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Metals, Volume 6, Issue 8 (August 2016)

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Research

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Open AccessArticle Effect of Mo Content on Microstructure and Property of Low-Carbon Bainitic Steels
Metals 2016, 6(8), 173; doi:10.3390/met6080173
Received: 17 June 2016 / Revised: 18 July 2016 / Accepted: 19 July 2016 / Published: 23 July 2016
Cited by 8 | PDF Full-text (4814 KB) | HTML Full-text | XML Full-text
Abstract
In this work, three low-carbon bainitic steels, with different Mo contents, were designed to investigate the effects of Mo addition on microstructure and mechanical properties. Two-step cooling, i.e., initial accelerated cooling and subsequent slow cooling, was used to obtain the desired bainite microstructure.
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In this work, three low-carbon bainitic steels, with different Mo contents, were designed to investigate the effects of Mo addition on microstructure and mechanical properties. Two-step cooling, i.e., initial accelerated cooling and subsequent slow cooling, was used to obtain the desired bainite microstructure. The results show that the product of strength and elongation first increases and then shows no significant change with increasing Mo. Compared with Mo-free steel, bainite in the Mo-containing steel tends to have a lath-like morphology due to a decrease in the bainitic transformation temperature. More martensite transformation occurs with the increasing Mo, resulting in greater hardness of the steel. Both the strength and elongation of the steel can be enhanced by Mo addition; however, the elongation may decrease with a further increase in Mo. From a practical viewpoint, the content of Mo could be ~0.14 wt. % for the composition design of low-carbon bainitic steels in the present work. To be noted, an optimal scheme may need to consider other situations such as the role of sheet thickness, toughness behavior and so on, which could require changes in the chemistry. Nevertheless, these results provide a reference for the composition design and processing method of low-carbon bainitic steels. Full article
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Open AccessArticle Leaching Behavior of Al, Co and W from the Al-Alloying Treated WC-Co Tool as a New Recycling Process for WC Hard Scrap
Metals 2016, 6(8), 174; doi:10.3390/met6080174
Received: 7 July 2016 / Revised: 20 July 2016 / Accepted: 21 July 2016 / Published: 25 July 2016
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Abstract
The Al-alloying treated tungsten carbide (WC)-Co tool was subjected to grinding using a jaw crusher and planetary mill followed by three wet chemical treatment steps to establish an effective recycling process for WC scraps, especially those generated as bulky and hard scrap. This
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The Al-alloying treated tungsten carbide (WC)-Co tool was subjected to grinding using a jaw crusher and planetary mill followed by three wet chemical treatment steps to establish an effective recycling process for WC scraps, especially those generated as bulky and hard scrap. This alloyed WC tool was readily ground to a powder of 1 mm or less and divided into two portions that were 150 µm in size. The wet chemical treatments enabled us to recover W to 69.44% from the under-sized 150 µm and also obtain WC powders from the over-sized 150 µm with a high purity of 98.9% or more. Full article
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Open AccessArticle Correlation between Zn-Rich Phase and Corrosion/Oxidation Behavior of Sn–8Zn–3Bi Alloy
Metals 2016, 6(8), 175; doi:10.3390/met6080175
Received: 13 June 2016 / Revised: 13 July 2016 / Accepted: 20 July 2016 / Published: 25 July 2016
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Abstract
The microstructure of Sn–8Zn–3Bi alloy was refined by increasing the solidification rate and the correlation between Zn-rich phase and the corrosion/oxidation behavior of the alloy was investigated. The Zn-rich phase transforms from coarse flakes to fine needles dispersed in the β-Sn matrix with
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The microstructure of Sn–8Zn–3Bi alloy was refined by increasing the solidification rate and the correlation between Zn-rich phase and the corrosion/oxidation behavior of the alloy was investigated. The Zn-rich phase transforms from coarse flakes to fine needles dispersed in the β-Sn matrix with the increase of the cooling rate. The transformation of Zn-rich precipitates enhances the anticorrosive ability of Sn–8Zn–3Bi alloy in 3.5 wt.% NaCl solution. On the contrary, Sn–8Zn–3Bi alloy with a fine needle-like Zn-rich phase shows poor oxidation resistance under air atmosphere, due to the fast diffusion of Zn atoms in Sn matrix. Full article
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Open AccessArticle Effects of Carboxylates on the Performance of Zn Electrode
Metals 2016, 6(8), 176; doi:10.3390/met6080176
Received: 28 June 2016 / Revised: 20 July 2016 / Accepted: 21 July 2016 / Published: 26 July 2016
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Abstract
