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Metals, Volume 8, Issue 7 (July 2018)

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Cover Story (view full-size image) Welded stainless steel tubes have several critical points during plastic deformation processes, so [...] Read more.
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Open AccessArticle Retained Austenite Control for the Soft Machining of High-Hardness Tool Steels
Metals 2018, 8(7), 564; https://doi.org/10.3390/met8070564
Received: 22 June 2018 / Revised: 19 July 2018 / Accepted: 20 July 2018 / Published: 23 July 2018
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Abstract
Most high-hardness tool steels comprising forming dies require expensive finish machining operations to compensate for the dimensional distortion and surface oxidation caused by the die heat treatment. Precipitation-hardening (PH) tool steels allow for soft finish machining followed by an aging treatment without major
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Most high-hardness tool steels comprising forming dies require expensive finish machining operations to compensate for the dimensional distortion and surface oxidation caused by the die heat treatment. Precipitation-hardening (PH) tool steels allow for soft finish machining followed by an aging treatment without major deformation or oxidation in the die, but exhibit poor wear performance owing to the lack of carbides in their structure. This drawback can be overcome by combining laser cladding technology, austenite retention, and cryogenic treatments. Hence, an alternative die manufacturing route based on laser cladding was explored. The forming surface of a modified chemistry tool steel die was subjected to cladding. The martensite finish (Mf) temperature of the steel was tuned to enhance austenite retention at room temperature. The cladded surface was then machined in a reduced-hardness condition resulting from retained austenite formation. Subsequent deep cryogenic treatment of the die favoured the retained-austenite-to-martensite transformation, thereby increasing the die hardness without major distortion or oxidation. This process combined the advantages of high-carbide-bearing tool steels and PH steels, allowing for a die with hardness exceeding 58 HRC to be finish machined at <52 HRC. Controlling the occurrence of retained austenite represents an effective strategy for achieving new manufacturing scenarios. Full article
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Open AccessArticle Effects of Nb and W Additions on the Microstructures and Mechanical Properties of Novel γ/γ’ Co-V-Ti-Based Superalloys
Metals 2018, 8(7), 563; https://doi.org/10.3390/met8070563
Received: 14 June 2018 / Revised: 1 July 2018 / Accepted: 16 July 2018 / Published: 23 July 2018
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Abstract
Microstructures, elemental partition behavior, phase stabilities and mechanical properties of Nb- and W-containing Co-V-Ti-based superalloys were investigated. Elemental partition coefficients (KX = Cγ’/Cγ) of Nb and W in Co-V-Ti-based superalloys are 2.07 and 1.10, respectively. The γ’
[...] Read more.
Microstructures, elemental partition behavior, phase stabilities and mechanical properties of Nb- and W-containing Co-V-Ti-based superalloys were investigated. Elemental partition coefficients (KX = Cγ’/Cγ) of Nb and W in Co-V-Ti-based superalloys are 2.07 and 1.10, respectively. The γ’ solvus temperatures are determined as 1023 °C, 1055 °C and 1035 °C in Co-12V-4Ti, Co-10V-4Ti-2Nb and Co-10V-4Ti-2W alloys, which are higher than those of Co-9Al-9W alloy (1000 °C). The mass densities of quaternary Co-10V-4Ti-2Nb and Co-10V-4Ti-2W alloys are about 8.31 and 8.50 g·cm−3, respectively, which are 15% lower than Co-Al-W-based superalloys (9.8 g·cm−3). All examined alloys exhibit an anomalous positive dependence on temperature rising from 600 to 750 °C. Strengths of all examined alloys are higher than those of MarM509 (traditional Cobalt-based superalloy) and Co-9Al-9W at all temperatures that we investigated. The maximum flow stress of Co-V-Ti-Nb alloy is about 638 MPa at 750 °C while that of Co-V-Ti-W alloy is about 588 MPa at 700 °C. Full article
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Open AccessArticle Energy Dissipation Characteristics and Dynamic Modeling of the Coated Damping Structure for Metal Rubber of Bellows
Metals 2018, 8(7), 562; https://doi.org/10.3390/met8070562
Received: 23 June 2018 / Revised: 17 July 2018 / Accepted: 19 July 2018 / Published: 23 July 2018
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Abstract
A novel coated damping structure for metal rubber (MR) of bellows is designed based on large-size metal rubber sheets. This structure is dynamically tested in the bending direction at normal temperature. According to the test results, a model of the nonlinear elastic restoring
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A novel coated damping structure for metal rubber (MR) of bellows is designed based on large-size metal rubber sheets. This structure is dynamically tested in the bending direction at normal temperature. According to the test results, a model of the nonlinear elastic restoring force is set up, which describes the dynamic characteristics of the coated damping structure for metal rubber of bellows, and identifies the parameters of the model. The results show that the coated damping structure for metal rubber of bellows has a strong damping energy dissipation ability, its dynamic vibration characteristics are related to the vibration amplitude and frequency, and it is a complex nonlinear hysteretic system with multiple damping components. After identification of the parameters, the model of nonlinear elastic restoring force shows highly accurate results. Full article
(This article belongs to the Special Issue Metals and Alloys for Energy Conversion and Storage Applications)
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Open AccessArticle Recovery of Gold and Iron from Cyanide Tailings with a Combined Direct Reduction Roasting and Leaching Process
Metals 2018, 8(7), 561; https://doi.org/10.3390/met8070561
Received: 25 June 2018 / Revised: 16 July 2018 / Accepted: 19 July 2018 / Published: 21 July 2018
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Abstract
Cyanide tailings are the hazardous waste discharged after gold cyanidation leaching. The recovery of gold and iron from cyanide tailings was investigated with a combined direct reduction roasting and leaching process. The effects of reduction temperature, coal dosage and CaO dosage on gold
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Cyanide tailings are the hazardous waste discharged after gold cyanidation leaching. The recovery of gold and iron from cyanide tailings was investigated with a combined direct reduction roasting and leaching process. The effects of reduction temperature, coal dosage and CaO dosage on gold enrichment into Au-Fe alloy (FexAu1−x) were studied in direct reduction roasting. Gold containing iron powders, i.e., Au-Fe alloy, had the gold grade of 8.23 g/t with a recovery of 97.46%. After separating gold and iron in iron powders with sulfuric acid leaching, ferrous sulfate in the leachate was crystallized to prepare FeSO4·7H2O with a yield of 222.42% to cyanide tailings. Gold enriched in acid-leaching residue with gold grade of 216.58 g/t was extracted into pregnant solution. The total gold recovery of the whole process reached as high as 94.23%. The tailings generated in the magnetic separation of roasted products, with a yield of 51.33% to cyanide tailings, had no toxic cyanide any more. The gold enrichment behaviors indicated that higher reduction temperature and larger dosage of coal and CaO could promote the allocation of more gold in iron phase rather than in slag phase. The mechanism for enriching gold from cyanide tailings into iron phase was proposed. This work provided a novel route to simultaneously recover gold and iron from cyanide tailings. Full article
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Open AccessArticle Production of Clean Steel Using the Nitrogen Elevating and Reducing Method
Metals 2018, 8(7), 560; https://doi.org/10.3390/met8070560
Received: 27 June 2018 / Revised: 16 July 2018 / Accepted: 16 July 2018 / Published: 21 July 2018
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Abstract
Nitrogen Elevating and Reducing Method (NERM) is a new technology developed to remove inclusions and oxygen in molten steel. The principle that underlies it is that nitrogenizing molten steel under low or normal pressure initially elevates the nitrogen content. Then, when the vacuum
[...] Read more.
