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Metals, Volume 12, Issue 8 (August 2022) – 164 articles

Cover Story (view full-size image): In this study, transient liquid-phase (TLP) bonding was adopted to obtain a reliable reduced-activation ferritic/martensitic (RAFM) steel joint with Fe-Si-B amorphous foil. The effect of creep stress on the microstructural evolution of the TLP joint was investigated. It was found that the main factors that affect the creep performance of TLP joints are the recovery of substructures and the coarsening and deformation of martensitic laths. The microstructure of the weld zone changes from large-sized ferrite to a mixed and fine microstructure of ferrite and martensite, which increases the heat resistance of the TLP joints, and thus results in creep fractures in the base metal. View this paper
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Article
Elastocaloric Effect in Aged Single Crystals of Ni54Fe19Ga27 Ferromagnetic Shape Memory Alloy
Metals 2022, 12(8), 1398; https://doi.org/10.3390/met12081398 - 22 Aug 2022
Viewed by 400
Abstract
In the present study, the effect of γ′-phase dispersed particles on both the L21(B2)-10M/14M-L10 martensitic transformations and the elastocaloric effect in aged Ni54Fe19Ga27 single crystals oriented along the [001]-direction was investigated. It was experimentally shown [...] Read more.
In the present study, the effect of γ′-phase dispersed particles on both the L21(B2)-10M/14M-L10 martensitic transformations and the elastocaloric effect in aged Ni54Fe19Ga27 single crystals oriented along the [001]-direction was investigated. It was experimentally shown that aging strongly affects the elastocaloric properties of these crystals. The precipitation of semi-coherent γ′-phase particles up to 500 nm in size in the crystals aged at 773 K for 1 h leads to a 1.4 times increase in the operating temperature range of the elastocaloric effect up to ΔTSE = 270 K as compared with the initial as-grown crystals (ΔTSE = 197 K). The adiabatic cooling values ΔTad are similar for the as-grown crystals ΔTad = 10.9 (±0.5) K and crystals aged at 773 K ΔTad = 11.1 (±0.5) K. The crystals containing incoherent γ′-phase particles sized 5–35 μm (after aging at 1373 K for 0.5 h) possess an operating temperature range of ΔTSE = 255 K with slightly smaller adiabatic cooling ΔTad below 9.7 (±0.5) K. The aged [001]-oriented Ni54Fe19Ga27 single crystals demonstrate high cyclic stability: the number of cycles does not influence the adiabatic cooling values and parameters of loading/unloading curves regardless of the particle size. The ways to improve the elastocaloric cooling parameters and stability of the elastocaloric effect by means of dispersed particles in the NiFeGa ferromagnetic shape memory alloy were discussed. Full article
(This article belongs to the Special Issue Magnetic Shape Memory Alloys)
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Review
A Review of Factors Affecting SCC Initiation and Propagation in Pipeline Carbon Steels
Metals 2022, 12(8), 1397; https://doi.org/10.3390/met12081397 - 22 Aug 2022
Viewed by 442
Abstract
Pipelines have been installed and operated around the globe to transport oil and gas for decades. They are considered to be an effective, economic and safe means of transportation. The major concern in their operation is corrosion. Among the different forms of corrosion, [...] Read more.
Pipelines have been installed and operated around the globe to transport oil and gas for decades. They are considered to be an effective, economic and safe means of transportation. The major concern in their operation is corrosion. Among the different forms of corrosion, stress corrosion cracking (SCC), which is caused by stresses induced by internal fluid flow or other external forces during the pipeline’s operation, in combined action with the presence of a corrosive medium, can lead to pipeline failure. In this paper, an extensive review of different factors affecting SCC of pipeline steels in various environmental conditions is carried out to understand their impact. Several factors such as temperature, presence of oxidizers (O2, CO2, H2S, etc.), composition and concentration of medium, pH, applied stress, and microstructure of the metal/alloy have been established to affect the SCC of pipeline steels. SCC susceptibility of a steel at a particular temperature strongly depends on the type and composition of the corrosive medium and microstructure. It was observed that pipeline steels with water quenched and quenched and tempered heat treatments, such as those that consist of acicular ferrite or bainitic ferrite grains, are more susceptible to SCC irrespective of solution type and composition. Applied stress, stress concentration and fluctuating stress facilitates SCC initiation and propagation. In general, the mechanisms for crack initiation and propagation in near-neutral solutions are anodic dissolution and hydrogen embrittlement. Full article
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Article
Electron Beam Welding and Post Heat Treatment of a New Near-Beta High-Strength Ti-4Al-5Mo-5V-5Cr-1Nb Alloy
Metals 2022, 12(8), 1396; https://doi.org/10.3390/met12081396 - 22 Aug 2022
Viewed by 411
Abstract
Ti-4Al-5Mo-5V-5Cr-1Nb (wt.%) is a new type of high-strength (~1300 MPa) titanium (Ti) alloy developed for aerospace applications. Until now, the research on its welding and subsequent heat treatment is barren. Herein, we employed electron beam welding (EBW) to a solutionized Ti-4Al-5Mo-5V-5Cr-1Nb with a [...] Read more.
Ti-4Al-5Mo-5V-5Cr-1Nb (wt.%) is a new type of high-strength (~1300 MPa) titanium (Ti) alloy developed for aerospace applications. Until now, the research on its welding and subsequent heat treatment is barren. Herein, we employed electron beam welding (EBW) to a solutionized Ti-4Al-5Mo-5V-5Cr-1Nb with a phase constituent of α + β and investigated its microstructure and mechanical properties in both as-welded (AW) and post-weld aging treated (PWAT) conditions. Results showed that due to the thermal input of the welding process, the α phase in the original microstructure of base material (BM) transformed into the β phase in the fusion zone (FZ). Similar microstructural evolution was observed for the heat-affected zone (HAZ) near the FZ (Near-HAZ), whereas the HAZ far away from FZ (Far-HAZ) contained a small amount of round α phase (ghost α) due to its slower cooling rate. Such a microstructural change resulted in poor tensile strength (~780 Mpa) for the as-welded joint. After PWAT, a large number of acicular α precipitated in the FZ and HAZ and its size (S) in different zones followed the order of SFar-HAZ < SFZ ≈ SNear-HAZ < SBM. The presence of αs precipitates remedied the tensile strength of the weld joint almost to the same as that of the BM. The present findings established the foundation of the application of this high-strength Ti alloy. Full article
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Article
Research on Conventional and High-Speed Machining Cutting Force of 7075-T6 Aluminum Alloy Based on Finite Element Modeling and Simulation
Metals 2022, 12(8), 1395; https://doi.org/10.3390/met12081395 - 22 Aug 2022
Viewed by 354
Abstract
In current industrial practice, the finite element modeling of the metal cutting process is essential. In this paper, finite element analysis of conventional and high-speed cutting of 7075-T6 aluminum alloy is carried out. A finite element model of the 7075-T6 aluminum alloy was [...] Read more.
