Designing, Processing and Properties of Advanced Engineering Materials

Paper Title Page

Authors: Dal Hee Bae, Myung Hyun Lee, D.H. Kim
Abstract: Deformation behavior of Ni-based metallic glass matrix composites reinforced by short brass-fibers, synthesized by warm extrusion of gas atomized powders, has been investigated under the uniaxial compression condition at room temperature. The brass-fibers are well distributed in the metallic glass matrix and enhanced macroscopic plasticity is observed due to the formation of multiple shear bands, initiated from the interface between brass-fiber and metallic glass matrix, as well as their confinement between the brass-fibers, stemming from the constrained plastic deformation of the reinforcing brass phase.
Authors: W.B. Kim, B.J. Ye, S. Yi
Abstract: The effects of partial replacements of Zr by Y in the alloy Ni60Zr25-xAl8Yx(x=0 and 7 at %) on the crystallization behaviors of amorphous alloys were studied using isothermally heattreated ribbons. With the partial replacement, the supercooled liquid region upon continuous heating was significantly extended indicating that crystallization can be effectively suppressed by the optimum amount of Zr replacement by Y. The first phase appeared during crystallization was identified as the ternary compound AlNi2Zr while the single exothermic event could be observed upon heating the amorphous ribbons. The AlNi2Zr phase was decomposed into binary compounds upon further heating. Therefore, the extended supercooled liquid region of the alloy Ni60Zr25Al8Y7 was attributed to the suppression of AlNi2Zr phase formation by the partial replacement of Zr by Y. The effects of Y on the crystallization behaviors were discussed on the basis of atomic configuration of the supercooled liquid.
Authors: Seung Y. Shin, J.H. Kim, D.M. Lee, Jong K. Lee, H.J. Kim, Ha Guk Jeong, Jung Chan Bae
Abstract: New Cu-based bulk amorphous alloys exhibiting a large supercooled liquid region and good mechanical properties were formed in a quaternary Cu-Ni-Zr-Ti systems consisting of only metallic elements. The compositional range for the formation of the amorphous alloys that have high glass forming ability (GFA) (> 3 mm diameter) and large supercooled liquid region (> 50 K) is defined in the pseudo-ternary phase diagram Cu-Ni-(Zr, Ti). A bulk amorphous Cu54Ni6Zr22Ti18 alloy with the diameter of 6 mm can be prepared by copper mold casting. The Cu54Ni6Zr22Ti18 alloy shows glass transition temperature (Tg) of 712 K, crystallization temperature (Tx) of 769 K and supercooled liquid region (ΔTx) of 57 K. The Cu54Ni6Zr22Ti18 alloy exhibits high compressive fracture strength of about 2130 MPa with a plastic strain of about 1.5 %. The new Cu-based bulk amorphous alloy with high GFA and good mechanical properties allows us to expect the extension of application fields as a new engineering material.
Authors: Sang Wook Kim, Nam Hee Cho, Seongil Im
Abstract: Si-rich SiO2 (SRSO) films were prepared by RF magnetron sputter techniques, and the structural and optical features of nanocrystalline Si (nc-Si) embedded in the SiO2matrix were investigated in terms of post-deposition heat-treatment conditions. The SRSO thin films exhibited PL phenomena in the wavelength range of (450 ~ 500 nm). Post-deposition heattreatment at relatively high temperature like 1000 ~ 1100 °C increased the crystallinity of the films as well as the volume of the Si nanocrystallites (and SiO2), and as a result, PL intensity was enhanced in the visible light region. The nc-Si embedded in SiO2matrix is a few nanometers in size. It is believed that the Si nanocrystallites in the post-deposition annealed films are isolated and well passivated by SiO2.
Authors: J.K. Park, Chang Hoi Kim, Kyung Joo Choi, H.D. Park, Se Young Choi
Abstract: We have synthesized a Eu2+-activated Sr2SiO4yellow phosphor and investigated an attempt to develop white LEDs by combining it with a GaN blue LED chip. Two distinct emission bands from the GaN-based LED and the Sr2SiO4:Eu phosphor are clearly observed at 400 nm and at around 550 nm, respectively. These two emission bands combine to give a spectrum that appears white to the naked eye. Our results show that GaN (400 nm chip)-based Sr2SiO4:Eu exhibits a better luminous efficiency than that of the industrially available product InGaN (460 nm chip)-based YAG:Ce.