Nitrogen Elevating and Reducing Method (NERM) is a new technology developed to remove inclusions and oxygen in molten steel. The principle that underlies it is that nitrogenizing molten steel under low or normal pressure initially elevates the nitrogen content. Then, when the vacuum treatment is started, the nitrogen bubbles can nucleate on the surface of the inclusions and carry them to slag, reducing the number of inclusions in steel significantly. The removal effects between the new method and the conventional method were compared by industrial trials in this paper. The results show that the average oxygen content of the billet produced by the conventional method was 16 ppm, while that produced by the new method dropped to 11.5 ppm. Besides, the new method shows better removal effect of inclusions, and the number of inclusions decreased by 52.8% compared to the conventional method. The new method has obvious removal effects on inclusions in different sizes. In addition, the differences between NERM and the Pressure Elevating and Reducing Method (PERM) were compared, and the mechanism of each method was analyzed in this paper. Full article
(This article belongs to the Special Issue 5th UK-China Steel Research Forum)
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Open AccessArticle Influence of Ultrafine Particles on Structure, Mechanical Properties, and Strengthening of Ductile Cast Iron
Metals 2018, 8(7), 559; https://doi.org/10.3390/met8070559
Received: 25 June 2018 / Revised: 13 July 2018 / Accepted: 19 July 2018 / Published: 20 July 2018
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Abstract
Integrated assessment of the influence of an ultrafine mixture TiO2 + ZrO2 + Na3AlF6 on the formation of the structure, mechanical properties, and strengthening of ductile cast iron was made in the paper. The structural-phase composition of ductile
[...] Read more.
Integrated assessment of the influence of an ultrafine mixture TiO2 + ZrO2 + Na3AlF6 on the formation of the structure, mechanical properties, and strengthening of ductile cast iron was made in the paper. The structural-phase composition of ductile cast iron was studied by means of scanning electron microscopy and a transmission electron microscope. Plastic deformation was determined during testing of uniaxial compression. The change in the structural state of the alloy and in its mechanical properties was observed. Quantitative assessment of contributions of separate physical mechanisms to strengthening characteristics of unmodified and modified ductile cast iron was made. Full article
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Open AccessArticle Speciation of Ruthenium(III) Chloro Complexes in Hydrochloric Acid Solutions and Their Extraction Characteristics with an Amide-Containing Amine Compound
Metals 2018, 8(7), 558; https://doi.org/10.3390/met8070558
Received: 29 June 2018 / Revised: 14 July 2018 / Accepted: 16 July 2018 / Published: 20 July 2018
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Abstract
The refining of platinum group metals is based mainly on solvent extraction methods, whereas Ru is selectively recovered by distillation as RuO4. Replacement of distillation by extraction is expected to simplify the purification process. To develop an effective extraction system for
[...] Read more.
