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Metals, Volume 6, Issue 10 (October 2016)

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Open AccessFeature PaperArticle Strong and Stable Nanocomposites Prepared by High-Pressure Torsion of Cu-Coated Fe Powders
Metals 2016, 6(10), 228; doi:10.3390/met6100228
Received: 30 August 2016 / Revised: 16 September 2016 / Accepted: 19 September 2016 / Published: 22 September 2016
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Abstract
Segregation and chemical inhomogeneity are well-known problems in powder metallurgy and are also an issue for new applications of powder mixtures, for example as starting materials for severe plastic deformation. In this study, Cu-coated Fe powder was prepared via immersion deposition, inductively hot-pressed
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Segregation and chemical inhomogeneity are well-known problems in powder metallurgy and are also an issue for new applications of powder mixtures, for example as starting materials for severe plastic deformation. In this study, Cu-coated Fe powder was prepared via immersion deposition, inductively hot-pressed and subsequently deformed using high-pressure torsion. The homogeneity of the pressed material was found to be much better than that of powder mixtures that were prepared for comparison. During severe plastic deformation, higher hardness was observed for the coated powder as compared to powder mixtures even after low strains. In the saturation state, the coated powder was found to result in a hardness of about 600 HV, which is significantly harder than for the powder mixtures. This is attributed to the greater amount of impurities introduced by the coating process. It is shown that coated powders are promising starting materials for severe plastic deformation in order to reduce the amount of strain necessary to reach the saturation state and to obtain high strength and more homogeneous mechanical alloying. Full article
(This article belongs to the Special Issue Mechanical Alloying)
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Open AccessArticle Effect of Welding Parameters on Microstructure and Mechanical Properties of Cast Fe-40Al Alloy
Metals 2016, 6(10), 229; doi:10.3390/met6100229
Received: 27 June 2016 / Revised: 8 September 2016 / Accepted: 20 September 2016 / Published: 23 September 2016
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Abstract
Friction welding of cast Fe-40Al alloy was carried out at 1000 rmp for various friction times, friction pressures, and forging pressures. The microstructures of the interface of welded samples were analyzed by optical and scanning electron microscopy (SEM). Micrographs demonstrated that excellent welding
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Friction welding of cast Fe-40Al alloy was carried out at 1000 rmp for various friction times, friction pressures, and forging pressures. The microstructures of the interface of welded samples were analyzed by optical and scanning electron microscopy (SEM). Micrographs demonstrated that excellent welding formed continuously along the interface, except for samples welded for 3 s. Chemical compositions of the interface of the friction welded samples and of the fractured surface of all the specimens were determined using energy dispersive spectroscopy (EDS). After the welding process, shear tests were applied to the welded samples to determine the shear strength of joints. Test results indicated that the maximum shear strength was 469.5 MPa. Full article
(This article belongs to the Special Issue Intermetallics 2016)
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Open AccessArticle Glass Forming Ability and Corrosion Resistance of Zr-Cu-Ni-Al-Ag Bulk Metallic Glass
Metals 2016, 6(10), 230; doi:10.3390/met6100230
Received: 13 July 2016 / Revised: 20 September 2016 / Accepted: 20 September 2016 / Published: 24 September 2016
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Abstract
Zr70−xCu12.5Ni10Al7.5Agx (x = 0–10) bulk metallic glasses (BMGs) have been prepared by copper mold casting. The glass-forming ability (GFA) and corrosion behavior of Zr-based BMGs have been investigated. It is found that
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Zr70−xCu12.5Ni10Al7.5Agx (x = 0–10) bulk metallic glasses (BMGs) have been prepared by copper mold casting. The glass-forming ability (GFA) and corrosion behavior of Zr-based BMGs have been investigated. It is found that the GFA of Zr-based BMGs first increases and then decreases with the increase of the Ag content, and the best glass former is Zr65Cu12.5Ni10Al7.5Ag5 with the maximum thickness of the glass phase region of 4.3 mm. The corrosion resistance is, however, found to be worsened with the increase of the Ag content. The mechanisms for the enhancement of GFA and the deterioration of corrosion resistance in the alloys are discussed. Full article
(This article belongs to the Special Issue Amorphous Alloys and Related Transitions)
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Open AccessFeature PaperArticle Distribution and Excretion of Arsenic Metabolites after Oral Administration of Seafood-Related Organoarsenicals in Rats
Metals 2016, 6(10), 231; doi:10.3390/met6100231
Received: 29 June 2016 / Revised: 13 September 2016 / Accepted: 13 September 2016 / Published: 27 September 2016
Cited by 2 | PDF Full-text (1549 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Less information is available on the metabolism of organic arsenicals compared to inorganic arsenic in mammals. In the present study, we investigated tissue distribution, metabolism and excretion in rats of organoarsenicals, dimethylarsinic acid (DMAV), arsenobetaine (AB), arsenocholine (AC) and trimethylarsine oxide
