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Metals, Volume 7, Issue 3 (March 2017)

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Cover Story Heavy-section castings of ferritic ductile cast iron suffer from microstructural modifications [...] Read more.
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Open AccessArticle Investigation on Friction and Wear of Cold Rolled High Strength Steel against an AISI52100 Counterpart
Metals 2017, 7(3), 90; doi:10.3390/met7030090
Received: 2 February 2017 / Revised: 25 February 2017 / Accepted: 6 March 2017 / Published: 10 March 2017
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Abstract
This article investigates the friction and wear of cold rolled high strength steel at various displacement amplitudes. Reciprocal sliding tests are carried out using a ball-on-flat testing apparatus. The tangential force occurring at the contact surface between a high strength steel specimen and
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This article investigates the friction and wear of cold rolled high strength steel at various displacement amplitudes. Reciprocal sliding tests are carried out using a ball-on-flat testing apparatus. The tangential force occurring at the contact surface between a high strength steel specimen and an AISI52100 ball is measured during the tests. After each test, the worn surface profile on the steel specimen is determined. Experimental results show that the ratio of the maximum tangential to the normal force remains at 0.7 after an initial rapid increase, and the ratio does not greatly change according to the imposed displacement amplitudes (in the range of 0.05 mm and 0.3 mm). The wear volume loss on the steel specimen increases according to the number of cycles. It is determined that the wear rate of the specimen changes with respect to the imposed displacement amplitude. That is, the wear rate rapidly increases within the displacement amplitude range of 0.05 mm to 0.09 mm, while the wear rate gradually increases when the displacement amplitude is greater than 0.2 mm. The obtained results provide the friction and wear behaviors of cold rolled high strength steel in fretting and reciprocal sliding regimes. Full article
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Open AccessArticle Precipitation Behavior of Carbides in H13 Hot Work Die Steel and Its Strengthening during Tempering
Metals 2017, 7(3), 70; doi:10.3390/met7030070
Received: 6 December 2016 / Revised: 3 February 2017 / Accepted: 18 February 2017 / Published: 23 February 2017
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Abstract
The properties of carbides, such as morphology, size, and type, in H13 hot work die steel were studied with optical microscopy, transmission electron microscopy, electron diffraction, and energy dispersive X-ray analysis; their size distribution and quantity after tempering, at different positions within the
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The properties of carbides, such as morphology, size, and type, in H13 hot work die steel were studied with optical microscopy, transmission electron microscopy, electron diffraction, and energy dispersive X-ray analysis; their size distribution and quantity after tempering, at different positions within the ingot, were analyzed using Image-Pro Plus software. Thermodynamic calculations were also performed for these carbides. The microstructures near the ingot surface were homogeneous and had slender martensite laths. Two kinds of carbide precipitates have been detected in H13: (1) MC and M6C, generally smaller than 200 nm; and (2) M23C6, usually larger than 200 nm. MC and M6C play the key role in precipitation hardening. These are the most frequent carbides precipitating at the halfway point from the center of the ingot, and the least frequent at the surface. From the center of the ingot to its surface, the size and volume fraction of the carbides decrease, and the toughness improves, while the contribution of the carbides to the yield strength increases. Full article
(This article belongs to the Special Issue Alloy Steels)
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Open AccessArticle Investigation of the Geometry of Metal Tube Walls after Necking in Uniaxial Tension
Metals 2017, 7(3), 100; doi:10.3390/met7030100
Received: 10 February 2017 / Revised: 5 March 2017 / Accepted: 14 March 2017 / Published: 17 March 2017
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Abstract
Abstract: In order to characterize the deformation and true stress–strain relation of metal tubes, the geometry of tube walls after necking in uniaxial tension need to be determined. The paper investigated the necking process of metal tube. A large number of tensile tests
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Abstract: In order to characterize the deformation and true stress–strain relation of metal tubes, the geometry of tube walls after necking in uniaxial tension need to be determined. The paper investigated the necking process of metal tube. A large number of tensile tests and finite element analysis of 1Cr18Ni9Ti tubes with different sizes were conducted. It was found that the geometry of outer tube wall in the necking region can be described using a logistic regression model. The final geometry of the tube is determined by original tube diameter and wall thickness. The offset of tube walls are affected by two competing factors: volume constancy and necking. The offset distances of outer and inner walls are mainly affected by original wall thickness. The length of the necking zone is more influenced by original tube diameter. Tube elongation at fracture increases slightly as tube diameter gets larger, while the wall thickness has almost no impact on the elongation.
Full article
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Open AccessArticle Primary Stability of Temporary Screws after Dentary and Orthopedic Forces under Static and Dynamic Load Cycles
Metals 2017, 7(3), 80; doi:10.3390/met7030080
Received: 28 December 2016 / Accepted: 16 February 2017 / Published: 3 March 2017
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Abstract
The objective was to analyze the influence of dentary and orthopedic forces under static and dynamic loads in temporary screw stability. Self-drilling titanium (Ti6Al4V) screws (6 × 1.5 mm) were inserted and removed from pig ribs. Screws were loaded by static loads of
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The objective was to analyze the influence of dentary and orthopedic forces under static and dynamic loads in temporary screw stability. Self-drilling titanium (Ti6Al4V) screws (6 × 1.5 mm) were inserted and removed from pig ribs. Screws were loaded by static loads of 2 N and 5 N for 5 weeks. Dynamic force was applied during 56,000 cycles for simulations of a patient’s opening–closing mouth movements. Dynamic applied loads ranged from 2 to 5 N and from 5 to 7 N under a frequency of 1 Hz. Torque peak values at placement and removal were measured before and after static and dynamic cycles. Similarities in torque peaks (p = 0.3139) were identified at placement (12.54 Ncm) and removal (11.2 Ncm) of screws after a static load of 2 N. Statistical comparisons showed significant stability loss after dynamic cycles under loads of 2 N (64.82% at p = 0.0005) and 5 N (64.63% at p = 0.0026). Limited stability loss occurred in temporary screws submitted to 2 N static forces (p = 0.3139). The detrimental effects of dynamic cycles in temporary screws stability was attested after the simulation of dentary and skeletal forces, being intermittent forces more relevant in the loss of mechanical stability. Full article
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Open AccessArticle The Effect of Nb/Ti Ratio on Hardness in High-Strength Ni-Based Superalloys
Metals 2017, 7(3), 71; doi:10.3390/met7030071
Received: 12 January 2017 / Accepted: 20 February 2017 / Published: 23 February 2017
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Abstract
The age-hardening behaviour and microstructure development of high strength Ni-based superalloys ABD-D2, D4, and D6 with varying Nb/Ti ratios have been studied. The studied alloys have large volume fractions and multimodal size distributions of the γ′ precipitates, making them sensitive to cooling conditions
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The age-hardening behaviour and microstructure development of high strength Ni-based superalloys ABD-D2, D4, and D6 with varying Nb/Ti ratios have been studied. The studied alloys have large volume fractions and multimodal size distributions of the γ′ precipitates, making them sensitive to cooling conditions following solution heat treatment. Differential scanning calorimetry was conducted with a thermal cycle that replicated a processing heat treatment. The hardness of these alloys was subsequently evaluated by nanoindentation. The Nb/Ti ratio was not observed to influence the size and distribution of primary and secondary γ′ precipitates; however, the difference in those of tertiary γ′ and precipitate morphology were observed. The nanoindentation hardness for all alloys reduces once they have been solution-heat-treated. The alloys exhibited specific peak hardness. The alloy with the greatest Nb content was found to have the best increase in hardness among the alloys studied due to its large tertiary γ′ precipitate. Full article
(This article belongs to the Special Issue Ni- and Co-Based Superalloys and Their Coatings)
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Open AccessArticle Effect of Sintering Time on the Densification, Microstructure, Weight Loss and Tensile Properties of a Powder Metallurgical Fe-Mn-Si Alloy
Metals 2017, 7(3), 81; doi:10.3390/met7030081
Received: 18 December 2016 / Revised: 20 February 2017 / Accepted: 28 February 2017 / Published: 3 March 2017
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Abstract
This work investigated the isothermal holding time dependence of the densification, microstructure, weight loss, and tensile properties of Fe-Mn-Si powder compacts. Elemental Fe, Mn, and Si powder mixtures with a nominal composition of Fe-28Mn-3Si (in weight percent) were ball milled for 5 h
