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Metals, Volume 7, Issue 9 (September 2017)

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Open AccessFeature PaperArticle Influence of Alkali Treatment on Anodized Titanium Alloys in Wollastonite Suspension
Metals 2017, 7(9), 322; doi:10.3390/met7090322
Received: 12 July 2017 / Revised: 3 August 2017 / Accepted: 17 August 2017 / Published: 23 August 2017
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Abstract
The surface modification of titanium alloys is an effective method to improve their biocompatibility and tailor the material to the desired profile of implant functionality. In this work, technologically-advanced titanium alloys—Ti-15Mo, Ti-13Nb-13Zr and Ti-6Al-7Nb—were anodized in suspensions, followed by treatment in alkali solutions,
[...] Read more.
The surface modification of titanium alloys is an effective method to improve their biocompatibility and tailor the material to the desired profile of implant functionality. In this work, technologically-advanced titanium alloys—Ti-15Mo, Ti-13Nb-13Zr and Ti-6Al-7Nb—were anodized in suspensions, followed by treatment in alkali solutions, with wollastonite deposition from the powder phase suspended in solution. The anodized samples were immersed in NaOH or KOH solution with various concentrations with a different set of temperatures and exposure times. Based on their morphologies (observed by scanning electron microscope), the selected samples were investigated by Raman and X-ray photoelectron spectroscopy (XPS). Titaniate compounds were formed on the previously anodized titanium surfaces. The surface wettability significantly decreased, mainly on the modified Ti-15Mo alloy surface. Titanium alloy compounds had an influence on the results of the titanium alloys’ surface modification, which caused the surfaces to exhibit differential physical properties. In this paper, we present the influence of the anodization procedure on alkali treatment effects and the properties of obtained hybrid coatings. Full article
(This article belongs to the Special Issue Plasma Electrolytic Oxidation)
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Open AccessFeature PaperArticle Influence of the Heating Rate on the Foaming Behavior of Various Aluminium Alloys
Metals 2017, 7(9), 323; doi:10.3390/met7090323
Received: 14 July 2017 / Revised: 28 July 2017 / Accepted: 11 August 2017 / Published: 23 August 2017
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Abstract
Powders of metallurgically prepared precursors expand to a foam differently depending on how fast they are heated to their foaming temperature. The foaming behavior of four alloys was studied with heating rates varying from 0.1 K/s to 18 K/s. It was found that
[...] Read more.
Powders of metallurgically prepared precursors expand to a foam differently depending on how fast they are heated to their foaming temperature. The foaming behavior of four alloys was studied with heating rates varying from 0.1 K/s to 18 K/s. It was found that each alloy shows its own non-linear behavior of expansion values. Alloys not containing magnesium exhibit a maximum at intermediate heating rates, whereas Mg-containing alloys tend to expand more for higher heating rates. Full article
(This article belongs to the Special Issue Porous Metals and Metallic Foams)
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Open AccessArticle Peculiar Spatiotemporal Behavior of Unstable Plastic Flow in an AlMgMnScZr Alloy with Coarse and Ultrafine Grains
Metals 2017, 7(9), 325; doi:10.3390/met7090325
Received: 20 July 2017 / Revised: 14 August 2017 / Accepted: 18 August 2017 / Published: 23 August 2017
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Abstract
The work addresses the effects of nanosize particles and grain refinement on the patterns of stress serrations and kinematics of deformation bands associated with the Portevin–Le Chatelier instability of plastic flow. Ultra-fine-grained microstructure was obtained using equal-channel angular pressing of the initial coarse-grained
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The work addresses the effects of nanosize particles and grain refinement on the patterns of stress serrations and kinematics of deformation bands associated with the Portevin–Le Chatelier instability of plastic flow. Ultra-fine-grained microstructure was obtained using equal-channel angular pressing of the initial coarse-grained alloy. Tensile tests were carried out on flat specimens at strain rates in the range from 3 × 10−5 to 1.4 × 10−2 s−1. Using local extensometry techniques, it was found that the presence of nanoscale precipitates promotes quasi-continuous propagation of deformation bands in the entire strain-rate range. The grain refinement leads to a transition to relay-race propagation at high strain rates and static strain localization at low rates. The results are discussed from the viewpoint of competition between various dynamical modes of plastic deformation associated with collective dynamics of dislocations. Full article
(This article belongs to the Special Issue Synthesis and Properties of Bulk Nanostructured Metallic Materials)
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Open AccessArticle Development of Direct Quenched Hot Rolled Martensitic Strip Steels
Metals 2017, 7(9), 326; doi:10.3390/met7090326
Received: 7 June 2017 / Revised: 21 August 2017 / Accepted: 22 August 2017 / Published: 24 August 2017
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Abstract
Metallurgical concepts for new ultra-high strength martensitic steels have been developed through direct quenching after hot rolling. In addition to the chemical composition, the hot rolling, quenching, and annealing parameters need to be optimized to fulfill the requirements for the demanding applications for
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Metallurgical concepts for new ultra-high strength martensitic steels have been developed through direct quenching after hot rolling. In addition to the chemical composition, the hot rolling, quenching, and annealing parameters need to be optimized to fulfill the requirements for the demanding applications for which these steels are used. It is also shown that the welding behavior is influenced by the choice of alloying concept. Typical applications also require a high fatigue resistance, especially of formed components. For that reason, a dedicated set-up was developed that allows differentiation between materials, which is illustrated through the effect of inclusions on the fatigue performance of a bent test piece. Full article
(This article belongs to the Special Issue Bainite and Martensite: Developments and Challenges)
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Open AccessArticle Experimental Analysis on the Molten-Phase Dewetting Characteristics of AuPd Alloy Films on Topographically-Structured Substrates
Metals 2017, 7(9), 327; doi:10.3390/met7090327
Received: 14 July 2017 / Revised: 21 August 2017 / Accepted: 22 August 2017 / Published: 25 August 2017
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Abstract
AuPd nanoparticles are formed on fluorine-doped tin oxide (FTO) by a nanosecond laser irradiation-induced dewetting process of deposited AuPd films. In particular, we analyze the effect of the surface topography of the substrate on the dewetting process and, so, on the final mean
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AuPd nanoparticles are formed on fluorine-doped tin oxide (FTO) by a nanosecond laser irradiation-induced dewetting process of deposited AuPd films. In particular, we analyze the effect of the surface topography of the substrate on the dewetting process and, so, on the final mean size of the formed nanoparticles. In fact, we used two supporting FTO substrates differing in the surface topography: we used a FTO layer which is un-intentionally patterned since it is formed by FTO pyramids randomly distributed on the glass slide as result of the deposition process of the same FTO layer, namely substrate A. We used, also, a further FTO substrate, namely substrate B, presenting, as a result of a chemical etching process, a higher roughness and higher mean distance between nearest-neighbor pyramids with respect to substrate A. The results concerning the size of the obtained AuPd NPs by the laser irradiations with the laser fluence fixed shows that the substrate topography impacts on the dewetting process. In particular, we found that below a critical thickness of the deposited AuPd film, the NPs formed on substrates A and B have similar size and a similar trend for the evolution of their size versus the film thickness (i.e., the dewetting process is not influenced by the substrate topography since the film does not interact with the substrate topography). On the other hand, however, above a critical thickness of the deposited AuPd film, the AuPd NPs show a higher mean size (versus the film thickness) on substrate B than on substrate A, indicating that the AuPd film interacts with the substrate topography during the dewetting process. These results are quantified and discussed by the description of the substrate topography effect on the excess of chemical potential driving the dewetting process. Full article
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Open AccessArticle Processing Map of NiTiNb Shape Memory Alloy Subjected to Plastic Deformation at High Temperatures
Metals 2017, 7(9), 328; doi:10.3390/met7090328
Received: 29 July 2017 / Revised: 13 August 2017 / Accepted: 23 August 2017 / Published: 25 August 2017
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Abstract
The processing map of Ni47Ti44Nb9 (at %) shape memory alloy (SMA), which possesses B2 austenite phases and β-Nb phases at room temperature, is established in order to optimize the hot working parameters. Based on true stress-strain curves of
[...] Read more.
The processing map of Ni47Ti44Nb9 (at %) shape memory alloy (SMA), which possesses B2 austenite phases and β-Nb phases at room temperature, is established in order to optimize the hot working parameters. Based on true stress-strain curves of NiTiNb SMA during uniaxial compression deformation at the temperatures ranging from 700 to 1000 °C and at the strain rates ranging from 0.0005 to 0.5 s−1, according to dynamic material model (DMM) principle, the processing map of NiTiNb SMA is obtained on the basis of power dissipation map and instability map. The instability region of NiTiNb SMA increases with increasing the true strain and it mainly focuses on the region with high strain rate. The workability of NiTiNb SMA becomes worse and worse with increasing plastic strain, as well as decreasing deformation temperature. There exist two stability zones which are suitable for hot working of NiTiNb SMA. In one stability region, the deformation temperature ranges from 750 to 840 °C and the strain rate ranges from 0.0003 to 0.001 s−1. In the other stability region, the deformation temperature ranges from 930 to 1000 °C and the strain rate ranges from 0.016 to 0.1 s−1. The severe microstructure defects, such as coarsening grains, band microstructure, and intercrystalline overfiring appear in the microstructures of NiTiNb SMA which is subjected to plastic deformation in the instability zone. Full article
(This article belongs to the Special Issue Shape Memory Alloys 2017)
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Open AccessArticle The Effect of the Sintering Temperature and Addition of Niobium and Vanadium on the Microstructure and Mechanical Properties of Microalloyed PM Steels
Metals 2017, 7(9), 329; doi:10.3390/met7090329
Received: 9 July 2017 / Revised: 23 August 2017 / Accepted: 24 August 2017 / Published: 26 August 2017
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Abstract
In this work, the effect of the sintering temperature on the microstructure and mechanical properties of Nb-V added powder metallurgy (PM) steels was investigated. The microstructure and mechanical properties of the Nb-V added PM microalloyed steel were examined by optical microscopy, scanning electron
[...] Read more.
In this work, the effect of the sintering temperature on the microstructure and mechanical properties of Nb-V added powder metallurgy (PM) steels was investigated. The microstructure and mechanical properties of the Nb-V added PM microalloyed steel were examined by optical microscopy, scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), optical emission spectrometer (OES), tensile and hardness tests. Results indicated that the optimal sintering temperature was 1350 °C and the addition of 0.1%, 0.15% or 0.2% of Nb-V increases the yield strength (YS), ultimate tensile strength (UTS) and hardness of the PM sintered steels. 0.2 wt % Nb-V added PM steel showed the highest values in yield strength (YS), ultimate tensile strength (UTS) and the highest hardness. Elongation also tends to improve with adding Nb-V content. In addition, Nb-V limited grain growth during austenitization. Full article
(This article belongs to the Special Issue Selected Papers from the 3rd International Iron and Steel Symposium)
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Open AccessArticle Method to Evaluate the Kinetics of Bainite Transformation in Low-Temperature Nanobainitic Steel Using Thermal Dilatation Curve Analysis
Metals 2017, 7(9), 330; doi:10.3390/met7090330
Received: 4 July 2017 / Revised: 14 August 2017 / Accepted: 23 August 2017 / Published: 28 August 2017
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Abstract
The aim of this work was to develop a method to evaluate the kinetics of bainite transformation by theoretical deduction and thermal dilatation curve analysis. A Gleeble-3500 thermomechanical simulator and dilatometer (DIL805A) were employed to study the isothermal transformation in deformed (360
[...] Read more.
