Metals

12 pages, 2666 KiB

Open AccessFeature PaperArticle

Penetration Recognition in GTAW Welding Based on Time and Spectrum Images of Arc Sound Using Deep Learning Method

by Jiazhou Wu, Jiawen Shi, Yanfeng Gao and Shan Gai

Metals 2022, 12(9), 1549; https://doi.org/10.3390/met12091549 - 19 Sep 2022

Cited by 6 | Viewed by 1834

The weld penetration rate is an important evaluation criterion for welding quality. However, it is difficult to identify the weld penetration state during GTAW welding process. This paper presents a new penetration recognition method based on time and spectrum images of arc sound [...] Read more.

The weld penetration rate is an important evaluation criterion for welding quality. However, it is difficult to identify the weld penetration state during GTAW welding process. This paper presents a new penetration recognition method based on time and spectrum images of arc sound using deep learning for DC GTAW welding. The time domain and spectrum images of the three penetration states from the non-periodic arc sound were used as the dataset for the penetration prediction model. VGG16, AlexNet, and custom convolutional neural network (CNN) were used to extract image features, and softmax was used to classify images for penetration recognition. The influence of image feature extraction networks, input methods, and different sampling methods on the recognition accuracy was deeply analyzed. The results show that the overall validation accuracy of the proposed model is approximately 96.2%. Particularly, the validation accuracy of the model in the excessive penetration state is approximately 100%. This study provides a new and feasible method for the online detection of weld penetration during the GTAW welding process. Full article

(This article belongs to the Section Welding and Joining)

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12 pages, 2961 KiB

Open AccessArticle

Improvement of the Fatigue Resistance of Super Duplex Stainless-Steel (SDSS) Components Fabricated by Wire Arc Additive Manufacturing (WAAM)

by Andrew Sales, Andrei Kotousov, Egon Perilli and Ling Yin

Metals 2022, 12(9), 1548; https://doi.org/10.3390/met12091548 - 19 Sep 2022

Cited by 5 | Viewed by 2081

Abstract

This study aimed to improve the overall fatigue properties of WAAM-produced SDSS by changing the interpass temperatures. Micro-computed tomography was used to quantitatively characterise the internal defects, such as porosity, in large-volume WAAM-fabricated SDSS materials. An increase in the interpass temperature led to [...] Read more.

This study aimed to improve the overall fatigue properties of WAAM-produced SDSS by changing the interpass temperatures. Micro-computed tomography was used to quantitatively characterise the internal defects, such as porosity, in large-volume WAAM-fabricated SDSS materials. An increase in the interpass temperature led to a reduction in the ferrite phase balance by up to 20%. The fatigue anisotropy was still evident, but the fatigue limit in the weakest (transverse) direction was increased to 250 MPa or by approximately 40%. Meanwhile, the increased interpass temperature had no significant effect on fatigue resistance in the longitudinal direction. This study suggests that the interpass temperature can be critical for both achieving isotropic mechanical properties and increasing fatigue life of structural components fabricated with the WAAM method. Full article

(This article belongs to the Special Issue Wire Arc Additive Manufacturing of Metallic Components)

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38 pages, 53916 KiB

Open AccessReview

An Overview on Atomistic Mechanisms of Heterogeneous Nucleation

by Zhongyun Fan and Hua Men

Metals 2022, 12(9), 1547; https://doi.org/10.3390/met12091547 - 19 Sep 2022

Cited by 12 | Viewed by 2549

Abstract

Our current understanding of heterogeneous nucleation has been dominated by the classical nucleation theory (CNT) with little progress of significance being made in past 100 years. In recent years under the financial support from EPSRC for the LiME Research Hub, we have made [...] Read more.

Our current understanding of heterogeneous nucleation has been dominated by the classical nucleation theory (CNT) with little progress of significance being made in past 100 years. In recent years under the financial support from EPSRC for the LiME Research Hub, we have made substantial progress on understanding heterogeneous nucleation at atomic level using a combination of molecular dynamics simulations and advanced high-resolution electron microscopy. We found that heterogeneous nucleation proceeds through a three-layer nucleation mechanism to produce a 2D nucleus. The atomistic mechanisms responsible for accommodating lattice misfit are dependent on misfit (f): (1) for systems with small negative misfit (−12.5% < f < 0), misfit is accommodated by dislocation mechanism; (2) for systems with small positive misfit (0 < f < 12.5%), misfit is accommodated by vacancy mechanism; and (3) for systems with large misfit (|f| > 12.5%), misfit is accommodated in two steps: formation of coincidence site lattice during prenucleation to accommodate the major misfit (f_csL) and the residual misfit (f_r) is accommodated during heterogeneous nucleation by the dislocation mechanism if the residual misfit is less than 0 or by the vacancy mechanism if the residual misfit is larger than 0. Further analysis suggests that heterogeneous nucleation is spontaneous thus barrierless and deterministic rather than stochastic. Full article

(This article belongs to the Special Issue Heterogeneous Nucleation, Grain Initiation and Grain Refinement: Reports from the LiME Research Hub in the UK)

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13 pages, 4308 KiB

Open AccessArticle

Martensitic Transition and Superelasticity of Ordered Heat Treatment Ni-Mn-Ga-Fe Microwires

by Yanfen Liu, Zirui Lang, Hongxian Shen, Jingshun Liu and Jianfei Sun

Metals 2022, 12(9), 1546; https://doi.org/10.3390/met12091546 - 19 Sep 2022

Cited by 2 | Viewed by 1193

Abstract

The preparation of Ni-Mn-Ga and Ni-Mn-Ga-Fe master alloy ingots and microwires was completed by high vacuum electric furnace melt melting furnace and melt drawing liquid forming equipment, and the lattice dislocations and defects formed inside the microwires during the preparation process were corrected [...] Read more.

The preparation of Ni-Mn-Ga and Ni-Mn-Ga-Fe master alloy ingots and microwires was completed by high vacuum electric furnace melt melting furnace and melt drawing liquid forming equipment, and the lattice dislocations and defects formed inside the microwires during the preparation process were corrected by stepwise ordered heat treatment. The micro-structure and phase structure were characterized using a SEM field emission scanning electron microscopy and an XRD diffractometer combined with an EDS energy spectrum analyzer; the martensitic phase transformation process of the microwires was analyzed using a DSC differential scanning calorimeter; and the superelasticity of the microwires was tested by a Q800 dynamic mechanical analyzer. The results indicate that Fe doping can refine the grain, transform the phase structure from parent phase to single 7M martensite, reduce the number of martensitic variants, and increase the mobility of the twin grain boundary interface. The MT phase transition temperature (M_S) is substantially increased in the martensite transition (MT) process by the increase of the number of free electrons in its lattice. During the superelasticity (SE) test, both microwires displayed superior recover-ability of SE curves, and the Fe doping curves showed similar characteristics of “linear superelasticity”, showing higher critical stress values and complete SE in the experiment. The critical stress satisfies the Clausius-Clapeyron equation and exhibits higher temperature sensitivity than Ni-Mn-Ga microwires. Full article

(This article belongs to the Special Issue Development and Application of Microscale Metallic Fibers)

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17 pages, 5777 KiB

Open AccessArticle

Electrochemical Noise Analysis of the X70 Pipeline Steel under Stress Conditions Using Symmetrical and Asymmetrical Electrode Systems

by Andres Carmona-Hernández, Ricardo Orozco-Cruz, Franco Antonio Carpio-Santamaria, Clarisa Campechano-Lira, Francisco López-Huerta, Edgar Mejía-Sánchez, Antonio Contreras and Ricardo Galván-Martínez

Metals 2022, 12(9), 1545; https://doi.org/10.3390/met12091545 - 19 Sep 2022

Cited by 3 | Viewed by 1741

Abstract

In this work, electrochemical monitoring of stress corrosion cracking (SCC) behavior of a X70 steel in acidic synthetic soil solution during the slow strain rate test (SSRT) was performed by electrochemical noise (EN) using the conventional arrangement of symmetrical electrodes and electrochemical emission [...] Read more.

