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Metals, Volume 7, Issue 11 (November 2017)

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Cover Story (view full-size image) Metallic alloy nanoparticles (NPs) are of great importance in order to optimize the corresponding [...] Read more.
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Open AccessArticle Microstructure and Microhardness of Laser Metal Deposition Shaping K465/Stellite-6 Laminated Material
Metals 2017, 7(11), 512; https://doi.org/10.3390/met7110512
Received: 18 October 2017 / Revised: 5 November 2017 / Accepted: 16 November 2017 / Published: 22 November 2017
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Abstract
K465 superalloy with high titanium and aluminum contents was easy to crack during laser metal deposition. In this study, the crack-free sample of K465/Stellite-6 laminated material was formed by laser metal deposition shaping to control the cracking behaviour in laser metal deposition of
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K465 superalloy with high titanium and aluminum contents was easy to crack during laser metal deposition. In this study, the crack-free sample of K465/Stellite-6 laminated material was formed by laser metal deposition shaping to control the cracking behaviour in laser metal deposition of K465 superalloy. The microstructure differences between the K465 superalloy with cracking and the laminated material were discussed. The microstructure and intermetallic phases were analyzed through scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The results showed that the microstructure of K465/Stellite-6 laminated material samples consisted of continuous dendrites with a similar structure size in different alloy deposition layers, and the second dendrite arm spacing was finer compared with laser metal deposition shaping K465. The intermetallic phases in the different alloy deposition layers varied, and the volume fraction of carbides in K465 deposition layer of the laminated material was higher than only K465 deposition under the fluid flow effect. In addition, the composition and microhardness distribution of laminated materials variation occurred along the deposition direction. Full article
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Open AccessArticle Wear of Shaped Surfaces of PVD Coated Dies for Clinching
Metals 2017, 7(11), 515; https://doi.org/10.3390/met7110515
Received: 10 October 2017 / Revised: 8 November 2017 / Accepted: 8 November 2017 / Published: 21 November 2017
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Abstract
A clinching method that uses a simple toolset consisting of a punch and a die, is utilized for joining lightweight materials. This paper is aimed at investigating the wear of the die cavity of a clinching tool. A clinching tool with a specially
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A clinching method that uses a simple toolset consisting of a punch and a die, is utilized for joining lightweight materials. This paper is aimed at investigating the wear of the die cavity of a clinching tool. A clinching tool with a specially shaped cavity was used for joining thin hot-dip galvanized steel sheets. Various types of physical vapour deposition (PVD) coatings such as ZrN, CrN and TiCN were deposited on the shaped surface of the die using Lateral Rotating Arc-Cathodes technology. Hot-dip galvanized steel sheets were used for testing the clinching tool. The material properties of PVD coatings that were deposited on the shaped part of the clinching die were evaluated. Finite Element Analysis was used to localize the area of the shaped part of the die and the part of surface area of the cylindrical die cavity of ϕ 5.0 mm, in which high contact pressure values were predicted. The prediction of the start of the wear cycle was verified experimentally by the clinching of 300 samples of hot-dip galvanized steel sheets. Unlike the CrN and ZrN coatings, the TiCN coating remained intact on the entire surface of the die. Full article
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Open AccessFeature PaperReview The Biological Responses to Magnesium-Based Biodegradable Medical Devices
Metals 2017, 7(11), 514; https://doi.org/10.3390/met7110514
Received: 20 September 2017 / Revised: 16 November 2017 / Accepted: 18 November 2017 / Published: 21 November 2017
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Abstract
The biocompatibility of Magnesium-based materials (MBMs) is critical to the safety of biodegradable medical devices. As a promising metallic biomaterial for medical devices, the issue of greatest concern is devices’ safety as degrading products are possibly interacting with local tissue during complete degradation.
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The biocompatibility of Magnesium-based materials (MBMs) is critical to the safety of biodegradable medical devices. As a promising metallic biomaterial for medical devices, the issue of greatest concern is devices’ safety as degrading products are possibly interacting with local tissue during complete degradation. The aim of this review is to summarize the biological responses to MBMs at the cellular/molecular level, including cell adhesion, transportation signaling, immune response, and tissue growth during the complex degradation process. We review the influence of MBMs on gene/protein biosynthesis and expression at the site of implantation, as well as throughout the body. This paper provides a systematic review of the cellular/molecular behavior of local tissue on the response to Mg degradation, which may facilitate a better prediction of long-term degradation and the safe use of magnesium-based implants through metal innovation. Full article
(This article belongs to the Special Issue Biodegradable Metals)
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Open AccessArticle Optimization of Thermo-Mechanical Processing for Forging of Newly Developed Creep-Resistant Magnesium Alloy ABaX633
Metals 2017, 7(11), 513; https://doi.org/10.3390/met7110513
Received: 28 October 2017 / Revised: 13 November 2017 / Accepted: 14 November 2017 / Published: 21 November 2017
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Abstract
The compressive strength and creep resistance of cast Mg-6Al-3Ba-3Ca (ABaX633) alloy has been measured in the temperature range of 25 to 250 °C, and compared with that of its predecessor ABaX422. The alloy is stronger and more creep-resistant than ABaX422, and exhibits only
[...] Read more.