The aim of this work was to develop a method to evaluate the kinetics of bainite transformation by theoretical deduction and thermal dilatation curve analysis. A Gleeble-3500 thermomechanical simulator and dilatometer (DIL805A) were employed to study the isothermal transformation in deformed (360 C , 600 C , and 860 C ) and undeformed conditions. The thermal dilatation information during isothermal transformation was recorded, and the dilatation curves were well smoothed. By taking a derivative of the dilation curve with respect to the transformation time, the peak time of transformation rate (PTTR) was obtained, which can serve as the essence of isothermal transformation time. The relative change of length ( Δ L / L ) due to phase transformation was theoretically deduced, and the effect of temperature was taken into consideration. Combing experimental data, the volume fraction of bainite in isothermal transformation was calculated. Making a graph of volume fraction versus PTTR was a good method to evaluate the kinetics of bainitic transformation clearly and concisely which facilitated optimization of the preparation technique for low-temperature nanobainitic steel. Full article
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Open AccessArticle Application of the Constitutive Model in Finite Element Simulation: Predicting the Flow Behavior for 5754 Aluminum Alloy during Hot Working
Metals 2017, 7(9), 331; doi:10.3390/met7090331
Received: 4 August 2017 / Revised: 22 August 2017 / Accepted: 25 August 2017 / Published: 28 August 2017
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Abstract
The flow behavior of 5754 aluminum alloy was researched using the plane strain compression test for the range of 300–500 °C and 0.1–10 s−1. The experimental flow curves acquired directly from Gleeble-3500 show that deformation parameters have a significant effect on the flow
[...] Read more.
The flow behavior of 5754 aluminum alloy was researched using the plane strain compression test for the range of 300–500 °C and 0.1–10 s−1. The experimental flow curves acquired directly from Gleeble-3500 show that deformation parameters have a significant effect on the flow curves. All curves show a broad peak due to the dynamic softening after the work hardening. In addition, the flow curves display a slight downward trend after reaching the peak stress at low and medium strain rates. This softening mechanism has been further investigated by the work hardening rate and the results show that the flow characteristics of 5754 aluminum alloy are mainly controlled by the mechanism of competition between hardening, dynamic recovery and continuous dynamic recrystallization. Based on the corrected true strain-stress curves, the constitutive model of the corresponding softening mechanism has been established by a linear regression method. Then, the developed model was embedded in the finite element (FE) analysis software (ABAQUS) by encoding the UHARD subroutine and the hot compression process of the alloy was simulated and analyzed. The simulation results show that the sample has an uneven flow in the deformation zone, which is consistent with the grain morphology of the corresponding region of the test sample. In addition, the simulated load-stroke values were well fitted to the experimental data. The predictive ability of the model was quantified by statistical indicators. It emerged that the FE of the embedded constitutive model effectively simulates the hot working process of 5754 aluminum alloy, which has reference value for actual processing. Full article
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Open AccessArticle Structural and Mechanical Evaluation of a Nanocrystalline Al–5 wt %Si Alloy Produced by Mechanical Alloying
Metals 2017, 7(9), 332; doi:10.3390/met7090332
Received: 7 July 2017 / Revised: 18 August 2017 / Accepted: 20 August 2017 / Published: 29 August 2017
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Abstract
High energy mechanical milling followed by hot-pressing consolidation has been used to produce nanostructured Al–5 wt %Si alloy. X-ray diffraction (XRD), scanning electron microscopy equipped with energy dispersive X-ray detector (SEM-EDX), Vickers hardness, and compression measurements were used to examine the effect of
[...] Read more.
High energy mechanical milling followed by hot-pressing consolidation has been used to produce nanostructured Al–5 wt %Si alloy. X-ray diffraction (XRD), scanning electron microscopy equipped with energy dispersive X-ray detector (SEM-EDX), Vickers hardness, and compression measurements were used to examine the effect of milling duration on microstructure and mechanical properties of the nanostructured consolidated alloys. Crystallite sizes and lattice strains were determined by X-ray peak broadening analysis using the Williamson-Hall (W-H) method. Increasing the milling time reduced the crystallite size, and the minimum crystallite size of about 33 nm was achieved for both consolidated and powdered samples after 50 h of milling. Based on the SEM-EDX observations, the best distribution of silicon into Al matrix was obtained after 20 h of milling and remained unchanged afterwards. Hardness of both consolidated and powder samples increased with milling time, which can be attributed to the reduction of crystallite size and the better distribution of silicon in the aluminum matrix. Similarly, increased milling time increased the yield and compressive strengths of consolidated samples. Full article
(This article belongs to the Special Issue Light Weight Alloys: Processing, Properties and Their Applications)
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Open AccessArticle Resistance Upset Welding of ODS Steel Fuel Claddings—Evaluation of a Process Parameter Range Based on Metallurgical Observations
Metals 2017, 7(9), 333; doi:10.3390/met7090333
Received: 18 July 2017 / Revised: 28 July 2017 / Accepted: 8 August 2017 / Published: 29 August 2017
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Abstract
Resistance upset welding is successfully applied to Oxide Dispersion Strengthened (ODS) steel fuel cladding. Due to the strong correlation between the mechanical properties and the microstructure of the ODS steel, this study focuses on the consequences of the welding process on the metallurgical
[...] Read more.
Resistance upset welding is successfully applied to Oxide Dispersion Strengthened (ODS) steel fuel cladding. Due to the strong correlation between the mechanical properties and the microstructure of the ODS steel, this study focuses on the consequences of the welding process on the metallurgical state of the PM2000 ODS steel. A range of process parameters is identified to achieve operative welding. Characterizations of the microstructure are correlated to measurements recorded during the welding process. The thinness of the clad is responsible for a thermal unbalance, leading to a higher temperature reached. Its deformation is important and may lead to a lack of joining between the faying surfaces located on the outer part of the join which can be avoided by increasing the dissipated energy or by limiting the clad stick-out. The deformation and the temperature reached trigger a recrystallization phenomenon in the welded area, usually combined with a modification of the yttrium dispersion, i.e., oxide dispersion, which can damage the long-life resistance of the fuel cladding. The process parameters are optimized to limit the deformation of the clad, preventing the compactness defect and the modification of the nanoscale oxide dispersion. Full article
(This article belongs to the Special Issue Alloy Steels)
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Open AccessArticle Emergence and Progression of Abnormal Grain Growth in Minimally Strained Nickel-200
Metals 2017, 7(9), 334; doi:10.3390/met7090334
Received: 1 July 2017 / Revised: 18 August 2017 / Accepted: 23 August 2017 / Published: 30 August 2017
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Abstract
Grain boundary engineering (GBE) is a thermomechanical processing technique used to control the distribution, arrangement, and identity of grain boundary networks, thereby improving their mechanical properties. In both GBE and non-GBE metals, the phenomena of abnormal grain growth (AGG) and its contributing factors
[...] Read more.
Grain boundary engineering (GBE) is a thermomechanical processing technique used to control the distribution, arrangement, and identity of grain boundary networks, thereby improving their mechanical properties. In both GBE and non-GBE metals, the phenomena of abnormal grain growth (AGG) and its contributing factors is still a subject of much interest and research. In a previous study, GBE was performed on minimally strained (ε < 10%), commercially pure Nickel-200 via cyclic annealing, wherein unique onset temperature and induced strain pairings were identified for the emergence of AGG. In this study, crystallographic segmentation of grain orientations from said experiments are leveraged in tandem with image processing to quantify growth rates for abnormal grains within the minimally strained regime. Advances in growth rates are shown to vary directly with initial strain content but inversely with initiating AGG onset temperature. A numeric estimator for advancement rates associated with AGG is also derived and presented. Full article
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Open AccessArticle Reduction of Induced Central Damage in Cold Extrusion of Dual-Phase Steel DP800 Using Double-Pass Dies
Metals 2017, 7(9), 335; doi:10.3390/met7090335
Received: 25 July 2017 / Revised: 29 August 2017 / Accepted: 30 August 2017 / Published: 31 August 2017
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Abstract
Advanced High Strength Steels (AHSS) are a promising family of materials for applications where a high strength-to-weight ratio is required. Central burst is a typical defect commonly found in parts formed by extrusion and it can be a serious problem for the in-service
[...] Read more.
Advanced High Strength Steels (AHSS) are a promising family of materials for applications where a high strength-to-weight ratio is required. Central burst is a typical defect commonly found in parts formed by extrusion and it can be a serious problem for the in-service performance of the extrudate. The finite element method is a very useful tool to predict this type of internal defect. In this work, the software DEFORM-F2 has been used to choose the best configurations of multiple-pass dies, proposed as an alternative to single-pass extrusions in order to minimize the central damage that can lead to central burst in extruded parts of AHSS, particularly, the dual-phase steel DP800. It has been demonstrated that some geometrical configurations in double-pass dies lead to a minimum value of the central damage, much lower than the one obtained in single-pass extrusion. As a general rule, the position of the minimum damage leads to choosing higher values of the contacting length between partial reductions (L) for high die semiangles (α) and to lower values of the reduction in the first pass (RA) for low total reductions (RT). This methodology could be extended to find the best configurations for other outstanding materials. Full article
(This article belongs to the Special Issue Advances in Plastic Forming of Metals)
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Open AccessArticle Characterization of Corrosion Products on Weathering Steel Bridges Influenced by Chloride Deposition
Metals 2017, 7(9), 336; doi:10.3390/met7090336
Received: 15 August 2017 / Revised: 25 August 2017 / Accepted: 26 August 2017 / Published: 31 August 2017
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Abstract
The article presents the results of experimental testing of corrosion processes on weathering steel bridges. Two bridge structures spanning various obstacles were selected for the experimental measurement. The tested bridges are situated in the same location and structural solution of these bridges is
[...] Read more.
The article presents the results of experimental testing of corrosion processes on weathering steel bridges. Two bridge structures spanning various obstacles were selected for the experimental measurement. The tested bridges are situated in the same location and structural solution of these bridges is similar. Differences in development of corrosion products are mainly affected by the microclimate below the bridge structure. Special attention is paid to a bridge over the motorway which is strongly affected by the deposition of chlorides. The dependences between the measured deposition of chlorides and parameters of corrosion layers (thickness of corrosion products, corrosion rates, and chemical composition) are discussed and evaluated in this article. Full article
(This article belongs to the Special Issue Mechanical Behavior of High-Strength Low-Alloy Steels)
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Open AccessArticle A Modified Johnson-Cook Model for Hot Deformation Behavior of 35CrMo Steel
Metals 2017, 7(9), 337; doi:10.3390/met7090337
Received: 20 June 2017 / Revised: 2 August 2017 / Accepted: 23 August 2017 / Published: 1 September 2017
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Abstract
In this work, a compression experiment of 35CrMo steel is carried out over a wide range of temperatures (1123–1423 K) and strain rates (0.1–10 s−1) to obtain further understandings of the flow behaviors. The results show that the strain hardening effect
[...] Read more.
In this work, a compression experiment of 35CrMo steel is carried out over a wide range of temperatures (1123–1423 K) and strain rates (0.1–10 s−1) to obtain further understandings of the flow behaviors. The results show that the strain hardening effect of 35CrMo steel is stronger than that of dynamic recrystallization at low temperature and high strain rate; on the contrary, the rheological curves show typical dynamic recrystallization characteristics at high temperature and low strain rate. This indicates that the strain hardening and recrystallization behavior of 35CrMo steel is affected by temperature, strain and strain rate, and its true stress-strain curves can be observed typical work hardening and dynamic softening features. A modified Johnson-Cook (JC) model is developed to predict the flow stress of the alloy. The results of the comparison show that the predicted values of the modified JC model are in good agreement with the experimental values. Full article
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Open AccessArticle Corrosion Behavior of Keyhole-Free Friction Stir Spot Welded Joints of Dissimilar 6082 Aluminum Alloy and DP600 Galvanized Steel in 3.5% NaCl Solution
Metals 2017, 7(9), 338; doi:10.3390/met7090338
Received: 23 July 2017 / Revised: 23 August 2017 / Accepted: 27 August 2017 / Published: 1 September 2017
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Abstract
The corrosion behavior of keyhole-free friction stir spot welded joints of dissimilar 6082 aluminum alloy and DP600 galvanized steel in 3.5% NaCl solution has been investigated by the immersion test and electrochemical analysis. The surface of the aluminum alloy produced exfoliation and pitting
[...] Read more.
