Metals

18 pages, 8148 KiB

Open AccessArticle

Mechanical Surface Treatment of Titanium Alloy Ti6Al4V Manufactured by Direct Metal Laser Sintering Using Laser Cavitation

by Chieko Kuji and Hitoshi Soyama

Metals 2023, 13(1), 181; https://doi.org/10.3390/met13010181 - 16 Jan 2023

Cited by 4 | Viewed by 1987

Abstract

Additive manufactured (AM) metals are attractive materials for medical implants, as their geometries are directly produced from computer-aided design (CAD)/computer-aided manufacturing (CAM) data. However, the fatigue properties of AM metals are weak compared with bulk metals, which is an obstacle to the practical [...] Read more.

Additive manufactured (AM) metals are attractive materials for medical implants, as their geometries are directly produced from computer-aided design (CAD)/computer-aided manufacturing (CAM) data. However, the fatigue properties of AM metals are weak compared with bulk metals, which is an obstacle to the practical applications of AM metals. To improve the fatigue properties of AM metals, we developed a mechanical surface treatment using laser cavitation. When we irradiate a pulsed laser to a metallic surface in water, laser ablation is generated, and a bubble that behaves like a cavitation is produced. The bubble is referred to as a “laser cavitation”. In the surface treatment using laser cavitation, we use the plastic deformation caused by the impact force at the bubble collapse and pulsed laser energy that produces local melting at the same time. Thus, the mechanical surface treatment using laser cavitation is a type of surface mechanical alloying. In this study, to demonstrate the improvement in the fatigue properties of AM metals, we treated titanium alloy Ti6Al4V, which was manufactured by direct metal laser sintering (DMLS), with laser cavitation, and we evaluated the surface morphology, roughness, residual stress, hardness, and finally tested it using a torsion fatigue test. Unmelted particles on the DMLS surface, which cause fatigue cracks, were melted and resolidified using laser cavitation, resulting in a reduction of the maximum heights of roughness (R_z) of about 75% and the arithmetical mean roughness (R_a) of about 84% of the non-peened one. Although tensile residual stresses of about 80–180 MPa were generated on the as-built surface, compressive residual stresses of about −80 MPa were introduced by laser cavitation. Furthermore, laser cavitation formed Ti₄O₅ oxide film, which increased the surface hardness by about 106%. Finally, we performed torsional fatigue tests and revealed that laser cavitation extended the fatigue life from 19,791 cycles to 36,288 cycles at an applied shear stress (τ_a) at 460 MPa, which is effective in suppressing crack initiation. Full article

(This article belongs to the Special Issue Mechanical Alloying 2022)

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16 pages, 12117 KiB

Open AccessArticle

Control of the Microstructure in a Al₅Co₁₅Cr₃₀Fe₂₅Ni₂₅ High Entropy Alloy through Thermo-Mechanical and Thermal Treatments

by Pablo Pérez, Judit Medina, María Fernanda Vega, Gerardo Garcés and Paloma Adeva

Metals 2023, 13(1), 180; https://doi.org/10.3390/met13010180 - 16 Jan 2023

Cited by 2 | Viewed by 1529

Abstract

The effect of thermos-mechanical processing and thermal treatments on the microstructure of a single phase fcc-based Al₅Co₁₅Cr₃₀Fe₂₅Ni₂₅ high entropy alloy is evaluated in this study. As-cast ingots of the high entropy alloy were thermo-mechanically [...] Read more.

The effect of thermos-mechanical processing and thermal treatments on the microstructure of a single phase fcc-based Al₅Co₁₅Cr₃₀Fe₂₅Ni₂₅ high entropy alloy is evaluated in this study. As-cast ingots of the high entropy alloy were thermo-mechanically processed following different routes involving forging, cold rolling, warm rolling or hot rolling. In addition, the microstructural evolution of highly deformed cold rolled sheets with the annealing temperature was analyzed. The data reveal that a high-volume fraction of the microstructure commences to recrystallize from 600 °C. In the absence of recrystallization, i.e., below 600 °C, the hardness of thermo-mechanically processed and annealed samples was very close. When recrystallization takes place, the thermo-mechanically treated alloys exhibit higher hardness than the annealed alloys because the recrystallized grains are strengthened by dislocations generated in further steps of the processing while the alloys in the annealed condition are free of dislocations. Maximum hardening is found for the alloy warm-rolled at 450 °C and the alloy cold-rolled plus annealing at 500 °C for 1 h. Diffusion of solute atoms to the core of dislocations, pinning its movement, accounts for the additional hardening. Full article

(This article belongs to the Special Issue Microstructural Tailoring of Metals and Alloys)

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15 pages, 5735 KiB

Open AccessArticle

Effect of CeO₂ Content on Melting Performance and Microstructure of CaO-Al₂O₃-SiO₂-MgO Refining Slag

by Bo Zhao, Wei Wu, Jianguo Zhi, Cheng Su and Tonglu Yao

Metals 2023, 13(1), 179; https://doi.org/10.3390/met13010179 - 16 Jan 2023

Cited by 2 | Viewed by 1464

Abstract

CeO₂ can be applied to refining slag to minimize the size of inclusions, speed up the deoxidization process, and adsorb Al₂O₃ inclusions. The impact through which CeO₂ content affects slag’s melting efficiency is still uncertain. The thermal analyzer [...] Read more.

CeO₂ can be applied to refining slag to minimize the size of inclusions, speed up the deoxidization process, and adsorb Al₂O₃ inclusions. The impact through which CeO₂ content affects slag’s melting efficiency is still uncertain. The thermal analyzer was used to measure the thermogravimetric analysis (TG) and differential scanning calorimetry (DSC) curves of the slag melting process. According to the study results, with the increase in CeO₂ content, the melting temperature of slag decreased first and then increased. The slag’s melting point fell from 1364 °C to 1324 °C and then rose to 1503 °C. XRD and SEM were used to analyze the CaO-Al₂O₃-SiO₂-MgO-CeO₂ slag’s microstructure. The mineral-phase structure of CeO₂-containing refining slag was primarily composed of Ca₂SiO₄ and 3CaO·Al₂O₃, MgO, SiO₂, CaO·Al₂O₃, and Ca₈Ce₆Al₆O₂₆. The proportion of 3CaO·Al₂O₃, CaO·Al₂O₃, and Ca₂SiO₄ decreased as the rare-earth-oxide content increased, while the proportion of Ca₈Ce₆Al₆O₂₆ increased. FactSage was used to estimate the equilibrium-phase compositions of slags with various compositions, and a model for predicting melting points was carried out by a linear regression model. Results were obtained through the analysis of equilibrium-phase composition and crystal structure transformation. The main reasons for the melting point decrease were the change of degree of polymerization and the decrease in contents and complete melting temperature of high-melting-point Ca₃Al₂O₆ and Ca₂SiO₄ compounds. The latter increase in melting point was due to the number of Ca₈Ce₆Al₆O₂₆ compounds and precipitation temperature increases and the complexity of the structural-network increases. Full article

(This article belongs to the Special Issue Advances in Refining, Solidification, and Casting of Steels and Alloys)

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21 pages, 12876 KiB

Open AccessArticle

Effects of Elements on the Microstructure and Mechanical Properties of AlCoCrFeNiTi High-Entropy Alloys

by Jingli Zhang, Shewei Xin, Yongqiang Zhang, Ping Guo, Huamei Sun, Ting Li and Cheng Qin

Metals 2023, 13(1), 178; https://doi.org/10.3390/met13010178 - 16 Jan 2023

Cited by 6 | Viewed by 2600

Abstract

AlCoCrFeNiTi high-entropy alloys (HEAs) have attracted much attention because of their excellent mechanical properties. Here, we systemically studied the effects of elements on the microstructure and mechanical properties of AlCoCrFeNiTi HEAs. The results showed that the phase composition and morphology are significantly affected [...] Read more.