In this work, electrochemical monitoring of stress corrosion cracking (SCC) behavior of a X70 steel in acidic synthetic soil solution during the slow strain rate test (SSRT) was performed by electrochemical noise (EN) using the conventional arrangement of symmetrical electrodes and electrochemical emission spectroscopy (EES) using the asymmetrical arrangement replacing the second working electrode for a platinum micro-cathode. The statistical method, fast Fourier transform, and discrete wavelet transform were used for analyzing the potential and current signals recorded by both arrangements. The results showed that EN arrangement was more effective to detect the crack initiation at a point close to yield strength despite stress-induced asymmetry in one of the electrodes. For the EES arrangement, the micro-cathode had a strong influence on the electrochemical noise of the current and potential under stress conditions. From the transient features, statistical parameters, and wavelet analysis, a discontinuous transgranular SCC mechanism was found. The resistance values obtained by EN measurements had better correlation with the electrochemical impedance spectroscopy results (EIS) than EES measurements. Full article

(This article belongs to the Special Issue Corrosion Electrochemical Measurement, Analysis and Research)

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Graphical abstract

10 pages, 1840 KiB

Open AccessArticle

The Use of Selective Laser Melting in Mandibular Retrognathia Correction

by Andrej Čretnik and Anita Fekonja

Metals 2022, 12(9), 1544; https://doi.org/10.3390/met12091544 - 19 Sep 2022

Viewed by 1448

Abstract

Digitalization and additive manufacturing offer new possibilities in the manufacturing of individualized medical and dental products. In the paper we present the results of the first 30 consecutive growing patients (15 males and 15 females), with a mean age of 13.69 years (SD [...] Read more.

Digitalization and additive manufacturing offer new possibilities in the manufacturing of individualized medical and dental products. In the paper we present the results of the first 30 consecutive growing patients (15 males and 15 females), with a mean age of 13.69 years (SD = 1.26), who were treated for mandibular retrognathia (skeletal Class II malocclusion), using fixed sagittal guidance (FSG) appliance, individually manufactured by selective laser melting (SLM). Lateral cephalometric radiographs were taken before (T0) and after (T1) treatment and a detailed cephalometric analysis was performed. with a special focus on a time period for malocclusion correction. The analyzed data were compared with the control group (CG; treated with intermaxillary Class II elastics) that was matched for pretreatment age and pretreatment cephalometric measurements. Both methods were effective in the correction of Class II malocclusion, but the time period of correction was significantly shorter (16.03 ± 1.09 months vs. 20.65 ± 4.12 months) with the FSG appliance. After treatment visual skeletal and dentoalveolar effects were achieved, with statistically significant differences measured in mandibular incisors inclination (0.45° in FSG and 2.84° in CG) and distance (−0.61 mm in FSG and 0.13 mm in CG), in mandibular first molar inclination (−1.07° in FSG and 1.18° in CG) and overbite (−3.82 mm in FSG and −2.46 mm in CG), all in favor of FSG appliance. After the final mean treatment time of 16.03 ± 1.09 months, visual skeletal and dentoalveolar effects were achieved, with significant differences in sagittal (SNB angle, SNPg angle, mandibular length (CoGn) and consequently decrease in ANB angle) as well as in vertical (lower anterior facial height (LAFH) and gonial angle) measurements noted, with no reported complications. As the time needed for malocclusion correction was comparable with the reports in the traditional use of the functional appliance and as all the cosmetical and functional changes in all the treated patients remained stable after a 2-year observational period, growing patients with Class II malocclusion could benefit with this type of treatment. As all the cosmetical and functional changes in all the treated patients remained stable after a 2-year observational period, growing patients with Class II malocclusion could benefit from the treatment with FSG appliance. Full article

(This article belongs to the Special Issue Selective Laser Melting: Advantages and Challenges)

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9 pages, 4382 KiB

Open AccessArticle

Magnetic Properties of the Mn₅₅Bi₄₅/Nd₂Fe₁₄B Hybrid Magnetic Alloys

by Shunda Lu, Yang Yang, Linfeng Chen, Zhen Xiang and Wei Lu

Metals 2022, 12(9), 1543; https://doi.org/10.3390/met12091543 - 19 Sep 2022

Viewed by 1401

Abstract

The (Mn₅₅Bi₄₅)_100−x/(Nd₂Fe₁₄B)_x hybrid magnetic alloys were prepared by the ball milling of the combined annealed Mn₅₅Bi₄₅ powders and Nd₂Fe₁₄B powders. The magnetic properties at [...] Read more.

The (Mn₅₅Bi₄₅)_100−x/(Nd₂Fe₁₄B)_x hybrid magnetic alloys were prepared by the ball milling of the combined annealed Mn₅₅Bi₄₅ powders and Nd₂Fe₁₄B powders. The magnetic properties at room temperature and elevated temperature were investigated. It was found that the saturation magnetization and the coercivity at room temperature increased significantly with the increasing Nd₂Fe₁₄B content. The enhanced energy product of 10.8 MGOe and 11.5 MGOe were obtained in (Mn₅₅Bi₄₅)₄₀/(Nd₂Fe₁₄B)₆₀ and (Mn₅₅Bi₄₅)₂₀/(Nd₂Fe₁₄B)₈₀. At elevated temperatures (350 K), the coercivities of 16.6 kOe and 16.1 kOe were obtained with Nd₂Fe₁₄B content of 20 wt.% and 40 wt.%, which were higher than those at room temperature. The temperature coefficients of coercivity of (Mn₅₅Bi₄₅)₈₀/(Nd₂Fe₁₄B)₂₀ and (Mn₅₅Bi₄₅)₆₀/(Nd₂Fe₁₄B)₄₀ were calculated to be positive, owing to the coercivity temperature characteristics of MnBi alloy. Finally, the energy products remained 10.5 MGOe and 10.1 MGOe in (Mn₅₅Bi₄₅)₄₀/(Nd₂Fe₁₄B)₆₀ and (Mn₅₅Bi₄₅)₂₀/(Nd₂Fe₁₄B)₈₀ at 350 K, which exhibited potential for high temperature applications. Full article

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11 pages, 2157 KiB

Open AccessArticle

Achieving Tunable Microwave Absorbing Properties by Phase Control of NiCoMnSn Alloy Flakes

by Xiaogang Sun, Jian Xu, Lian Huang, Daitao Kuang, Jinrong Liu, Guanxi Wang, Qifei Zhang and Yonghua Duan

Metals 2022, 12(9), 1542; https://doi.org/10.3390/met12091542 - 18 Sep 2022

Viewed by 1327

Abstract

Microwave absorption performance of metal alloys are highly dependent on their phase structures. However, the phase control of Ni–Mn-based alloys to achieve effective microwave absorption properties has been rarely reported. In this work, Ni₄₃Co₇Mn₃₉Sn₁₁ alloy flakes [...] Read more.

