Materials Science Forum Vols. 510-511

Abstract: Recently, there has been increased interest in using aluminum alloys in ship construction instead of fiber-reinforced plastic (FRP). This is because aluminum alloy ships are faster, have a greater load capacity, and are easier to recycle than FRP ships. In this study, we investigated the mechanical and electrochemical properties of aluminum alloys using the slow strain rate and potentiostatic tests under various potential conditions. The optimum protection potential range with regards to hydrogen embrittlement and stress corrosion cracking was determined to lie between -1.5 and -0.7 V (SSCE). These results can be used as reference data for ship design.

Abstract: Magnesium must be surface treated to prevent corrosion, since it is a very active metal electrochemically. On anodizing, a compact film several tens of micrometers thick forms on magnesium, which imparts good corrosion resistance. The Mg-Al alloy (AZ91) was anodized in 1 M NaOH solution. The surface morphology of the anodized films was observed using scanning electron microscopy (SEM), energy-dispersive x-ray (EDX), and electrochemical methods. The effects of current density on the formation of anodic oxide films for a Mg-Al alloy in 1 M NaOH were investigated. In the anodic polarization curve, the reference corrosion potentials were far greater at 4-9 mA/cm2 than at 1 mA/cm2. The film that formed at 1 mA/cm2 was thin, suggesting that parts of the film had been dissolved or destroyed during the anodic polarization test. Corrosion resistance differed owing to concentric differences in current flow. Thick anodic oxide films were formed at higher applied currents.

Abstract: Highly luminescent lipophilic CdSe/ZnS core-shell QDs with an emission maximum at 556 nm were synthesized. These QDs were successfully encapsulated into solid lipid nanoparticles (SLNs) using the thin-layer ultrasonication technique. Transmission electron microscopy (TEM), photon correlation spectroscopy (PCS), and zeta potential measurement were employed to characterize the QDs-loaded SLNs for morphology, particle size with polydispersity index (PI), and zeta potential. The nanocomposite particles obtained appeared in a shape of spherical or near spherical with the average size of 92.3 nm, PI of 0.235 and zeta potential of -28.74 mV. Each nanocomposite particle contains tens of QDs observed by TEM. Fluorescence measurements show that the encapsulated QDs maintain their high luminescence and narrow/symmetric emission spectra. The experiment result indicates that the nanocomposite particles are stable and slow to photobleach. These luminescent nanocomposite particles have good potentials in biological imaging applications.

Abstract: Abstract. Hot concentrated alkaline corrosion and wearing corrosion environment exists in alumina metallurgical industry. Iron and steel materials with outstanding alkaline corrosion resistance are strongly demanded for their fabrication equipments. In this paper, corrosion resistance in static hot concentrated alkaline solution of several kinds of martensite chromium cast iron and steel was studied through polarization curves, potential-time curves, weight loss in the corrosion, and corrosive morphology analysis. Experimental results indicated that corrosion processes can be divided into three stages: dissolving of passivating films, exposed surface corrosion, and corrosion beneath the corroded product. Protection effect of the passivating films was transitory, and the corrosion rate during the exposed surface corrosion reached the maximum. Corrosion of the testing materials was composed of active dissolving corrosion of the metal matrix and caustic embrittlement cracking of the matrix, as well as grain boundary corrosion for the cast iron. Dissolving corrosion of the metal matrix was the main cause that induced the weight loss, while severe caustic embrittlement cracking of the metal matrix was disadvantageous. With an increase of the chromium content in the cast iron or steel, active dissolving corrosion of the metal matrix increased. However, the tendency of caustic embrittlement cracking decreased.

