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Metals, Volume 9, Issue 11 (November 2019)

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Cover Story (view full-size image) A process-structure-properties-performance modeling framework is presented for selective laser [...] Read more.
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Open AccessArticle
Effect of Vanadium and Titanium on Desulfurization of CaO Slag in Liquid Iron
Metals 2019, 9(11), 1239; https://doi.org/10.3390/met9111239 - 19 Nov 2019
Abstract
The possibility of vanadium and titanium participating in the CaO desulfurization reaction has been evaluated. The desulfurization products of CaO which were added to liquid iron containing vanadium–titanium in lab conditions were observed. At the early stage of adding CaO, titanium and sulfur [...] Read more.
The possibility of vanadium and titanium participating in the CaO desulfurization reaction has been evaluated. The desulfurization products of CaO which were added to liquid iron containing vanadium–titanium in lab conditions were observed. At the early stage of adding CaO, titanium and sulfur ware agglomerated on the surface of CaO particles. The particles were composed of CaO, TiO2, and CaS. However, vanadium oxide was not detected. It was proposed that the titanium rather than the vanadium could react with CaO and sulfur. The desulfurization kinetics experiment showed that the high titanium content in liquid iron reduced desulfurization velocity, while vanadium had little effect on the desulfurization. The reason for this was that the TiO2 which surrounded the CaO particle impeded the mass transfer of sulfur. The vanadium and titanium had a little influence on the final sulfur content of CaO desulfurization. The theoretical discussion of these phenomena was carried out. The controlling reaction of final sulfur content was (CaO) + [S] + [C] = (CaS) + CO(g). Full article
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Open AccessArticle
Modelling the Damage of Structural Components with Macrostructure Defects
Metals 2019, 9(11), 1238; https://doi.org/10.3390/met9111238 - 19 Nov 2019
Abstract
The article presents a numerical analysis of the process of damage of structural steel, the scope of which encompassed the estimation of the time to failure of a structural component. The analysis was conducted using the Gurson–Tvergaard–Needleman material model, which takes into account [...] Read more.
The article presents a numerical analysis of the process of damage of structural steel, the scope of which encompassed the estimation of the time to failure of a structural component. The analysis was conducted using the Gurson–Tvergaard–Needleman material model, which takes into account the influence of microdefects on material strength. Considered was a plate element with a central hole modelling the material discontinuity that may arise in a structural component as a result of corrosion. The conducted simulation permitted an analysis of the phenomenon of nucleation and evolution of microdamage in S235JR steel, which allowed, for the analysed component, the detection of the initiation of microdamages and their development in the area susceptible to damage. Changes to the state of stress taking place during plastic deformation of structural steel due to the evolution of microdefects of the material structure were analysed. Presented are the results of this research, in which the stress state described by the stress triaxiality in relation to the changes in the volumetric fraction of voids determining the size of microdefects was given a detailed analysis. Full article
(This article belongs to the Special Issue Quasi-Static and Dynamic Testing of Metallic Materials)
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Open AccessArticle
The Effect of Laser Shock Peening on the Corrosion Behavior of Biocompatible Magnesium Alloy ZK60
Metals 2019, 9(11), 1237; https://doi.org/10.3390/met9111237 - 19 Nov 2019
Abstract
The influences of different laser power density in LSP (laser shock peening) on the corrosion performance of biocompatible magnesium alloy ZK60 were researched via SBF (Simulated Body Fliud) immersion testing and electrochemical testing. Corrosion morphology and corrosion products were observed and analyzed using [...] Read more.
The influences of different laser power density in LSP (laser shock peening) on the corrosion performance of biocompatible magnesium alloy ZK60 were researched via SBF (Simulated Body Fliud) immersion testing and electrochemical testing. Corrosion morphology and corrosion products were observed and analyzed using SEM (Scanning Electron Microscope) outfitted with EDS (Energy Dispersive Spectrometer) and XRD (X-ray Diffraction). Simultaneously, 3D morphology, surface roughness, residual stress, and microstructure were also characterized. Results reveal that the modified samples can obtain higher residual compressive stress, which can lead to lower degradation rates in SBF solution. In terms of the weight loss of the samples, corrosion resistance increased by 52.1% maximally. The corrosion potential of modified samples in the SBF solution positively shifted from −1.3884 V to −1.1094 V and the corrosion current density decreased by 13.2% at most. The anti-corrosion ability of ZK60 is significantly enhanced by the LSP process. Full article
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Open AccessArticle
Thermal Cycles and Deformation Characters During High-Speed Micro Friction Stir Welding Process of AA7075-T6 Sheets
Metals 2019, 9(11), 1236; https://doi.org/10.3390/met9111236 - 18 Nov 2019
Abstract
Thermal cycles and deformations during high-speed micro friction stir welding (μFSW) under different welding conditions were studied by experimental methods. The results show that the peak temperature and elevated-temperature exposure time (t150) increased with the increasing of rotational speed and decreased [...] Read more.
Thermal cycles and deformations during high-speed micro friction stir welding (μFSW) under different welding conditions were studied by experimental methods. The results show that the peak temperature and elevated-temperature exposure time (t150) increased with the increasing of rotational speed and decreased with the increasing of welding speed. Increasing rotational speed or welding speed led to an increase in both heating and cooling rates. The joint fabricated by the pinless tool experienced a lower peak temperature, a shorter elevated-temperature exposure time, and a larger temperature gradient than that by the pin tool. The welded sheet presented an anti-saddle deformation character, with convex bending in a longitudinal direction and concave angular bending in a transverse direction. In comparison to the pin tool, the longitudinal maximum bending deformation, Zmax, of the joint fabricated by the pinless tool was reduced by 12.35%, and the transverse angular deformation, α, was reduced by 6.67%. In comparison to the steel backing plate, the Zmax of the joint produced using a copper backing plate was reduced by 40.66%, but the α was increased by 53.27%. Full article
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Open AccessArticle
Effects of Mg Content on Hydrogen Content and Melt Quality of Al-Mg Alloys
Metals 2019, 9(11), 1235; https://doi.org/10.3390/met9111235 - 18 Nov 2019
Abstract
In Al-Mg alloys with Mg content 0 ≤ XMg ≤ 6 wt. %, the effects of XMg on dissolved hydrogen content ([H]) and melt quality were investigated. [H] was measured using the Closed-Loop Recirculation method, and the melt quality was quantified [...] Read more.
