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Metals, Volume 7, Issue 6 (June 2017)

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Open AccessArticle
Influence of Thickness and Chemical Composition of Hot-Rolled Bands on the Final Microstructure and Magnetic Properties of Non-Oriented Electrical Steel Sheets Subjected to Two Different Decarburizing Atmospheres
Metals 2017, 7(6), 229; https://doi.org/10.3390/met7060229 - 21 Jun 2017
Cited by 4 | Viewed by 2382
Abstract
During electrical steel processing, there are usually small variations in both chemical composition and thickness in the hot-rolled material that may lead to different magnetic properties for the same steel grade. Therefore, it is of great importance to know the effects of such [...] Read more.
During electrical steel processing, there are usually small variations in both chemical composition and thickness in the hot-rolled material that may lead to different magnetic properties for the same steel grade. Therefore, it is of great importance to know the effects of such variations on the final microstructure and magnetic properties of these steels. In the present investigation, samples of a specific grade of a commercial hot-rolled grain non-oriented (GNO) electrical steel were taken from different steel batches to investigate the effects of thickness and chemical composition (C, Sn, Mn and Ti) in the hot-rolled material on the final microstructure and magnetic properties (core losses and magnetic permeability) resulting from two different decarburizing annealing cycles. Hot-rolled samples were processed by cold rolling, intermediate annealing, temper-rolling and final decarburization annealing using the same processing parameters. The experimental results show that the minimum core losses and maximum magnetic permeability are obtained with the thinnest steel thickness and the largest grain size. Increasing Sb and Mn contents, and reducing the C and Ti concentrations also improve the magnetic behavior of these steels. It was also found the effect of grain size on the magnetic behavior is more significant than the one of crystallographic texture. Full article
(This article belongs to the Special Issue Alloy Steels) Printed Edition available
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Open AccessArticle
Influence of Temperature-Dependent Properties of Aluminum Alloy on Evolution of Plastic Strain and Residual Stress during Quenching Process
Metals 2017, 7(6), 228; https://doi.org/10.3390/met7060228 - 21 Jun 2017
Cited by 2 | Viewed by 2233
Abstract
To lessen quenching residual stresses in aluminum alloy components, theory analysis, quenching experiments, and numerical simulation were applied to investigate the influence of temperature-dependent material properties on the evolution of plastic strain and stress in the forged 2A14 aluminum alloy components during quenching [...] Read more.
To lessen quenching residual stresses in aluminum alloy components, theory analysis, quenching experiments, and numerical simulation were applied to investigate the influence of temperature-dependent material properties on the evolution of plastic strain and stress in the forged 2A14 aluminum alloy components during quenching process. The results show that the thermal expansion coefficients, yield strengths, and elastic moduli played key roles in determining the magnitude of plastic strains. To produce a certain plastic strain, the temperature difference increased with decreasing temperature. It means that the cooling rates at high temperatures play an important role in determining residual stresses. Only reducing the cooling rate at low temperatures does not reduce residual stresses. An optimized quenching process can minimize the residual stresses and guarantee superior mechanical properties. In the quenching process, the cooling rates were low at temperatures above 450 °C and were high at temperatures below 400 °C. Full article
(This article belongs to the Special Issue Light Weight Alloys: Processing, Properties and Their Applications)
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Open AccessArticle
Effect of Al-5Ti-0.62C-0.2Ce Master Alloy on the Microstructure and Tensile Properties of Commercial Pure Al and Hypoeutectic Al-8Si Alloy
Metals 2017, 7(6), 227; https://doi.org/10.3390/met7060227 - 20 Jun 2017
Cited by 5 | Viewed by 1840
Abstract
Al-5Ti-0.62C-0.2Ce master alloy was synthesized by a method of thermal explosion reaction in pure molten aluminum and used to modify commercial pure Al and hypoeutectic Al-8Si alloy. The microstructure and tensile properties of commercial pure Al and hypoeutectic Al-8Si alloy with different additions [...] Read more.
Al-5Ti-0.62C-0.2Ce master alloy was synthesized by a method of thermal explosion reaction in pure molten aluminum and used to modify commercial pure Al and hypoeutectic Al-8Si alloy. The microstructure and tensile properties of commercial pure Al and hypoeutectic Al-8Si alloy with different additions of Al-5Ti-0.62C-0.2Ce master alloy were investigated. The results show that the Al-5Ti-0.62C-0.2Ce alloy was composed of α-Al, granular TiC, lump-like TiAl3 and block-like Ti2Al20Ce. Al-5Ti-0.62C-0.2Ce master alloy (0.3 wt %, 5 min) can significantly refine macro grains of commercial pure Al into tiny equiaxed grains. The Al-5Ti-0.62C-0.2Ce master alloy (0.3 wt %, 30 min) still has a good refinement effect. The tensile strength and elongation of commercial pure Al modified by the Al-5Ti-0.62C-0.2Ce master alloy (0.3 wt %, 5 min) increased by roughly 19.26% and 61.83%, respectively. Al-5Ti-0.62C-0.2Ce master alloy (1.5 wt %, 10 min) can significantly refine both α-Al grains and eutectic Si of hypoeutectic Al-8Si alloy. The dendritic α-Al grains were significantly refined to tiny equiaxed grains. The morphology of the eutectic Si crystals was significantly refined from coarse needle-shape or lath-shape to short rod-like or grain-like eutectic Si. The tensile strength and elongation of hypoeutectic Al-8Si alloy modified by the Al-5Ti-0.62C-0.2Ce master alloy (1.5 wt %, 10 min) increased by roughly 20.53% and 50%, respectively. The change in mechanical properties corresponds to evolution of the microstructure. Full article
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Open AccessArticle
High Temperature Oxidation and Wear Behaviors of Ti–V–Cr Fireproof Titanium Alloy
Metals 2017, 7(6), 226; https://doi.org/10.3390/met7060226 - 19 Jun 2017
Cited by 4 | Viewed by 1841
Abstract
The high temperature oxidation and wear behaviors of Ti–35V–15Cr–0.3Si–0.1C fireproof titanium alloy were examined at 873 and 1073 K. The oxidation weight gain after oxidation at 1073 K for 100 h was significantly larger than that at 873 K. Based on the analyses [...] Read more.