Microwave absorption performance of metal alloys are highly dependent on their phase structures. However, the phase control of Ni–Mn-based alloys to achieve effective microwave absorption properties has been rarely reported. In this work, Ni₄₃Co₇Mn₃₉Sn₁₁ alloy flakes were fabricated by balling milling method, and the contents of γ phase in the flakes were tuned by the subsequent heat treatment process. The as-fabricated Ni₄₃Co₇Mn₃₉Sn₁₁ alloy flakes exhibited excellent tunable microwave absorption by control of their phase structures. The optimal reflection loss was lower, up to −56.4 dB at 8.8 GHz, and was achieved at a single thickness of 2.0 mm. This can be attributed to the optimal structure of Ni₄₃Co₇Mn₃₉Sn₁₁ alloy flakes by phase control, and thus achieving improved attenuation property and impedance matching. This study proved Ni₄₃Co₇Mn₃₉Sn₁₁ alloy flakes should be a promising microwave absorption material. It is also demonstrated that phase control is an effected strategy for optimal microwave absorption properties of metal alloys and may have some reference value for related studies. Full article

(This article belongs to the Special Issue Preparation, Properties, Computational Simulations of Precious and Rare Metal Materials and Their Compounds)

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9 pages, 2598 KiB

Open AccessArticle

Sr²⁺ Ion Substitution Enhanced Dielectric Properties of Co₍₂₎Z Ferrites for VHF Antenna Substrate

by Ji Wang, Kunlong Li and Gongwen Gan

Metals 2022, 12(9), 1541; https://doi.org/10.3390/met12091541 - 18 Sep 2022

Viewed by 1358

Abstract

The effect of Sr²⁺ ions on the microstructure and high frequency properties of 2.5 wt% Bi₂O₃ added to Co₍₂₎Z hexaferrites (3Ba_(1-x)Sr_xO•2CoO•12Fe₂O₃, x = 0.0, 0.2, 0.4 and 0.6) synthesised [...] Read more.

The effect of Sr²⁺ ions on the microstructure and high frequency properties of 2.5 wt% Bi₂O₃ added to Co₍₂₎Z hexaferrites (3Ba_(1-x)Sr_xO•2CoO•12Fe₂O₃, x = 0.0, 0.2, 0.4 and 0.6) synthesised using the solid-state reaction method was investigated. Experimental results indicate that the dielectric properties were markedly enhanced with the increase in the content of Sr²⁺ ions, thereby increasing the miniaturisation factor, which enables a size reduction in a long frequency range. Slight changes to saturation magnetisation (M_s) and coercivity (H_c) were observed, i.e., the saturation magnetisation (M_s) decreased from 39.99 to 38.11 emu/g, and coercivity (H_c) increased from 59.05 to 65.21 Oe when x increased from 0.0 to 0.6. Meanwhile, ε′ increased from approximately 8 to 12, indicating the invariability in μ′. In addition, the processed materials exhibit relatively low magnetic loss and dielectric loss (magnetic loss tanδ_μ ≈ 0.08 and dielectric loss (tanδ_ε ≈ 0.007)). These results indicate that the substituted CO₍₂₎Z ferrites have excellent potential in high-frequency antenna applications. Full article

(This article belongs to the Special Issue Metal-Ceramic Composites Fabricated by Powder Metallurgy Method)

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16 pages, 3554 KiB

Open AccessFeature PaperArticle

Analysis of the Effect of Magnetic Field on Solidification of Stainless Steel in Laser Surface Processing and Additive Manufacturing

by Svetlana A. Gruzd, Stepan L. Lomaev, Nikolay N. Simakov, Georgii A. Gordeev, Anton S. Bychkov, Artem A. Gapeev, Elena B. Cherepetskaya, Mikhail D. Krivilyov and Ivan A. Ivanov

Metals 2022, 12(9), 1540; https://doi.org/10.3390/met12091540 - 17 Sep 2022

Cited by 4 | Viewed by 1844

Abstract

The problem of surface processing and microstructure refinement in stainless steels in laser surface processing in the presence of an external magnetic field has been studied experimentally and theoretically. The effect of both alternating and permanent magnetic fields is discussed. The experimental part [...] Read more.

The problem of surface processing and microstructure refinement in stainless steels in laser surface processing in the presence of an external magnetic field has been studied experimentally and theoretically. The effect of both alternating and permanent magnetic fields is discussed. The experimental part includes microstructure assessment of a thin stainless plate annealed by a quasi-continuous laser in the presence of an electromagnetic acoustic transducer. Complementary analytical calculus and numerical simulations of complex transport phenomena in the melting zone are performed. Based on the received data, the effect of the electromagnetic field on the molten zone under laser melting conditions is evaluated and quantified. The obtained results are relevant to laser surface hardening and additive manufacturing. Full article

(This article belongs to the Section Additive Manufacturing)

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16 pages, 9070 KiB

Open AccessFeature PaperArticle

Characterization of Stainless Steel Spent Pickling Sludge and Prospects for Its Valorization

by Fernando Castro, Pedro B. Tavares, Nuno Cristelo, Tiago Teixeira, Joana F. Garcia and Nuno M. G. Parreira

Metals 2022, 12(9), 1539; https://doi.org/10.3390/met12091539 - 17 Sep 2022

Viewed by 1439

Abstract

Fluorspar is considered a critical raw material for the European Union, due to its industrial uses and lack of sufficient extraction in European countries. It is a source for hydrofluoric acid manufacture, this latter chemical being employed, among other uses, in the pickling [...] Read more.

Fluorspar is considered a critical raw material for the European Union, due to its industrial uses and lack of sufficient extraction in European countries. It is a source for hydrofluoric acid manufacture, this latter chemical being employed, among other uses, in the pickling of stainless steels. From this latter activity, sludge is generated due to the need for used water treatment. In this article, we report a full characterization of this residue, obtained in an industrial plant in Vieira de Leiria, Portugal. Its chemical and mineralogical characteristics were determined, showing that it is mostly a mixture of calcium fluoride and calcium sulfate with some heavy metals content. Thermal behavior allowed us to determine that the material melts at around 950 °C. The influence of calcining operation on the residue was determined, especially concerned with the leachability of some elements. Taking into account the results of the characterization of this residue, some considerations are presented about the potential for the valorization of this industrial residue. Full article

(This article belongs to the Special Issue Recovery of Critical Metals and Materials from Residues)

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19 pages, 3483 KiB

Open AccessFeature PaperArticle

Environment-Friendly Corrosion Inhibitors for Aluminum in Hydrochloric Acid: Quantum and Experimental Research

by Tarek A. Yousef, Rageh. K. Hussein, Abdulrahman G. Alhamzani, Ahmed T. Al-Enazi, Mohammed B. AL-Osimi and Mortaga M. Abou-Krisha

Metals 2022, 12(9), 1538; https://doi.org/10.3390/met12091538 - 17 Sep 2022

Cited by 5 | Viewed by 2346

Abstract

Environment-friendly materials (e.g., Honey and Mint) are used as corrosion inhibitors for aluminum in hydrochloric acid (HCl) using both the density functional theory (DFT) at the B3LYP/6–31G* basis set level and semi-empirical methods (AM1, PM3, MINDO, and RM1). The aim of this study [...] Read more.