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Less information is available on the metabolism of organic arsenicals compared to inorganic arsenic in mammals. In the present study, we investigated tissue distribution, metabolism and excretion in rats of organoarsenicals, dimethylarsinic acid (DMAV), arsenobetaine (AB), arsenocholine (AC) and trimethylarsine oxide (TMAOV). Among these animals, arsenic concentrations in red blood cells (RBCs) and spleen increased remarkably only in the DMAV group. Hepatic arsenic concentration increased significantly only in the AC group. Approximately 17%, 72% and 60% of the dose was excreted in urine in two days in the DMAV, AB and AC groups, respectively; virtually the entire dose was excreted in urine in one day in the TMAOV group. On the other hand, approximately 18%, 0.2%, 0.5% and 0.1% of the dose was excreted in feces in two days in the DMAV, AB, AC and TMAOV groups, respectively. A large amount of arsenic was accumulated in RBCs in the form of protein-bound dimethylarsinous acid (DMAIII), and dimethylmonothioarsinic acid (DMMTAV), a reportedly toxic thio-arsenical, was found in urine and fecal extract in the DMAV group. These results suggest that intake of DMAV is a potential health hazard, given that the metabolites of DMAV, such as DMAIII and DMMTAV, are known to be highly toxic. Full article
(This article belongs to the Special Issue Metallomics)
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Open AccessArticle Erosion Behaviour of API X100 Pipeline Steel at Various Impact Angles and Particle Speeds
Metals 2016, 6(10), 232; doi:10.3390/met6100232
Received: 12 July 2016 / Revised: 22 August 2016 / Accepted: 31 August 2016 / Published: 27 September 2016
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Abstract
Erosion is the gradual removal of material due to solid particle impingement and results in a failure of pipeline materials. In this study, a series of erosion tests were carried out to investigate the influence of particle speed and impact angle on the
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Erosion is the gradual removal of material due to solid particle impingement and results in a failure of pipeline materials. In this study, a series of erosion tests were carried out to investigate the influence of particle speed and impact angle on the erosion mechanism of API X100 pipeline steel. A dry erosion machine was used as the test equipment, while the particle speed ranged from 20 to 80 m/s and impact angles of 30° and 90° were used as test parameters. The eroded API X100 steel surface was characterized using scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). The weight loss and erosion rate were also investigated. The results showed that at a 90° impact angle, a ploughing mechanism was occurring on the tested specimens, while material removal through low-angle cutting was the dominant mechanism at lower impact angles. Embedment of alumina particles on the target steel surface, micro-cutting, and low-angle cutting were observed at low impact angles. Therefore, the scratches, cuttings, and severe ploughings observed on some failed oil and gas pipelines could be attributed to the erosion mechanism. Full article
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Open AccessArticle The Evolution of Microstructures and the Properties of Bulk Metallic Glass with Consubstantial Composition Laser Welding
Metals 2016, 6(10), 233; doi:10.3390/met6100233
Received: 20 July 2016 / Revised: 29 August 2016 / Accepted: 13 September 2016 / Published: 29 September 2016
Cited by 1 | PDF Full-text (9849 KB) | HTML Full-text | XML Full-text
Abstract
A Zr55Cu30Ni5Al10 plate-like bulk metallic glass (BMG) was prepared using copper mold suction casting. Additionally, alloy powders with the same nominal composition were synthesized. The alloy powders were welded or melted to the cleaned surface of
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A Zr55Cu30Ni5Al10 plate-like bulk metallic glass (BMG) was prepared using copper mold suction casting. Additionally, alloy powders with the same nominal composition were synthesized. The alloy powders were welded or melted to the cleaned surface of the BMG with a laser beam acceleration voltage of 60 kV, a beam current range from 60 to 100 mA, a welding speed of 60 mm/s, as well as an impulse width of 3.0 ms. The effect of consubstantial composition welding on the microstructures and properties was investigated. The molten and subsequently solidified metallic mixtures remain an amorphous structure, but the enthalpy of the welded or melted position varies due to the combination of the micro-structural relaxation and nano-crystals precipitated during the energy inputs. The surface layers of the BMG can be significantly intensified after welding processes; however, the heat-affected zones (HAZs) exhibit a slight degradation in mechanical properties with respect to the BMG matrix. This study has important reference value for specialists working on the promotion of applications of BMGs. Full article
(This article belongs to the Special Issue Amorphous Alloys and Related Transitions)
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Open AccessArticle Study on the Thermal Conductivity Characteristics of Graphene Prepared by the Planetary Ball Mill
Metals 2016, 6(10), 234; doi:10.3390/met6100234
Received: 16 August 2016 / Revised: 13 September 2016 / Accepted: 26 September 2016 / Published: 29 September 2016
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Abstract
This study was designed to examine the physical disintegration of graphene (GN), an excellent heat conductor, by using the planetary ball mill, a simple and convenient means to produce particles arbitrarily. The conditions for the disintegration of GN were distinguished by the rotation
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This study was designed to examine the physical disintegration of graphene (GN), an excellent heat conductor, by using the planetary ball mill, a simple and convenient means to produce particles arbitrarily. The conditions for the disintegration of GN were distinguished by the rotation of the planetary ball mill (200 rpm, 400 rpm, and 600 rpm) and by the duration of its operation (30 min, 60 min, and 90 min), respectively. From the results, we saw that, when experimental conditions are 200 rpm with 60 min, the particle size was the smallest (at 328 nm) and the results of thermal conductivity were the highest. In the absorbance results, GN was well dispersed because the value of its absorbance is high. Full article
(This article belongs to the Special Issue Mechanical Alloying)