The high temperature oxidation and wear behaviors of Ti–35V–15Cr–0.3Si–0.1C fireproof titanium alloy were examined at 873 and 1073 K. The oxidation weight gain after oxidation at 1073 K for 100 h was significantly larger than that at 873 K. Based on the analyses of the oxidation reaction index and oxide layer, the oxidation process at 1073 K was mainly controlled by oxidation reaction at the interface between the substrate and oxide layer. Dry sliding wear tests were performed on a pin-on-disk tester in air conditions. The friction coefficient was smaller at 1073 K than that at 873 K, while the volume wear rate at 1073 K was larger due to formation of amount of oxides on the worn surface. When the wearing temperature increased from 873 to 1073 K, the wear mechanism underwent a transition from a combination of abrasive wear and oxidative wear to only oxidative wear. Full article
(This article belongs to the Special Issue Titanium Alloys 2017) Printed Edition available
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Open AccessFeature PaperArticle
Enhanced Adsorption Removal of Pb(II) and Cr(III) by Using Nickel Ferrite-Reduced Graphene Oxide Nanocomposite
Metals 2017, 7(6), 225; https://doi.org/10.3390/met7060225 - 19 Jun 2017
Cited by 12 | Viewed by 2710
Abstract
The heavy metals, such as Pb(II) and radioisotope Cr(III), in aqueous solutions are toxic even at trace levels and have caused adverse health impacts on human beings. Hence the removal of these heavy metals from the aqueous environment is of the utmost importance [...] Read more.
The heavy metals, such as Pb(II) and radioisotope Cr(III), in aqueous solutions are toxic even at trace levels and have caused adverse health impacts on human beings. Hence the removal of these heavy metals from the aqueous environment is of the utmost importance to protect biodiversity, hydrosphere ecosystems, and human beings. In this study, the reduced graphene oxide based inverse spinel nickel ferrite (rGONF) nanocomposite has been prepared and was utilized for the removal of Pb(II) and Cr(III) from aqueous solutions. The prepared rGONF has been confirmed by X-ray photoelectron (XPS) and Raman spectroscopy. The surface characteristics of rGONF were measured by scanning electron microscopy (SEM), High-Resolution Transmission Electron Microscope (HR-TEM), and Brunauer-Emmett-Teller (BET) surface analysis. The average particle size of rGONF was found to be 32.0 ± 2.0 nm. The surface site density for the specific surface area (Ns) of rGONF was found to be 0.00238 mol·g−1, which was higher than that of the graphene oxide (GO) and NiFe2O4, which was expected. The prepared rGONF has been successfully applied for the removal of Pb(II) and Cr(III) by batch mode. The batch adsorption studies concluded that the adsorption of Pb(II) and Cr(III) onto rGONF was rapid and the adsorption percentage was more than 99% for both metal ions. The adsorption isotherm results found that the adsorptive removal of both metal ions onto rGONF occurred through monolayer adsorption on a homogeneous surface of rGONF. The pH-edge adsorption results suggest the adsorption occurs through an inner-sphere surface complex, which is proved by 2-pKa-diffusion model fitting, where the pH-edge adsorption data was well fitted. The adsorption of metal ions increased with increasing temperature. The overall obtained results demonstrated that the rGONF was an effective adsorbent for Pb(II) and Cr(III) removal from wastewater. Full article
(This article belongs to the Special Issue Heavy Metal Determination and Removal)
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Open AccessArticle
Thermal Model of Rotary Friction Welding for Similar and Dissimilar Metals
Metals 2017, 7(6), 224; https://doi.org/10.3390/met7060224 - 16 Jun 2017
Cited by 3 | Viewed by 2481
Abstract
Friction welding is one of the foremost welding processes for similar and dissimilar metals. Previously, the process has been modeled utilizing the rudimentary techniques of constant friction and slip-stick friction. The motivation behind this article is to present a new characteristic for temperature [...] Read more.
Friction welding is one of the foremost welding processes for similar and dissimilar metals. Previously, the process has been modeled utilizing the rudimentary techniques of constant friction and slip-stick friction. The motivation behind this article is to present a new characteristic for temperature profile estimation in modeling of the rotary friction welding process. For the first time, a unified model has been exhibited, with an implementation of the phase transformation of similar and dissimilar materials. The model was generated on COMSOL Multiphysics® and thermal and structural modules were used to plot the temperature curve. The curve for the welding of dissimilar metals using the model was generated, compared and analyzed with that of practical curves already acquired through experimentation available in the literature, and then the effect of varying the parameters on the welding of similar metals was also studied. Full article
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Open AccessArticle
The Effect of Niobium on the Changing Behavior of Non-Metallic Inclusions in Solid Alloys Deoxidized with Mn and Si during Heat Treatment at 1473 K
Metals 2017, 7(6), 223; https://doi.org/10.3390/met7060223 - 16 Jun 2017
Cited by 2 | Viewed by 1601
Abstract
To clarify the effect of niobium (Nb) on the changing behavior of oxide inclusions in alloys containing different concentrations of Mn, Si, and Nb, heat treatment experiments at 1473 K were conducted and changes in the morphology, size, quantity, and composition of these [...] Read more.
To clarify the effect of niobium (Nb) on the changing behavior of oxide inclusions in alloys containing different concentrations of Mn, Si, and Nb, heat treatment experiments at 1473 K were conducted and changes in the morphology, size, quantity, and composition of these inclusions were investigated. The stability of the oxide inclusions in both molten and solid Fe-Mn-Si-Nb alloys was also estimated by thermodynamic calculation using available data. Results showed that the change in the composition of the oxide inclusions owing to heat treatment depended on the concentrations of Nb and Si in the alloy. MnO-SiO2-type oxide inclusions gradually transformed into MnO-Nb2O5-type or MnO-SiO2- & MnO-Nb2O5-type inclusions in low-Si and high-Nb alloys after heating for 60 min. However, the shape of the inclusions did not change clearly. It was indicated that, during the heat treatment at 1473 K, an interface chemical reaction between the Fe-Mn-Si-Nb alloys and the MnO-SiO2-type oxide inclusions occurred according to the experimental and calculation results. Full article
(This article belongs to the Special Issue Alloy Steels) Printed Edition available
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Open AccessReview
A Review of Thiosulfate Leaching of Gold: Focus on Thiosulfate Consumption and Gold Recovery from Pregnant Solution
Metals 2017, 7(6), 222; https://doi.org/10.3390/met7060222 - 15 Jun 2017
Cited by 25 | Viewed by 2245
Abstract
Thiosulfate leaching is a promising alternative to cyanidation, and the main hindrances for its wide commercial application are the high thiosulfate consumption and the difficult recovery of dissolved gold. In this review, the four solutions to reduce the consumption of thiosulfate, including the [...] Read more.