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This work investigated the isothermal holding time dependence of the densification, microstructure, weight loss, and tensile properties of Fe-Mn-Si powder compacts. Elemental Fe, Mn, and Si powder mixtures with a nominal composition of Fe-28Mn-3Si (in weight percent) were ball milled for 5 h and subsequently pressed under a uniaxial pressure of 400 MPa. The compacted Fe-Mn-Si powder mixtures were sintered at 1200 °C for 0, 1, 2, and 3 h, respectively. In general, the density, weight loss, and tensile properties increased with the increase of the isothermal holding time. A significant increase in density, weight loss, and tensile properties occurred in the compacts being isothermally held for 1 h, as compared to those with no isothermal holding. However, further extension of the isothermal holding time (2 and 3 h) only played a limited role in promoting the sintered density and tensile properties. The weight loss of the sintered compacts was mainly caused by the sublimation of Mn in the Mn depletion region on the surface layer of the sintered Fe-Mn-Si compacts. The length of the Mn depletion region increased with the isothermal holding time. A single α-Fe phase was detected on the surface of all of the sintered compacts, and the locations beyond the Mn depletion region were comprised of a dual dominant γ-austenite and minor ε-martensite. Full article
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Open AccessArticle Comparison of Single Ti6Al4V Struts Made Using Selective Laser Melting and Electron Beam Melting Subject to Part Orientation
Metals 2017, 7(3), 91; doi:10.3390/met7030091
Received: 1 December 2016 / Revised: 8 March 2017 / Accepted: 9 March 2017 / Published: 11 March 2017
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Abstract
The use of additive manufacturing technologies to produce lightweight or functional structures is widespread. Especially Ti6Al4V plays an important role in this development field and parts are manufactured and analyzed with the aim to characterize the mechanical properties of
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The use of additive manufacturing technologies to produce lightweight or functional structures is widespread. Especially Ti6Al4V plays an important role in this development field and parts are manufactured and analyzed with the aim to characterize the mechanical properties of open-porous structures and to generate scaffolds with properties specific to their intended application. An SLM and an EBM process were used respectively to fabricate the Ti6Al4V single struts. For mechanical characterization, uniaxial compression tests and hardness measurements were conducted. Furthermore, the struts were manufactured in different orientations for the determination of the mechanical properties. Roughness measurements and a microscopic characterization of the struts were also carried out. Some parts were characterized following heat treatment (hot isostatic pressing). A functional correlation was found between the compressive strength and the slenderness ratio (λ) as well as the equivalent diameter (d) and the height (L) of EBM and SLM parts. Hardness investigations revealed considerable differences related to the microstructure. An influence of heat treatment as well as of orientation could be determined. In this work, we demonstrate the influence of the fabrication quality of single struts, the roughness and the microstructure on mechanical properties as a function of orientation. Full article
(This article belongs to the Special Issue 3D Printing of Metals)
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Open AccessArticle Evolution of Anode Porosity under Air Oxidation: The Unveiling of the Active Pore Size
Metals 2017, 7(3), 101; doi:10.3390/met7030101
Received: 18 January 2017 / Revised: 14 March 2017 / Accepted: 15 March 2017 / Published: 18 March 2017
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Abstract
The carbon anode, used in aluminum electrolysis (Hall–Héroult process), is over-consumed by air oxidation and carboxy-reaction (with CO2). Several anode features may affect this over-consumption, such as impurity content, graphitization level and anode porosity features (e.g., porosity volume fraction or pore
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The carbon anode, used in aluminum electrolysis (Hall–Héroult process), is over-consumed by air oxidation and carboxy-reaction (with CO2). Several anode features may affect this over-consumption, such as impurity content, graphitization level and anode porosity features (e.g., porosity volume fraction or pore size distribution). The two first parameters are basically related to the quality of raw materials and coke calcination conditions. Anode porosity is, however, greatly affected by anode manufacturing conditions, and is possible to be modified, to some extent, by adjusting the anode recipe and the processing parameters. This work aims to investigate the effect of anode porosity on its air reactivity. Baked anode samples were prepared in laboratory scale and then crushed into powder form (−4760 + 4000 µm). The recipe for anode preparation was similar to a typical industrial recipe, except that in the lab scale no butt particles were used in the recipe. Anode particles were then gasified at six different conversion levels (0, 5, 15, 25, 35 and 50 wt %) under air at 525 °C. The porosity was characterized in several pore size ranges, measured by nitrogen adsorption and mercury intrusion (0.0014–0.020, 0.002–0.025, 0.025–0.100, 0.1–40.0 and superior at 40 µm). The volume variation of each pore range, as a function of carbon conversion, was assessed and used to determine the size of the most active pores for air oxidation. The most active pore size was found to be the pores inferior at 40 µm before 15 wt % of gasification and pores superior at 40 µm between 15 and 50 wt % of carbon conversion. Limitation of pore size range could be used as an additional guideline, along with other targets such as high homogeneity and density, to set the optimum anode manufacturing parameters. Full article
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Open AccessArticle Synthesis and Characterization of Copper-Based Composites Reinforced by CuZrAlNiTi Amorphous Particles with Enhanced Mechanical Properties
Metals 2017, 7(3), 92; doi:10.3390/met7030092
Received: 9 February 2017 / Revised: 28 February 2017 / Accepted: 8 March 2017 / Published: 11 March 2017
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Abstract
Novel amorphous/crystalline composites were developed combining the ductile copper matrix with hard CuZr-based amorphous powder. The amorphous powders of two compositions, Cu39.2Zr36All4.8Ni10Ti10 and Cu39.2Zr35.2Al5.6Ni10Ti10,
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Novel amorphous/crystalline composites were developed combining the ductile copper matrix with hard CuZr-based amorphous powder. The amorphous powders of two compositions, Cu39.2Zr36All4.8Ni10Ti10 and Cu39.2Zr35.2Al5.6Ni10Ti10, produced by ball milling were used for reinforcement of the composites. Different mixing techniques, magnetic mixing, ultrasonic mixing and high-energy ball milling, were applied in order to create a homogenous mixture of the powders. The composites were produced by hot pressing under a purified argon atmosphere. Their microstructure, homogeneity and mechanical properties were investigated. It was observed that before hot pressing, minimal porosity had been obtained for the composite blended for 15 min by the ball-mill with a ball-to-powder ratio of 80:1. Its copper content was 50 wt %, which is the minimum to produce a compact composite. Reinforcing the copper by amorphous powders, the maximal compressive strength was enhanced to 490 MPa and 470 MPa, respectively, for the abovementioned composites. The yield strength of the copper due to reinforcement increased drastically from 150 MPa to 400 MPa and 420 MPa. Full article
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Open AccessArticle Assessment of the Residual Life of Steam Pipeline Material beyond the Computational Working Time
Metals 2017, 7(3), 82; doi:10.3390/met7030082
Received: 19 December 2016 / Revised: 23 February 2017 / Accepted: 28 February 2017 / Published: 6 March 2017
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Abstract
This paper presents the evaluation of durability for the material of repair welded joints made from (13HMF) 14MoV6-3 steel after long-term service, and from material in the as-received condition and after long-term service. Microstructure examinations using a scanning electron microscope, hardness measurements and
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This paper presents the evaluation of durability for the material of repair welded joints made from (13HMF) 14MoV6-3 steel after long-term service, and from material in the as-received condition and after long-term service. Microstructure examinations using a scanning electron microscope, hardness measurements and creep tests of the basic material and welded joints of these steels were carried out. These tests enabled the time of further safe service of the examined repair welded joints to be determined in relation to the residual life of the materials. The evaluation of residual life and disposable life, and thus the estimation and determination of the time of safe service, is of great importance for the operation of components beyond the design service life. The obtained test results are part of the materials’ characteristics developed by the Institute for Ferrous Metallurgy for steels and welded joints made from these steels to work under creep conditions. Full article
(This article belongs to the Special Issue Alloy Steels)
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Open AccessArticle Effects of Gas Nitriding Temperature on the Surface Properties of a High Manganese TWIP Steel
Metals 2017, 7(3), 102; doi:10.3390/met7030102
Received: 18 February 2017 / Revised: 9 March 2017 / Accepted: 17 March 2017 / Published: 21 March 2017
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Abstract
The effects of gas nitriding temperature on the cross section morphology, element nitrogen distribution, and surface layer compositions of a cold rolled and pre-strained high manganese austenitic TWIP steel 25Mn-3Cr-3Al-0.3C-0.01N and the corresponding anti-corrosion ability have been studied. The results show that, depending
[...] Read more.