The compressive strength and creep resistance of cast Mg-6Al-3Ba-3Ca (ABaX633) alloy has been measured in the temperature range of 25 to 250 °C, and compared with that of its predecessor ABaX422. The alloy is stronger and more creep-resistant than ABaX422, and exhibits only a small decrease of yield stress with temperature. The higher strength of ABaX633 is attributed to a larger volume fraction of intermetallic particles (Al, Mg)2Ca and Mg21Al3Ba2 in its microstructure. Hot deformation mechanisms in ABaX633 have been characterized by developing a processing map in the temperature and strain rate ranges of 300 to 500 °C and 0.0003 to 10 s−1. The processing map exhibits two workability domains in the temperature and strain rate ranges of: (1) 380 to 475 °C and 0.0003 to 0.003 s−1, and (2) 480–500 °C and 0.003 to 0.5 s−1. The apparent activation energy values estimated in the above two domains (204 and 216 kJ/mol) are higher than that for lattice self-diffusion of Mg, which is attributed to the large back-stress that is caused by the intermetallic particles. Optimum condition for bulk working is 500 °C and 0.01 s−1 at which hot workability will be maximum. Flow instability is exhibited at lower temperatures and higher strain rates, as well as at higher temperatures and higher strain rates. The predictions of the processing map on the workability domains, as well as the instability regimes are fully validated by the forging of a rib-web (cup) shaped component under optimized conditions. 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 Ni-Content on the Transformation Temperatures in NiTi-20 at. % Zr High Temperature Shape Memory Alloys
Metals 2017, 7(11), 511; https://doi.org/10.3390/met7110511
Received: 18 October 2017 / Revised: 15 November 2017 / Accepted: 16 November 2017 / Published: 21 November 2017
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Abstract
The effect of Ni-content on phase transformation behavior of NiTi-20 at. % Zr high temperature shape memory alloy (HTSMA) is investigated over a small composition range, i.e., 49.8, 50.0 and 50.2 at. % Ni, by differential scanning calorimetry (DSC), high-energy synchrotron radiation X-ray
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The effect of Ni-content on phase transformation behavior of NiTi-20 at. % Zr high temperature shape memory alloy (HTSMA) is investigated over a small composition range, i.e., 49.8, 50.0 and 50.2 at. % Ni, by differential scanning calorimetry (DSC), high-energy synchrotron radiation X-ray diffraction (SR-XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). All samples show a monoclinic B19 martensitic structure at room temperature. It is shown that even with these small variations in Ni-content, the alloy shows vastly different transformation temperatures and responds in a drastically different manner to aging treatments at 550 and 600 °C. Lastly, a discussion on H-phase composition with respect to bulk composition is presented. Full article
(This article belongs to the Special Issue Shape Memory Alloys 2017) Printed Edition available
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Open AccessFeature PaperArticle Effect of the Ultrasonic Nanocrystalline Surface Modification (UNSM) on Bulk and 3D-Printed AISI H13 Tool Steels
Metals 2017, 7(11), 510; https://doi.org/10.3390/met7110510
Received: 18 October 2017 / Revised: 14 November 2017 / Accepted: 17 November 2017 / Published: 21 November 2017
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Abstract
A comparative study of the microstructure, hardness, and tribological properties of two different AISI H13 tool steels—classified as the bulk with no heat treatment steel or the 3D-printed steel—was undertaken. Both samples were subjected to ultrasonic nanocrystalline surface modification (UNSM) to further enhance
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A comparative study of the microstructure, hardness, and tribological properties of two different AISI H13 tool steels—classified as the bulk with no heat treatment steel or the 3D-printed steel—was undertaken. Both samples were subjected to ultrasonic nanocrystalline surface modification (UNSM) to further enhance their mechanical properties and improve their tribological behavior. The objective of this study was to compare the mechanical properties and tribological behavior of these tool steels since steel can exhibit a wide variety of mechanical properties depending on different manufacturing processes. The surface hardness of the samples was measured using a micro-Vickers hardness tester. The hardness of the 3D-printed AISI H13 tool steel was found to be much higher than that of the bulk one. The surface morphology of the samples was characterized by electron backscattered diffraction (EBSD) in order to analyze the grain size and number of fractions with respect to the misorientation angle. The results revealed that the grain size of the 3D-printed AISI H13 tool steel was less than 0.5 μm, whereas that of the bulk tool steel was greater than 4 μm. The number of fractions of the bulk tool steel was about 0.5 μm at a low misorientation angle, and it decreased gradually with increasing misorientation angle. The low-angle grain boundary (LAGB) and high-angle grain boundary (HAGB) of the bulk sample were about 21% and 79%, respectively, and those of the 3D-printed sample were about 8% and 92%, respectively. Moreover, the friction and wear behavior of the UNSM-treated AISI H13 tool steel specimen was better than those of the untreated one. This study demonstrated the capability of 3D-printed AISI H13 tool steel to exhibit excellent mechanical and tribological properties for industrial applications. Full article
(This article belongs to the Special Issue Synthesis and Properties of Bulk Nanostructured Metallic Materials)
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Open AccessArticle Entropy Change Caused by Martensitic Transformations of Ferromagnetic Shape Memory Alloys
Metals 2017, 7(11), 509; https://doi.org/10.3390/met7110509
Received: 26 October 2017 / Revised: 11 November 2017 / Accepted: 13 November 2017 / Published: 19 November 2017
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Abstract
In this paper, our most recent findings on the influence of magnetic order on the main transformational caloric and elastic properties of shape memory alloys (SMAs) are reviewed. It is argued that ferromagnetic order has a strong influence on the temperature interval of
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In this paper, our most recent findings on the influence of magnetic order on the main transformational caloric and elastic properties of shape memory alloys (SMAs) are reviewed. It is argued that ferromagnetic order has a strong influence on the temperature interval of martensitic transformation (MT), the characteristics of stress-induced MT, and the shear elastic modulus of SMA. The problem of separation of the magnetic contributions to the entropy change ΔS and heat Q exchanged in the course of martensitic transformation (MT) of SMA is considered in general terms, and theoretical formulas enabling the solution of the problem are presented. As an example, the ΔS and Q values, which were experimentally determined for Ni-Mn-Ga and Ni-Fe-Ga alloys with different Curie temperatures TC and MT temperatures TM, are theoretically analyzed. It is shown that for Ni-Mn-Ga martensites with TM < TC, the ratio of elastic and magnetic contributions to the entropy change may be greater or smaller than unity, depending on the temperature difference TCTM. Full article