AlCoCrFeNiTi high-entropy alloys (HEAs) have attracted much attention because of their excellent mechanical properties. Here, we systemically studied the effects of elements on the microstructure and mechanical properties of AlCoCrFeNiTi HEAs. The results showed that the phase composition and morphology are significantly affected by the elements. With increasing Ti addition, the lattice parameters of the solid solution phase increased slightly, and lattice distortion occurred. Al changes the crystal structure of FCC to BCC and reduces the lattice distortion energy of the alloy. The BCC phase obviously increases with increasing Al content. However, excessive Al, Ti and Cr promote the formation of intermetallic compound phases, while Ni, Fe and Co promote the transformation of the alloy into a solid solution. The properties of AlCoCrFeNiTi HEAs are closely related to their phase composition and morphology. When HEAs consist only of FCC and BCC phases, their ductility and strength are greatly improved. The presence of an intermetallic compound phase in the microstructure can significantly reduce the configurational entropy of adjacent solid solutions, thus reducing the strengthening effect of solid solutions. Additionally, the AlCoCrFeNiTi HEAs with different microstructures show different deformation mechanisms. The deformation of FCC + BCC HEAs with cellular structures is uniform and presents great plasticity and strength. When the cellular-structure HEAs contain equiaxed BCC, thick lamellar BCC/FCC or intermetallic compound phases, cracks tend to occur and propagate along the phase boundary due to the local nonuniform deformation. For AlCoCrFeNiTi HEAs with dendrite structures, after initiation at the phase boundary, the crack does not easily spread to the dendrite FCC phase but causes the interdendritic BCC phase to crack. Full article

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15 pages, 10570 KiB

Open AccessArticle

Analysis of Design Method and Mechanical Properties of Plug-In Composite Shear Wall

by Xiang Sun, Peiyu Liu, Zhelong Jiang, Yuqing Yang, Zhe Wang and Zaigen Mu

Metals 2023, 13(1), 177; https://doi.org/10.3390/met13010177 - 16 Jan 2023

Cited by 1 | Viewed by 1270

Abstract

Assembly buildings are an important direction for the future development of the construction field. They can be prefabricated in the factories and then assembled on-site, which significantly improves construction efficiency. The shear walls are the most important lateral force-resisting elements in building structures, [...] Read more.

Assembly buildings are an important direction for the future development of the construction field. They can be prefabricated in the factories and then assembled on-site, which significantly improves construction efficiency. The shear walls are the most important lateral force-resisting elements in building structures, and at this stage, there are more and more studies on the prefabricated shear wall. In this paper, a new composite shear wall structure is proposed. The composite shear wall is a part of a prefabricated building, which is prefabricated into a single shear wall unit in the factory. During the construction, the upper and lower prefabricated shear wall units are connected by the plug-in. The design methods of splicing connection are given for the design of this composite shear wall structure. Eleven composite wall models under different parameters are established by using the finite element method, especially the fine modeling of the upper and lower connection parts. Compared with the conventional composite shear wall model of the same dimensions, the mechanical behaviors of the two models are similar. In the simulation of cyclic loading, the new composite shear wall shows good ductility and energy dissipation capacity, and also meets the established requirements of building seismic performance. Therefore, it can be concluded that the new prefabricated composite shear walls have good development prospects and application values. Full article

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20 pages, 2322 KiB

Open AccessReview

Using Mini-CT Specimens for the Fracture Characterization of Ferritic Steels within the Ductile to Brittle Transition Range: A Review

by Marcos Sánchez, Sergio Cicero, Mark Kirk, Eberhard Altstadt, William Server and Masato Yamamoto

Metals 2023, 13(1), 176; https://doi.org/10.3390/met13010176 - 15 Jan 2023

Cited by 8 | Viewed by 2159

Abstract

The use of mini-CT specimens for the fracture characterization of structural steels is currently a topic of great interest from both scientific and technical points of view, mainly driven by the needs and requirements of the nuclear industry. In fact, the long-term operation [...] Read more.

The use of mini-CT specimens for the fracture characterization of structural steels is currently a topic of great interest from both scientific and technical points of view, mainly driven by the needs and requirements of the nuclear industry. In fact, the long-term operation of nuclear plants requires accurate characterization of the reactor pressure vessel materials and evaluation of the embrittlement caused by neutron irradiation without applying excessive conservatism. However, the amount of material placed inside the surveillance capsules used to characterize the resulting degradation is generally small. Consequently, in order to increase the reliability of fracture toughness measurements and reduce the volume of material needed for the tests, it is necessary to develop innovative characterization techniques, among which the use of mini-CT specimens stands out. In this context, this paper provides a review of the use of mini-CT specimens for the fracture characterization of ferritic steels, with particular emphasis on those used by the nuclear industry. The main results obtained so far, revealing the potential of this technique, together with the main scientific and technical issues will be thoroughly discussed. Recommendations for several key topics for future research are also provided. Full article

(This article belongs to the Special Issue Deformation, Fracture and Microstructure of Metallic Materials)

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13 pages, 2420 KiB

Open AccessArticle

The Effect of Bio-Coal Agglomeration and High-Fluidity Coking Coal on Bio-Coke Quality

by Asmaa A. El-Tawil, Bo Björkman, Maria Lundgren and Lena Sundqvist Ökvist

Metals 2023, 13(1), 175; https://doi.org/10.3390/met13010175 - 15 Jan 2023

Viewed by 1478

Abstract

Metallurgical coke with high strength and low reactivity is used in the ironmaking blast furnace. Replacement of some coking coal with bio-coal was shown to result in lower strength and higher reactivity of produced coke due to introduction of reactive bio-coal carbon and [...] Read more.

Metallurgical coke with high strength and low reactivity is used in the ironmaking blast furnace. Replacement of some coking coal with bio-coal was shown to result in lower strength and higher reactivity of produced coke due to introduction of reactive bio-coal carbon and ash components catalyzing the Boudouard reaction, but also due to lowering of the coking coal blend fluidity, which influences coke strength and reactivity negatively. The current study aims to investigate the possibility to counteract negative impact from bio-coal addition on fluidity and coke reactivity by using high-fluidity coking coal and by agglomeration of bio-coal before addition. Original bio-coal and micro-agglomerate of bio-coal was added at 10%, 15% and 20% to the coking coal blend. The influence of bio-coals on the coke reactivity was measured by using CO₂ in a thermogravimetric analyzer. Selected cokes and bio-cokes were produced in technical scale, and their reactivity and strength were measured in standard tests. The effect on dilatation of adding bio-coal or crushed agglomerates of bio-coal to the coking coal blends was measured in an optical dilatometer. The results show that by using a coking coal blend containing high-fluidity coal with agglomerated bio-coal, the max. contraction is increased, whereas the opposite occurs by using original bio-coal. The results show overlapping between contraction occurring before dilatation and during dilation, which affects max. dilatation. The bio-coke containing high-fluidity coal with agglomerated bio-coal has lower reactivity in comparison to bio-cokes with original bio-coal or bio-coke with agglomerated bio-coal produced from a coking coal blend without high-fluidity coal. The reactivity of coke produced in technical scale, as measured in CRI/CSR tests, shows a similar trend regarding reactivity, as measured by thermogravimetric analysis, on coke produced in laboratory scale. Full article

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22 pages, 15838 KiB

Open AccessArticle

Research on Buckling Load of Cylindrical Shell with an Inclined through Crack under External Pressure and Its Solution

by Shou-Chao Li, Yu-Chen Zhang, Le Chang, Chang-Yu Zhou and Xiao-Hua He

Metals 2023, 13(1), 174; https://doi.org/10.3390/met13010174 - 15 Jan 2023

Cited by 2 | Viewed by 1485

Abstract

In order to evaluate the reliability of cracked cylindrical shell effectively and reasonably, study the load capacity of cracked structures and understand the failure modes of cracked structures, in this paper the finite element method is adopted for cylindrical shells with mixed mode [...] Read more.