The effects of gas nitriding temperature on the cross section morphology, element nitrogen distribution, and surface layer compositions of a cold rolled and pre-strained high manganese austenitic TWIP steel 25Mn-3Cr-3Al-0.3C-0.01N and the corresponding anti-corrosion ability have been studied. The results show that, depending on nitriding temperature, the distribution of element nitrogen and main phase compositions are significantly different in the nitriding layers. At a temperature lower than 500 °C, the main composition in the modified layer is S-phase and the nitrogen concentration linearly decreases from the surface to the center, while Fe4N forms with S-phase and a step-like distribution of nitrogen content is present at nitriding temperature of 600 °C. Caused by the increasing of modified layer thickness and the formation of S-phase and Fe4N, the surface hardness was obviously enhanced. Anodic polarization curves in 3.5 wt. % NaCl solution indicate that the nitrided processes have a tremendous modification effect on anti-corrosion ability. Moreover, the increase of (111) oriented grain, caused by the elevated nitriding temperature, has a positive effect on the corrosion resistance. Full article
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Open AccessArticle Effects of EMS Induced Flow on Solidification and Solute Transport in Bloom Mold
Metals 2017, 7(3), 72; doi:10.3390/met7030072
Received: 13 December 2016 / Revised: 11 February 2017 / Accepted: 17 February 2017 / Published: 24 February 2017
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Abstract
The flow, temperature, solidification, and solute concentration field in a continuous casting bloom mold were solved simultaneously by a multiphysics numerical model by considering the effect of in-mold electromagnetic stirring (M-EMS). The mold metallurgical differences between cases with and without EMS are discussed
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The flow, temperature, solidification, and solute concentration field in a continuous casting bloom mold were solved simultaneously by a multiphysics numerical model by considering the effect of in-mold electromagnetic stirring (M-EMS). The mold metallurgical differences between cases with and without EMS are discussed first, and then the solute transport model verified. Moreover, the effects of EMS current intensity on the metallurgical behavior in the bloom mold were also investigated. The simulated solute distributions were basically consistent with the test results. The simulations showed that M-EMS can apparently homogenize the initial solidified shell, liquid steel temperature, and solute element in the EMS effective zone. Meanwhile, the impingement effect of jet flow and molten steel superheat can be reduced, and the degree of negative segregation in the solidified shell at the mold corner alleviated from 0.74 to 0.78. However, the level fluctuation and segregation degree in the shell around the center of the wide and narrow sides were aggravated from 4.5 mm to 6.2 mm and from 0.84 to 0.738, respectively. With the rise of current intensity the bloom surface temperature, level fluctuation, stirring intensity, uniformity of molten steel temperature, and solute distribution also increased, while the growth velocity of the solidifying shell in the EMS effective zone declined and the solute mass fraction at the center of the computational outlet (z = 1.5 m) decreased. M-EMS with a current intensity of 600 A is more suitable for big bloom castings. Full article
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Open AccessArticle Vitrification and Crystallization of Phase-Separated Metallic Liquid
Metals 2017, 7(3), 73; doi:10.3390/met7030073
Received: 5 October 2016 / Revised: 5 February 2017 / Accepted: 17 February 2017 / Published: 24 February 2017
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Abstract
The liquid–liquid phase separation (LLPS) behavior of Fe50Cu50 melt from 3500 K to 300 K with different rapid quenching is investigated by molecular dynamics (MD) simulation based on the embedded atom method (EAM). The liquid undergoes metastable phase separation by
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The liquid–liquid phase separation (LLPS) behavior of Fe50Cu50 melt from 3500 K to 300 K with different rapid quenching is investigated by molecular dynamics (MD) simulation based on the embedded atom method (EAM). The liquid undergoes metastable phase separation by spinodal decomposition in the undercooled regime and subsequently solidifies into three different Fe-rich microstructures: the interconnected-type structure is kept in the glass and crystal at a higher cooling rate, while the Fe-rich droplets are found to crystalize at a lower cooling rate. During the crystallization process, only Fe-rich clusters can act as the solid nuclei. The twinning planes can be observed in the crystal and only the homogeneous atomic stacking shows mirror symmetry along the twinning boundary. Our present work provides atomic-scale understanding of LLPS melt during the cooling process. Full article
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Open AccessArticle Experimental and Numerical Simulation Investigation on Laser Flexible Shock Micro-Bulging
Metals 2017, 7(3), 93; doi:10.3390/met7030093
Received: 13 February 2017 / Revised: 6 March 2017 / Accepted: 10 March 2017 / Published: 12 March 2017
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Abstract
Laser flexible shock micro-bulging (LFSB) is a novel micro fabrication technology, which combines laser dynamic forming and flexible die forming, which is a type of high strain rate micro-forming. The LFSB of 304 stainless steel foils was investigated in this paper. Experimental and
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Laser flexible shock micro-bulging (LFSB) is a novel micro fabrication technology, which combines laser dynamic forming and flexible die forming, which is a type of high strain rate micro-forming. The LFSB of 304 stainless steel foils was investigated in this paper. Experimental and simulated results indicated that the bulging depth and thickness thinning rate of bulging parts increased with an increase of laser energy and a decrease of workpiece thickness. Experimental results also showed the surface morphology of bulging parts. The hardness distribution in the cross section of bulging parts was revealed by nanoindentation experiments. The internal microstructure of micro bulging parts was observed by TEM. In addition, the equivalent stress and plastic strain distribution of bulging parts were shown in the numerical simulation under different workpiece thicknesses and laser energies. Full article
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Open AccessArticle Finite Element Based Physical Chemical Modeling of Corrosion in Magnesium Alloys
Metals 2017, 7(3), 83; doi:10.3390/met7030083
Received: 18 January 2017 / Revised: 25 February 2017 / Accepted: 28 February 2017 / Published: 7 March 2017
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Abstract
Magnesium alloys have found widespread applications in diverse fields such as aerospace, automotive, bio-medical and electronics industries due to its relatively high strength-to-weight ratio. However, stress corrosion cracking of these alloys severely restricts their applications in several novel technologies. Hence, it will be
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Magnesium alloys have found widespread applications in diverse fields such as aerospace, automotive, bio-medical and electronics industries due to its relatively high strength-to-weight ratio. However, stress corrosion cracking of these alloys severely restricts their applications in several novel technologies. Hence, it will be useful to identify the corrosion mechanics of magnesium alloys under external stresses as it can provide further insights on design of these alloys for critical applications. In the present study, the corrosion mechanics of a commonly used magnesium alloy, AZ31, is studied using finite element simulation with a modified constitutive material damage model. The data obtained from the finite element modeling were further used to formulate a mathematical model using computational intelligence algorithm. Sensitivity and parametric analysis of the derived model further corroborated the mechanical response of the alloy in line with the corrosion physics. The proposed approach is anticipated to be useful for materials engineers for optimizing the design criteria for magnesium alloys catered for high temperature applications. Full article
(This article belongs to the Special Issue Corrosion of Magnesium Alloys)