In Al-Mg alloys with Mg content 0 ≤ XMg ≤ 6 wt. %, the effects of XMg on dissolved hydrogen content ([H]) and melt quality were investigated. [H] was measured using the Closed-Loop Recirculation method, and the melt quality was quantified using the density index (DI), bifilm index (BI), and porosity measurement. [H] in the molten alloys increased with increasing XMg and melt temperature TMelt; these trends agree with theoretical calculations for hydrogen solubility. The tendency of melt quality vs XMg was similar in DI, BI, and porosity measurements, and the poorest melt quality was observed in the Al-4Mg alloy that had XMg = 4 wt. %, whereas the highest [H] was obtained in the Al-6Mg alloy melt that had XMg = 6 wt. % Mg. During thermogravimetric/differential thermal analysis, rapid oxidation occurred in the Al-4Mg alloy melt during the holding time between 45 and 60 min at 800 °C, i.e., just before the molten metal was cast. The inferior melt quality of Al-4Mg alloy may have been caused by high-temperature oxidation. Full article
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Open AccessArticle
Effects of Tool Edge Geometry on Chip Segmentation and Exit Burr: A Finite Element Approach
Metals 2019, 9(11), 1234; https://doi.org/10.3390/met9111234 - 18 Nov 2019
Abstract
The effects of different tool edge geometries (hone and chamfer (T-land)) on quantitative measurement of end (exit) burr and chip segmentation (frequency and degree) in machining of AA2024-T351 are presented in this work. The finite element (FE) approach is adopted to perform cutting [...] Read more.
The effects of different tool edge geometries (hone and chamfer (T-land)) on quantitative measurement of end (exit) burr and chip segmentation (frequency and degree) in machining of AA2024-T351 are presented in this work. The finite element (FE) approach is adopted to perform cutting simulations for various combinations of cutting speed, feed, and tool edge geometries. Results show an increasing trend in degree of chip segmentation and end burr as hone edge tool radius or chamfer tool geometry macro parameters concerning chamfer length and chamfer angle increase. Conversely, the least effects for chip segmentation frequency have been figured out. Statistical optimization techniques, such as response surface methodology, Taguchi’s design of experiment, and analysis of variance (ANOVA), are applied to present predictive models, figure out optimum cutting parameters, and their significance and relative contributions to results of end burr and chip segmentation. Various numerical findings are successfully compared with experimental data. The ultimate goal is to help optimize tool edge design and select optimum cutting parameters for improved productivity. Full article
(This article belongs to the Special Issue Metal Machining—Recent Advances, Applications and Challenges)
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Open AccessReview
A Review of Austenite Memory Effect in HAZ of B Containing 9% Cr Martensitic Heat Resistant Steel
Metals 2019, 9(11), 1233; https://doi.org/10.3390/met9111233 - 18 Nov 2019
Abstract
During the welding process of B containing 9% Cr martensitic heat resistant steel (9Cr-B steel), austenite memory effect (referred to that the prior austenite grains in the heat affected zone (HAZ) after welding inherit the shape and size of prior austenite grains before [...] Read more.
During the welding process of B containing 9% Cr martensitic heat resistant steel (9Cr-B steel), austenite memory effect (referred to that the prior austenite grains in the heat affected zone (HAZ) after welding inherit the shape and size of prior austenite grains before welding) occurs in its normalized sub-zone of HAZ and the grain refinement is suppressed, which can effectively prevent type IV crack, and improve the service life of the welded joint at high temperatures. In the present article, α/γ reverse transformation behavior in the normalized sub-zone of 9Cr-B steel HAZ is reviewed. Austenite memory effect of 9Cr-B steel is derived from B addition. The main mechanisms of austenite memory effect during α/γ reverse transformation are discussed. Various models of boron causing austenite memory effect are discussed in detail. Matrix microstructure also plays an important role in austenite memory effect. Effects of heating rate, peak temperature, and holding time at peak temperature on austenite memory effect are also discussed. Full article
(This article belongs to the Special Issue Microstructure and Properties of Metallic Heat-Affected Zones)
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Open AccessArticle
Application of Cold Metal Transfer Welding for High Pressure Die Casting Mold Restoration
Metals 2019, 9(11), 1232; https://doi.org/10.3390/met9111232 - 18 Nov 2019
Abstract
This paper presents results of the research focused on the possibility of the restoration of the shape parts of molds made of X15CrNiSi20-12 (EN 100 95) heat-resistant austenitic chromium-nickel stainless steel working in high-pressure die casting of aluminum alloys by clad welding. There [...] Read more.