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Open AccessArticle Combustion Synthesis of MoSi2-Al2O3 Composites from Thermite-Based Reagents
Metals 2016, 6(10), 235; doi:10.3390/met6100235
Received: 15 July 2016 / Revised: 21 September 2016 / Accepted: 28 September 2016 / Published: 30 September 2016
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Abstract
Formation of MoSi2–Al2O3 composites with a broad range of the MoSi2/Al2O3 ratio was conducted by thermite-based combustion synthesis in the SHS mode. The addition of two thermite mixtures composed of MoO3 +
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Formation of MoSi2–Al2O3 composites with a broad range of the MoSi2/Al2O3 ratio was conducted by thermite-based combustion synthesis in the SHS mode. The addition of two thermite mixtures composed of MoO3 + 2Al and 0.6MoO3 + 0.6SiO2 + 2Al into the Mo–Si reaction systems facilitated self-sustaining combustion and contributed to in situ formation of MoSi2 and Al2O3. The samples adopting the former thermite reagent were more exothermic and produced composites with MoSi2/Al2O3 from 2.0 to 4.5, beyond which combustion failed to proceed. Because of lower exothermicity of the reactions, the final products with MoSi2/Al2O3 from 1.2 to 2.5 were fabricated from the SHS process involving the latter thermite mixture. Combustion temperatures of both reaction systems decreased from about 1640 to 1150 °C with increasing MoSi2/Al2O3 proportion, which led to a phase transition of MoSi2. It was found that the dominant silicide was β-MoSi2 when the combustion temperature of the synthesis reaction exceeded 1550 °C and shifted to α-MoSi2 as the combustion temperature fell below 1320 °C. The results of this study showed an energy-efficient fabrication route to tailor the phase and content of MoSi2 in the MoSi2–Al2O3 composite. Full article
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Open AccessArticle Influence of Hardness, Matrix and Carbides in Combination with Nitridation on Abrasive Wear Resistance of X210Cr12 Tool Steel
Metals 2016, 6(10), 236; doi:10.3390/met6100236
Received: 19 May 2016 / Revised: 9 September 2016 / Accepted: 13 September 2016 / Published: 2 October 2016
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Abstract
Materials used in abrasive wear conditions are usually selected according to their microstructure and hardness, however, other factors such as grain size, matrix saturation, carbides size and morphology are rarely considered. Therefore, the present study deals with the influence of different heat and
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Materials used in abrasive wear conditions are usually selected according to their microstructure and hardness, however, other factors such as grain size, matrix saturation, carbides size and morphology are rarely considered. Therefore, the present study deals with the influence of different heat and chemical-heat treatments including their combination on abrasive wear resistance of X210Cr12 tool steel. The effects of material hardness, carbide morphology and microstructure on wear resistance after quenching and nitriding were also investigated. One sample series was quenched after austenitization at 960 °C for 20 min and tempered at 180 °C for 2 h. The second sample series was quenched from 1060 °C austenitization for 20 min and afterwards twice tempered at 530 °C for 1 h. From both the quenched and tempered states, one half of the samples was gas nitrided in NH3 atmosphere for 3 h and then diffusion annealed in N2 atmosphere for 4 h. Abrasion wear tests were performed by sliding the samples on Al2O3 paper. The samples weight loss was considered the main criterion for the wear resistance evaluation. The microstructures, nitrided layers and worn surfaces were observed using SEM microscopy. The highest abrasion wear resistance was obtained for the nitrided samples that were previously quenched from 1060 °C and tempered at 530 °C. Full article
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Open AccessArticle The Effects of Pulse Parameters on Weld Geometry and Microstructure of a Pulsed Laser Welding Ni-Base Alloy Thin Sheet with Filler Wire
Metals 2016, 6(10), 237; doi:10.3390/met6100237
Received: 31 August 2016 / Revised: 23 September 2016 / Accepted: 28 September 2016 / Published: 8 October 2016
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Abstract
Due to its excellent resistance to corrosive environments and its superior mechanical properties, the Ni-based Hastelloy C-276 alloy was chosen as the material of the stator and rotor cans of a nuclear main pump. In the present work, the Hastelloy C-276 thin sheet
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Due to its excellent resistance to corrosive environments and its superior mechanical properties, the Ni-based Hastelloy C-276 alloy was chosen as the material of the stator and rotor cans of a nuclear main pump. In the present work, the Hastelloy C-276 thin sheet 0.5 mm in thickness was welded with filler wire by a pulsed laser. The results indicated that the weld pool geometry and microstructure were significantly affected by the duty ratio, which was determined by the pulse duration and repetition rate under a certain heat input. The fusion zone area was mainly affected by the duty ratio, and the relationship was given by a quadratic polynomial equation. The increase in the duty ratio coarsened the grain size, but did not obviously affect microhardness. The weld geometry and base metal dilution rate was manipulated by controlling pulsed parameters without causing significant change to the performance of the weld. However, it should be noted that, with a larger duty ratio, the partial molten zone is a potential weakness of the weld. Full article
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Open AccessArticle Effects of the Hot Isostatic Pressing Process on Crack Healing of the Laser Repair-Welded CM247LC Superalloy
Metals 2016, 6(10), 238; doi:10.3390/met6100238
Received: 30 July 2016 / Revised: 28 September 2016 / Accepted: 29 September 2016 / Published: 10 October 2016
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Abstract
