Metals

14 pages, 4198 KiB

Open AccessArticle

Analysis of Thickness Variation in 2219 Aluminum Alloy Ellipsoid Shell with Differential Thickness by Hydroforming

by Chen Mo, Yongchao Xu and Shijian Yuan

Metals 2024, 14(10), 1140; https://doi.org/10.3390/met14101140 (registering DOI) - 6 Oct 2024

The process of spinning and machining for heavy plates has the problems of a large amount of machining, large springback, and easy cracking. Aiming to address these issues, we proposed a deep drawing forming method for a plate with differential thickness to manufacture [...] Read more.

The process of spinning and machining for heavy plates has the problems of a large amount of machining, large springback, and easy cracking. Aiming to address these issues, we proposed a deep drawing forming method for a plate with differential thickness to manufacture an integral ellipsoid component with a thin zone in the middle and a thick zone in the periphery. The plate with a differential thickness was initially produced through machining, followed by the execution of deep drawing deformation. During the deformation process of plates with differential thickness, the thin zone is prone to rupture defects. Therefore, a hydroforming method utilizing an elastic auxiliary plate was adopted to solve this problem. Through mechanical analysis and deep drawing experiments, the influences of hydraulic pressure and elastic auxiliary plate on the distributions of thickness and strain were studied, and the influence of friction on hydroforming was analyzed. The results indicate that increasing the hydraulic pressure and setting elastic auxiliary plates can increase the interfacial friction, reduce the thickness thinning rate, and improve the thickness distribution and deformation uniformity within the thin zone. When the hydraulic pressure is 5.2 MPa and the thickness of the elastic plate is 5 mm, the maximum thickness thinning rate of the ellipsoid shell is 8.8%, which is 34% lower than that of the ellipsoid shell obtained via conventional deep drawing. Full article

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14 pages, 2306 KiB

Open AccessArticle

Dynamic Evolution of Local Atomic Environments in a Cu₆₆Zr₃₄ Bulk Metallic Glass

by Luan de Moraes Pereira, Marcela Bergamaschi Tercini, Alejandro Zúñiga and Roberto Gomes de Aguiar Veiga

Metals 2024, 14(10), 1139; https://doi.org/10.3390/met14101139 (registering DOI) - 6 Oct 2024

Abstract

This study presents a molecular dynamics (MD) investigation of the evolution of local atomic environments (LAEs) in a Cu₆₆Zr₃₄ bulk metallic glass (BMG), both at rest and under constant shear deformation. LAEs were characterized using Voronoi polyhedra analysis. Even in [...] Read more.

This study presents a molecular dynamics (MD) investigation of the evolution of local atomic environments (LAEs) in a Cu₆₆Zr₃₄ bulk metallic glass (BMG), both at rest and under constant shear deformation. LAEs were characterized using Voronoi polyhedra analysis. Even in the absence of external load, LAEs frequently transformed into one another due to short-ranged atomic position fluctuations. However, as expected, each transition from one polyhedra to another was balanced by the reverse transition, thereby preserving the proportions of the different polyhedra. Cu-centered icosahedral LAEs were observed to preferentially transform into and from <1,0,9,3,0>, <0,1,10,2,0>, and <0,2,8,2,0> LAEs. Upon applying pure shear, the simulation box was first deformed in one direction up to a strain of 25% and then in the opposite direction to the same strain level. Shear deformation induced large nonaffine atomic displacements in the directions parallel to the shear, which were concentrated in specific regions of the BMG, forming band-like regions. From the onset, shear deformation led to the destabilization of Cu-centered icosahedral LAEs, as indicated by more frequent transitions to and from other polyhedra. Unlike other Cu-centered LAEs, icosahedra were also found to be more sensitive to yielding. The destruction of Cu-centered icosahedra was primarily a result of net transformations into <1,0,9,3,0> and <0,2,8,2,0> LAEs in the BMG subjected to pure shear, with a minor contribution of transformations involving the <0,1,10,2,0> polyhedra. Full article

(This article belongs to the Special Issue Deformation of Metals and Alloys: Theory, Simulations and Experiments—2nd Edition)

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16 pages, 1651 KiB

Open AccessArticle

The Determination of the Elastoplastic and Phase-Field Parameters for Monotonic and Fatigue Fracture of Sintered Steel Astaloy™ Mo+0.2C

by Tomislav Polančec, Tomislav Lesičar and Zdenko Tonković

Metals 2024, 14(10), 1138; https://doi.org/10.3390/met14101138 (registering DOI) - 5 Oct 2024

Abstract

This paper presents a procedure for determining the elastoplastic parameters of phase-field fracture of sintered material. The material considered was sintered steel Astaloy™ Mo+0.2C of three densities: 6.5, 6.8 and 7.1 g/cm³. The stress–strain curve and Wöhler curve, which are experimentally [...] Read more.