In current industrial practice, the finite element modeling of the metal cutting process is essential. In this paper, finite element analysis of conventional and high-speed cutting of 7075-T6 aluminum alloy is carried out. A finite element model of the 7075-T6 aluminum alloy was developed using the Johnson Cook instant on equation to investigate the milling behavior of the alloy under conventional and high-speed conditions. The cutting forces in the X-direction, Y-direction, and Z-direction were predicted analytically for five groups of different Johnson Cook models with different material constants, and the predicted results were compared with the experimentally determined cutting forces to investigate the influence of the Johnson Cook constitutive model parameters on the simulation of the cutting forces of the 7075-T6 aluminum alloy. The results showed that the constitutive model parameters are inconsistent for conventional and higher speed cutting conditions. Under conventional cutting conditions, the JC4 model predicts the material factor cutting forces in good agreement with the experimental results, while under high-speed cutting conditions, the JC5 model predicts the material factor cutting forces in good agreement with the experimental results, but that the finite element model has good applicability in predicting machining performance. Only the experimental data obtained by covering the real strain, strain rate and temperature range to determine the material constant of the Johnson Cook constitutive equation can accurately predict the cutting force in all directions. Full article
(This article belongs to the Topic Advanced Forming Technology of Metallic Materials)
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Article
Ductile Fracture Investigation of High-Strength Steel SM570 under Low Stress Triaxiality
Metals 2022, 12(8), 1394; https://doi.org/10.3390/met12081394 - 22 Aug 2022
Viewed by 320
Abstract
A comprehensive understanding of the fracture behavior of high-strength steel is of great significance for its structural application. In this study, experiments were conducted to investigate the ductile fracture mechanism of high-strength steel SM570, one type of conventional structural steel. Two types of [...] Read more.
A comprehensive understanding of the fracture behavior of high-strength steel is of great significance for its structural application. In this study, experiments were conducted to investigate the ductile fracture mechanism of high-strength steel SM570, one type of conventional structural steel. Two types of shear specimens, one with symmetrical notches and the other with asymmetrical notches, were designed, and by changing the notch angles, a wide range of low-stress triaxiality could be obtained. Based on the discussion of the experimental results, crack initiation, and its propagation up to fracture failure were clarified. Compared with the fracture behavior of SM490 (one type of conventional normal-strength structural steel), the SM570 with higher yield stress has relatively severe stress concentration, the crack initiation appears earlier, and the brittle fracture is more likely to occur. Numerical simulations based on the finite element method (FEM) were performed with ABAQUS to obtain the stress triaxialities and equivalent plastic strain of the symmetrical and asymmetrical specimens. A modified N-VG model with a fracture criterion at a negative and low-stress triaxiality range from −0.6 to 1/3 was proposed for evaluating the fracture behavior of steel SM570. Full article
(This article belongs to the Special Issue Modelling, Test and Practice of Steel Structures)
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Article
Quasi-Static Three-Point Bending Behavior of Aluminum Foam Sandwich with CFRP Face-Sheets
Metals 2022, 12(8), 1393; https://doi.org/10.3390/met12081393 - 22 Aug 2022
Viewed by 378
Abstract
Aluminum foam sandwich panels are excellent structure–function integrated materials. With high specific strength, cushioning energy absorption and sound absorption of aluminum foam material, they overcome the disadvantage of the low strength of single aluminum foam materials. In this paper, the response of aluminum [...] Read more.
Aluminum foam sandwich panels are excellent structure–function integrated materials. With high specific strength, cushioning energy absorption and sound absorption of aluminum foam material, they overcome the disadvantage of the low strength of single aluminum foam materials. In this paper, the response of aluminum sandwich panels comprising aluminum foam cores and carbon fiber reinforced plastic (CFRP) face-sheets was investigated under quasi-static three-point bending, and the effect of core thickness as well as core density on flexural loads and deformation modes was studied. The experimental results show that increasing the thickness and the density of the core materials can increase the flexural load and bending stiffness in the bending process. The aluminum foam sandwich panels mainly include the following deformation modes in the three-point bending process: indentation, core shear, face-sheet fracture and debonding. Full article
(This article belongs to the Special Issue Synthesis and Applications of Metallic Foams)
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Review
Development of Carbon Nanotube (CNT)-Reinforced Mg Alloys: Fabrication Routes and Mechanical Properties
Metals 2022, 12(8), 1392; https://doi.org/10.3390/met12081392 - 22 Aug 2022
Viewed by 421
Abstract
Properties such as superior specific strength, being imponderous, and the ability to reprocess are the key features that have drawn attention to magnesium. In the last few years, applications such as automotive, aerospace, and medical applications have been seeking light-weight equipment, and light-weight [...] Read more.
Properties such as superior specific strength, being imponderous, and the ability to reprocess are the key features that have drawn attention to magnesium. In the last few years, applications such as automotive, aerospace, and medical applications have been seeking light-weight equipment, and light-weight materials are required for making them. These demands were matched by developing metal matrix composites with magnesium as a base and reinforced with carbon nanotubes (CNTs), grapheme nanoplatelets (GNPs), or ceramic nanoparticles. CNTs have been adopted for developing high-strength metal matrix composites (MMCs) because of their delicately superior thermal conductivity, surface-to-volume ratio, and tensile strength, but lower density. In developing high-performance light-weight magnesium-based MMCs, a small number of CNTs result in refined properties. However, making Mg-based MMCs has specific challenges, such as achieving uniform reinforcement distribution, which directly relates to the processing parameters. The composition of CNT, CNT sizes, their uniform distribution, Mg-CNT interfacial bonding, and their in-between alignment are the characteristic deciding factors of Mg-CNT MMCs. The current review article studies the modern methods to develop Mg-CNT MMCs, specifications of the developed MMCs, and their vital applications in various fields. This review focuses on sifting and summarizing the most relevant studies carried out on the methods to develop Mg-CNT metal matrix composites. The article consists of the approach to subdue the tangled situations in highlighting the Mg-CNT composites as imminent fabrication material that is applicable in aerospace, medical, and automotive fields. Full article
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Article
Synthesis, Characterization and Antimicrobial Studies of Ti-40Nb-10Ag Implant Biomaterials
Metals 2022, 12(8), 1391; https://doi.org/10.3390/met12081391 - 22 Aug 2022
Viewed by 312
Abstract
Bacterial infection and stress shielding are important issues in orthopedic implants. In this study, Ag element was selected as an antibacterial agent to develop an antibacterial Ti-40Nb-10Ag alloy by spark plasma sintering (SPS). The microstructure, phase constitution, mechanical properties, microhardness, and antibacterial properties [...] Read more.