This paper presents results of the research focused on the possibility of the restoration of the shape parts of molds made of X15CrNiSi20-12 (EN 100 95) heat-resistant austenitic chromium-nickel stainless steel working in high-pressure die casting of aluminum alloys by clad welding. There were tested two welding wires—E Ni 6625 and E 18 8 Mn B 2 2—deposited on X15CrNiSi20-12 (EN 100 95) tool steel using cold metal transfer (CMT) welding in a protective atmosphere of Ar. The resistance of welds was tested against dissolution in molten aluminum alloy ENAC-AlSi9 and the testing procedure was designed. The resistance of welds against dissolution were assessed by exposition of welded clads in an aluminum melt for 120 and 300 min. The EDX semi-quantitative microanalyses of element distribution were performed at the welding–melt interface, and build-ups were also observed on the surface of welded clads. Full article
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Open AccessArticle
Construction of Cellular Substructure in Laser Powder Bed Fusion
Metals 2019, 9(11), 1231; https://doi.org/10.3390/met9111231 - 18 Nov 2019
Abstract
Cellular substructure has been widely observed in the sample fabricated by laser powder bed fusion, while its growth direction and the crystallographic orientation have seldom been studied. This research tries to build a general model to construct the substructure from its two-dimensional morphology. [...] Read more.
Cellular substructure has been widely observed in the sample fabricated by laser powder bed fusion, while its growth direction and the crystallographic orientation have seldom been studied. This research tries to build a general model to construct the substructure from its two-dimensional morphology. All the three Bunge Euler angles to specify a unique growth direction are determined, and the crystallographic orientation corresponding to the growth direction is also obtained. Based on the crystallographic orientation, the substructure in the single track of austenitic stainless steel 316L is distinguished between the cell-like dendrite and the cell. It is found that, with the increase of scanning velocity, the substructure transits from cell-like dendrite to cell. When the power is 200 W, the critical growth rate of the transition in the single track can be around 0.31 ms−1. Full article
(This article belongs to the Special Issue Additive Manufacturing of Metals with Lasers)
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Open AccessArticle
Study of Nanometer-Sized Precipitation and Properties of Fire Resistant Hot-Rolled Steel
Metals 2019, 9(11), 1230; https://doi.org/10.3390/met9111230 - 18 Nov 2019
Abstract
Nanometer-sized precipitated carbides in a low carbon Ti-V-Mo bearing steel were obtained through hot rolling and air cooling and were investigated by transmission electron microscopy (TEM). The nanometer-sized interphase-precipitated carbides have been found to exhibit an average diameter of ~6.1 ± 2.7 nm, [...] Read more.
Nanometer-sized precipitated carbides in a low carbon Ti-V-Mo bearing steel were obtained through hot rolling and air cooling and were investigated by transmission electron microscopy (TEM). The nanometer-sized interphase-precipitated carbides have been found to exhibit an average diameter of ~6.1 ± 2.7 nm, with an average spacing of ~24–34 nm. Yield strength of 578 ± 20 MPa and tensile strength of 813 ± 25 MPa were achieved with high elongation of 25.0 ± 0.5% at room temperature. The nanometer-sized precipitation exhibited high stability after annealing at high temperatures of 600 °C and 650 °C for 3 h. Average diameters of carbides were statistically measured to be ~6.9 ± 2.3 nm and 8.4 ± 2.6 nm after tempering at high temperatures of 600 °C and 650 °C, respectively. The micro-hardness was ~263–268 HV0.1 after high temperature tempering, which was similar to the hot-rolled sample (273 HV0.1), and yield strength of 325 ± 13 MPa and 278 ± 4 MPa was achieved at elevated temperatures of 600 °C and 650 °C, respectively. The significant decrease of yield strength at 650 °C was attributed to the large decrease in shear modulus. Full article
(This article belongs to the Special Issue High-Strength Low-Alloy Steels)
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Open AccessArticle
Effect of Deposition Parameters on Microstructure of the Ti-Mg Immiscible Alloy Thin Film Deposited by Multi-Arc Ion Plating
Metals 2019, 9(11), 1229; https://doi.org/10.3390/met9111229 - 17 Nov 2019
Abstract
Ti-Mg immiscible alloy thin films were prepared using a multi-arc ion plating technique with various deposition parameters. The surface and cross-section morphologies, crystal structures, and chemical compositions of the Ti-Mg films were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), and transmission [...] Read more.
Ti-Mg immiscible alloy thin films were prepared using a multi-arc ion plating technique with various deposition parameters. The surface and cross-section morphologies, crystal structures, and chemical compositions of the Ti-Mg films were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The influence of the substrate negative bias voltage and Ar gas pressure on the microstructure of the Ti-Mg films was systematically studied. Mg atoms were incorporated into the Ti lattice to form an FCC immiscible supersaturated solid solution phase in the thin film. Microparticles were observed on the film surface, and the number of microparticles could be significantly reduced by decreasing the substrate bias voltage and increasing the Ar gas pressure. The appropriate substrate bias voltage and Ar gas pressure increased the deposition rate. The TEM results indicated that columnar, nanolayer, and equiaxed nanocrystals were present in the thin films. Ti and Mg fluctuations were still evident in the nanoscale structures. Full article
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Open AccessEditorial
Critical Raw Materials Recovery through Bio/Hydrometallurgy from Secondary Resources
Metals 2019, 9(11), 1228; https://doi.org/10.3390/met9111228 - 16 Nov 2019
Abstract
Demand for critical raw materials (CRMs) to be used in consumer products is growing rapidly [...] Full article
Open AccessArticle
Refined Microstructure and Enhanced Hardness in Friction Stir-Welded AZ31 Magnesium Alloy Induced by Heat Pipe with Different Cooling Liquid
Metals 2019, 9(11), 1227; https://doi.org/10.3390/met9111227 - 16 Nov 2019
Abstract
The temperature field in welded plates has a significant influence on the microstructure and thereby their properties during friction stir welding (FSW). In this work, a self-designed heat pipe with different cooling liquid was applied in the FSW process for AZ31 magnesium alloy. [...] Read more.
