Metals, Volume 6, Issue 6 (June 2016) – 20 articles

Cobalt sulfide (Co₉S₈) particles are compounded as the electrode materials of supercapacitors by a mechanical alloying method. They show excellent properties including good cycling stability and high specific capacitance. A supercapacitor is assembled using Co₉S₈ as the anode and activated carbon (AC) as the cathode. It gains a maximum specific capacitance of 55 F·g⁻¹ at a current density of 0.5 A·g⁻¹, and also an energy density of 15 Wh·kg⁻¹. Those results show that the novel and facile synthetic route may be able to offer a new way to synthesize alloy compounds with excellent supercapacitive properties. Full article

[μ-(linker)L₂(dipyrido[3,2-a:2′,3′-c]phenazine)₂(phenanthroline)₂Ru(II)₂]²⁺ with linker: 1,3-bis-(4-pyridyl)-propane, L: PF₆ (bis-Ru-bpp) was synthesized and their binding properties to a various polynucleotides were investigated by spectroscopy, including normal absorption, circular dichroism(CD), linear dichroism(LD), and luminescence techniques in this study. On binding to polynucleotides, the bis-Ru-bpp complex with poly[d(A-T)₂], and poly[d(I-C)₂] exhibited a negative LD^r signal whose intensity was as large as that in the DNA absorption region, followed by a complicated LD^r signal in the metal-to-ligand charge transfer region. Also, the emission intensity and equilibrium constant of the bis-Ru-bpp complex with poly[d(A-T)₂], and poly[d(I-C)₂] were enhanced. It was reported that both of dppz ligand of the bis-Ru-bpp complex intercalated between DNA base-pairs when bound to native, mixed sequence DNA. Observed spectral properties resemble to those observed for poly[d(A-T)₂] and poly[d(I-C)₂], led us to be concluded that both dppz ligands intercalate between alternated AT and IC bases-pairs In contrast when bis-Ru-bpp complex was bound to poly[d(G-C)₂], the magnitude of the LD^r in the dppz absorption region, as well as the emission intensity, was half in comparison to that of bound to poly[d(A-T)₂], and poly[d(I-C)₂]. Therefore the spectral properties of the bis-Ru-bpp-poly[d(G-C)₂] complex suggested deviation from bis-intercalation model in the poly[d(G-C)₂] case. These results can be explained by a model whereby one of the dppz ligands is intercalated while the other is exposed to solvent or may exist near to phosphate. Also it is indicative that the amine group of guanine in the minor groove provides the steric hindrance for incoming intercalation binder and it also takes an important role in a difference in binding of bis-Ru-bpp bound to poly[d(A-T)₂] and poly[d(I-C)₂]. Full article

The corrosion resistance of nanocrystalline Al, Al-10 wt. % Fe and Al-10 wt. % Fe-5 wt. % Cr alloys was investigated in 3.5% NaCl solution using cyclic potentiodynamic polarization (CPP) and electrochemical impedance spectroscopy (EIS) techniques. The alloys were fabricated using mechanical alloying (MA) and heat induction sintering. When compared with the corrosion resistance of pure Al, the experimental results indicated that the addition of 10 wt. % Fe and 10 wt. % Fe-5 wt. % Cr to pure Al has resulted in an enhancement in the corrosion resistance of these newly fabricated alloys. The resistance to corrosion is due to enhanced microstructural stability along with the formation of stable oxide layer. Full article

The element Al in molten aluminum containing steel reacts with the liquid mold flux and thus be transferred into the mold flux during the continuous casting process. Additionally, the increase in alumina in a mold flux changes its performance significantly. Thus, in this paper, the heat transfer properties of mold fluxes with the Al₂O₃ content ranging from 7 to 40 wt. % were studied with the Infrared Emitter Technique (IET). Results found that heat flux at the final steady state decreased from 423 kW·m⁻² to 372 kW·m⁻² with the increase in Al₂O₃ content from 7% to 30%, but it increased to 383 kW·m⁻² when the Al₂O₃ content was further increased to 40%. Both crystalline layer thickness and crystalline fraction first increased, then decreased with the further addition of A₂O₃ content. Moreover, it indicated that the heat transfer process inside the mold was dominated by both a crystallization of mold flux and the resulting interfacial thermal resistance. Further, the R_int increased from 9.2 × 10⁻⁴ m²·kW⁻¹ to 11.0 × 10⁻⁴ m²·kW⁻¹ and then to 16.0 × 10⁻⁴ m²·kW⁻¹ when the addition of Al₂O₃ content increased from 7% to 20% and then to 30%, respectively; however, it decreased to 13.6 × 10⁻⁴ m²·kW⁻¹ when the Al₂O₃ content reached 40%. Full article