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Open AccessArticle Assessment of the Contour Method for 2-D Cross Sectional Residual Stress Measurements of Friction Stir Welded Parts of AA2024-T3—Numerical and Experimental Comparison
Metals 2017, 7(11), 508; https://doi.org/10.3390/met7110508
Received: 25 October 2017 / Revised: 6 November 2017 / Accepted: 14 November 2017 / Published: 19 November 2017
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Abstract
The contour method is one of the newest techniques for obtaining residual stress fields from friction stir welded (FSW) parts, experimentally. This method has many advantages; however, edge effects coming from the process itself might introduce artifacts in the obtained results, and this
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The contour method is one of the newest techniques for obtaining residual stress fields from friction stir welded (FSW) parts, experimentally. This method has many advantages; however, edge effects coming from the process itself might introduce artifacts in the obtained results, and this was slightly touched upon in the very first paper on the method. This concern is further assessed in the present work, where the contour method is compared with the results that were obtained numerically via a thermomechanical model and experimentally via the cut-compliance method. For the two-dimensional (2-D) cross sectional map obtained by the method, peak stresses in tension are observed in the mid-section of the FSW butt-welded plates at the distance of the tool radius from the centerline. The corresponding numerical simulation indicates the same behavior because of the particular clamping conditions, and consequently this should not be interpreted as a misleading result of the contour method. Edge effects from the cutting process involved in the contour method should, however, be taken into consideration, most likely resulting in the residual stresses observed near the surfaces of the cross section being less extreme in reality than observed. Full article
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Open AccessArticle Effect of High-Pressure Torsion on Structure and Microhardness of Ti/TiB Metal–Matrix Composite
Metals 2017, 7(11), 507; https://doi.org/10.3390/met7110507
Received: 19 October 2017 / Revised: 10 November 2017 / Accepted: 13 November 2017 / Published: 16 November 2017
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Abstract
Effect of high-pressure torsion (HPT) at 400 °C on microstructure and microhardness of a Ti/TiB metal–matrix composite was studied. The starting material was produced by spark plasma sintering of a mixture of a pure Ti and TiB2 (10 wt %) powders at
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Effect of high-pressure torsion (HPT) at 400 °C on microstructure and microhardness of a Ti/TiB metal–matrix composite was studied. The starting material was produced by spark plasma sintering of a mixture of a pure Ti and TiB2 (10 wt %) powders at 1000 °C. The microstructure evolution during HPT was associated with an increase in dislocation density and substructure development that resulted in a gradual microstructure refinement of the Ti matrix and shortening/redistribution of TiB whiskers. After five revolutions, a nanostructure with (sub) grain size of ~30 nm was produced in Ti matrix. The microhardness increased with strain attaining the value ~520 HV after five revolutions. The contribution of different hardening mechanisms into the hardness of the Ti/TiB metal–matrix composite was quantitatively analyzed. Full article
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Open AccessArticle Thermo-Calc Prediction of Mushy Zone in AlSiFeMn Alloys
Metals 2017, 7(11), 506; https://doi.org/10.3390/met7110506
Received: 22 October 2017 / Revised: 10 November 2017 / Accepted: 13 November 2017 / Published: 16 November 2017
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Abstract
Convection forces can cause significant segregation within the liquid during directional solidification, influencing the structure of the mushy zone and the type and distribution of phases present in the solidified alloy. The solidification behavior of AlSiFeMn alloys with strong convection was investigated via
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Convection forces can cause significant segregation within the liquid during directional solidification, influencing the structure of the mushy zone and the type and distribution of phases present in the solidified alloy. The solidification behavior of AlSiFeMn alloys with strong convection was investigated via experimental results combined with thermodynamic calculations. Experimental specimens were processed in a directional solidification facility with forced melt flow, resulting in high levels of elemental segregation across samples. The resulting local compositions were located on phase diagrams Al-Si-Fe, Al-Si-Mn and Al-Fe-Mn for prediction of the variation in solidification behavior. Phase mass fraction diagrams created in Thermo-Calc showed the effect of segregation on the characteristic temperatures, mushy zone length and the order of occurring phases precipitating across specimens. These findings were used to create 2D maps for visualization of the mushy zone, mass fraction of α-Al dendrites, β-Al5FeSi, Al15Si2Mn4 and their spatial location. The specimen centers showed enrichment in AlSi-eutectic but for β-Al5FeSi and Al15Si2Mn4 results are ambiguous. Fe-phases start to grow mainly behind the dendrites tips and in general may flow between them. Mn-rich phases start to precipitate at higher temperatures than β and in many places before α-Al and in this way may flow in the melt above the mushy zone. Full article
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Open AccessFeature PaperReview Recycling of Palladium from Spent Catalysts Using Solvent Extraction—Some Critical Points
Metals 2017, 7(11), 505; https://doi.org/10.3390/met7110505
Received: 15 September 2017 / Revised: 3 November 2017 / Accepted: 9 November 2017 / Published: 16 November 2017
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Abstract
Electrical and electronics equipment and automotive and industrial catalysts are some examples of top technological devices whose functioning rely on the use of platinum-group metals (PGMs). The PGMs’ high economic value and difficult to replace technological properties, together with their scarcity in the
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Electrical and electronics equipment and automotive and industrial catalysts are some examples of top technological devices whose functioning rely on the use of platinum-group metals (PGMs). The PGMs’ high economic value and difficult to replace technological properties, together with their scarcity in the Earth’s crust, justify concerns about their critical condition and reinforce the importance of developing recycling practices for PGM end-of-life materials. This article presents and discusses recent advances regarding the use of hydrometallurgical solvent extraction to recover one PGM, palladium, from spent catalysts. Two different tendencies are implicit in the literature concerning Pd(II) extraction: a few groups focus on the adjustment and optimization of current commercial extractants, while others prefer to design new extracting compounds. Actually, the leach solutions obtained from the treatment of anthropogenic materials generally exhibit different compositions when compared to those coming from the primary resources. The pros and cons of both approaches are critically discussed, and the assumptions backing some of the reported achievements are also appraised. Full article