This study investigated the effects of the hot isostatic pressing process on the crack healing, microstructure, and mechanical properties of the laser repair-welded CM247LC precipitation-hardened superalloy. To ensure the strength of the repair-welded area, this study used the direct re-melting approach, and simulated
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This study investigated the effects of the hot isostatic pressing process on the crack healing, microstructure, and mechanical properties of the laser repair-welded CM247LC precipitation-hardened superalloy. To ensure the strength of the repair-welded area, this study used the direct re-melting approach, and simulated the repair welding with the filler addition, which has a chemical composition matching that of the base superalloy. As expected, different types of cracks, including the solidification crack in the weld fusion zone and various types of liquidation cracks in the heat-affected zone, were observed. Through a proper hot isostatic pressing healing process, all cracks in the weld fusion zone and the heat-affected zone of the repair-welded pieces were healed. At the same time, some nano- and micro-sized carbides tended to form discontinuously along the healed crack trace. A micro-hardness test was conducted in the repair-welded area, and the results were similar to that of the as-cast material. Full article
(This article belongs to the Special Issue Ni- and Co-Based Superalloys and Their Coatings)
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Open AccessArticle On the Step Cooling Treatment for the Assessment of Temper Embrittlement Susceptibility of Heavy Forgings in Superclean Steels
Metals 2016, 6(10), 239; doi:10.3390/met6100239
Received: 20 July 2016 / Revised: 14 September 2016 / Accepted: 29 September 2016 / Published: 10 October 2016
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Abstract
When subjected to extended exposure to intermediate service temperatures, Cr–Mo steels, Ni–Cr steels, and 5% Ni steels can become embrittled, with an associated decrease in fracture toughness and a shift in the ductile-to-brittle transition temperature to higher temperatures. Two methods for the investigation
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When subjected to extended exposure to intermediate service temperatures, Cr–Mo steels, Ni–Cr steels, and 5% Ni steels can become embrittled, with an associated decrease in fracture toughness and a shift in the ductile-to-brittle transition temperature to higher temperatures. Two methods for the investigation of temper embrittlement phenomena are isothermal aging or the use of a step cooling aging treatment, which is less time consuming and is considered to be the most severe test to evaluate steel’s susceptibility to this phenomenon. In the present work, the effectiveness of the step cooling treatment in the assessment of temper embrittlement in a superclean 26NiCrMoV14.5 steel for heavy section forgings has been studied. Some isothermal aging treatments in the critical temperature range have also been carried out. Results of a Charpy V impact test on not-aged and aged specimens, and observation of the fracture surfaces led to the following conclusions: the steel does not undergo temper embrittlement upon step cooling treatment or after aging at different temperatures and times in the critical temperature range; the most negative effect on the shift of the ductile-to-brittle transition curve—compared with not aged steel—has been observed after aging at 593 °C for 2 h (ΔT54J = 9 °C); further aging up to 8 h produced a ΔT54J of only 1 °C. Neither step cooling nor aging at various critical temperatures gave rise to an intergranular brittle fracture; the amount of embrittling impurity elements in a superclean steel does not seem to be enough to cause embrittlement and a pure intergranular decohesion. Full article
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Open AccessArticle Short-to-Medium-Range Order and Atomic Packing in Zr48Cu36Ag8Al8 Bulk Metallic Glass
Metals 2016, 6(10), 240; doi:10.3390/met6100240
Received: 13 May 2016 / Revised: 19 September 2016 / Accepted: 19 September 2016 / Published: 12 October 2016
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Abstract
Due to its excellent glass-forming ability (GFA), the Zr48Cu36Al8Ag8 bulk metallic glass (BMG) is of great importance in glass transition investigations and new materials development. However, due to the lack of detailed structural information, the local
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Due to its excellent glass-forming ability (GFA), the Zr48Cu36Al8Ag8 bulk metallic glass (BMG) is of great importance in glass transition investigations and new materials development. However, due to the lack of detailed structural information, the local structure and atomic packing of this alloy is still unknown. In this work, synchrotron measurement and reverse Monte Carlo simulation are performed on the atomic configuration of a Zr-based bulk metallic glass. The local structure is characterized in terms of bond pairs and Voronoi tessellation. It is found that there are mainly two types of bond pairs in the configuration, as the body-centered cubic (bcc)-type and icosahedral (ico)-type bond pairs. On the other hand, the main polyhedra in the configuration are icosahedra and the bcc structure. That is, the bcc-type bond pairs, together with the ico-type bond pairs, form the bcc polyhedra, introducing the distortion in bcc clusters in short range. However, in the medium range, the atoms formed linear or planar structures, other than the tridimensional clusters. That is, the medium-range order in glass is of 1D or 2D structure, suggesting the imperfect ordered packing feature. Full article
(This article belongs to the Special Issue Amorphous Alloys and Related Transitions)
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Open AccessFeature PaperArticle Similarities and Differences in Mechanical Alloying Processes of V-Si-B and Mo-Si-B Powders
Metals 2016, 6(10), 241; doi:10.3390/met6100241
Received: 31 August 2016 / Revised: 29 September 2016 / Accepted: 8 October 2016 / Published: 14 October 2016
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Abstract