The temperature field in welded plates has a significant influence on the microstructure and thereby their properties during friction stir welding (FSW). In this work, a self-designed heat pipe with different cooling liquid was applied in the FSW process for AZ31 magnesium alloy. The temperature fields, microstructures and properties of the welded joints were investigated. The peak temperatures and the durations of high temperature at both the advancing side and the retreating side decrease during the FSW process after applying the heat pipe and adding the ambient temperature water in the condensing tank. The top part of the weld nugget zone of the joint shows a significant decrease as well as its middle part due to the cooling effect of the heat pipe. The microstructure of the weld nugget zone is refined, associated with the increase in the hardness after applying the heat pipe. When the cooling liquid turns into ice water, grains in the weld nugget zone become significantly smaller and have a more homogeneous size. The mean value of hardness increases and the corresponding deviation is declined. Therefore, these results indicate that the application of the heat pipe and the employment of ice water as the cooling liquid can further refine the microstructure and enhance the strength of the material. Full article
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Open AccessArticle
Effect of Welding Heat Input on Simulated HAZ Areas in S960QL High Strength Steel
Metals 2019, 9(11), 1226; https://doi.org/10.3390/met9111226 - 16 Nov 2019
Abstract
When the weldability of high strength steels is analyzed, it is the softening in the heat-affected zone (HAZ) that is mostly investigated, and the reduction of toughness properties is generally less considered. The outstanding toughness properties of quenched and tempered high strength steels [...] Read more.
When the weldability of high strength steels is analyzed, it is the softening in the heat-affected zone (HAZ) that is mostly investigated, and the reduction of toughness properties is generally less considered. The outstanding toughness properties of quenched and tempered high strength steels cannot be adequately preserved during the welding due to the unfavorable microstructural changes in the HAZ. Relevant technological variants (t8/5 = 2.5–100 s) for arc welding technologies were applied during the HAZ simulation of S960QL steel (EN 10025-6) in a Gleeble 3500 physical simulator, and the effect of cooling time on the critical HAZ areas of single and multipass welded joints was analyzed. Thermal cycles were determined according to the Rykalin 3D model. The properties of the selected coarse-grained (CGHAZ), intercritical (ICHAZ) and intercritically reheated coarse-grained (ICCGHAZ) zones were investigated by scanning electron microscope, macro and micro hardness tests and instrumented Charpy V-notch pendulum impact tests. The examined HAZ subzones indicated higher sensitivity to the welding heat input compared to conventional structural steels. Due to the observed brittle behavior of all subzones in the whole t8/5 range, the possible lowest welding heat input should be applied in order to minimize the volume of HAZ that does not put fulfillment of the allowed maximal (450 HV10) hardness at risk and does not lead to the formation of cold cracks. Full article
(This article belongs to the Special Issue High-Strength Low-Alloy Steels)
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Open AccessFeature PaperArticle
Fe3O4 Nanoparticle-Reinforced Magnesium Nanocomposites Processed via Disintegrated Melt Deposition and Turning-Induced Deformation Techniques
Metals 2019, 9(11), 1225; https://doi.org/10.3390/met9111225 - 16 Nov 2019
Abstract
Magnesium nanocomposites, with nano-scale ceramic reinforcements, have attracted a great deal of attention for several engineering and biomedical applications in the recent past. In this work, superparamagnetic iron oxide nanoparticles, Fe3O4, with their unique magnetic properties and the ability [...] Read more.
Magnesium nanocomposites, with nano-scale ceramic reinforcements, have attracted a great deal of attention for several engineering and biomedical applications in the recent past. In this work, superparamagnetic iron oxide nanoparticles, Fe3O4, with their unique magnetic properties and the ability of being bio-compatible and non-toxic, are reinforced to magnesium to form Mg/(1, 2, and 3 wt %) Fe3O4 nanocomposites. These nanocomposites were fabricated using the conventional disintegrated melt deposition (DMD) technique followed by extrusion. Further, the materials were also processed using the novel turning-induced-deformation technique where the chips from turning process are collected, cold compacted, and hot extruded. The materials processed via the two techniques were compared in terms of microstructure and properties. Overall, the Mg/Fe3O4 nanocomposites, processed via both routes, exhibited a superior property profile. Further, the turning-induced deformation method showed promising results in terms of improved properties of the nanocomposites and serves as a great route for the recycling of metallic materials. Full article
(This article belongs to the Special Issue Production and Properties of Light Metal Matrix Nanocomposites)
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Open AccessArticle
Effects of Temperature on Wear Properties and Mechanisms of HVOF Sprayed CoCrAlYTa-10%Al2O3 Coatings and H13 Steel
Metals 2019, 9(11), 1224; https://doi.org/10.3390/met9111224 - 16 Nov 2019
Abstract
In this study, the CoCrAlYTa-10%Al2O3 coatings were prepared by the high-velocity oxygen-fuel (HVOF) spraying. A series of ball-on-disk sliding wear tests were conducted to evaluate the tribological properties of the coatings at different temperatures (25 °C, 200 °C, 400 °C, [...] Read more.
In this study, the CoCrAlYTa-10%Al2O3 coatings were prepared by the high-velocity oxygen-fuel (HVOF) spraying. A series of ball-on-disk sliding wear tests were conducted to evaluate the tribological properties of the coatings at different temperatures (25 °C, 200 °C, 400 °C, and 600 °C). The results showed that the average coefficients of friction (COFs) of the CoCrAlYTa-10%Al2O3 coatings were lower than that of H13 steel at different temperatures. The average COFs of the CoCrAlYTa-10%Al2O3 coatings and H13 steel both decreased with increasing temperature. The wear rate of the CoCrAlYTa-10%Al2O3 coatings increased first and then decreased. The microhardness of worn surface of the CoCrAlYTa-10%Al2O3 coatings increased with increasing temperature, while the microhardness of worn surface of H13 steel at 25 °C and 200°C was higher than that at 400 °C and 600 °C. The wear mechanism of the two materials was mainly abrasive wear. The tribofilms were formed on the worn surface of the CoCrAlYTa-10%Al2O3 coatings, which had a good protective effect. Due to thermal softening and low binding strength of debris, it was difficult for H13 steel to form the tribofilms. The wear rate of H13 steel was much higher than that of the CoCrAlYTa-10%Al2O3 coatings at 400 °C and 600 °C, indicating that the high temperature wear resistance of the coatings was much better than that of H13 steel. Full article
(This article belongs to the Special Issue Wear Properties of Metallic Coatings)
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Open AccessArticle
Metallothermic Al-Sc Co-Reduction by Vacuum Induction Melting Using Ca
Metals 2019, 9(11), 1223; https://doi.org/10.3390/met9111223 - 14 Nov 2019
Abstract
Due to its enhancing properties in high-tech material applications, the rare earth element Scandium (Sc) is continuously gaining interest from researchers and material developers. The aim of this research is to establish an energy and resource efficient process scheme for an in situ [...] Read more.