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Open AccessArticle Very High Cycle Fatigue of Butt-Welded High-Strength Steel Plate
Metals 2017, 7(3), 103; doi:10.3390/met7030103
Received: 2 January 2017 / Revised: 2 March 2017 / Accepted: 6 March 2017 / Published: 21 March 2017
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Abstract
Welded parts fabricated from high-strength steel (HSS) require an almost infinite lifetime, i.e., a gigacycle (109). Therefore, it is necessary to test its high-cycle fatigue behavior. In this paper, an accelerated fatigue test method using ultrasonic resonance is proposed. This method
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Welded parts fabricated from high-strength steel (HSS) require an almost infinite lifetime, i.e., a gigacycle (109). Therefore, it is necessary to test its high-cycle fatigue behavior. In this paper, an accelerated fatigue test method using ultrasonic resonance is proposed. This method reduces the experimental time required in comparison with a conventional fatigue test setup. The operating principle of the accelerated ultrasonic fatigue test involved the use of a 20-kHz resonant frequency. Therefore, it was necessary to design a specimen specifically for the test setup. In the study, ultrasonic fatigue testing equipment was used to test butt-welded 590- and 780-MPa ferrite–bainite steel plates. In order to design the specimen, a dynamic Young’s modulus was measured using piezoelectric element, a laser Doppler vibrometer, and a digital signal analyzer. The S–N curves of fatigue behavior of the original and butt-welded specimens were compared. The fatigue test results showed that the infinite (i.e., gigacycle) fatigue strengths of the welded specimens were approximately 8% less than those of the original specimen.
Full article
(This article belongs to the Special Issue Fatigue Damage)
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Open AccessArticle Improved Compressive, Damping and Coefficient of Thermal Expansion Response of Mg–3Al–2.5La Alloy Using Y2O3 Nano Reinforcement
Metals 2017, 7(3), 104; doi:10.3390/met7030104
Received: 6 March 2017 / Revised: 9 March 2017 / Accepted: 14 March 2017 / Published: 21 March 2017
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Abstract
In the present study, the effects of the addition of Y2O3 nanoparticles on Mg–3Al–2.5La alloy were investigated. Materials were synthesized using a disintegrated melt deposition technique followed by hot extrusion. The samples were then characterized for microstructure, compression properties, damping
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In the present study, the effects of the addition of Y2O3 nanoparticles on Mg–3Al–2.5La alloy were investigated. Materials were synthesized using a disintegrated melt deposition technique followed by hot extrusion. The samples were then characterized for microstructure, compression properties, damping properties, CTE (coefficient of thermal expansion) and fracture morphology. The grain size of Mg–3Al–2.5La was significantly reduced by the addition of the Y2O3 nano-sized reinforcement (~3.6 μm, 43% of Mg–3Al–2.5La grain size). SEM and X-ray studies revealed that the size of uniformly distributed intermetallic phases, Al 11 La 3 , Al 2 La , and Al 2.12 La 0.88 reduced by the addition of Y2O3 to Mg–3Al–2.5La alloy. The coefficient of thermal expansion (CTE) was slightly improved by the addition of nanoparticles. The results of the damping measurement revealed that the damping capacity of the Mg–3Al–2.5La alloy increased due to the presence of Y2O3. The compression results showed that the addition of Y2O3 to Mg–3Al–2.5La improved the compressive yield strength (from ~141 MPa to ~156 MPa) and the ultimate compressive strength (from ~456 MPa to ~520 MPa), which are superior than those of the Mg–3Al alloy (Compressive Yield Strength, CYS ~154 MPa and Ultimate Compressive Strength, UCS ~481 MPa). The results further revealed that there is no significant effect on the fracture strain value of Mg–3Al–2.5La due to the addition of Y2O3. Full article
(This article belongs to the Special Issue Metal Matrix Composites)
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Open AccessArticle The Effect of Varying Mixing Temperatures and Baking Level on the Quality of Pilot Scale Anodes—A Factorial Design Analysis
Metals 2017, 7(3), 74; doi:10.3390/met7030074
Received: 20 December 2016 / Revised: 7 February 2017 / Accepted: 13 February 2017 / Published: 25 February 2017
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Abstract
Identifying optimum anode baking level and mixing temperature are important when producing high quality anodes. The effect of varying mixing temperature and baking level were investigated in terms of the resulting apparent anode density, specific electrical resistivity (SER), air permeability, coefficient of thermal
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Identifying optimum anode baking level and mixing temperature are important when producing high quality anodes. The effect of varying mixing temperature and baking level were investigated in terms of the resulting apparent anode density, specific electrical resistivity (SER), air permeability, coefficient of thermal expansion (CTE), air reactivity, and CO2 reactivity. Six pilot-scale anodes were prepared at Hydro Aluminium using a single source petroleum coke and <2 mm coke fractions. A coal tar pitch was used with Mettler softening point of 119.1 °C. The aggregate was mixed at 150 °C or 210 °C and baked to a low, medium, or high baking level. A 22 full-factorial design analysis was performed to determine the response of the analyzed properties to the applied mixing and baking temperature. Apparent density, SER, and air permeability were found to be highly dependent on mixing temperature. Apparent density and SER were also slightly affected by baking level. CTE was found to be independent of both baking level and mixing temperature. Air reactivity was found to be mainly dependent on baking level, while CO2 reactivity was dependent on both mixing temperature and baking level. Full article
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Open AccessArticle Effect of Heat Treatment on the Microstructure and Mechanical Properties of Nitrogen-Alloyed High-Mn Austenitic Hot Work Die Steel
Metals 2017, 7(3), 94; doi:10.3390/met7030094
Received: 27 January 2017 / Revised: 9 March 2017 / Accepted: 10 March 2017 / Published: 14 March 2017
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Abstract
In view of the requirements for mechanical properties and service life above 650 °C, a high-Mn austenitic hot work die steel, instead of traditional martensitic hot work die steel such as H13, was developed in the present study. The effect of heat treatment
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In view of the requirements for mechanical properties and service life above 650 °C, a high-Mn austenitic hot work die steel, instead of traditional martensitic hot work die steel such as H13, was developed in the present study. The effect of heat treatment on the microstructure and mechanical properties of the newly developed work die steel was studied. The results show that the microstructure of the high-Mn as-cast electroslag remelting (ESR) ingot is composed of γ-Fe, V(C,N), and Mo2C. V(C,N) is an irregular multilateral strip or slice shape with severe angles. Most eutectic Mo2C carbides are lamellar fish-skeleton-like, except for a few that are rod-shaped. With increasing solid solution time and temperature, the increased hardness caused by solid solution strengthening exceeds the effect of decreased hardness caused by grain size growth, but this trend is reversed later. As a result, the hardness of specimens after various solid solution heat treatments increases first and then decreases. The optimal combination of hardness and austenitic grain size can be obtained by soaking for 2 h at 1170 °C. The maximum Rockwell hardness (HRC) is 47.24 HRC, and the corresponding austenite average grain size is 58.4 μm. When the solid solution time is 3 h at 1230 °C, bimodality presented in the histogram of the austenite grain size as a result of further progress in secondary recrystallization. Compared with the single-stage aging, the maximum impact energy of the specimen after two-stage aging heat treatment was reached at 16.2 J and increased by 29.6%, while the hardness decreased by 1–2 HRC. After two-stage aging heat treatment, the hardness of steel reached the requirements of superior grade H13, and the maximum impact energy was 19.6% higher than that of superior grade H13, as specified in NADCA#207-2003. Full article