V-Si-B and Mo-Si-B alloys are currently the focus of materials research due to their excellent high temperature capabilities. To optimize the mechanical alloying (MA) process for these materials, we compare microstructures, morphology and particles size as well as hardness evolution during the milling
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V-Si-B and Mo-Si-B alloys are currently the focus of materials research due to their excellent high temperature capabilities. To optimize the mechanical alloying (MA) process for these materials, we compare microstructures, morphology and particles size as well as hardness evolution during the milling process for the model alloys V-9Si-13B and Mo-9Si-8B. A variation of the rotational speed of the planetary ball mill and the type of grinding materials is therefore investigated. These modifications result in different impact energies during ball-powder-wall collisions, which are quantitatively described in this comparative study. Processing with tungsten carbide vials and balls provides slightly improved impact energies compared to vials and balls made of steel. However, contamination of the mechanically alloyed powders with flaked particles of tungsten carbide is unavoidable. In the case of using steel grinding materials, Fe contaminations are also detectable, which are solved in the V and Mo solid solution phases, respectively. Typical mechanisms that occur during the MA process such as fracturing and comminution are analyzed using the comminution rate KP. In both alloys, the welding processes are more pronounced compared to the fracturing processes. Full article
(This article belongs to the Special Issue Mechanical Alloying)
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Open AccessArticle An Assessment of the Mechanical Properties and Microstructural Analysis of Dissimilar Material Welded Joint between Alloy 617 and 12Cr Steel
Metals 2016, 6(10), 242; doi:10.3390/met6100242
Received: 29 August 2016 / Revised: 29 September 2016 / Accepted: 10 October 2016 / Published: 14 October 2016
Cited by 1 | PDF Full-text (4191 KB) | HTML Full-text | XML Full-text
Abstract
The most effective method to reduce CO2 gas emission from the steam power plant is to improve its performance by elevating the steam temperature to more than 700 °C. For this, it is necessary to develop applicable materials at high temperatures. Ni-based
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The most effective method to reduce CO2 gas emission from the steam power plant is to improve its performance by elevating the steam temperature to more than 700 °C. For this, it is necessary to develop applicable materials at high temperatures. Ni-based Alloy 617 and 12Cr steel are used in steam power plants, due to their remarkable mechanical properties, high corrosion resistance, and creep strength. However, since Alloy 617 and 12Cr steel have different chemical compositions and thermal and mechanical properties, it is necessary to develop dissimilar material welding technologies. Moreover, in order to guarantee the reliability of dissimilar material welded structures, the assessment of mechanical and metallurgical properties, fatigue strength, fracture mechanical analysis, and welding residual stress analysis should be conducted on dissimilar material welded joints. In this study, first, multi-pass dissimilar material welding between Alloy 617 and 12Cr steel was performed under optimum welding conditions. Next, mechanical properties were assessed, including the static tensile strength, hardness distribution, and microstructural analysis of a dissimilar material welded joint. The results indicated that the yield strength and tensile strength of the dissimilar metal welded joint were higher than those of the Alloy 617 base metal, and lower than those of the 12Cr steel base metal. The hardness distribution of the 12Cr steel side was higher than that of Alloy 617 and the dissimilar material weld metal zone. It was observed that the microstructure of Alloy 617 HAZ was irregular austenite grain, while that of 12Cr steel HAZ was collapsed martensite grain, due to repeatable heat input during multi-pass welding. Full article
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Open AccessFeature PaperArticle TIG Dressing Effects on Weld Pores and Pore Cracking of Titanium Weldments
Metals 2016, 6(10), 243; doi:10.3390/met6100243
Received: 10 August 2016 / Revised: 30 September 2016 / Accepted: 10 October 2016 / Published: 17 October 2016
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Abstract
Weld pores redistribution, the effectiveness of using tungsten inert gas (TIG) dressing to remove weld pores, and changes in the mechanical properties due to the TIG dressing of Ti-3Al-2.5V weldments were studied. Moreover, weld cracks due to pores were investigated. The results show
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Weld pores redistribution, the effectiveness of using tungsten inert gas (TIG) dressing to remove weld pores, and changes in the mechanical properties due to the TIG dressing of Ti-3Al-2.5V weldments were studied. Moreover, weld cracks due to pores were investigated. The results show that weld pores less than 300 μm in size are redistributed or removed via remelting due to TIG dressing. Regardless of the temperature condition, TIG dressing welding showed ductility, and there was a loss of 7% tensile strength of the weldments. Additionally, it was considered that porosity redistribution by TIG dressing was due to fluid flow during the remelting of the weld pool. Weld cracks in titanium weldment create branch cracks around pores that propagate via the intragranular fracture, and oxygen is dispersed around the pores. It is suggested that the pore locations around the LBZ (local brittle zone) and stress concentration due to the pores have significant effects on crack initiation and propagation. Full article
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Open AccessArticle A Proposal of a Constitutive Description for Aluminium Alloys in Both Cold and Hot Working
Metals 2016, 6(10), 244; doi:10.3390/met6100244
Received: 1 July 2016 / Revised: 29 September 2016 / Accepted: 29 September 2016 / Published: 17 October 2016
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Abstract