Due to its enhancing properties in high-tech material applications, the rare earth element Scandium (Sc) is continuously gaining interest from researchers and material developers. The aim of this research is to establish an energy and resource efficient process scheme for an in situ extraction of Al-Sc master alloys, which offers usable products for the metallurgical industry. An AlSc20 alloy is targeted with an oxyfluoridic slag as a usable by-product. The thermochemical baseline is presented by modelling using the software tool FactSage; the experimental metal extraction is conducted in a vacuum induction furnace with various parameters, whereas kinetic aspects are investigated by thermogravimetric analysis. The Sc-containing products are analyzed by ICP-OES/IC concerning their chemical composition. Optimum parameters are derived from a statistical evaluation of the Sc content in the obtained slag phase. The material obtained was high in Ta due to the crucible material and remarkably low in Al and F; a comparison between the modelled and the obtained phases indicates kinetic effects inhibiting the accomplishment of equilibrium conditions. The formation of a Sc-rich Al-Sc phase (32.5 wt.-% Sc) is detected by SEM-EDS analysis of the metal phase. An in situ extraction of Al from Ca with subsequent metallothermic reduction of ScF 3 as a process controlling mechanism is presumed. Full article
(This article belongs to the Special Issue Advances in Pyrometallurgy)
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Open AccessArticle
Effect of Crown Shape of Rolls on the Distribution of Stress and Elastic Deformation for Rolling Processes
Metals 2019, 9(11), 1222; https://doi.org/10.3390/met9111222 - 14 Nov 2019
Abstract
The present work analyzes the influence of crown shape on the distribution of stresses and deformation for rolling processes. This study consists of a Finite Element Analysis considering combinations of crown shape for Back Up Roll and Work Roll, rolling forces, properties of [...] Read more.
The present work analyzes the influence of crown shape on the distribution of stresses and deformation for rolling processes. This study consists of a Finite Element Analysis considering combinations of crown shape for Back Up Roll and Work Roll, rolling forces, properties of materials and dimensions of rolls and strip. An analysis of the rolls based on a double cantilever model with the fulcrum of the beams in a centerline mill was carried out. The results show that maximum stress concentrations for all combinations of crown shape analyzed appear on both sides 787.4 mm from the mill centerline, exactly on the sides of the strip. In this area, the maximum stress for the best combination of crown shape is larger than in the centerline mill, increasing from 34.2 MPa to 163.0 MPa. This is proportional according to Hooke’s law for which strain of rolls increases from 3.4067 × 10−4 to 4.8368 × 10−4. The worst combinations of crown shapes were obtained when the shapes of the barrel are the same for the BUR and WR; for example: Combination 1 (BUR Positive–WR Positive), Combination 5 (BUR Flat–WR Flat), and Combination 9 (BUR Negative–WR Negative). Full article
(This article belongs to the Special Issue Rolling of Metals)
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Open AccessArticle
Influence of Carbide Morphology on the Deformation and Fracture Mechanisms of Spheroidized 14CrMoR Steel
Metals 2019, 9(11), 1221; https://doi.org/10.3390/met9111221 - 13 Nov 2019
Abstract
The influence of carbide morphology on the deformation and fracture mechanisms of as-received and complete spheroidization 14Cr1MoR steel was investigated using an in situ scanning electron microscope (SEM) under tension testing. During spheroidization damage, the carbide morphology changed from the original lamellar cementite [...] Read more.
The influence of carbide morphology on the deformation and fracture mechanisms of as-received and complete spheroidization 14Cr1MoR steel was investigated using an in situ scanning electron microscope (SEM) under tension testing. During spheroidization damage, the carbide morphology changed from the original lamellar cementite present in pearlite to granular M23C6 carbide, which was concentrated along the ferrite grain boundaries. The yield strength and tensile strength of 14Cr1MoR steel decreased with the increasing degree of spheroidization damage. In situ SEM observations revealed that the deformation and crack initiation started from the ferrite matrix in both as-received and completely spheroidization-damaged 14Cr1MoR steel samples. However, the extension of slip bands and crack propagation behavior of both samples were different during the in situ tensile process, which could be ascribed to the difference in carbide morphology. In the as-received 14Cr1MoR steel sample, hard and brittle lamellar pearlite resulted in high-strength ferrite/ pearlite boundaries, which inhibited the movement of slip bands. With further deformation, the concentration of stress at the crack tip resulted in the emergence and propagation of cracks along the ferrite/pearlite boundaries. In the case of the completely spheroidized 14Cr1MoR steel sample, slip bands bypassed the grain boundary carbide and continuously expanded into the neighboring ferrite grain. In addition, micro-voids and fractures of grain boundary carbides were observed due to the large stress concentration at the front of crack tip. Then, the micro-voids connected with the main crack to complete the crack propagation behavior. The morphological changes of carbides deteriorated the mechanical properties and altered the fracture behavior of 14Cr1MoR steel. It is worth noting that the fracture surface morphology of 14Cr1MoR steel changed from a combination of lamellar fracture and dimpled morphology to a completely dimples-dominated morphology after spheroidization. Full article
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Open AccessArticle
Properties of TiC and TiN Reinforced Alumina–Zirconia Composites Sintered with Spark Plasma Technique
Metals 2019, 9(11), 1220; https://doi.org/10.3390/met9111220 - 13 Nov 2019
Abstract
In this paper, Al2O3–ZrO2 composites with an addition of 20 wt% TiN and 10 wt% TiC were modified. The addition of zirconia in a range from 2 to 5 wt% of the monoclinic phase and 10 wt% of [...] Read more.