The refining of platinum group metals is based mainly on solvent extraction methods, whereas Ru is selectively recovered by distillation as RuO4. Replacement of distillation by extraction is expected to simplify the purification process. To develop an effective extraction system for Ru, we analyzed the Ru species in HCl with ultraviolet-visible (UV-Vis) and Ru K-edge extended X-ray absorption fine structure (EXAFS) spectroscopies, and we examined the properties of Ru extracted with N-2-ethylhexyl-bis(N-di-2-ethylhexyl-ethylamide) amine (EHBAA) and trioctylamine (TOA). EXAFS and UV-Vis spectra of Ru in HCl solutions revealed that the predominant Ru species in 0.5–10 M HCl solutions changed from [RuCl4(H2O)2] to [RuCl6]3− with the HCl concentration. The extraction percentages (E%) of Ru in the EHBAA system increased with increasing HCl concentration, reached 80% at [HCl] = 5 M, and decreased at higher HCl concentrations; the corresponding E% for TOA were low. EXAFS analysis of the extracted complex indicated that the Ru3+ had 5 Cl and 1 H2O in its inner coordination sphere. The similarity of the dependence on HCl concentrations of the E% in the EHBAA system and the distribution profile of [RuCl5(H2O)]2− on [RuCln(H2O)6n]3−n suggested that the EHBAA extracted the pentachlorido species. Full article
(This article belongs to the Special Issue Solvent Extraction of Critical Metals)
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Open AccessArticle An Original Tribometer to Analyze the Behavior of Abrasive Grains in the Grinding Process
Metals 2018, 8(7), 557; https://doi.org/10.3390/met8070557
Received: 10 July 2018 / Revised: 17 July 2018 / Accepted: 18 July 2018 / Published: 20 July 2018
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Abstract
Manufacturing of grinding wheels is continuously adapting to new industrial requirements. New abrasives and new wheel configurations, together with wheel wear control allow for grinding process optimization. However, the wear behavior of the new abrasive materials is not usually studied from a scientific
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Manufacturing of grinding wheels is continuously adapting to new industrial requirements. New abrasives and new wheel configurations, together with wheel wear control allow for grinding process optimization. However, the wear behavior of the new abrasive materials is not usually studied from a scientific point of view due to the difficulty to control and monitor all the variables affecting the tribochemical wear mechanisms. In this work, an original design of pin-on-disk tribometer is developed in a CNC (Computer Numerical Control) grinding machine. An Alumina grinding wheel with special characteristics is employed and two types of abrasive are compared: White Fused Alumina (WFA) and Sol-Gel Alumina (SG). The implemented tribometer reaches sliding speeds of between 20 and 30 m/s and real contact pressures up to 190 MPa. The results show that the wear behavior of the abrasive grains is strongly influenced by their crystallographic structure and the tribometer appears to be a very good tool for characterizing the wear mechanisms of grinding wheels, depending on the abrasive grains. Full article
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Open AccessArticle Recovery of Metals from Secondary Raw Materials by Coupled Electroleaching and Electrodeposition in Aqueous or Ionic Liquid Media
Metals 2018, 8(7), 556; https://doi.org/10.3390/met8070556
Received: 15 June 2018 / Revised: 12 July 2018 / Accepted: 17 July 2018 / Published: 20 July 2018
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Abstract
This paper presents recent views on a hybrid process for beneficiation of secondary raw materials by combined electroleaching of targeted metals and electrodeposition. On the basis of several case studies with aqueous solutions or in ionic liquid media, the paper describes the potential
[...] Read more.
This paper presents recent views on a hybrid process for beneficiation of secondary raw materials by combined electroleaching of targeted metals and electrodeposition. On the basis of several case studies with aqueous solutions or in ionic liquid media, the paper describes the potential and the limits of the novel, hybrid technique, together with the methodology employed, combining determination of speciation, physical chemistry, electrochemistry, and chemical engineering. On one hand, the case of electroleaching/electrodeposition (E/E) process in aqueous media, although often investigated at the bench scale, appears nevertheless relatively mature, because of the developed methodology, and the appreciable current density allowed, and so it can be used to successfully treat electrode materials of spent Zn/MnO2 batteries or Ni/Cd accumulators and Waelz oxide. On the other hand, the use of ionic liquids as promising media for the recovery of various metals can be considered for other types of wastes, as shown here for the case of electrodes of aged fuel cells. The combined (E/E) technique could be successfully used for the above waste, in particular by the tricky selection of ionic liquid media. Nevertheless, further investigations in physical chemistry and chemical engineering appear necessary for possible developments of larger-scale processes for the recovery of these strategic resources. Full article
(This article belongs to the Special Issue Advances in Hydrometallurgy)
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Open AccessArticle A Simple and Efficient Method for Obtaining the Whole-Range Uniaxial Tensile Properties of Pipeline Steel
Metals 2018, 8(7), 555; https://doi.org/10.3390/met8070555
Received: 25 June 2018 / Revised: 12 July 2018 / Accepted: 17 July 2018 / Published: 19 July 2018
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Abstract
To obtain the whole-range true stress-true strain curves of API X65, a method is proposed based on the equal proportion principle and digital images. The tensile elongation was obtained by tracing the gauge points on the specimen surface, and the true strain and
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To obtain the whole-range true stress-true strain curves of API X65, a method is proposed based on the equal proportion principle and digital images. The tensile elongation was obtained by tracing the gauge points on the specimen surface, and the true strain and true stress of API X65 were calculated according to the formulae. The obtained true stress-true strain curves were validated by a 3-D finite element model. The true stress-true strain curve was set as the input data, while the engineering stress-engineering strain curve was set as the output data. The output data of the finite element model was the same as that of the experiment test. The findings imply that the proposed method could acquire reliable, whole-range true stress-true stain curves. These curves, which depict the material behavior of pipeline steel from initial elongation to fracture, could provide basic data for pipeline defect tolerance limit analysis and fracture assessment. Full article
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Open AccessFeature PaperReview Strongly Orthotropic Open Cell Porous Metal Structures for Heat Transfer Applications
Metals 2018, 8(7), 554; https://doi.org/10.3390/met8070554
Received: 20 May 2018 / Revised: 5 July 2018 / Accepted: 9 July 2018 / Published: 19 July 2018
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Abstract
For modern thermal applications, open cell porous metals provide interesting opportunities to increase performance. Several types of cellular metals show an anisotropic morphology. Thus, using different orientations of the structure can boost or destroy the performance in thermal applications. Examples of such cellular
[...] Read more.