Authors: Jai Hyun Kim, Kyung Shin Koh, Woong Kil Choo
Abstract: We have investigated the ferroelectric and electrical properties of PZT 40/60 films on the bottom La1/2Sr1/2CoO3(LSCO) electrode. The LSCO bottom electrode was sputtered on the SiO2/Si(100). As the annealing temperature of PZT capacitors on the LSCO is increased, the ferroelectric properties gradually increase with the annealing temperature up to 650°C. However, for the PZT capacitors annealed above 650°C, electrical measurement cannot be performed.
Authors: Sung Kil Hong, J.Y. Moon, W.K. Kee, Si Young Chang
Abstract: TiO2, Al2O3 and SiO2 single layer films were deposited in the oxygen gas atmosphere by plasma assisted e-beam evaporation(PAEBE) at various RF power and low temperature on p-type Si wafer(100) and glasses. The effects of plasma assistance on the optical and microstructual properties of three kinds of single layer films were investigated. In addition, those of the films were compared with the films deposited by conventional e-beam evaporation at high temperature(100~ 300 °C) condition. The n-values of TiO2 films gradually increased from 2.405 (λ =550nm) at 150W RF power to 2.54 at 200W. The XPS result indicated that TiO2 films deposited without plasma assistance have Ti2+, Ti3+ and Ti4+ charge states. Whereas the films prepared at 200W, 250W RF power have only Ti3+and Ti4+ charge states. Al2O3 layers had maximum reflective index (n=1.604 at λ =1200nm) at 200W RF power, but slightly decreased to 1.57 at 400W RF power. The measured transmittance spectra show that all the sample deposited by PAEBE are free from absorption and homogenous as well as the surface roughness, packing density and absorption of TiO2, Al2O3 films improved dramatically compared with films deposited conventional e-beam evaporation. However, The reflective index and surface morphologies of SiO2 films had no changed with increasing RF power.
Authors: Hirohisa Sato, K. Ochi, Naoki Kamegashira
Abstract: Ln2MnNiO6 were synthesized by the usual ceramic method for Ln = Sm, Eu, Gd, Tb and Dy and by the wet method for Ln = La, Nd Ho and Er. Heat capacities of these compounds were measured by using DSC and ACC. The thermal anomalies accompanying by magnetic transition from ferromagnetism to paramagnetism were observed for some rare earths and the magnetic contribution of heat capacity was estimated
Authors: G. Chen, Hiromi Nakano, Hirohisa Sato, Naoki Kamegashira
Abstract: The complex oxide Eu2Mn2/3Nb4/3O7 structurally characterized by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results of XRD structure analysis shown that the X-ray diffraction profile calculated with monoclinic C2/c model is in a good agreement with the observed X-ray diffraction patterns. In addition to fundamental reflection peaks, super lattice lines could be also assigned with C2/c symmetry. Therefore, it is derived that Eu2Mn2/3Nb4/3O7 phase has not a pyrochlore structure but has a zirconolite-type structure (pyrochlore-related structure) with a C2/c space group. Eu2Mn2/3Nb4/3O7 has two kinds of distorted MO6 octahedra and HTB layers, which deviates from the regular forms. The microstructure of Eu2Mn2/3Nb4/3O7 investigated by TEM also proved the results of XRD structural analysis. It was viewed that HRTEM image of a characteristic twin structure in Eu2Mn2/3Nb4/3O7 which a zirconolite-type structure has.
Authors: Dong Ho Park, Yeon Gil Jung, Ung Yu Paik, Jeong Wook Kim, Jin Young Yu
Abstract: Herein, we report the effects of external electrode and heat treatment on stress anisotropy and residual stress on margins of MLCCs in each direction perpendicular and parallel to internal electrode at length plane. The residual stresses estimated using an indentation method are compared in regions with and without the external electrode as a function of heat treatment. The stress anisotropy is not affected by both heat treatment and external electrode, showing residual compressive stresses in all directions. However, at the boundary, the crack length in the perpendicular direction is longer than that in the parallel direction.

Showing 231 to 240 of 328 Paper Titles