and magnetic characteristics of the metal of pipelines that are part of heat and power equipment, after long-term operation, made of structural and heat-resistant steels in the zones of [...] Read more.
The paper presents the results of the analysis of the microstructure, mechanical properties, acoustic and magnetic characteristics of the metal of pipelines that are part of heat and power equipment, after long-term operation, made of structural and heat-resistant steels in the zones of localization of plastic deformation. Samples of 0.2 C steel and 0.12C-1Cr-1Mo-1V steel were studied in the initial state, as well as after operation for 219 and 360 thousand hours, respectively. As a result of the studies carried out for each sample, the phase composition was determined (qualitatively and quantitatively), and the following parameters of the fine structure were calculated: volume fractions of structural components of steel (pearlite and ferrite), scalar ρ and excess ρ± dislocation density, curvature-torsion of the crystal lattice χ, amplitude of internal stresses (shear stress and long-range stresses). All quantitative parameters of the structure are determined both in each structural component of steel, and in general for each sample. The structure of the metal of all specimens after deformation before the formation of zones of stable localization of deformations consists of a ferrite-pearlite mixture, and for specimens after operation before fracture only of unfragmented and fragmented ferrite. Ferrite, which occupies the bulk of the material, is present both unfragmented and fragmented. For all samples, the ratios ρ ≥ ρ±, χ = χpl, σL ≥ σd were calculated, which indicate whether there is a danger of the initiation of microcracks in metal samples. For specimens without operation and after operation without damage in zones of stable localization of deformations, these conditions are met, and for specimens after operation until destruction, they are not met. It was found that the structural-phase state in the zones of localization of deformations has a direct effect on the characteristics of non-destructive tests. Thus, for all investigated samples, the values of such parameters as the delay time of the surface acoustic wave, the attenuation coefficient, the amplitude of the received signal, and the intensity of magnetic noise in the zones of deformation localization were established. Full article
(This article belongs to the Special Issue Kinetics of Plastic Deformation in Metallic Materials)
Show Figures

Figure 1

Article
Interfacial Behavior and Shear Strength of Al-25Si-4Cu-1Mg Joints by Transient Liquid Phase Bonding with Cu as Interlayer
Metals 2021, 11(10), 1637; https://doi.org/10.3390/met11101637 - 14 Oct 2021
Viewed by 219
Abstract
Spray-formed hypereutectic Al-Si-Cu-Mg alloy is the candidate for automotive and aerospace industries due to its superior wear resistance, lower thermal expansion coefficient and density, and higher thermal conductivity. This paper aims to investigate the bonding properties of hypereutectic Al-25Si-4Cu-1Mg alloys using the transient [...] Read more.
Spray-formed hypereutectic Al-Si-Cu-Mg alloy is the candidate for automotive and aerospace industries due to its superior wear resistance, lower thermal expansion coefficient and density, and higher thermal conductivity. This paper aims to investigate the bonding properties of hypereutectic Al-25Si-4Cu-1Mg alloys using the transient liquid phase (TLP) method with Cu as an interlayer. To obtain the suitable bonding parameters, the interfacial microstructure and shear strength of Al-25Si-4Cu-1Mg joints were investigated with the effect of different bonding temperatures and holding times. The results showed that TLP bonding between Al-Si-Mg-Cu alloy was mainly realized by large amounts of Al2Cu intermetallic compounds (IMCs), primary Si and α-Al phases. With the brazing temperature increasing, the width of the brazing seam gradually increased, and the voids began to be produced. With the holding time increasing, θ-Al2Cu phases approached into the base metal and Si particles in the brazing seam were obviously coarsened. With the formation of θ-Al2Cu phases into the base metal, more Si particles were segregated at the interface between brazing seam and base metal, and the shear test confirmed that it was the weakest bonding location. Finally, the effect of bonding parameters on the joint strength indicated that the joint brazed at 540 °C for 7.5 min presented the best shear performance with the shear strength reaching 75 MPa because the size of Si particles in the brazing seam was closest to the size of Si particles in base metal under this parameter. Full article
Show Figures

Figure 1

Article
The Recovery of Cu, Co, Zn, and Mn from a Complex Oxide Ore Using an Enhanced Reduction Leaching
Metals 2021, 11(10), 1636; https://doi.org/10.3390/met11101636 - 14 Oct 2021
Viewed by 217
Abstract
The processing of Cu, Co, and Zn at the Boleo project in Mexico involves two-stage (oxidation–reduction) leaching to extract a total of 85–88% Cu in 4 h. The first stage is an oxidation leaching using sulphuric acid (120 kg/tonne ore) at an Eh [...] Read more.
The processing of Cu, Co, and Zn at the Boleo project in Mexico involves two-stage (oxidation–reduction) leaching to extract a total of 85–88% Cu in 4 h. The first stage is an oxidation leaching using sulphuric acid (120 kg/tonne ore) at an Eh of 900 mV for 2 h. Then, the reduction stage takes place in 2 h with SO2 gas sparging for Mn and Co extraction at an Eh of 350–370 mV. The final extraction rates of metal values are 92% of Mn, 80% of Co, and 60% of Co, respectively, after 4 h of leaching at 70 °C. However, the same metal recoveries were obtained within 2 h using an equal amount of sulphuric acid and the addition of 25 kg of SO2 per tonne of ore in a single stage leaching in this research. In this case, the Fe extracted from the ore as Fe2+/Fe3+ is believed to have acted as an electrochemical couple contiguously leaching the Cu sulphide and Mn oxides, which also increased the Cu recovery as the Cu mineralised mostly intergrowths in these mineral structure matrices. A significant improvement was made in which the leaching time was halved to 2 h compared to 4 h in the previous plant design and current operation, involving the two-stage oxidation–reduction leaching. Full article
(This article belongs to the Special Issue Metallurgy and Recycling of Nonferrous Metals)
Show Figures

Figure 1

Article
Effect of Laser Shock Peening Parameters on Residual Stresses and Corrosion Fatigue of AA5083
Metals 2021, 11(10), 1635; https://doi.org/10.3390/met11101635 - 14 Oct 2021
Viewed by 206
Abstract
Aluminium alloy 5083 was subjected to Laser Shock Peening both with (LSP) and without protective coating (LPwC) at multiple pulse densities. A second LPwC treatment was conducted fully submersed under water, in addition to the standard laminar water flow condition. The results show [...] Read more.
Aluminium alloy 5083 was subjected to Laser Shock Peening both with (LSP) and without protective coating (LPwC) at multiple pulse densities. A second LPwC treatment was conducted fully submersed under water, in addition to the standard laminar water flow condition. The results show that compressive residual stresses were generated in all cases, although their character varied depending on the peening strategy and method of confinement. In all cases, higher pulse density lead to an increase in compressive stresses with a saturation point of −325 MPa at 1089 p/cm2 for the LPwC treatments. Corrosion fatigue testing of sensitized samples then showed 59% and 69% improvement in fatigue strength after the LSP and LPwC treatments, respectively. Full article
(This article belongs to the Special Issue Laser Peening for Improving Fatigue Properties of Aluminium Alloys)
Show Figures

Figure 1

Previous Issue
Next Issue
Back to TopTop