(This article belongs to the Special Issue Alloy Steels)
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Open AccessArticle Mechanical Properties Improvement of Laser Tailor Welded Blanks of DP600 Steel by Magnetic Treatment
Metals 2017, 7(3), 85; doi:10.3390/met7030085
Received: 6 February 2017 / Revised: 25 February 2017 / Accepted: 28 February 2017 / Published: 8 March 2017
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Abstract
The influence of magnetic treatment on the yield strength, the ultimate tensile strength and the elongation of laser tailor welded blanks (TWBs) of DP600 steel was investigated by uniaxial tensile tests. The experimental results showed that the yield strength and the ultimate tensile
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The influence of magnetic treatment on the yield strength, the ultimate tensile strength and the elongation of laser tailor welded blanks (TWBs) of DP600 steel was investigated by uniaxial tensile tests. The experimental results showed that the yield strength and the ultimate tensile strength of the TWBs had only a slight change, but the elongation increased by 13.90%–36.23% after the magnetic treatment. The dislocation distributions in the fusion zone (FZ) and the heat-affected zone (HAZ) were observed respectively by transmission electron microscopy (TEM). It was found that after magnetic treatment, the dislocations in both the FZ and the HAZ of the TWBs increased and showed a relatively uniform distribution. The mechanism of the mechanical property improvement of the TWBs by the magnetic treatment was then revealed on the basis of the relationship model between the dislocation and shear strain, considering the evolution of magnetic domains and Frank-Read dislocation multiplication in a magnetic field. Full article
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Open AccessArticle Microstructure Evolution and Biodegradation Behavior of Laser Rapid Solidified Mg–Al–Zn Alloy
Metals 2017, 7(3), 105; doi:10.3390/met7030105
Received: 2 February 2017 / Revised: 3 March 2017 / Accepted: 20 March 2017 / Published: 22 March 2017
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Abstract
The too fast degradation of magnesium (Mg) alloys is a major impediment hindering their orthopedic application, despite their superior mechanical properties and favorable biocompatibility. In this study, the degradation resistance of AZ61 (Al 6 wt. %, Zn 1 wt. %, remaining Mg) was
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The too fast degradation of magnesium (Mg) alloys is a major impediment hindering their orthopedic application, despite their superior mechanical properties and favorable biocompatibility. In this study, the degradation resistance of AZ61 (Al 6 wt. %, Zn 1 wt. %, remaining Mg) was enhanced by rapid solidification via selective laser melting (SLM). The results indicated that an increase of the laser power was beneficial for enhancing degradation resistance and microhardness due to the increase of relative density and formation of uniformed equiaxed grains. However, too high a laser power led to the increase of mass loss and decrease of microhardness due to coarsened equiaxed grains and a reduced solid solution of Al in the Mg matrix. In addition, immersion tests showed that the apatite increased with the increase of immersion time, which indicated that SLMed AZ61 possessed good bioactivity. Full article
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Open AccessArticle A Novel Methods for Fracture Toughness Evaluation of Tool Steels with Post-Tempering Cryogenic Treatment
Metals 2017, 7(3), 75; doi:10.3390/met7030075
Received: 11 January 2017 / Revised: 6 February 2017 / Accepted: 20 February 2017 / Published: 27 February 2017
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Abstract
Cryogenic treatments are usually carried out immediately after quenching, but their use can be extended to post tempering in order to improve their fracture toughness. This research paper focuses on the influence of post-tempering cryogenic treatment on the microstructure and mechanical properties of
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Cryogenic treatments are usually carried out immediately after quenching, but their use can be extended to post tempering in order to improve their fracture toughness. This research paper focuses on the influence of post-tempering cryogenic treatment on the microstructure and mechanical properties of tempered AISI M2, AISI D2, and X105CrCoMo18 steels. The aforementioned steels have been analysed after tempering and tempering + cryogenic treatment with scanning electron microscopy, X-ray diffraction for residual stress measurements, and micro- and nano-indentation to determine Young’s modulus and plasticity factor measurement. Besides the improvement of toughness, a further aim of the present work is the investigation of the pertinence of a novel technique for characterizing the fracture toughness via scratch experiments on cryogenically-treated steels. Results show that the application of post-tempering cryogenic treatment on AISI M2, AISI D2, and X105CrCoMo18 steels induce precipitation of fine and homogeneously dispersed sub-micrometric carbides which do not alter hardness and Young’s modulus values, but reduce residual stresses and increase fracture toughness. Finally, scratch test proved to be an alternative simple technique to determine the fracture toughness of cryogenically treated steels. Full article
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Open AccessArticle Magnesium–Gold Alloy Formation by Underpotential Deposition of Magnesium onto Gold from Nitrate Melts
Metals 2017, 7(3), 95; doi:10.3390/met7030095
Received: 22 November 2016 / Revised: 3 March 2017 / Accepted: 10 March 2017 / Published: 15 March 2017
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Abstract
Magnesium underpotential deposition on gold electrodes from magnesium nitrate –ammonium nitrate melts has been investigated. Linear sweep voltammetry and potential step were used as electrochemical techniques. Scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD) were used for characterization of
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Magnesium underpotential deposition on gold electrodes from magnesium nitrate –ammonium nitrate melts has been investigated. Linear sweep voltammetry and potential step were used as electrochemical techniques. Scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD) were used for characterization of obtained electrode surfaces. It was observed that reduction processes of nitrate, nitrite and traces of water (when present), in the Mg underpotential range studied, proceeded simultaneously with magnesium underpotential deposition. There was no clear evidence of Mg/Au alloy formation induced by Mg UPD from the melt made from eutectic mixture [Mg(NO3)2·6H2O + NH4NO3·XH2O]. However, EDS and XRD analysis showed magnesium present in the gold substrate and four different Mg/Au alloys being formed as a result of magnesium underpotential deposition and interdiffusion between Mg deposit and Au substrate from the melt made of a nonaqueous [Mg(NO3)2 + NH4NO3] eutectic mixture at 460 K. Full article
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Open AccessArticle Weibull Statistical Reliability Analysis of Mechanical and Magnetic Properties of FeCuNbxSiB Amorphous Fibers
Metals 2017, 7(3), 76; doi:10.3390/met7030076
Received: 16 December 2016 / Revised: 1 February 2017 / Accepted: 17 February 2017 / Published: 28 February 2017
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Abstract
Glass-coated Fe76.5−xCu1NbxSi13.5B9 (x = 0, 1, 2, 3, 3.5) fibers were successfully fabricated by a modified Taylor method. The fibers showed circular morphology and smooth surface with different diameters. The mechanical properties
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Glass-coated Fe76.5−xCu1NbxSi13.5B9 (x = 0, 1, 2, 3, 3.5) fibers were successfully fabricated by a modified Taylor method. The fibers showed circular morphology and smooth surface with different diameters. The mechanical properties of the fibers were evaluated and the Weibull statistical analysis has been introduced to characterize the strength reliability of the fibers, with the modulus m of the amorphous fibers reaching above 20. The magnetic properties were also studied. Lower coercivity was found for the fibers with amorphous, nanocrystalline, and microcrystalline structures rather than that for the coarse crystalline ones. The glass-coated FeCuNbSiB amorphous fibers have excellent comprehensive performance compared with the other kind of fibers. Full article