Zinc is widely used as a negative electrode material for batteries due to its excellent electrochemical properties. Zinc is prone to corrosion and the formation of zinc dendrites cause short circuits of the battery, which leads to reduced battery capacity and shortens the
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Zinc is widely used as a negative electrode material for batteries due to its excellent electrochemical properties. Zinc is prone to corrosion and the formation of zinc dendrites cause short circuits of the battery, which leads to reduced battery capacity and shortens the battery’s life, hindering its use in weak acidic electrolytes (for example, aqueous Zn-polyaniline batteries). The effects of carboxylates (sodium formate, sodium acetate, sodium propionate, sodium butyrate, sodium valerate, disodium malonate, and disodium succinate) and their concentrations on zinc electrode performance were studied with electrochemical methods to improve the zinc electrode activity for long-life Zn-polyaniline batteries. It was found that the ability of inhibiting corrosion of the zinc electrode is better in the aqueous electrolyte containing 0.2 M disodium malonate. The charge/discharge performance of a Zn-polyaniline battery electrodeposited with polyaniline on a carbon substrate is carried out in the aqueous electrolyte. the results show that the initial discharge specific capacity of the polyaniline in the Zn-polyaniline battery is as high as 131.1 mAh·g−1, and maintains a discharge specific capacity of 114.8 mAh·g−1 and a coulombic efficiency over 92% after 100 cycles at a charge/discharge current density of 1 A·g−1 in the voltage range of 1.5–0.7 V. Full article
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Open AccessArticle Effect of Rare-Earth Ce on Macrosegregation in Al-Bi Immiscible Alloys
Metals 2016, 6(8), 177; doi:10.3390/met6080177
Received: 8 July 2016 / Revised: 19 July 2016 / Accepted: 21 July 2016 / Published: 27 July 2016
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Abstract
Liquid phase segregation of immiscible alloys has been investigated for decades. In this work, rare-earth Ce was studied as an additive for Al-Bi immiscible alloys. The addition of Ce restrained liquid phase segregation to obtain a uniformly dispersive microstructure. The experimental results indicated
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Liquid phase segregation of immiscible alloys has been investigated for decades. In this work, rare-earth Ce was studied as an additive for Al-Bi immiscible alloys. The addition of Ce restrained liquid phase segregation to obtain a uniformly dispersive microstructure. The experimental results indicated that in situ-precipitated intermetallic CeBi2 compound acted as an inoculant for the heterogeneous nucleation of the Bi-rich droplets. The Bi-rich droplets nucleated on the CeBi2 compound surface—a homogenous dispersed microstructure obtained via a heterogeneous nucleation route. We concluded that gravity segregation can be suppressed by the addition of rare-earth Ce. Full article
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Open AccessArticle Understanding Low Cycle Fatigue Behavior of Alloy 617 Base Metal and Weldments at 900 °C
Metals 2016, 6(8), 178; doi:10.3390/met6080178
Received: 4 July 2016 / Revised: 25 July 2016 / Accepted: 26 July 2016 / Published: 2 August 2016
Cited by 2 | PDF Full-text (7821 KB) | HTML Full-text | XML Full-text
Abstract
In order to better understand the high temperature low cycle fatigue behavior of Alloy 617 weldments, this work focuses on the comparative study of the low cycle fatigue behavior of Alloy 617 base metal and weldments, made from automated gas tungsten arc welding
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In order to better understand the high temperature low cycle fatigue behavior of Alloy 617 weldments, this work focuses on the comparative study of the low cycle fatigue behavior of Alloy 617 base metal and weldments, made from automated gas tungsten arc welding with Alloy 617 filler wire. Low cycle fatigue tests were carried out by a series of fully reversed strain-controls (strain ratio, Rε = −1), i.e., 0.6%, 0.9%, 1.2% and 1.5% at a high temperature of 900 °C and a constant strain rate of 10−3/s. At all the testing conditions, the weldment specimens showed lower fatigue lives compared with the base metal due to their microstructural heterogeneities. The effect of very high temperature deformation behavior regarding cyclic stress response varied as a complex function of material property and total strain range. The Alloy 617 base weldments showed some cyclic hardening as a function of total strain range. However, the Alloy 617 base metal showed some cyclic softening induced by solute drag creep during low cycle fatigue. An analysis of the low cycle fatigue data based on a Coffin-Manson relationship was carried out. Fracture surface characterizations were performed on selected fractured specimens using standard metallographic techniques. Full article
(This article belongs to the Special Issue Fatigue Damage)
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Open AccessArticle Investigation on a Novel Laser Impact Spot Welding