Environment-friendly materials (e.g., Honey and Mint) are used as corrosion inhibitors for aluminum in hydrochloric acid (HCl) using both the density functional theory (DFT) at the B3LYP/6–31G* basis set level and semi-empirical methods (AM1, PM3, MINDO, and RM1). The aim of this study is to investigate the inhibition efficiency (%IE) in terms of their molecular structure. The quantum chemical parameters such as the highest occupied molecular orbital energy (E_HOMO), the lowest unoccupied molecular orbital energy (E_LUMO), the energy gap (ΔE), the charge on the reactive core, the hardness (η), and the total energy have all been computed. The MINDO method was used to measure the electronic energies and charge densities of the inhibitors that were used. Theoretical calculations were also carried out, with the findings correlating well with the experimental data. Gravimetry and gasometry measurements were used to investigate the effects of honey and mint on aluminum corrosion in a 1.0 M hydrochloric acid (HCl) solution. In acid solutions, honey and mint were found to be effective inhibitors of aluminum corrosion, with honey being the better option. Because of the adsorption of its components on aluminum surfaces, the inhibitory effect of the used inhibitors was addressed. The higher dipole moment of honey than that of mint caused the adsorption of honey on the aluminum surface better. The IEs measured by gravimetry and gasometry are almost identical. Full article

(This article belongs to the Section Corrosion and Protection)

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16 pages, 4485 KiB

Open AccessArticle

Effect of Heat Treatment on Microstructure, Tensile Properties and High-Temperature Corrosion Resistance of the FeCrMnNi High Entropy Alloy

by Zhen Cai, Na Wei, Yaolei Han, Fang Si, Lei Mi, Chenhui Zhang, Xiaohua Liu, Fengyang Jiang and Tiandong Wu

Metals 2022, 12(9), 1537; https://doi.org/10.3390/met12091537 - 16 Sep 2022

Cited by 3 | Viewed by 2008

Abstract

FeCrMnNi high-entropy alloys prepared by vacuum induction melting were tested and characterized using an X-ray diffractometer, a scanning electron microscope, a micro hardness tester and a universal tensile tester to investigate the effects of the heat treatment temperature on the microstructure and mechanical [...] Read more.

FeCrMnNi high-entropy alloys prepared by vacuum induction melting were tested and characterized using an X-ray diffractometer, a scanning electron microscope, a micro hardness tester and a universal tensile tester to investigate the effects of the heat treatment temperature on the microstructure and mechanical properties of the alloys and the heat-resistant corrosion properties of FeCrMnNi alloy after annealing at 800 °C. It is a high-entropy alloy with a typical dendritic (DR) morphology. With the increase in the heat-treatment temperature, the amount of ultrafine precipitates with the BCC structure in the matrix increased; furthermore, the amount of ultrafine precipitates started to decrease at temperatures above 900 °C, and the DR structure gradually weakened. After heat treatment at temperatures above 800 °C, the alloy showed a tensile strength of 721.1 MPa and an elongation at break of 26.7%, which indicates improved strength of the alloy while maintaining good plasticity, mainly because a large amount of nanoscale particles precipitated between the DR structures and enabled fine grain strengthening. Therefore, an appropriate heat-treatment temperature helps to improve the overall mechanical properties of the high-entropy alloy. Full article

(This article belongs to the Special Issue High-Entropy Alloys: Structures, Properties and Applications)

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7 pages, 2180 KiB

Open AccessCommunication

Enhanced Magnetocaloric Properties of Annealed Melt-Extracted Mn_1.3Fe_0.6P_0.5Si_0.5 Microwires

by Lin Luo, Jia Yan Law, Hongxian Shen, Luis M. Moreno-Ramírez, Victorino Franco, Shu Guo, Nguyen Thi My Duc, Jianfei Sun and Manh-Huong Phan

Metals 2022, 12(9), 1536; https://doi.org/10.3390/met12091536 - 16 Sep 2022

Cited by 3 | Viewed by 1166

Abstract

The highly regarded Fe₂P-based magnetocaloric materials are usually fabricated by ball milling, and require an additional extended annealing treatment at high temperatures (at temperatures up to 1423 K for several hours to days). In this work, we show that fabricating Mn [...] Read more.

The highly regarded Fe₂P-based magnetocaloric materials are usually fabricated by ball milling, and require an additional extended annealing treatment at high temperatures (at temperatures up to 1423 K for several hours to days). In this work, we show that fabricating Mn_1.3Fe_0.6P_0.5Si_0.5 into the form of microwires attained 82.1 wt.% of the desired Fe₂P phase in the as-cast state. The microwires show a variable solidification structure along the radial direction; close to the copper wheel contact, Fe₂P phase is in fine grains, followed by dendritic Fe₂P grains and finally secondary (Mn,Fe)₅Si₃ phase in addition to the dendritic Fe₂P grains. The as-cast microwires undergo a ferro- to para-magnetic transition with a Curie temperature of 138 K, showing a maximum isothermal magnetic entropy change of 4.6 J kg⁻¹ K⁻¹ for a magnetic field change of 5 T. With further annealing, a two-fold increase in the maximum isothermal magnetic entropy change is found in the annealed microwires, which reveal 88.1 wt.% of Fe₂P phase. Full article

(This article belongs to the Special Issue Development and Application of Microscale Metallic Fibers)

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14 pages, 46588 KiB

Open AccessArticle

Features of Changes in the Surface Structure and Phase Composition of the of α + β Titanium Alloy after Electromechanical and Thermal Treatment

by Vyacheslav Petrovich Bagmutov, Valentin Ivanovich Vodopyanov, Igor Nikolaevich Zakharov, Alexander Yurievich Ivannikov, Artem Igorevich Bogdanov, Mikhail Dmitrievich Romanenko and Vladislav Valerievich Barinov

Metals 2022, 12(9), 1535; https://doi.org/10.3390/met12091535 - 16 Sep 2022

Cited by 5 | Viewed by 1666

Abstract

Changes of structure, phase composition and microhardness in high-strength α + β titanium alloy were investigated after electromechanical treatment (EMT) and subsequent aging. The EMT was performed with alternating current density (j of 300 and 600 A/mm²). The aging was [...] Read more.