This paper presents a procedure for determining the elastoplastic parameters of phase-field fracture of sintered material. The material considered was sintered steel Astaloy™ Mo+0.2C of three densities: 6.5, 6.8 and 7.1 g/cm³. The stress–strain curve and Wöhler curve, which are experimentally obtained, are utilized for validation of the numerical simulations. For modelling of damage evolution, a CCPF (Convergence check phase-field) algorithm was used as a numerical framework. During calibration of the numerical parameters, two-dimensional as well as three-dimensional modelling was used. A comparison of different fatigue degradation functions known from the literature is also made. To improve the efficiency of numerical simulations of fatigue behaviour, the cycle skip technique is also employed. Full article

(This article belongs to the Special Issue Research on Fatigue Behavior of Additively Manufactured Materials)

26 pages, 9197 KiB

Open AccessArticle

Accelerating Laser Powder Bed Fusion: The Influence of Roller-Spreading Speed on Powder Spreading Performance

by Mohamed Awad Salim, Stephen Tullis and Mohamed Elbestawi

Metals 2024, 14(10), 1137; https://doi.org/10.3390/met14101137 (registering DOI) - 5 Oct 2024

Abstract

The powder spreading process is a fundamental element within the laser powder bed fusion (PBF-LP) framework given its pivotal role in configuring the powder bed. This configuration significantly influences subsequent processing steps and ultimately determines the quality of the final manufactured part. This [...] Read more.

The powder spreading process is a fundamental element within the laser powder bed fusion (PBF-LP) framework given its pivotal role in configuring the powder bed. This configuration significantly influences subsequent processing steps and ultimately determines the quality of the final manufactured part. This research paper presents a comprehensive analysis of the impacts of varying spreading speeds, which are enabled by different roller configurations, on powder distribution in PBF-LP. By utilizing extensive Discrete Element Method (DEM) modelling, we systematically examine how spreading speed affects vital parameters within the spreading process, including packing density, mass fraction, and actual layer thickness. Our exploration of various roller configurations has revealed that increasing spreading speed generally decreases packing density and layer thickness for non-rotating, counter-rotating, and forward-rotating rollers with low clockwise rotational speeds (sub-rolling) due to powder dragging. However, a forward-rotating roller with a high clockwise rotational speed (super-rolling) balances momentum transfer, enhancing packing density and layer thickness while increasing surface roughness. This configuration significantly improves the uniformity and density of the powder bed, providing a technique to accelerate the spreading process while maintaining and not reducing packing density. Furthermore, this configuration offers crucial insights into optimizing additive manufacturing processes by considering the complex relationships between spreading speed, roller configuration, and powder spreading quality. Full article

12 pages, 1496 KiB

Open AccessArticle

Microstructure and Wear Resistance of FeCrV15 Coatings by Laser Cladding

by Zhiwei Bi and Tianqing Li

Metals 2024, 14(10), 1136; https://doi.org/10.3390/met14101136 (registering DOI) - 5 Oct 2024

Abstract

Improving the surface performance and service life of 60Si2Mn steel is an important issue in agricultural machinery. A FeCrV15 coating layer may exhibit excellent performance in wear resistance. This research focuses on studying the microstructure and wear resistance of the FeCrV15 coating [...] Read more.

Improving the surface performance and service life of 60Si2Mn steel is an important issue in agricultural machinery. A FeCrV15 coating layer may exhibit excellent performance in wear resistance. This research focuses on studying the microstructure and wear resistance of the FeCrV15 coating layer at various scanning speeds through laser cladding. Microstructure, phase distribution, surface hardness, and wear resistance of the coating layers are analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), a microhardness tester, and laser confocal microscopy. The results indicate that the FeCrV15 alloy coating consists of γ-Fe, V₈C₇, and Cr₇C₃. The microhardness of the FeCrV15 coatings increases with the increase in the scanning speed. At a scanning speed of 8 mm/s, the highest microhardness reaches 727.5 ± 27 HV, approximately 2.5 times higher than the substrate. The friction and wear test of the coating is conducted using a 4 mm diameter Si₃N₄ ball grinding pair. The coatings prepared at different scanning speeds exhibit lower average coefficients of friction and wear rates compared to the substrate. Both the average coefficient of friction and wear rate decrease with increasing scanning speed. At a scanning speed of 8 mm/s, the lowest average coefficient of friction and the lowest wear rate were observed. The main wear mechanisms of the coating are oxidative wear and adhesive wear, with a small amount of abrasive wear. Full article