The most important difficulties when the behaviour of a part that is subjected to external mechanical forces is simulated deal with the determination of both the material thermo-mechanical properties and its boundary conditions. The accuracy of the results obtained from the simulation is
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The most important difficulties when the behaviour of a part that is subjected to external mechanical forces is simulated deal with the determination of both the material thermo-mechanical properties and its boundary conditions. The accuracy of the results obtained from the simulation is directly related to the knowledge of the flow stress curve. Therefore, the determination of a material flow rule which is valid for both a wide temperature range and different initial deformation conditions in the starting material presents a great deal of interest when simulation results close to the experimental values are required to be obtained. In this present study, a novel flow stress curve is proposed that is able to accurately predict the behaviour of both materials with no previous accumulated strain and materials that have been previously subjected to severe plastic deformation processes. Moreover, it is possible to use it both for hot and cold working. The results are analysed in a wide test temperature range, which varies from room temperature to 300 °C, and from material previously processed by angular channel extrusion or with no previous strain accumulated. It is shown that the flow rule proposed is effective to model the material behaviour in a wide temperature range and it makes it possible to take the recrystallization phenomena that appear in previously deformed materials into account. In addition, the results obtained are compared with those predicted by other flow rules that exist in the prior literature. Furthermore, the study is complemented with finite element simulations and with a comparison between simulation and experimental results. Full article
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Open AccessArticle The Optimization of Process Parameters and Microstructural Characterization of Fiber Laser Welded Dissimilar HSLA and MART Steel Joints
Metals 2016, 6(10), 245; doi:10.3390/met6100245
Received: 22 July 2016 / Revised: 9 October 2016 / Accepted: 10 October 2016 / Published: 18 October 2016
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Abstract
Nowadays, environmental impact, safety and fuel efficiency are fundamental issues for the automotive industry. These objectives are met by using a combination of different types of steels in the auto bodies. Therefore, it is important to have an understanding of how dissimilar materials
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Nowadays, environmental impact, safety and fuel efficiency are fundamental issues for the automotive industry. These objectives are met by using a combination of different types of steels in the auto bodies. Therefore, it is important to have an understanding of how dissimilar materials behave when they are welded. This paper presents the process parameters’ optimization procedure of fiber laser welded dissimilar high strength low alloy (HSLA) and martensitic steel (MART) steel using a Taguchi approach. The influence of laser power, welding speed and focal position on the mechanical and microstructural properties of the joints was determined. The optimum parameters for the maximum tensile load-minimum heat input were predicted, and the individual significance of parameters on the response was evaluated by ANOVA results. The optimum levels of the process parameters were defined. Furthermore, microstructural examination and microhardness measurements of the selected welds were conducted. The samples of the dissimilar joints showed a remarkable microstructural change from nearly fully martensitic in the weld bead to the unchanged microstructure in the base metals. The heat affected zone (HAZ) region of joints was divided into five subzones. The fusion zone resulted in an important hardness increase, but the formation of a soft zone in the HAZ region. Full article
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Open AccessArticle High Cycle Fatigue Property of Carburized 20Cr Gear Steel under Axial Loading
Metals 2016, 6(10), 246; doi:10.3390/met6100246
Received: 31 March 2016 / Revised: 1 September 2016 / Accepted: 11 October 2016 / Published: 18 October 2016
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Abstract
The high cycle fatigue property of carburized 20Cr gear steel was experimentally investigated under axial loading with a stress ratio of zero. The test results show that this steel exhibits gradually decreasing S-N characteristics, and the fatigue strength corresponding to 10
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The high cycle fatigue property of carburized 20Cr gear steel was experimentally investigated under axial loading with a stress ratio of zero. The test results show that this steel exhibits gradually decreasing S-N characteristics, and the fatigue strength corresponding to 109 cycles is about 455 MPa. Based on the observation of fracture surfaces, the interior inclusion fisheye-induced fracture is the predominant fracture mode in the life regime beyond 105 cycles. The fine granular area (FGA) cannot be found clearly around the inclusion. Based on the evaluation of stress intensity factor ranges (ΔK) at the front of inclusion and fisheye, the interior crack growth rate (da/dN) equation can be characterized by da/dN = 2.39 × 10−21K)12.32. Corresponding to the tested specimen, the predicted maximum inclusion size is about 52.02 μm. The predicted fatigue strength corresponding to 109 cycles by using Wang’s model is slightly higher than the experimental result, but that by using Murakami’s model is relatively conservative. Full article
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Open AccessArticle Phase Equilibrium and Austenite Decomposition in Advanced High-Strength Medium-Mn Bainitic Steels
Metals 2016, 6(10), 248; doi:10.3390/met6100248
Received: 15 September 2016 / Revised: 11 October 2016 / Accepted: 14 October 2016 / Published: 20 October 2016
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Abstract