Thiosulfate leaching is a promising alternative to cyanidation, and the main hindrances for its wide commercial application are the high thiosulfate consumption and the difficult recovery of dissolved gold. In this review, the four solutions to reduce the consumption of thiosulfate, including the control of reaction conditions, the use of additives, the generation of thiosulfate in situ, and the replacement of traditional cupric-ammonia catalysis, are introduced and evaluated after the presentation of background knowledge about thiosulfate consumption. The replacement of cupric-ammonia catalysis with other metals, such as nickel- and cobalt-based catalysts, is proposed. The reason is that it not only reduces thiosulfate consumption observably via decreasing the redox potential of leach solution significantly but also is beneficial to gold recovery mainly owing to eliminating the interference of cuprous thiosulfate [Cu(S2O3)3]5−. Based on the comparative analysis for five common recovery techniques of rare-noble metals from pregnant leach solution, ion-exchange resin adsorption is considered to be the most appropriate to recover aurothiosulfate [Au(S2O3)2]3− because the resin can be employed in the form of resin-in-leach/pulp and, furthermore, is able to be eluted and regenerated simultaneously at ambient temperature. At last, how to reduce the process cost of the resin adsorption technique is discussed. In order to simplify the complex two-stage elution process for loaded resins, the traditional catalysis is suggested to be replaced. Full article
(This article belongs to the Special Issue Valuable Metal Recycling)
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Open AccessArticle
Robotic Nd:YAG Fiber Laser Welding of Ti-6Al-4V Alloy
Metals 2017, 7(6), 221; https://doi.org/10.3390/met7060221 - 15 Jun 2017
Cited by 10 | Viewed by 4036
Abstract
In the present study, Ti6Al4V titanium alloy plates were joined using a robotic fiber laser welding method. The laser welding process was carried out at two different welding speeds. Effects of different heat input conditions on the microstructure and mechanical properties of robotic [...] Read more.
In the present study, Ti6Al4V titanium alloy plates were joined using a robotic fiber laser welding method. The laser welding process was carried out at two different welding speeds. Effects of different heat input conditions on the microstructure and mechanical properties of robotic fiber laser welded joints were investigated. Some grain coarsening was observed in the microstructure of weld metal in samples joined using high heat input, compared to those using low heat input, and volume rates of primary α structures increased in the weld metal. The microstructure of weld metal in samples joined using low heat input was made of basket-weave or acicular α' grains and primary β grains in grain boundaries. Tensile and yield strength of samples joined using low heat input were higher than for those joined using high heat input, but their ductility was lower. Full article
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Open AccessArticle
TiO2 Nanotubes on Ti Dental Implant. Part 2: EIS Characterization in Hank’s Solution
Metals 2017, 7(6), 220; https://doi.org/10.3390/met7060220 - 14 Jun 2017
Cited by 8 | Viewed by 1998
Abstract
Titania nanotubes are widely studied for their potential applications in several fields. In this paper, the electrochemical characterization of a dental implant, made of commercially pure titanium grade 2, covered by titania nanotubes, when immersed in Hank’s solution, is proposed. Few papers were [...] Read more.
Titania nanotubes are widely studied for their potential applications in several fields. In this paper, the electrochemical characterization of a dental implant, made of commercially pure titanium grade 2, covered by titania nanotubes, when immersed in Hank’s solution, is proposed. Few papers were found in the scientific literature regarding this topic, so a brief review is reported, concerning the use of some equivalent circuits to model experimental data. The analysis of results, obtained by using Electrochemical Impedance Spectroscopy, showed that: (i) a good correlation exists between the variation of Ecorr and the estimated values of the charge transfer resistance for both the bare- and the nanotube-covered samples, (ii) the nanostructured surface seems to possess a more active behaviour, while the effect could be over-estimated due to the real extent of the surface covered by nanotubes, (iii) the analysis of the “n” parameter, used to fit the experimental data, confirms the complex nature of nanostructured layer as well as that the nanotubes are partially filled by compounds containing Ca, P and Mg, when immersed in Hank’s solution. The results obtained in this work give a better understanding of the electrochemical behaviour of the nanotubes layer when immersed in Hank’s solution and could help to design a surface able to improve the implant osseointegration. Full article
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Open AccessArticle
Effect of the Temperature in the Mechanical Properties of Austenite, Ferrite and Sigma Phases of Duplex Stainless Steels Using Hardness, Microhardness and Nanoindentation Techniques
Metals 2017, 7(6), 219; https://doi.org/10.3390/met7060219 - 14 Jun 2017
Cited by 6 | Viewed by 2488
Abstract
The aim of this work is to study the hardness of the ferrite, austenite and sigma phases of a UNS S32760 superduplex stainless steel submitted to different thermal treatments, thus leading to different percentages of the mentioned phases. A comparative study has been [...] Read more.
The aim of this work is to study the hardness of the ferrite, austenite and sigma phases of a UNS S32760 superduplex stainless steel submitted to different thermal treatments, thus leading to different percentages of the mentioned phases. A comparative study has been performed in order to evaluate the resulting mechanical properties of these phases by using hardness, microhardness and nanoindentation techniques. In addition, optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD) have been also used to identify their presence and distribution. Finally, the experimental results have shown that the resulting hardness values were increased as a function of a longer heat treatment duration which it is associated to the formation of a higher percentage of the sigma phase. However, nanoindentation hardness measurements of this sigma phase showed lower values than expected, being a combination of two main factors, namely the complexity of the sigma phase structure as well as the surface finish (roughness). Full article
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Open AccessFeature PaperArticle
Multiphysics Simulation and Experimental Investigation of Aluminum Wettability on a Titanium Substrate for Laser Welding-Brazing Process
Metals 2017, 7(6), 218; https://doi.org/10.3390/met7060218 - 13 Jun 2017
Cited by 3 | Viewed by 1741
Abstract
The control of metal wettability is a key-factor in the field of brazing or welding-brazing. The present paper deals with the numerical simulation of the whole phenomena occurring during the assembly of dissimilar alloys. The study is realized in the frame of potential [...] Read more.