20 pages, 23822 KiB

Open AccessArticle

Fatigue Life Assessment of Corroded AlSi10MgMn Specimens

by Markus Schönowitz, Stefan Fladischer, Peter Oberreiter, Bernd Maier, Florian Grün and Kathrin Bauer-Troßmann

Metals 2024, 14(10), 1135; https://doi.org/10.3390/met14101135 (registering DOI) - 5 Oct 2024

Abstract

This study investigates the influence of pre-corrosion damage on the fatigue behavior of AlSi10MgMn high-pressure die-cast specimens, using the statistical distribution of corrosion depths. The analysis is conducted on two different surface conditions: an unmachined rough surface (

R_{a} = 5.05

[...] Read more.

This study investigates the influence of pre-corrosion damage on the fatigue behavior of AlSi10MgMn high-pressure die-cast specimens, using the statistical distribution of corrosion depths. The analysis is conducted on two different surface conditions: an unmachined rough surface (

R_{a} = 5.05

μ m

) and a machined, polished surface (

R_{a} = 0.25

μ m

). For the unmachined specimens, the corrosive damage manifests as homogeneously spread localized corrosion, whereas the polished specimens exhibit less uniform but deeper corrosion. The average corrosion depth of the polished specimens is found to be slightly higher (313

μ m

compared to 267

μ m

) with a broader depth distribution. Specimens are tested under a constant bending load amplitude in laboratory conditions at a stress ratio of

R = 0

until fracture. A fracture mechanics-based methodology is developed to assess the remaining fatigue life of corroded specimens, utilizing short and long crack fracture mechanical parameters derived from SENB specimens. This model incorporates a thickness reduction of the critical specimen cross-section based on the corrosion depth distribution and combines it with a small initial crack of the intrinsic defect size (

a_{e f f} = 14

μ m

). Regardless of the surface condition, using the most frequent corrosion depth for thickness reduction provides a good estimate of the long-life fatigue strength, while using the 90th percentile depth allows for a conservative assessment. Full article

(This article belongs to the Special Issue Fatigue Assessment of Metals)

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13 pages, 4520 KiB

Open AccessArticle

Effects of Solidification Thermal Variables on the Microstructure and Hardness of the Silicon Aluminum Bronze Alloy CuAl₆Si₂

by Paulo Henrique Tedardi do Nascimento, Vinicius Torres dos Santos, Ricardo de Luca, Marcio Rodrigues da Silva, Flavia Goncalves Lobo, Rogerio Teram, Mauricio Silva Nascimento, Ronaldo Camara Cozza, Antonio Augusto Couto, Givanildo Alves dos Santos and Anibal de Andrade Mendes Filho

Metals 2024, 14(10), 1134; https://doi.org/10.3390/met14101134 (registering DOI) - 5 Oct 2024

Abstract

The properties of the final product obtained by solidification directly result from the thermal variables during solidification. This study aims to analyze the influence of thermal solidification variables on the hardness, microstructure, and phases of the CuAl₆Si₂ alloy. The material [...] Read more.

The properties of the final product obtained by solidification directly result from the thermal variables during solidification. This study aims to analyze the influence of thermal solidification variables on the hardness, microstructure, and phases of the CuAl₆Si₂ alloy. The material was solidified using unidirectional solidification equipment under non-stationary heat flow conditions, where heat extraction is conducted through a water-cooled graphite base. The thermal solidification variables were extracted using a data acquisition system, and temperature was monitored at six different positions, with cooling rates ranging from 217 to 3 °C/min from the nearest to the farthest position from the heat extraction point. An optical microscope, scanning electron microscope (SEM), and X-ray diffraction (XRD) were used to verify the fusion structure and determine the volumetric fraction of the formed phases. The XRD results showed the presence of β phases, α phases, and possible Fe₃Si₂ and Fe₅Si₃ intermetallics with different morphologies and volumetric fractions. Positions with lower cooling rates showed an increased volume fraction of the α phase and possible intermetallics compared to positions with faster cooling. High cooling rates increased the Brinell hardness of the alloy due to the refined and equiaxed β metastable phase, varying from 143 HB to 126 HB for the highest and lowest rates, respectively. Full article

(This article belongs to the Special Issue Microstructure, Mechanical Properties and Solidification Behavior of Metals and Alloys (2nd Edition))

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12 pages, 717 KiB

Open AccessArticle

Fluidity of Pure Aluminum in a Narrow Channel Die Gap during Die Casting

by Toshio Haga and Hiroshi Fuse

Metals 2024, 14(10), 1133; https://doi.org/10.3390/met14101133 - 4 Oct 2024

Abstract

Fluidity tests of 99.9%Al and 99.7%Al were conducted using a die casting machine equipped with a spiral die with a channel gap of 0.5 mm. The effects of die temperature and plunger speed on the fluidity were investigated. To clarify the flow length [...] Read more.