The corrosion behavior of keyhole-free friction stir spot welded joints of dissimilar 6082 aluminum alloy and DP600 galvanized steel in 3.5% NaCl solution has been investigated by the immersion test and electrochemical analysis. The surface of the aluminum alloy produced exfoliation and pitting corrosion. The pitting occurred seriously on the interface of the 6082 aluminum alloy, but the steel had no corrosion. The corrosion galvanic couples were formed between elements of Si and Fe with a high electrode potential, and Mg and Al with a low electrode potential, around them. Mg and Al elements of Mg2Si and Si-containing solid-solution phase α (Al) preferentially became an anodic dissolution and formed exfoliation corrosion around the Si elements. Fe-rich phase θ (Al3Fe) as the cathode caused corrosion of Mg and formed pitting around Mg-rich phase β (Al3Mg2) as the anode. The sequence of the corrosion resistance of different areas of the joints (with decreasing corrosion resistance) was WNZ (Weld Nugget Zone) > TMAZ (Thermo-mechanically Affected Zone) > BM (Base Metal) > HAZ (Heat-affected Zone). The joints of keyhole-free FSSW (Fiction Stir Spot Welding) of dissimilar 6082 aluminum alloy and DP600 galvanized steel have better corrosion resistance than base metal in 3.5% NaCl solution. Full article
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Open AccessArticle Steel Weld Metal Deposit Measured Properties after Immediate Micro-Jet Cooling
Metals 2017, 7(9), 339; doi:10.3390/met7090339
Received: 31 May 2017 / Revised: 24 July 2017 / Accepted: 31 July 2017 / Published: 1 September 2017
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Abstract
The aim of this paper is to present a welding process connected with micro-jet cooling. This method allowed us to guide the metallographic structure, and furthermore, the properties of the weld metal deposit. The main conclusion of this paper was that after welding
[...] Read more.
The aim of this paper is to present a welding process connected with micro-jet cooling. This method allowed us to guide the metallographic structure, and furthermore, the properties of the weld metal deposit. The main conclusion of this paper was that after welding with micro-jet cooling, it was possible to achieve beneficial metallographic structures that are impossible to obtain in any other way. These structures corresponded to very good mechanical properties of the welds. The research results described the influence of an artificially enhanced amount of acicular ferrite in the weld metal deposit (WMD) even above 65% when using micro-jet cooling. The results of this process were very positive due to the very high impact toughness of welds at negative temperature. The main parameters of micro-jet cooling are: cooling stream diameter (about 60 µm), gas pressure (about 0.6 MPa), the use of various gases and gas mixtures (main micro-jet gases: argon, helium, nitrogen, carbon dioxide, oxygen, air). Full article
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Open AccessArticle Experimental and Numerical Modeling of the Stress Rupture Behavior of Nickel-Based Single Crystal Superalloys Subject to Multi-Row Film Cooling Holes
Metals 2017, 7(9), 340; doi:10.3390/met7090340
Received: 20 July 2017 / Revised: 21 August 2017 / Accepted: 24 August 2017 / Published: 1 September 2017
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Abstract
The stress rupture behavior of nickel-base single crystal superalloys is a primary issue facing aero-engine design, which has been studied for more than 40 years. To a large degree, it is the existence of film cooling holes with the introduction of air cooling
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The stress rupture behavior of nickel-base single crystal superalloys is a primary issue facing aero-engine design, which has been studied for more than 40 years. To a large degree, it is the existence of film cooling holes with the introduction of air cooling techniques that adds the extra challenge to the problem. Using both experimental and numerical methods, we explore here the stress rupture behavior of nickel base single crystal plate specimens subject to multi-row film cooling holes. As the numerical simulation part, finite element analysis using Abaqus was performed. Numerical results reveal that the existence of film-holes causes stress concentration and transforms local stress from uniaxial to multi-axial. For the stress distribution of different types of specimens, we defined a stress multiaxiality factor to quantitatively characterize the degree of the stress complexity and examined its effect on the rupture behaviors of the specimens along with the true stress concentration factor. The test was also carried out and results indicated that the creep rupture lives of one- and two-row specimens turn out to be longer than those of non-hole specimen. However, the three- and four-row configuration showed the opposite trend. Among the geometric parameters of film-hole configuration, film-hole row spacing is a predominant one influencing the creep rupture properties. Numerical results agree well with the fracture positions and shapes of specimens. Full article
(This article belongs to the Special Issue Ni- and Co-Based Superalloys and Their Coatings)
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Open AccessArticle Definition of a First Process Window for Purification of Aluminum via “Cooled Finger” Crystallization Technique
Metals 2017, 7(9), 341; doi:10.3390/met7090341
Received: 25 July 2017 / Revised: 25 August 2017 / Accepted: 29 August 2017 / Published: 1 September 2017
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Abstract
Aluminum ultra-purification is commonly realized through a combination of three-layer electrolytic refining and fractional crystallization, mostly using zone melting. In order to achieve a purity over 6N with the aid of zone melting, many passes have to be performed, taking several days to
[...] Read more.
Aluminum ultra-purification is commonly realized through a combination of three-layer electrolytic refining and fractional crystallization, mostly using zone melting. In order to achieve a purity over 6N with the aid of zone melting, many passes have to be performed, taking several days to be accomplished. This paper focuses on a fractional crystallization methodology using a rotating and internally gas cooled crystallizer (“cooled finger”), based on a Japanese patent from the 1980s, about which no scientific investigation or publication has yet been found. This paper focuses on the impact of process conditions (mainly cooling gas flow and rotation velocity) on the growth rate of the crystallized material as well as on the reduction factor of the impurities Fe, Si, Pb, and Zn in aluminum in relationship to their initial concentration and their interaction in a multi-component system. This technique can be considered as a promising alternative for purification of aluminum as well as other metallic systems. Full article
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Open AccessArticle Behavior of the Steel T91 under Multi Axial Loading in Contact with Liquid and Solid Pb
Metals 2017, 7(9), 342; doi:10.3390/met7090342
Received: 2 August 2017 / Revised: 21 August 2017 / Accepted: 22 August 2017 / Published: 4 September 2017
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Abstract
In this work, the conditions for the occurrence of Liquid Metal Embrittlement (LME) in the ferritic-martensitic steel T91 in contact with lead, Pb, were examined. Slow tensile tests with notched specimens revealed that in a temperature range close to the melting point of
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In this work, the conditions for the occurrence of Liquid Metal Embrittlement (LME) in the ferritic-martensitic steel T91 in contact with lead, Pb, were examined. Slow tensile tests with notched specimens revealed that in a temperature range close to the melting point of Pb, the steel is sensitive to LME (350–400 °C) and to Solid Metal Induced Embrittlement (SMIE) (300 °C). The cracking was stimulated by wetting (using a chemical flux) and the notch effect. It was found that the multi axial stresses state and the high level of plastic strain in front of the notch were the key factors triggering crack initiation. Full article
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Open AccessArticle Stress Corrosion Cracking Behavior of Fine-Grained AZ61 Magnesium Alloys Processed by Equal-Channel Angular Pressing
Metals 2017, 7(9), 343; doi:10.3390/met7090343
Received: 21 July 2017 / Revised: 25 August 2017 / Accepted: 25 August 2017 / Published: 4 September 2017
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Abstract
The effect of equal-channel angular pressing (ECAP) on stress corrosion cracking (SCC) behavior of a cast AZ61 Mg alloy was investigated in distilled water (DW) using the slow strain rate tensile test (SSRT) at a strain rate of 1 × 10−6 s
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The effect of equal-channel angular pressing (ECAP) on stress corrosion cracking (SCC) behavior of a cast AZ61 Mg alloy was investigated in distilled water (DW) using the slow strain rate tensile test (SSRT) at a strain rate of 1 × 10−6 s−1. The fine-grained alloy after ECAP showed a greater SCC susceptibility but a higher ultimate tensile strength, compared with the as-cast counterpart. The results were attributed to refined grains, high-density dislocations and increased proportion of high-angle grain boundaries induced by severe plastic deformation, as well as isolated fine β-phase particles transiting from net-like β-phase. Full article
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Open AccessArticle Demonstrating the Effect of Precipitation on the Mechanical Stability of Fine-Grained Austenite in Reversion-Treated 301LN Stainless Steel
Metals 2017, 7(9), 344; doi:10.3390/met7090344
Received: 2 August 2017 / Revised: 28 August 2017 / Accepted: 31 August 2017 / Published: 4 September 2017
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Abstract
According to recent investigations, a huge difference exists in the mechanical stability of austenite between the grain-refined structure states obtained in reversion annealing at 800–700 °C or at 900 °C, in a 301LN type austenitic stainless steel. Precipitation of chromium nitride occurring at
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According to recent investigations, a huge difference exists in the mechanical stability of austenite between the grain-refined structure states obtained in reversion annealing at 800–700 °C or at 900 °C, in a 301LN type austenitic stainless steel. Precipitation of chromium nitride occurring at these lower temperatures has been argued to be the factor reducing the stability. To prove this argument, a fine-grained, very stable austenitic structure was created at 900 °C in 1 s, and subsequently annealed at lower temperatures between 850 and 750 °C, up to 1000 s. It was found that the subsequent annealing at 750 and 800 °C resulted in prominent gradual decrease of the mechanical stability under tensile straining, detectable after 10 s annealing duration and continued until 1000 s. Only minimal grain growth occurred, which decreased the stability very marginally. The degree of the stability drop followed the predicted kinetics of the Cr2N precipitation with regards as its dependence on annealing duration and temperature. Further, the tensile yield strength of the fine-grained structure increased slightly due to the annealing. The presence of nano-sized Cr2N particles was verified after 1000 s holding at 750 °C. These observations and predictions yield firm evidence for the imperative contribution of precipitation to the highly reduced mechanical stability of grain-refined austenite in this steel. Full article
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Open AccessArticle A Hybrid Multi-Scale Model of Crystal Plasticity for Handling Stress Concentrations
Metals 2017, 7(9), 345; doi:10.3390/met7090345
Received: 17 August 2017 / Revised: 29 August 2017 / Accepted: 30 August 2017 / Published: 4 September 2017
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Abstract
Microstructural effects become important at regions of stress concentrators such as notches, cracks and contact surfaces. A multiscale model is presented that efficiently captures microstructural details at such critical regions. The approach is based on a multiresolution mesh that includes an explicit microstructure
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Microstructural effects become important at regions of stress concentrators such as notches, cracks and contact surfaces. A multiscale model is presented that efficiently captures microstructural details at such critical regions. The approach is based on a multiresolution mesh that includes an explicit microstructure representation at critical regions where stresses are localized. At regions farther away from the stress concentration, a reduced order model that statistically captures the effect of the microstructure is employed. The statistical model is based on a finite element representation of the orientation distribution function (ODF). As an illustrative example, we have applied the multiscaling method to compute the stress intensity factor K I around the crack tip in a wedge-opening load specimen. The approach is verified with an analytical solution within linear elasticity approximation and is then extended to allow modeling of microstructural effects on crack tip plasticity. Full article
(This article belongs to the Special Issue Microstructure based Modeling of Metallic Materials)
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Open AccessArticle In Situ Study of Phase Transformations during Non-Isothermal Tempering of Bainitic and Martensitic Microstructures
Metals 2017, 7(9), 346; doi:10.3390/met7090346
Received: 30 July 2017 / Revised: 31 August 2017 / Accepted: 1 September 2017 / Published: 4 September 2017
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Abstract
Phase transformations during non-isothermal tempering of bainitic or martensitic microstructures obtained after quenching of a medium-carbon low-alloy steel was studied. The microstructures correspond to different locations of an as-quenched large-sized forged ingot used as a die material in the automotive industry. High-resolution dilatometry
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Phase transformations during non-isothermal tempering of bainitic or martensitic microstructures obtained after quenching of a medium-carbon low-alloy steel was studied. The microstructures correspond to different locations of an as-quenched large-sized forged ingot used as a die material in the automotive industry. High-resolution dilatometry experiments were conducted to simulate the heat treatment process, as well as to investigate different phenomena occurring during non-isothermal tempering. The microstructures were characterized using optical and scanning electron microscopy. Dilatometry analyses demonstrated that tempering behavior varied significantly from bainitic to martensitic microstructures. Retained austenite, which exists between bainitic ferrite sheaves, decomposes to lower bainite causing a remarkable volume increase. It was found that this decomposition finishes below 386 °C. By contrast, martensite tempering was accompanied with a volume decrease due to the decomposition of medium-carbon martensite to low carbon martensite and carbides. Full article
(This article belongs to the Special Issue Bainite and Martensite: Developments and Challenges)
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Open AccessArticle Pitting Corrosion of Steel Induced by Al2O3 Inclusions
Metals 2017, 7(9), 347; doi:10.3390/met7090347
Received: 13 July 2017 / Revised: 23 August 2017 / Accepted: 26 August 2017 / Published: 5 September 2017
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Abstract
To study the effect of Al2O3 inclusions on pitting corrosion in steel, our researchers utilized industrial pure iron as the raw material with the addition of a proper amount of pure aluminum powder to form Al2O3 inclusions.
