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The effect of the strain rate at a range of 10?4 ~ 3 × 102 s?1 on the tensile characteristics of a olled AZ31 magnesium alloy was studied. The normal tensile specimens were tested using a high rate hydraulic testing machine. Specimens were machined from four sheets with different thicknesses, 1, 1.5, 2 and 3 mm, along three directions, 0˚, 45˚, and 90˚to the rolling direction. The results revealed that all the specimens had a positive strain rate sensitivity of strength, that is, the strength increased with increasing strain rate. This is the same tendency as other automotive steels have. Our results suggest that the AZ31 magnesium alloy has better collision characteristics at high strain rates because of improved strength with an increasing strain rate. Ductility decreased with an increasing strain rate with a strain rate under 1 s?1, but it increased with an increasing strain rate over 1 s?1. The mechanical properties of the AZ31 magnesium alloy depend on the different microstructures according to the thickness. Two and 3 mm thickness specimens with a coarse and non-uniform grain structure exhibited worse mechanical properties while the 1.5 mm thickness specimens with a fine and uniform grain structure had better mechanical properties. Specimens machined at 0˚ and 45˚to the rolling direction had higher absorbed energy than that of the 90˚specimen. Thus, we demonstrate it is necessary to choose materials with proper thickness and machining direction for use in automotive applications. (Received December 28, 2012)

keyword : metals, rolling, mechanical properties, tensile test, high strain rate

The mechanical properties and molecular structure of rubber materials for reducing the vibration of elevator cabins were studied with respect to the hardnesses change to confirm the degradation behavior by temperature (85 ℃) and humidity (85% R.H.). To examine the effects of hardness on the mechanical properties after thermal and hydrothermal aging, the international rubber hardness degree (IRHD), tensile strength, and elongation % were compared with the elastic modulus as a function of degradation time. The microstructure showed that the crack growth of the rubber material with high hardness was fast after hydrothermal aging. It originated from a C = C bonding decrease, and the C = O and C-O-C bonding were increased by the penetration of humidity. In the results of solid-state 13C nuclear magnetic resonance (NMR) spectroscopy to confirm the molecular structure, several peaks were assigned to respective vulcanized structures along with mechanical properties. Therefore, the degradation behavior after thermal/ hydrothermal aging was different according to low/high hardness: The mechanical properties of the rubber material with high hardness rapidly decreased due to the high density of cross-links and chain scission. (Received March 18, 2013)

keyword : rubber materials, international rubber hardness degree, mechanical properties, solid state 13C NMR, polymer structure

CrAlMgN films were deposited on SKD 11 tool steel by cathodic arc plasma deposition. The oxidation characteristics of the films were studied at a temperature range from 800 to 1000 ℃ for up to 50 h in air. The films displayed good oxidation resistance owing to the formation of oxide crystallites of Cr2O3 and α-Al2O3. The oxidation of CrAlMgN film occurred via complex routes such as outward diffusion of Cr, Al and nitrogen and inward transport of oxygen. The apparent activation energy for oxidation of the CrAlMgN film was determined to be 200 kJ/mol. Iron oxides were detected for specimens oxidized at 1000 ℃. (Received March 18, 2013)

keyword : CrAlMgN thin film, surface modification, oxidation, scanning electron microscopy

The degradation behavior of TiN coatings with different thicknesses deposited on Inconel 617 substrates was investigated in terms of surface and interface microstructures after pulsed laser thermal shock. The specimens with coating thicknesses of 1.0 and 4.5 ?m were exposed to repetitive laser shock using a pulsed laser ablation system (LSX-213). The TiN coating with a 1.0 ?m thickness contained cracks along the columnar grains in the coating layer, and spalling and delamination with interface cracks appeared with an increase in the number of ablations. In contrast, the 4.5 ?m thick TiN coating still maintained adhesion to the substrate until the substrate elements dissolved out to the surface. Surface and cross-sectional observation showed that the pulsed laser seems to simultaneously induce normal and shear stress to the surface at the ablated spots with high thermal stress. (Received March 18, 2013)

keyword : thin films, sputtering, fracture, focused ion beam, FIB, laser thermal shock

Atmospheric plasma surface treatment (APST) was applied on the soda-lime glass and silicon wafer(Si-wafer) substrates for surface modification. The surface energy for the surface treated samples was measured using the wetting angle. The effect of APST on surface energy and interface properties between sputtered chromium (Cr) coatings and substrates was investigated. The surface energy increased linearly and reached a maximum value of 74 mJ/m2 by APST. The increase in surface energy is due to the increased value of the polar component in surface energy. When the samples were exposed to the air, the increased surface energy decreased and tended to have hydrophobicity. The work of adhesion for the surface treated samples was calculated using the data of surface tension for water. We demonstrated that the trend of work of adhesion for the samples was similar to the change of adhesion strength between sputtered Cr coatings and the surface treated substrates. (Received March 13, 2013)

keyword : glasses, surface modification, wetting, optical microscopy, surface energy