In order to evaluate the reliability of cracked cylindrical shell effectively and reasonably, study the load capacity of cracked structures and understand the failure modes of cracked structures, in this paper the finite element method is adopted for cylindrical shells with mixed mode crack. The finite element models of cylindrical shell with an inclined through crack under external pressure were established by finite element method, the elastic and elastic-plastic buckling loads were calculated. The influences of crack length (c), crack angle (θ), cylindrical shell length-radius ratio (L/R), radius-thickness ratio (R/T), boundary conditions on buckling load were explored. The analysis of cracked cylindrical shells with simple support on buckling load shows that the load bearing capacity of cracked cylindrical shells decreases with the increase of length- radius ratio, radius-thickness ratio and crack inclination angle. The increase of crack length can weaken the bearing capacity of cylindrical shell. The variation of elastic-plastic buckling load is consistent with that of elastic buckling load. Under the clamped support, the variation of buckling load is consistent with the buckling load of cracked cylindrical shell with simple support, and the buckling load of cracked cylindrical shell with clamped support is evidently higher than that of simple support. The post-buckling analysis further shows that the changes of crack inclination angle and crack length do not affect the variation modes of pre-buckling and post-buckling deformation of cracked cylindrical shells, but affect the load capacity. The relationship between buckling load of different boundary conditions (simply supported and clamp-supported) and geometrical parameters (length-radius ratio, radius-thickness ratio, crack length and crack Angle) was obtained by nonlinear regression. The results of solution can predict the buckling load of cylindrical shell with an inclined through crack. Full article

(This article belongs to the Special Issue Fracture Mechanics of Metals)

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14 pages, 2893 KiB

Open AccessArticle

Effect of Heat Treatments on Microstructure and Mechanical Properties of Low-Cost Ti-6Al-4V Alloy Produced by Thermomechanical Powder Consolidation Route

by Ajit Pal Singh, Rob Torrens, Brian Gabbitas and Giribaskar Sivaswamy

Metals 2023, 13(1), 173; https://doi.org/10.3390/met13010173 - 14 Jan 2023

Viewed by 1521

Abstract

This paper investigates the level of properties enhancement achievable by heat-treating Ti-6Al-4V alloy produced from a blended powder mixture using a thermomechanical powder consolidation route involving warm uniaxial pressing and vacuum sintering followed by extrusion at super transus temperature (1150 °C). The as-extruded [...] Read more.

This paper investigates the level of properties enhancement achievable by heat-treating Ti-6Al-4V alloy produced from a blended powder mixture using a thermomechanical powder consolidation route involving warm uniaxial pressing and vacuum sintering followed by extrusion at super transus temperature (1150 °C). The as-extruded material with a higher oxygen content of 0.55 wt.% was subjected to two different sub-transus annealing treatments: HT-A: 955 °C/1 h-furnace cooling and HT-B: 925 °C/4 h-cooling @ 50 °C/h to 760 °C-furnace cooling. Room temperature Charpy v-notch impact toughness tests and tensile tests were performed to ascertain the effect of microstructural changes during post-extrusion annealing treatments. After impact tests, analysis of microstructures and fracture surfaces of samples was carried out using optical and scanning electron microscopy. The as-extruded material displayed mean impact toughness of 4 J along with a yield strength of 956 MPa, an ultimate tensile strength of 1150 MPa, and an elongation to fracture of 2.4%. The annealing treatments gave a noticeable enhancement in the impact toughness (average values 5–6 J obtained) while maintaining a yield strength and ultimate tensile strength level of about 992 MPa and 1164–1181 MPa, respectively. Additionally, the level of change in ductility was limited for each sub-transus annealing treatment, and HT-A has given only a 30% increase compared to as-extruded material. Full article

(This article belongs to the Special Issue Hot Forming/Processing of Metallic Materials)

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13 pages, 4920 KiB

Open AccessFeature PaperArticle

Rapid Electrodeposition and Corrosion Behavior of Zn Coating from a Designed Deep Eutectic Solvent

by Jiayi Chen, Mengjun Zhu, Mingtao Gan, Xiuli Wang, Changdong Gu and Jiangping Tu

Metals 2023, 13(1), 172; https://doi.org/10.3390/met13010172 - 14 Jan 2023

Cited by 5 | Viewed by 1951

Abstract

This work aimed to develop a new type of deep eutectic solvent containing high concentrations of zinc ions as an electrolyte to improve the electrodeposition rate for zinc plating. Two typical deep eutectic solvent systems, choline chloride (ChCl)–urea and ChCl–ethylene glycol (EG), were [...] Read more.

This work aimed to develop a new type of deep eutectic solvent containing high concentrations of zinc ions as an electrolyte to improve the electrodeposition rate for zinc plating. Two typical deep eutectic solvent systems, choline chloride (ChCl)–urea and ChCl–ethylene glycol (EG), were combined to prepare a stable electrolyte at room temperature with a zinc ion concentration up to 2 M. Cyclic voltammetry experiments of the electrolyte at different temperatures were conducted. The effects of key electrodeposition parameters (bath temperature and current density) on the morphology, structure, and corrosion resistance of zinc coatings deposited on mild steel were investigated. It was found that the crystal orientation of the as-deposited zinc particle is related to the electrodeposition temperature and current density. The experimental results show that the zinc coating deposited at 60 °C and the current density of 4 mA·cm⁻² exhibited the most compact and crack-free morphology, thus had the optimum corrosion resistance property. Full article

(This article belongs to the Special Issue Recent Surface Treatments of Metals and Their Alloys)

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15 pages, 3457 KiB

Open AccessReview

WC-Based Cemented Carbides with High Entropy Alloyed Binders: A Review

by Boris Straumal and Igor Konyashin

Metals 2023, 13(1), 171; https://doi.org/10.3390/met13010171 - 14 Jan 2023

Cited by 10 | Viewed by 2417

Abstract

Cemented carbides have belonged to the most important engineering materials since their invention in the 1920s. Commonly, they consist of hard WC grains embedded in a cobalt-based ductile binder. Recently, attempts have been made to substitute the cobalt using multicomponent alloys without a [...] Read more.