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To study the effect of Al2O3 inclusions on pitting corrosion in steel, our researchers utilized industrial pure iron as the raw material with the addition of a proper amount of pure aluminum powder to form Al2O3 inclusions. Corrosion experiments were performed by exposing the samples to a 6% FeCl3 solution at room temperature (25 °C) for different lengths of time. Microscopic corrosion morphology was observed by scanning electron microscope (SEM), and the size change of the inclusions was quantitatively analyzed with Image Pro Plus. The experimental results showed that pitting corrosion arose preferentially around the Al2O3 inclusions, and that pitting corrosion initiated at the junction of the Al2O3 inclusions. The steel matrix dissolved and micro-cracks occurred as the Al2O3 inclusions that were buried shallowly below the surface of the steel matrix promoted corrosion of the steel matrix. As corrosion progressed, the shallowly buried Al2O3 inclusions began to appear on the surface, and the small, shallow inclusions fell off and formed micro pits. Furthermore, the clustered distribution of alumina inclusions had a greater effect on pitting initiation than the alumina inclusions distributed alone. Full article
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Open AccessArticle Misorientation-Dependent Twinning Induced Hardening and Texture Evolution of TWIP Steel Sheet in Plastic Deformation Process
Metals 2017, 7(9), 348; doi:10.3390/met7090348
Received: 31 July 2017 / Revised: 29 August 2017 / Accepted: 30 August 2017 / Published: 5 September 2017
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Abstract
The quantitative contribution of twinning to hardening behavior and its effect on crystal orientation need to be explored in greater depth for design and forming of twinning-induced-plasticity (TWIP) steel products. To address this issue, the characteristics of twinning formation in the plastic deformation
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The quantitative contribution of twinning to hardening behavior and its effect on crystal orientation need to be explored in greater depth for design and forming of twinning-induced-plasticity (TWIP) steel products. To address this issue, the characteristics of twinning formation in the plastic deformation of Fe-30Mn-3Si-2Al TWIP steel are investigated in terms of intergranular misorientation distribution using electron back-scattering diffraction (EBSD), which reveals that most deformation twins adhere to the high-angle grain boundaries (HAGBs) of the face-center-cube (FCC) type TWIP steel. Texture measurements are conducted to show a stable volume fraction of major components including Goss, S and A orientations, while Copper shifts towards Brass orientation. A crystal plasticity finite element (CPFE) model based on virtual polycrystalline microstructure adopting representative volume element (RVE) is employed to simulate the deformation to reveal the correlation between misorientation-dependent twinning and hardening behavior of TWIP steel. The results demonstrate that the proportion of twinning hardening to overall hardening is larger than slip hardening. The stability of texture evolution is simulated to predict the anisotropy of TWIP steel. This research substantiates the twinning induced hardening and texture evolution in deformation of TWIP steel and thus is essential for accurate prediction of the mechanical behaviors. Full article
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Open AccessArticle Effect of Welding Process on Microstructural and Mechanical Characteristics of Hardox 600 Steel
Metals 2017, 7(9), 349; doi:10.3390/met7090349
Received: 17 July 2017 / Revised: 29 August 2017 / Accepted: 31 August 2017 / Published: 5 September 2017
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Abstract
In the article, the structure and selected mechanical properties of welded Hardox 600 steel are presented. It is shown that, after welding of this material in as-delivered condition (i.e., with post-martensitic structure), structures of lower wear resistance are created within heat-affected zones. These
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In the article, the structure and selected mechanical properties of welded Hardox 600 steel are presented. It is shown that, after welding of this material in as-delivered condition (i.e., with post-martensitic structure), structures of lower wear resistance are created within heat-affected zones. These zones are over 80 mm wide, which makes them susceptible to uneven and fast wear in their intended applications. On the grounds of microscopic tests and hardness measurements, a thermal treatment of welded joints is suggested, consisting of quenching and low-temperature tempering of heat-affected zones. As a result of this treatment, the material structure in these areas becomes similar to the base material structure. Under laboratory conditions, the performed heat treatment does not cause any incompatibilities (cracks) in the welds. Full article
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Open AccessFeature PaperArticle Influence of Process Parameters on the Vertical Forces Generated during Friction Stir Welding of AA6082-T6 and on the Mechanical Properties of the Joints
Metals 2017, 7(9), 350; doi:10.3390/met7090350
Received: 31 July 2017 / Revised: 28 August 2017 / Accepted: 31 August 2017 / Published: 5 September 2017
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Abstract
The influence of the process parameters on the vertical force generated during friction stir welding of AA6082-T6 aluminium alloy sheet blanks was studied by performing experiments with constant values of the rotational speed, varying between 1200 and 2500 rpm, and welding speed, ranging
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The influence of the process parameters on the vertical force generated during friction stir welding of AA6082-T6 aluminium alloy sheet blanks was studied by performing experiments with constant values of the rotational speed, varying between 1200 and 2500 rpm, and welding speed, ranging between 30 and 100 mm/min. The effect of the tool dwelling was also analysed. The force vs. processing time curve has shown a very complex behaviour during the lowering motion of the pin tool related to the occurrence of both primary and secondary plunging. The tool dwelling produces a quick decrease in the vertical force with growing processing time until reaching a constant value. It was also seen that the tool dwelling does not influence the vertical force in the subsequent stage. As the tool began its welding motion, the vertical force immediately gets to a constant value until tool pulling out takes place. Furthermore, it was shown that the growth in the welding speed and the decrease in the rotational speed lead to an increase in the vertical force. The mechanical properties of the joints were evaluated versus the process parameters and the relationships among the ultimate tensile strength and ultimate elongation and the vertical force were defined. Finally, the microstructure developed during the friction stir welding was investigated and related to the mechanical properties of the joints. Full article
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Open AccessArticle Study of 13Cr-4Ni-(Mo) (F6NM) Steel Grade Heat Treatment for Maximum Hardness Control in Industrial Heats
Metals 2017, 7(9), 351; doi:10.3390/met7090351
Received: 16 June 2017 / Revised: 30 August 2017 / Accepted: 31 August 2017 / Published: 6 September 2017
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Abstract
The standard NACE MR0175 (ISO 15156) requires a maximum hardness value of 23 HRC for 13Cr-4Ni-(Mo) steel grade for sour service, requiring a double tempering heat treatment at temperature in the range 648–691 °C for the first tempering and 593–621 °C for the
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The standard NACE MR0175 (ISO 15156) requires a maximum hardness value of 23 HRC for 13Cr-4Ni-(Mo) steel grade for sour service, requiring a double tempering heat treatment at temperature in the range 648–691 °C for the first tempering and 593–621 °C for the second tempering. Difficulties in limiting alloy hardness after the tempering of forged mechanical components (F6NM) are often faced. Variables affecting the thermal behavior of 13Cr-4Ni-(Mo) during single and double tempering treatments have been studied by means of transmission electron microscopy (TEM) observations, X-ray diffraction measurements, dilatometry, and thermo-mechanical simulations. It has been found that relatively low Ac1 temperatures in this alloy induce the formation of austenite phase above 600 °C during tempering, and that the formed, reverted austenite tends to be unstable upon cooling, thus contributing to the increase of final hardness via transformation to virgin martensite. Therefore, it is necessary to increase the Ac1 temperature as much as possible to allow the tempering of martensite at the temperature range required by NACE without the detrimental formation of virgin martensite upon final cooling. Attempts to do so have been carried out by reducing both carbon (<0.02% C) and nitrogen (<100 ppm) levels. Results obtained herein show final hardness below NACE limits without an unacceptable loss of mechanical strength. Full article
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Open AccessArticle Optimization by Using Taguchi Method of the Production of Magnesium-Matrix Carbide Reinforced Composites by Powder Metallurgy Method
Metals 2017, 7(9), 352; doi:10.3390/met7090352
Received: 28 July 2017 / Revised: 22 August 2017 / Accepted: 3 September 2017 / Published: 7 September 2017
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Abstract
The aim of this study was to determine the optimum production parameters in the production of magnesium matrix carbide-reinforced composites by using the powder metallurgy method. The parameter levels maximizing density (%), hardness (HB10), and bending strength (MPa) values were found by using
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The aim of this study was to determine the optimum production parameters in the production of magnesium matrix carbide-reinforced composites by using the powder metallurgy method. The parameter levels maximizing density (%), hardness (HB10), and bending strength (MPa) values were found by using the Taguchi method. The type of reinforcement, the amount of reinforcement, the sintering time, the sintering temperature, additive type, and additive rate were selected as the production parameters. Since the production of Mg and its alloys by using casting methods is problematic, the hot pressing method, a powder metallurgy method, was preferred in this study. Ceramic-based carbide particles were used as reinforcing materials in Mg matrix composite materials. B4C, SiC, Mo2C, and TiC carbides were preferred as the carbide. Microstructure and phase composition of the produced materials was examined with scanning electron microscope (SEM), X-ray diffractogram (XRD) and X-ray energy dispersive spectrometry (EDS). The hardness of the materials was measured by using a Universal Hardness device. The relative densities of the materials were determined according to Archimedes’ principle. The bending strength properties of the materials were determined by using the three-point bending test. The optimum conditions were a sintering temperature of 500 °C, sintering duration of 5 min, additive type of B4C and additive rate of 2.5%, and the results obtained at these conditions were found to be as follows; relative density of 98.74 (%), hardness of 87.16 HB10 and bending strength of 193.65 MPa. SEM images taken from the fracture surfaces showed that the carbides added to the matrix had a relatively homogeneous distribution. XRD analyses revealed that the matrix was oxidized very little, and no phase formation occurred between the matrix and the carbides. Carbide addition caused a distinct hardness increase by showing the effect of distribution strengthening in the matrix. Full article
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Open AccessArticle Characterisation of Calcium- and Phosphorus-Enriched Porous Coatings on CP Titanium Grade 2 Fabricated by Plasma Electrolytic Oxidation
Metals 2017, 7(9), 354; doi:10.3390/met7090354
Received: 1 August 2017 / Revised: 16 August 2017 / Accepted: 1 September 2017 / Published: 8 September 2017
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Abstract
In the paper, Scanning Electron Microscopy (SEM), Energy-dispersive X-ray Spectroscopy (EDS), X-ray Photoelectron Spectroscopy (XPS), and Glow Discharge Optical Emission Spectroscopy (GDOES) analyses of calcium- and phosphorus-enriched coatings obtained on commercial purity (CP) Titanium Grade 2 by plasma electrolytic oxidation (PEO), known also
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In the paper, Scanning Electron Microscopy (SEM), Energy-dispersive X-ray Spectroscopy (EDS), X-ray Photoelectron Spectroscopy (XPS), and Glow Discharge Optical Emission Spectroscopy (GDOES) analyses of calcium- and phosphorus-enriched coatings obtained on commercial purity (CP) Titanium Grade 2 by plasma electrolytic oxidation (PEO), known also as micro arc oxidation (MAO), in electrolytes based on concentrated phosphoric acid with calcium nitrate tetrahydrate, are presented. The preliminary studies were performed in electrolytes containing 10, 300, and 600 g/L of calcium nitrate tetrahydrate, whereas for the main research the solution contained 500 g/L of the same hydrated salt. It was found that non-porous coatings, with very small amounts of calcium and phosphorus in them, were formed in the solution with 10 g/L Ca(NO3)2·4H2O, whereas the other coatings, fabricated in the consecutive electrolytes containing from 300 up to 650 g/L Ca(NO3)2·4H2O, were porous. Based on the GDOES data, it was also found that the obtained porous PEO coating may be divided into three sub-layers: the first, top, porous layer was the thinnest; the second, semi-porous layer was about 12 times thicker than the first; and the third, transition sub-layer was about 10 times thicker than the first. Based on the recorded XPS spectra, it was possible to state that the top 10-nm layer of porous PEO coatings included chemical compounds containing titanium (Ti4+), calcium (Ca2+), as well as phosphorus and oxygen (PO43− and/or HPO42− and/or H2PO4, and/or P2O74−). Full article
(This article belongs to the Special Issue Plasma Electrolytic Oxidation)
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Open AccessFeature PaperArticle Mechanical Characterization of Composite Coatings Formed by Reactive Detonation Spraying of Titanium
Metals 2017, 7(9), 355; doi:10.3390/met7090355
Received: 18 August 2017 / Revised: 5 September 2017 / Accepted: 5 September 2017 / Published: 8 September 2017
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Abstract