Bacterial infection and stress shielding are important issues in orthopedic implants. In this study, Ag element was selected as an antibacterial agent to develop an antibacterial Ti-40Nb-10Ag alloy by spark plasma sintering (SPS). The microstructure, phase constitution, mechanical properties, microhardness, and antibacterial properties of the Ti-40Nb-10Ag sintered alloys with different sintering temperatures were systematically studied by X-ray diffraction (XRD), scanning electron microscope (SEM), microhardness tests, compressive tests, and antibacterial tests. The Ti-40Nb-10Ag alloys were mainly composed of α-Ti, β-Ti, and Ti2Ag intermetallic phases. This study shows that the change in sintering temperature affects the microstructure of the alloy, which results in changes in its microhardness, compressive strength, elastic modulus, and antibacterial properties. At the sintering temperature of 975 °C, good metallurgical bonding was developed on the surface of the alloy, which led to excellent microhardness, compressive strength, elastic modulus, and antibacterial ability with an antibacterial rate of 95.6%. In conclusion, the Ti-40Nb-10Ag alloy prepared by SPS at 975 °C is ideal and effective for orthopedic implant. Full article
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Article
Microstructure Characterization and Mechanical Property of the GH4065A Superalloy Inertia Friction Welded Joints
Metals 2022, 12(8), 1390; https://doi.org/10.3390/met12081390 - 22 Aug 2022
Viewed by 334
Abstract
Structural characteristics and design requirements for the integration of the integral rotor and disc shaft of the engine, the welding quality, and mechanical properties of superalloy weldments have received more and more attention in recent years. Inertia friction welding (IFW) was carried out [...] Read more.
Structural characteristics and design requirements for the integration of the integral rotor and disc shaft of the engine, the welding quality, and mechanical properties of superalloy weldments have received more and more attention in recent years. Inertia friction welding (IFW) was carried out with the typical fiber structure of the solid solution GH4065A alloy as the research object, the microstructure evolution rules of the plastic deformation zone (PDMZ), the thermally affected zone (TMAZ), and the welding zone (WZ) were studied, and the formation mechanism of metallurgical joints was explored. The size difference of the γ′ phase at the grain boundary and in the fiber structure was revealed. The reason is that the γ′ phase located at the grain boundary has lower diffusion activation energy and higher diffusion rate. The microhardness and tensile properties of the IFW joints were explored, the study found that the microhardness of the TAMZ is the highest, followed by the PDMZ and the WZ. The tensile test results show that with the increase in temperature, the fracture position shifts from the BM to the WZ, the microstructure at the fracture changed significantly, and the yield strength decreased from 1372 to 1085 MPa. Full article
(This article belongs to the Special Issue Characterization and Processing Technology of Superalloys)
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Article
On Agreement of Experimental Data and Calculated Results in Grain Boundary Segregation
Metals 2022, 12(8), 1389; https://doi.org/10.3390/met12081389 - 21 Aug 2022
Viewed by 374
Abstract
There are two sources of quantitative data on grain boundary segregation: careful experimental results and calculated data. These values can be compared in various ways. Here we show a comparison of average concentrations of silicon, vanadium, and tin at the grain boundaries of [...] Read more.
There are two sources of quantitative data on grain boundary segregation: careful experimental results and calculated data. These values can be compared in various ways. Here we show a comparison of average concentrations of silicon, vanadium, and tin at the grain boundaries of bcc iron determined in three ways: (i) on the basis of calculations of the segregation energy for individual sites; (ii) experimentally; and (iii) using a phenomenological prediction for selected systems characterized by satisfactory solid solubility of the segregant in bulk. We found very good agreement between the results of these approaches for all three of the segregants. The results clearly show the indispensable role of so-called ‘anti-segregation sites’ in the determination of average grain boundary concentration as well as the importance of segregation entropy and consequently, of entropy-dominated grain boundary segregation. Full article
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Review
Recent Advances in the Grain Refinement Effects of Zr on Mg Alloys: A Review
Metals 2022, 12(8), 1388; https://doi.org/10.3390/met12081388 - 21 Aug 2022
Cited by 1 | Viewed by 443
Abstract
As the lightest structural materials, Mg alloys show great effectiveness at energy saving and emission reduction when applied in the automotive and aerospace fields. In particular, Zr-bearing Mg alloys (non-Al containing) exhibit high strengths and elevated-temperature usage values. Zr is the most powerful [...] Read more.
As the lightest structural materials, Mg alloys show great effectiveness at energy saving and emission reduction when applied in the automotive and aerospace fields. In particular, Zr-bearing Mg alloys (non-Al containing) exhibit high strengths and elevated-temperature usage values. Zr is the most powerful grain refiner, and it provides fine grain sizes, uniformities in microstructural and mechanical properties and processing formability for Mg alloys. Due to the importance of Zr alloying, this review paper systematically summarizes the latest research progress in the grain refinement effects of Zr on Mg alloys. The main points are reviewed, including the alloying process of Zr, the grain refinement mechanism of Zr, factors affecting the grain refinement effects of Zr, and methods improving grain refinement efficiency of Zr. This paper provides a comprehensive understating of grain refinement effects of Zr on Mg alloys for the researchers and engineers. Full article
(This article belongs to the Special Issue Casting and Forming of Light Alloys)
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Article
The Influence of Processing Parameters on the Al-Mn Enriched Nano-Precipitates Formation in a Novel Al-Mn-Cr-Zr Alloy Tailored for Power Bed Fusion-Laser Beam Process
Metals 2022, 12(8), 1387; https://doi.org/10.3390/met12081387 - 20 Aug 2022
Viewed by 619
Abstract
Among the recently developed compositions tailored for the power bed fusion-laser beam process (PBF-LB), the novel Al-Mn-Cr-Zr alloy stands out. This composition exploits high solid solution strengthening, achieving a high hardness value in the as-built condition. The produced samples are inherently crack-free and [...] Read more.