In this paper, Al2O3–ZrO2 composites with an addition of 20 wt% TiN and 10 wt% TiC were modified. The addition of zirconia in a range from 2 to 5 wt% of the monoclinic phase and 10 wt% of Y2O3 stabilised ZrO2 affected the mechanical properties of the composites. A new type of sintering technique—the spark plasma sintering (SPS) method—within a temperature range from 1575 °C to 1675 °C, was used. Vickers hardness, apparent density, wear resistance and indentation fracture toughness KIC(HV) were evaluated at room temperature. An increase of the sintering temperature resulted in an improvement of Vickers hardness and an increase of the fracture toughness of the tested composites. The tribological properties of the samples were tested using the ball-on-disc method. The friction coefficient was in a range from 0.31 to 0.55, depending on the sintering temperature. An enhancement of the specific wear rate was dependent on the sintering temperature. The mechanical properties of the samples sintered by pressureless sintering (PS) were compared. X-ray diffraction patterns were presented in order to determine the phase composition. SEM microstructure of the tested composites sintered at different temperatures was observed. Full article
(This article belongs to the Special Issue Metal Oxides)
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Open AccessArticle
Mechanical Properties of Some Metallic Powder Alloys and Their Contribution to the Performance of Diamond Tools Used for Cutting Granite
Metals 2019, 9(11), 1219; https://doi.org/10.3390/met9111219 - 13 Nov 2019
Abstract
This work examined some pre-alloyed cobalt-, iron-, and copper-based powder binder systems—such as those launched commercially under the brand names of Cobalite and Next—in terms of their as-sintered physical-mechanical properties, namely, apparent density, Young´s modulus, yield strength, rupture strength, rupture strain, toughness modulus, [...] Read more.
This work examined some pre-alloyed cobalt-, iron-, and copper-based powder binder systems—such as those launched commercially under the brand names of Cobalite and Next—in terms of their as-sintered physical-mechanical properties, namely, apparent density, Young´s modulus, yield strength, rupture strength, rupture strain, toughness modulus, and Vickers hardness. These types of sintered products are traditionally used in the fabrication of diamond impregnated tools for cutting granite stones. The following powder binder systems were evaluated: Cobalite HDR pre-alloyed powder, Next 300 pre-alloyed powder, and four other mixtures of these with Cu and Fe powders: Cobalite HDR + 20 wt% Cu; Cobalite HDR + 20 wt% Fe; Next 300 + 20 wt% Cu; Next 300 + 20 wt% Fe. The evaluation methodology aimed to establish criteria for developing new diamond tools and, therefore, it included the measurement of several technological parameters directly related to the cutting performance of the tools (e.g., energy consumption measurements made exclusively in the tool drive motor, forces generated in the tool, tool consumption per unit weight of stone removed by the cutting). The results show the adequacy of the methodology for the optimisation of diamond retention capacity of these types of metal matrices and for improving the working performance of the diamond tools. Full article
(This article belongs to the Special Issue Metals Powders: Synthesis and Processing)
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Open AccessArticle
Extension of Experimentally Assembled Processing Maps of 10CrMo9-10 Steel via a Predicted Dataset and the Influence on Overall Informative Possibilities
Metals 2019, 9(11), 1218; https://doi.org/10.3390/met9111218 - 13 Nov 2019
Abstract
Processing maps embody a supportive tool for the optimization of hot forming processes. In the present work, based on the dynamic material model, the processing maps of 10CrMo9-10 low-alloy steel were assembled with the use of two flow curve datasets. The first one [...] Read more.
Processing maps embody a supportive tool for the optimization of hot forming processes. In the present work, based on the dynamic material model, the processing maps of 10CrMo9-10 low-alloy steel were assembled with the use of two flow curve datasets. The first one was obtained on the basis of uniaxial hot compression tests in a temperature range of 1073–1523 K and a strain rate range of 0.1–100 s−1. This experimental dataset was subsequently approximated by means of an artificial neural network approach. Based on this approximation, the second dataset was calculated. An important finding was that the additional dataset contributed significantly to improving the informative ability of the assembled processing maps in terms of revealing potentially inappropriate forming conditions. Full article
(This article belongs to the Special Issue Forming and Heat Treatment of Modern Metallic Materials)
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Open AccessArticle
Large-Scale Molecular Dynamics Simulations of Homogeneous Nucleation of Pure Aluminium
Metals 2019, 9(11), 1217; https://doi.org/10.3390/met9111217 - 12 Nov 2019
Abstract
Despite the continuous and remarkable development of experimental techniques for the investigation of microstructures and the growth of nuclei during the solidification of metals, there are still unknown territories around this topic. The solidification in nanoscale can be effectively investigated by means of [...] Read more.