The structure and mechanical properties of the coatings formed by reactive detonation spraying of titanium in a wide range of spraying conditions were studied. The variable deposition parameters were the nature of the carrier gas, the spraying distance, the O2/C2
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The structure and mechanical properties of the coatings formed by reactive detonation spraying of titanium in a wide range of spraying conditions were studied. The variable deposition parameters were the nature of the carrier gas, the spraying distance, the O2/C2H2 ratio, and the volume of the explosive mixture. The phase composition of the coatings and the influence of the spraying parameters on the mechanical properties of the coatings were investigated. In addition, nanohardness of the individual phases contained in the coatings was evaluated. It was found that the composition of the strengthening phases in the coatings depends on the O2/C2H2 ratio and the nature of the carrier gas. Detonation spraying conditions ensuring the formation of composite coatings with a set of improved mechanical properties are discussed. The strength of the coatings was determined through the microhardness measurements and local characterization of the phases via nanoindentation. Three-point bending tests were employed in order to evaluate the crack resistance of the coatings. The strengthening mechanisms of the coatings by oxide or carbonitride phases were discussed. Full article
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Open AccessArticle A Combined Experimental-Numerical Approach for Investigating Texture Evolution of NiTi Shape Memory Alloy under Uniaxial Compression
Metals 2017, 7(9), 356; doi:10.3390/met7090356
Received: 26 July 2017 / Revised: 29 August 2017 / Accepted: 7 September 2017 / Published: 9 September 2017
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Abstract
Texture evolution of NiTi shape memory alloy was investigated during uniaxial compression deformation at 673 K (400 °C) by combining crystal plasticity finite element method with electron back-scattered diffraction experiment and transmission electron microscope experiment. Transmission electron microscope observation indicates that dislocation slip
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Texture evolution of NiTi shape memory alloy was investigated during uniaxial compression deformation at 673 K (400 °C) by combining crystal plasticity finite element method with electron back-scattered diffraction experiment and transmission electron microscope experiment. Transmission electron microscope observation indicates that dislocation slip rather than deformation twinning plays a dominant role in plastic deformation of B2 austenite NiTi shape memory alloy at 673 K (400 °C). Electron back-scattered diffraction experiment illustrates heterogeneous microstructure evolution resulting from dislocation slip in NiTi shape memory alloy at 673 K (400 °C). {110}<100>, {010}<100> and {110}<111> slip systems are introduced into a crystal plasticity constitutive model. Based on the constructed representative volume element model and the extracted crystallographic orientations, particle swarm optimization algorithm is used to identify crystal plasticity parameters from experimental results of NiTi shape memory alloy. Using the fitted material parameters, a crystal plasticity finite element method is used to predict texture evolution of NiTi shape memory alloy during uniaxial compression deformation. The simulation results agree well with the experimental ones. With the progression of plastic deformation, a crystallographic plane of NiTi shape memory alloy gradually rotates to be vertical to the loading direction, which lays the foundation for forming the <111> fiber texture. Full article
(This article belongs to the Special Issue Shape Memory Alloys 2017)
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Open AccessFeature PaperArticle Significantly Enhancing the Ignition/Compression/Damping Response of Monolithic Magnesium by Addition of Sm2O3 Nanoparticles
Metals 2017, 7(9), 357; doi:10.3390/met7090357
Received: 7 July 2017 / Revised: 3 September 2017 / Accepted: 6 September 2017 / Published: 9 September 2017
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Abstract
The present study reports the development of Mg–Sm2O3 nanocomposites as light-weight materials for weight critical applications targeted to reduce CO2 emissions, particularly in the transportation sector. Mg-0.5, 1.0, and 1.5 vol % Sm2O3 nanocomposites are synthesized
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The present study reports the development of Mg–Sm2O3 nanocomposites as light-weight materials for weight critical applications targeted to reduce CO2 emissions, particularly in the transportation sector. Mg-0.5, 1.0, and 1.5 vol % Sm2O3 nanocomposites are synthesized using a powder metallurgy method incorporating hybrid microwave sintering and hot extrusion. The microstructural studies showed dispersed Sm2O3 nanoparticles (NPs), refinement of grain size due to the presence of Sm2O3 NPs, and presence of limited porosity. Microhardness and dimensional stability of pure Mg increased with the progressive addition of Sm2O3 NPs. The addition of 1.5 vol % of Sm2O3 NPs to the Mg matrix enhanced the ignition temperature by ~69 °C. The ability of pure Mg to absorb vibration also progressively enhanced with the addition of Sm2O3 NPs. The room temperature compressive strengths (CYS and UCS) of Mg–Sm2O3 nanocomposites were found to be higher without having any adverse effect on ductility, leading to a significant increase in energy absorbed prior to compressive failure. Further, microstructural characteristics are correlated with the enhancement of various properties exhibited by nanocomposites. Full article
(This article belongs to the Special Issue Metal Matrix Composites)
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Open AccessArticle In Vitro Corrosion Properties of Mg Matrix In Situ Composites Fabricated by Spark Plasma Sintering
Metals 2017, 7(9), 358; doi:10.3390/met7090358
Received: 8 August 2017 / Revised: 4 September 2017 / Accepted: 7 September 2017 / Published: 9 September 2017
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Abstract
Mg matrix in situ composites were fabricated from Mg and ZnO powder by a spark plasma sintering method. The composition and microstructure of the sintered samples were characterized. Corrosion properties of fabricated composites were evaluated by immersion and by electrochemical tests using Hanks’
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Mg matrix in situ composites were fabricated from Mg and ZnO powder by a spark plasma sintering method. The composition and microstructure of the sintered samples were characterized. Corrosion properties of fabricated composites were evaluated by immersion and by electrochemical tests using Hanks’ solution. The results showed that the formation of in situ products improved significantly the corrosion resistance of the fabricated composites compared with pure Mg; Mg-10 wt % ZnO composites especially exhibited the lowest corrosion rate. In addition, an energy-dispersive X-ray (EDX) analysis showed that calcium phosphate formed as a corrosion product on the surface of Mg-10 wt % ZnO composites, while Mg(OH)2 appeared as a corrosion product on the surface of Mg-20 wt % ZnO composite. The findings suggested Mg-10 wt % ZnO composite as a potential candidate for temporary implant application. Full article
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Open AccessArticle Effect of Al2O3 Nanoparticles as Reinforcement on the Tensile Behavior of Al-12Si Composites
Metals 2017, 7(9), 359; doi:10.3390/met7090359
Received: 16 August 2017 / Revised: 5 September 2017 / Accepted: 7 September 2017 / Published: 10 September 2017
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Abstract
Al2O3 nanoparticle-reinforced Al-12Si matrix composites were successfully fabricated by hot pressing and subsequent hot extrusion. The influence of weight fraction of Al2O3 particles on the microstructure, mechanical properties, and the corresponding strengthening mechanisms were investigated in detail.
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Al2O3 nanoparticle-reinforced Al-12Si matrix composites were successfully fabricated by hot pressing and subsequent hot extrusion. The influence of weight fraction of Al2O3 particles on the microstructure, mechanical properties, and the corresponding strengthening mechanisms were investigated in detail. The Al2O3 particles are uniformly distributed in the matrix, when 2 and 5 wt. % of Al2O3 particles were added to the Al-12Si matrix. Significant agglomeration can be found in composites with 10 wt. % addition of Al2O3 nanoparticles. The maximum hardness, the yield strength, and tensile strength were obtained for the composite with 5 wt. % Al2O3 addition, which showed an increase of about ~11%, 23%, and 26%, respectively, compared with the Al-12Si matrix. Meanwhile, the elongation increased to about ~30%. The contribution of different mechanisms including Orowan strengthening, thermal mismatch strengthening, and load transfer strengthening were analyzed. It was shown that the thermal mismatch strengthening has a more significant contribution to strengthening these composites than the Orowan and load transfer strengthening mechanisms. Full article
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Open AccessArticle Preparation of Vanadium Nitride Using a Thermally Processed Precursor with Coating Structure
Metals 2017, 7(9), 360; doi:10.3390/met7090360
Received: 30 July 2017 / Revised: 22 August 2017 / Accepted: 5 September 2017 / Published: 11 September 2017
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Abstract
A new effective method is proposed to prepare vanadium nitride (VN) via carbothermal reduction–nitridation (CRN) of the precursor, obtained by adding carbon black (C) to the stripping solution during the vanadium recovery from black shale. VN was successfully prepared at a low temperature
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A new effective method is proposed to prepare vanadium nitride (VN) via carbothermal reduction–nitridation (CRN) of the precursor, obtained by adding carbon black (C) to the stripping solution during the vanadium recovery from black shale. VN was successfully prepared at a low temperature of 1150 °C for only 1 h with a C/V2O5 mass ratio of 0.30 in N2 atmosphere, but a temperature of 1300–1500 °C is required for several hours in the traditional CRN method. The low synthesis temperature and short period for the preparation of VN was due to the vanadium-coated carbon structure of the precursor, which enlarged the contact area between reactants significantly and provided more homogeneous chemical composition. In addition, the simultaneous direct reduction and indirect reduction of the interphase caused by the coating structure obviously accelerated the reaction. The phase evolution of the precursor was as follows: (NH4)2V6O16·1.5H2O → V2O5 → V6O13 → VO2 → V4O7 → V2O3 → VC → VN. The precursor converted to V6O13 and VO2 completely after being calcined at 550 °C, indicating that the pre-reduction of V2O5 in the traditional CRN method can be omitted. This method combined the synthesis of VN with the vanadium extraction creatively, having the advantages of simple reaction conditions, low cost and short processing time. Full article
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Open AccessArticle Microstructure and Mechanical Properties of Ultrasonic Welded Joint of 1060 Aluminum Alloy and T2 Pure Copper
Metals 2017, 7(9), 361; doi:10.3390/met7090361
Received: 20 July 2017 / Revised: 19 August 2017 / Accepted: 7 September 2017 / Published: 11 September 2017
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Abstract
The microstructure and mechanical properties of Al/Cu ultrasonic welding joints were investigated. Results show that: (i) the joint strength increased when the welding time increased within a certain range, and a maximal resistant force of 163.04 N was obtained when the welding duration
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The microstructure and mechanical properties of Al/Cu ultrasonic welding joints were investigated. Results show that: (i) the joint strength increased when the welding time increased within a certain range, and a maximal resistant force of 163.04 N was obtained when the welding duration and welding static pressure were 200 ms and 7.2 MPa, respectively; (ii) with a further increase of welding time, the bonding interface was gradually occupied by a thick strip layer of brittle Al2Cu (θ2) phase, thus decreasing the strength; (iii) the maximum temperature in the welding region was 360 °C during the welding process, and a recrystallization phenomenon was identified near the welding interface; (iv) the average nanohardness of Cu, the Cu-Al interfacial reaction layer and Al were 1.04 GPa, 1.34 GPa, and 0.53 GPa, respectively, which is consistent with the formation of the intermetallic compound identified by energy-dispersive X-ray spectroscopy (EDS) and XRD analysis. Full article
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Open AccessArticle Dynamic Strain Aging Behaviour in AISI 316L Austenitic Stainless Steel under As-Received and As-Welded Conditions
Metals 2017, 7(9), 362; doi:10.3390/met7090362
Received: 15 August 2017 / Revised: 27 August 2017 / Accepted: 5 September 2017 / Published: 12 September 2017
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Abstract
In the current study, dynamic strain ageing (DSA) phenomena in 316L austenitic stainless steel was investigated under as-received and as-welded conditions. A tensile test was carried out on as-received and as-welded samples for the temperatures of 25–800 °C at a strain rate of
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In the current study, dynamic strain ageing (DSA) phenomena in 316L austenitic stainless steel was investigated under as-received and as-welded conditions. A tensile test was carried out on as-received and as-welded samples for the temperatures of 25–800 °C at a strain rate of 1 × 10−3 s−1. Microstructure and fracture surfaces were investigated by optic and scanning electron microscopes (SEM). 316L austenitic stainless steel showed different DSA behavior under as-received and as-welded conditions, which are discussed in terms of microstructure and mechanical properties. Full article
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Open AccessArticle Mushy Zone Morphology Calculation with Application of CALPHAD Technique
Metals 2017, 7(9), 363; doi:10.3390/met7090363
Received: 20 July 2017 / Revised: 5 September 2017 / Accepted: 5 September 2017 / Published: 12 September 2017
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Abstract
Mushy zone morphology in AlSiMn alloys was studied using directional solidification, and the CALPHAD (Computer Coupling of Phase Diagrams and Thermochemistry) technique was applied for thermodynamic calculations. The specimens solidified with forced convection presented segregation across the sample diameter, and the measured compositions