Cemented carbides have belonged to the most important engineering materials since their invention in the 1920s. Commonly, they consist of hard WC grains embedded in a cobalt-based ductile binder. Recently, attempts have been made to substitute the cobalt using multicomponent alloys without a principal component (also known as high entropy alloys—HEAs). HEAs usually contain at least five components in more or less equal amounts. The substitution of a cobalt binder with HEAs can lead to the refinement of WC grains; it increases the hardness, fracture toughness, corrosion resistance and oxidation resistance of cemented carbides. For example, a hardness of 2358 HV, fracture toughness of 12.1 MPa.m^1/2 and compression strength of 5420 MPa were reached for a WC-based cemented carbide with 20 wt.% of the equimolar AlFeCoNiCrTi HEA with a bcc lattice. The cemented carbide with 10 wt.% of the Co₂₇.₄Cr₁₃.₈Fe₂₇.₄Ni₂₇.₄Mo₄ HEA with an fcc lattice had a hardness of 2141 HV and fracture toughness of 10.5 MPa.m^1/2. These values are higher than those for the typical WC–10 wt.% Co composite. The substitution of Co with HEAs also influences the phase transitions in the binder (between the fcc, bcc and hcp phases). These phase transformations can be successfully used for the purposeful modifications of the properties of the WC-HEA cemented carbides. The shape of the WC/binder interfaces (e.g., their faceting–roughening) can influence the mechanical properties of cemented carbides. The most possible reason for such a behavior is the modification of conditions for dislocation glide as well as the development and growth of cracks at the last stages of deformation. Thus, the substitution of a cobalt binder with HEAs is very promising for the further development of cemented carbides. Full article

(This article belongs to the Special Issue Microstructure, Properties and Modelling of High-Entropy Alloys)

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12 pages, 20820 KiB

Open AccessArticle

Effect of Copper on Microstructure and Corrosion Resistance of Hot Rolled 301 Stainless Steel

by Na Li, Hangxin Yan, Xuyuan Wang, Lei Xia, Yuchuan Zhu, Yan Li and Zhengyi Jiang

Metals 2023, 13(1), 170; https://doi.org/10.3390/met13010170 - 14 Jan 2023

Cited by 2 | Viewed by 1657

Abstract

The effect of copper (Cu) on hot-rolled 301 austenitic stainless steel (ASS) was studied by observing the microstructures and testing the electrochemical corrosion resistance properties. The results showed that, with the increase in Cu content, the size of shear zones in 301 ASS [...] Read more.

The effect of copper (Cu) on hot-rolled 301 austenitic stainless steel (ASS) was studied by observing the microstructures and testing the electrochemical corrosion resistance properties. The results showed that, with the increase in Cu content, the size of shear zones in 301 ASS decreased, and the number increased, which increased the uniformity of the microstructure macroscopically. The presence of Cu decreased the stacking fault energy of 301 ASS at elevated temperatures. Meanwhile, the amount of chromium (Cr) carbides decreased gradually with the increase in Cu content, which implies that the solid solution of Cu in hot-rolled 301 stainless steel promotes the solid solution of Cr and C in the steel, which is conducive to the formation of Cr-rich passivation films. As a result, the corrosion resistance of hot rolled Cu-bearing 301 stainless steel is improved, with both lower corrosion current density (I_corr) and passivation current (I_pass), and more positive corrosion potentials (E_corr) and passivation potential (E_p), even though it does not show a higher pitting resistance. As Cu content in the steel was increased from 0.4% to 1.1%, the corrosion resistance was not further improved. Full article

(This article belongs to the Special Issue Trends in Technology of Surface Engineering of Metals and Alloys)

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23 pages, 3087 KiB

Open AccessArticle

Machine Learning Potential Model Based on Ensemble Bispectrum Feature Selection and Its Applicability Analysis

by Jiawei Jiang, Li-Chun Xu, Fenglian Li and Jianli Shao

Metals 2023, 13(1), 169; https://doi.org/10.3390/met13010169 - 13 Jan 2023

Cited by 3 | Viewed by 1431

Abstract

With the continuous improvement of machine learning methods, building the interatomic machine learning potential (MLP) based on the datasets from quantum mechanics calculations has become an effective technical approach to improving the accuracy of classical molecular dynamics simulation. The Spectral Neighbor Analysis Potential [...] Read more.

With the continuous improvement of machine learning methods, building the interatomic machine learning potential (MLP) based on the datasets from quantum mechanics calculations has become an effective technical approach to improving the accuracy of classical molecular dynamics simulation. The Spectral Neighbor Analysis Potential (SNAP) is one of the most commonly used machine learning potentials. It uses the bispectrum to encode the local environment of each atom in the lattice. The hyperparameter j_max controls the mapping complexity and precision between the local environment and the bispectrum descriptor. As the hyperparameter j_max increases, the description will become more accurate, but the number of parameters in the bispectrum descriptor will increase dramatically, increasing the computational complexity. In order to reduce the computational complexity without losing the computational accuracy, this paper proposes a two-level ensemble feature selection method (EFS) for a bispectrum descriptor, combining the perturbation method and the feature selector ensemble strategy. Based on the proposed method, the feature subset is selected from the original dataset of the bispectrum descriptor for building the dimension-reduced MLP. As a method application and validation, the data of Fe, Ni, Cu, Li, Mo, Si, and Ge metal elements are used to train the linear regression model based on SNAP for predicting these metals’ atomic energies and forces them to evaluate the performance of the feature subsets. The experimental results show that, compared to the features of SNAP and qSNAP, the training complexity improvement of our EFS method on the qSNAP feature is more effective than SNAP. Compared with the existing methods, when the feature subset size is 0.7 times that of the original features, the proposed EFS method based on the SSWRP ensemble strategy can achieve the best performance in terms of stability, achieving an average stability of 0.94 across all datasets. The training complexity of the linear regression model is reduced by about half, and the prediction complexity is reduced by about 30%. Full article

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12 pages, 4167 KiB

Open AccessArticle

The Preparation, Corrosion Resistance and Formation Mechanism of a New-Type Mo-Based Composite Conversion Coating on 6061 Aluminum Alloy

by Xuzheng Qian, Feng Huang, Xu Teng, Yiqun Wang, Yingsong Fang, Jingjing Pan, Wenhao Wang, Yingpeng Li and Wen Zhan

Metals 2023, 13(1), 168; https://doi.org/10.3390/met13010168 - 13 Jan 2023

Cited by 1 | Viewed by 1121

Abstract

This paper aims to explore a new-type Mo-based composite conversion coating on 6061 aluminum alloy, systematically evaluate its corrosion resistance, and further reveal the formation mechanism. The effects of pH, conversion time (CTI) and H₂ZrF₆ content on the corrosion resistance [...] Read more.

This paper aims to explore a new-type Mo-based composite conversion coating on 6061 aluminum alloy, systematically evaluate its corrosion resistance, and further reveal the formation mechanism. The effects of pH, conversion time (CTI) and H₂ZrF₆ content on the corrosion resistance were determined by the dropping test and electrochemical tests, and the average corrosion rate (ACR) in neutral 3.5 wt.% NaCl solution under different temperatures was calculated by the immersion test. The micro-morphology and phase compositions were systematically investigated by SEM, EDS and XPS. The results showed that the optimal pH and CTI were 4.5 and 12 min respectively, and the most suitable addition amount of H₂ZrF₆ was 1.2 mL/L. The micro-morphology of the Mo/Ti/Zr conversion coating (MoTiZrCC) under the best conversion condition was relatively smooth and dense, and its phase compositions mainly consisted of MoO₃, Mo₂O₅, TiO₂, ZrO₂ and Al₂O₃. The MoTiZrCC could significantly improve corrosion resistance with the lower icorr and higher R_p, and the ACR of the MoTiZrCC could be reduced to 16.7% of the Al alloy matrix. Additionally, based on the above results, the formation mechanism for the MoTiZrCC was logically deduced. Full article

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

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22 pages, 8929 KiB

Open AccessArticle

Effect of EMBr on Flow in Slab Continuous Casting Mold and Industrial Experiment of Nail Dipping Measurement

by Limin Zhang, Pengcheng Xiao, Yan Wang, Caijun Zhang and Liguang Zhu

Metals 2023, 13(1), 167; https://doi.org/10.3390/met13010167 - 13 Jan 2023

Cited by 1 | Viewed by 1620

Abstract

In this study, a funnel mold (FM) model of a multi-mode electromagnetic braking (EMBr) device was developed, and the magnetic flux density at different currents was obtained by MAXWELL software. By using the magnetohydrodynamics (MHD) module of FLUENT software, the volume of fluid [...] Read more.