Among the recently developed compositions tailored for the power bed fusion-laser beam process (PBF-LB), the novel Al-Mn-Cr-Zr alloy stands out. This composition exploits high solid solution strengthening, achieving a high hardness value in the as-built condition. The produced samples are inherently crack-free and have a good level of densification (~99.5%). The goal of this study is to investigate how this quaternary system is affected by the laser power while retaining a similar volumetric energy density. A comparison between the microstructural features and the mechanical performance was performed on a set of samples processed with power values ranging from 100 to 170 W. Microstructural features were investigated through optical microscopy, Electron Back Scattered Diffraction (EBSD) investigation and feature analysis using advanced microscopy to examine the amount, distribution, and shape of precipitates in the different process conditions. Although the quantitative feature analysis permitted analysis of more than 60 k precipitates for each power condition, all samples demonstrated a low level of precipitation (below 0.3%) with nanometric size (around 75 nm). The mechanical performances of this quaternary system as a function of the laser power value were evaluated with a microhardness test, recording very similar values for the different process conditions with a mean value of approximately 104 HV. The results suggested a very stable system over the tested range of process parameters. In addition, considering the low level of precipitation of nanometric phases enriched in Al-Mn, a supersaturated state could be established in each process condition. Full article
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Article
Effect of Microstructure on Electrochemical Properties of the EN S275 Mild Steel under Chlorine-Rich and Chlorine-Free Media at Different pHs
Metals 2022, 12(8), 1386; https://doi.org/10.3390/met12081386 - 20 Aug 2022
Viewed by 458
Abstract
This study examines microstructural modification as an effective strategy for reducing corrosion and its impact on the mechanical properties of mild steel. The effect of heat treatment on morphology, strength, toughness, and ductility was studied using optical microscopy, SEM, Scherrer equation, Vickers’s hardness [...] Read more.
This study examines microstructural modification as an effective strategy for reducing corrosion and its impact on the mechanical properties of mild steel. The effect of heat treatment on morphology, strength, toughness, and ductility was studied using optical microscopy, SEM, Scherrer equation, Vickers’s hardness test, and tensile-strength measurement. The heat treatment changed the microstructures, grain sizes, and particle sizes of the samples. It also increased the material strength by 56% and 25% for the quenched and tempered samples, respectively. The hardness was increased to 95% by quenching. The effect of the microstructural changes on the corrosion rate in chlorine-rich and chlorine-free media at different pH was studied using linear-polarization-resistance and dynamic-polarization-resistance methods. In both media, the quenched samples showed a lower corrosion rate compared to the original and tempered samples. The heat treatment resulted in the formation of homogenous martensite with coarse grains and small particle sizes that seemed to reduce the corrosion rate significantly. It also had an impact on the corrosion mechanism of these materials. The original and tempered samples showed pitting-corrosion behavior with high corrosion rates, while the quenched samples were more susceptible to intergranular corrosion. The rate of corrosion was investigated further at different pH, and it was shown to decrease when the pH was raised. This study confirms the impact of microstructural changes on the corrosion behavior of S275 structural steel. Full article
(This article belongs to the Section Metal Casting, Forming and Heat Treatment)
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Article
Experimental Set-Up of the Production Process and Mechanical Characterization of Metal Foams Manufactured by Lost-PLA Technique with Different Cell Morphology
Metals 2022, 12(8), 1385; https://doi.org/10.3390/met12081385 - 20 Aug 2022
Viewed by 306
Abstract
A flexible and versatile method for manufacturing open-cell metal foams, called lost-PLA, is presented in this work. With a double extruder 3D printer (FDM, Ultimaker S3, Utrecht, The Netherlands), it is possible to make polymer-based samples of the lost model. Through CAD modeling, [...] Read more.
A flexible and versatile method for manufacturing open-cell metal foams, called lost-PLA, is presented in this work. With a double extruder 3D printer (FDM, Ultimaker S3, Utrecht, The Netherlands), it is possible to make polymer-based samples of the lost model. Through CAD modeling, different geometries were replicated so as to get black PLA samples. This method combines the advantages of rapid prototyping with the possibility of manufacturing Al-alloy specimens with low time to market. The production process is articulated in many steps: PLA foams are inserted into an ultra-resistant plaster mix, after which the polymer is thermally degraded. The next step consists of the gravity casting of the EN-6082 alloy in the plaster form, obtaining metal foams that are interesting from a technological point of view as well as with respect to their mechanical properties. These foam prototypes can find application in the automotive, civil and aeronautical fields due to their high surface/weight ratio, making them optimal for heat exchange and for the ability to absorb energy during compression. The main aspects on which we focus are the set-up of the process parameters and the characterization of the mechanical properties of the manufactured samples. The main production steps are examined at first. After that, the results obtained for mechanical performance during static compression tests with different geometry porosities are compared and discussed. The foam with truncated octahedron cells was found to show the highest absorbed energy/relative density ratio. Full article
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Article
The Mechanical Performance of Aluminum Foam Fabricated by Melt Processing with Different Foaming Agents: A Comparative Analysis
Metals 2022, 12(8), 1384; https://doi.org/10.3390/met12081384 - 20 Aug 2022
Viewed by 360
Abstract
The study presents the comparative analysis of the compressive response for the experimental aluminium foams of different parent alloys fabricated by melt processing with/without Ca additive and an expensive conventional TiH2 foaming agent or a cheap alternative CaCO3. It was [...] Read more.