Fluidity tests of 99.9%Al and 99.7%Al were conducted using a die casting machine equipped with a spiral die with a channel gap of 0.5 mm. The effects of die temperature and plunger speed on the fluidity were investigated. To clarify the flow length for these alloys, ADC12 and Al-X%Fe (X ≤ 1.1) were also cast. A 1.0 mm channel gap was also used to compare the fluidity in a wider gap. The fluidity of 99.9%Al and 99.7%Al at a die temperature of 30 °C and a plunger speed of 0.2 m/s was superior to that at 150 °C and 0.8 m/s when the channel gap was 0.5 mm, and similar results were found for ADC12 and Al-X%Fe. When the die temperature was 30 °C, the fluidity of 99.9%Al and 99.7%Al decreased as the plunger speed increased when the channel gap was 0.5 mm, and similar results were also found for ADC12 and Al-X%Fe. These results did not align with conventional expectations. A discussion of the results based on the peeling and re-melting of the solidified layer was provided. Full article

(This article belongs to the Special Issue Structure and Properties of Aluminium Alloys 2024)

13 pages, 41685 KiB

Open AccessArticle

Evaluating the Effect of Blended and Pure Hydrogen in X60 Pipeline Steel for Low-Pressure Transmission Using Hollow-Specimen Slow-Strain-Rate Tensile Testing

by Rashiga Walallawita, Matthew C. Hinchliff, Dimitry Sediako, John Quinn, Vincent Chou, Kim Walker and Matthew Hill

Metals 2024, 14(10), 1132; https://doi.org/10.3390/met14101132 - 4 Oct 2024

Abstract

This study employs a custom hollow specimen setup to investigate the HE in API 5L X60 pipeline base and welded materials exposed to pure hydrogen and a 20% hydrogen–natural gas blend at 2.07 MPa. Results indicate embrittlement with increasing hydrogen concentration. The base [...] Read more.

This study employs a custom hollow specimen setup to investigate the HE in API 5L X60 pipeline base and welded materials exposed to pure hydrogen and a 20% hydrogen–natural gas blend at 2.07 MPa. Results indicate embrittlement with increasing hydrogen concentration. The base material showed a hydrogen embrittlement index (HEI) of 11.6% at 20% hydrogen and 12.4% at 100% hydrogen. For the welded material, the HEI was 14.6% at 20% hydrogen and 18.0% at 100% hydrogen. Fractography analysis revealed that the base and welded materials exhibited typical ductile fracture features in the absence of hydrogen, transitioning to a mixture of quasi-cleavage and micro-void coalescence (MVC) features in hydrogen environments. Additionally, with hydrogen, increased formation of secondary cracks was observed. Notably, the study identified the Hydrogen-Enhanced Localized Plasticity (HELP) mechanism as a probable contributor to hydrogen-assisted fracture. Full article

(This article belongs to the Special Issue Hydrogen Embrittlement of Metals and Alloys)

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15 pages, 8559 KiB

Open AccessArticle

Characterization of Corrosion Products on TiSi, TiAl, and WTi Coatings

by Oscar Gordillo, Williams Steve Hincapie, Oscar Piamba, Jhon Olaya, José Edgar Alfonso, Gil Capote and Vladimir Trava-Airoldi

Metals 2024, 14(10), 1131; https://doi.org/10.3390/met14101131 - 4 Oct 2024

Abstract

This study investigates the corrosion products present on TiSi, AlTi, and WTi coatings deposited onto Ti6Al4V titanium alloy substrates using the RF sputtering PVD technique. Following deposition, the coatings underwent exposure to a temperature of 600 °C for 100 h. The corroded surfaces [...] Read more.