Electric arc furnace (EAF) dust, together with a mill scale and coke were smelted in a laboratory electric arc furnace. These metallurgical wastes consist of a many different phases and elements, making the reaction process complex. Thermo-chemical analysis of the reactions in metal, slag, and gas phases was done, and used for modeling of the mixture composition and energy consumption required for smelting. Modelling was performed with the software named RikiAlC. The crude ZnO, slag, and metal phase were analyzed using the atomic absorption spectrometry (AAS), the optical emission spectrometry with inductively coupled plasma (ICP-OES), the X-ray diffraction (XRD), the scanning electron microscopy (SEM) equipped with energy dispersive spectrometry (EDS), and reflected and transmitted light microscopy. Also, in order to follow the behavior of this process the exhausted gases were monitored. The synergetic effects of the designed mixture may be recognized in minimizing energy consumption for the smelting process, improving the product yield efficiency, and reducing the negative environmental effects. Full article

The oxidation behavior of silicon-containing steel was studied by applying segmented heating routes similar to the atmosphere and heating process in an industrial reheating furnace. The oxidation tests were carried out on a simultaneous thermal analyzer at heating temperatures of 1150 °C–1300 °C. The morphologies of Fe₂SiO₄ were observed by SEM, and the penetration depths of the Fe₂SiO₄ layer at different oxidation temperatures were determined by using the Image-Pro Plus 6.0 software. The results show that at heating temperatures ≥1235 °C, the oxidation rate and total oxidation mass gain have no relation with the heating temperature; the mass gain versus time follows a linear law after about 1164 °C (lower than the eutectic temperature of fayalite). In addition, the oxidation rate first decreases slowly and then drops from 1190 °C to 1210 °C during the isothermal holding stage. With the increase in temperature, the oxidation rate and mass gain also increase gradually; the relationship between the mass gain and time is close to a parabolic law. Moreover, at a heating temperature of 1150 °C, the oxidation rate decreases rapidly during the isothermal holding stage, and the mass gain versus time follows a parabolic law. Full article

Tube spinning is an effective plastic-forming technology for forming light-weight, high-precision and high-reliability components in high-tech fields, such as aviation and aerospace. However, cracks commonly occur in tube spinning due to the complexity of stress state, which severely restricts the improvement of the forming quality and forming limit of components. In this study, a finite element (FE) model coupled with Gurson-Tvergaard-Needleman (GTN) damage model for forward tube spinning of 3A21-O aluminum alloy is established and its applicability is evaluated by experiment. Meanwhile, the GTN damage model is employed to study the damage evolution for forward tube spinning of 3A21-O aluminum alloy. The results show that the FE model is appropriate for predicting the macroscopic crack appearing in uplift area for forward tube spinning, while the damage evolution in deformation area could not be predicted well due to the negative stress triaxiality and the neglect of shear deformation. Accumulation of damage in forward tube spinning occurs mainly in the uplift area. Void volume fraction (VVF) in the outer surface of the tube is higher than that in the inner surface. In addition, it is prone to cracking in the outer surface of tube in the material uplift area. Full article

The cold spray coating process involves many process parameters which make the process very complex, and highly dependent and sensitive to small changes in these parameters. This results in a small operational window of the parameters. Consequently, mathematical optimization of the process parameters is key, not only to achieving deposition but also improving the coating quality. This study focuses on the mathematical identification and experimental justification of the optimum process parameters for cold spray coating of titanium alloy with silicon carbide (SiC). The continuity, momentum and the energy equations governing the flow through the low-pressure cold spray nozzle were solved by introducing a constitutive equation to close the system. This was used to calculate the critical velocity for the deposition of SiC. In order to determine the input temperature that yields the calculated velocity, the distribution of velocity, temperature, and pressure in the cold spray nozzle were analyzed, and the exit values were predicted using the meshing tool of Solidworks. Coatings fabricated using the optimized parameters and some non-optimized parameters are compared. The coating of the CFD-optimized parameters yielded lower porosity and higher hardness. Full article