The study presents the comparative analysis of the compressive response for the experimental aluminium foams of different parent alloys fabricated by melt processing with/without Ca additive and an expensive conventional TiH2 foaming agent or a cheap alternative CaCO3. It was recognized that the response of the foams is significantly dependent on the type of foaming agent and Ca additive due to the formation of low ductile and brittle products created in the foaming process. The presence of deformation bands and brittle eutectics in material, Al3Ti particles/layers, partially decomposed TiH2, Ca containing compounds, etc. cause a reduction of the foam’s compressive strength and deviation of its mechanical profile from the theoretical predictions. In addition, the usage of an inexpensive CaCO3 foaming agent offers numerous indisputable advantages compared to TiH2, resulting, particularly, in enhancing the energy absorption ability of foams. Full article
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Article
Effect of Temperature and Solidification Structure Evolution of S355 Slabs with Different Corner Shapes on Transverse Corner Cracks
Metals 2022, 12(8), 1383; https://doi.org/10.3390/met12081383 - 20 Aug 2022
Viewed by 283
Abstract
The evolution process of corner temperatures for a typical micro-alloyed steel S355 is numerically simulated under various working conditions. The microstructure near the corner cracks of the S355 slab is experimentally examined, and the austenite/ferrite transformation temperatures of S355 steel during heating and [...] Read more.
The evolution process of corner temperatures for a typical micro-alloyed steel S355 is numerically simulated under various working conditions. The microstructure near the corner cracks of the S355 slab is experimentally examined, and the austenite/ferrite transformation temperatures of S355 steel during heating and cooling are measured. The results indicate that the right-angle slab corner temperature at the exit of the mould rapidly decreased to below Ar3 under intensive cooling in the foot roller zone. The film-like ferrite began to precipitate along the austenite grain boundary at the slab corner. The transformation from ferrite to austenite cannot be fully realized because the corner temperature cannot be quickly returned to Ac3 or higher. The slab transverse corner cracks occur along the film-like ferrite during the bending process. The chamfered slab, which modifies the original right angle of the slab into the 30° chamfered angle with a chamfered length of 60 mm, can significantly weaken the heat transfer and cooling effect of the slab corner. The chamfered slab corner temperature always remained above Ar3 during the bending and straightening processes. Precipitation of the pro-eutectoid film-like ferrite along the grain boundary cannot occur during cooling for the chamfered slab. The chamfered slab can keep the corner temperature above Ar3 and effectively avoid the occurrence of transverse corner cracks caused by grain boundary embrittlement. Full article
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Article
Influence of the Machining Process on the Service Life and Pitting Morphology of Gear-Tooth Surfaces
Metals 2022, 12(8), 1382; https://doi.org/10.3390/met12081382 - 20 Aug 2022
Viewed by 298
Abstract
Pitting, which results from contact fatigue, is a common failure mode in gear transmission systems and is influenced by the material strength and stress state of the contact area, which is further influenced by lubrication and roughness because of stress fluctuations. In this [...] Read more.
Pitting, which results from contact fatigue, is a common failure mode in gear transmission systems and is influenced by the material strength and stress state of the contact area, which is further influenced by lubrication and roughness because of stress fluctuations. In this study, a comparative contact-fatigue test was conducted on two types of gears with different terminal machining processes. The contact stress of the tooth surface considering the microtopography was analyzed using the fractal method based on surface microtopography data measured from the surface formed by the two processes. Test results show that the average service life of gears machined using the barrel-finishing process was approximately 5–7 times that of gears machined using grinding. The pitting morphologies of gears fabricated using different processes exhibited evident differences. The maximum stress level of the gears machined with barrel finishing was approximately twice that of the gears machined through grinding. Different stress levels resulted in different micropitting load-bearing capacities, which could be attributed to the different service lives of gears manufactured through different machining processes. The different presence features of the pitting morphology were due to the different micromorphologies of the surface formed by the different finishing processes. In particular, the randomly distributed pitting morphology of the gear surface machined using the barrel-finishing process was due to its flattening and polishing effect. Optimization of the surface-microgeometry distribution via the finishing process is an effective method for prolonging the service life of gears. Full article
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Article
Effect of Welding Polarity on Mechanical Properties of Submerged Arc Welded Railway Vehicle Wheels
Metals 2022, 12(8), 1381; https://doi.org/10.3390/met12081381 - 19 Aug 2022
Viewed by 370
Abstract
When a railway vehicle moves on a curved rail, sliding contact between the rail head side and wheel flange causes wear on the wheel flange. Traditionally, a wheel with thinned flange is machined to get a minimum flange thickness specified for structural safety. [...] Read more.
When a railway vehicle moves on a curved rail, sliding contact between the rail head side and wheel flange causes wear on the wheel flange. Traditionally, a wheel with thinned flange is machined to get a minimum flange thickness specified for structural safety. This operation reduces the rim thickness and shortens the life of the wheel. In the present study, the thinned flanges were hard-faced by submerged arc welding. A welding wire, which has good weldability to the base material of the wheel and does not generate thermal cracking, was developed. The effects of welding polarity on the microstructure, hardness, friction coefficient, and wear characteristics of the welded wheel were studied. The hardness of the wheel welded with reverse polarity was similar to that of welded with straight polarity. The wear rates of the wheel disc welded with reverse polarity and its counterpart rail disc were 11% and 27% lower than those welded with straight polarity. Delamination wear due to subsurface crack propagation and oxidation wear were mixed. The hardness of the rail before the wear test was in the range of 250–300 HV. After the wear test, it soared to 500 HV. Full article
(This article belongs to the Special Issue Welding and Fatigue of Railway Metallic Materials)
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Article
Study of the Printability, Microstructures, and Mechanical Performances of Laser Powder Bed Fusion Built Haynes 230
Metals 2022, 12(8), 1380; https://doi.org/10.3390/met12081380 - 19 Aug 2022
Viewed by 556
Abstract
The nickel-based superalloy, Haynes 230 (H230), is widely used in high-temperature applications, e.g., heat exchangers, because of its excellent high-temperature mechanical properties and corrosion resistance. As of today, H230 is not yet in common use for 3D printing, i.e., metal additive manufacturing (AM), [...] Read more.