Metals 2016, 6(8), 179; doi:10.3390/met6080179
Received: 29 June 2016 / Revised: 20 July 2016 / Accepted: 28 July 2016 / Published: 3 August 2016
Cited by 4 | PDF Full-text (6985 KB) | HTML Full-text | XML Full-text
Abstract
In this paper a novel laser impact spot welding (LISW) method is described, in which a hump was formed on the flyer plate on the intended welding spot location by local pre-forming. When the flyer and base plates were placed together to perform
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In this paper a novel laser impact spot welding (LISW) method is described, in which a hump was formed on the flyer plate on the intended welding spot location by local pre-forming. When the flyer and base plates were placed together to perform welding, the two plates kept in contact over their entire surfaces except at the hump, where a local air gap was enough to guarantee the impact velocity and collision angle to achieve spot welding using laser pulse energy. The presented approach was implemented to join thin titanium foils to copper foils under low laser energy system. Joints with regular shapes were obtained. The microstructure in the weld interface was studied with scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). It was found that the jetting occurred at the central region of the weld spots due to oblique impact. Wave features were observed in the weld interfaces. The impact energy was found to have significant influence on the wave’s characteristics. Moreover, SEM images and EDS analysis did not show apparent element diffusion across the weld interface. Besides, the lap shearing test was used to characterize the mechanical properties of the spot welded joints. Full article
(This article belongs to the Special Issue Laser Shock Processing on Metal)
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Open AccessArticle Differential Scanning Calorimetry and Thermodynamic Predictions—A Comparative Study of Al-Zn-Mg-Cu Alloys
Metals 2016, 6(8), 180; doi:10.3390/met6080180
Received: 31 May 2016 / Revised: 28 July 2016 / Accepted: 29 July 2016 / Published: 3 August 2016
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Abstract
Al-Zn-Mg-Cu alloys are widely used in aircraft applications because of their superior mechanical properties and strength/weight ratios. Commercial Al-Zn-Mg-Cu alloys have been intensively studied over the last few decades. However, well-considered thermodynamic calculations, via the CALPHAD approach, on a variation of alloying elements
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Al-Zn-Mg-Cu alloys are widely used in aircraft applications because of their superior mechanical properties and strength/weight ratios. Commercial Al-Zn-Mg-Cu alloys have been intensively studied over the last few decades. However, well-considered thermodynamic calculations, via the CALPHAD approach, on a variation of alloying elements can guide the fine-tuning of known alloy systems and the development of optimized heat treatments. In this study, a comparison was made of the solidus temperatures of different Al-Zn-Mg-Cu alloys determined from thermodynamic predictions and differential scanning calorimetry (DSC) measurements. A variation of the main alloying elements Zn, Mg, and Cu generated 38 experimentally produced alloys. An experimental determination of the solidus temperature via DSC was carried out according to a user-defined method, because the broad melting interval present in Al-Zn-Mg-Cu alloys does not allow the use of the classical onset method for pure substances. The software algorithms implemented in FactSage®, Pandat™, and MatCalc with corresponding commercially available databases were deployed for thermodynamic predictions. Based on these investigations, the predictive power of the commercially available CALPHAD databases and software packages was critically reviewed. Full article
(This article belongs to the Special Issue Aluminum Alloys)
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Open AccessArticle Structure and Physical Properties of NiO/Co3O4 Nanoparticles
Metals 2016, 6(8), 181; doi:10.3390/met6080181
Received: 24 March 2016 / Revised: 8 June 2016 / Accepted: 28 June 2016 / Published: 5 August 2016
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Abstract
The thermal treatment method was employed to prepare nickel-cobalt oxide (NiO/Co3O4) nanoparticles. This method was attempted to achieve the higher homogeneity of the final product. Specimens of nickel-cobalt oxide were characterized by various experimental techniques, including X-ray diffraction (XRD),
