Advanced Materials Research Vols. 560-561

Abstract: Polycrystalline bulk sample Zn_0.99Fe_0.01O was fabricated by a solid-state reaction method and modified by high-pressure treatment technique at a pressure of 5GPa. The structure, morphology and magnetic properties of these samples were investigated in order to clarify the effect of pressure on magnetism of Zn-Fe-O system. It is found that the particle size of the modified samples becomes larger as well as the physical contact between neighboring particles becomes better. All samples show obvious ferromagnetic behaviors at room temperature, and the magnetization of modified samples greatly increases. It is believed that the larger particle size and the closer contact between neighbouring particles resulted from high-pressure treatment cause stronger ferromagnetic exchange interaction in Zn-Fe-O system.

Abstract: Polycrystalline pure titanium was irradiated by high-current pulsed electron beam (HCPEB). The microstructure changes and material strength were investigated by using microhardness tester, optical microscope, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) technique. The experimental results indicate that many craters are inevitably formed on the irradiated surface. The eruption of the craters makes the material surface cleaned, which can improve the corrosion resistance of materials. Furthermore, martensitic structure, ultra-fine grains and high-density dislocations are formed on the irradiated surface, which increase the hardness of the treated samples. The microhardness of 20-pulsed sample reaches 286Hv, which is 71% higher than the initial sample. Martensitic transformation, grain refinement and dislocation strengthening induced by HCPEB treatment are the dominating mechanism for the improvements of material strength. It is suggested that HCPEB technique is becoming an effective approach to surface modification for pure titanium and titanium alloy.

Abstract: It is obviously different mechanical properties of the rolled magnesium alloy plate when stretched along different directions at room temperature. In this study, three groups of samples for uniaxial tension were cut from the as-rolled AZ80 plate with their tension directions either at 0°, 45°or 90°to the rolled direction (RD) of the sheet. Results show that the ductility of the 45°samples was significantly better than that of 0°and 90°samples. The electron backscatter diffraction (EBSD) technique was used to investigate the microstructure and textures evolution. Along with the increase of deformation, more low-angle grain boundaries arise in the 0°and 45°samples than the 90°samples. At the same time, the texture components that {10-10} prismatic plane perpendicular to the tension direction were significantly enhanced in three groups of samples.

Abstract: Porous copper with an open-cellular structure was prepared basing on space-holder method. Depending on the volume fraction and size of the space holding particle, the porosity can be varied in a wide range of 40-85%, and the pore size can be tailored from micron to millimeter in order. The effects of pore size on compressive behavior and energy absorption properties were investigated by quasi-static compression measurement. The results showed that the pore size shows a significant effect on compressive behavior and energy absorption properties. The compressive stress-strain curves were increased with increasing the pore size. The energy absorption capacity and energy absorption efficiency were greatly improved at the same strain, when the pore sizes transferred from micron to millimeter in order, indicating a more desirable energy absorption property of larger pore size.

Abstract: The RE–Mg–Ni-based A2B7-type La0.75−xPrxMg0.25Ni3.2 Co0.2Al0.1 (x = 0, 0.1, 0.2, 0.3, 0.4) electrode alloys were fabricated by casting and melt spinning. The microstructures and electrochemical characteristics of the as-cast and spun alloys were investigated in detail. The results indicate that the as-cast and spun alloys have a multiphase structure, consisting of two main phases (La, Mg)2Ni7 and LaNi5 as well as a residual phase LaNi2. The substitution of Pr for La results in a notable grain refinement of the as-cast alloys without altering the phase structure of the alloys. The discharge capacity of the alloys first rises and then falls with the variation of the Pr content. As Pr content grows from 0 to 0.4, the discharge capacity increases from 389.4 (x = 0) to 392.4 (x = 0.1) and then drops to 383.7 mAh/g (x = 0.4) for the as-cast alloy. And it mounts up from 393.5 (x = 0) to 397.9 (x = 0.1) and then declines to 382.5 mAh/g for the as spun (5 m/s) alloys. Furthermore, the measurements of the electrochemical hydrogen storage kinetics reveal that the high rate discharge ability (HRD), the limiting current density (IL) and the hydrogen diffusion coefficient (D) of the alloys first increases then decreases with the rising amount of Pr substitution.