This study investigates the corrosion products present on TiSi, AlTi, and WTi coatings deposited onto Ti6Al4V titanium alloy substrates using the RF sputtering PVD technique. Following deposition, the coatings underwent exposure to a temperature of 600 °C for 100 h. The corroded surfaces were meticulously characterized to identify the resultant corrosion products. Utilizing scanning electron microscopy (SEM), X-ray diffraction, optical profilometry, and XPS spectroscopy, the coatings were comprehensively examined. Furthermore, Raman mapping with multivariate analysis was employed to determine the spatial distribution of oxides in the coating post-high-temperature corrosion. Additionally, XPS spectroscopy unveiled the presence of species undetected by Raman spectroscopy, such as silicon oxide SiO₂, aluminum oxide Al₂O₃, and tungsten oxide WO₂, in oxidation studies on TiSi, AlTi, and WTi coatings, corroborated by XRD analysis. The results allowed us to propose the corrosion mechanisms of these coatings and to determine that the TiSi coating exhibits a superior high-temperature corrosion response compared to the AlTi and WTi coatings. The AlTi coating experiences aluminum depletion, whereas the WTi coating shows accumulations of tungsten oxides that resemble pitting. Full article

(This article belongs to the Special Issue Advances in Titanium and Titanium Alloys)

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21 pages, 10386 KiB

Open AccessArticle

Microscopic Simulation of RE³⁺ Migration in Ion-Type Rare Earth Ores Based on Navier–Stokes Equation—Exchange Reaction—Ion Migration Coupling

by Dan Wang, Fuyu Wu, Yunzhang Rao, Zhilian Zhao, Wei Xu and Min Han

Metals 2024, 14(10), 1130; https://doi.org/10.3390/met14101130 - 4 Oct 2024

Abstract

In the in-situ leaching method of ionic rare earth, ion exchange reaction between rare earth ions and leaching agent ions is carried out, which allows the rare earth ions to be leached from the ore body as the leaching solution flows through the [...] Read more.

In the in-situ leaching method of ionic rare earth, ion exchange reaction between rare earth ions and leaching agent ions is carried out, which allows the rare earth ions to be leached from the ore body as the leaching solution flows through the pores. This indicates that the leaching process of rare earth ions is closely related to the seepage field, ion exchange field, and ion migration process of the leaching solution. In this study, an ionic rare earth mine located in Longnan of Jiangxi Province was taken as the research object. By conducting nuclear magnetic resonance scanning on the ore samples of this mine and vectorizing the nuclear magnetic resonance images, a two-dimensional geometric model of pores was obtained. Then, COMSOL Multiphysics software was used to establish a coupled numerical model of seepage–exchange–migration of the ionic rare earth mine during the leaching process at the pore scale to study the seepage situation of leaching solution with different injection strengths and concentrations, as well as the exchange and migration process. The results show that increasing the concentration of magnesium ions can increase the difference of ion diffusion concentration, accelerate the forward exchange rate of ions, promote the forward exchange reaction, and improve the concentration gradient of rare earth ions in the leaching solution. The more significant the diffusion effect, the higher the ion migration rate, while at the same time inhibiting the reverse adsorption of rare earth ions, and accelerating the leaching efficiency of rare earth ions. In addition, increasing the strength of the injection solution allows rare earth ions to leach out of the ore body earlier, shortens the leaching cycle, and thus reduces the peak concentration of leached rare earth ions. By analyzing the effects of the strength of the injection solution and leaching concentration on ionic rare earth leaching, the influence of those two factors on engineering economy can be briefly evaluated, which can be provided as a reference for the optimization of ionic rare earth mining technology. Full article

(This article belongs to the Special Issue Advances in Mineral Processing and Hydrometallurgy—3rd Edition)

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9 pages, 3911 KiB

Open AccessArticle

Experimental Investigation on Quasi-Freckle Phenomenon in Single-Crystal-Blade Castings of Superalloys

by Dexin Ma, Lv Li, Yunxing Zhao, Yangpi Deng, Bowen Cheng and Fuze Xu

Metals 2024, 14(10), 1129; https://doi.org/10.3390/met14101129 - 4 Oct 2024

Abstract

During the production of single-crystal superalloy blades, a kind of channel-type defect, named “quasi-freckle”, was found on the casting surface, which is similar to typical freckles in macroscopic appearance but different in microstructure. In the as-cast microstructure of the quasi-freckle channels, the γ/γ’ [...] Read more.