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Mushy zone morphology in AlSiMn alloys was studied using directional solidification, and the CALPHAD (Computer Coupling of Phase Diagrams and Thermochemistry) technique was applied for thermodynamic calculations. The specimens solidified with forced convection presented segregation across the sample diameter, and the measured compositions were located on the Al-Si-Mn phase diagram. Scheil-Gulliver calculations for measured compositions were used to determine various solidification paths that may occur in specimens. Property diagrams and solidification paths presented the segregation effect on the characteristic temperatures, mushy zone length and the sequence of occurring phases whilst 2D maps enabled visualization of the mushy zone during directional solidification. Melt stirring was found to change solidification range, as well as mushy zone length and shape, and the dendrite tips formed a rough profile across the specimens. The study revealed mushy zones with dense dendritic structure and liquid channels empty of Mn phases, where intermetallics had no possibility to flow in the liquid, whilst in other samples with channels filled with Al15Si2Mn4, Mn-precipitates also flowed above the α-Al. The melt flow may lead to a mainly dendritic mushy zone or to a mushy zone with dendrites reaching only lower half of mushy length with intermetallics forming and freely flowing above dendrites in the liquid upper half. Full article
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Open AccessFeature PaperArticle High Field X-ray Diffraction Study for Ni46.4Mn38.8In12.8Co2.0 Metamagnetic Shape Memory Film
Metals 2017, 7(9), 364; doi:10.3390/met7090364
Received: 4 August 2017 / Revised: 6 September 2017 / Accepted: 7 September 2017 / Published: 12 September 2017
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Abstract
The transformation behaviors on metamagnetic shape memory Ni46.4Mn38.8In12.8Co2.0 film were investigated by X-ray diffraction experiments in the temperature up to 473 K and magnetic fields µ0H up to 5 T. The prepared film showed
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The transformation behaviors on metamagnetic shape memory Ni46.4Mn38.8In12.8Co2.0 film were investigated by X-ray diffraction experiments in the temperature up to 473 K and magnetic fields µ0H up to 5 T. The prepared film showed the parent phase with L21 structure at 473 K, and with preferred orientation along the 111 plane. The magnetic field induced reverse transformation was directly observed at T = 366 K, which was just around the reverse transformation starting temperature. Full article
(This article belongs to the Special Issue Shape Memory Alloys 2017)
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Open AccessArticle Effects of the Preparation Solvent on the Catalytic Properties of Cobalt–Boron Alloy for the Hydrolysis of Alkaline Sodium Borohydride
Metals 2017, 7(9), 365; doi:10.3390/met7090365
Received: 9 August 2017 / Revised: 3 September 2017 / Accepted: 10 September 2017 / Published: 12 September 2017
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Abstract
In this study, the effects of the solvent used to prepare Co–B alloy on its catalytic properties were investigated. The solvent effects on the morphology, composition, and specific surface area of the alloy particles were also examined. The morphology of the alloy particles
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In this study, the effects of the solvent used to prepare Co–B alloy on its catalytic properties were investigated. The solvent effects on the morphology, composition, and specific surface area of the alloy particles were also examined. The morphology of the alloy particles was found to be dependent on the solvent. The particles were granular in water, methanol, and acetone, although the particle diameters differed, whereas they were nanoflake-like in acetonitrile. Acetonitrile produced the largest surface area of the alloy particles, but the lowest catalytic activity for the hydrolysis of NaBH4 owing to the ready oxidation of the particles in air. The Co–B in acetone exhibited the highest catalytic activity, represented by a hydrogen generation rate of 5733 mL·min−1·g−1 during the hydrolysis of 1.5 wt % NaBH4 at 298 K. This hydrogen generation rate is more than twice that produced by the Co–B in water. Full article
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Open AccessFeature PaperArticle DFT Modelling of Cu Segregation in Al-Cu Alloys Covered by an Ultrathin Oxide Film and Possible Links with Passivity
Metals 2017, 7(9), 366; doi:10.3390/met7090366
Received: 15 August 2017 / Revised: 5 September 2017 / Accepted: 7 September 2017 / Published: 12 September 2017
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Abstract
We modelled with Density Functional Theory (DFT) an Al-Cu alloy covered with a passive film, with several Cu concentrations (from the limit of the isolated atom to the monolayer) at the interface with the oxide, as well as Guinier-Preston 1 (GP1) zones. At
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We modelled with Density Functional Theory (DFT) an Al-Cu alloy covered with a passive film, with several Cu concentrations (from the limit of the isolated atom to the monolayer) at the interface with the oxide, as well as Guinier-Preston 1 (GP1) zones. At low (respectively high) concentration, Cu segregates in the first (respectively second) metal layer underneath the passive film. The Cu monolayer is the most stable configuration (−0.37 eV/Cu atom). GP1 zones were modelled, with a three-copper atom cluster in the alloy. The GP1 zone is slightly favoured with respect to the Cu monolayer under the oxide film. A low (respectively high) Cu concentration induces an electronic workfunction increase (respectively decrease) by 0.3 eV (respectively −0.4 to −0.6 eV) as compared to pure Al. In contrast, without oxide, Cu segregation at the Al surface induces no workfunction change at low concentration and an increase of 0.3 eV of the workfunction at high concentration. Thus, the presence of oxide modifies the expected tendency of workfunction increase by adding a more noble metal. For the studied models, no spontaneous electron transfer occurs to the O2 molecule. Full article
(This article belongs to the Special Issue Corrosion Inhibition)
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Open AccessArticle Influence of Powder Surface Contamination in the Ni-Based Superalloy Alloy718 Fabricated by Selective Laser Melting and Hot Isostatic Pressing
Metals 2017, 7(9), 367; doi:10.3390/met7090367
Received: 9 May 2017 / Revised: 5 September 2017 / Accepted: 7 September 2017 / Published: 13 September 2017
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Abstract
The aim of this study was to gain a deep understanding of the microstructure-mechanical relationship between solid-state sintering and full-melting processes. The IN718 superalloy was fabricated by hot isostatic pressing (HIP) and selective laser melting (SLM). Continuous precipitates were clearly localized along the
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The aim of this study was to gain a deep understanding of the microstructure-mechanical relationship between solid-state sintering and full-melting processes. The IN718 superalloy was fabricated by hot isostatic pressing (HIP) and selective laser melting (SLM). Continuous precipitates were clearly localized along the prior particle boundary (PPB) in the HIP materials, while SLM materials showed a microstructure free of PPB. The mechanical properties of specimens that underwent SLM + solution treatment and aging were comparable to those of conventional wrought specimens both at room temperature and 650 °C. However, a drop was observed in the ductility of HIP material at 650 °C. The brittle particles along the PPB were found to affect the HIP materials’ creep life and ductility during solid-state sintering. Full article
(This article belongs to the Special Issue Powder Synthesis and Processing)
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Open AccessArticle Isothermal Austenite–Ferrite Phase Transformations and Microstructural Evolution during Annealing in Super Duplex Stainless Steels
Metals 2017, 7(9), 368; doi:10.3390/met7090368
Received: 17 July 2017 / Revised: 29 August 2017 / Accepted: 8 September 2017 / Published: 14 September 2017
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Abstract
Super Duplex Stainless Steels (SDSSs) are composed of α-ferrite and γ-austenite grains, the simultaneous presence of which forms an optimal microstructure to achieve the best combination of mechanical and corrosion resistance properties. Moreover, international quality standards are strict about the phase fraction ratio.
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Super Duplex Stainless Steels (SDSSs) are composed of α-ferrite and γ-austenite grains, the simultaneous presence of which forms an optimal microstructure to achieve the best combination of mechanical and corrosion resistance properties. Moreover, international quality standards are strict about the phase fraction ratio. The purpose of this work is the achievement of a better description of the phase ratio evolution taking place during annealing at 1080 °C in the super duplex stainless steels F53–S32750 and F55–S32760. The experimental results show a damped sinusoidal trend in the α/γ phase ratio evolution with the increase of the soaking time of thermal treatment. This can be described by coupling both the competitive coarsening growth regime and the concept of the local equilibrium phase transformations, pointing out a good correspondence with the experimental data. Further, recrystallization phenomena also play a major role. Finally, the additivity character of the observed processes has been proven. Full article
(This article belongs to the Special Issue Microstructure based Modeling of Metallic Materials)
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Open AccessArticle Electrical Resistivity Measurement of Carbon Anodes Using the Van der Pauw Method
Metals 2017, 7(9), 369; doi:10.3390/met7090369
Received: 27 July 2017 / Revised: 7 September 2017 / Accepted: 8 September 2017 / Published: 13 September 2017
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Abstract
The electrical resistivity of carbon anodes is an important parameter in the overall efficiency of the aluminum smelting process. The aim of this work is to explore the Van der Pauw (VdP) method as an alternative technique to the standard method, which is
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The electrical resistivity of carbon anodes is an important parameter in the overall efficiency of the aluminum smelting process. The aim of this work is to explore the Van der Pauw (VdP) method as an alternative technique to the standard method, which is commonly used in the aluminum industry, in order to characterize the electrical resistivity of carbon anodes and to assess the accuracy of the method. For this purpose, a cylindrical core is extracted from the top of the anodes. The electrical resistivity of the core samples is measured according to the ISO 11713 standard method. This method consists of applying a 1 A current along the revolution axis of the sample, and then measuring the voltage drop on its side, along the same direction. Theoretically, this technique appears to be satisfying, but cracks in the sample that are generated either during the anode production or while coring the sample may induce high variations in the measured signal. The VdP method, as presented in 1958 by L.J. Van der Pauw, enables the electrical resistivity of any plain sample with an arbitrary shape and low thickness to be measured, even in the presence of cracks. In this work, measurements were performed using both the standard method and the Van der Pauw method, on both flawless and cracked samples. Results provided by the VdP method appeared to be more reliable and repeatable. Furthermore, numerical simulations using the finite element method (FEM) were performed in order to assess the effect of the presence of cracks and their thicknesses on the accuracy of the VdP method. Full article
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Open AccessFeature PaperArticle Effects of Post-Sinter Processing on an Al–Zn–Mg–Cu Powder Metallurgy Alloy
Metals 2017, 7(9), 370; doi:10.3390/met7090370
Received: 16 August 2017 / Revised: 7 September 2017 / Accepted: 8 September 2017 / Published: 13 September 2017
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Abstract
The objective of this work was to study the effects of several post-sinter processing operations (heat-treatment, sizing, shot peening) on a press-and-sinter 7xxx series aluminum powder metallurgy (PM) alloy. The characterization of the products was completed through a combination of non-contact surface profiling,
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The objective of this work was to study the effects of several post-sinter processing operations (heat-treatment, sizing, shot peening) on a press-and-sinter 7xxx series aluminum powder metallurgy (PM) alloy. The characterization of the products was completed through a combination of non-contact surface profiling, hardness measurements, differential scanning calorimetry (DSC), transmission electron microscopy (TEM), X-ray diffraction (XRD), tensile, and three-point bend fatigue testing. It was determined that sizing in the as-quenched state imparted appreciable reductions in surface hardness (78 HRB) and fatigue strength (168 MPa) relative to counterpart specimens that were sized prior to solutionizing (85 HRB and 228 MPa). These declines in performance were ascribed to the annihilation of quenched in vacancies that subsequently altered the nature of precipitates within the finished product. The system responded well to shot peening, as this process increased fatigue strength to 294 MPa. However, thermal exposure at 353 K (80 °C) and 433 K (160 °C) then reduced fatigue performance to 260 MPa and 173 MPa, respectively, as a result of residual stress relaxation and in-situ over-aging. Full article
(This article belongs to the Special Issue Advanced Mechanical Testing of Powder Metallurgy Alloys)
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Open AccessArticle An Eco-Friendly Neutralization Process by Carbon Mineralization for Ca-Rich Alkaline Wastewater Generated from Concrete Sludge
Metals 2017, 7(9), 371; doi:10.3390/met7090371
Received: 28 July 2017 / Revised: 11 September 2017 / Accepted: 11 September 2017 / Published: 13 September 2017
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Abstract
Waste-concrete recycling processes using wet-based crushing methods inevitably generate a large amount of alkaline concrete sludge, as well as wastewater, which contains abundant Ca ions. The Ca-rich alkaline wastewater must then be neutralized for reuse in the waste-concrete recycling process. In this study,