Double-sided laser beam welding of skin-stringer joints is an established method for many applications. However, in certain cases with limited accessibility, single-sided laser beam joining is considered. In the present study, single-sided welding of titanium alloy Ti₆Al₄V and nickel-based alloy Inconel 600 in a T-joint configuration was carried out using continuous-wave (CW), low-power Ytterbium (Yb)-fiber laser. The influence of the overlapping factor and welding speed of the laser beam on weld morphology and properties was investigated using scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. XRD analysis revealed the presence of intermetallic layers containing NiTi and NiTi₂ at the skin-stringer joint. The strength of the joints was evaluated using pull testing, while the hardness of the joints was analyzed using Vickers hardness measurement at the base metal (BM), fusion zone (FZ) and heat-affected zone (HAZ). The results showed that the highest force needed to break the samples apart was approximately 150 N at a laser welding power of 250 W, welding speed of 40 mm/s and overlapping factor of 50%. During low-power single-sided laser welding, the properties of the T-joints were affected by the overlapping factor and laser welding speed. Full article

Friction Stir Welding (FSW) is a solid-state welding process used for welding similar and dissimilar materials. FSW is especially suitable to join sheet Al alloys, and this technique allows different material couples to be welded continuously. In this study, 1050 Al alloys and commercially pure Cu were produced at three different tool rotation speeds (630, 1330, 2440 rpm) and three different tool traverse speeds (20, 30, 50 mm/min) with four different tool position (0, 1, 1.5, 2 mm) by friction stir welding. The influence of the welding parameters on the microstructure and mechanical properties of the joints was investigated. Tensile and bending tests and microhardness measurements were used to determine the mechanical properties. The microstructures of the weld zone were investigated by optical microscope and scanning electron microscope (SEM) and were analyzed in an energy dispersed spectrometer (EDS). Intermetallic phases were detected based on the X-ray diffraction (XRD) analysis results that evaluated the formation of phases in the weld zone. When the welding performance of the friction stir welded butt joints was evaluated, the maximum value obtained was 89.55% with a 1330 rpm tool rotational speed, 20 mm/min traverse speed and a 1 mm tool position configuration. The higher tensile strength is attributed to the dispersion strengthening of the fine Cu particles distributed over the Al material in the stir zone region. Full article

The critical role of manganese sulphide (MnS) inclusions for the initiation of the short-term growth of pitting or localized corrosion of low carbon steels has long been recognized. Classical results show that pitting probability and pitting severity increases with increased sulphide concentration for low carbon steels as a result of magnesium sulphides acting as local cathodes for initiating pitting corrosion. However, the iron carbides (cementite) in steels can also act as local cathodes for initiation of pitting corrosion. Herein it is proposed that there is competition between pits for cathodic area and that this will determine the severity of pitting and general corrosion observed in extended exposures. Preliminary experimental data for immersion exposures of up to 56 days in natural seawater of three low carbon steels show, contrary to conventional wisdom, greater pit depths for the steels with lower S content. However, the pit depth results are consistent with lower C/S ratios. This is considered to support the concept of cathodic competition between C and S. It is proposed that this offers explanations for a number of other phenomena, including the thus far unexplained apparently higher reactivity of some MnS inclusions. Full article

This paper reports the current status of Mg melt protection in view to identify near-future challenges, but also opportunities, for Mg melt protection of Mg-Al based alloys. The goal is to design and manufacture sustainable Mg alloys for resource efficiency, recycling and minimising waste. Among alternative cover gas technologies for Mg melt protection other than SF₆: commercially available technologies containing―HFC-134a, fluorinated ketone and dilute SO₂―and developed technologies containing solid CO₂, BF₃ and SO₂F₂, can potentially produce toxic and/or corrosive by-products. On the other hand, additions of alkaline earth metal oxides to Mg and its alloys have developed a strong comparative advantage in the field of Mg melt protection. The near-future challenges and opportunities for Mg-Al based alloys include optimising and using CO₂ gas as feedstock for both melt protection and grain refinement and TiO₂ additions for melt protection. Full article