During the production of single-crystal superalloy blades, a kind of channel-type defect, named “quasi-freckle”, was found on the casting surface, which is similar to typical freckles in macroscopic appearance but different in microstructure. In the as-cast microstructure of the quasi-freckle channels, the γ/γ’ eutectic is significantly accumulated and can be dissolved during the solution heat treatment. Since no disoriented grains were detected, the quasi-freckles have a basically identical crystal orientation with the matrix. The quasi-freckle channels actually appear as thermosolutal convection traces in the directional solidification process of single-crystal casting. Because the convection was not strong enough to break dendrite arms, the single-crystal consistency of the castings was not destroyed. However, with the deterioration of the solidification condition and the increase in solutal convection, quasi-freckles often develop into typical freckle defects. Full article

(This article belongs to the Special Issue Research Progress on Fatigue, Corrosion and Mechanical Properties of Advanced Superalloys)

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13 pages, 1855 KiB

Open AccessArticle

Modeling and Parametric Study of Spent Refractory Material Dissolution in an Aluminum Reduction Cell

by Xia Hu, Wenyuan Hou, Wei Liu, Mao Li and Hesong Li

Metals 2024, 14(10), 1128; https://doi.org/10.3390/met14101128 - 3 Oct 2024

Abstract

Utilizing spent refractory material (SRM), generated after the overhaul of aluminum electrolytic cells, as a raw material for producing Al-Si alloys presents an efficient approach towards achieving full resource utilization of SRM. However, a bottleneck restricting this technology has become the dissolution of [...] Read more.

Utilizing spent refractory material (SRM), generated after the overhaul of aluminum electrolytic cells, as a raw material for producing Al-Si alloys presents an efficient approach towards achieving full resource utilization of SRM. However, a bottleneck restricting this technology has become the dissolution of SRM. Based on the heat and mass transfer mechanism, the shrinkage core model of SRM particle dissolution was established. The effects of alumina concentration, silica concentration, electrolyte superheat, particle temperature, and turbulent kinetic energy dissipation rate on the mass dissolution rate and dissolution time of SRM particles were investigated. Calculation results and experimental data were compared to confirm the accuracy of the established model. The results show that by maintaining low alumina and silica concentrations, increasing the electrolyte superheat and particle preheating temperature, and increasing the electrolyte turbulent kinetic energy dissipation rate, SRM particles can dissolve faster. The dissolution of agglomerated particles is greatly influenced by the turbulent kinetic energy dissipation rate and superheat. The present research provides promising guidance for practical application in predicting particle dissolution time, controlling process parameters, and accelerating the dissolution of SRM particles. Full article

14 pages, 12129 KiB

Open AccessArticle

Dislocation Strengthening and Texture Evolution of Non-Oriented Fe-3.3 wt% Si Steel in Double Cold Rolling

by Yijing Gao, Yunbo Xu, Haoran Chen, Bingyu Yuan, Zhenyu Gao and Lifeng Zhou

Metals 2024, 14(10), 1127; https://doi.org/10.3390/met14101127 - 3 Oct 2024

Abstract

An excellent Fe-3.3 wt% Si steel was fabricated by double cold rolling and final annealing. The evolution of the microstructure and texture was studied by optical microscope (OM), X-ray diffraction (XRD), ex situ, and quasi-in situ electron backscattered diffraction (EBSD) to investigate the [...] Read more.

An excellent Fe-3.3 wt% Si steel was fabricated by double cold rolling and final annealing. The evolution of the microstructure and texture was studied by optical microscope (OM), X-ray diffraction (XRD), ex situ, and quasi-in situ electron backscattered diffraction (EBSD) to investigate the recrystallization behavior. Double cold rolling significantly reduced the adverse γ texture in the final annealed sheets, and a stronger η texture was observed. With a reduction ratio of 50% and 65% during double cold rolling, the γ texture almost disappeared, whereas the η texture was obviously improved. Consequently, the texture factor reached its peak, leading to a reduction in iron loss and an enhancement of magnetic induction. By combining texture regulation with dislocation strengthening, the magnetic properties of Fe-3.3 wt% Si steel were improved, and the yield strength also increased. The final sheet exhibiting exceptional magnetic characteristics and enhanced strength attained a reduction in iron loss (P_10/400 = 21.84 W/kg) of 6.43 W/kg, along with an enhancement of magnetic induction (B₅₀ = 1.698 T) of 0.038 T and yield strength (R_p0.2 = 578 MPa) of 37 MPa compared to a single-stage cold rolling process. Full article

(This article belongs to the Special Issue Novel Insights and Advances in Steels and Cast Irons)

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12 pages, 4900 KiB

Open AccessArticle

Effect of Heating Rate on Hydride Reorientation Behavior of Zirconium Alloy Tubes under Non-Stress Loading

by Boning Hui, Mingju Chen, Xinyi Li, Biao Chen, Yuli Li, Jun Zhou, Rongtao Tang and Jinshan Li

Metals 2024, 14(10), 1126; https://doi.org/10.3390/met14101126 - 3 Oct 2024

Abstract

Zirconium alloys are widely used in nuclear water reactors as cladding materials. The cladding materials will absorb hydrogen from high temperature water during the operation of nuclear reactor. In cladding tubes, it has been common sense that circumferential hydrides form without stress, while [...] Read more.