Abstract: The poor electrochemical cycle stability of Re-Mg-Ni system A2B7-type electrode alloys has limited their practical application as the negative electrode materials of Ni-MH battery. In order to improve the electrochemical cycle stability of the La-Mg-Ni system A2B7-type electrode alloys, the partial substitution of Zr for La has been performed. The La0.75-xZrxMg0.25Ni3.2Co0.2Al0.1 (x = 0–0.2) electrode alloys were fabricated by casting and melt-spinning. The microstructures and the electrochemical cycle stability and kinetics of the alloys were investigated. The structure characterized by XRD, SEM and HRTEM reveals that the as-cast and spun alloys have a multiphase structure, composing of two main phases (La, Mg)2Ni7 and LaNi5 as well as a residual phase LaNi2. The as-spun Zr-free alloy displays an entire nanocrystalline structure, but a like amorphous structure is detected in the as-spun alloy substituted by Zr, suggesting that the substitution of Zr for La facilitates the formation of an amorphous structure. The electrochemical measurement indicates that both the substitution of Zr for La and the melt spinning remarkably ameliorate electrochemical cycle stability of the alloys. Furthermore, the high rate discharge ability (HRD), the electrochemical impedance spectrum (EIS) and the potential-step measurements all indicate that both of the melt spinning and the Zr substitution bring on a notable decline of the electrochemical kinetics of the alloys.

Abstract: Titanium dioxide (TiO₂), which was doped by Ce and Fe, was coated on multi-walled carbon nanotubes (MWCNTs) through a conventional sol-gel method. We use IR to evaluate the possible functional groups and XRD, UV and SEM to characterize the structure and surface morphology of MWCNTs. The results suggest that the TiO₂, which composed of nano-scale particles, was well coated on MWCNTs via chemistry bond. The visible light photo catalytic was mentioned of its red shift in UV spectrum. And we suggest that there may be a certain mechanism between TiO₂ and MWCNTs during visible light processing that MWCNTs has play an important role in red shift and visible light absorption.

Abstract: In order to find out the optimum thermodynamic conditions for hot metal dephosphorization and predict phosphorus content after demanganization pretreatment, thermodynamic equilibrium experiments between CaO-FetO-SiO2-MnO-P2O5 slag and silver/solid iron were carried out in an iron crucible at different temperature under pure argon atmosphere in an electric resistant furnace. The results indicate that phosphorus distribution ratios increase with an increase of basicity in the slag at the experiment temperature, and then they decrease with an increase of basicity at 1573K and 1623K. The phosphorus distribution ratios decrease with an increase of FetO content in the slag at 1573K, while they increase with an increase of FetO content in the slag and then decrease with an increase of FetO content in the slag at 1623K. The results indicate that the maximum phosphorus distribution ratio between slag and hot metal is 92.4 when basicity of the slag is 1.7 and FetO content in slag is 49.75 mass% at 1623K, and the correspondent phosphorus content in the carbon saturated iron is 0.019mass%. Dephosphorization is easier under low temperature. The equilibrium quotient of phosphorus obtained in the present work is formulated as a function of slag compositions and temperature using the multiple regression method which is used to predict phosphorus content equilibrium with the demanganization slag and optimum conditions needed for ideal phosphorus contents in demanganization pretreatment.

Abstract: The aim of this study was to investigate the effect of activated fluxes on the weld morphology, angular distortion, and mechanical properties obtained with activated tungsten inert gas (TIG) process applied to the welding of 6 mm thick mild steel and stainless steel plates. A novel variant of the TIG welding, specific oxides were applied to mild steel and stainless steel through a thin layer of the flux to produce a butt joint. The CaO, SiO2, Fe2O3, and Cr2O3 fluxes used were packed in powdered form. The experimental results indicated that the SiO2, Fe2O3, and Cr2O3 fluxes can increase joint penetration and weld depth-to-width ratio. The reversed Marangoni convection are considered to the main factors for increasing penetration of A-TIG on dissimilar welds in this study. Furthermore, TIG welding with SiO2 powder can significantly reduce the angular distortion of the dissimilar weldment.

Abstract: In this work, Al/SiO₂ composite coatings were deposited on the surface of aluminum alloy through atmospheric plasma spray. The effects of SiO₂ volume in Al/SiO₂ composite powders on the deposition behavior were investigated. It was found that the deposition of the Al/SiO₂ composite powder became more difficult through plasma spray with the increasing of SiO₂ contents. There were reactions between aluminium and silicon oxide during the deposition of Al/SiO₂ powders in the plasma flame. The reactions were helpful to interface cohesions between aluminium and silicon oxide. Al/SiO₂(60:40, 80:20) composites were more suitable for deposition and well interface cohesion through atmospheric plasma spray.