For modern thermal applications, open cell porous metals provide interesting opportunities to increase performance. Several types of cellular metals show an anisotropic morphology. Thus, using different orientations of the structure can boost or destroy the performance in thermal applications. Examples of such cellular anisotropic structures are lotus-type structures, expanded sheet metal, and metal fiber structures. Lotus-type structures are made by casting and show unidirectional pores, whereas expanded sheet metal structures and metal fiber structures are made from loose semi-finished products that are joined by sintering and form a fully open porous structure. Depending on the type of structure and the manufacturing process, the value of the direction-dependent heat conductivity may differ by a factor of 2 to 25. The influence of the measurement direction is less pronounced for the pressure drop; here, the difference varies between a factor of 1.5 to 2.8, depending on the type of material and the flow velocity. Literature data as well as own measurement methods and results of these properties are presented and the reasons for this strongly anisotropic behavior are discussed. Examples of advantageous applications, for example a latent heat storage device and a heat exchanger, where the preferential orientations are exploited in order to gain the full capacity of the structure’s performance, are introduced. Full article
(This article belongs to the Special Issue Porous Metals and Metallic Foams)
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Open AccessArticle Fe-Si/MnZn(Fe2O4)2 Core-shell Composites with Excellent Magnetic Properties by Mechanical Milling and Spark Plasma Sintering (SPS)
Metals 2018, 8(7), 553; https://doi.org/10.3390/met8070553
Received: 18 May 2018 / Revised: 26 June 2018 / Accepted: 29 June 2018 / Published: 19 July 2018
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Abstract
The Fe-Si/MnZn(Fe2O4)2 composite powders are synthetized by means of the mechanical milling, and Fe-Si/MnZn(Fe2O4)2 soft magnetic composites are prepared by spark plasma sintering (SPS). The impact of milling time on particle size, phase
[...] Read more.
The Fe-Si/MnZn(Fe2O4)2 composite powders are synthetized by means of the mechanical milling, and Fe-Si/MnZn(Fe2O4)2 soft magnetic composites are prepared by spark plasma sintering (SPS). The impact of milling time on particle size, phase structure and magnetic properties of the investigative core-shell structure powders along with that of sintering temperature on microstructure and magnetic properties of FeSi-MnZn(Fe2O4)2 soft magnetic composite are studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometer (VSM). The experimental results demonstrate a layer of MnZn(Fe2O4)2 forming a coating on the surface of Fe-Si powder after mechanical milling, and the soft magnetic composites exhibiting excellent magnetic performance at 900 °C: 212.49 emu/g for saturation magnetization, with 6.89 Oe for coercivity, 3 × 10−4 Ω.m for electrical resistivity and stable amplitude permeability and low core loss over a wide frequency range. Therefore, SPS offers a convenient and swift way to enhance performance of soft magnetic composites using magnetic materials as insulting layer. Full article
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Open AccessFeature PaperArticle Characterization of Microstructural Refinement and Hardness Profile Resulting from Friction Stir Processing of 6061-T6 Aluminum Alloy Extrusions
Metals 2018, 8(7), 552; https://doi.org/10.3390/met8070552
Received: 13 June 2018 / Revised: 11 July 2018 / Accepted: 15 July 2018 / Published: 19 July 2018
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Abstract
In this study, the change in microstructure and microhardness adjacent to the tool during the friction stir processing (FSP) of 6061-T6 extrusions was investigated. Results showed that the as-received extrusions contained Fe-rich constituent particles with two distinct size distributions: coarse particles in bands
[...] Read more.
In this study, the change in microstructure and microhardness adjacent to the tool during the friction stir processing (FSP) of 6061-T6 extrusions was investigated. Results showed that the as-received extrusions contained Fe-rich constituent particles with two distinct size distributions: coarse particles in bands and finer particles in the matrix. After FSP, Fe-containing particles exhibited single-size distribution and the coarse particles appeared to be completely eliminated through refinement. Microhardness tests showed the presence of four distinct zones and that hardness increased progressively from the dynamically recrystallized closest to the tool, outward through two distinct zones to the base material. The similarities and differences between the results of this study and others in the literature are discussed in detail. Full article
(This article belongs to the Special Issue Friction Stir Welding and Processing in Alloy Manufacturing)
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Open AccessCommunication On the Formation of Micro-Shrinkage Porosities in Ductile Iron Cast Components
Metals 2018, 8(7), 551; https://doi.org/10.3390/met8070551
Received: 4 July 2018 / Revised: 15 July 2018 / Accepted: 16 July 2018 / Published: 18 July 2018
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Abstract
A combination of direct austempering after solidification (DAAS) treatment and electron backscatter diffraction (EBSD) method was used to study the formation of micro-shrinkage porosities in ductile iron. Analyzing the aus-ferritic microstructure revealed that most of micro-shrinkage porosities are formed at the retained austenite
[...] Read more.
A combination of direct austempering after solidification (DAAS) treatment and electron backscatter diffraction (EBSD) method was used to study the formation of micro-shrinkage porosities in ductile iron. Analyzing the aus-ferritic microstructure revealed that most of micro-shrinkage porosities are formed at the retained austenite grain boundaries. There was no obvious correlation between the ferrite grains or graphite nodules and micro-shrinkage porosities. Due to the absolute pressure change at the (purely) shrinkage porosities, the dendrite fragmentation rate during the DAAS process would be altered locally, which caused a relatively finer parent-austenite grain structure near such porosities. Full article
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Open AccessArticle Metastable Eutectoid Transformation in Spheroidal Graphite Cast Iron: Modeling and Validation
Metals 2018, 8(7), 550; https://doi.org/10.3390/met8070550
Received: 28 June 2018 / Revised: 13 July 2018 / Accepted: 14 July 2018 / Published: 18 July 2018
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Abstract
This paper presents a new microstructural model of the metastable eutectoid transformation in spheroidal graphite cast irons. The model takes into account the nucleation and growth of pearlite nodules. The nucleation is assumed to be continuous and dependent on the metastable undercooling associated
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This paper presents a new microstructural model of the metastable eutectoid transformation in spheroidal graphite cast irons. The model takes into account the nucleation and growth of pearlite nodules. The nucleation is assumed to be continuous and dependent on the metastable undercooling associated with the upper limit of the three-phase field, while the growth rate is considered to be ruled by the silicon partitioning between ferrite and cementite at the pearlite/austenite front. The initial conditions for the metastable transformation are obtained from a microstructural simulation of solidification, graphite growth, and stable eutectoid transformation. These microstructural models are coupled with the thermal balance solved at a macroscopic level via the finite element method. The experimental validation of the metastable eutectoid model achieved by comparison with measured values of ferrite, graphite, and pearlite fractions at the end of the cooling process demonstrates the sound predictive capabilities of the proposed model. Full article
(This article belongs to the Special Issue Microstructure based Modeling of Metallic Materials)
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Open AccessArticle Effect of Turning and Surface Polishing Treatments on Surface Integrity and Fatigue Performance of Nickel-Based Alloy GH4169
Metals 2018, 8(7), 549; https://doi.org/10.3390/met8070549
Received: 19 June 2018 / Revised: 1 July 2018 / Accepted: 11 July 2018 / Published: 18 July 2018
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Abstract
In this paper, the effects of turning and surface polishing treatments on surface integrity and fatigue properties of superalloy GH4169 were investigated. Finish turning (FT), surface circumferential polishing treatment (TCP), surface oblique texture (TCPO), and surface axial texture (TCPA) were applied to GH4169
[...] Read more.