Zirconium alloys are widely used in nuclear water reactors as cladding materials. The cladding materials will absorb hydrogen from high temperature water during the operation of nuclear reactor. In cladding tubes, it has been common sense that circumferential hydrides form without stress, while radial hydrides can form when the hydrides are reoriented under stress loading. In this study, we found that a high heating rate can result in hydride reorientation behavior even without stress. At elevated heating rates, the zirconium alloy clad tube developed a non-uniform strain gradient along the direction of heat conduction. Hydrogen atoms migrate preferentially to areas of elevated stress and precipitate as hydrides that are perpendicular to the direction of tensile stress, resulting in the formation of radial hydrides that appear as “sun spots” macroscopically. Additionally, the high heating rate disrupts the {0001}_α∥{111}_δ, <11–20>_α∥<110>_δ orientation relationship between the hydride and the substrate, which potentially facilitates crack propagation. Full article

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12 pages, 5876 KiB

Open AccessArticle

Effect of Carbon Addition and Mechanical Activation on FeNi Alloys for Permanent Magnet Applications

by Valmir R. da Silva, Øystein S. Fjellvåg, Anuj Pokle, Bjørn C. Hauback and Stefano Deledda

Metals 2024, 14(10), 1125; https://doi.org/10.3390/met14101125 - 2 Oct 2024

Abstract

Tetrataenite is a promising candidate for rare earth-free permanent magnets due to its low cost and intrinsic magnetic properties. This work investigates the effect of combined milling at liquid nitrogen temperatures (cryomilling) and the addition of carbon as an interstitial element for promoting [...] Read more.

Tetrataenite is a promising candidate for rare earth-free permanent magnets due to its low cost and intrinsic magnetic properties. This work investigates the effect of combined milling at liquid nitrogen temperatures (cryomilling) and the addition of carbon as an interstitial element for promoting the formation of tetrataenite. Crystal structure, microstructure, and magnetic properties are investigated to understand the influence of mechanical processing and compositional modifications. No unambiguous evidence of the ordered phase of tetrataenite is found in the structural characterization. However, using Scanning Transmission Electron Microscopy (STEM) and powder X-ray diffraction (PXD) analyses, the occurrence of both twinning and stacking faults resulting from the high-energy milling process is observed, which is a relevant factor for identifying tetrataenite in FeNi alloys. The probability of a stacking fault and twinning occurring for a carbon-free FeNi sample before annealing is found to be 2% and 1.4%, respectively. After annealing, the stacking fault probability decreased to 1.2%, while that of twinning was 1.4%. By increasing the carbon concentration to 5 at.%, the stacking faults and twinning probabilities decrease slightly to 1.2% and 1.3%, respectively. The occurrence of stacking faults combined with small crystallite sizes was a hindering factor in identifying the presence of tetrataenite. Full article

(This article belongs to the Section Crystallography and Applications of Metallic Materials)

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18 pages, 15965 KiB

Open AccessArticle

Numerical Simulation of Gas Atomization and Powder Flowability for Metallic Additive Manufacturing

by Yonglong Du, Xin Liu, Songzhe Xu, Enxiang Fan, Lixiao Zhao, Chaoyue Chen and Zhongming Ren

Metals 2024, 14(10), 1124; https://doi.org/10.3390/met14101124 - 2 Oct 2024

Abstract

The quality of metal powder is essential in additive manufacturing (AM). The defects and mechanical properties of alloy parts manufactured through AM are significantly influenced by the particle size, sphericity, and flowability of the metal powder. Gas atomization (GA) technology is a widely [...] Read more.

The quality of metal powder is essential in additive manufacturing (AM). The defects and mechanical properties of alloy parts manufactured through AM are significantly influenced by the particle size, sphericity, and flowability of the metal powder. Gas atomization (GA) technology is a widely used method for producing metal powders due to its high efficiency and cost-effectiveness. In this work, a multi-phase numerical model is developed to compute the alloy liquid breaking in the GA process by capturing the gas–liquid interface using the Coupled Level Set and Volume-of-Fluid (CLSVOF) method and the realizable k-ε turbulence model. A GA experiment is carried out, and a statistical comparison between the particle-size distributions obtained from the simulation and GA experiment shows that the relative errors of the cumulative frequency for the particle sizes sampled in two regions of the GA chamber are 5.28% and 5.39%, respectively. The mechanism of powder formation is discussed based on the numerical results. In addition, a discrete element model (DEM) is developed to compute the powder flowability by simulating a Hall flow experiment using the particle-size distribution obtained from the GA experiment. The relative error of the time that finishes the Hall flow in the simulation and experiment is obtained to be 1.9%. Full article