The control of metal wettability is a key-factor in the field of brazing or welding-brazing. The present paper deals with the numerical simulation of the whole phenomena occurring during the assembly of dissimilar alloys. The study is realized in the frame of potential applications for the aircraft industry, considering the case of the welding-brazing of aluminum Al5754 and quasi-pure titanium Ti40. The assembly configuration, presented here, is a simplification of the real experiment. We have reduced the three-dimensional overlap configuration to a bi-dimensional case. In the present case, an aluminum cylinder is fused onto a titanium substrate. The main physical phenomena which are considered here are: the heat transfers, the fluid flows with free boundaries and the mass transfer in terms of chemical species diffusion. The numerical problem is implemented with the commercial software Comsol Multiphysics™, by coupling heat equation, Navier-Stokes and continuity equations and the free boundary motion. The latter is treated with the Arbitrary Lagrangian Eulerian method, with a particular focus on the contact angle implementation. The comparison between numerical and experimental results shows a very satisfactory agreement in terms of droplet shape, thermal field and intermetallic layer thickness. The model validates our numerical approach. Full article
(This article belongs to the Special Issue Laser Welding)
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Open AccessArticle
The Role of Mechanical Connection during Friction Stir Keyholeless Spot Welding Joints of Dissimilar Materials
Metals 2017, 7(6), 217; https://doi.org/10.3390/met7060217 - 13 Jun 2017
Cited by 1 | Viewed by 2163
Abstract
Contrast experiments of lap joints among dissimilar AZ31B Mg alloy, Mg99.50, zinc-coated DP600 sheet, and non-zinc-coated DP600 sheet were made by friction stir keyholeless spot welding (FSKSW) and vacuum diffusion welding (VDW), respectively. Scanning electron microscopy (SEM) and energy disperse spectroscopy (EDS) were [...] Read more.
Contrast experiments of lap joints among dissimilar AZ31B Mg alloy, Mg99.50, zinc-coated DP600 sheet, and non-zinc-coated DP600 sheet were made by friction stir keyholeless spot welding (FSKSW) and vacuum diffusion welding (VDW), respectively. Scanning electron microscopy (SEM) and energy disperse spectroscopy (EDS) were used to investigate the microstructures and components of the joints welded. The experimental results show that the FSKSW bonding method is a kind of compound mode that contains a mechanical connection and element diffusion fusion connection, in which mechanical connection has the main decisive function on joints of Mg/steel. Elements diffusion exists in the interfacial region of the joints and the elements diffusion extent is basically the same to that of VDW. The elements’ diffusion in Mg/steel using FSKSW is defined in the reaction between small amounts elements of the base metal and zinc-coated metals. The intermetallic compounds and composite oxide perform some reinforcement on the mechanical connection strength. Full article
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Open AccessArticle
Microwave and Ultrasound Augmented Leaching of Complicated Zinc Oxide Ores in Ammonia and Ammonium Citrate Solutions
Metals 2017, 7(6), 216; https://doi.org/10.3390/met7060216 - 12 Jun 2017
Cited by 2 | Viewed by 1665
Abstract
Recovery of zinc from low grade zinc oxide ore is attempted with ammonia and ammonium citrate solutions augmented by microwave roasting and ultrasound radiation. The influence of the ammonia-ammonium ratio, roasting temperature, ultrasound power, and leaching time were assessed on the recovery of [...] Read more.
Recovery of zinc from low grade zinc oxide ore is attempted with ammonia and ammonium citrate solutions augmented by microwave roasting and ultrasound radiation. The influence of the ammonia-ammonium ratio, roasting temperature, ultrasound power, and leaching time were assessed on the recovery of zinc. A maximum zinc recovery of 88.57% could be achieved at a roasting temperature of 673 K, leaching temperature of 298 K, stirring speed of 300 rpm, total ammonia concentration of 5 mol/L with an ammonium citrate concentration of 1.2 mol/L, liquid to solid ratio of 5:1, the ultrasound power was 600 W and the leaching time was 120 min. The enhancement in recovery with increases in the roasting temperature up to 673 K was attributed to the conversion of ZnCO3 to ZnO. The phases of mineral samples and the reaction residues were characterized by X-ray diffraction (XRD). Full article
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Open AccessFeature PaperArticle
Low Field Magnetic and Thermal Hysteresis in Antiferromagnetic Dysprosium
Metals 2017, 7(6), 215; https://doi.org/10.3390/met7060215 - 12 Jun 2017
Cited by 3 | Viewed by 2604
Abstract
Magnetic and thermal hysteresis (difference in magnetic properties on cooling and heating) have been studied in polycrystalline Dy (dysprosium) between 80 and 250 K using measurements of the reversible Villari effect and alternating current (AC) susceptibility. We argue that measurement of the reversible [...] Read more.
Magnetic and thermal hysteresis (difference in magnetic properties on cooling and heating) have been studied in polycrystalline Dy (dysprosium) between 80 and 250 K using measurements of the reversible Villari effect and alternating current (AC) susceptibility. We argue that measurement of the reversible Villari effect in the antiferromagnetic phase is a more sensitive method to detect magnetic hysteresis than the registration of conventional B(H) loops. We found that the Villari point, recently reported in the antiferromagnetic phase of Dy at 166 K, controls the essential features of magnetic hysteresis and AC susceptibility on heating from the ferromagnetic state: (i) thermal hysteresis in AC susceptibility and in the reversible Villari effect disappears abruptly at the temperature of the Villari point; (ii) the imaginary part of AC susceptibility is strongly frequency dependent, but only up to the temperature of the Villari point; (iii) the imaginary part of the susceptibility drops sharply also at the Villari point. We attribute these effects observed at the Villari point to the disappearance of the residual ferromagnetic phase. The strong influence of the Villari point on several magnetic properties allows this temperature to be ranked almost as important as the Curie and Néel temperatures in Dy and likely also for other rare earth elements and their alloys. Full article
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Open AccessArticle
Preparation and Characterization of Aminated Hydroxyethyl Cellulose-Induced Biomimetic Hydroxyapatite Coatings on the AZ31 Magnesium Alloy
Metals 2017, 7(6), 214; https://doi.org/10.3390/met7060214 - 08 Jun 2017
Cited by 6 | Viewed by 2226
Abstract
The purpose of this work is to improve the cytocompatibility and corrosion resistance of magnesium alloy in the hope of preparing a biodegradable medical material. The aminated hydroxyethyl cellulose-induced biomimetic hydroxyapatite coating was successfully prepared on AZ31 magnesium alloy surface with a sol-gel [...] Read more.