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The thermal treatment method was employed to prepare nickel-cobalt oxide (NiO/Co3O4) nanoparticles. This method was attempted to achieve the higher homogeneity of the final product. Specimens of nickel-cobalt oxide were characterized by various experimental techniques, including X-ray diffraction (XRD), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR). X-ray diffraction results showed that there was no crystallinity in the predecessor, and it still had the amorphous phase. The formations of the crystalline phases of the nickel-cobalt oxide nanoparticles started from 350–500 °C, and the final products had different crystallite sizes ranging from 11–35 nm. Furthermore, the variation of DC conductivity (σdc), impedance, tangent loss (tgδ) and dielectric constant (ε′) of the calcined specimens with frequency in the range of 102–106 Hz was investigated. σdc showed a value of 1.9 × 10−6 S/m, 1.3 × 10−6 S/m and 1.6 × 10−6 S/m for the specimens calcined at 350, 400 and 450 °C, respectively. Additionally, a decrease in tgδ values with an increase in temperature was observed. Finally, the formed nanoparticles exhibited ferromagnetic behaviors, which were confirmed by using a vibrating sample magnetometer (VSM). Full article
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Open AccessArticle Effects of Current Stressing on the Grain Structure and Mechanical Properties of Ag-Alloy Bonding Wires with Various Pd and Au Contents
Metals 2016, 6(8), 182; doi:10.3390/met6080182
Received: 9 May 2016 / Revised: 19 July 2016 / Accepted: 1 August 2016 / Published: 4 August 2016
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Abstract
Ag-alloy bonding wires containing various Pd and Au elements and traditional 4 N Au and Pd-coated 4 N Cu bonding wires were stressed with a current density of 1.23 × 105 A/cm2 in air. The amounts of annealing twins in the
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Ag-alloy bonding wires containing various Pd and Au elements and traditional 4 N Au and Pd-coated 4 N Cu bonding wires were stressed with a current density of 1.23 × 105 A/cm2 in air. The amounts of annealing twins in the Ag-alloy wires were much higher than those in Au and Pd-coated Cu wires. The percentages of twinned grains in these Ag-alloy wires increased obviously with current stressing. However, the grains in Ag-3Pd and Ag-15Au-3Pd grew moderately under current stressing, in contrast to the dramatic grain growth in the other bonding wires. In addition, the breaking loads and elongations of the various Ag-alloy wires changed slightly, similar to the case of Au wire. The results implied that degradation of the mechanical properties of these annealing twinned Ag-alloy wires due to electromigration was limited. Pd-coated Cu wire was severely oxidized after current stressing for only 1 h in air, which drastically degraded both the breaking load and elongation. Full article
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Open AccessArticle High-Temperature Compressive Resistance and Mechanical Properties Improvement of Strain-Induced Melt Activation-Processed Al-Mg-Si Aluminum Alloy
Metals 2016, 6(8), 183; doi:10.3390/met6080183
Received: 13 June 2016 / Revised: 12 July 2016 / Accepted: 21 July 2016 / Published: 5 August 2016
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Abstract
Even though the high-temperature formability of Al alloys can be enhanced by the strain-induced melt activation (SIMA) process, the mechanical properties of the formed alloys are necessary for estimation. In this research, a modified two-step SIMA (TS-SIMA) process that omits the cold working
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Even though the high-temperature formability of Al alloys can be enhanced by the strain-induced melt activation (SIMA) process, the mechanical properties of the formed alloys are necessary for estimation. In this research, a modified two-step SIMA (TS-SIMA) process that omits the cold working step of the traditional SIMA process is adopted for the 6066 Al-Mg-Si alloy to obtain globular grains with a short-duration salt bath. The high-temperature compressive resistance and mechanical properties of TS-SIMA alloys were investigated. The TS-SIMA alloys were subjected to artificial aging heat treatment to improve their mechanical properties. The results show that the TS-SIMA process can reduce compression loading by about 35%. High-temperature compressive resistance can be reduced by the TS-SIMA process. After high-temperature compression, the mechanical properties of the TS-SIMA alloys were significantly improved. Furthermore, artificial aging treatment can be used to enhance formed alloys via the TS-SIMA process. After artificial aging treatment, the mechanical properties of TS-SIMA alloys are comparable to those of general artificially-aged materials. Full article
(This article belongs to the Special Issue Aluminum Alloys)
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Open AccessArticle The Effects of Laser Welding Direction on Joint Quality for Non-Uniform Part-to-Part Gaps
Metals 2016, 6(8), 184; doi:10.3390/met6080184
Received: 25 May 2016 / Revised: 2 August 2016 / Accepted: 3 August 2016 / Published: 6 August 2016
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Abstract
Controlling part-to-part gaps is a crucial task in the laser welding of galvanized steel sheets for ensuring the quality of the assembly joint. However, part-to-part gaps are frequently non-uniform. Hence, elevations and depressions from the perspective of the heading direction of the laser