Changes of structure, phase composition and microhardness in high-strength α + β titanium alloy were investigated after electromechanical treatment (EMT) and subsequent aging. The EMT was performed with alternating current density (j of 300 and 600 A/mm²). The aging was performed upon heating at 600 °C and exposure for 14 h. Methods of scanning electron microscopy, X-ray phase structure, micro X-ray spectral and durometric analyses were used. Modified layers (up to 200–250 µm in depth) on the surface of α + β titanium alloy were formed due to intensive thermo-deformation during the EMT and the following aging. The structure of the surface layer was characterized by high dispersivity (with particle sizes of about 30–500 nm), significant concentration heterogeneity (due to redistribution of the alloying elements and changes in the volume ratio of α- and β-phases), distortions in the crystal structure, increased levels of microstrain and microstress (2–2.5 times as compared to the initial) and increases in microhardness (by 30–40%). Full article

(This article belongs to the Section Metal Casting, Forming and Heat Treatment)

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23 pages, 16781 KiB

Open AccessArticle

Strength-Toughness Balance and Hydrogen Embrittlement Susceptibility of a Precipitation-Strengthened Steel Adopted Tempering Process

by Ning Zhao, Yanlin He, Li Lin, Rendong Liu, Qiangqiang Zhao and Weisen Zheng

Metals 2022, 12(9), 1534; https://doi.org/10.3390/met12091534 - 16 Sep 2022

Viewed by 1547

Abstract

Two steels with different nickel (Ni) content were investigated to reveal the role of Ni on strength-toughness balance and hydrogen embrittlement susceptibility. Although they were similar in microstructure, i.e., nano-particles were precipitated on martensitic laths, different mechanical behaviors were exhibited. After tempering, the [...] Read more.

Two steels with different nickel (Ni) content were investigated to reveal the role of Ni on strength-toughness balance and hydrogen embrittlement susceptibility. Although they were similar in microstructure, i.e., nano-particles were precipitated on martensitic laths, different mechanical behaviors were exhibited. After tempering, the yield strength of 3.5 Ni steel reached a peak at 500 °C, while that of 2.5 Ni steel kept a downward trend, indicating that precipitation strengthening was significant in 3.5 Ni steel. Combined with thermodynamic and kinetic analyses, it was shown that when the Ni content increased, the rich-copper (Cu) precipitation transformation driving force would be enhanced and the reverse of austenite transformation accelerated to improve its stability. Moreover, the increase of Ni content also induced the increase in high-angle grain boundaries (HAGBs), which could inhibit crack propagation. Under the comprehensive effects of strengthening and ductility mechanism, 3.5 Ni steel exhibited excellent cryogenic toughness. Although it was not possible to obtain the ideal balancing of strength-toughness for the steel with lower Ni content, its hydrogen embrittlement susceptibility is satisfying. The results showed that the increase of grain boundary density caused by the grain refinement of 2.5 Ni steel is the key factor for its lower hydrogen embrittlement sensitivity index. Moreover, with the reduction of Ni content, the decrease of HAGBs and the increase in Σ11 boundary were conducive to reducing hydrogen-assisted cracking, while the residual Fe₃C in 3.5 Ni steel would deteriorate the hydrogen embrittlement resistance. Full article

(This article belongs to the Special Issue Advances in High-Strength Low-Alloy Steels)

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12 pages, 18753 KiB

Open AccessArticle

Enhanced Separation Behavior of Metals from Simulated Printed Circuit Boards by Supergravity

by Long Meng, Yudong Liu and Zhancheng Guo

Metals 2022, 12(9), 1533; https://doi.org/10.3390/met12091533 - 16 Sep 2022

Viewed by 1286

Abstract

Printed circuit boards (PCBs) contain valuable metals, epoxy resin, and glass fiber, resulting in them being considered as attractive secondary sources of metals. Due to the complex metal compositions in PCBs, it is difficult to clarify the mechanism of metal separation behavior in [...] Read more.

Printed circuit boards (PCBs) contain valuable metals, epoxy resin, and glass fiber, resulting in them being considered as attractive secondary sources of metals. Due to the complex metal compositions in PCBs, it is difficult to clarify the mechanism of metal separation behavior in the pyrometallurgical recovery process. In this paper, pure Pb, Sn and Cu were used to simulate the effects of temperature, time, particle size and shape on the reaction and separation process. With the increase of temperature and time, the thickness of the interface reaction layer was improved. Under the same temperature and time, the reaction degree of Cu with Sn was greater than that of Cu with Pb. In the separation process, reducing temperature, time and increasing Cu particle size were conducive to the separation and recovery of Pb-Sn alloy by supergravity. Under the same or similar particle size, the recovery of Pb-Sn alloy in irregular Cu particles was lower than that in regular Cu spheres. Improving the gravity coefficient benefited the recoveries of Pb and Sn. The results will provide technical guidance for the separation and recovery of Pb, Sn and Cu from real PCBs. Full article

(This article belongs to the Special Issue Metal Recovery from Secondary Resources)

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9 pages, 1053 KiB

Open AccessArticle

Influences of Anisotropic Equivalent Field and Magnetic Damping Coefficient on Giant Magnetoimpedance Effect of Cylindrical Alloy Fibers: Theoretical Magnetoimpedance Calculations

by Tao Wang, Yingjie Zhang, Jingtao Lei, Qiuyuan Wang, Jinbo Chen, Hengyu Li, Zhizheng Wu, Ze Cui, Mei Liu and Jinjun Rao

Metals 2022, 12(9), 1532; https://doi.org/10.3390/met12091532 - 16 Sep 2022

Cited by 1 | Viewed by 1082

Abstract

In this paper, the giant magneto-impedance (GMI) model of a cylindrical alloy fiber was established by the Maxwell equation and Landau–Lifshitz equation to simulate the influence of physical parameters of cylindrical alloy fiber on GMI under different control parameters. MATLAB was employed to [...] Read more.

In this paper, the giant magneto-impedance (GMI) model of a cylindrical alloy fiber was established by the Maxwell equation and Landau–Lifshitz equation to simulate the influence of physical parameters of cylindrical alloy fiber on GMI under different control parameters. MATLAB was employed to calculate the magneto-impedance of cylindrical fibers and draw its curves. We found that when the anisotropic equivalent field of the fiber changes from 10Oe to 50Oe, the peak position of the GMI ratio also moves from about 10Oe to 50Oe, and the peak value gradually increases from 100% to 300%. The GMI ratio increased rapidly with the decrease in the magnetization damping coefficient. Our findings could further guide the design of supersensitive micro GMI sensors by optimally regulating the magnetic damping coefficient, the angle between the external magnetic field and easy axis and the anisotropic equivalent field of cylindrical alloy fibers. Full article

(This article belongs to the Special Issue Development and Application of Microscale Metallic Fibers)

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15 pages, 5032 KiB

Open AccessArticle

Effect of Deoxidizing and Alloying Routes on the Evolution of Non-Metallic Inclusions in 55SiCr Spring Steel

by Jinwen Liu, Haiyan Tang, Luzhao Guo and Jiaquan Zhang

Metals 2022, 12(9), 1531; https://doi.org/10.3390/met12091531 - 16 Sep 2022

Cited by 2 | Viewed by 1674

Abstract

Compared to the conventional deoxidation process with Al or Si-Mn for 55SiCr spring steel production, the possibility of using a Si-Ca-Ba compounded deoxidizer to control the behavior of non-metallic inclusions in spring steel was explored in this study. The effect of the addition [...] Read more.