The purpose of this work is to improve the cytocompatibility and corrosion resistance of magnesium alloy in the hope of preparing a biodegradable medical material. The aminated hydroxyethyl cellulose-induced biomimetic hydroxyapatite coating was successfully prepared on AZ31 magnesium alloy surface with a sol-gel spin coating method and biomimetic mineralization. Potentiodynamic polarization tests and electrochemical impedance spectroscopy showed that the hydroxyapatite/aminated hydroxyethyl cellulose (HA/AHEC) coating can greatly improve the corrosion resistance of AZ31 magnesium alloy and reduce the degradation speed in simulated body fluid (SBF). The MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium bromide] method and cell morphology observation results showed that the HA/AHEC coating on AZ31 magnesium alloy has excellent cytocompatibility and biological activity. Full article
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Open AccessArticle
Kinetics of Roasting Decomposition of the Rare Earth Elements by CaO and Coal
Metals 2017, 7(6), 213; https://doi.org/10.3390/met7060213 - 08 Jun 2017
Cited by 2 | Viewed by 1481
Abstract
The roasting method of magnetic tailing mixed with CaO and coal was used to recycle the rare earth elements (REE) in magnetic tailing. The phase transformation and decomposition process were researched during the roasting processes. The results showed that the decomposition processes of [...] Read more.
The roasting method of magnetic tailing mixed with CaO and coal was used to recycle the rare earth elements (REE) in magnetic tailing. The phase transformation and decomposition process were researched during the roasting processes. The results showed that the decomposition processes of REE in magnetic tailing were divided into two steps. The first step from 380 to 431 °C mainly entailed the decomposition of bastnaesite (REFCO3). The second step from 605 to 716 °C mainly included the decomposition of monazite (REPO4). The decomposition products were primarily RE2O3, Ce0.75Nd0.25O1.875, CeO2, Ca5F(PO4)3, and CaF2. Adding CaO could reduce the decomposition temperature of REFCO3 and REPO4. Meanwhile, the decomposition effect of CaO on bastnaesite and monazite was significant. Besides, the effects of the roasting time, roasting temperature, and CaO addition level on the decomposition rate were studied. The optimum technological conditions were a roasting time of 60 min; roasting temperature of 750 °C; and CaO addition level of 20% (w/w). The maximum decomposition rate of REFCO3 and REPO4 was 99.87%. The roasting time and temperature were the major factors influencing the decomposition rate. The kinetics process of the decomposition of REFCO3 and REPO4 accorded with the interfacial reaction kinetics model. The reaction rate controlling steps were divided into two steps. The first step (at low temperature) was controlled by a chemical reaction with an activation energy of 52.67 kJ/mol. The second step (at high temperature) was controlled by diffusion with an activation energy of 8.5 kJ/mol. Full article
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Open AccessArticle
Fatigue Behavior of the Rare Earth Rich EV31A Mg Alloy: Influence of Plasma Electrolytic Oxidation
Metals 2017, 7(6), 212; https://doi.org/10.3390/met7060212 - 08 Jun 2017
Cited by 6 | Viewed by 1561
Abstract
Rare earth rich magnesium alloys are used in aerospace and automotive fields because of their high specific strength and good castability. However, due to their low corrosion resistance, protective surface treatments, such as conversion coating or electroless plating are necessary, when they have [...] Read more.
Rare earth rich magnesium alloys are used in aerospace and automotive fields because of their high specific strength and good castability. However, due to their low corrosion resistance, protective surface treatments, such as conversion coating or electroless plating are necessary, when they have to be used in humid or corrosive environments. The present study was aimed at evaluating the effect of plasma electrolytic oxidation (PEO) and different surface roughness (Ra ≈ 0.8 μm and Ra ≈ 0.3 μm) on the rotating bending fatigue of an innovative Mg alloy, with a high content of Nd (up to 3.1 wt %) and Gd (up to 1.7 wt %). Fatigue tests revealed a 15% decrease in the fatigue strength of the PEO-treated alloy (fatigue strength = 88 MPa) with respect to the bare alloy (fatigue strength = 103 MPa). The reduction of fatigue strength was mainly due to the residual tensile stresses induced by the PEO treatment. The effect of surface roughness on the bare alloy was, instead, negligible. The mechanisms of crack initiation were similar in the untreated and PEO-treated alloy, with crack nucleation sites located in correspondence to large facets of the cleavage planes. Full article
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Open AccessArticle
Hydrogen Evolution Reaction Property in Alkaline Solution of Molybdenum Disulfide Modified by Surface Anchor of Nickel–Phosphorus Coating
Metals 2017, 7(6), 211; https://doi.org/10.3390/met7060211 - 07 Jun 2017
Cited by 3 | Viewed by 2568
Abstract
Molybdenum disulfide (MoS2) is unfavorable for practical application in the hydrogen evolution reaction (HER) process due to its inert basal surface, inferior conductivity, and limited amount of active edge sites. For the purpose of enhancing the HER performance of this catalyst, [...] Read more.