(This article belongs to the Special Issue Solvent Extraction of Critical Metals)
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Open AccessFeature PaperArticle Laser Welding of BTi-6431S High Temperature Titanium Alloy
Metals 2017, 7(11), 504; https://doi.org/10.3390/met7110504
Received: 27 September 2017 / Revised: 10 November 2017 / Accepted: 13 November 2017 / Published: 15 November 2017
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Abstract
A new type of high temperature titanium alloy, BTi-6431S, has recently become the focus of attention as a potential material for aircraft engine applications, which could be used up to 700 °C. Pulsed laser welding was used to butt join the BTi-6431S titanium
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A new type of high temperature titanium alloy, BTi-6431S, has recently become the focus of attention as a potential material for aircraft engine applications, which could be used up to 700 °C. Pulsed laser welding was used to butt join the BTi-6431S titanium alloy in order to understand the feasibility of using fusion-based welding techniques on this material. The effect of laser energy on the microstructure and mechanical properties of the joints was investigated. The microstructural features of the joints were characterized by means of microscopy and X-ray diffraction. Tensile testing was conducted at both room temperature and high temperature to simulate potential service conditions. The results show that the microstructure of the laser welded joints consists of primary α phase and needle α’ phase, while the microstructure of the heat affected zone consists of α, β, and needle α’ phases. The tensile strength of the welded joints at room temperature was similar to that of the base material, despite a reduction in the maximum elongation was observed. This was related to the unfavorable microstructure in the welded joints. Nonetheless, based on these results, it is suggested that laser welding is a promising joining technique for the new BTi-6431S titanium alloy for aerospace applications. Full article
(This article belongs to the Special Issue Laser Welding)
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Open AccessArticle Effects of Matte Grade on the Distribution of Minor Elements (Pb, Zn, As, Sb, and Bi) in the Bottom Blown Copper Smelting Process
Metals 2017, 7(11), 502; https://doi.org/10.3390/met7110502
Received: 19 September 2017 / Revised: 9 November 2017 / Accepted: 9 November 2017 / Published: 14 November 2017
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Abstract
With increasing impurity contents in concentrates, the control of the minor elements is an important issue for the oxygen bottom blown copper smelting process (Shuikoushan process or SKS process). In this work, the distribution behaviors of the minor elements (such as Pb, Zn,
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With increasing impurity contents in concentrates, the control of the minor elements is an important issue for the oxygen bottom blown copper smelting process (Shuikoushan process or SKS process). In this work, the distribution behaviors of the minor elements (such as Pb, Zn, As, Sb, and Bi) among the matte, slag, and gas phases as a function of matte grades was investigated by adjusting the ratios of oxygen/ore in the SKS process. With a matte grade around 70%, about 82% As and 70% Bi enters the gas phase, and about 70% Sb and 64% Zn reports to the slag phase, while 55% lead enters the matte phase. The tendency of changes in the distribution of the minor elements in the SKS process is different from that in the Isasmelt process and the Flash smelting process. It may be concluded from this study that the distributions of the minor elements could be optimized to reduce adverse effects in the SKS process by regulating the matte grade. Full article
(This article belongs to the Special Issue Heavy Metal Determination and Removal)
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Open AccessArticle Effect of Nitrogen on Deformation-Induced Martensitic Transformation in an Austenitic 301 Stainless Steels
Metals 2017, 7(11), 503; https://doi.org/10.3390/met7110503
Received: 15 October 2017 / Revised: 7 November 2017 / Accepted: 10 November 2017 / Published: 13 November 2017
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Abstract
The effect of nitrogen on deformation-induced martensitic transformation (DIMT) in metastable 301 austenitic stainless steel has been studied based on the inelastic deformation theory. DIMT is regarded here as continuous relaxation process of internal strain energy accumulated during inelastic deformation. Using the kinetics
[...] Read more.
The effect of nitrogen on deformation-induced martensitic transformation (DIMT) in metastable 301 austenitic stainless steel has been studied based on the inelastic deformation theory. DIMT is regarded here as continuous relaxation process of internal strain energy accumulated during inelastic deformation. Using the kinetics equation based on the inelastic deformation theory the relationship between the volume fraction of transformed martensite and inelastic strain for DIMT has been successfully verified with the parameter representing the stability of austenite. The addition of nitrogen is experimentally found to increase austenite stability and the critical inelastic strain below which any DIMT is not observed to occur and to decrease the saturation volume fraction of α’ martensite. On the other hand, DIMT has been analyzed with its effect on stress-strain curve shape and mechanical properties in relation to the addition of nitrogen. The characteristic transition from sigmoidal to parabolic curve shape in stress-strain response has disappeared with the addition of nitrogen. Full article
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Open AccessArticle Fabrication and Characterization of a Low Magnetic Zr-1Mo Alloy by Powder Bed Fusion Using a Fiber Laser
Metals 2017, 7(11), 501; https://doi.org/10.3390/met7110501
Received: 19 October 2017 / Revised: 4 November 2017 / Accepted: 8 November 2017 / Published: 13 November 2017
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Abstract
A low magnetic Zr-1Mo alloy was fabricated by a powder bed fusion (PBF) process using a fiber laser. The microstructure, surface morphology, and pore distribution of the as-built Zr-1Mo alloy were observed. Its magnetic susceptibility and Vickers hardness were evaluated by magnetic susceptibility
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A low magnetic Zr-1Mo alloy was fabricated by a powder bed fusion (PBF) process using a fiber laser. The microstructure, surface morphology, and pore distribution of the as-built Zr-1Mo alloy were observed. Its magnetic susceptibility and Vickers hardness were evaluated by magnetic susceptibility balance and a microindentation tester, respectively. The as-built Zr-1Mo alloy mainly consisted of an α′ phase with an acicular structure. From the processing maps of the surface morphology and pore distribution, open pores on the top surface due to the lack of fusion corresponded to grid-like distributed pores, and large pores corresponded to balling particles on the top surface. The Vickers hardness was influenced by the oxygen and nitrogen contents rather than the porosity. The magnetic susceptibilities of the as-built Zr-1Mo alloy still were one-third those of Ti-6Al-4V and Ti-6Al-7Nb, thus PBF can be applicable to the fabrication process for the low magnetic Zr-1Mo alloy. Full article