In this study, a funnel mold (FM) model of a multi-mode electromagnetic braking (EMBr) device was developed, and the magnetic flux density at different currents was obtained by MAXWELL software. By using the magnetohydrodynamics (MHD) module of FLUENT software, the volume of fluid binomial flow turbulence model and the EMBr mathematical model of the steel/slag flow field were coupled, and the characteristics of the molten steel flow and the liquid-level fluctuation in the 1520 mm × 90 mm FM with the casting speed of 6 m/min were calculated under the effect of the electromagnetic field. The FM liquid-level characteristic information under production conditions was obtained in a nail board industrial experiment and compared with the magnetic-fluid coupling model. The results show that the EMBr can significantly change the flow behavior of molten steel. When the magnetic pole current is not less than 800-600 A, the maximum liquid-level fluctuation height decreases from 18 mm without EMBr to less than 5 mm, and the liquid-level cannot easily entrap slag. Considering the EMBr effect and production cost, the reasonable magnetic pole current should be 800-600 A. The reliability of numerical simulation was also verified by the industrial test results of the nail board. Full article

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25 pages, 6539 KiB

Open AccessArticle

Interpretable Calibration of Crystal Plasticity Model Using a Bayesian Surrogate-Assisted Genetic Algorithm

by Shuaiyi Yang, Xuefeng Tang, Lei Deng, Pan Gong, Mao Zhang, Junsong Jin and Xinyun Wang

Metals 2023, 13(1), 166; https://doi.org/10.3390/met13010166 - 13 Jan 2023

Cited by 1 | Viewed by 1404

Abstract

The accurate calibration of material parameters in crystal plasticity models is essential for applying crystal plasticity (CP) simulations. Identifying these parameters usually requires unfeasible single-crystal experiments or expensive time costs due to the use of traditional genetic algorithm (GA) optimization. This study proposed [...] Read more.

The accurate calibration of material parameters in crystal plasticity models is essential for applying crystal plasticity (CP) simulations. Identifying these parameters usually requires unfeasible single-crystal experiments or expensive time costs due to the use of traditional genetic algorithm (GA) optimization. This study proposed an efficient and interpretable method for calibrating the constitutive parameters with macroscopic mechanical tests. This approach utilized the Bayesian neural network (BNN)-based surrogate-assisted GA (SGA) optimization method to identify a group of constitutive parameters that can reproduce the experimental stress–strain curve and crystallographic orientation by crystal plasticity simulation. The proposed approach was performed on the calibration of typical high-entropy alloy material parameters in two different CP models. The use of the surrogate model reduces the call count of simulation in the parameter searching process and speeds up the calibration significantly. With the help of infill sampling, the accuracy of this optimization method is consistent with the CP simulation and not limited by the accuracy of the surrogate model. Another merit of this method is that the pattern that the BNN surrogate found in the model parameters can be interpreted with its integrated gradients, which helps us to understand the relationship between constitutive parameters and the output mechanical response. The interpretation of BNN can guide further experiment design to decouple particular parameters and add constraints provided by the attached experiment or prior knowledge. Full article

(This article belongs to the Special Issue Plastic Forming, Microstructure, and Property Optimization of Metals)

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10 pages, 16090 KiB

Open AccessArticle

Evolution of the Shadow Effect with Film Thickness and Substrate Conductivity on a Hemispherical Workpiece during Magnetron Sputtering

by Huaiyuan Liu, Donglin Ma, Yantao Li, Lina You and Yongxiang Leng

Metals 2023, 13(1), 165; https://doi.org/10.3390/met13010165 - 13 Jan 2023

Cited by 1 | Viewed by 1460

Abstract

When depositing films on a complex workpiece surface by magnetron sputtering, the shadow effect occurs and causes the columnar structure to tilt toward the substrate owing to the oblique incident angle of the plasma flux, affecting the microstructure and properties of the films. [...] Read more.

When depositing films on a complex workpiece surface by magnetron sputtering, the shadow effect occurs and causes the columnar structure to tilt toward the substrate owing to the oblique incident angle of the plasma flux, affecting the microstructure and properties of the films. Improving the surface diffusion could alleviate the shadow effect, whereas changing the energy of the deposited particles could improve surface diffusion. Different substrate conductivities could affect the energy of the deposited particles when they reach the substrate. In this study, Si (semiconductor) and SiO₂ (insulator) sheets are mounted on the inner surface of a hemispherical workpiece, and Ti films with different thicknesses (adjusted by the deposition time) are deposited on the inner surface of the hemispherical workpiece by direct current magnetron sputtering. The results show that there is a threshold thickness and incident angle before the films are affected by the shadow effect. The threshold could be affected by the film thickness, the incident angle, and the conductivity of the substrate. The threshold would decrease as the film thickness or incidence angle increased or the conductivity of the substrate decreased. When the film thickness or incident angle does not reach the threshold, the film would not be affected by the shadow effect. In addition, the film deposited later would tilt the vertical columnar structure of the film deposited earlier. Owing to the different conductivities, the shadow effect manifest earlier for Ti films deposited on the insulator SiO₂ than for films deposited on the semiconductor Si when the film thickness is >500 nm. Full article

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15 pages, 8330 KiB

Open AccessArticle

Numerical Simulation of the Donor-Assisted Stir Material for Friction Stir Welding of Aluminum Alloys and Carbon Steel

by Joseph Maniscalco, Abdelmageed A. Elmustafa, Srinivasa Bhukya and Zhenhua Wu

Metals 2023, 13(1), 164; https://doi.org/10.3390/met13010164 - 13 Jan 2023

Cited by 5 | Viewed by 1437

Abstract

In this research effort, we explore the use of a donor material to help heat workpieces without wearing the tool or adding more heat than necessary to the system. The donor material would typically be a small piece (or pieces) of material, presumably [...] Read more.