(This article belongs to the Special Issue Amorphous Alloys and Related Transitions)
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Open AccessArticle Mechanical, In Vitro Corrosion Resistance and Biological Compatibility of Cast and Annealed Ti25Nb10Zr Alloy
Metals 2017, 7(3), 86; doi:10.3390/met7030086
Received: 2 December 2016 / Revised: 21 February 2017 / Accepted: 2 March 2017 / Published: 8 March 2017
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Abstract
Compared to other alloys, Ti6Al4V is the most used in medicine. In recent years, concerns regarding the toxicity of Al and V elements found in the composition of Ti6Al4V have drawn the attention of the scientific community, due to the release of Al
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Compared to other alloys, Ti6Al4V is the most used in medicine. In recent years, concerns regarding the toxicity of Al and V elements found in the composition of Ti6Al4V have drawn the attention of the scientific community, due to the release of Al or V ions after long term exposure to human body fluids which can lead to a negative response of the human host. Based on this, the aim of the paper was to manufacture a Ti25Nb10Zr alloy consisting of biocompatible elements which can replace Ti6Al4V usage in medical applications. In order to prove that this alloy possessed improved properties, the mechanical, wear and corrosion resistance, wettability, and cell viability were performed in comparison with those of the Ti6Al4V alloy. The corrosion behavior of this new alloy in simulated body fluid (SBF) and Hank solutions is superior to that of Ti6Al4V. The cast Ti25Nb10Zr alloy has a good tribological performance in SBF, while annealed Ti25Nb10Zr alloy is better in Hank solution. Cell viability and proliferation assay after five days indicated that Ti25Nb10Zr presented a good viability and proliferation with values of approximately 7% and 10% higher, respectively, than the ones registered for pure Ti. When compared with Ti6Al4V, the obtained results for Ti25Nb10Zr indicated smaller values with 20% in the case of both tests. Overall, it can be concluded that cell proliferation and viability tests indicated that the biocompatibility of the Ti25Nb10Zr alloy is as good as pure Ti and Ti6Al4V alloy. Full article
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Open AccessArticle Preparation of Highly Pure Vanadyl Sulfate from Sulfate Solutions Containing Impurities of Iron and Aluminum by Solvent Extraction Using EHEHPA
Metals 2017, 7(3), 106; doi:10.3390/met7030106
Received: 11 February 2017 / Revised: 17 March 2017 / Accepted: 17 March 2017 / Published: 22 March 2017
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Abstract
The preparation of highly pure vanadyl sulfate from sulfate solutions containing impurities of iron and aluminumwas investigated by solvent extraction with 2-ethylhexyl phosphoric acid mono-2-ethylhexyl ester (EHEHPA) and tri-n-butyl phosphate (TBP) as the phase modifier. The extraction and stripping conditions of
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The preparation of highly pure vanadyl sulfate from sulfate solutions containing impurities of iron and aluminumwas investigated by solvent extraction with 2-ethylhexyl phosphoric acid mono-2-ethylhexyl ester (EHEHPA) and tri-n-butyl phosphate (TBP) as the phase modifier. The extraction and stripping conditions of vanadium (IV) and its separation from iron and aluminum were optimized. Under the optimal extraction conditions, the extraction of vanadium (IV) and iron were 68% and 53%, respectively, while only 2% aluminum was extracted in a single contact, suggesting good separation of vanadium (IV) from aluminum. Sulfuric acid solution was used for the stripping. Nearly 100% vanadium (IV) and 95% aluminum were stripped, while only 10% iron was stripped under the optimal stripping conditions in a single contact, suggesting good separation of vanadium (IV) from iron. After five stages of extraction and stripping, highly pure vanadyl sulfate containing 76.5 g/L V (IV) with the impurities of 12 mg/L Fe and 10 mg/L Al was obtained, which is suitable for the electrolyte of a vanadium redox flow battery. Organic solution was well regenerated after stripping by oxalic acid solution to remove the remaining iron. The mechanism of vanadium (IV) extraction using EHEHPA was also discussed based on the Fourier transform infrared spectroscopy (FT-IR) analysis. Full article
(This article belongs to the Special Issue Valuable Metal Recycling)
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Open AccessArticle Method of Preparation for High-Purity Nanocrystalline Anhydrous Cesium Perrhenate
Metals 2017, 7(3), 96; doi:10.3390/met7030096
Received: 23 December 2016 / Revised: 3 March 2017 / Accepted: 9 March 2017 / Published: 15 March 2017
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Abstract
This paper is devoted to the preparation of high-purity anhydrous nanocrystalline cesium perrhenate, which is applied in catalyst preparation. It was found that anhydrous cesium perrhenate with a crystal size <45 nm can be obtained using cesium ion sorption and elution using aqueous
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This paper is devoted to the preparation of high-purity anhydrous nanocrystalline cesium perrhenate, which is applied in catalyst preparation. It was found that anhydrous cesium perrhenate with a crystal size <45 nm can be obtained using cesium ion sorption and elution using aqueous solutions of perrhenic acid with subsequent crystallisation, purification, and drying. The following composition of the as-obtained product was reported: 34.7% Cs; 48.6% Re and <2 ppm Bi; <3 ppm Zn; <2 ppm As; <10 ppm Ni; < 3 ppm Mg; <5 ppm Cu; <5 ppm Mo; <5 ppm Pb; <10 ppm K; <2 ppm Na; <5 ppm Ca; <3 ppm Fe. Full article
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Open AccessArticle Impact of the Solidification Rate on the Chemical Composition of Frozen Cryolite Bath
Metals 2017, 7(3), 97; doi:10.3390/met7030097
Received: 15 December 2016 / Revised: 6 March 2017 / Accepted: 10 March 2017 / Published: 16 March 2017
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Abstract
Solidification of cryolite (Na3AlF6)-based bath takes place at different rates along the sideledge, and around alumina rafts and new anodes. The solidification rate has a significant impact on the structure and the chemical composition that determine the thermal conductivity and thus the thickness
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Solidification of cryolite (Na3AlF6)-based bath takes place at different rates along the sideledge, and around alumina rafts and new anodes. The solidification rate has a significant impact on the structure and the chemical composition that determine the thermal conductivity and thus the thickness of sideledge, or the duration of the existence of the temporary frozen bath layers in other cases. Unfortunately, samples that can be collected in industrial cells are formed under unknown, spatially and temporally varying conditions. For this reason, frozen bath samples were created under different heat flux conditions in a well-controlled laboratory environment using the so-called cold finger technique. The samples were analyzed by X-ray Diffractometer (XRD) and Scanning Electron Microscope (SEM) in Back Scattering (BS) mode in order to obtain spatial distribution of chemical composition. Results were correlated with structural analysis. XRD confirmed our earlier hypothesis of recrystallization of cryolite to chiolite under medium heat flux regime. Lower α-alumina, and higher γ-alumina content in the samples obtained with very high heating rate suggest that fast cooling reduces α–γ conversion. In accordance with the expectation, SEM-BS revealed significant variation of the Na/Al ratio in the transient sample. Full article
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Open AccessArticle Investigation of the Weld Properties of Dissimilar S32205 Duplex Stainless Steel with AISI 304 Steel Joints Produced by Arc Stud Welding
Metals 2017, 7(3), 77; doi:10.3390/met7030077
Received: 28 November 2016 / Revised: 22 February 2017 / Accepted: 23 February 2017 / Published: 1 March 2017
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Abstract
UNS S32205 duplex stainless steel plates with a thickness of 3 mm are arc stud welded by M8 × 40 mm AISI 304 austenitic stainless steel studs with constant stud lifts in order to investigate the effects of welding arc voltages on mechanical