This study investigated the high temperature oxidation behaviors of Fe-Cr-Al powder porous metal (565 μm pore size) and a strip (as a reference of bulk material). A 24-hour TGA test was conducted at three different temperatures, 900 ℃, 1000 ℃, and 1100 ℃. High temperature oxidation results showed that the strip exhibited even higher levels of oxidation resistance than that of porous metal regardless of temperature. Oxidation weight gain gradually increased with increasing oxidation temperature. In the porous metal oxidized at 900 ℃ and 1000 ℃, the oxides Al2O3 and Cr2O3 were mainly observed. The porous metal oxidized at 1100 ℃ also revealed the presence of Fe-based oxides in a large quantity in addition to the oxides formed at lower temperature. The porous metal with a larger specific area represented increasingly faster dwindling of Al and Cr elements and easy progress to internal oxidation, compared to the oxidation of the bulk strip. (Received January 28, 2013)

keyword : Foams/Thin films, High temperature oxidation, TGA, thermo gravimetric analysis, Powder porous metals

Co or Ni was added to cemented (W,Ti)C as a binder for forming composite structures. The high cost of Co or Ni and the low corrosion resistance of (W,Ti)C-Co or (W,Ti)C-Ni cermet have generated interest in recent years in the search to find alternative binder phases. It has been reported that aluminides have a higher oxidation resistance, a higher hardness and are cheaper materials than Co and Ni. Using a pulsed current activated sintering (PCAS) method, the densification of (W,Ti)C and (W,Ti)C-NiAl3 hard materials were accomplished within 3 minutes. The advantage of this process is not only rapid densification to near theoretical density but also the prohibition of grain growth in nano-structured materials. Highly dense (W,Ti)C and (W,Ti)C-NiAl3 with a relative density of up to 99% were obtained within 3 minutes by PCAS under a pressure of 80 MPa. The average grain sizes of the (W,Ti)C was lower than 100 nm. The hardness and fracture toughness of the dense (W,Ti)C and (W,Ti)C-NiAl3 produced by PCAS were also investigated. (Received March 22, 2013)

keyword : nanomaterials, sintering, hardness, fracture toughness

In this work, MgH2 was used as a starting material. Samples with compositions of 94 wt% MgH2- 6 wt% Ni, 88 wt% MgH2-12 wt% Ni, 85 wt% MgH2-15 wt% Ni, and 82 wt% MgH2-18 wt% Ni were prepared by reactive mechanical grinding. The variations of the hydriding and dehydriding properties at the first hydriding-dehydriding cycle with Ni content were then investigated. MgH2-12Ni had the highest hydriding rate and the largest quantity of hydrogen absorbed for 60 min, followed in order by MgH2-6Ni, MgH2-15Ni, and MgH2-18Ni. The effects of reactive mechanical grinding were the strongest in the MgH2-12Ni sample. As the Ni content increased from 6 wt% to 18 wt%, the percentage of the hydrogen quantity desorbed for 30 min to the theoretical capacity increased. (Received October 5, 2012)

keyword : hydrogen absorbing materials, mechanical alloying/milling, microstructure, X-ray diffraction, MgH2-x wt% Ni

We propose a working electrode with a scattering layer inserted for dye-sensitized solar cells (DSSCs) with the following structure: glass/FTO/blocking layer/TiO2/scattering layer/dye/electrolyte/Pt/ FTO/glass. A working electrode without a scattering layer was also prepared using a similar method for comparison. The microstructure was examined by optical microscopy and field emission scanning electron microscopy (FE-SEM). The photovoltaic properties, such as the short circuit current density (Jsc), open circuit voltage (Voc), fill factor (FF), energy conversion efficiency (ECE) and impedance were characterized using a solar simulator and potentiostat. FE-SEM confirmed that the blocking layer with 20 nm grains and the scattering layer with 350-450 nm grains had been prepared. The Jsc and Voc increased, and impedance analysis revealed a decrease in the electron transfer resistance and electron recombination resistance at the TiO2/electrolye interface. The ECE with the scattering layer was 6.35%, which was 20% higher than that observed in the ECE without the scattering layer. (Received January 3, 2013)

keyword : solar cells, sputtering, optical properties, optical microscopy, scattering layer

Carbon nanotubes (CNTs) have recently emerged as a reinforcement for metal matrix composites (MMCs), but the problem of dispersion of CNTs and the interface between the metal matrix (MM) and CNTs makes it difficult to utilize MM-CNTs composites. In this study, in order to decrease the floatation and clustering of CNTs and improve the wettability between CNTs and an Al melt, CNTs were decorated with Cu particles by a metal displacement reaction. To investigate the effects of their morphology on the metal displacement reaction, flake-and spherical-type Zn powders were respectively added to precipitate Cu particles in a Cu salt solution. The flake-type Zn powders were fully displaced by Cu in the solution, but in case of the spherical-type Zn powders, Cu was deposited on the surface only. The reaction temperature did not affect the characteristics of the metal displacement reaction. This result was attributed to the fact that the rate of the metal displacement reaction was decreased in ethanol due to an increase in viscosity in diffusion of Cu2+ from the solution to the metallic Zn surface. Cu/CNTs nanocomposite powders were manufactured by the addition of copper chloride (CuCl2) to an ethanol suspension containing pre-treated CNTs. The CNTs were mixed with precipitated Cu nanoparticles and others were entrapped between the Cu particles or agglomerates. It was attributed to the lack of the active sites on the CNTs surface for the nucleation of Cu crystal. (Received November 1, 2012)

keyword : Composites, metal displacement reaction, inferfaces, scanning electron microscopy, carbon nanotube