In this research effort, we explore the use of a donor material to help heat workpieces without wearing the tool or adding more heat than necessary to the system. The donor material would typically be a small piece (or pieces) of material, presumably of lower strength than the workpiece but with a comparable melting point. The donor, a sandwich material, is positioned between the tool head and the material to be welded, where the tool initially plunges and heats up in the same manner as the parent material that is intended for welding. The donor material heats up subsequent to tool penetration due to friction and as a result heats up the material beneath it. This preheating technique softens the harder parent material, which helps to minimize tool wear and produce better weld performance. The goal is to investigate the use of the donor material as a preheating technique that minimizes wear and tear on the tool head without negatively impacting the structural properties of the weld. To demonstrate the donor material concept, a combination of Cu-Al, Cu-1045 Carbon steel (CS), and Al-1045 CS sets of donor and parent materials were used in the simulation, in addition to control samples Al-Al and CS-CS. We simulated two thicknesses of donor material 25 and 50% of the parent material thickness, respectively. The simulation suggests that the donor material concept generates phenomenal results by reducing the temperature and axial forces for the friction stir welding of aluminum AA6061 and carbon steel 1045. It also assists downstream during welding, resulting from frictional mechanical work which is converted into stored heat. Full article

(This article belongs to the Special Issue Numerical Simulation of Metals Welding Process)

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12 pages, 4477 KiB

Open AccessArticle

Microstructure and High Temperature-Mechanical Properties of TiC/Graphene/Ti6Al4V Composite Formed by Laser Powder Bed Fusion

by Shijie Chang, Wenbo Du, Zhanyong Zhao and Peikang Bai

Metals 2023, 13(1), 163; https://doi.org/10.3390/met13010163 - 12 Jan 2023

Cited by 4 | Viewed by 1877

Abstract

TiC/graphene/Ti6Al4V composites were prepared by laser powder bed fusion using graphene and Ti6Al4V powder. The differences in microstructure and high-temperature mechanical properties between the Ti6Al4V alloy and the TiC/graphene/Ti6Al4V composite were studied. The tensile and microhardness of the two materials were tested at [...] Read more.

TiC/graphene/Ti6Al4V composites were prepared by laser powder bed fusion using graphene and Ti6Al4V powder. The differences in microstructure and high-temperature mechanical properties between the Ti6Al4V alloy and the TiC/graphene/Ti6Al4V composite were studied. The tensile and microhardness of the two materials were tested at 400 °C, 500 °C, and 600 °C; the results of the TiC/graphene/Ti6Al4V composite were 126 MPa, 162 MPa, and 76 MPa and 70 HV, 59 HV, and 61HV, respectively, higher than those of the Ti6Al4V alloy. These results happened because graphene reacted with Ti to form TiC particles, which were homogeneously distributed amongst α’ acicular martensite. The addition of graphene refined the size of the acicular α’ martensite. At the same time, the graphene and TiC particles showed a dispersion-strengthening effect. The mechanical properties of the TiC/graphene/Ti6Al4V composite were improved by the combination of fine-grain strengthening and dispersion strengthening mechanisms. Full article

(This article belongs to the Special Issue 3D Printing of Metal)

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16 pages, 3722 KiB

Open AccessArticle

Experimental Investigation of the Porous Free Zone of Silicon Cemented Layer Obtained through Pack Cementation

by Mihai Ovidiu Cojocaru, Mihai Branzei, Mircea Dan Morariu, Cosmin Mihai Cotrut and Daniela Dragomir

Metals 2023, 13(1), 162; https://doi.org/10.3390/met13010162 - 12 Jan 2023

Viewed by 1120

Abstract

The development of a porous free zone of the silicon cemented layer represents a scientific and technical challenge. The limitation of the effects of the Kirkendall–Frenkel phenomena requires the right control of the thermochemical processing parameters (temperature, time, and chemical) and thorough knowledge [...] Read more.

The development of a porous free zone of the silicon cemented layer represents a scientific and technical challenge. The limitation of the effects of the Kirkendall–Frenkel phenomena requires the right control of the thermochemical processing parameters (temperature, time, and chemical) and thorough knowledge of the related interaction with the specific elements of the metallic matrix of the thermochemically processed product. Through the experimental programming method, the individual and cumulated effects of the thermochemical processing parameters on (Fe-Armco) high-purity iron cemented by silicon in ferrosilicon (FeSi75C) powdered solid media have been quantified. It was concluded that ferrosilicon with silicon concentrations higher than 60% (FeSi75C) represents a redoubtable active component, especially in a temperature range higher than 1100 °C. In the layer cemented with silicon, the presence of nitrogen was also observed, as a direct consequence of the composition of the medium used for cementation. The presence of this element is the predominant result of the manifestation of the ionic phenomenon of adsorption. The correlations between these parameters and the dimension of the porous free zone of the silicon cemented layer in the vicinity of the thermochemically processed surface have been determined. Full article

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13 pages, 3415 KiB

Open AccessArticle

Research on Roll Shape Design for Quarter Wave Control of High-Strength Steel

by Chao Liu, Hairui Wu, Anrui He, Fenjia Wang, Wenquan Sun, Jian Shao, Ruilin Miao, Xuegang Zhou and Bo Ma

Metals 2023, 13(1), 161; https://doi.org/10.3390/met13010161 - 12 Jan 2023

Viewed by 1229

Abstract

Quarter wave defects often occur in high-strength steel production in wide rolling mills, which seriously affect product quality and production stability. The existing shape control actuators, such as roll bending, roll shifting, and CVC roll shape, can not adjust the high-order wave, and [...] Read more.

Quarter wave defects often occur in high-strength steel production in wide rolling mills, which seriously affect product quality and production stability. The existing shape control actuators, such as roll bending, roll shifting, and CVC roll shape, can not adjust the high-order wave, and the upgraded CVCplus roll shape also has limited effects on the quarter wave. Therefore, the MVCplus roll shape is developed based on the superposition principle in order to realize the local roll shape modification at the wave position. Two cosine curves are superposed on the CVC roll shape within the strip width to decrease the reduction at the quarter of the strip width, and maximum reduction is achieved at the position of maximum wave height. The new roll shape can significantly reduce the quarter wave defects in practical application, and has little effect on the adjustment characteristics of the original CVC roll shape. Full article

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12 pages, 4504 KiB

Open AccessArticle

Ablation Mechanism of AlSiB-C/C Composites under an Oxy-Acetylene Torch

by Qiuchen Han, Lei Chang, Zhaoqun Sun, Jiaqi Sun, Zengyan Wei, Pingping Wang, Ziyang Xiu, Huasong Gou, Pengchao Kang and Gaohui Wu

Metals 2023, 13(1), 160; https://doi.org/10.3390/met13010160 - 12 Jan 2023

Cited by 1 | Viewed by 1106

Abstract

In order to improve the ablation resistance of C/C composites, an AlSiB alloy (mass ratio of Al/Si/B = 2:4:1) was used as a dissipative agent to fill the pores of a C/C composites matrix by reactive melt infiltration to prepare AlSiB-C/C composites. The [...] Read more.

In order to improve the ablation resistance of C/C composites, an AlSiB alloy (mass ratio of Al/Si/B = 2:4:1) was used as a dissipative agent to fill the pores of a C/C composites matrix by reactive melt infiltration to prepare AlSiB-C/C composites. The microstructure evolution and ablation behavior of the obtained AlSiB-C/C composites (mass ratio of Al/Si/B = 2:4:1) under oxy-acetylene flame were investigated by SEM after ablating for 25 s, 50 s, 100 s and 150 s. At the beginning of the ablation process, thermal chemical erosion played a leading part. By using the heat-absorption effect of sweating and the sealing protection effect of the oxide layer, AlSiB-C/C composites significantly reduced the ablation surface temperature, and the linear ablation rate was 4.04 μm/s. With the process of ablation, thermal mechanical erosion tended to dominate. The specimen surface could not form a continuous covering of oxide film to slow down the flame scour, resulting in non-uniform ablation and further expansion of the ablation pit. The self-transpiration cooling behavior and the self-sealing of the ablation products of the dissipative agent played an important role in reducing the extent of thermal chemical erosion and preventing matrix ablation. Full article

(This article belongs to the Special Issue Advances in Thermal Protection Composite Materials: Fabrication, Structures, Properties and Applications)

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13 pages, 7793 KiB

Open AccessArticle

Simultaneous Improvement of Strength, Ductility and Damping Capacity of Single β-Phase Mg–Li–Al–Zn Alloys

by Xinhe Yang, Yang Jin, Ruizhi Wu, Jiahao Wang, Dan Wang, Xiaochun Ma, Legan Hou, Vladimir Serebryany, Iya I. Tashlykova-Bushkevich and Sergey Ya. Betsofen

Metals 2023, 13(1), 159; https://doi.org/10.3390/met13010159 - 12 Jan 2023

Cited by 5 | Viewed by 1431

Abstract

Body-centered cubic (BCC) Mg–Li alloy can be effectively strengthened by with the addition of Al and Zn. However, adding excessive amounts result in reduced mechanical properties and damping capacity of the alloy during subsequent heat treatment and deformation. The effects of solution-hot rolling-aging [...] Read more.