Compared to the conventional deoxidation process with Al or Si-Mn for 55SiCr spring steel production, the possibility of using a Si-Ca-Ba compounded deoxidizer to control the behavior of non-metallic inclusions in spring steel was explored in this study. The effect of the addition sequence of deoxidizer and alloys into molten steel on the morphology, size, and composition of the inclusions was emphatically studied at 1873 K (1600 °C) using a high-temperature electric resistance furnace. The results indicate that adding alloy first can form less harmful inclusions in steel, which are roughly spherical and smaller than 3 μm in diameter, and its inclusion evolution path is MnO-SiO₂-Al₂O₃→CaO-SiO₂-Al₂O₃ and CaO-Al₂O₃-MgO. While adding deoxidizer first, the inclusions in steel are harmful due to its mostly irregular geometry and relatively large size over 5 μm. The inclusion evolution path is Fe-O→CaO-Al₂O₃(-SiO₂) and CaO-Al₂O₃-MgO. The formation and evolution mechanism of inclusions under different addition sequences were discussed. In addition, the solubility limits of MgO from refractory into steel were studied to inhibit its corrosion by molten steel. Full article

(This article belongs to the Special Issue Numerical and Physical Modeling in Steel Refining and Casting)

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13 pages, 3870 KiB

Open AccessArticle

Evaluation of Flux Basicity Concept Geared toward Estimation for Oxygen Content in Submerged Arc Welded Metal

by Guoyou Shao, Zhongqiu Liu, Jun Fan, Yan Guo, Qiong Xu and Jin Zhang

Metals 2022, 12(9), 1530; https://doi.org/10.3390/met12091530 - 16 Sep 2022

Cited by 6 | Viewed by 1663

Abstract

The present study has been undertaken to evaluate the basicity concept of oxygen content estimation subject to submerged arc welded metal. The investigated fluxes cover a wide range of basicity indices from 0.31 to 19.00 at full coverage with acidic, neutral, and basic [...] Read more.

The present study has been undertaken to evaluate the basicity concept of oxygen content estimation subject to submerged arc welded metal. The investigated fluxes cover a wide range of basicity indices from 0.31 to 19.00 at full coverage with acidic, neutral, and basic fluxes. The oxygen content of the submerged arc welded metal (flux oxygen potential) is predicted by employing traditional flux basicity index models and the CALPHAD technique (gas–slag–metal equilibrium model). It is revealed that the gas–slag–metal equilibrium model in this study is capable of remedying the shortcomings of the basicity index models with respect to predicting the oxygen potentials of the fluxes with CaF₂, CaO, SiO₂, MnO, and FeO as major components. This study may provide a vital way to address technical difficulties in flux design. Based on the measured and thermodynamic data, thermodynamic parameters pertinent to flux oxygen potential have been systematically assessed. Full article

(This article belongs to the Section Welding and Joining)

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14 pages, 3590 KiB

Open AccessArticle

Molecular Dynamics Simulations on Effect of Surface Roughness of Amorphous Substrate on Nucleation in Liquid Al

by Hua Men and Zhongyun Fan

Metals 2022, 12(9), 1529; https://doi.org/10.3390/met12091529 - 15 Sep 2022

Cited by 3 | Viewed by 1380

Abstract

In this study, we used molecular dynamics (MD) simulations to investigate the atomic ordering in the liquid aluminum (Al) adjacent to the amorphous substrate with smooth and rough surfaces. This study revealed that the liquid exhibited layering within about 5 atomic layers but [...] Read more.

In this study, we used molecular dynamics (MD) simulations to investigate the atomic ordering in the liquid aluminum (Al) adjacent to the amorphous substrate with smooth and rough surfaces. This study revealed that the liquid exhibited layering within about 5 atomic layers but no visible in-plane atomic ordering at the interface with the smooth amorphous surface, and neither layering nor in-plane atomic ordering with the rough surface of the amorphous substrate. However, the smooth amorphous surface induced some local ordered structure in the liquid at the interface by a structural templating mechanism, which promoted heterogeneous nucleation by creating a 2-dimensional (2D) nucleus in the third layer. The amorphous substrate with a rough surface had no effect on the nucleation in the liquid, leading to the occurrence of homogeneous nucleation with an undercooling 100 K larger than that of heterogeneous nucleation on the smooth amorphous substrate. This study confirmed that structural templating is a general mechanism for heterogeneous nucleation. Full article

(This article belongs to the Special Issue Heterogeneous Nucleation, Grain Initiation and Grain Refinement: Reports from the LiME Research Hub in the UK)

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11 pages, 2960 KiB

Open AccessArticle

Effect of Nb Addition on the Phase Stability, Microstructure, and Mechanical Properties of Powder Metallurgy Ti-5Fe-xNb Alloys

by Balakrishnan Manogar, Fei Yang and Leandro Bolzoni

Metals 2022, 12(9), 1528; https://doi.org/10.3390/met12091528 - 15 Sep 2022

Cited by 3 | Viewed by 1812

Abstract

Ti alloys contemplating the simultaneous addition of Fe and Nb are available in the literature as Fe enhances the strength and Nb improves the biological behaviour of Ti. Nevertheless, casting has been the main manufacturing process, the Nb content is normally ≥10 wt.%, [...] Read more.

Ti alloys contemplating the simultaneous addition of Fe and Nb are available in the literature as Fe enhances the strength and Nb improves the biological behaviour of Ti. Nevertheless, casting has been the main manufacturing process, the Nb content is normally ≥10 wt.%, and no tensile properties are available. In this study, Ti-5Fe-xNb alloys (x = 2, 6, and 9 wt.%) were produced via powder metallurgy, which is more energy efficient than casting, with the aim of understanding the relationship between the mechanical behaviour and the microstructural changes brought about by the progressive addition of a greater amount of Nb. This study shows that the increment of the Nb content reduces the densification of the alloys, as the relative density decreases from 98.2% to 95.0%, but remarkably increases the volume fraction of the stabilised β phase (14→36%). Accordingly, the Ti-5Fe-xNb alloys are characterised by Widmanstätten microstructures, which become finer for higher Nb contents, and progressively higher mechanical properties including yield stress (725–949 MPa), ultimate tensile strength (828–995 MPa), and hardness (66.5–67.6 HRA), but lower elongation to fracture (4.0–5.1%). It is found that the ductility is much more influenced by the presence of the residual pores, whereas the strength greatly depends on the microstructural changes brought about by the addition of the alloying elements. Full article

(This article belongs to the Topic Processing, Analysis, Modelling and Mechanics of Materials and Structures)

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14 pages, 8087 KiB

Open AccessArticle

Formation of the Structure and Properties of Deposited Multilayer Specimens from Austenitic Steel under Various Heat Removal Conditions

by Dmitry A. Chinakhov and Kirill O. Akimov

Metals 2022, 12(9), 1527; https://doi.org/10.3390/met12091527 - 15 Sep 2022

Cited by 3 | Viewed by 1208

Abstract

The effect of side limiters (shaping blocks) on the formation of the structure and hardness of AISI 308LSi stainless steel workpieces obtained by multilayer build-up welding in an argon environment has been studied. The studies were carried out on specimens deposited using graphite [...] Read more.