The nickel-based superalloy, Haynes 230 (H230), is widely used in high-temperature applications, e.g., heat exchangers, because of its excellent high-temperature mechanical properties and corrosion resistance. As of today, H230 is not yet in common use for 3D printing, i.e., metal additive manufacturing (AM), primarily because of its hot cracking tendency under fast solidification. The ability to additively fabricate components in H230 attracts many applications that require the additional advantages leveraged by adopting AM, e.g., higher design complexity and faster prototyping. In this study, we fabricated nearly fully dense H230 in a laser powder bed fusion (L-PBF) process through parameter optimization. The efforts revealed the optimal process space which could guide future fabrication of H230 in various metal powder bed fusion processes. The metallurgical analysis identified the cracking problem, which was resolved by increasing the pre-heat temperature from 80 °C to 200 °C. A finite element simulation suggested that the pre-heat temperature has limited impacts on the maximum stress experienced by each location during solidification. Additionally, the crack morphology and the microstructural features imply that solidification and liquation cracking are the more probable mechanisms. Both the room temperature tensile test and the creep tests under two conditions, (a) 760 °C and 100 MPa and (b) 816 °C and 121 MPa, confirmed that the AM H230 has properties comparable to its wrought counterpart. The fractography showed that the heat treatment (anneal at 1200 °C for 2 h, followed by water quench) balances the strength and the ductility, while the printing defects did not appreciably accelerate part failure. Full article
(This article belongs to the Special Issue Superalloy—Microstructural Characterization of Ni-Based Superalloys)
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Review
Research Progress of Low Density and High Stiffness of Be-Al Alloy Fabricated by Investment Casting
Metals 2022, 12(8), 1379; https://doi.org/10.3390/met12081379 - 19 Aug 2022
Viewed by 326
Abstract
Be-Al alloy is a type of in situ metal matrix composite composed of a primary Be phase for strength and stiffness and a continuous Al matrix for ductility and toughness. Be-Al alloy (AlBe-Cast®910) has the characteristics of low density (2.17 g/cm [...] Read more.
Be-Al alloy is a type of in situ metal matrix composite composed of a primary Be phase for strength and stiffness and a continuous Al matrix for ductility and toughness. Be-Al alloy (AlBe-Cast®910) has the characteristics of low density (2.17 g/cm3), high elastic modulus (193 GPa) and specific stiffness (88.94 GPa/(g/cm3)) as a preferred material for lightweight aerospace products. Investment casting technology can be employed to prepare the components with thin-walled complex structures for aerospace; however, the wide solidification range for Be-Al leads to difficulty in feeding a casting and results in extensive shrinkage and porosity in cast parts. In this paper, the characteristics of Be-Al alloy are introduced first. Secondly, the mechanisms of influence of adding elements on the casting process, mechanical properties (strength increases more than 20% by adding elements) and microstructure evolution are explained in detail. In addition, the heat treatment technology (strength increases at least 10% after heat treatment) and the repair of defects by electron beam welding are discussed. Finally, Be-Al alloy is a new type of composite material, and China is a major research and application country; this paper introduces its research status and analyzes existing problems and shortcomings and points out the direction of Be-Al alloy development in China in the next few years. Full article
(This article belongs to the Special Issue Light Alloy and Its Application)
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Article
Phase Transformations of 5Cr-0.5Mo-0.1C Steel after Heat Treatment and Isothermal Exposure
Metals 2022, 12(8), 1378; https://doi.org/10.3390/met12081378 - 19 Aug 2022
Viewed by 267
Abstract
This study consists of the experimental and numerical analysis of the phase transformations of 5Cr-0.5Mo.0.1C steel after heat treatment. The microstructure of the as-received steel comprised ferrite and bainite, which is in agreement with the microconstituents predicted by the Calphad-calculated TTT diagram. Calphad-based [...] Read more.
This study consists of the experimental and numerical analysis of the phase transformations of 5Cr-0.5Mo.0.1C steel after heat treatment. The microstructure of the as-received steel comprised ferrite and bainite, which is in agreement with the microconstituents predicted by the Calphad-calculated TTT diagram. Calphad-based precipitation calculations show that the cooling stage of normalizing treatment did not cause carbide formation. In contrast, tempering at 700 °C for 15 min promotes the intergranular precipitation of Fe3C, M7C3 and M23C6 carbides, which is consistent with experimental results. Aging at 600 °C for short periods caused the precipitation of both M7C3 and M23C6 carbides; however, M23C6 is the dominant phase after prolonged aging. This is in agreement with experimental results. A rapid decrease in the steel hardness was observed after short aging, which is attributable to bainite transformation. Further reduction in hardness is associated with the diffusion-controlled coarsening of M23C6 carbide. Full article
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Article
Prediction of Spherical Sheet Springback Based on a Sparrow-Search-Algorithm-Optimized BP Neural Network
Metals 2022, 12(8), 1377; https://doi.org/10.3390/met12081377 - 19 Aug 2022
Viewed by 278
Abstract
Springback is an unavoidable problem in cold-forming processes and affects the efficiency and quality of the processing of outer sheets for ships. Therefore, effective control and prediction of sheet-forming springback is particularly important in the field of cold-bending processes. To this end, this [...] Read more.
Springback is an unavoidable problem in cold-forming processes and affects the efficiency and quality of the processing of outer sheets for ships. Therefore, effective control and prediction of sheet-forming springback is particularly important in the field of cold-bending processes. To this end, this paper presents research on cold-bending springback prediction based on a study of the multipoint cold-bending process combined with intelligent algorithms, as well as research on the multipoint cold-bending production of ship-hull plates. The forming process of spherical sheets was simulated by a finite element simulation. The amount of springback under different processes was studied, and the forming state and springback state were briefly analyzed. Then an in-depth study of machine learning was carried out, and the sparrow search algorithm (SSA) was introduced based on a back-propagation neural network (BPNN). The purpose of this integration was to prevent the BP neural network model from falling into local optimal solution problems. Then simulation data were obtained with the help of a simulation to build a backpropagation neural network prediction model, which was optimized based on the sparrow search algorithm, and training tests were conducted. Then the prediction results of the model were compared with the simulation data to verify that the prediction accuracy performance of the sparrow-search-algorithm-optimized BPNN model was improved. Finally, the prediction model based on the SSA–BPNN algorithm was compared with the prediction models of different algorithms, and the prediction results showed that SSA–BPNN outperformed other algorithms in prediction accuracy and speed; its prediction error was within 4%, which meets on-site processing requirements. The sparrow-search-algorithm-based optimization of BPNN was confirmed to have strong applicability in springback prediction. Full article
(This article belongs to the Special Issue Application of Neural Networks in Processing of Metallic Materials)
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Article
Characteristics of the Dissimilar AA7075 and Q235 Steel Joints Fabricated by Friction Stir Welding
Metals 2022, 12(8), 1376; https://doi.org/10.3390/met12081376 - 19 Aug 2022
Viewed by 358
Abstract
In this study, dissimilar AA7075/Q235 steel joints were successfully fabricated by friction stir welding (FSW), and the grains of AA7075 in the nugget zone (NZ) were refined and mixed with the broken Q235 fragments (i.e., the steel particles, strips, and blocks). Meanwhile, intermetallic [...] Read more.