Abstract: We focused on the surface reinforcement of Al casting alloys with Ni-Al intermetallic compounds by in-situ combustion reaction to improve the surface properties of Al casting components. Microstructure and phase formation behavior of Ni-Al based intermetallic compounds synthesized by combustion reaction were investigated in terms of thermal and phase analysis using scanning electron microscope(SEM) equipped with energy dispersive x-ray spectrometer (EDS) and x-ray diffractometer(XRD) in Ni-Al intermetallic compounds. Three kinds of nickel aluminides, NiAl3, NiAl and Ni3Al, were synthesized by emission heat from the Al molten metal in order to form a coating layer of intermetallic phase simultaneously on the solidifed Al alloy surface. The synthesized shapes and microstructures of nickel aluminides were varied by casting temperature, Si contents, and the mixing ratio of elemental powders. The synthesized reaction products formed in nickel aluminides were observed to be different depending on the mixing ratio of elemental powders. The reaction layer of about 25
m thickness was formed at the interface, and it mainly consisted of NiAl3 phase by the reaction between liquid molten Al alloy and solid Ni powders in green compact. With this information, we successfully produced a coating layer of Ni3Al intermetallic compound onto the casting Al alloy surface using molten metal heat without any additional process. These findings led us to conclude that a near-net shaped nickel aluminide coating layer can be formed using this unique process.

Abstract: Eco-friendly development and on-going research strategy of Rotation-Cylinder Method (RCM) is given for SiCp/AZ91 Mg composites, identifying some of the key factors that need to be controlled and indicating subsequent casting processes. RCM produces U-shaped laminar melt surface with a Rankine vortex even at high rotation speed in an ambient atmosphere, which allows quick and efficient incorporation and homogeneous distribution of SiC particulates into molten Mg alloys. Therefore, sound SiCp/AZ91 Mg composites can be manufactured in conjunction with subsequent casting processes, such as investment casting and thixocasting. A transmission electron microscopy study showed that the interfacial reaction products consist of Mg2Si, MgO, Mg17Al12 and Al6Mn, which were analyzed using primitive cell volume and zero order Laue zone pattern and single convergent beam electron diffraction pattern containing higher order Laue zone ring from a nanosized region.

Abstract: Plate-on-disc type sliding friction and wear test was conducted to investigate the friction and wear properties of mullite reinforced composite (M composite), and compared with glass fiber reinforced composite (GF composite). The friction and wear test revealed that M composite has good wear resistance under mild sliding conditions, but the wear rate gradually increases under severe sliding conditions. M composite exhibited higher friction coefficient than GF composite at room temperature and maintained the friction coefficient stably at higher temperatures. The composite film formed on counter material against M composite showed influences on the friction and wear properties under severe sliding conditions.

Abstract: We investigated the characteristics of the HfO2 layer deposited by ALD method in MOSFET devices where the HfO2 film is incorporated as the gate dielectric layer. The HfO2 film was annealed with forming gas (FG) or high-pressure D2 gas to investigate the effect of annealing on the characteristics of the MOSFET device. It was found that the drain current and transconductance of the D2-annealed MOSFET device increased remarkably by ~10% compared with those of FG-annealed MOSFET device, which is a definite improvement that may contribute to reliable operation of the ultra high-density MOSFET devices.

Abstract: The magnetic domain refinement was carried out by laser pulse scribing in order to reduce the core loss of SiFe. The laser pulses were generated by a Q-switched Nd:YAG laser, and the optical frequencies of the laser pulses were altered by using the SHG and the THG. The core losses were measured and analyzed to find optimal parameters of the laser treatment. The laser beam was focused with a spot size of 0.2 mm, and pulse energy of 10~30 mJ and the lines were scribed with a period of ~5 mm. The core loss was improved up to 19 % with the THG of Q-switched Nd:YAG laser in 3% SiFe.

Abstract: We investigated the feasibility of preparing nanocrystalline oxotitanium phthalocyanine (TiOPc) from crude TiOPc using liquid-phase direct recrystallization under the microwave irradiation. Different crystal structures and morphologies of TiOPc were obtained through acidtreatment and recrystallization method. The nanocrystalline TiOPcs prepared in various conditions were characterized by the means of an X-ray diffractometry (XRD), a transmission electron microscopy (TEM) and a photoconductivity measuring device.