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Waste-concrete recycling processes using wet-based crushing methods inevitably generate a large amount of alkaline concrete sludge, as well as wastewater, which contains abundant Ca ions. The Ca-rich alkaline wastewater must then be neutralized for reuse in the waste-concrete recycling process. In this study, the feasibility of a carbon mineralization process for the neutralization of alkaline wastewater was considered from both environmental and economic perspectives. The optimal reaction time, efficiency of Ca removal and CO2 sequestration as a function of the CO2 gas flow rate were assessed. The carbon mineralization process resulted in sequestering CO2 (85–100% efficiency) and removing Ca from the solution (84–99%) by precipitating pure CaCO3. Increasing the gas flow rate reduced the reaction time (65.0 down to 3.4 min for 2.5 L of solution), but decreased CO2 sequestration (from 463.3 down to 7.3 mg CO2 for 2.5 L of solution). Optimization of the gas flow rate is essential for efficient CO2 sequestration, Ca removal, CaCO3 production and, therefore, successful wastewater neutralization following the wet-based crushing process. The method presented here is an eco-friendly and economically viable substitute for dealing with alkaline wastewater. It may also provide a practical guide for the design of carbon mineralization processes for the neutralization of alkaline solutions containing large amounts of Ca. Full article
(This article belongs to the Special Issue Valuable Metal Recycling)
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Open AccessFeature PaperArticle The Fabrication of All-Solid-State Lithium-Ion Batteries via Spark Plasma Sintering
Metals 2017, 7(9), 372; doi:10.3390/met7090372
Received: 23 July 2017 / Revised: 31 August 2017 / Accepted: 11 September 2017 / Published: 14 September 2017
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Abstract
Spark plasma sintering (SPS) has been successfully used to produce all-solid-state lithium-ion batteries (ASSLibs). Both regular and functionally graded electrodes are implemented into novel three-layer and five-layer battery designs together with solid-state composite electrolyte. The electrical capacities and the conductivities of the SPS-processed
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Spark plasma sintering (SPS) has been successfully used to produce all-solid-state lithium-ion batteries (ASSLibs). Both regular and functionally graded electrodes are implemented into novel three-layer and five-layer battery designs together with solid-state composite electrolyte. The electrical capacities and the conductivities of the SPS-processed ASSLibs are evaluated using the galvanostatic charge-discharge test. Experimental results have shown that, compared to the three-layer battery, the five-layer battery is able to improve energy and power densities. Scanning electron microscopy (SEM) is employed to examine the microstructures of the batteries especially at the electrode–electrolyte interfaces. It reveals that the functionally graded structure can eliminate the delamination effect at the electrode–electrolyte interface and, therefore, retains better performance. Full article
(This article belongs to the Special Issue Powder Synthesis and Processing)
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Open AccessArticle Fretting Wear Behaviors of Aluminum Cable Steel Reinforced (ACSR) Conductors in High-Voltage Transmission Line
Metals 2017, 7(9), 373; doi:10.3390/met7090373
Received: 9 August 2017 / Revised: 29 August 2017 / Accepted: 12 September 2017 / Published: 14 September 2017
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Abstract
This work reports the fretting wear behavior of aluminum cable steel reinforced (ACSR) conductors for use in high-voltage transmission line. Fretting wear tests of Al wires were conducted on a servo-controlled fatigue testing machine with self-made assistant apparatus, and their fretting process characteristics,
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This work reports the fretting wear behavior of aluminum cable steel reinforced (ACSR) conductors for use in high-voltage transmission line. Fretting wear tests of Al wires were conducted on a servo-controlled fatigue testing machine with self-made assistant apparatus, and their fretting process characteristics, friction force, wear damage, and wear surface morphology were detailed analyzed. The results show that the running regime of Al wires changes from a gross slip regime to a mixed regime more quickly as increasing contact load. With increasing amplitudes, gross slip regimes are more dominant under contact loads of lower than 30 N. The maximum friction force is relatively smaller in the NaCl solution than in a dry friction environment. The primary wear mechanisms in dry friction environments are abrasive wear and adhesive wear whereas abrasive wear and fatigue damage are dominant in NaCl solution. Full article
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Open AccessArticle Investigation of the Frozen Bath Layer under Cold Anodes
Metals 2017, 7(9), 374; doi:10.3390/met7090374
Received: 6 July 2017 / Revised: 16 August 2017 / Accepted: 4 September 2017 / Published: 15 September 2017
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Abstract
Hall-Héroult cell stability is highly affected by anode changing operations. Upon the insertion of a cold anode in the cell, a layer of molten cryolite freezes under the anode. The thickness, microstructure, and chemical composition of this layer vary as a function of
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Hall-Héroult cell stability is highly affected by anode changing operations. Upon the insertion of a cold anode in the cell, a layer of molten cryolite freezes under the anode. The thickness, microstructure, and chemical composition of this layer vary as a function of time and its location in the cell. To better understand the evolution of the frozen layer, mandatory for the validation of numerical models, a measurement campaign was conducted on the anodes having a few hours of operation in the cell. The macrostructure of the selected frozen bath samples has been investigated using computed tomography while scanning electron microscope (SEM) has been used to qualify its microstructure. An energy-dispersive X-ray spectroscope (EDS) coupled to the SEM has revealed the chemical content. The results showed not only very different macrostructures between samples, but also significantly heterogeneous structure within the same sample. Nevertheless, for all samples, there is a clear distinction between the frozen cryolite and alumina/dusting phases, with the latter surrounding the cryolite matrix. Full article
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Open AccessArticle Torsional Fatigue Strength of Newly Developed Case Hardening TRIP-Aided Steel
Metals 2017, 7(9), 375; doi:10.3390/met7090375
Received: 4 August 2017 / Revised: 13 September 2017 / Accepted: 13 September 2017 / Published: 15 September 2017
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Abstract
The torsional fatigue strength of newly developed case hardening steel, i.e., transformation-induced plasticity-aided martensitic steel subjected to vacuum carburizing followed by fine particle peening, was investigated for the fabrication of downsized precision gears with high torque capacity and wear resistance. The surface-hardened layer
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The torsional fatigue strength of newly developed case hardening steel, i.e., transformation-induced plasticity-aided martensitic steel subjected to vacuum carburizing followed by fine particle peening, was investigated for the fabrication of downsized precision gears with high torque capacity and wear resistance. The surface-hardened layer properties—i.e., high Vickers hardness, high compressive residual stress, and a large amount of retained austenite—considerably increased the torsional fatigue limits of vacuum-carburized and fine particle peened TM and JIS-SNCM420 steels, although the notch-sensitivity to fatigue was increased. The relation between torsional and rotational bending fatigue limits for the smooth specimens was found to be between the maximum principal stress and the minimum shear strain energy criterions. On the other hand, this relation for the notched specimens was represented through the maximum principal stress criterion. Full article
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Open AccessArticle A Numerical Study on Contact Condition and Wear of Roller in Cold Rolling
Metals 2017, 7(9), 376; doi:10.3390/met7090376
Received: 7 July 2017 / Revised: 10 September 2017 / Accepted: 11 September 2017 / Published: 15 September 2017
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Abstract
An accurate determination of the contact pressure and local sliding in a cold rolling process is an essential step towards the prediction of the roller’s life due to wear damage. This investigation utilized finite element analysis to quantify the local contact pressure and
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An accurate determination of the contact pressure and local sliding in a cold rolling process is an essential step towards the prediction of the roller’s life due to wear damage. This investigation utilized finite element analysis to quantify the local contact pressure and local sliding over the rolling bite in a plate cold rolling process. It was the first study to quantify the local sliding distance in a rolling process using the Finite Element Analysis (FEA). The numerical results indicate that the local contact pressure over the rolling bite demonstrates a hill profile, and the peak coincides with the neutral plane. The local sliding distance over the rolling bite demonstrates a double-peak profile with the two peaks appearing at the forward slip and backward slip zones respectively. The amplitude of sliding distance in the backward slip zone is larger than that in the forward slip zone. A stick zone was confirmed between the forward slip and backward slip zones. According to a parametric study, the local contact pressure and sliding distance decrease when the thickness reduction is reduced or the diameter of the roller is decreased. The location of the neutral plane always presents at the rolling exit side of the rolling bite’s center. The size of the stick zone enlarges and the sizes of slip zones shrink significantly when the friction coefficient is increased. Finally, a novel concept of wear intensity was defined to examine the wear of the roller based on the local contact pressure and local sliding distance. The results show that a two-peak wear response exists in the backward and forward slip zones. The magnitude of the wear in the backward slip zone is larger than that in the forward slip zone. For a given roller and blank material combination, using a smaller thickness reduction, a smaller diameter roller and a higher friction coefficient condition can reduce the wear of the roller for a single rolling cycle. The current paper develops an understanding of rolling contact responses to the wear of the roller in rolling process. The research method can also be applied to study other rolling or sliding wear problems. Full article
(This article belongs to the Special Issue Researches and Simulations in Steel Rolling)
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Open AccessArticle The Influence of La and Ce Addition on Inclusion Modification in Cast Niobium Microalloyed Steels
Metals 2017, 7(9), 377; doi:10.3390/met7090377
Received: 7 August 2017 / Revised: 28 August 2017 / Accepted: 29 August 2017 / Published: 15 September 2017
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Abstract
The main role of Rare Earth (RE) elements in the steelmaking industry is to affect the nature of inclusions (composition, geometry, size and volume fraction), which can potentially lead to the improvement of some mechanical properties such as the toughness in steels. In
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The main role of Rare Earth (RE) elements in the steelmaking industry is to affect the nature of inclusions (composition, geometry, size and volume fraction), which can potentially lead to the improvement of some mechanical properties such as the toughness in steels. In this study, different amounts of RE were added to a niobium microalloyed steel in as-cast condition to investigate its influence on: (i) type of inclusions and (ii) precipitation of niobium carbides. The characterization of the microstructure by optical, scanning and transmission electron microscopy shows that: (1) the addition of RE elements change the inclusion formation route during solidification; RE > 200 ppm promote formation of complex inclusions with a (La,Ce)(S,O) matrix instead of Al2O3-MnS inclusions; (2) the roundness of inclusions increases with RE, whereas more than 200 ppm addition would increase the area fraction and size of the inclusions; (3) it was found that the presence of MnS in the base and low RE-added steel provide nucleation sites for the precipitation of coarse niobium carbides and/or carbonitrides at the matrix–MnS interface. Thermodynamic calculations show that temperatures of the order of 1200 °C would be necessary to dissolve these coarse Nb-rich carbides so as to reprecipitate them as nanoparticles in the matrix. Full article
(This article belongs to the Special Issue Advances in Microalloyed Steels)
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Open AccessArticle Ceramic Materials in a Ti–C–Co–Ca3(PO4)2–Ag–Mg System Obtained by MA SHS for the Deposition of Biomedical Coatings
Metals 2017, 7(9), 378; doi:10.3390/met7090378
Received: 11 August 2017 / Revised: 6 September 2017 / Accepted: 11 September 2017 / Published: 15 September 2017
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Abstract
This study aimed to obtain biocompatible ceramic materials in a Ti–C–Co–Ca3(PO4)2–Ag–Mg system by the combustion mode of mechanically activated (MA) reaction mixtures. The influence of the MA time on the reaction ability capability of the mixtures, on