Despite the continuous and remarkable development of experimental techniques for the investigation of microstructures and the growth of nuclei during the solidification of metals, there are still unknown territories around this topic. The solidification in nanoscale can be effectively investigated by means of molecular dynamics (MD) simulations which can provide a deep insight into the mechanisms of the formation of nuclei and the induced crystal structures. In this study, MD simulations were performed to investigate the solidification of pure Aluminium and the effects of the cooling rate on the final properties of the solidified material. A large number of Aluminium atoms were used in order to investigate the grain growth over time and the formation of stacking faults during solidification. The number of face-centred cubic (FCC), hexagonal close-packed (HCP) and body-centred cubic (BCC) was recorded during the evolution of the process to illustrate the nanoscale mechanisms initiating solidification. The current investigation also focuses on the exothermic nature of the solidification process which has been effectively captured by means of MD simulations using 3 dimensional representations of the kinetic energy across the simulation domain. Full article
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Open AccessArticle
The Effect of Stress Relief on the Mechanical and Fatigue Properties of Additively Manufactured AlSi10Mg Parts
Metals 2019, 9(11), 1216; https://doi.org/10.3390/met9111216 - 12 Nov 2019
Abstract
The heating and cooling profiles experienced during laser additive manufacturing results in residual stresses build up in the component. Therefore, it is necessary to perform post build stress relieving towards the retention and improvement of the mechanical properties. However the thermal treatments for [...] Read more.
The heating and cooling profiles experienced during laser additive manufacturing results in residual stresses build up in the component. Therefore, it is necessary to perform post build stress relieving towards the retention and improvement of the mechanical properties. However the thermal treatments for conventional manufacturing do not seem to completely accommodate these rapid heating and cooling cycles of laser processing techniques such as powder bed fusion. Characterizations such as density measurements on the samples were performed employing the Archimedes principle; hardness testing was performed on the Zwick micro/macro (Hv) hardness tester, SEM and Electron backscatter diffraction (EBSD). Fracture toughness and crack growth was conducted on a fatigue crack machine. All characterization was done after stress relieving of Selective Laser Melting (SLM) produced samples at 300 °C for 2 hrs was performed in a furnace. The mechanical properties appear to be rather compromised instead of being enhanced desirably. As-built SLM produced tensile specimens built in different directions exhibited significantly favorable mechanical properties. However, post stress relieve thermal treatment technique deteriorated the strength while increasing the ductility significantly. Nonetheless, fatigue crack growth and fracture toughness illustrated positive outcome in terms of fatigue life on SLM produced AlSi10Mg components in application. Full article
(This article belongs to the Special Issue Additive Manufacturing of Metals)
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Open AccessArticle
Stress Relaxation Aging Behavior and Constitutive Modelling of AA7150-T7751 under Different Temperatures, Initial Stress Levels and Pre-Strains
Metals 2019, 9(11), 1215; https://doi.org/10.3390/met9111215 - 12 Nov 2019
Abstract
Age forming is an advanced manufacture technology for forming large aluminum panels. Temperature, initial stress level and pre-strains have a great effect on the formability and performance. The stress relaxation aging behavior of AA7150-T7751 under different temperatures, initial stress levels and pre-strains was [...] Read more.
Age forming is an advanced manufacture technology for forming large aluminum panels. Temperature, initial stress level and pre-strains have a great effect on the formability and performance. The stress relaxation aging behavior of AA7150-T7751 under different temperatures, initial stress levels and pre-strains was studied through stress relaxation tests, tensile tests and TEM observations. The results show that the formability can be improved with the increase of temperature, initial stress levels and pre-strains. Deformation mechanisms during stress relaxation of the material were analyzed on the basis of creep stress exponent and apparent activation energy. The aging precipitates of the studied alloy were not sensitive to the age forming conditions, but drastically coarsened at over aging temperature, which decreased the mechanical properties. In addition, the relationship between stress relaxation behavior and aging strengthening is discussed. Based on the dislocation theory and the modified Arrhenius equation, a stress relaxation constitutive equation considering the initial mobile dislocation density and temperature dependent activation energy was established. This model can predict very well the stress relaxation behavior under various temperature, stress level and pre-strain conditions, with an average error of 2%. Full article
(This article belongs to the Special Issue Metal Plasticity and Fatigue at High Temperature)
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Open AccessArticle
Mechanical, Thermal, and Acoustic Properties of Aluminum Foams Impregnated with Epoxy/Graphene Oxide Nanocomposites
Metals 2019, 9(11), 1214; https://doi.org/10.3390/met9111214 - 12 Nov 2019
Abstract
Hybrid structures with epoxy embedded in open-cell aluminum foam were developed by combining open-cell aluminum foam specimens with unreinforced and reinforced epoxy resin using graphene oxide. These new hybrid structures were fabricated by infiltrating an open-cell aluminum foam specimen with pure epoxy or [...] Read more.
Hybrid structures with epoxy embedded in open-cell aluminum foam were developed by combining open-cell aluminum foam specimens with unreinforced and reinforced epoxy resin using graphene oxide. These new hybrid structures were fabricated by infiltrating an open-cell aluminum foam specimen with pure epoxy or mixtures of epoxy and graphene oxide, completely filling the pores. The effects of graphene oxide on the mechanical, thermal, and acoustic performance of epoxy/graphene oxide-based nanocomposites are reported. Mechanical compression analysis was conducted through quasi-static uniaxial compression tests at two loading rates (0.1 mm/s and 1 mm/s). Results show that the thermal stability and the sound absorption coefficient of the hybrid structures were improved by the incorporation of the graphene oxide within the epoxy matrix. However, the incorporation of the graphene oxide into the epoxy matrix can create voids inside the epoxy resin, leading to a decrease of the compressive strength of the hybrid structures, thus no significant increase in the energy absorption capability was observed. Full article
(This article belongs to the Special Issue Cellular Metals: Fabrication, Properties and Applications)
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Open AccessArticle
Corrosion and Tensile Behaviors of Ti-4Al-2V-1Mo-1Fe and Ti-6Al-4V Titanium Alloys
Metals 2019, 9(11), 1213; https://doi.org/10.3390/met9111213 - 11 Nov 2019
Abstract
X-ray diffraction (XRD), scanning electron microscope (SEM), immersion, electrochemical, and tensile tests were employed to analyze the phase constitution, microstructure, corrosion behaviors, and tensile properties of a Ti-6Al-4V alloy and a newly-developed low cost titanium alloy Ti-4Al-2V-1Mo-1Fe. The results showed that both the [...] Read more.