(This article belongs to the Special Issue Zirconium Alloys)
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Open AccessArticle Microstructure and Properties of Porous Si3N4/Dense Si3N4 Joints Bonded Using RE–Si–Al–O–N (RE = Y or Yb) Glasses
Metals 2017, 7(11), 500; https://doi.org/10.3390/met7110500
Received: 15 October 2017 / Revised: 6 November 2017 / Accepted: 9 November 2017 / Published: 13 November 2017
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Abstract
The joining of porous Si3N4 to dense Si3N4 ceramics has been successfully performed using mixed RE2O3 (RE = Y or Yb), Al2O3, SiO2, and α-Si3N4
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The joining of porous Si3N4 to dense Si3N4 ceramics has been successfully performed using mixed RE2O3 (RE = Y or Yb), Al2O3, SiO2, and α-Si3N4 powders. The results suggested that the α-Si3N4 powders partly transformed into β-SiAlON and partly dissolved into oxide glass to form oxynitride glass. Thus, composites of glass/β-SiAlON-ceramic formed in the seam of joints. Due to the capillary action of the porous Si3N4 ceramic, the molten glass solder infiltrated into the porous Si3N4 ceramic side during the joining process and formed the “infiltration zone” with a thickness of about 400 μm, which contributed to the heterogeneous distribution of the RE–Si–Al–O–N glasses in the porous Si3N4 substrate. In-situ formation of β-SiAlON in the seam resulted in a high bonding strength. The maximum bending strength of 103 MPa and 88 MPa was reached for the porous Si3N4/dense Si3N4 joints using Y–Si–Al–O–N and Yb–Si–Al–O–N glass solders, respectively. Full article
(This article belongs to the Special Issue Diffusion Bonding and Brazing of Advanced Materials)
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Open AccessArticle Reduced Graphene Oxide Reinforced 7075 Al Matrix Composites: Powder Synthesis and Mechanical Properties
Metals 2017, 7(11), 499; https://doi.org/10.3390/met7110499
Received: 25 September 2017 / Revised: 7 November 2017 / Accepted: 7 November 2017 / Published: 13 November 2017
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Abstract
Reduced graphene oxide (rGO) reinforced 7075 Al matrix composites were fabricated by electrostatic self-assembly and powder metallurgy. 7075 Al powders were surface modified by introducing a cetyl trimethyl ammonium bromide (CTAB) membrane on the surface, which was able to form a strong bonding
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Reduced graphene oxide (rGO) reinforced 7075 Al matrix composites were fabricated by electrostatic self-assembly and powder metallurgy. 7075 Al powders were surface modified by introducing a cetyl trimethyl ammonium bromide (CTAB) membrane on the surface, which was able to form a strong bonding with graphene oxide (GO) through electrostatic interaction. During the vacuum sintering process, CTAB was effectively removed and GO was thermally reduced into rGO. Morphologies of GO nanosheets, GO/7075 Al powders, microstructures, and tensile fractographs of the composites were observed. The effect of rGO content on mechanical properties of rGO/7075 Al composites was investigated. The results show that a good bonding between rGO and matrix is achieved. With the rGO content increasing, the hardness increases gradually, while the ultimate tensile strength and yield strength initially increase and later decrease. The improvement in strength of rGO/7075 Al composites was attributed to stress transfer and dislocation strengthening. With rGO content reaching 0.50 wt %, the excessive addition of rGO gave rise to a weakening in the enhancement of the tensile properties due to the increasing amounts of brittle Al4C3 and cracks. Full article
(This article belongs to the Special Issue Metal Matrix Composites) Printed Edition available
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Open AccessArticle Investigation of the Deformation Mechanism of a near β Titanium Alloy through Isothermal Compression
Metals 2017, 7(11), 498; https://doi.org/10.3390/met7110498
Received: 17 October 2017 / Revised: 3 November 2017 / Accepted: 7 November 2017 / Published: 12 November 2017
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Abstract
This study investigated the hot deformation behavior of Ti-4Al-1Sn-2Zr-5Mo-8V-2.5Cr alloy through isothermal compression tests at temperatures from 780 to 930 °C with strain rates ranging from 0.001 to 1 s−1. The flow stress decreases with a decreased strain rate and an
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This study investigated the hot deformation behavior of Ti-4Al-1Sn-2Zr-5Mo-8V-2.5Cr alloy through isothermal compression tests at temperatures from 780 to 930 °C with strain rates ranging from 0.001 to 1 s−1. The flow stress decreases with a decreased strain rate and an increased temperature. A constitutive equation was established for this alloy and the dependence of activation energy on temperature and strain rate is discussed. We further proposed a processing map using the dynamic materials model. On the processing map various domains of flow stability and flow instability can be identified. The deformation mechanisms associated with flow stability regions are mainly dynamic recrystallization (DRX) and dynamic recovery (DRV). The flow instability is manifested in the form of the band of flow localizations. The optimum processing conditions are suggested such that the temperature range is from 780 to 880 °C and the strain rate ranges from 0.001 to 0.01 s−1. Full article
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Open AccessArticle The Formation of Composite Ti-Al-N Coatings Using Filtered Vacuum Arc Deposition with Separate Cathodes
Metals 2017, 7(11), 497; https://doi.org/10.3390/met7110497
Received: 15 October 2017 / Revised: 7 November 2017 / Accepted: 7 November 2017 / Published: 12 November 2017
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Abstract
Ti-Al-N coatings were deposited on high-speed steel substrates by filtered vacuum arc deposition (FVAD) during evaporation of aluminum and titanium cathodes. Distribution of elements, phase composition, and mechanical properties of Ti-Al-N coatings were investigated using Auger electron spectroscopy (AES), X-ray diffraction (XRD), transmission
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Ti-Al-N coatings were deposited on high-speed steel substrates by filtered vacuum arc deposition (FVAD) during evaporation of aluminum and titanium cathodes. Distribution of elements, phase composition, and mechanical properties of Ti-Al-N coatings were investigated using Auger electron spectroscopy (AES), X-ray diffraction (XRD), transmission electron microscopy (TEM) and nanoindentation, respectively. Additionally, tribological tests and scratch tests of the coatings were performed. The stoichiometry of the coating changes from Ti0.6Al0.4N to Ti0.48Al0.52N with increasing aluminum arc current from 70 A to 90 A, respectively. XRD and TEM showed only face-centered cubic Ti-Al-N phase with preferred orientation of the crystallites in (220) direction with respect to the sample normal and without precipitates of AlN or intermetallics inside the coatings. Incorporation of Al into the TiN lattice caused shifting of the (220) reflex to a higher 2θ angle with increasing Al content. Low content and size of microdroplets were obtained using coaxial plasma filters, which provides good mechanical and tribological properties of the coatings. The highest value of microhardness (36 GPa) and the best wear-resistance were achieved for the coating with higher Al content, thus for Ti0.48Al0.52N. These coatings exhibit good adhesive properties up to 30 N load in the scratch tests. Full article