In the present work the influence of vanadium on the hardenability and the bainitic transformation of a medium carbon steel is analyzed. While V in solid solution enhances the former, it hardly affects bainitic transformation. The results also reveal an unexpected result, an increase of the prior austenite grain size as the V content increases. Full article

The viscosity of feedstock materials is directly related to its processability during injection molding; therefore, being able to predict the viscosity of feedstock materials based on the individual properties of their components can greatly facilitate the formulation of these materials to tailor properties to improve their processability. Many empirical and semi-empirical models are available in the literature that can be used to predict the viscosity of polymeric blends and concentrated suspensions as a function of their formulation; these models can partly be used also for metal injection molding binders and feedstock materials. Among all available models, we made a narrow selection and used only simple models that do not require knowledge of molecular weight or density and have parameters with physical background. In this paper, we investigated the applicability of several of these models for two types of feedstock materials each one with different binder composition and powder loading. For each material, an optimal model was found, but each model was different; therefore, there is not a universal model that fits both materials investigated, which puts under question the underlying physical meaning of these models. Full article

Carbon anodes are consumed in electrolysis cells during aluminum production. Carbon consumption in pre-bake anode cells is 400–450 kg C/t Al, considerably higher than the theoretical consumption of 334 kg C/t Al. This excess carbon consumption is partly due to the anode manufacturing processes. Net carbon consumption over the last three years at Emirates Aluminium (EMAL, also known as Emirates Global Aluminium (EGA) Al Taweelah) was analyzed with respect to anode manufacturing processes/parameters. The analysis indicates a relationship between net carbon consumption and many manufacturing processes, including anode desulfurization during anode baking. Anode desulfurization appears to increase the reaction surface area, thereby helping the Boudouard reaction between carbon and carbon dioxide in the electrolysis zone, as well as reducing the presence of sulfur which could inhibit this reaction. This paper presents correlations noted between anode manufacturing parameters and baked anode properties, and their impact on the net carbon consumption in electrolytic pots. Anode reactivities affect the carbon consumption in the pots during the electrolysis of alumina. Pitch content in anodes, impurities in anodes, and anode desulfurization during baking were studied to find their influence on anode reactivities. The understanding gained through this analysis helped reduce net carbon consumption by adjusting manufacturing processes. For an aluminum smelter producing one million tonnes of aluminum per year, the annual savings could be as much as US $0.45 million for every kg reduction in net carbon consumption. Full article

In the present study, the influence of substitutional elements (Ti and Al) on the structural stability, mechanical properties, electronic properties and Debye temperature of Ta₅Si₃ with a D8_m structure were investigated by first principle calculations. The Ta₅Si₃ alloyed with Ti and Al shows negative values of formation enthalpies, indicating that these compounds are energetically stable. Based on the values of formation enthalpies, Ti exhibits a preferential occupying the Ta^4b site and Al has a strong site preference for the Si^8h site. From the values of the bulk modulus (B), shear modulus (G) and Young’s modulus (E), we determined that both Ti and Al additions decrease both the shear deformation resistance and the elastic stiffness of D8_m structured Ta₅Si₃. Using the shear modulus/bulk modulus ratio (G/B), Poisson’s ratio (υ) and Cauchy’s pressure, the effect of Ti and Al additions on the ductility of D8_m-structured Ta₅Si₃ are explored. The results show that Ti and Al additions reduce the hardness, resulting in solid solution softening, but improve the ductility of D8_m-structured Ta₅Si₃. The electronic calculations reveal that Ti and Al additions change hybridization between Ta-Si and Si-Si atoms for the binary D8_m-structured Ta₅Si₃. The new Ta-Al bond is weaker than the Ta-Si covalent bonds, reducing the covalent property of bonding in D8_m-structured Ta₅Si₃, while the new strong Ti^4b-Ti^4b anti-bonding enhances the metallic behavior of the binary D8_m-structured Ta₅Si₃. The change in the nature of bonding can well explain the improved ductility of D8_m-structured Ta₅Si₃ doped by Ti and Al. Moreover, the Debye temperatures, Θ_D, of D8_m-structured Ta₅Si₃ alloying with Ti and Al are decreased as compared to the binary Ta₅Si₃. Full article