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UNS S32205 duplex stainless steel plates with a thickness of 3 mm are arc stud welded by M8 × 40 mm AISI 304 austenitic stainless steel studs with constant stud lifts in order to investigate the effects of welding arc voltages on mechanical and microstructural behaviors of the joints. As the welding arc voltage increases starting from 140 V, the tensile strength of the weldment also increases but the higher arc values results in more spatters around the weld seam up to 180 V. Conversely, the lower arc voltages causes poor tensile strength values to weldments. Tensile tests proved that all of the samples are split from each other in the welding zone but deformation occurs in duplex plates during the tensile testing of weldments so that the elongation values are not practically notable. The satisfactory tensile strength and bending values are determined by applying 180 volts of welding arc voltage according to ISO 14555 standard. Peak values of micro hardness occurred in weld metal most probably as a consequence of increasing heat input decreasing the delta ferrite ratios. As the arc voltage increases, the width of the heat affected zone increases. Coarsening of delta-ferrite and austenite grains was observed in the weld metal peak temperature zone but it especially becomes visible closer to the duplex side in all samples. The large voids and unwelded zones up to approximately 1 mm by length are observed by macro-structure inspections. Besides visual tests and micro-structural surveys; bending and microhardness tests with radiographic inspection were applied to samples for maintaining the correct welding parameters in obtaining well-qualified weldments of these two distinct groups of stainless steel materials. Full article
(This article belongs to the Special Issue Selected Papers from ICWET16)
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Open AccessArticle Fatigue and Fracture Resistance of Heavy-Section Ferritic Ductile Cast Iron
Metals 2017, 7(3), 88; doi:10.3390/met7030088
Received: 15 February 2017 / Revised: 1 March 2017 / Accepted: 6 March 2017 / Published: 10 March 2017
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Abstract
In this paper, we explore the effect of a long solidification time (12 h) on the mechanical properties of an EN-GJS-400-type ferritic ductile cast iron (DCI). For this purpose, static tensile, rotating bending fatigue, fatigue crack growth and fracture toughness tests are carried
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In this paper, we explore the effect of a long solidification time (12 h) on the mechanical properties of an EN-GJS-400-type ferritic ductile cast iron (DCI). For this purpose, static tensile, rotating bending fatigue, fatigue crack growth and fracture toughness tests are carried out on specimens extracted from the same casting. The obtained results are compared with those of similar materials published in the technical literature. Moreover, the discussion is complemented with metallurgical and fractographic analyses. It has been found that the long solidification time, representative of conditions arising in heavy-section castings, leads to an overgrowth of the graphite nodules and a partial degeneration into chunky graphite. With respect to minimum values prescribed for thick-walled (t > 60 mm) EN-GJS-400-15, the reduction in tensile strength and total elongation is equal to 20% and 75%, respectively. The rotating bending fatigue limit is reduced by 30% with respect to the standard EN-1563, reporting the results of fatigue tests employing laboratory samples extracted from thin-walled castings. Conversely, the resistance to fatigue crack growth is even superior and the fracture toughness comparable to that of conventional DCI. Full article
(This article belongs to the Special Issue Fatigue Damage)
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Open AccessArticle Effects of Charcoal Addition on the Properties of Carbon Anodes
Metals 2017, 7(3), 98; doi:10.3390/met7030098
Received: 26 January 2017 / Revised: 10 March 2017 / Accepted: 13 March 2017 / Published: 16 March 2017
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Abstract
Wood charcoal is an attractive alternative to petroleum coke in production of carbon anodes for the aluminum smelting process. Calcined petroleum coke is the major component in the anode recipe and its consumption results in a direct greenhouse gas (GHG) footprint for the
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Wood charcoal is an attractive alternative to petroleum coke in production of carbon anodes for the aluminum smelting process. Calcined petroleum coke is the major component in the anode recipe and its consumption results in a direct greenhouse gas (GHG) footprint for the industry. Charcoal, on the other hand, is considered as a green and abundant source of sulfur-free carbon. However, its amorphous carbon structure and high contents of alkali and alkaline earth metals (e.g., Na and Ca) make charcoal highly reactive to air and CO2. Acid washing and heat treatment were employed in order to reduce the reactivity of charcoal. The pre-treated charcoal was used to substitute up to 10% of coke in the anode recipe in an attempt to investigate the effect of this substitution on final anode properties. The results showed deterioration in the anode properties by increasing the charcoal content. However, by adjusting the anode recipe, this negative effect can be considerably mitigated. Increasing the pitch content was found to be helpful to improve the physical properties of the anodes containing charcoal. Full article
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Open AccessArticle Comparison of Hydrostatic Extrusion between Pressure-Load and Displacement-Load Models
Metals 2017, 7(3), 78; doi:10.3390/met7030078
Received: 25 October 2016 / Accepted: 27 February 2017 / Published: 1 March 2017
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Abstract
Two finite element analysis (FEA) models simulating hydrostatic extrusion (HE) are designed, one for the case under pressure load and another for the case under displacement load. Comparison is made of the equivalent stress distribution, stress state ratio distribution and extrusion pressure between
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Two finite element analysis (FEA) models simulating hydrostatic extrusion (HE) are designed, one for the case under pressure load and another for the case under displacement load. Comparison is made of the equivalent stress distribution, stress state ratio distribution and extrusion pressure between the two models, which work at the same extrusion ratio (R) and the same die angle (2α). A uniform Von-Mises equivalent stress gradient distribution and stress state ratio gradient distribution are observed in the pressure-load model. A linear relationship is found between the extrusion pressure (P) and the logarithm of the extrusion ratio (lnR), and a parabolic relationship between P and 2α, in both models. The P-value under pressure load is smaller than that under displacement load, though at the same R and α, and the difference between the two pressures becomes larger as R and α grow. Full article
(This article belongs to the Special Issue Advances in Plastic Forming of Metals)
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Open AccessArticle Microstructural Evolution in AlMgSi Alloys during Solidification under Electromagnetic Stirring
Metals 2017, 7(3), 89; doi:10.3390/met7030089
Received: 19 December 2016 / Revised: 14 February 2017 / Accepted: 6 March 2017 / Published: 10 March 2017
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Abstract
Equiaxed solidification of AlMgSi alloys with Fe and Mn was studied by electromagnetic stirring to understand the effect of forced flow. The specimens solidified with a low cooling rate, low temperature gradient, and forced convection. Stirring induced by a coil system around the
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Equiaxed solidification of AlMgSi alloys with Fe and Mn was studied by electromagnetic stirring to understand the effect of forced flow. The specimens solidified with a low cooling rate, low temperature gradient, and forced convection. Stirring induced by a coil system around the specimens caused a transformation from equiaxed dendritic to rosette morphology with minor dendrites and, occasionally, spheroids. This evolution was quantitatively observed with specific surface Sv. The precipitation sequence of the phases was calculated using the CALPHAD (Computer Coupling of Phase Diagrams and Thermochemistry) technique. Melt flow decreased secondary dendrite arm spacing λ2 in the AlSi5Fe1.0 alloy, while λ2 increased slightly in Mg-containing alloys. The length of detrimental β-Al5FeSi phases decreased only in AlSi5Fe1.0 alloy under stirring, whereas in Mg-containing alloys, changes to the β-Al5FeSi phase were negligible; however, in all specimens, the number density increased. The modification of Mn-rich phases, spacing of eutectics, and Mg2Si phases was analyzed. It was found that the occurrence of Mg2Si phase regions reduced fluid flow in the late stages of solidification and, consequentially, reduced shortening of β-Al5FeSi, diminished secondary arm-ripening caused by forced convection, and supported diffusive ripening. However, the Mg2Si phase was found to have not disturbed stirring in the early stage of solidification, and transformation from dendrites to rosettes was unaffected. Full article
