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Metals, Volume 7, Issue 3 (March 2017)

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Cover Story (view full-size image) Heavy-section castings of ferritic ductile cast iron suffer from microstructural modifications [...] Read more.
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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; https://doi.org/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 Microstructure Evolution and Biodegradation Behavior of Laser Rapid Solidified Mg–Al–Zn Alloy
Metals 2017, 7(3), 105; https://doi.org/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 Improved Compressive, Damping and Coefficient of Thermal Expansion Response of Mg–3Al–2.5La Alloy Using Y2O3 Nano Reinforcement
Metals 2017, 7(3), 104; https://doi.org/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 Very High Cycle Fatigue of Butt-Welded High-Strength Steel Plate
Metals 2017, 7(3), 103; https://doi.org/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) Printed Edition available
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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; https://doi.org/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
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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 Evolution of Anode Porosity under Air Oxidation: The Unveiling of the Active Pore Size
Metals 2017, 7(3), 101; https://doi.org/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 The Effects of Prestrain and Subsequent Annealing on Tensile Properties of CP-Ti
Metals 2017, 7(3), 99; https://doi.org/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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Open AccessArticle Investigation of the Geometry of Metal Tube Walls after Necking in Uniaxial Tension
Metals 2017, 7(3), 100; https://doi.org/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 Effects of Charcoal Addition on the Properties of Carbon Anodes
Metals 2017, 7(3), 98; https://doi.org/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 Impact of the Solidification Rate on the Chemical Composition of Frozen Cryolite Bath
Metals 2017, 7(3), 97; https://doi.org/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 Method of Preparation for High-Purity Nanocrystalline Anhydrous Cesium Perrhenate
Metals 2017, 7(3), 96; https://doi.org/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 Magnesium–Gold Alloy Formation by Underpotential Deposition of Magnesium onto Gold from Nitrate Melts
Metals 2017, 7(3), 95; https://doi.org/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 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; https://doi.org/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) Printed Edition available
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Open AccessArticle Experimental and Numerical Simulation Investigation on Laser Flexible Shock Micro-Bulging
Metals 2017, 7(3), 93; https://doi.org/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 Synthesis and Characterization of Copper-Based Composites Reinforced by CuZrAlNiTi Amorphous Particles with Enhanced Mechanical Properties
Metals 2017, 7(3), 92; https://doi.org/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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