In this paper, the effects of turning and surface polishing treatments on surface integrity and fatigue properties of superalloy GH4169 were investigated. Finish turning (FT), surface circumferential polishing treatment (TCP), surface oblique texture (TCPO), and surface axial texture (TCPA) were applied to GH4169 superalloy. The surface roughness, surface topography, residual stress, microhardness, and microstructure after different processes were studied. Rotating bending fatigue tests were carried out to investigate the effects of surface integrity and surface texture direction on the fatigue performance of GH4169. The experiments reveal that the TCPA specimens present the longest fatigue life of 15.01 × 104 cycles. By comparison with the FT, TCP, and TCPO specimens, the fatigue lives of TCPA specimens are increased by 134.2%, 183.7%, and 96.2%, respectively. Single crack initiation source is observed for TCPA specimen. It is mainly attributed to the small surface stress concentration factor and surface axial texture. Full article
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Open AccessArticle 316L Stainless Steel Manufactured by Selective Laser Melting and Its Biocompatibility with or without Hydroxyapatite Coating
Metals 2018, 8(7), 548; https://doi.org/10.3390/met8070548
Received: 2 June 2018 / Revised: 10 July 2018 / Accepted: 10 July 2018 / Published: 18 July 2018
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Abstract
To fabricate metallic 316L/HA (hydroxyapatite) materials which meet the requirements of an implant’s mechanical properties and bioactivity for its function as human bone replacement, selective laser melting (SLM) has been employed in this study to prepare a 316L stainless steel matrix, which was
[...] Read more.
To fabricate metallic 316L/HA (hydroxyapatite) materials which meet the requirements of an implant’s mechanical properties and bioactivity for its function as human bone replacement, selective laser melting (SLM) has been employed in this study to prepare a 316L stainless steel matrix, which was subsequently covered with a hydroxyapatite (HA) coating using the sol-gel method. High density (98.9%) as-printed parts were prepared using a laser power of 230 W and a scanning speed of 800 mm/s. Austenite and residual acicular ferrite existed in the microstructure of the as-printed 316L stainless steel, and the sub-grain was uniform, whose primary dendrite spacing was around 0.35 μm. The as-printed 316L stainless steel showed the highest Vickers hardness, elastic modulus, and tensile strength at ~ (~ means about; same applies below unless stated otherwise) 247 HV, ~214.2 GPa, and ~730 MPa, respectively. The elongation corresponding to the highest tensile strength was ~38.8%. The 316L/HA structure, measured by the Relative Growth Rate (RGR) value, exhibited no cell cytotoxicity, and presented better biocompatibility than the uncoated as-printed and as-cast 316L samples. Full article
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Open AccessArticle Zinc Recovery from Steelmaking Dust by Hydrometallurgical Methods
Metals 2018, 8(7), 547; https://doi.org/10.3390/met8070547
Received: 17 June 2018 / Revised: 9 July 2018 / Accepted: 16 July 2018 / Published: 18 July 2018
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Abstract
Hydrometallurgical recovery of zinc from electric arc furnace dust was investigated on a laboratory scale, using aqueous sodium hydroxide solution as a leaching agent. Special attention was paid to the effect of NaOH concentration, temperature and liquid/solid phase ratio on the zinc leachability.
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Hydrometallurgical recovery of zinc from electric arc furnace dust was investigated on a laboratory scale, using aqueous sodium hydroxide solution as a leaching agent. Special attention was paid to the effect of NaOH concentration, temperature and liquid/solid phase ratio on the zinc leachability. It was found that all tested factors increased the leachability, with the maximum efficiency of 88% obtained in a 6 M NaOH solution at a temperature of 80 °C and the liquid/solid phase ratio of 40. The test results confirmed the high selectivity of the zinc leaching agent. In spite of this, complete recovery of zinc from steelmaking dust has proved to be very difficult due to the occurrence of this element in the form of stable and sparingly soluble ZnFe2O4 ferrite. Purification of the solution by cementation and electrolysis gave zinc of purity 99.88% in powder form. Full article
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Open AccessArticle A New Method to Recycle Stainless–Steel Duplex UNS S31803 Chips
Metals 2018, 8(7), 546; https://doi.org/10.3390/met8070546
Received: 25 May 2018 / Revised: 5 July 2018 / Accepted: 10 July 2018 / Published: 17 July 2018
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Abstract
Due to the increased consumption of raw materials, energy, and the waste it generates, recycling has become very important and fundamental for the environment and the industrial sector. The production of duplex stainless–steel powders with the addition of vanadium carbide in the high
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Due to the increased consumption of raw materials, energy, and the waste it generates, recycling has become very important and fundamental for the environment and the industrial sector. The production of duplex stainless–steel powders with the addition of vanadium carbide in the high energy mechanical milling process is a new method for recycling materials for the manufacture of components in the industrial sector. This study aims to reuse the chips from the duplex stainless–steel UNS S31803 by powder metallurgy with the addition of Vanadium carbide (VC). The mechanical milling was performed using a planetary ball mill for 50 h at a milling speed of 350 rpm and a ball-to-powder weight ratio of 20:1, and the addition of 3 wt % of VC. The material submitted to milling with an addition of carbide has a particle size of less than 140 μm. After milling, the sample went through a stress relief treatment performed at 1050 °C for 1 h and the isostatic compaction process loaded with 300 MPa. The sintered powders and material was characterized by scanning electron microscopy, X-ray diffraction, and micro-hardness tests. The milling process with an addition of 3% VC produced a particle size smaller than the initial chip size. The measurement of micrometric sizes obtained was between 26 and 132 μm. The sintered material had a measurement of porosity evaluated at 15%. The obtained density of the material was 84% compared to the initial density of the material as stainless–steel duplex UNS S31803. The value of the microhardness measurement was 232 HV. The material submitted for grinding presented the formation of a martensitic structure and after the thermal treatment, the presence of ferrite and austenite phases was observed. Thus, in conclusion, this study demonstrates the efficacy in the production of a metal-ceramic composite using a new method to recycle stainless–steel duplex UNS S31803 chips. Full article