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Open AccessArticle Virtual Testing of Composite Structures Made of High Entropy Alloys and Steel
Metals 2017, 7(11), 496; https://doi.org/10.3390/met7110496
Received: 19 September 2017 / Revised: 3 November 2017 / Accepted: 8 November 2017 / Published: 11 November 2017
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Abstract
High entropy alloys (HEA) are metallic materials obtained from a mixture of at least five atomic-scale chemical elements. They are characterized by high mechanical strength, good thermal stability and hardenability. AlCrFeCoNi alloys have high compression strength and tensile strength values of 2004 MPa,
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High entropy alloys (HEA) are metallic materials obtained from a mixture of at least five atomic-scale chemical elements. They are characterized by high mechanical strength, good thermal stability and hardenability. AlCrFeCoNi alloys have high compression strength and tensile strength values of 2004 MPa, respectively 1250 MPa and elongation of about 32.7%. These materials can be used to create HEA-steel type composite structures which resist to dynamic deformation during high speed impacts. The paper presents four different composite structures made from a combination of HEA and carbon steel plates, using different joining processes. The numerical simulation of the impact behavior of the composite structures was performed by virtual methods, taking into account the mechanical properties of both materials. For analyzing each constructive variant, three virtual shootings were designed, using a 7.62 × 39 mm cal. incendiary armor-piercing bullet and different impact velocities. The best ballistic behavior was provided by the composite structures obtained by welding and brazing that have good continuity and rigidity. The other composite structures, which do not have good surface adhesion, show high fragmentation risk, because the rear plate can fragment on the axis of shooting due to the combination between the shock waves and the reflected ones. The order of materials in the composite structure has a very important role in decreasing the impact energy. Full article
(This article belongs to the Special Issue High-Entropy Alloys (HEAs))
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Open AccessArticle Effect of Si and Zr on the Microstructure and Properties of Al-Fe-Si-Zr Alloys
Metals 2017, 7(11), 495; https://doi.org/10.3390/met7110495
Received: 10 October 2017 / Revised: 7 November 2017 / Accepted: 8 November 2017 / Published: 11 November 2017
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Abstract
The effects of Si and Zr on the microstructure, microhardness and electrical conductivity of Al-Fe-Si-Zr alloys were studied. An increase in the Zr content over 0.3 wt. % leads to the formation of primary Al3Zr inclusions and also decreases mechanical properties.
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The effects of Si and Zr on the microstructure, microhardness and electrical conductivity of Al-Fe-Si-Zr alloys were studied. An increase in the Zr content over 0.3 wt. % leads to the formation of primary Al3Zr inclusions and also decreases mechanical properties. Therefore, the Zr content should not be more than 0.3 wt. %, although the smaller content is insufficient for the strengthening by the secondary Al3Zr precipitates. The present results indicate that high content of Si significantly affects the hardness and electrical conductivity of the investigated alloys. However, the absence of Si led to the formation of harmful needle-shaped Al3Fe particles in the microstructure of the investigated alloys after annealing. Therefore, the optimum amount of Si was 0.25–0.50 wt. % due to the formation of the Al8Fe2Si phase with the preferable platelet morphology. The maximum microhardness and strengthening effects in Al-1% Fe-0.25% Si-0.3% Zr were observed after annealing at 400–450 °C due to the formation of nanosized coherent Al3Zr (L12) dispersoids. The effect of the increasing of the electrical conductivity can be explained by the decomposition of the solid solution. Thus, Al-1% Fe-0.25% Si-0.3% Zr alloy annealed at 450 °C has been studied in detail as the most attractive with respect to the special focus on transmission line applications. Full article
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Open AccessArticle Annealing Behavior of 6061 Al Alloy Subjected to Differential Speed Rolling Deformation
Metals 2017, 7(11), 494; https://doi.org/10.3390/met7110494
Received: 27 October 2017 / Revised: 3 November 2017 / Accepted: 6 November 2017 / Published: 10 November 2017
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Abstract
This study investigated the effects of heat treatment (annealing) on the microstructure of ultrafine grained 6061 Al alloy samples fabricated by a differential speed rolling (DSR) process. The samples were fabricated using two passes DSR with 75% thickness reduction and a speed ratio
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This study investigated the effects of heat treatment (annealing) on the microstructure of ultrafine grained 6061 Al alloy samples fabricated by a differential speed rolling (DSR) process. The samples were fabricated using two passes DSR with 75% thickness reduction and a speed ratio of 1:4. The DSR-deformed 6061 Al alloy sample exhibited a lamellar boundary structure composed mostly of subgrains surrounded by low-angle grain boundaries. After annealing, the DSR-deformed 6061 Al alloy samples exhibited coarse grained structure and transformed from lamellar to equiaxed, where both the grain size and grain shape aspect ratio increased with increasing annealing temperature. The fraction of grain boundaries with high misorientation angles increased progressively during annealing, to ~77% at annealing temperature of 350 °C. Full article
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Open AccessArticle Effect of Hydrogen on the Elastic and Anelastic Properties of the R Phase in Ti50Ni46.1Fe3.9 Alloy
Metals 2017, 7(11), 493; https://doi.org/10.3390/met7110493
Received: 12 October 2017 / Revised: 1 November 2017 / Accepted: 7 November 2017 / Published: 10 November 2017
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Abstract
The linear and non-linear internal friction, effective Young’s modulus, and amplitude-dependent modulus defect of a Ti50Ni46.1Fe3.9 alloy have been studied after different heat treatments, affecting hydrogen content, at temperatures of 13–300 K, and frequencies near 90 kHz. It
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The linear and non-linear internal friction, effective Young’s modulus, and amplitude-dependent modulus defect of a Ti50Ni46.1Fe3.9 alloy have been studied after different heat treatments, affecting hydrogen content, at temperatures of 13–300 K, and frequencies near 90 kHz. It has been shown that the contamination of the alloy by hydrogen gives rise to an internal friction maximum in the R martensitic phase and a complicated pinning stage in the temperature dependence of the effective Young’s modulus at temperatures corresponding to the high-temperature side of the maximum. Dehydrogenation of the H-contaminated alloy transforms the internal friction maximum into a plateau and minimizes the pinning stage. The internal friction maximum is associated with a competition of two different temperature-dependent processes affecting the hydrogen concentration in the core regions of twin boundaries. The amplitude-dependent anelasticity of the R phase is also very sensitive to hydrogen content, its temperature dependence reflects the evolution of extended hydrogen atmospheres near twin boundaries. Full article