In this study, dissimilar AA7075/Q235 steel joints were successfully fabricated by friction stir welding (FSW), and the grains of AA7075 in the nugget zone (NZ) were refined and mixed with the broken Q235 fragments (i.e., the steel particles, strips, and blocks). Meanwhile, intermetallic compound (IMC) layers were generated along the aluminum/steel (Al/steel) interface due to the occurrence of Al/steel diffusion. The results also revealed that the macro- and microstructures of the FSW joints varied depending on the welding heat input; under the cold FSW condition, micro-defects formed because of the weak and chaotic material flow in the NZ, reducing the welding heat input gave rise to inhomogeneous grain refinement; and the dynamic recrystallization of Al only occurred in the regions that lacked large steel blocks. In contrast, elevating the welding heat input led to the homogenization of the grain refinement and increased the thickness of the IMC layers. The FSW quality was controlled by both the thickness of the IMC layers and the size of the steel fragments simultaneously. Both the optimal-thickness IMC layers (about 2 μm) and fine steel particles were required to strengthen the joints, and a more than 30 MPa increment in the tensile strength could be obtained by manufacturing the above microstructures. Unfortunately, all the FSW joints failed in a brittle manner and the elongation was lower than 5%. Two kinds of fracture surfaces were observed inside the NZ: one was flat along the Al/steel interface, and the other was uneven due to the pulling out of the large steel strips and blocks. Full article
(This article belongs to the Special Issue Advances in Dissimilar Welding and Joining)
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Article
Simulation for Discrete Elements of the Powder Laying System in Laser Powder Bed Fusion
Metals 2022, 12(8), 1375; https://doi.org/10.3390/met12081375 - 19 Aug 2022
Viewed by 297
Abstract
For analyzing the influence of the system parameters on the density of the powder layers in laser powder bed fusion (LPBF) technology, an experimental method is proposed to improve the structure of the recoater in the powder laying system and optimize the parameters [...] Read more.
For analyzing the influence of the system parameters on the density of the powder layers in laser powder bed fusion (LPBF) technology, an experimental method is proposed to improve the structure of the recoater in the powder laying system and optimize the parameters of the powder laying system. With this experimental method, the appropriate density of the powder layers can be attained. In the proposed experimental method, the recoater in the powder laying system was taken as the research object and the forces affecting the powder and recoater when the powder was in contact with the recoater were analyzed. The discrete element model of the powder laying system was established to simulate and analyze the influences of the recoater’s radius, translational velocity and angular velocity on the density of powder layers. In addition, orthogonal experiments were designed to discuss the magnitude of the influence of each of the powder laying system’s parameters on the density of powder layers. Finally, the optimized parameter combination plan was put forward. The results show that increasing the recoater’s radius can enhance the density of powder layers within a certain range; but, as the recoater’s radius is increased continuously, its impact on the recoater’s radius on f powder layers’ density decreases. When the translational velocity of the recoater rises, powder layers’ density increases first and then decreases. The coater’s angular velocity has little effect on powder layers’ density. Eventually, the optimized processing parameters were determined, which are 25 mm for the recoater’s radius, 30 mm/s for the recoater’s translational velocity, and 12 s−1 for the recoater’s angular velocity. The results provide some significance and guidance in improving the recoater’s structure and optimizing the powder laying system’s parameters. Full article
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Article
Effects of Residual Stresses on Fatigue Crack Propagation of T-Joint Using Extended Finite Element Method (XFEM)
Metals 2022, 12(8), 1368; https://doi.org/10.3390/met12081368 - 19 Aug 2022
Viewed by 329
Abstract
The welds of T-joints are prone to fatigue cracking owing to stress concentrations and welding residual stresses. Previous studies investigated the crack propagation rate using numerical simulations; however, most employed two-dimensional models and ignored the effect of residual stresses. In this study, reliable [...] Read more.
The welds of T-joints are prone to fatigue cracking owing to stress concentrations and welding residual stresses. Previous studies investigated the crack propagation rate using numerical simulations; however, most employed two-dimensional models and ignored the effect of residual stresses. In this study, reliable temperature and residual stress fields were obtained through numerical simulations and verified experimentally. The effects of residual stresses on crack propagation were then investigated under different loading conditions. The residual stress field caused the direction of crack propagation to shift towards the web and accelerated the crack propagation speed with increasing displacement loading. Full article
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Article
The Effect of Strain Rate on the Deformation Behavior of Fe-30Mn-8Al-1.0C Austenitic Low-Density Steel
Metals 2022, 12(8), 1374; https://doi.org/10.3390/met12081374 - 18 Aug 2022
Viewed by 391
Abstract
Automotive steels suffer different strain rates during their processing and service. In this study, the effect of strain rates on the tensile properties of fully austenitic Fe-30Mn-8Al-1.0C (wt.%) steel was investigated, and the dominant deformation mechanism was clarified. Conventional and interrupted tension tests [...] Read more.
Automotive steels suffer different strain rates during their processing and service. In this study, the effect of strain rates on the tensile properties of fully austenitic Fe-30Mn-8Al-1.0C (wt.%) steel was investigated, and the dominant deformation mechanism was clarified. Conventional and interrupted tension tests and various microscopic characterization methods were carried out in this study. The results indicate that the yield strength increases with the increasing strain rate in the range of 10−4–10−1 s−1, and a good strength–ductility combination was achieved in the sample deformed at 10−3 s−1. In the process of straining at 10−3 s−1, microbands and deformation twins were observed. Thus, the combination of microband induced plasticity (MBIP) together with twinning induced plasticity (TWIP) leads to a continuous strain hardening behavior, and consequently to superior mechanical properties. However, adiabatic heating that leads to the increase in stacking fault energy (SFE) and inhibits the TWIP effect, as well as thermal softening jointly induces an anomalous decrease in tensile strength at the high strain rate of 10−1 s−1. Full article
(This article belongs to the Special Issue Deformation, Fracture and Microstructure of Metallic Materials)
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Article
Influence of Austenitisation Temperature and Time on Martensitic and Isothermal Bainite Phase Transformation of Spring Steel
Metals 2022, 12(8), 1373; https://doi.org/10.3390/met12081373 - 18 Aug 2022
Viewed by 333
Abstract
The influence of austenitisation temperature and time on the martensitic and isothermal bainite transformation of 51CrV4 spring steel was analysed. Based on the analysis of dilatometric curves, the martensite start temperatures (MS) were determined at different austenitisation temperatures (800–960 °C) and [...] Read more.