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Open AccessArticle Recovery of Gallium from Corundum Flue Dust by Two-Stage Alkali Leaching, Carbonation, Acid Leaching and Solvent Extraction Process
Metals 2018, 8(7), 545; https://doi.org/10.3390/met8070545
Received: 21 June 2018 / Revised: 13 July 2018 / Accepted: 14 July 2018 / Published: 17 July 2018
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Abstract
Flue dust generated during the process of manufacturing corundum is a carrier of critical metal gallium. In this study, a process of alkali leaching-carbonation-acid leaching-solvent extraction was developed to recover and enrich gallium from corundum flue dust. Over 93% of the gallium in
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Flue dust generated during the process of manufacturing corundum is a carrier of critical metal gallium. In this study, a process of alkali leaching-carbonation-acid leaching-solvent extraction was developed to recover and enrich gallium from corundum flue dust. Over 93% of the gallium in corundum flue dust could be recovered through a two-stage alkali leaching process, which consists of 120 min of concentrated alkali leaching in NaOH solution and a subsequent 30-min dilute alkali leaching (after dilution), with an alkali-to-ore mass ratio of 1.2:1. Liquid to solid ratios in two alkali leaching stages were 1.5:1 and 8:1, respectively. The carbonation process was employed to remove high-level Si in alkali leachate. After carbonation and HCl leaching, over 96% of gallium in the NaOH leachate could be dissolved into acid solution. After extracting gallium from the HCl leachate using N235 as extracting agent, 1% NaOH solution was used to strip gallium from the organic phase. The extraction and stripping efficiency of gallium was over 99% and 97%, respectively. Full article
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Open AccessArticle Microstructural, Mechanical and Corrosion Investigations of Ship Steel-Aluminum Bimetal Composites Produced by Explosive Welding
Metals 2018, 8(7), 544; https://doi.org/10.3390/met8070544
Received: 19 June 2018 / Revised: 11 July 2018 / Accepted: 12 July 2018 / Published: 15 July 2018
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Abstract
In this study, explosive welding was used in the cladding of aluminum plates to ship steel plates at different explosive ratios. Ship steel-aluminum bimetal composite plates were manufactured and the influence of the explosive ratio on the cladded bonding interface was examined. Optical
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In this study, explosive welding was used in the cladding of aluminum plates to ship steel plates at different explosive ratios. Ship steel-aluminum bimetal composite plates were manufactured and the influence of the explosive ratio on the cladded bonding interface was examined. Optical microscopy (OM), scanning electron microscopy (SEM), and energy dispersive spectrometry (EDS) studies were employed for the characterization of the bonding interface of the manufactured ship steel-aluminum bimetal composites. Tensile-shear, notch impact toughness, bending and twisting tests, and microhardness studies were implemented to determine the mechanical features of the bimetal composite materials. In addition, neutral salt spray (NSS) tests were performed in order to examine the corrosion behavior of the bimetal composites. Full article
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Open AccessArticle Hole Making by Electrical Discharge Machining (EDM) of γ-TiAl Intermetallic Alloys
Metals 2018, 8(7), 543; https://doi.org/10.3390/met8070543
Received: 18 June 2018 / Revised: 4 July 2018 / Accepted: 11 July 2018 / Published: 14 July 2018
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Abstract
Due to their excellent strength-to-weight ratio and corrosion and wear resistance, γ-TiAl alloys are selected for aerospace and automotive applications. Since these materials are difficult to cut and machine by conventional methods, this study performed drilling tests using Electro Discharge Machining (EDM) to
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Due to their excellent strength-to-weight ratio and corrosion and wear resistance, γ-TiAl alloys are selected for aerospace and automotive applications. Since these materials are difficult to cut and machine by conventional methods, this study performed drilling tests using Electro Discharge Machining (EDM) to compare the machinability between two different types of γ-TiAl: extruded MoCusi and ingot MoCuSi. Different electrode materials and machining parameters were tested and wear, surface hardness, roughness and integrity were analyzed. The results indicate that extruded MoCuSi is preferable over MoCuSi ingots. Full article
(This article belongs to the Special Issue Machining and Finishing of Nickel and Titanium Alloys)
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Open AccessArticle Extraction of Metal Arsenic from Waste Sodium Arsenate by Roasting with Charcoal Powder
Metals 2018, 8(7), 542; https://doi.org/10.3390/met8070542
Received: 25 June 2018 / Revised: 7 July 2018 / Accepted: 11 July 2018 / Published: 13 July 2018
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Abstract
The current paper explored the directly reductive decomposition of waste sodium arsenate by roasting it with charcoal powder to volatilize less toxic As0 and to simultaneously obtain sodium salts with potential commercial value, serving the purpose of developing a more sustainable route
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The current paper explored the directly reductive decomposition of waste sodium arsenate by roasting it with charcoal powder to volatilize less toxic As0 and to simultaneously obtain sodium salts with potential commercial value, serving the purpose of developing a more sustainable route to deal with the environmental issues faced by the antimony production industry in China. The process was firstly evaluated by thermogravimetric (TG) analysis and thermochemical calculations. The effects of N2 flow rate, roasting temperature, dosage of charcoal powder, and roasting time were then investigated. The results showed that the arsenic extraction could reach 99.84% under optimal conditions. The roasting residue, containing arsenic as low as 0.0598%, was a promising source for the production of Na2CO3 as expected. In addition, X-ray diffraction (XRD), scanning electron micrograph (SEM), and X-ray photoelectron spectroscopy (XPS) were conducted to reveal the roasting mechanism and formation of metal arsenic was thereby confirmed. Full article
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Open AccessArticle Electrochemical Behavior of Biodegradable FeMnSi–MgCa Alloy
Metals 2018, 8(7), 541; https://doi.org/10.3390/met8070541
Received: 6 June 2018 / Revised: 11 July 2018 / Accepted: 11 July 2018 / Published: 13 July 2018