The work addresses the phase equilibrium analysis and austenite decomposition of two Nb-microalloyed medium-Mn steels containing 3% and 5% Mn. The pseudobinary Fe-C diagrams of the steels were calculated using Thermo-Calc. Thermodynamic calculations of the volume fraction evolution of microstructural constituents vs. temperature
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The work addresses the phase equilibrium analysis and austenite decomposition of two Nb-microalloyed medium-Mn steels containing 3% and 5% Mn. The pseudobinary Fe-C diagrams of the steels were calculated using Thermo-Calc. Thermodynamic calculations of the volume fraction evolution of microstructural constituents vs. temperature were carried out. The study comprised the determination of the time-temperature-transformation (TTT) diagrams and continuous cooling transformation (CCT) diagrams of the investigated steels. The diagrams were used to determine continuous and isothermal cooling paths suitable for production of bainite-based steels. It was found that the various Mn content strongly influences the hardenability of the steels and hence the austenite decomposition during cooling. The knowledge of CCT diagrams and the analysis of experimental dilatometric curves enabled to produce bainite-austenite mixtures in the thermomechanical simulator. Light microscopy (LM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used to assess the effect of heat treatment on morphological details of produced multiphase microstructures. Full article
(This article belongs to the Special Issue Bainite and Martensite: Developments and Challenges)
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Open AccessFeature PaperArticle Microstructure and Mechanical Properties of Dissimilar Friction Stir Welding between Ultrafine Grained 1050 and 6061-T6 Aluminum Alloys
Metals 2016, 6(10), 249; doi:10.3390/met6100249
Received: 25 August 2016 / Revised: 12 October 2016 / Accepted: 15 October 2016 / Published: 21 October 2016
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Abstract
The ultrafine grained (UFGed) 1050 Al plates with a thickness of 2 mm, which were produced by the accumulative roll bonding technique after five cycles, were friction stir butt welded to 2 mm thick 6061-T6 Al alloy plates at a different revolutionary pitch
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The ultrafine grained (UFGed) 1050 Al plates with a thickness of 2 mm, which were produced by the accumulative roll bonding technique after five cycles, were friction stir butt welded to 2 mm thick 6061-T6 Al alloy plates at a different revolutionary pitch that varied from 0.5 to 1.25 mm/rev. In the stir zone, the initial nano-sized lamellar structure of the UFGed 1050 Al alloy plate transformed into an equiaxial grain structure with a larger average grain size due to the dynamic recrystallization and subsequent grain growth. However, an equiaxial grain structure with a much smaller grain size was simultaneously formed in the 6061 Al alloy plates, together with coarsening of the precipitates. Tensile tests of the welds obtained at different welding speeds revealed that two kinds of fracture modes occurred for the specimens depending on their revolutionary pitches. The maximum tensile strength was about 110 MPa and the fractures were all located in the stir zone close to the 1050 Al side. Full article
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Open AccessCommunication Effect of Mg17Al12 Fraction on Mechanical Properties of Mg-9%Al-1%Zn Cast Alloy
Metals 2016, 6(10), 251; doi:10.3390/met6100251
Received: 4 September 2016 / Revised: 4 October 2016 / Accepted: 18 October 2016 / Published: 24 October 2016
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Abstract
In the current study it was observed that the offset yield point of Mg-9%Al-1%Zn alloy was strongly influenced by the connectivity of Mg17Al12. It was suggested that an increase in the fraction of Mg17Al12 from 8%
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In the current study it was observed that the offset yield point of Mg-9%Al-1%Zn alloy was strongly influenced by the connectivity of Mg17Al12. It was suggested that an increase in the fraction of Mg17Al12 from 8% to 11% could lead to the formation of a Mg17Al12 network which resulted in a higher offset yield point. In addition, it was observed that elongation to failure of the Mg-9%Al-1%Zn alloy strongly depended on the fraction of Mg17Al12. Moreover, the apparent toughness showed a strong inverse relation to the secondary dendrite arm spacing. This approach might be extended to forecast the behavior in other magnesium alloys forming a network of the Mg-Al phase. Full article
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Open AccessFeature PaperArticle Microstructure and Mechanical Properties of Friction Stir Welded Dissimilar Titanium Alloys: TIMET-54M and ATI-425
Metals 2016, 6(10), 252; doi:10.3390/met6100252
Received: 14 September 2016 / Revised: 10 October 2016 / Accepted: 17 October 2016 / Published: 24 October 2016
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Abstract
Weight reduction in automobiles and in aerospace industries can profoundly register for the behemoth change in the consumption of the fossil fuels and, in turn, CO2 emission. With a promising hope in hindsight for weight reduction, we have successfully produced butt joints
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Weight reduction in automobiles and in aerospace industries can profoundly register for the behemoth change in the consumption of the fossil fuels and, in turn, CO2 emission. With a promising hope in hindsight for weight reduction, we have successfully produced butt joints of friction stir welded (FSWed) dissimilar, and rather novice, α-β titanium alloys—ATI-425 and TIMET-54M. The study presented in this article encompasses the microstructural and mechanical properties of the joints for two cases, (1) ATI-425 on the advancing side; and (2) TIMET-54M on the advancing side. The evolution of microstructure and concomitant mechanical properties are characterized by optical microscopy, microhardness, and tensile properties. A detailed description of the microstructural evolution and its correlation with the mechanical properties have been presented in this study. Our investigations suggest that mixing patterns are dependent on the location (advancing, or retreating) of the alloying sheet. However, the microstructure in the weld nugget (WN) is quite similar (grain boundary α, and basket weave morphology consisting of α + β lamellae) in both cases with traces of untransformed β. The thermo-mechanically affected zone (TMAZ) on the either side of the weld is primarily affected by the microstructure of the base material (BM). A noticeable increase in the hardness values in the WN is accompanied by significant deflection on the advancing and retreating sides. The tensile properties extracted from the global stress strain curves are comparable with minimal difference for both cases. In both cases, the fracture occurred on the retreating side of the weld. Full article