Molybdenum disulfide (MoS2) is unfavorable for practical application in the hydrogen evolution reaction (HER) process due to its inert basal surface, inferior conductivity, and limited amount of active edge sites. For the purpose of enhancing the HER performance of this catalyst, the HER activity of its basal surface should be increased. Herein, three types of nickel-phosphorus (Ni–P) coatings—namely, low phosphorus (LP), medium phosphorus (MP) and high phosphorus (HP) —were anchored onto the surfaces of MoS2 nanoparticles via an electroless plating process; thus, three Ni–P/MoS2 composites (Ni–LP/MoS2, Ni–MP/MoS2, and Ni–HP/MoS2) were fabricated. Crystal structures, morphologies, chemical components, and HER performances of each in an alkaline solution were characterized. Both Ni–LP/MoS2 and Ni–MP/MoS2 showed a crystal nature, while the amorphous feature for Ni–HP/MoS2 was validated. The three Ni–P/MoS2 composites exhibited a higher HER activity than the pure MoS2. The HER performance of the Ni–MP/MoS2 composite was more outstanding than those of other two composites, which could be attributed to the presence of metastable nickel phosphides, and the excellent conductivity of Ni–MP coating anchored on the basal surface of MoS2. Full article
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Open AccessArticle
Influence of Solution Treatment Temperature on Microstructural Properties of an Industrially Forged UNS S32750/1.4410/F53 Super Duplex Stainless Steel (SDSS) Alloy
Metals 2017, 7(6), 210; https://doi.org/10.3390/met7060210 - 07 Jun 2017
Cited by 5 | Viewed by 1872
Abstract
In this present study, the influence of solution annealing temperature on microstructural properties of a forged Super Duplex Stainless Steel (SDSS) was investigated by SEM-BSE (Scanning Electron Microscopy-Backscattered Electrons) and SEM-EBSD (Scanning Electron Microscopy-Electron Backscatter Diffraction) techniques. A brief solution treatment was applied [...] Read more.
In this present study, the influence of solution annealing temperature on microstructural properties of a forged Super Duplex Stainless Steel (SDSS) was investigated by SEM-BSE (Scanning Electron Microscopy-Backscattered Electrons) and SEM-EBSD (Scanning Electron Microscopy-Electron Backscatter Diffraction) techniques. A brief solution treatment was applied to the forged super duplex alloy, at different temperatures between 800 °C and 1100 °C, with a constant holding time of 0.6 ks (10 min). Microstructural characteristics such as nature, weight fraction, distribution and morphology of constituent phases, average grain-size and grain misorientation were analysed in relation to the solution annealing temperature. Experimental results have shown that the constituent phases in the SDSS alloy are δ-Fe, γ-Fe and σ (Cr-Fe) and that their properties are influenced by the solution treatment temperature. SEM examinations revealed microstructural modifications induced by the Cr rich precipitates along the δ/γ and δ/δ grain boundaries, which may significantly affect the toughness and the corrosion resistance of the alloy. Solution annealing at 1100 °C led to complete dissolution of σ (Cr-Fe) phase, the microstructure being formed of primary δ-Fe and γ-Fe. The orientation relationship between δ/δ, γ/γ and δ/γ grains was determined by electron back scattering diffraction (EBSD). Both primary constituent phase’s microhardness and global microhardness were determined. Full article
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Open AccessArticle
Three-Dimensional Numerical Modeling of Macrosegregation in Continuously Cast Billets
Metals 2017, 7(6), 209; https://doi.org/10.3390/met7060209 - 06 Jun 2017
Cited by 7 | Viewed by 1929
Abstract
Macrosegregation, serving as a major defect in billets, can severely degrade material homogeneity. Better understanding of the physical characteristics of macrosegregation through numerical simulation could significantly contribute to the segregation control. The main purpose of this study was to predict macrosegregation in continuously [...] Read more.
Macrosegregation, serving as a major defect in billets, can severely degrade material homogeneity. Better understanding of the physical characteristics of macrosegregation through numerical simulation could significantly contribute to the segregation control. The main purpose of this study was to predict macrosegregation in continuously cast billets with a newly developed three-dimensional macrosegregation model. The fluid flow, solidification, and solute transport in the entire billet region were solved and analyzed. Flow patterns, revealing a typical melt recirculation at the upper region of mold and thermosolutal convection at the secondary cooling zone, significantly affect the solidification and solute distribution. The solute redistribution occurring with thermosolutal convection at the solidification front contributes significantly to continued macrosegregation as solidification proceeds. The results of this study show that the equilibrium partition coefficient is mostly responsible for the magnitude of macrosegregation, while comparison between solute P and S indicated that diffusion coefficients also have some amount of influence. Typical macrosegregation patterns containing a positively segregated peak at the centerline and negatively segregated minima at either side were obtained via the proposed three-dimensional macrosegregation model, which validated by the measured surface temperatures and segregation degree. Full article
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Open AccessArticle
Investigation of Dynamic Recrystallization of NiTi Shape Memory Alloy Subjected to Local Canning Compression
Metals 2017, 7(6), 208; https://doi.org/10.3390/met7060208 - 06 Jun 2017
Cited by 2 | Viewed by 2048
Abstract
Physical mechanism for dynamic recrystallization of NiTi shape memory alloy subjected to local canning compression at various temperatures, 600, 700 and 800 °C, was investigated via electron backscattered diffraction experiments and transmission electron microscopy observations. With increasing deformation temperature, fractions of recrystallized grains [...] Read more.
Physical mechanism for dynamic recrystallization of NiTi shape memory alloy subjected to local canning compression at various temperatures, 600, 700 and 800 °C, was investigated via electron backscattered diffraction experiments and transmission electron microscopy observations. With increasing deformation temperature, fractions of recrystallized grains and substructures increase, whereas fraction of deformed grains decreases. In the case of 600 and 700 °C, continuous dynamic recrystallization and discontinuous dynamic recrystallization coexist in NiTi shape memory alloy. In the case of discontinuous dynamic recrystallization, the recrystallized grains are found to be nucleated at grain boundaries and even in grain interior. The pile-up of statistically stored dislocation lays the foundation for the nucleation of the recrystallized grains during discontinuous dynamic recrystallization of NiTi shape memory alloy. Geometrically necessary dislocation plays as an important role in the formation of new recrystallized grains during continuous dynamic recrystallization of NiTi shape memory alloy. Full article
(This article belongs to the Special Issue Shape Memory Alloys 2017) Printed Edition available
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Open AccessFeature PaperReview
Bio-Reclamation of Strategic and Energy Critical Metals from Secondary Resources
Metals 2017, 7(6), 207; https://doi.org/10.3390/met7060207 - 06 Jun 2017
Cited by 17 | Viewed by 2182
Abstract
Metals with an average crustal abundance of <0.01 ppm, which are high in supply shortage due to soaring demand, can, under the excessive environmental risk and <1% recycling rate of their production, be termed as ‘critical’ in a limited geo-boundary. A global trend [...] Read more.