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Abstract
Nowadays, alongside metallic biomaterials, there is increasing interest in using degradable metals in an appreciable number of medical applications. There are new kinds of metallic biomaterials for medical applications and many new findings have been reported over the past few years. Iron-based materials
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Nowadays, alongside metallic biomaterials, there is increasing interest in using degradable metals in an appreciable number of medical applications. There are new kinds of metallic biomaterials for medical applications and many new findings have been reported over the past few years. Iron-based materials are a solution for biodegradable applications based on their mechanical and chemical properties. In order to control the corrosion rate of the Fe10Mn6Si alloy, we proposed the use of two additional elements, Ca and Mg, as corrosion promoters. The new material was obtained in an air-controlled atmosphere furnace after five melting operations. The material was in vitro analyzed from a corrosion resistance point of view. The experiments were realized by immersion (7, 14, and 30 days) in simulated body fluid (SBF) solution at 37 °C and a constant pH, and by electrochemical tests (electrochemical impedance spectroscopy (EIS), linear polarization (LP), cyclic polarization (CP)). Material surfaces before and after corrosion tests were analyzed through scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD) techniques. A discussion on the degradation rate of the material was realized from a comparison of the results. The results presented good composition homogeneity after the re-melting stages, with low percentages of Ca and Mg in the material, but with an adequate spread in the alloy. Full article
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Open AccessFeature PaperArticle Effects of Chemical Composition and Austenite Deformation on the Onset of Ferrite Formation for Arbitrary Cooling Paths
Metals 2018, 8(7), 540; https://doi.org/10.3390/met8070540
Received: 5 June 2018 / Revised: 6 July 2018 / Accepted: 10 July 2018 / Published: 12 July 2018
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Abstract
We present a computational method for calculating the phase transformation start for arbitrary cooling paths and for different steel compositions after thermomechanical treatments. We apply the method to quantitatively estimate how much austenite deformation and how many different alloying elements affect the transformation
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We present a computational method for calculating the phase transformation start for arbitrary cooling paths and for different steel compositions after thermomechanical treatments. We apply the method to quantitatively estimate how much austenite deformation and how many different alloying elements affect the transformation start at different temperatures. The calculations are done for recrystallized steel as well as strain hardened steel, and the results are compared. The method is parameterized using continuous cooling transformation (CCT) data as an input, and it can be easily adapted for different thermomechanical treatments when corresponding CCT data is available. The analysis can also be used to obtain estimates for the range of values for parameters in more detailed microstructure models. Full article
(This article belongs to the Special Issue Advances in Low-carbon and Stainless Steels)
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Open AccessArticle Influences of Compression Ratios on Sound Absorption Performance of Porous Nickel–Iron Alloy
Metals 2018, 8(7), 539; https://doi.org/10.3390/met8070539
Received: 25 June 2018 / Revised: 10 July 2018 / Accepted: 11 July 2018 / Published: 12 July 2018
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Abstract
The improvement of sound absorption performance of porous metal is a focus of research in the field of noise reduction. Influences of compression ratios on sound absorption performance of a porous nickel-iron (Ni-Fe) alloy were investigated. The samples were compressed with ratios from
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The improvement of sound absorption performance of porous metal is a focus of research in the field of noise reduction. Influences of compression ratios on sound absorption performance of a porous nickel-iron (Ni-Fe) alloy were investigated. The samples were compressed with ratios from 10% to 80% at an interval of 10%. Based on the standing wave method, sound absorption coefficients of compressed samples with different thicknesses were obtained. It could be found that with the same compression ratio, sound absorption performance was improved with the increase of thickness. Based on the modified Johnson-Allard model with a correction factor, the sound absorption coefficient of the porous Ni-Fe with a thickness of 20 mm for different compression ratios was derived, whose aim was to quantificationally analyze influences of the compression ratio. The results indicated that the sample with a compression ratio of 70% exhibited optimal sound absorption performance, and its average sound absorption coefficient reached 88.97% in a frequency range of 1000–6000 Hz. Meanwhile, the section morphologies of compressed samples were investigated by a scanning electron microscope, which studied the sound absorption performance by analyzing structures of the porous Ni-Fe samples with different compression ratios. The obtained achievements will promote the application of the porous Ni-Fe alloy in the field of acoustics. Full article
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Open AccessCommunication Electric Current-Assisted Joining of Copper Plates Using Silver Formed by In-Situ Decomposition of Ag2C2O4
Metals 2018, 8(7), 538; https://doi.org/10.3390/met8070538
Received: 8 June 2018 / Revised: 9 July 2018 / Accepted: 11 July 2018 / Published: 12 July 2018
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Abstract
Pulsed electric current can be used for the fast sintering of powders as well as joining of macroobjects. In this work, we brazed copper plates using a silver layer that was formed in situ by the decomposition of a silver oxalate Ag2
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Pulsed electric current can be used for the fast sintering of powders as well as joining of macroobjects. In this work, we brazed copper plates using a silver layer that was formed in situ by the decomposition of a silver oxalate Ag2C2O4 powder placed between the plates. Joining was conducted in the chamber of a Spark Plasma Sintering (SPS) facility with and without a graphite die. In the die-assisted tooling configuration, indirect heating of the assembly from the graphite die carrying electric current occurred until the brazing layer transformed into metallic silver. The passage of electric current through a Cu/Ag2C2O4/Cu stack placed between the electrodes without a die was possible because of the formation of Cu/Cu contacts in the areas free from the Ag2C2O4 particles. Joints that were formed in the die-assisted experiments showed a slightly higher shear strength (45 MPa) in comparison with joints formed without a die (41 MPa). The shear strength of the reference sample (obtained without a die), a stack of copper plates joined without any brazing layer, was only 31 MPa, which indicates a key role of the silver in producing strong bonding between the plates. This study shows that both die-assisted tooling configurations and those without a die can be used for the SPS brazing of materials by the oxalate-derived silver interlayer. Full article