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Open AccessFeature PaperArticle Tribocorrosion Study of Ordinary and Laser-Melted Ti6Al4V Alloy
Metals 2016, 6(10), 253; doi:10.3390/met6100253
Received: 7 August 2016 / Revised: 13 October 2016 / Accepted: 18 October 2016 / Published: 24 October 2016
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Abstract
Titanium alloys are used in biomedical implants, as well as in other applications, due to the excellent combination of corrosion resistance and mechanical properties. However, the tribocorrosion resistance of titanium alloy is normally not satisfactory. Therefore, surface modification is a way to improve
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Titanium alloys are used in biomedical implants, as well as in other applications, due to the excellent combination of corrosion resistance and mechanical properties. However, the tribocorrosion resistance of titanium alloy is normally not satisfactory. Therefore, surface modification is a way to improve this specific performance. In the present paper, laser surface-modified samples were tested in corrosion and pin-on-disk tribocorrosion testing in 0.90% NaCl under an average Hertzian pressure of 410 MPa against an alumina sphere. Laser-modified samples of Ti6Al4V were compared with ordinary Ti6Al4V alloy. Electrochemical impedance showed higher modulus for laser-treated samples than for ordinary Ti6Al4V ones. Moreover, atomic force microscopy revealed that laser-treated surfaces presented less wear than ordinary alloy for the initial exposure. For a further exposure to wear, i.e., when the wear depth is beyond the initial laser-affected layer, both materials showed similar corrosion behavior. Microstructure analysis and finite element method simulations revealed that the different behavior between the initial and the extensive rubbing was related to a fine martensite-rich external layer developed on the irradiated surface of the fusion zone. Full article
(This article belongs to the Special Issue Intermetallics 2016)
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Review

Jump to: Research

Open AccessReview An Evaluation of Mechanical Properties with the Hardness of Building Steel Structural Members for Reuse by NDT
Metals 2016, 6(10), 247; doi:10.3390/met6100247
Received: 9 June 2016 / Revised: 12 October 2016 / Accepted: 13 October 2016 / Published: 19 October 2016
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Abstract
The reuse system proposed by the authors is one method to reduce the environmental burden in the structural field. As for reusable members, we take up building steel structures used for plants and warehouses. These buildings are assumed to be demolished within approximately
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The reuse system proposed by the authors is one method to reduce the environmental burden in the structural field. As for reusable members, we take up building steel structures used for plants and warehouses. These buildings are assumed to be demolished within approximately 30 years or more for physical, architectural, economic, or social reasons in Japan. In this paper, the performance of steel structural members of a gable frame is evaluated with a non-destructive test for reuse. First, the flow to estimate mechanical properties of steel structural members such as tensile strength, yield strength, and elongation is shown via a non-destructive test. Next, tensile strength, yield strength, and elongation of steel structural members are estimated, with hardness measured with a portable ultrasonic hardness tester. Finally, the mechanical properties of steel structural members for reuse are estimated based on the proposed flow. Full article
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Open AccessReview Physical Properties of the NbC Carbide
Metals 2016, 6(10), 250; doi:10.3390/met6100250
Received: 10 June 2016 / Revised: 16 September 2016 / Accepted: 27 September 2016 / Published: 21 October 2016
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Abstract
Transition metal carbides are interesting materials with a singular combination of properties, such as high melting points, high hardness, good transport properties and relatively low costs, which makes them excellent candidates for several technological applications. The possible applications of NbC carbide remained unexplored
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Transition metal carbides are interesting materials with a singular combination of properties, such as high melting points, high hardness, good transport properties and relatively low costs, which makes them excellent candidates for several technological applications. The possible applications of NbC carbide remained unexplored as it was in the past expensive and available in limited volumes. In order to guide investigations of the applicability of NbC, a deeper understanding of the physical properties of this carbide is fundamental. In this review paper, key physical properties of NbC are compiled with emphasis on its chemical bonding, a careful description of the C-Nb phase diagram, the phases formed and the crystal structures. Thermal properties are discussed and correlated with the intrinsic and extrinsic features of NbC. Finally, elastic properties are discussed. Full article
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