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Controlling part-to-part gaps is a crucial task in the laser welding of galvanized steel sheets for ensuring the quality of the assembly joint. However, part-to-part gaps are frequently non-uniform. Hence, elevations and depressions from the perspective of the heading direction of the laser beam always exist throughout the gap, creating ascending, descending, and flat travelling paths for laser welding. In this study, assuming non-uniform part-to-part gaps, the effects of welding direction on the quality of the joint of galvanized steel sheets—SGARC440 (lower part) and SGAFC590DP (upper part)—were examined using 2-kW fiber and 6.6-kW disk laser welding systems. The experimental analysis of coupon tests confirmed that there is no statistically significant correlation between the direction of welding and weld pool quality if the gap exceeds the tolerable range. However, when the gap is controlled within the tolerable range, the welding direction can be considered as an important process control variable to enhance the quality of the joint. Full article
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Open AccessFeature PaperArticle On the Improvement of AA2024 Wear Properties through the Deposition of a Cold-Sprayed Titanium Coating
Metals 2016, 6(8), 185; doi:10.3390/met6080185
Received: 25 March 2016 / Revised: 29 July 2016 / Accepted: 4 August 2016 / Published: 11 August 2016
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Abstract
This paper deals with the study of the enhancement of the tribological properties of AA2024 through the deposition of a titanium coating. In particular two different coatings were studied: (1) untreated titanium coating; and (2) post-deposition laser-treated titanium coating. Titanium grade 2 powders
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This paper deals with the study of the enhancement of the tribological properties of AA2024 through the deposition of a titanium coating. In particular two different coatings were studied: (1) untreated titanium coating; and (2) post-deposition laser-treated titanium coating. Titanium grade 2 powders were deposited onto an aluminium alloy AA2024-T3 sheet through the cold gas dynamic spray process. The selective laser post treatment was carried out by using a 220 W diode laser to further enhance the wear properties of the coating. Tribo-tests were executed to analyse the tribological behaviour of materials in contact with an alternative moving counterpart under a controlled normal load. Four different samples were tested to assess the effectiveness of the treatments: untreated aluminium sheets, titanium grade 2 sheets, as-sprayed titanium powders and the laser-treated coating layer. The results obtained proved the effectiveness of the coating in improving the tribological behaviour of the AA2024. In particular the laser-treated coating showed the best results in terms of both the friction coefficient and mass lost. The laser treatment promotes a change of the wear mechanism, switching from a severe adhesive wear, resulting in galling, to an abrasive wear mechanism. Full article
(This article belongs to the Special Issue Aluminum Alloys)
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Open AccessArticle Effect of Microstructure on Fracture Toughness and Fatigue Crack Growth Behavior of Ti17 Alloy
Metals 2016, 6(8), 186; doi:10.3390/met6080186
Received: 18 April 2016 / Revised: 13 July 2016 / Accepted: 20 July 2016 / Published: 12 August 2016
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Abstract
Ti-5Al-2Sn-2Zr-4Mo-4Cr (Ti17) is used extensively in turbine engines, where fracture toughness and fatigue crack growth (FCG) resistance are important properties. However, most research on the alloy was mainly focused on deformation behavior and microstructural evolution, and there have been few studies to examine
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Ti-5Al-2Sn-2Zr-4Mo-4Cr (Ti17) is used extensively in turbine engines, where fracture toughness and fatigue crack growth (FCG) resistance are important properties. However, most research on the alloy was mainly focused on deformation behavior and microstructural evolution, and there have been few studies to examine the effect of microstructure on the properties. Accordingly, the present work studied the influences of the microstructure types (bimodal and lamellar) on the mechanical properties of Ti17 alloy, including fracture toughness, FCG resistance and tensile property. In addition, the fracture modes associated with different microstructures were also analyzed via the observation of the fracture surface. The results found that the lamellar microstructure had a much higher fracture toughness and superior resistance to FCG. These results were discussed in terms of the tortuous crack path and the intrinsic microstructural contributions. Full article
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Open AccessArticle Impurity Antimony-Induced Creep Property Deterioration and Its Suppression by Rare Earth Ceriumfor a 9Cr-1Mo Ferritic Heat-Resistant Steel
Metals 2016, 6(8), 187; doi:10.3390/met6080187
Received: 9 July 2016 / Revised: 23 July 2016 / Accepted: 9 August 2016 / Published: 12 August 2016
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Abstract