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Open AccessArticle Electrochemical Corrosion Behavior of Near-Nano and Nanostructured WC-Co Cemented Carbides
Metals 2017, 7(3), 69; doi:10.3390/met7030069
Received: 1 December 2016 / Revised: 29 January 2017 / Accepted: 17 February 2017 / Published: 23 February 2017
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Abstract
In this paper, the electrochemical corrosion resistance of near-nano and nanostructured WC-Co cemented carbides was investigated. WC powders with an average grain size dBET in the range from 95 nm to 150 nm and with an addition of vanadium carbide (VC) and
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In this paper, the electrochemical corrosion resistance of near-nano and nanostructured WC-Co cemented carbides was investigated. WC powders with an average grain size dBET in the range from 95 nm to 150 nm and with an addition of vanadium carbide (VC) and chromium carbide Cr3C2 as grain growth inhibitors were used as starting powders. The mixtures with 6 wt. % and 9 wt. % Co were consolidated by two different processes; sintering in hydrogen atmosphere and the sinter-HIP process. WC-Co samples were researched by direct current and alternating current techniques in the solution of 3.5% NaCl at room temperature. Corrosion parameters such as corrosion potential (Ecorr), corrosion current density (jcorr) and polarization resistance (Rp) were determined by electrochemical techniques. From the conducted research, it was found that the consolidation processes and microstructural characteristics—grain growth inhibitors, grain size of the starting WC powders and η-phase—influenced the electrochemical corrosion resistance. η-phase enhanced the formation of a passive layer on the samples’ surfaces, thereby reducing the tendency of the sample dissolution and increasing the stability of oxides forming therewith a passive layer on the sample surface. Full article
(This article belongs to the Special Issue Cermets and Hardmetals)
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Open AccessArticle Application of Boron Oxide as a Protective Surface Treatment to Decrease the Air Reactivity of Carbon Anodes
Metals 2017, 7(3), 79; doi:10.3390/met7030079
Received: 18 January 2017 / Revised: 13 February 2017 / Accepted: 28 February 2017 / Published: 3 March 2017
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Abstract
The oxidation of a carbon anode with air and CO2 occurs during the electrolysis of alumina in Hall-Héroult cells, resulting in a significant overconsumption of carbon and dusting. Boron is well known to decrease the rate of this reaction for graphite. In
[...] Read more.
The oxidation of a carbon anode with air and CO2 occurs during the electrolysis of alumina in Hall-Héroult cells, resulting in a significant overconsumption of carbon and dusting. Boron is well known to decrease the rate of this reaction for graphite. In this work, the application of boron oxide has been investigated to evaluate its inhibition effect on the air oxidation reaction, and to provide an effective protection for anodes. Different methods of impregnation coating have been explored. Impregnated anode samples were gasified under air at 525 °C according to the standard measurement methods. X-ray tomography was used to obtain the microstructural information of the samples before and after air-burning tests. The impregnated samples showed a very low oxidation reaction rate and dust generation. Full article
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Open AccessArticle The Effects of Prestrain and Subsequent Annealing on Tensile Properties of CP-Ti
Metals 2017, 7(3), 99; doi:10.3390/met7030099
Received: 14 February 2017 / Revised: 12 March 2017 / Accepted: 14 March 2017 / Published: 17 March 2017
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Abstract
The aim of the present work is to investigate the effects of prestrain and subsequent annealing on tensile properties of commercial pure titanium (CP-Ti). According to tensile test results, yield strength and ultimate tensile strength increase with the increase of prestrain. Elongation and
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The aim of the present work is to investigate the effects of prestrain and subsequent annealing on tensile properties of commercial pure titanium (CP-Ti). According to tensile test results, yield strength and ultimate tensile strength increase with the increase of prestrain. Elongation and uniform strain decrease linearly with prestrain. In the case of prestrain that is higher than 3.5%, the macro-yield of specimens changes from gradual yielding to discontinuous yielding. It is supposed that considerable numbers of dislocations introduced into the material lead to the appearance of yield plateau. The quantitative analysis of the contribution of dislocation hardening to the strain hardening shows that dislocation-associated mechanisms play an important role in strain hardening. Moreover, a modified Fields-Backofen model is proposed to predict the flow stress of prestrained CP-Ti at different strain rates. Both strain rate sensitivity and strain hardening exponent decrease with prestrain. Fracture surfaces of the specimens show that fracture mechanism of all tested specimens is dimple fracture. The more ductile deformation in prestrained CP-Ti after annealing indicates that its ductility is improved by annealing. Full article
(This article belongs to the Special Issue Titanium Alloys 2017)
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Review

Jump to: Research, Other

Open AccessReview A Summary of Corrosion Properties of Al-Rich Solid Solution and Secondary Phase Particles in Al Alloys
Metals 2017, 7(3), 84; doi:10.3390/met7030084
Received: 28 November 2016 / Revised: 19 February 2017 / Accepted: 28 February 2017 / Published: 7 March 2017
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Abstract
The heterogeneous structure of Al alloys renders them susceptible to localized corrosion due to the different electrochemical properties existing in the Al-rich solid solution matrix and secondary phase particles. The galvanic interactions between these two phases can result in pit formation either through
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The heterogeneous structure of Al alloys renders them susceptible to localized corrosion due to the different electrochemical properties existing in the Al-rich solid solution matrix and secondary phase particles. The galvanic interactions between these two phases can result in pit formation either through dissolution of the particles or corrosion of the matrix adjacent to the particles. This detrimentally localized corrosion behavior is closely related to the corrosion properties of the particles and the Al-rich matrix. The comprehensive characterization of this behavior under various and varying conditions is critical to understanding the mechanism of pit formation, selecting appropriate inhibitors, and developing protection strategies. The corrosion properties (corrosion potential, pitting potential and corrosion rate) of both secondary phase particles and Al-solid solutions in Al alloys are summarized in this review, aiming to provide a database for corrosion research applicable to the localized corrosion of Al alloys. Full article
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Other

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Open AccessErratum Erratum: Liu, Z.; Ji, F.; Wang, M.; Zhu, T. One-Dimensional Constitutive Model for Porous Titanium Alloy at Various Strain Rates and Temperatures. Metals 2017, 7, 24
Metals 2017, 7(3), 87; doi:10.3390/met7030087
Received: 7 March 2017 / Accepted: 7 March 2017 / Published: 8 March 2017
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Abstract The Metals Editorial Office wishes to report the following erratum to this paper [1]. In the paper, Figure 4a,b is the same as Figure 4c. Full article
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