Metals with an average crustal abundance of <0.01 ppm, which are high in supply shortage due to soaring demand, can, under the excessive environmental risk and <1% recycling rate of their production, be termed as ‘critical’ in a limited geo-boundary. A global trend to the green energy and low carbon technologies with geopolitical scenario is challenging for the sustainable reclamation of these metals from secondary resources. Among the available processes, bio-reclamation can be a sustainable technique for extracting and concentrating these metals. Therefore, in the present paper, the potential reclamation of critical metals (including rare earth elements, precious metals, and a common nuclear fuel element, uranium) via their interaction with microbe/s has been reviewed. Full article
(This article belongs to the Special Issue Valuable Metal Recycling)
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Open AccessArticle
Multi-Objective Parameter Optimization for Cross-Sectional Deformation of Double-Ridged Rectangular Tube in Rotary Draw Bending by Using Response Surface Methodology and NSGA-II
Metals 2017, 7(6), 206; https://doi.org/10.3390/met7060206 - 05 Jun 2017
Viewed by 1821
Abstract
Cross-sectional deformation of double-ridged rectangular tube (DRRT) inevitably occurs due to the inhomogeneous deformation induced by external boundary conditions in rotary draw bending (RDB). Unreasonable factor combination would aggravate the cross-sectional deformation of DRRT. So, a powerful and efficient method combining Response Surface [...] Read more.
Cross-sectional deformation of double-ridged rectangular tube (DRRT) inevitably occurs due to the inhomogeneous deformation induced by external boundary conditions in rotary draw bending (RDB). Unreasonable factor combination would aggravate the cross-sectional deformation of DRRT. So, a powerful and efficient method combining Response Surface Methodology (RSM) and Non-Sorted Genetic Algorithm II (NSGA-II) was proposed to optimize the factors to control the cross-sectional deformation of DRRT in RDB. Firstly, an orthogonal experiment was used to screen out the important factors. It was obtained that three factors—clearance between DRRT and mandrel, clearance between DRRT and bending die, and boosting of pressure die—have an important influence on the cross-sectional deformation of DRRT. It can also be observed that the variation trend of flange sagging (FS) is always consistent with that of space deformation between ridges (SDR) with the changing of factors. RSM based on a Box-Behnken design was then used to establish response surface models. The proposed response surface models were used to analyze the relationship of the important parameters to the responses, such as space deformation between ridges, and width deformation of outer and inner ridge grooves (WDO and WDI). Finally, multi-objective parameter optimization for the cross-sectional deformation of DRRT in RDB was performed by using the established model and NSGA-II algorithm. The interaction of responses was revealed and the value range of each response in the space of Pareto optimal solutions was determined. It can be observed that there is always an evident conflict between SDR and WDO in the space of Pareto optimal solutions. By using this optimization method, the absolute values of SDR and WDI were significantly reduced—by 13.17% and 17.97%, respectively—compared with those before optimization, while WDO just increase only a little. Full article
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Open AccessArticle
Bayesian Correlation Prediction Model between Hydrogen-Induced Cracking in Structural Members
Metals 2017, 7(6), 205; https://doi.org/10.3390/met7060205 - 05 Jun 2017
Cited by 4 | Viewed by 1808
Abstract
Background: A quantitative model was developed and applied for analyzing the correlation between hydrogen-induced corrosion cracking in both main cable wires and degraded stiffening of the girders of a cable suspension bridge, considering maintenance effects across time and space. Method: Bayesian inference is [...] Read more.
Background: A quantitative model was developed and applied for analyzing the correlation between hydrogen-induced corrosion cracking in both main cable wires and degraded stiffening of the girders of a cable suspension bridge, considering maintenance effects across time and space. Method: Bayesian inference is applied for predicting the correlations among the wires in the main cables owed to hydrogen-induced cracking (HIC) in the cable wires of a steel bridge, by using the improved hierarchical Bayesian models proposed here. Results: The simulated risk prediction under decreased strength of cable wires, due to the corrosion cracking, yields posterior distributions based on prior distributions and likelihoods. The Bayesian inference model can be applied to the design and maintenance of highly corroded and correlated components Data are updated through analyzed information from previous crack steps. A numerical example including not only reliability indices but also probabilities of failure for cable wires, damaged by HIC, is then presented. Compared with a conventional linear prediction model, the one herein developed provides highly improved convergence and closeness to the analyzed data. Conclusion: The proposed model can be used as a diagnostic or prognostic prediction tool for the performance of corroded bridge cable wires with crack propagation, allowing the development of maintenance plans for mechanical components and the overall structural system. Full article
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Open AccessArticle
Effect of Cooling Rate on Microstructure and Grain Refining Behavior of In Situ CeB6/Al Composite Inoculant in Aluminum
Metals 2017, 7(6), 204; https://doi.org/10.3390/met7060204 - 02 Jun 2017
Cited by 8 | Viewed by 2244
Abstract
Melt spinning was performed to process an in situ CeB6/Al inoculant at different rotating speeds to investigate the influence of cooling rate on the grain refining behavior of inoculants. It has been found that a high cooling rate caused two obvious [...] Read more.