Body-centered cubic (BCC) Mg–Li alloy can be effectively strengthened by with the addition of Al and Zn. However, adding excessive amounts result in reduced mechanical properties and damping capacity of the alloy during subsequent heat treatment and deformation. The effects of solution-hot rolling-aging on the mechanical properties and damping capacity of LAZ1333 alloy and LAZ1366 alloy were studied. The solid solution strengthening greatly increases the hardness of the alloy, but the ductility is extremely poor. The AlLi softening phase precipitated during the subsequent hot rolling and aging process greatly improves the ductility of the alloy, but the excess precipitation of in the AlLi softening phase and the solid solution of excess Zn element are not conducive to the substantial improvement of the strength and ductility of the alloy. Excessive addition of alloying elements is detrimental to the damping capacity of the alloy, but the damping capacity of the alloy can be significantly improved by depleting the number of solute atoms through subsequent ageing treatments. The UTS and FE of as-cast LAZ 1333 alloy are 111 MPa and 16.9%, respectively. The as-aged LAZ1333 alloy has the best mechanical properties and damping capacity, and the UTS and FE are increased by 65.8% and 89.3%, respectively, compared to the as-cast alloy, and the damping capacity increased from 0.011 to 0.015. Full article

(This article belongs to the Special Issue Preparation and Processing Technology of Advanced Magnesium Alloys)

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15 pages, 13088 KiB

Open AccessArticle

Microstructure and High-Temperature Mechanical Properties of Mg-1Al-12Y Alloy Containing LPSO Phase

by Qianlong Ren, Shuai Yuan, Jinhui Wang, Deqing Ma, Wei Li and Lei Wang

Metals 2023, 13(1), 158; https://doi.org/10.3390/met13010158 - 12 Jan 2023

Viewed by 1233

Abstract

This paper describes our study on the effect of the long-period stacking order (LPSO) phase on the comprehensive mechanical properties of the as-cast Mg-1Al-12Y (wt. %) alloy. The microstructure and tensile mechanical properties of as-cast alloy and solution treatment alloy were evaluated. The [...] Read more.

This paper describes our study on the effect of the long-period stacking order (LPSO) phase on the comprehensive mechanical properties of the as-cast Mg-1Al-12Y (wt. %) alloy. The microstructure and tensile mechanical properties of as-cast alloy and solution treatment alloy were evaluated. The results showed that α-Mg matrix, Al₂Y phase and β-Mg₂₄Y₅ phase were present in the as-cast alloy. After solution treatment, the β-Mg₂₄Y₅ phase in the alloy was dissolved and the LPSO phase was precipitated. The solution treatment did not cause grain growth or Al₂Y phase change, but the comprehensive mechanical properties of the alloy were significantly improved. This was mainly due to the precipitation of the LPSO phase in the solid solution alloy. In addition, the dissolution of the β-Mg₂₄Y₅ phase after solution treatment could also improve the mechanical properties. The improvement of the comprehensive mechanical properties of solution treatment alloys at room temperature was due to the dispersion strengthening caused by the intragranular LPSO phase dispersed within the alloy, which had a good blocking effect on the movement of dislocations. The ductility of the solid-solution alloy was greatly improved at a high temperature while maintaining high strength because the LPSO phase is kinked, the dislocation density was reduced, and more non-basal slip was activated during the high-temperature tension. Full article

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14 pages, 6175 KiB

Open AccessArticle

The Precipitation Behavior in Al_0.3CoCrFeNi High-Entropy Alloy Affected by Deformation and Annealing

by Jinlong Zhang, Risheng Qiu, Xinu Tan, Xuantong Quan, Bo Song and Qing Liu

Metals 2023, 13(1), 157; https://doi.org/10.3390/met13010157 - 12 Jan 2023

Cited by 1 | Viewed by 1448

Abstract

The effects of deformation and annealing on the precipitation behaviors, including the structure and chemical composition of the L1₂, B2, BCC and σ phases, in Al_0.3CoCrFeNi high entropy alloy were analyzed. Firstly, the thermodynamic factors controlled the precipitation pathway [...] Read more.

The effects of deformation and annealing on the precipitation behaviors, including the structure and chemical composition of the L1₂, B2, BCC and σ phases, in Al_0.3CoCrFeNi high entropy alloy were analyzed. Firstly, the thermodynamic factors controlled the precipitation pathway in as-cast alloys, which led to the L1₂ precipitating homogeneously in the FCC matrix under a low annealing temperature, while the B2 precipitated under a high annealing temperature. In contrast, if the deformation was introduced before annealing, the precipitation pathway of the second phase was completely changed to the B2, BCC and σ phases because of the combination of thermodynamic and kinetic conditions. In particular, the B2 and σ phases promoted the precipitation behavior reciprocally due to the complementary chemical compositions. The elaborate precipitation behaviors of the L1₂, B2, BCC and σ phases were analyzed to identify the phase transformation in the Al_0.3CoCrFeNi HEA. These transformation pathways and elaborate structural features of the L1₂, B2, BCC and σ phases provide various design possibilities for the microstructures and properties of single FCC HEAs. Full article

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

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13 pages, 7610 KiB

Open AccessArticle

Mechanism of Layer Formation during Gas Nitriding of Remelted Ledeburitic Surface Layers on Unalloyed Cast Irons

by Anja Holst, Stefan Kante, Andreas Leineweber and Anja Buchwalder

Metals 2023, 13(1), 156; https://doi.org/10.3390/met13010156 - 12 Jan 2023

Cited by 2 | Viewed by 1403

Abstract

Unalloyed cast iron materials exhibit low tribological and corrosive resistance. In this respect, nitriding has a wide range of applications for steels. In the case of cast iron, the advantageous properties of nitrided layers are impaired by the presence of graphite. Electron beam [...] Read more.