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This study aimed to obtain biocompatible ceramic materials in a Ti–C–Co–Ca3(PO4)2–Ag–Mg system by the combustion mode of mechanically activated (MA) reaction mixtures. The influence of the MA time on the reaction ability capability of the mixtures, on their structural and chemical homogeneity, on the combustion parameters and structural-phase conversions in the combustion wave, as well as on the structure and phase composition of the electrode materials has been researched. It was found that the intense treatment of powder mixtures causes plastic deformation of components, the formation of lamellar composite granules, a reduction in the sizes of coherent scattering regions, and also the formation of minor amounts of products. The influence of the activation duration of the ignition temperature and heat release during the combustion of the reaction mixtures was studied. By the method of quenching the combustion front, it was demonstrated that in a combustion wave, chemical transformations occur within the lamellar structures formed during the process of mechanoactivation. It was shown that in the combustion wave, parallel chemical reactions of Ti with C as well as Ti with Co and Ca3(PO4)2 occur, with a Ti–Co-based melt forming the reaction surface. Ceramic electrodes with different contents of Ag and Mg were synthesized by force self-propagating high-temperature synthesis (SHS)-pressing technology using the MA mixtures. The microstructure of the materials consisted of round-shaped grains of nonstoichiometric titanium carbide TiCx grains, intermetallic matrix (TiCo, TiCo2, CoTiP), inclusions of Ca and Mg oxides, and grains of the Ag-based solid solution. An increased content of Ag and Mg in the composition of the electrodes, as well as an increased MA duration, leads to an enlargement of the inclusions of the Ag-containing phase size and deterioration in the uniformity of their distribution. Full article
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Open AccessArticle Physical-Mechanism Exploration of the Low-Cycle Unified Creep-Fatigue Formulation
Metals 2017, 7(9), 379; doi:10.3390/met7090379
Received: 18 August 2017 / Revised: 15 September 2017 / Accepted: 15 September 2017 / Published: 18 September 2017
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Abstract
Background—Creep-fatigue behavior is identified as the incorporated effects of fatigue and creep. One class of constitutive-based models attempts to evaluate creep and fatigue separately, but the interaction of fatigue and creep is neglected. Other models treat the damage as a single component, but
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Background—Creep-fatigue behavior is identified as the incorporated effects of fatigue and creep. One class of constitutive-based models attempts to evaluate creep and fatigue separately, but the interaction of fatigue and creep is neglected. Other models treat the damage as a single component, but the complex numerical structures that result are inconvenient for engineering application. The models derived through a curve-fitting method avoid these problems. However, the method of curving fitting cannot translate the numerical formulation to underlying physical mechanisms. Need—Therefore, there is a need to develop a new creep-fatigue formulation for metal that accommodates all relevant variables and where the relationships between them are consistent with physical mechanisms of fatigue and creep. Method—In the present work, the main dependencies and relationships for the unified creep-fatigue equation were presented through exploring what the literature says about the mechanisms. Outcomes—This shows that temperature, cyclic time and grain size have significant influences on creep-fatigue behavior, and the relationships between them (such as linear relation, logarithmical relation and power-law relation) are consistent with phenomena of diffusion creep and crack growth. Significantly, the numerical form of “1 − x” is presented to show the consumption of creep effect on fatigue capacity, and the introduction of the reference condition gives the threshold of creep effect. Originality—By this means, the unified creep-fatigue equation is linked to physical phenomena, where the influence of different dependencies on creep fatigue was explored and relationships shown in this equation were investigated in a microstructural level. Particularly, a physical explanation of the grain-size exponent via consideration of crack-growth planes was proposed. Full article
(This article belongs to the Special Issue Fatigue Damage)
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Open AccessArticle Effect of Computational Parameters on Springback Prediction by Numerical Simulation
Metals 2017, 7(9), 380; doi:10.3390/met7090380
Received: 27 August 2017 / Revised: 14 September 2017 / Accepted: 15 September 2017 / Published: 19 September 2017
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Abstract
Elastic recovery of the material, called springback, is one of the problems in sheet metal forming of drawpieces, especially with a complex shape. The springback can be influenced by various technological, geometrical, and material parameters. In this paper the results of experimental testing
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Elastic recovery of the material, called springback, is one of the problems in sheet metal forming of drawpieces, especially with a complex shape. The springback can be influenced by various technological, geometrical, and material parameters. In this paper the results of experimental testing and numerical study are presented. The experiments are conducted on DC04 steel sheets, commonly used in the automotive industry. The numerical analysis of V-die air bending tests is carried out with the finite element method (FEM)-based ABAQUS/Standard 2016 program. A quadratic Hill anisotropic yield criterion is compared with an isotropic material described by the von Mises yield criterion. The effect of a number of integration points and integration rules on the springback amount and computation time is also considered. Two integration rules available in ABAQUS: the Gauss’ integration rule and Simpson’s integration rule are considered. The effect of sample orientation according to the sheet rolling direction and friction contact behaviour on the prediction of springback is also analysed. It is observed that the width of the sample bend in the V-bending test influences the stress-state in the cross-section of the sample. Different stress-states in the sample bend of the V-shaped die cause that the sheet undergoes springback in different planes. Friction contact phenomena slightly influences the springback behaviour. Full article
(This article belongs to the Special Issue Advances in Plastic Forming of Metals)
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Open AccessArticle Study of the Microstructure Evolution and Properties Response of a Friction-Stir-Welded Copper-Chromium-Zirconium Alloy
Metals 2017, 7(9), 381; doi:10.3390/met7090381
Received: 17 August 2017 / Revised: 9 September 2017 / Accepted: 11 September 2017 / Published: 19 September 2017
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Abstract
In this article, the copper-chromium-zirconium (CuCrZr) alloys plates with 21 mm in thickness were butt joined together by means of FSW (friction stir welding). The properties of the FSW joints are studied. The microstructure variations during the process of FSW were investigated by
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In this article, the copper-chromium-zirconium (CuCrZr) alloys plates with 21 mm in thickness were butt joined together by means of FSW (friction stir welding). The properties of the FSW joints are studied. The microstructure variations during the process of FSW were investigated by optical microscopy (OM), electron back-scattered diffraction (EBSD), and transmission electron microscopy (TEM). The results show that the grains size in the nugget zone (NZ) are significantly refined, which can be attributed to the dynamic recrystallization (DRX). The microstructure distribution in the NZ is inhomogeneous and the size of equiaxed grains are decreased gradually along the thickness direction from the top to bottom area of the welds. Meanwhile, it is found that the micro-hardness and tensile strength of the welds are slightly increased along the thickness direction from the top to the bottom area of the welds. All the nano-strengthening precipitates in the BM are dissolved into the Cu matrix in the NZ. Therefore, the decreases in hardness, tensile strength, and electrical conductivity can be attributed to the comprehensive effect of dissolution of nano-strengthening precipitates into the supersaturation matrix and severe DRX in the welded NZ. Full article
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Open AccessArticle Study of the Heat-Treatments Effect on High Strength Ductile Cast Iron Welded Joints
Metals 2017, 7(9), 382; doi:10.3390/met7090382
Received: 12 August 2017 / Revised: 13 September 2017 / Accepted: 13 September 2017 / Published: 19 September 2017
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Abstract
Nowadays, ultimate tensile strengths above 400 MPa become usual for ductile irons, thus allowing the implementation of new design paradigms. Large concentrations of carbon and other influencing elements can negatively interfere with the welding process of ductile cast irons. Efforts made by researchers
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Nowadays, ultimate tensile strengths above 400 MPa become usual for ductile irons, thus allowing the implementation of new design paradigms. Large concentrations of carbon and other influencing elements can negatively interfere with the welding process of ductile cast irons. Efforts made by researchers have led to the discovery of solutions which enable good enough operational results to consider welding as a viable repairing or joining method. Although these alloys have been available for quite some time, researchers have mainly focused on issues relating to microstructural phenomena tied to casting and similar processes, leaving much to explore in terms of their weldability. Thus, this work intends to investigate the effect of different heat-treatments on the weldability of a high strength ductile cast iron by assessing the mechanical properties of welded joints as well as structural modifications induced by thermal cycles imposed before and after welding. Successful weld joints were achieved showing a clear heat affected zone (HAZ) close to the joint area. This area is coincident with the fracture area of the welded samples when loaded on a tensile test bench, having obtained promising results regarding mechanical strength and strain. The hardness of the welded zone was also carefully investigated, showing clear changes throughout the joint. Full article
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Open AccessArticle Numerical and Experimental Investigation of the Influence of Growth Restriction on Grain Size in Binary Cu Alloys
Metals 2017, 7(9), 383; doi:10.3390/met7090383
Received: 2 September 2017 / Revised: 16 September 2017 / Accepted: 18 September 2017 / Published: 20 September 2017
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Abstract
Grain refinement by elemental addition has been extensively investigated within the last decades in Al or Mg alloys. In contrast, in the Cu system, the role of solute on grain size is less investigated. In this study, the grain refinement potency of several
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Grain refinement by elemental addition has been extensively investigated within the last decades in Al or Mg alloys. In contrast, in the Cu system, the role of solute on grain size is less investigated. In this study, the grain refinement potency of several alloying elements of the Cu system was examined. To predict grain size depending on the growth restriction factor Q, grain size modelling was performed. The results obtained by the grain size model were compared to variations in the grain size of binary Cu alloys with increasing solute content under defined cooling conditions of the TP-1 grain refiner test of the Aluminium Association©. It was found that the experimental results differed significantly from the predicted grain size values for several alloying elements. A decreasing grain size with increasing alloy concentration was observed independently of the growth restriction potency of the alloying elements. Furthermore, excessive grain coarsening was found for several solutes beyond a transition point. It is assumed that contradictory variations in grain size result from a change in the nucleating particle density of the melt. Significant decreases in grain size are supposed to be due to the in-situ formation of potent nucleation sites. Excessive grain coarsening with increasing solute content may occur due to the removal of nucleating particles. The model shows that the difference in the actual number of particles before and beyond the transition point must be in the range of several orders of magnitude. Full article
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Review

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Open AccessReview A Critical Review of Mg-Based Hydrogen Storage Materials Processed by Equal Channel Angular Pressing
Metals 2017, 7(9), 324; doi:10.3390/met7090324
Received: 16 July 2017 / Revised: 9 August 2017 / Accepted: 18 August 2017 / Published: 23 August 2017
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Abstract
As a kind of cost-efficient hydrogen storage materials with high hydrogen capacity and light weight, Mg-based alloys have attracted much attention. This review introduces an effective technique in producing bulk ultrafine-grained (UFG) Mg alloys and promoting its hydrogen storage property, namely, equal-channel angular
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As a kind of cost-efficient hydrogen storage materials with high hydrogen capacity and light weight, Mg-based alloys have attracted much attention. This review introduces an effective technique in producing bulk ultrafine-grained (UFG) Mg alloys and promoting its hydrogen storage property, namely, equal-channel angular pressing (ECAP). This paper briefly describes the technical principle of ECAP and reviews the research progress on hydrogen storage properties of ECAP-processed Mg alloys. Special attention is given to their hydrogen storage behaviors including hydrogen storage dynamics, capacity, and cycling stability. Finally, it analyzes the factors that affect the hydrogen storage properties of ECAP-processed Mg alloys, such as the grain sizes, lattice defects, catalysts, and textures introduced by ECAP process. Full article
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Other

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Open AccessCorrection Correction: Liss, K.-D., et al. Hydrostatic Compression Behavior and High-Pressure Stabilized β-Phase in γ-Based Titanium Aluminide Intermetallics. Metals 2016, 6, 165
Metals 2017, 7(9), 353; doi:10.3390/met7090353
Received: 15 August 2017 / Accepted: 22 August 2017 / Published: 7 September 2017
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Abstract
The authors would like to apologize for any inconvenience regarding misleading errors and inconsistencies in some of the units and one number, and wish to make the following corrections to this paper [1]:[...] Full article
(This article belongs to the Special Issue Metals Challenged by Neutron and Synchrotron Radiation)
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