Melt spinning was performed to process an in situ CeB6/Al inoculant at different rotating speeds to investigate the influence of cooling rate on the grain refining behavior of inoculants. It has been found that a high cooling rate caused two obvious changes in the inoculant: the supersaturated solid solution of Ce in the α-Al matrix and the miniaturization of CeB6 particles. At high cooling rates of ~108 K/s, the Ce content is largely beyond the theoretical solid solubility of Ce in Al, and the size of the CeB6 particles in ribbons is reduced to ~100 nm. The grain refining effect of melt-spun CeB6/Al composite inoculant shows significant dependence on holding time of which the best value should be no more than 2 min. The excellent grain refinement of the inoculant can be attributed to the combined effect of the nano-sized refiner particles and the large undercooling caused by the sudden melting of supersaturated Al–Ce solution. Full article
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Open AccessArticle
Investigation of the Effectiveness of Dental Implant Osseointegration Characterized by Different Surface Types
Metals 2017, 7(6), 203; https://doi.org/10.3390/met7060203 - 02 Jun 2017
Viewed by 1632
Abstract
Different surfaces were obtained by Plasma Electrolytic Oxidation (PEO) of the Ti–6Al–4V alloy; followed by hydrothermal treatment (HT). The surfaces were studied by scanning electron microscopy (SEM); Energy Dispersive Spectroscopy (EDS); X-ray Diffraction (XRD); Brunauer–Emmett–Teller (BET) absorption and abrasion wear tests. The resulting [...] Read more.
Different surfaces were obtained by Plasma Electrolytic Oxidation (PEO) of the Ti–6Al–4V alloy; followed by hydrothermal treatment (HT). The surfaces were studied by scanning electron microscopy (SEM); Energy Dispersive Spectroscopy (EDS); X-ray Diffraction (XRD); Brunauer–Emmett–Teller (BET) absorption and abrasion wear tests. The resulting surface contains hydroxyapatite (HA); which contributes to superior implant osseointegration. Treated implants were introduced into rabbits and their osseointegration was studied after two and six months. It was established that implant surface area increases due to pore formation. Pore formation and hydroxyapatite on the surface of the implant qualitatively change contact osseogenesis processes with reduced duration of osseointegration of implants. The treatment of the surface of the implants by the combination of PEO and HT provided better results in the medico-biological investigations than PEO alone. Abrasion tests demonstrated that the HA will be preserved after the procedure of implantation; ensuring effective osseointegration. Full article
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Open AccessFeature PaperArticle
Investigation on Mechanical Behavior of Biodegradable Iron Foams under Different Compression Test Conditions
Metals 2017, 7(6), 202; https://doi.org/10.3390/met7060202 - 02 Jun 2017
Cited by 15 | Viewed by 3012
Abstract
Biodegradable metal foams have been studied as potential materials for bone scaffolds. Their mechanical properties largely depend on the relative density and micro-structural geometry. In this work, mechanical behavior of iron foams with different cell sizes was investigated under various compression tests in [...] Read more.
Biodegradable metal foams have been studied as potential materials for bone scaffolds. Their mechanical properties largely depend on the relative density and micro-structural geometry. In this work, mechanical behavior of iron foams with different cell sizes was investigated under various compression tests in dry and wet conditions and after subjected to degradation in Hanks’ solution. Statistical analysis was performed using hypothesis and non-parametric tests. The deformation behavior of the foams under compression was also evaluated. Results show that the mechanical properties of the foams under dry compression tests had a “V-type” variation, which is explained as a function of different geometrical properties by using a simple tabular method. The wet environment did not change the compression behavior of the iron foams significantly while degradation decreased the elastic modulus, yield and compression strengths and the energy absorbability of the specimens. The deformation of open cell iron foams under compression is viewed as a complex phenomenon which could be the product of multiple mechanism such as bending, buckling and torsion. Full article
(This article belongs to the Special Issue Biodegradable Metals) Printed Edition available
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Open AccessArticle
The Microstructure Evolution, Mechanical Properties and Densification Mechanism of TiAl-Based Alloys Prepared by Spark Plasma Sintering
Metals 2017, 7(6), 201; https://doi.org/10.3390/met7060201 - 02 Jun 2017
Cited by 7 | Viewed by 2001
Abstract
The microstructure evolution and mechanical properties of a Ti-Al-Cr-Nb alloy prepared by spark plasma sintering (SPS) at different temperatures and stresses were investigated in detail. Sintering temperature plays a key role in the densification process and phase transformation, which determines the microstructure. The [...] Read more.
The microstructure evolution and mechanical properties of a Ti-Al-Cr-Nb alloy prepared by spark plasma sintering (SPS) at different temperatures and stresses were investigated in detail. Sintering temperature plays a key role in the densification process and phase transformation, which determines the microstructure. The mechanical properties of the sintered alloys depend on the microstructure caused by the sintering. Furthermore, the densification process and mechanism of TiAl-based metallic powders during SPS were studied based on experimental results and theoretical analysis, the results of which will help fabricate these kinds of intermetallic alloys using a powder metallurgy technique and accelerate their industrial applications. Full article
(This article belongs to the Special Issue Titanium Alloys 2017) Printed Edition available
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Open AccessArticle
The Effect of Initial Structure on Phase Transformation in Continuous Heating of a TA15 Titanium Alloy
Metals 2017, 7(6), 200; https://doi.org/10.3390/met7060200 - 01 Jun 2017
Cited by 5 | Viewed by 1992
Abstract
The effect of initial structure on phase evolution in continuous heating of a near-α TA15 titanium alloy (Ti-6Al-2Zr-1Mo-1V) was experimentally investigated. To this end; three microstructures were obtained by multiple heat treatment: I-bimodal structure with 50% equaixed α, II-bimodal structure with 15% equiaxed [...] Read more.
The effect of initial structure on phase evolution in continuous heating of a near-α TA15 titanium alloy (Ti-6Al-2Zr-1Mo-1V) was experimentally investigated. To this end; three microstructures were obtained by multiple heat treatment: I-bimodal structure with 50% equaixed α, II-bimodal structure with 15% equiaxed α, III-trimodal structure with 18% equiaxed α and 25% lamellar α. Differential scanning calorimetry (DSC), dilatometry and quantitative metallography were carried out on specimens with the three initial structures at heating rates from 5 to 40 °C/min. The transformation kinetics was modeled with the Johnson–Mehl–Avrami (JMA) approach under non-isothermal condition. It was found that there exists a four-stage transformation for microstructures I and III. The secondary and third stages overlap for microstructure II. The four stages of phase transformation overlap with increasing heating rate. In the presence of α laths, the phase transformation kinetics is affected by the composition difference between lamellar α and primary equiaxed α. Phase transformation is controlled by the growth of existing large β phase. Full article
(This article belongs to the Special Issue Titanium Alloys 2017) Printed Edition available
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