The high temperature creep properties of three groups of modified 9Cr-1Mo steel samples, undoped, doped with Sb, and doped with Sb and Ce, are evaluated under the applied stresses from 150 MPa to 210 MPa and at the temperatures from 873–923 K. The
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The high temperature creep properties of three groups of modified 9Cr-1Mo steel samples, undoped, doped with Sb, and doped with Sb and Ce, are evaluated under the applied stresses from 150 MPa to 210 MPa and at the temperatures from 873–923 K. The creep behavior follows the temperature-compensated power law as well as the Monkman-Grant relation. The creep activation energy for the Sb-doped steel (519 kJ/mol) is apparently lower than that for the undoped one (541 kJ/mol), but it is considerably higher for the Sb+Ce-doped steel (621 kJ/mol). Based on the obtained relations, both the creep lifetimes under 50 MPa, 80 MPa, and 100 MPa in the range 853–923 K and the 105 h creep rupture strengths at 853 K, 873 K, and 893 K are predicted. It is demonstrated that the creep properties of the Sb-doped steel are considerably deteriorated but those of the Sb+Ce-doped steel are significantly improved as compared with the undoped steel. Microstructural and microchemical characterizations indicate that the minor addition of Ce can stabilize the microstructure of the steel by segregating to grain boundaries and dislocations, thereby offsetting the deleterious effect of Sb by coarsening the microstructure and weakening the grain boundary. Full article
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Open AccessFeature PaperArticle Evaluation of Chill Cast Co-Cr Alloys for Biomedical Applications
Metals 2016, 6(8), 188; doi:10.3390/met6080188
Received: 15 April 2016 / Revised: 3 August 2016 / Accepted: 11 August 2016 / Published: 16 August 2016
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Abstract
Binary Co-Cr alloys containing various Cr contents were vacuum induction melted and cast into wedge-shaped copper molds. It was intended to develop a microstructure (1) free from interdendritic segregation and porosity; (2) having minimal intermetallic precipitates; and (3) suitable for biomedical applications. The
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Binary Co-Cr alloys containing various Cr contents were vacuum induction melted and cast into wedge-shaped copper molds. It was intended to develop a microstructure (1) free from interdendritic segregation and porosity; (2) having minimal intermetallic precipitates; and (3) suitable for biomedical applications. The resultant microstructures were evaluated from sections obtained longitudinally and centrally in the plane normal to the diverging wedge faces. All ingots showed a dendritic microstructure with some characteristic features. For instance, in Co-20–30 wt. % Cr alloys, the chilled cast microstructures consisted of columnar dendrites without interdendritic segregation, a minimum of intermetallic precipitates, and the presence of a predominantly athermal HCP ε-martensite (>80 vol. %). In addition, the metastable FCC γ-Co phase was identified by X-ray diffraction and scanning electron microscopy. In the case of 35–44 wt. % Cr cobalt alloys, a eutectic constituent including the σ-phase were found to develop in the interdendritic regions. From this work, a Co-20 wt. % Cr alloy was chosen for further investigation after heat treating below the γ/ε transition temperature. The resultant tensile strength and ductility were further improved after applying a heat treatment at 730 °C for 30 min, obtaining values of elongation of 26% as compared with 2.55 < 5 of elongation in the as cast condition. Also, the alloy corrosion resistance in artificial saliva was investigated. It was found that the exhibited corrosion rates for the as-cast and heat-treated conditions are between those reported for other similar systems. Full article
(This article belongs to the Special Issue Metallic Biomaterials)
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Open AccessArticle Effect of Creep Aging Process on Microstructures and Properties of the Retrogressed Al-Zn-Mg-Cu Alloy
Metals 2016, 6(8), 189; doi:10.3390/met6080189
Received: 31 May 2016 / Revised: 25 July 2016 / Accepted: 5 August 2016 / Published: 17 August 2016
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Abstract
The creep aging behaviors of retrogressed Al-Zn-Mg-Cu alloy were studied by uniaxial tensile creep tests at 140 °C. The effects of creep aging time and applied stress on microstructures and properties of the studied alloy were investigated by using transmission electron microscope (TEM),