To study the effects of warm laser peening (WLP) on the thermal stability and mechanical properties of A356 alloy, the samples were treated by WLP using a Nd:YAG solid-state laser and temperature control device. The residual stress, micro-hardness and microstructures of samples treated by WLP were observed. The result shows that the temperature significantly affects the strengthening effect of laser peening (LP). The residual stress induced by WLP decreases with the increasing temperature. The micro-hardness and dislocation density increase first, and then decrease with the increases of temperature. The grain refinement degree of the samples treated by WLP is much higher than that of LP. In addition, after aging for 100 min at 220 °C, the samples treated by LP and WLP were comparatively investigated in thermal stability. Obviously, the residual compressive stress, micro-hardness and microstructure induced by WLP present a better thermal stability property than that of LP. The residual stress and micro-hardness of WLP samples are obviously improved, and the increasing degrees are 23.31% and 19.70%, respectively. The dislocation density remains at a high level, while the grains are still in fine crystalline state. Full article

Due to hydrogen possessing a relatively large neutron scattering length, hydrogen absorption and desorption behaviors in metal thin films can straightforwardly be investigated by neutron reflectometry. However, to further elucidate the chemical structure of the hydrogen absorbing materials, complementary techniques such as high resolution X-ray reflectometry and diffraction remain important too. Examples of work on such systems include Nb- and Pd-based multilayers, where Nb and Pd both have strong affinity to hydrogen. W/Nb and Fe/Nb multilayers were measured in situ with unpolarized and polarized neutron reflectometry under hydrogen gas charging conditions. The gas-pressure/hydrogen-concentration dependence, the hydrogen-induced macroscopic film swelling as well as the increase in crystal lattice plane distances of the films were determined. Ferromagnetic-Co/Pd multilayers were studied with polarized neutron reflectometry and in situ ferromagnetic resonance measurements to understand the effect of hydrogen absorption on the magnetic properties of the system. This electronic effect enables a novel approach for hydrogen sensing using a magnetic readout scheme. Full article

As Eulerian description is generally used for the simulation of filling flow problems in the powder injection molding process, and the governing equation of the filling state takes the form of an advection equation, the distortion can be easily produced when dealing with the filling process in complex cavities, such as the similar channels in shapes of $\perp$ and L, inside which the phenomena of opposite joining and bypass are involved. In order to improve the precision, causes of the unrealistic results were analyzed in the present paper. A notion similar to the upwind method was introduced and a corresponding correction method was proposed to settle this problem. Based on the efficient explicit algorithm for PIM simulation, and by means of systematic operation to modify the fluid velocity field, the untrue impact of air flow, represented by the velocity field in front of the filling fronts, can be weakened. Then, the advection of the filling state can be mainly affected by the flow field behind the filling front. The simulation results show that the correction algorithm can effectively inhibit the distortion. The simulation of the filling processes in the complex cavities, inside which the flow directions will be subject to the sudden changes, can be realized correctly. Full article

In this paper, an effective method was developed to remove phosphorus and upgrade iron from high phosphorus oolitic hematite ore by high temperature flash reduction—a wet magnetic separation process. A thermodynamic analysis of iron and phosphorus mineral reactions and experiments with Fe-P separation process were performed, and the mechanism of phosphorus removal and beneficiation of iron is discussed as well. The results show that under the proper conditions, a final metallic iron powder assaying over 91% Fe and 0.25% P was obtained with iron recovery of 90% and phosphorus removal rate of 91.79% using the new process, indicating that the high temperature flash reduction process is a feasible and efficient way to process this kind of complex and refractory iron ore. Moreover, sodium sulfate is found to be capable of improving the removal of phosphorus and the upgrading of iron, as well as enhancing the growth of metallic iron grains significantly for higher recovery of iron. Full article