(This article belongs to the Special Issue Shape Memory Alloys 2017) Printed Edition available
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Open AccessArticle Microstructures and Mechanical Properties of Dissimilar Al/Steel Butt Joints Produced by Autogenous Laser Keyhole Welding
Metals 2017, 7(11), 492; https://doi.org/10.3390/met7110492
Received: 30 September 2017 / Revised: 7 November 2017 / Accepted: 8 November 2017 / Published: 10 November 2017
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Abstract
Dissimilar Al/steel butt joints of 6.0 mm thick plates have been achieved using fiber laser keyhole welding autogenously. The cross sections, interface microstructures, hardness and tensile properties of Al/steel butt joints obtained under different travel speeds and laser beam offsets were investigated. The
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Dissimilar Al/steel butt joints of 6.0 mm thick plates have been achieved using fiber laser keyhole welding autogenously. The cross sections, interface microstructures, hardness and tensile properties of Al/steel butt joints obtained under different travel speeds and laser beam offsets were investigated. The phase morphology and thickness of the intermetallic compound (IMC) layers at the interface were analyzed by scanning electronic microscopes (SEM) using the energy-dispersive spectrometry (EDS) and electron back-scattered diffraction (EBSD) techniques. The results show that travel speeds and laser beam offsets are of considerable importance for the weld shape, morphology and thickness of IMC layers, and ultimate tensile strength (UTS) of Al/steel butt joints. This proves that the IMC layers consist of Fe2Al5 phases and Fe4Al13 phases by EBSD phase mapping. Increasing laser beam offsets from 0.3 mm to 0.7 mm significantly decreases the quantity of Fe4Al13 phases and the thickness of Fe2Al5 layers at the interface. During tensile processing, the Fe2Al5 layer with the weakest bonding strength is the most brittle region at the interface. However, an intergranular fracture that occurred at Fe2Al5 layers leads to a relatively high UTS of Al/steel butt joints. Full article
(This article belongs to the Special Issue Laser Welding)
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Open AccessArticle Experimental Validation of an FSW Model with an Enhanced Friction Law: Application to a Threaded Cylindrical Pin Tool
Metals 2017, 7(11), 491; https://doi.org/10.3390/met7110491
Received: 6 October 2017 / Revised: 3 November 2017 / Accepted: 6 November 2017 / Published: 10 November 2017
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Abstract
This work adopts a fast and accurate two-stage computational strategy for the analysis of FSW (Friction stir welding) processes using threaded cylindrical pin tools. The coupled thermo-mechanical problem is equipped with an enhanced friction model to include the effect of non-uniform pressure distribution
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This work adopts a fast and accurate two-stage computational strategy for the analysis of FSW (Friction stir welding) processes using threaded cylindrical pin tools. The coupled thermo-mechanical problem is equipped with an enhanced friction model to include the effect of non-uniform pressure distribution under the pin shoulder. The overall numerical strategy is successfully validated by the experimental measurements provided by the industrial partner (Sapa). The verification of the numerical model using the experimental evidence is not only accomplished in terms of temperature evolution but also in terms of torque, longitudinal, transversal and vertical forces. Full article
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Open AccessArticle Effect of Dynamic Reheating Induced by Weaving on the Microstructure of GTAW Weld Metal of 25% Cr Super Duplex Stainless Steel Weld Metal
Metals 2017, 7(11), 490; https://doi.org/10.3390/met7110490
Received: 16 October 2017 / Revised: 2 November 2017 / Accepted: 6 November 2017 / Published: 9 November 2017
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Abstract
The importance of the additional growth and/or transformation of the austenite phase that occurs in weld metals of super duplex stainless steel upon reheating is known. However, the effects have not been fully investigated, especially with respect to reheating induced by weaving during
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The importance of the additional growth and/or transformation of the austenite phase that occurs in weld metals of super duplex stainless steel upon reheating is known. However, the effects have not been fully investigated, especially with respect to reheating induced by weaving during single-pass welding. In this work, bead-on-pipe gas tungsten arc welding (GTAW) was conducted on super duplex stainless steel to understand the effect of weaving on the microstructure of weld metal. Microstructural analysis, electron backscatter diffraction (EBSD), and focused ion beam transmission electron microscopy (FIB-TEM) were carried out to investigate the relationship between weaving and microstructural change. The weaving of GTAW produced a dynamic reheated area just before the weld bead during welding. It was revealed that extensive reheated weld existed even after one welding pass, and that the content of the austenite phase in the reheated area was higher than that in the non-reheated area, indicating the existence of a large quantity of intragranular austenite phase. In addition, the Cr2N content in the reheated area was lower than that in the non-reheated area. This reduction of Cr2N was closely related to the reheating resulting from weaving. TEM analysis revealed that Cr2N in the non-reheated area was dispersed following heating and transformed to secondary austenite. Full article
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Open AccessArticle Revisiting Mg–Mg2Ni System from Electronic Perspective
Metals 2017, 7(11), 489; https://doi.org/10.3390/met7110489
Received: 14 September 2017 / Revised: 1 November 2017 / Accepted: 6 November 2017 / Published: 9 November 2017
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Abstract
Both Mg and Mg2Ni are promising electrode materials in conversion-type secondary batteries. Earlier studies have shown their single-phase prospects in electro-devices, while in this work, we have quantitatively reported the electronic properties of their dual-phase materials, that is, Mg–Mg2Ni