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The creep aging behaviors of retrogressed Al-Zn-Mg-Cu alloy were studied by uniaxial tensile creep tests at 140 °C. The effects of creep aging time and applied stress on microstructures and properties of the studied alloy were investigated by using transmission electron microscope (TEM), hardness, and corrosion resistance tests. Results show that the effects of the creep aging process on microstructures and properties are significant. The size of matrix precipitate (MPt), distance between MPts, width of precipitate-free zone (PFZ), and distance between grain boundary precipitates (GBPs) increase with the increase of creep aging time and applied stress. With the increase of creep aging time and applied stress, the corrosion resistance of the studied alloy improved. After creep aging for 20 h, the electrical conductivity varied with different applied stress from 35.99% to 37.24% International Annealed Copper Standard (IACS), and the exfoliation corrosion (EXCO) resistance increased to the corrosion rating of “EB”, which express slight surface corrosion. Compared with the traditional retrogression and re-aging process (RRA), the retrogression and creep aging process (RCA) can increase the MPt size, widen the precipitates distribution, narrow the PFZ width, and enhance the corrosion resistance while offering the hardness comparable to that of the RRA process. Full article
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Open AccessArticle Gas-Solid Reaction Route toward the Production of Intermetallics from Their Corresponding Oxide Mixtures
Metals 2016, 6(8), 190; doi:10.3390/met6080190
Received: 29 June 2016 / Revised: 3 August 2016 / Accepted: 10 August 2016 / Published: 17 August 2016
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Abstract
Near-net shape forming of metallic components from metallic powders produced in situ from reduction of corresponding pure metal oxides has not been explored to a large extent. Such a process can be probably termed in short as the “Reduction-Sintering” process. This methodology can
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Near-net shape forming of metallic components from metallic powders produced in situ from reduction of corresponding pure metal oxides has not been explored to a large extent. Such a process can be probably termed in short as the “Reduction-Sintering” process. This methodology can be especially effective in producing components containing refractory metals. Additionally, in situ production of metallic powder from complex oxides containing more than one metallic element may result in in situ alloying during reduction, possibly at lower temperatures. With this motivation, in situ reduction of complex oxides mixtures containing more than one metallic element has been investigated intensively over a period of years in the department of materials science, KTH, Sweden. This review highlights the most important features of that investigation. The investigation includes not only synthesis of intermetallics and refractory metals using the gas solid reaction route but also study the reaction kinetics and mechanism. Environmentally friendly gases like H2, CH4 and N2 were used for simultaneous reduction, carburization and nitridation, respectively. Different techniques have been utilized. A thermogravimetric analyzer was used to accurately control the process conditions and obtain reaction kinetics. The fluidized bed technique has been utilized to study the possibility of bulk production of intermetallics compared to milligrams in TGA. Carburization and nitridation of nascent formed intermetallics were successfully carried out. A novel method based on material thermal property was explored to track the reaction progress and estimate the reaction kinetics. This method implies the dynamic measure of thermal diffusivity using laser flash method. These efforts end up with a successful preparation of nanograined intermetallics like Fe-Mo and Ni-W. In addition, it ends up with simultaneous reduction and synthesis of Ni-WN and Ni-WC from their oxide mixtures in single step. Full article
(This article belongs to the Special Issue Intermetallics 2016)
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Open AccessArticle Serration Behavior in Pd77.5Cu6Si16.5 Alloy
Metals 2016, 6(8), 191; doi:10.3390/met6080191
Received: 18 May 2016 / Revised: 1 August 2016 / Accepted: 1 August 2016 / Published: 17 August 2016
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Abstract
The strain-rate-dependent plasticity under uniaxial compression at the strain rates of 2 × 10−3, 2 × 10−4 and 2 × 10−5 s−1 in a Pd77.5Cu6Si16.5 alloy is investigated. At different strain rates, the
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The strain-rate-dependent plasticity under uniaxial compression at the strain rates of 2 × 10−3, 2 × 10−4 and 2 × 10−5 s−1 in a Pd77.5Cu6Si16.5 alloy is investigated. At different strain rates, the serration events exhibit different amplitudes and time scales. The intersection effects take place obviously, and the loading time is much longer than the relaxation time in the serration event at three strain rates. However, the time intervals between two neighboring serrations lack any time scale, and the elastic energy density displays a power-law distribution at the strain rate of 2 × 10−3 s−1, which means that the self-organized critical (SOC) behavior emerges with increasing strain rates. Full article
(This article belongs to the Special Issue High-Entropy Alloys (HEAs))
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Open AccessArticle Leaching Kinetics of Zinc from Metal Oxide Varistors (MOVs) with Sulfuric Acid
Metals 2016, 6(8), 192; doi:10.3390/met6080192
Received: 22 July 2016 / Revised: 13 August 2016 / Accepted: 17 August 2016 / Published: 19 August 2016
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Abstract