X-ray diffraction (XRD), scanning electron microscope (SEM), immersion, electrochemical, and tensile tests were employed to analyze the phase constitution, microstructure, corrosion behaviors, and tensile properties of a Ti-6Al-4V alloy and a newly-developed low cost titanium alloy Ti-4Al-2V-1Mo-1Fe. The results showed that both the Ti-6Al-4V and Ti-4Al-2V-1Mo-1Fe alloys were composed of α and β phases. The volume fractions of β phase for these two alloys were 7.4% and 47.3%, respectively. The mass losses after 180-day immersion tests in 3.5 wt.% NaCl solution of these alloys were negligible. The corrosion resistance of the Ti-4Al-2V-1Mo-1Fe alloy was higher than that of the Ti-6Al-4V alloy. The tensile tests showed that the Ti-4Al-2V-1Mo-1Fe alloy presented a slightly higher strength but a lower ductility compared to the Ti-6Al-4V alloy. Full article
(This article belongs to the Special Issue Titanium Alloys and Titanium-Based Matrix Composites)
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Open AccessArticle
Effect of Ca Content on the Mechanical Properties and Corrosion Behaviors of Extruded Mg–7Li–3Al Alloys
Metals 2019, 9(11), 1212; https://doi.org/10.3390/met9111212 - 11 Nov 2019
Abstract
The effect of Ca addition on the microstructure, mechanical properties, and corrosion behaviors of the extruded Mg–7Li–3Al alloys was investigated. The results showed that the extruded Mg–7Li–3Al–xCa alloys consisted of α-Mg (hcp) + β-Li (bcc) matrix phases and Al2Ca. With increasing [...] Read more.
The effect of Ca addition on the microstructure, mechanical properties, and corrosion behaviors of the extruded Mg–7Li–3Al alloys was investigated. The results showed that the extruded Mg–7Li–3Al–xCa alloys consisted of α-Mg (hcp) + β-Li (bcc) matrix phases and Al2Ca. With increasing Ca content, the amount and morphology of the Al2Ca phase changed significantly. The grains of the extruded Mg–7Li–3Al–xCa alloys were refined by dynamic recrystallization during the extrusion process. The tensile tests results indicated that the extruded Mg–7Li–3Al–0.4Ca alloy exhibited favorable comprehensive mechanical properties; its ultimate tensile strength was 286 MPa, the yield strength was 249 MPa, and the elongation was 18.7%. The corrosion results showed that this alloy with 0.4 wt.% Ca addition exhibited superior corrosion resistance, with a corrosion potential Ecorr of −1.48742 VVSE, attributed to the formation of protective Al2Ca phases. Full article
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Open AccessArticle
Evaluation of Support Structure Removability for Additively Manufactured Ti6Al4V Overhangs via Electron Beam Melting
Metals 2019, 9(11), 1211; https://doi.org/10.3390/met9111211 - 11 Nov 2019
Abstract
The addition of support structures is essential for the successful fabrication of overhang structures through additive manufacturing (AM). The support structures protect the overhang portion from distortions. They are fabricated with the functional parts and are removed later after the fabrication of the [...] Read more.
The addition of support structures is essential for the successful fabrication of overhang structures through additive manufacturing (AM). The support structures protect the overhang portion from distortions. They are fabricated with the functional parts and are removed later after the fabrication of the AM part. While structures bearing insufficient support result in defective overhangs, structures with excessive support result in higher material consumption, time and higher post-processing costs. The objective of this study is to investigate the effects of design and process parameters of support structures on support removability during the electron beam melting (EBM)-based additive manufacturing of the Ti6Al4V overhang part. The support design parameters include tooth parameters, no support offset, fragmentation parameters and perforation parameters. The EBM process parameters consist of beam current, beam scan speed and beam focus offset. The results show that both support design and process parameters have a significant effect on support removability. In addition, with the appropriate selection of design and process parameters, it is possible to significantly reduce the support removal time and protect the surface quality of the part. Full article
(This article belongs to the Special Issue Metal Additive Manufacturing – State of the Art 2020)
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Open AccessArticle
Effects of High-Intensity Ultrasound on Microstructure and Mechanical Property of In situ TiB2/2A14 Composites
Metals 2019, 9(11), 1210; https://doi.org/10.3390/met9111210 - 11 Nov 2019
Abstract
In situ TiB2/2A14 composites with a 3% volume fraction were prepared by mixing salt reaction and high energy ultrasound. The effects of high-intensity ultrasonic on the microstructure and mechanical properties of TiB2/2A14 composites were systematically investigated. The microstructures of [...] Read more.
In situ TiB2/2A14 composites with a 3% volume fraction were prepared by mixing salt reaction and high energy ultrasound. The effects of high-intensity ultrasonic on the microstructure and mechanical properties of TiB2/2A14 composites were systematically investigated. The microstructures of the composites were analyzed using scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD). The phase composition was examined by X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). The results showed that after introducing ultrasonic vibration into the melt, due to the cavitation and acoustic streaming effect, the particle agglomerations were significantly reduced and particles of different sizes were evenly dispersed in the matrix. With ultrasonic vibration treatment of 120 s, the agglomerations were basically eliminated, and the particles were uniformly distributed to the most. The yield strength, tensile strength and elongation of the composites were increased by 53%, 21% and 30%, respectively, compared with that without ultrasonic vibration treatment (UVT). Full article
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