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Both Mg and Mg2Ni are promising electrode materials in conversion-type secondary batteries. Earlier studies have shown their single-phase prospects in electro-devices, while in this work, we have quantitatively reported the electronic properties of their dual-phase materials, that is, Mg–Mg2Ni alloys, and analyzed the underlying reasons behind the property changes of materials. The hypoeutectic Mg–Mg2Ni alloys are found to be evidently more conductive than the hypereutectic Mg–Mg2Ni system. The density functional theory (DFT) calculations give the intrinsic origin of electronic structures of both Mg2Ni and Mg. The morphology of quasi-nanoscale eutectics is another factor that can affect the electronic properties of the investigated alloy system; that is, the electrical property change of the investigated alloys system is due to a combination of the intrinsic property difference between the two constituting phases and the change of eutectic microstructures that affect electron scattering. In addition, regarding the Mg–Mg2Ni alloy design for device applications, the electronic property and mechanical aspect should be well balanced. Full article
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Open AccessFeature PaperArticle Inhibition of Brass (80/20) by 5-Mercaptopentyl-3-Amino-1,2,4-Triazole in Neutral Solutions
Metals 2017, 7(11), 488; https://doi.org/10.3390/met7110488
Received: 12 September 2017 / Revised: 31 October 2017 / Accepted: 5 November 2017 / Published: 9 November 2017
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Abstract
The effect of the adsorption of 5-mercaptopentyl-3-amino-1,2,4-triazole (MPATA) on the corrosive behavior of brass (Cu80/Zn20) in neutral (pH 7.4) borate buffer solutions with and without 0.01 M NaCl was studied. Electrochemical methods show significant decrease of the anodic and cathodic currents on the
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The effect of the adsorption of 5-mercaptopentyl-3-amino-1,2,4-triazole (MPATA) on the corrosive behavior of brass (Cu80/Zn20) in neutral (pH 7.4) borate buffer solutions with and without 0.01 M NaCl was studied. Electrochemical methods show significant decrease of the anodic and cathodic currents on the polarization curves in the presence of MPATA. X-ray photoelectron spectroscopy (XPS) reveals MPATA adsorption on the brass surface from an inhibitor solution. After 17 h of exposure, a mixed complex [CuxZnyMPATAz] with a thickness of about 3–3.5 nm is formed on the surface. This nanolayer has sufficient protective ability to withstand corrosion tests in a salt fog chamber: after 5 days of testing, the samples remain glossy and less than 1% of the surface has been damaged. After corrosion tests in a salt fog chamber, the surface of unprotected samples is enriched with zinc, while at the surface of inhibitor-treated samples, the copper and zinc are present in practically equal contents. Full article
(This article belongs to the Special Issue Corrosion Inhibition)
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Open AccessArticle Evaluation of Surface Mechanical Properties and Grindability of Binary Ti Alloys Containing 5 wt % Al, Cr, Sn, and V
Metals 2017, 7(11), 487; https://doi.org/10.3390/met7110487
Received: 26 September 2017 / Revised: 25 October 2017 / Accepted: 6 November 2017 / Published: 9 November 2017
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Abstract
This study aimed to investigate the relationship between the surface mechanical properties and the grindability of Ti alloys. Binary Ti alloys containing 5 wt % concentrations of Al, Cr, Sn, or V were prepared using a vacuum arc melting furnace, and their surface
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This study aimed to investigate the relationship between the surface mechanical properties and the grindability of Ti alloys. Binary Ti alloys containing 5 wt % concentrations of Al, Cr, Sn, or V were prepared using a vacuum arc melting furnace, and their surface properties and grindability were compared to those of commercially pure Ti (cp-Ti). Ti alloys containing Al and Sn had microstructures that consisted of only α phase, while Ti alloys containing Cr and V had lamellar microstructures that consisted of α + β phases. The Vickers microhardness of Ti alloys was increased compared to those of cp-Ti by the solid solution strengthening effect. Among Ti alloys, Ti alloy containing Al had the highest Vickers microhardness. At a low SiC wheel speed of 5000 rpm, the grinding rates of Ti alloys showed an increasing tendency as the hardness values of Ti alloys decreased. At a high SiC wheel speed of 10,000 rpm, the grinding rates of Ti alloys showed an increasing tendency as the tensile strength values increased. The Ti alloy containing Al, which showed the lowest tensile strength, had the lowest grinding rate. The grinding ratios of the Ti alloys were higher than those of cp-Ti at both wheel revolution speeds of 5000 and 10,000 rpm. The grinding ratio of the Ti alloy containing Al was significantly increased at 10,000 rpm (p < 0.05). Full article
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Open AccessArticle An Investigation of the Micro-Electrical Discharge Machining of Nickel-Titanium Shape Memory Alloy Using Grey Relations Coupled with Principal Component Analysis
Metals 2017, 7(11), 486; https://doi.org/10.3390/met7110486
Received: 27 September 2017 / Revised: 26 October 2017 / Accepted: 5 November 2017 / Published: 9 November 2017
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Abstract
Shape memory alloys (SMAs) are advanced engineering materials which possess shape memory effects and super-elastic properties. Their high strength, high wear-resistance, pseudo plasticity, etc., makes the machining of Ni-Ti based SMAs difficult using traditional techniques. Among all non-conventional processes, micro-electric discharge machining (micro-EDM)
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Shape memory alloys (SMAs) are advanced engineering materials which possess shape memory effects and super-elastic properties. Their high strength, high wear-resistance, pseudo plasticity, etc., makes the machining of Ni-Ti based SMAs difficult using traditional techniques. Among all non-conventional processes, micro-electric discharge machining (micro-EDM) is considered one of the leading processes for micro-machining, owing to its high aspect ratio and capability to machine hard-to-cut materials with good surface finish.The selection of the most appropriate input parameter combination to provide the optimum values for various responses is very important in micro-EDM. This article demonstrates the methodology for optimizing multiple quality characteristics (overcut, taper angle and surface roughness) to enhance the quality of micro-holes in Ni-Ti based alloy, using the Grey–Taguchi method. A Taguchi-based grey relational analysis coupled with principal component analysis (Grey-PCA) methodology was implemented to investigate the effect of three important micro-EDM process parameters, namely capacitance, voltage and electrode material.The analysis of the individual responses established the importance of multi-response optimization. The main effects plots for the micro-EDM parameters and Analysis of Variance (ANOVA) indicate that every parameter does not produce same effect on individual responses, and also that the percent contribution of each parameter to individual response is highly varied. As a result, multi-response optimization was implemented using Grey-PCA. Further, this study revealed that the electrode material had the strongest effect on the multi-response parameter, followed by the voltage and capacitance. The main effects plot for the Grey-PCA shows that the micro-EDM parameters “capacitance” at level-2 (i.e., 475 pF), “discharge voltage” at level-1 (i.e., 80 V) and the “electrode material” Cu provided the best multi-response. Full article
(This article belongs to the Special Issue Machining and Finishing of Nickel and Titanium Alloys)
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