The leaching kinetics of zinc from zinc oxide-based metal oxide varistors (MOVs) was investigated in H2SO4 at atmospheric pressure. Kinetics experiments were carried out at various agitation speeds, particle sizes, initial H2SO4 concentrations, and reaction temperatures. It
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The leaching kinetics of zinc from zinc oxide-based metal oxide varistors (MOVs) was investigated in H2SO4 at atmospheric pressure. Kinetics experiments were carried out at various agitation speeds, particle sizes, initial H2SO4 concentrations, and reaction temperatures. It was determined that the leaching rate of zinc was independent of agitation speed above 300 rpm and also independent of particle size below 105 μm, whereas it dramatically increased with an increasing H2SO4 concentration. Except for when the H2SO4 concentration was varied, the m-values were almost constant at varying agitation speeds (m-values: 0.554–0.579), particle sizes (m-values: 0.507–0.560) and reaction temperature (m-values: 0.530–0.560) conditions. All of the m-values in these experiments were found to be below 0.580. Therefore, it is proposed that the extraction of zinc is a diffusion-controlled reaction. The leaching kinetics followed the D3 kinetic equation with a rate-controlling diffusion step through the ash layers, and the corresponding apparent activation energy was calculated as 20.7 kJ/mol in the temperature range of 313 K to 353 K. Full article
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Open AccessArticle Effect of Titanium on the Microstructure and Mechanical Properties of High-Carbon Martensitic Stainless Steel 8Cr13MoV
Metals 2016, 6(8), 193; doi:10.3390/met6080193
Received: 20 May 2016 / Revised: 16 August 2016 / Accepted: 17 August 2016 / Published: 22 August 2016
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Abstract
The effect of titanium on the carbides and mechanical properties of martensitic stainless steel 8Cr13MoV was studied. The results showed that TiCs not only acted as nucleation sites for δ-Fe and eutectic carbides, leading to the refinement of the microstructure, but also inhibited
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The effect of titanium on the carbides and mechanical properties of martensitic stainless steel 8Cr13MoV was studied. The results showed that TiCs not only acted as nucleation sites for δ-Fe and eutectic carbides, leading to the refinement of the microstructure, but also inhibited the formation of eutectic carbides M7C3. The addition of titanium in steel also promoted the transformation of M7C3-type to M23C6-type carbides, and consequently more carbides could be dissolved into the matrix during hot processing as demonstrated by the determination of extracted carbides from the steel matrix. Meanwhile, titanium suppressed the precipitation of secondary carbides during annealing. The appropriate amount of titanium addition decreased the size and fraction of primary carbides in the as-cast ingot, and improved the mechanical properties of the annealed steel. Full article
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Review

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Open AccessReview Review of Electromagnetic-Based Crack Sensors for Metallic Materials (Recent Research and Future Perspectives)
Metals 2016, 6(8), 172; doi:10.3390/met6080172
Received: 20 May 2016 / Revised: 8 July 2016 / Accepted: 20 July 2016 / Published: 25 July 2016
Cited by 1 | PDF Full-text (16182 KB) | HTML Full-text | XML Full-text
Abstract
Evaluation and non-destructive identification of stress-induced cracks or failures in metals is a vital problem in many sensitive environments, including transportation (steel railway tracks, bridges, car wheels, etc.), power plants (steam generator tubing, etc.) and aerospace transportation (landing gear, aircraft fuselages, etc.). There
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Evaluation and non-destructive identification of stress-induced cracks or failures in metals is a vital problem in many sensitive environments, including transportation (steel railway tracks, bridges, car wheels, etc.), power plants (steam generator tubing, etc.) and aerospace transportation (landing gear, aircraft fuselages, etc.). There are many traditional non-destructive detection and evaluation techniques; recently, near-field millimeter waves and microwave methods have shown incredible promise for augmenting currently available non-destructive techniques. This article serves as a review of developments made until now on this topic; it provides an overview of microwave scanning techniques for crack detection. This article summarizes the abilities of these methods to identify and evaluate cracks (including describing their different physical properties). These methods include applying filters based on dual-behavior resonators (DBRs), using complementary split-ring resonators (CSRRs) for the perturbation of electric fields, using waveguide probe-loaded CSRRs and using a substrate-integrated-waveguide (SIW) cavity for the detection of sub-millimeter surface and subsurface cracks. Full article
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