Unalloyed cast iron materials exhibit low tribological and corrosive resistance. In this respect, nitriding has a wide range of applications for steels. In the case of cast iron, the advantageous properties of nitrided layers are impaired by the presence of graphite. Electron beam remelting of cast iron surfaces prior to nitriding removes graphite. The homogeneous ledeburitic microstructure within the approx. 1 mm-thick remelted layer enables the formation of a dense compound layer during subsequent nitriding. The main objective of this study is to investigate the nitriding mechanism of unalloyed ledeburitic microstructures. Due to the complex relationships, investigations were carried out on both conventional ferritic and pearlitic cast irons and Fe-based model alloys containing one to four additional alloying elements, i.e., C, Si, Mn and Cu. The iron (carbo-)nitride composition (γ’, ε) of this compound layer depends on the gas nitriding conditions, the chemical composition of the substrates and the microstructural constituents. As a result, a schematic model of the nitriding mechanism is developed that includes the effects of the nitriding parameters and alloy composition on the phase composition of the nitriding layer. These findings enable targeted parameter selection and a further optimization of both the process and the properties. Full article

(This article belongs to the Special Issue Advances in Metallic Heat Treatment and Surface Engineering)

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19 pages, 10481 KiB

Open AccessReview

by Xiaowu Li, Xianjun Guan, Zipeng Jia, Peng Chen, Chengxue Fan and Feng Shi

Metals 2023, 13(1), 155; https://doi.org/10.3390/met13010155 - 12 Jan 2023

Cited by 7 | Viewed by 2151

Abstract

On the basis of reiterating the concept of grain boundary engineering (GBE), the recent progress in the theoretical models and mechanisms of twin-related GBE optimization and its effect on the mechanical properties is systematically summarized in this review. First, several important GBE-quantifying parameters [...] Read more.

On the basis of reiterating the concept of grain boundary engineering (GBE), the recent progress in the theoretical models and mechanisms of twin-related GBE optimization and its effect on the mechanical properties is systematically summarized in this review. First, several important GBE-quantifying parameters are introduced, e.g., the fraction of special grain boundaries (GBs), the distribution of triple-junctions, and the ratio of twin-related domain size to grain size. Subsequently, some theoretical models for the GBE optimization in face-centered cubic (FCC) metals are sketched, with a focus on the model of “twin cluster growth” by summarizing the in-situ and quasi-in-situ observations on the evolution of grain boundary character distribution during the thermal-mechanical process. Finally, some case studies are presented on the applications of twin-related GBE in improving the various mechanical properties of FCC metals, involving room-temperature tensile ductility, high-temperature strength-ductility match, creep resistance, and fatigue properties. It has been well recognized that the mechanical properties of FCC materials could be obviously improved by a GBE treatment, especially at high temperatures or under high cyclic loads; under these circumstances, the materials are prone to intergranular cracking. In short, GBE has tremendous potential for improving the mechanical properties of FCC metallic materials, and it is a feasible method for designing high-performance metallic materials. Full article

(This article belongs to the Special Issue Deformation, Fracture and Microstructure of Metallic Materials)

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14 pages, 10556 KiB

Open AccessArticle

Effect of Toughness and Ductility on the Cavitation Erosion of Martensitic Stainless Steel

by Lianqing Zhao, Hongxiang Hu and Xuming Guo

Metals 2023, 13(1), 154; https://doi.org/10.3390/met13010154 - 12 Jan 2023

Cited by 4 | Viewed by 1399

Abstract

Martensitic stainless steel containing 13% Cr–4% Ni suffers cavitation erosion (CE) as the common material of hydro turbine impellers. Two 13% Cr–4% Ni stainless steel samples were obtained by different melting and heating processes. One was of relatively low toughness but high ductility [...] Read more.

Martensitic stainless steel containing 13% Cr–4% Ni suffers cavitation erosion (CE) as the common material of hydro turbine impellers. Two 13% Cr–4% Ni stainless steel samples were obtained by different melting and heating processes. One was of relatively low toughness but high ductility (LTHD), and the other was of relatively high toughness but low ductility (HTLD). This paper is to clarify the relationship between the mechanical properties and the CE resistance of the experimental steel samples. The CE of the two materials was studied using an ultrasonic vibration cavitation erosion rig. Mass loss, morphological observation, nanoindentation characterization, and tensile tests were employed to clarify the erosion mechanism. The results showed that LTHD stainless steel had slightly higher ductility, but lower toughness than HTLD material. The mass loss method verified that the CE resistance of LTHD material was higher than that for the HTLD material. In addition, both materials had an incubation stage of 2 h in the distilled water. The SEM revealed that material removal was preferentially initiated from the grain boundaries and slip zone after the incubation period. The ductility could delay the fracture of the material, which contributed more to cavitation erosion resistance than the toughness of the materials. The hardness test showed few relationships with the CE resistance. Full article

(This article belongs to the Special Issue Corrosion and Protection of Metallic Materials)

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11 pages, 2015 KiB

Open AccessFeature PaperArticle

Control of Copper Content in Flash Smelting Slag and the Recovery of Valuable Metals from Slag—A Thermodynamic Consideration

by Sui Xie, Xinhua Yuan, Fupeng Liu and Baojun Zhao

Metals 2023, 13(1), 153; https://doi.org/10.3390/met13010153 - 11 Jan 2023

Cited by 3 | Viewed by 2284

Abstract

To determine slag properties and the factors influencing these properties for optimization of operating conditions in the copper flash smelting process, the composition and microstructures of the quenched smelting and converting slags have been analyzed. Thermodynamic software FactSage 8.2 has been used to [...] Read more.

To determine slag properties and the factors influencing these properties for optimization of operating conditions in the copper flash smelting process, the composition and microstructures of the quenched smelting and converting slags have been analyzed. Thermodynamic software FactSage 8.2 has been used to investigate the effects of matte grade, SO₂ partial pressure, and the Fe/SiO₂ ratio on the liquidus temperature and the copper content of the smelting slag. The possibility to recover valuable metals from the smelting and converting slags through pyrometallurgical reduction by carbon is also discussed. It was found that the flash smelting slag temperature is usually higher than its liquidus temperature and the copper (1.2% Cu) is mainly present in the slag as dissolved copper. In the copper flash smelting process, the copper content in the slag can be decreased by decreasing the Fe/SiO₂ ratio and temperature. In pyrometallurgical slag reduction, most Cu, Mo, and Ni can be recovered as an alloy. The conditions of recovery such as the ratio of smelting slag to converting slag, temperature, and reduction extent have been discussed. Full article

(This article belongs to the Special Issue Fundamentals of Advanced Pyrometallurgy)

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19 pages, 4733 KiB

Open AccessArticle

An Overview of Synthesis and Structural Regulation of Magnetic Nanomaterials Prepared by Chemical Coprecipitation

by Zelin Li, Yuanjun Sun, Songwei Ge, Fei Zhu, Fei Yin, Lina Gu, Fan Yang, Ping Hu, Guoju Chen, Kuaishe Wang and Alex A. Volinsky

Metals 2023, 13(1), 152; https://doi.org/10.3390/met13010152 - 11 Jan 2023

Cited by 4 | Viewed by 2251

Abstract

Magnetic nanomaterials are widely used in biosynthesis, catalysis, as electronic and microwave-absorbing materials, and in environmental treatment because of their high specific surface area, strong magnetism, chemical stability, and good biocompatibility. The chemical coprecipitation method is widely used for the preparation of magnetic [...] Read more.

Magnetic nanomaterials are widely used in biosynthesis, catalysis, as electronic and microwave-absorbing materials, and in environmental treatment because of their high specific surface area, strong magnetism, chemical stability, and good biocompatibility. The chemical coprecipitation method is widely used for the preparation of magnetic nanomaterials due to its simplicity, low cost, and easily-controlled operating conditions. The magnetic nanomaterials prepared by the chemical coprecipitation method are summarized according to the different compositions, including the basic preparation principles, and the factors affecting their morphology, size, and microstructure. The mechanisms of preparing magnetic nanomaterials by chemical precipitation and the process control factors are emphasized. Finally, the preparation of magnetic nanomaterials by chemical coprecipitation is summarized and prospected. Full article

(This article belongs to the Special Issue Preparation of High-Performance Non-ferrous Metals and Composites)

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