The effect of side limiters (shaping blocks) on the formation of the structure and hardness of AISI 308LSi stainless steel workpieces obtained by multilayer build-up welding in an argon environment has been studied. The studies were carried out on specimens deposited using graphite limiters, copper limiters and without limiters. As a result of numerical simulation, it was found that the lowest temperatures of the specimen metal are observed when using copper limiters, and the highest when using graphite limiters (different thermal conductivity of materials) in comparison with the temperatures of the specimen obtained without limiters. With the use of graphite limiters, most of the specimen’s metal is in the temperature range of austenite formation (45%) and a more uniform growth of structural elements is observed, without sharp transitions between the deposited layers, in contrast to the other two types of specimens. The high value of the thermal conductivity of copper leads to an increase in the difference in the size of the dendrites between the central and peripheral side parts of the deposited specimen. The highest values of hardness are observed in the specimen obtained using graphite blocks, due to the more active diffusion of δ-ferrite into austenite by an average of 12%, compared with the other investigated specimens, despite the overall increase in size dendrites. The technology of electric arc multilayer build-up welding with the use of shaping graphite blocks makes it possible to produce a workpiece with a uniform structure and properties. The above makes it a promising direction in electric arc additive manufacturing. Full article

(This article belongs to the Special Issue Additive Technologies, Advanced Joining Technology and Study of Weld Joints)

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12 pages, 5891 KiB

Open AccessArticle

Experimental Investigation of the Tribological Contact between Ti6Al4V-EBM Pin and UHMWPE Rotating Sheet for Prosthetic Applications

by Annamaria Visco, Fabio Giudice, Eugenio Guglielmino, Cristina Scolaro and Andrea Sili

Metals 2022, 12(9), 1526; https://doi.org/10.3390/met12091526 - 15 Sep 2022

Cited by 2 | Viewed by 1280

Abstract

This work is aimed at studying the tribological contact between a titanium–aluminum–vanadium alloy pin (Ti6Al4V), produced by Electron Beam Melting (EBM), and a sheet of ultra high molecular weight polyethylene (UHMWPE), which are widely utilized materials for prosthetic applications. Using a “pin on [...] Read more.

This work is aimed at studying the tribological contact between a titanium–aluminum–vanadium alloy pin (Ti6Al4V), produced by Electron Beam Melting (EBM), and a sheet of ultra high molecular weight polyethylene (UHMWPE), which are widely utilized materials for prosthetic applications. Using a “pin on disc” system, tribometric tests of different duration (up to 240 min) were carried out in order to trace the trend of the polymer mass loss as a function of test time. In this way it was possible to identify the stationary phase of adhesive friction, at which the specific wear rate, which characterizes the tribological system under different lubrication conditions, was obtained. As for the pin, no weight losses were measured, while the optical observations on the tip showed a compressive effect after the entire test campaign. Full article

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7 pages, 4004 KiB

Open AccessArticle

Structural Evolution of Bulk Silver during Cold Rolling and Annealing

by Zheda Ning, Qunshou Wang, Dong Zhao, Wenli Pei and Ming Wen

Metals 2022, 12(9), 1525; https://doi.org/10.3390/met12091525 - 15 Sep 2022

Cited by 2 | Viewed by 1325

Abstract

Sputtering target is commonly used in semiconductor manufacturing for the preparation of thin films. Cold rolling and annealing treatment of bulk Ag is the routine process to prepare Ag sputtering target. In this paper, the microstructure evolution of Ag after cold rolling and [...] Read more.

Sputtering target is commonly used in semiconductor manufacturing for the preparation of thin films. Cold rolling and annealing treatment of bulk Ag is the routine process to prepare Ag sputtering target. In this paper, the microstructure evolution of Ag after cold rolling and annealing treatment was studied, and the results showed that annealing temperature affects the recrystallized structure of Ag and that 600 °C/1 h treatment can achieve complete recrystallization. At the same time, the texture evolution was also observed and discussed. Full article

(This article belongs to the Special Issue Metallic Functional Materials)

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22 pages, 6842 KiB

Open AccessArticle

On the Transferability of Fatigue and Cyclic Deformation Data to 100 µm Thin Structures

by Florian Himmelbauer, Gerhard Winter, Florian Grün and Constantin Kiesling

Metals 2022, 12(9), 1524; https://doi.org/10.3390/met12091524 - 15 Sep 2022

Cited by 2 | Viewed by 1382

Abstract

The fatigue properties and cyclic deformation behaviour of materials are usually determined using cylindrical specimens (e.g., Ø7.5 mm). Since the transferability to very small dimensions has not been comprehensively considered so far, this study investigates the transferability of specimen data from high-strength steel [...] Read more.

The fatigue properties and cyclic deformation behaviour of materials are usually determined using cylindrical specimens (e.g., Ø7.5 mm). Since the transferability to very small dimensions has not been comprehensively considered so far, this study investigates the transferability of specimen data from high-strength steel X5CrNiCuNb16-4 to real structures characterised by a wall thickness of 100 µm. Regarding fatigue, extensive calculations demonstrate that for notched specimens and thin structures, both the material-mechanical support factor concept according to the FKM guideline and the point method of the Theory of Critical Distance (TCD) make correct predictions of the local fatigue strength, with a maximum deviation from experimental values of less than 5%. However, the study points out that the TCD is only conditionally applicable for thin-walled structures, as the material parameter

a_{0}

must be significantly smaller than the wall thickness. Regarding the deformation behaviour, the material reveals special flow characteristics in the first hysteresis. Nevertheless, a combined hardening approach is suitable for modelling. The validation of the model by a plastic deformation of the structure seems plausible, although geometric influences prove to be dominant. In conclusion, even 100 µm thin structures can be evaluated using conventional specimen tests and established assessment or modelling methods. Full article

(This article belongs to the Section Structural Integrity of Metals)

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12 pages, 2227 KiB

Open AccessArticle

Metallic Porphyrazine Networks: Synthesis, as Well as Thermal and Optical Properties for Accelerating the Oxidation of Thiols to Their Disulfides

by Tarfah Al-Warhi, Matokah Abualnaja, Ola A. Abu Ali, Hamada H. Abdel-Razik, Sarah M. Albogami and Eman Fayad

Metals 2022, 12(9), 1523; https://doi.org/10.3390/met12091523 - 15 Sep 2022

Cited by 1 | Viewed by 1391

Abstract

A condensation reaction of 2,3,5,6-tetraamino-1,4-benzoquinone 1 with 4,5-Dichloro-3,6-dihydroxy-phthalonitrile 2 produced p-benzoquinone [2,3-b:2,3-b]bis[(5,8-dihydroxybenzopyrazine)-6,7-dinitrile] 3. Utilizing acetic acid with lithium/pentanol, the tetra-nitrile monomer was cyclo-tetramerized, yielding the matching network polymer, tetra p-benzoquinone[2,3-b:2,3-b]. bis[(5,8-dihydroxybenzopyrazino) porphyrazine (2H-Pz) 4a. The equivalent tetra p-benzoquinone[2,3-b:2,3-b]bis[(5,8-dihydroxybenzopyrazino) metallic porphyrazine networks [...] Read more.