The influence of austenitisation temperature and time on the martensitic and isothermal bainite transformation of 51CrV4 spring steel was analysed. Based on the analysis of dilatometric curves, the martensite start temperatures (MS) were determined at different austenitisation temperatures (800–960 °C) and austenitisation times (5–30 min). At a temperature of 800 °C, a partial austenitic transformation occurred, and undissolved chromium carbides were present in the matrix. At higher temperatures, the austenitic transformation was complete, and the temperature MS increased with the austenitisation temperature. The temperature of the isothermal phase transformation has a stronger effect on the bainite transformation, which has different effects on the stability of the austenite and the diffusion processes. The microstructure of isothermal bainite transformation samples at 330, 430 and 520 °C was characterised by optical microscopy and dilatometric curves. Lower bainite was formed at a bainitic transformation temperature of 330 °C, and a combination of upper and lower bainite was characterised at a transformation temperature of 430 °C. In the samples transformed at 520 °C, a smaller proportion of lower bainite formed in addition to the upper bainite and martensite. Some allotriomorphic ferrite formed along the boundaries of the austenitic grains. Full article
(This article belongs to the Special Issue Forming and Heat Treatment of Steel)
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Article
Data-Driven Dynamic Simulations of Gold Extraction Which Incorporate Head Grade Distribution Statistics
Metals 2022, 12(8), 1372; https://doi.org/10.3390/met12081372 - 18 Aug 2022
Viewed by 327
Abstract
The Alhué mining district, Chile, is an example of a high-grade Au-Ag-Zn(-Pb) deposit with mineralized veins that contain variable amounts of copper sulfides, which are detrimental to the cyanidation process. Similar deposits can be found in the central zone of Chile, with polymetallic [...] Read more.
The Alhué mining district, Chile, is an example of a high-grade Au-Ag-Zn(-Pb) deposit with mineralized veins that contain variable amounts of copper sulfides, which are detrimental to the cyanidation process. Similar deposits can be found in the central zone of Chile, with polymetallic veins (Au, Ag, Cu, Pb, and Zn) that are related to subvolcanic intrusive events, the development of collapse calderas, and extensive hydrothermal alteration, such as Bronces de Petorca, the Chancón mining district and Cerro Cantillana; areas of the world with similar formations include the western United States and the Henan Province in central China, for example. Mineralogical variation can be managed within the metallurgical process by alternating its operational modes. The decision to switch between modes is governed by current and forecasted stockpile levels feeding into the process, according to a discrete rate simulation (DRS) framework that has now been developed to incorporate head grade data for gold. Customized simulations that incorporate probability distribution models using head grade have now been developed, following a statistical analysis based on data from the Alhué district. This study applies data-driven simulation modeling to represent standardized operational modes and their impact on the operational performance of gold extraction. Full article
(This article belongs to the Special Issue Flotation and Leaching Processes in Metallurgy)
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Article
Impact of Corrosion on the Degradation of the Mechanical Properties of 2195 and 2297 Al Alloys in the Marine Environment
Metals 2022, 12(8), 1371; https://doi.org/10.3390/met12081371 - 18 Aug 2022
Viewed by 305
Abstract
The objective of this work was to study the corrosion behavior of 2xxx aluminum alloys in the marine environment and the degradation of mechanical properties caused by corrosion as well as to provide support for the lightweight design of marine equipment. The corrosion [...] Read more.
The objective of this work was to study the corrosion behavior of 2xxx aluminum alloys in the marine environment and the degradation of mechanical properties caused by corrosion as well as to provide support for the lightweight design of marine equipment. The corrosion characteristics of 2297-T8 and 2195-T8 were observed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) at 3, 6, 9, and 12 months of exposure, and the mechanical properties were obtained via uniaxial tensile testing. The results of the study showed the following: (1) With an increase in the exposure time, the corrosion products on the surface of 2297-T8 gradually increase, and the corrosion products on the surface of 2195-T8 accumulate rapidly. (2) The results of EDS show that the corrosion products of 2297 are mainly Al oxides and that those of 2195 are composed of Al, Fe, Mn, Si, etc. (3) Through the corrosion pit diameter, corrosion pit depth, and corrosion mass reduction rate surface, the trend of an increasing average radius of the corrosion pits and the corrosion mass reduction rate surface varies linearly, and the average depth of the corrosion pits increases dramatically after 9 months of exposure time. (4) According to the mechanical properties of the study surface, in a marine atmosphere, the degradation of 2297-T8 ductility is higher than that of 2195-T8, while the degradation of the yield stress is lower than that of 2195-T8. Full article
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Article
Atomic Layer Deposited SiOX-Based Resistive Switching Memory for Multi-Level Cell Storage
Metals 2022, 12(8), 1370; https://doi.org/10.3390/met12081370 - 18 Aug 2022
Viewed by 349
Abstract
Herein, stable resistive switching characteristics are demonstrated in an atomic-layer-deposited SiOX-based resistive memory device. The thickness and chemical properties of the Pt/SiOX/TaN stack are verified by transmission electron microscopy (TEM) and X-ray photoemission spectroscopy (XPS). It is demonstrated that [...] Read more.
Herein, stable resistive switching characteristics are demonstrated in an atomic-layer-deposited SiOX-based resistive memory device. The thickness and chemical properties of the Pt/SiOX/TaN stack are verified by transmission electron microscopy (TEM) and X-ray photoemission spectroscopy (XPS). It is demonstrated that much better resistive switching is obtained using a negative set and positive reset compared to the opposite polarity. In addition, multi-level switching is demonstrated by changing the compliance current (CC) and the reset stop voltage, and potentiation and depression are emulated by applying pulses to achieve a synaptic device. Finally, a pulse endurance of 10,000 cycles and a retention time of 5000 s are confirmed by modulating the pulse input and reading voltage, respectively. Full article
(This article belongs to the Special Issue Metal Oxides Characterization for Emerging Memory Device Applications)
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