(This article belongs to the Special Issue Numerical Simulation and Data-Driven Modeling of Metallic Materials Formed by Laser Additive Manufacturing)

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12 pages, 7808 KiB

Open AccessArticle

Decreasing Electrical Resistivity of Ag Film by Low-Temperature Evaporation and Sintering through Azeotrope Application

by Sang Hoon Jung, Jae Eun Park and Jong-Hyun Lee

Metals 2024, 14(10), 1123; https://doi.org/10.3390/met14101123 - 2 Oct 2024

Abstract

In the temperature-sensitive components, such as perovskite solar cells, large-area electrical connections with high electrical conductivity are also required. To fulfill the requirements, low-temperature evaporation was realized by preparing binder-free pastes with Ag flakes and a solvent mixture, followed by sintering at 140 [...] Read more.

In the temperature-sensitive components, such as perovskite solar cells, large-area electrical connections with high electrical conductivity are also required. To fulfill the requirements, low-temperature evaporation was realized by preparing binder-free pastes with Ag flakes and a solvent mixture, followed by sintering at 140 °C. The mixed solvent was based on viscous α-terpineol with the addition of an appropriate amount of dipropylene glycol methyl ether acetate or diethylene glycol diethyl ether to achieve an azeotrope composition, followed by the addition of a low-molecular-weight hydroxypropyl cellulose to increase the viscosity and thixotropy. During sintering at 140 °C in air for up to 30 min, the paste with 49.5 wt% α-terpineol, 49.5 wt% dipropylene glycol monomethyl ether acetate, and 1 wt% hydroxypropyl cellulose mixture exhibited an excellent electrical conductivity of 7.72 × 10⁻⁶ Ω·cm despite the implementation of low-temperature sintering. The excellent processability of the prepared Ag-based pastes at 140 °C demonstrated their potential for novel application areas. Full article

(This article belongs to the Special Issue Metallic Functional Materials: Development and Applications)

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14 pages, 10343 KiB

Open AccessArticle

Crystallographic Study of Transformation Products of Heat-Affected Zone and Correlation with Properties of FH690 Heavy-Gauge Marine Steel by Multi-Pass Submerged Arc Welding

by Yun Bai, Liqin Bai, Gang Qian, Xianjin Sun, Guanyou Liu, Zhenjia Xie and Chengjia Shang

Metals 2024, 14(10), 1122; https://doi.org/10.3390/met14101122 (registering DOI) - 1 Oct 2024

Abstract

In this work, the microstructure–property relationship of the heat-affected zone (HAZ) of a FH690 ultra-heavy marine steel plate was investigated based on insight of microstructure and crystallographic features. After multi-pass welding with a heat input of ~30 kJ/cm, an ~8 mm wide HAZ [...] Read more.

In this work, the microstructure–property relationship of the heat-affected zone (HAZ) of a FH690 ultra-heavy marine steel plate was investigated based on insight of microstructure and crystallographic features. After multi-pass welding with a heat input of ~30 kJ/cm, an ~8 mm wide HAZ was obtained with a coarse grain HAZ (CGHAZ) of ~3.8 mm, fine grain HAZ (FGHAZ) of ~3.4 mm, and intercritical HAZ (ICHAZ) of ~1 mm. High impact toughness values of ~120 and 140 J at −60 °C were obtained for coarse grain HAZ and fine grain HAZ, respectively. The microstructure of the CGHAZ and FGHAZ was fine lath bainite. Although the average prior austenite grain size for the CGHAZ was ~75 μm, which was five times that of the FGHAZ (15 μm), a high density of high-angle grain boundaries (HAGBs) with misorientation higher than 45° was obtained in the CGHAZ. This is the underlying reason for the excellent low-temperature toughness of the HAZ. Thermo-dynamic calculations indicated that the high density of HAGBs in the CGHAZ was attributed to the decreased bainitic transformation temperature due to the reduced phase transformation driving force via the high nickel addition, leading to weak variant selection. In addition, the high nickel addition offered high hardenability for high hardness in the FGHAZ. The outcome of this study could provide an experimental and fundamental basis for designing high-strength ultra-heavy steel plates with excellent weldability. Full article

(This article belongs to the Section Crystallography and Applications of Metallic Materials)

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