A condensation reaction of 2,3,5,6-tetraamino-1,4-benzoquinone 1 with 4,5-Dichloro-3,6-dihydroxy-phthalonitrile 2 produced p-benzoquinone [2,3-b:2,3-b]bis[(5,8-dihydroxybenzopyrazine)-6,7-dinitrile] 3. Utilizing acetic acid with lithium/pentanol, the tetra-nitrile monomer was cyclo-tetramerized, yielding the matching network polymer, tetra p-benzoquinone[2,3-b:2,3-b]. bis[(5,8-dihydroxybenzopyrazino) porphyrazine (2H-Pz) 4a. The equivalent tetra p-benzoquinone[2,3-b:2,3-b]bis[(5,8-dihydroxybenzopyrazino) metallic porphyrazine networks (M-Pz) M = Zn 4b or Ni 4c, were obtained by cyclo-tetramerizing the tetra-nitril monomer 3 using metal salt and quinoline. The synthesized molecules’ elemental analytical results, as well as their IR and NMR spectral data, are consistent with their assigned structures. The prepared compounds have large molecular weights and metal content, indicating that reactions of tetramerization, polymerization, and chelation were all productive. The synthesized porphyrazines were proved to be excellent substrates for oxidizing thiophenol and benzyl thiol to their respective disulfides in atmospheric oxygen. The maximal production of the corresponding disulfides after 15 min was 96 percent for thiophenol and 93 percent for benzyl thiol, respectively. Full article

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19 pages, 16464 KiB

Open AccessArticle

Phase and Microstructure Transition of High Cu Content Cu-W Composite Powder Fabricated by Spray Drying

by Qi Wang, Xiuqing Li, Shizhong Wei, Wenpeng Lou, Liujie Xu and Yucheng Zhou

Metals 2022, 12(9), 1522; https://doi.org/10.3390/met12091522 - 15 Sep 2022

Cited by 1 | Viewed by 1152

Abstract

Cu-W composite powder with various W contents (0, 10, 20, and 30 wt%) has been fabricated by spray drying, calcination, and two-stage hydrogen reduction in this work. The microstructures and phase evolution of Cu-W composite powder were studied by FESEM, HRTEM, and XRD. [...] Read more.

Cu-W composite powder with various W contents (0, 10, 20, and 30 wt%) has been fabricated by spray drying, calcination, and two-stage hydrogen reduction in this work. The microstructures and phase evolution of Cu-W composite powder were studied by FESEM, HRTEM, and XRD. Results show that precursor powder is composed of Cu₂(OH)₃NO₃ and H₂WO₄·H₂O. Spherical CuWO₄ with a particle size of about 50 nm and micron-scale flat flake CuO were obtained when the calcination temperature was 500 °C. Through chemical vapor transport (CVT) during the reduction process, volatile WO₂(OH)₂ continuously migrates to the copper surface and is reduced to W, resulting in a W-coated Cu structure. This coating structure can inhibit the aggregation and growth of copper particles. The particle sizes of Cu-10 wt%W, Cu-20 wt%W, and Cu-30 wt%W composite powders are 9.309 μm, 8.440 μm, and 6.290 μm, reduced by 40.51%, 46.06%, and 59.80%, respectively, compared to the particle size of pure copper powder, 15.648 μm. With increasing W content, the W-coated Cu particles gradually become denser and trend to grow from sphere to flake. Full article

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11 pages, 84258 KiB

Open AccessArticle

Investigation of the Heat Treatment Process and Formation Mechanism of Grain Boundary Serration for GH4795 Superalloy

by Shuo Huang, Wenyun Zhang, Bingchao Xie, Hao Yu, Yongquan Ning and Beijiang Zhang

Metals 2022, 12(9), 1521; https://doi.org/10.3390/met12091521 - 14 Sep 2022

Cited by 2 | Viewed by 1587

Abstract

Heat treatments, including solution treatment and isothermal heat treatment, were conducted to investigate the grain boundary serration of GH4975 superalloy. The two different heat treatment processes could both promote the formation of serrated grain boundaries within the present temperature and soaking time ranges, [...] Read more.

Heat treatments, including solution treatment and isothermal heat treatment, were conducted to investigate the grain boundary serration of GH4975 superalloy. The two different heat treatment processes could both promote the formation of serrated grain boundaries within the present temperature and soaking time ranges, provided that the cooling rates were controlled to be quite slow. The samples subjected to furnace cooling exhibited a more obvious serrated grain boundary morphology by comparison with those subjected to air cooling. The interaction between precipitated phases and grain boundaries was focused to explore the formation mechanisms of serrated grain boundaries within GH4975 superalloy. Heat treatment temperature and soaking time strongly affected the morphology and size of precipitated phases, and consequently influenced the formation of serrated grain boundaries. The directional growth of grain boundary precipitates and its pinning effects on the migration of grain boundaries also affected the grain boundary morphology. Full article

(This article belongs to the Special Issue Characterization and Processing Technology of Superalloys)

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12 pages, 3625 KiB

Open AccessArticle

Cracking during High-Temperature Deformation of a High-Strength Polycrystalline CoNi-Base Superalloy

by Daniel Hausmann, Lisa Patricia Freund, Cecilia Solís, Sven Giese, Mathias Göken, Ralph Gilles and Steffen Neumeier

Metals 2022, 12(9), 1520; https://doi.org/10.3390/met12091520 - 14 Sep 2022

Viewed by 1226

Abstract

The crack susceptibility during processing has a crucial influence on the workability of wrought alloys. In particular, the processing of high-strength alloys that are prone to cracking is challenging and various process parameters have to be optimized to achieve a good formability. The [...] Read more.

The crack susceptibility during processing has a crucial influence on the workability of wrought alloys. In particular, the processing of high-strength alloys that are prone to cracking is challenging and various process parameters have to be optimized to achieve a good formability. The polycrystalline CoNi-base superalloy CoWAlloy1 provides a high potential for high-temperature applications due to it having a large forging window, a high γ′ fraction and excellent creep properties. In order to study its formability during hot rolling, its deformation behavior and susceptibility to cracking were characterized by sub- and supersolvus compression tests at temperatures between 1000–1150 °C. At temperatures around the γ′ solvus temperature, no cracks formed during the compression testing, while at lower temperatures, cracking occurred. Additionally, an in-situ high-temperature small-angle neutron scattering revealed the phase fractions and the precipitate size distributions at different processing temperatures. It was found that a high fraction of γ′ forms during cooling and cracking starts at the surface of the bar, when the hot bar encounters the cold rolls during hot rolling. Apparently, the precipitation of γ′, which causes a high strength and reduced ductility, and the absent recrystallization leads to pronounced crack propagation and limited formability below the γ′ solvus temperature. Full article

(This article belongs to the Special Issue Study of Microstructure Evolution and Deformation Behavior of Superalloys)

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