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Open AccessArticle Numerical Simulation of Densification of Cu–Al Mixed Metal Powder during Axial Compaction
Metals 2018, 8(7), 537; https://doi.org/10.3390/met8070537
Received: 26 June 2018 / Accepted: 5 July 2018 / Published: 12 July 2018
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Abstract
The densification mechanism of Cu–Al mixed metal powder during a double-action die compaction was investigated by numerical simulation. The finite element method and experiment were performed to compare the effect of the forming method, such as single-action die compaction and double-action die compaction,
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The densification mechanism of Cu–Al mixed metal powder during a double-action die compaction was investigated by numerical simulation. The finite element method and experiment were performed to compare the effect of the forming method, such as single-action die compaction and double-action die compaction, on the properties of compact. The results showed that the latter could significantly raise the densification rate and were in good agreement with Van Der Zwan–Siskens compaction equation. The effects of the different initial packing structures on the properties of the compact were studied. The results showed that a high-performance compact could be obtained using a dense initial packing structure at a given compaction pressure. Additionally, the effects of the Al content and compaction pressure on the relative density and stress distribution were analyzed. It was observed that, with an increase in the Al content at a given compaction pressure, the relative density of the compact increased, whereas the stress decreased. Furthermore, when the Al content was fixed, the relative density and stress increased with increasing compaction pressure. The relationship between the relative density and the compaction pressure under different friction conditions was characterized and fitted according to the Van Der Zwan–Siskens compaction equation. The influence mechanisms of die wall friction on the compaction behavior were investigated. It was revealed that friction is a key factor that causes the inhomogeneity of the powder flow and stress distribution. Finally, the effects of the dwell time and height–diameter ratio on the densification behavior were analyzed, and it was found that an increase in the dwell time promoted the densification process, whereas an increase of the height–diameter ratio could hinder the process. Full article
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Open AccessArticle Numerical Model for Predicting Bead Geometry and Microstructure in Laser Beam Welding of Inconel 718 Sheets
Metals 2018, 8(7), 536; https://doi.org/10.3390/met8070536
Received: 19 June 2018 / Revised: 29 June 2018 / Accepted: 4 July 2018 / Published: 12 July 2018
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Abstract
A numerical model was developed for predicting the bead geometry and microstructure in laser beam welding of 2 mm thickness Inconel 718 sheets. The experiments were carried out with a 1 kW maximum power fiber laser coupled with a galvanometric scanner. Wobble strategy
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A numerical model was developed for predicting the bead geometry and microstructure in laser beam welding of 2 mm thickness Inconel 718 sheets. The experiments were carried out with a 1 kW maximum power fiber laser coupled with a galvanometric scanner. Wobble strategy was employed for sweeping 1 mm wide circular areas for creating the weld seams, and a specific tooling was manufactured for supplying protective argon gas during the welding process. The numerical model takes into account both the laser beam absorption and the melt-pool fluid movement along the bead section, resulting in a weld geometry that depends on the process input parameters, such as feed rate and laser power. The microstructure of the beads was also estimated based on the cooling rate of the material. Features such as bead upper and bottom final shapes, weld penetration, and dendritic arm spacing, were numerically and experimentally analyzed and discussed. The results given by the numerical analysis agree with the tests, making the model a robust predictive tool. Full article
(This article belongs to the Special Issue Laser Welding of Industrial Metal Alloys)
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Open AccessArticle The Effect of Growth Rate on the Microstructure and Tensile Behaviour of Directionally Solidified Ti-44Al-9Nb-1Cr-0.2W-0.2Y Alloys
Metals 2018, 8(7), 535; https://doi.org/10.3390/met8070535
Received: 23 June 2018 / Revised: 2 July 2018 / Accepted: 9 July 2018 / Published: 11 July 2018
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Abstract
Ti-44Al-9Nb-1Cr-0.2W-0.2Y alloys were directionally solidified (DS) at different growth rates varying from 10 to 20 μm/s using a modified liquid metal cooling (LMC) method. The results show that an increase in the growth rate leads to both a decrease in the size of
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Ti-44Al-9Nb-1Cr-0.2W-0.2Y alloys were directionally solidified (DS) at different growth rates varying from 10 to 20 μm/s using a modified liquid metal cooling (LMC) method. The results show that an increase in the growth rate leads to both a decrease in the size of the columnar grains in the directional solidification stable growth zone and a deterioration of the preferred orientation of the α2(Ti3Al)/γ(TiAl) lamellar structure in the columnar grains. The growth direction of the primary dendrite in the quenching zone gradually deflected along the axial direction as the growth rate increased. At the same time, the morphology changed from dendrite to a cystiform dendritic structure, with considerable B2 phase segregation in the dendritic core. Correspondingly, the tensile properties of the alloy decreased at 800 °C with a gradual increase in the cleavage fracture area. These findings show that the low growth rate is beneficial for the preferred orientation and the mechanical properties of the alloy. The content of the B2 phase and the change in the lamellar orientation are the main limiting factors for the tensile properties of the materials at high temperatures. Full article
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