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Authors: I.S. Kim, H.S. Kim, I.C. Hur, K.S. Son, Je Hyun Lee, J.H. Yoon, H.S. Kim
Abstract: ASTM A355, SUS422 and Nimonic 901 steel were nitrided and their wear characteristics such as the wear coefficient, amount of wear, shape and composition of wear debris were evaluated. Fe3N and Fe4N were observed in the nitrided layer of ASTM A355. Fe3N, Fe4N and CrN were appeared in the nitride of SUS422. However, only CrN phase was observed in the layer of Nimonic 901. The amount of wear and wear coefficient for the nitride specimen decreased remarkably compared with non-nitrided specimens. Also, the surface hardness and ductility increased and small debris was formed in the nitrided specimen.
Authors: K.S. Park, B.J. Kim, Young Hoon Moon
Abstract: Tube hydroforming provides a number of advantages over conventional stamping process, including fewer secondary operations, weight reduction, assembly simplification, adaptability to forming of complex structural components and improved structural strength and stiffness. It can produce wide range of products such as sub-frame, engine cradle, and exhaust manifold. In this study, the effect of heat treatment conditions, such as post seam annealing(PSA) and bright annealing(BA), on the ovality and hydro-formability of steel tubes has been investigated. Hydroformability has been estimated as the bulging height obtained depending on the various process parameters such as an internal pressure, axial feeding, and heat treatment conditions. The ovality and forming height were found to strongly depend on material properties after heat treatments.
Authors: Byeong Soo Lim, C.S. Jeong, Si Yon Bae, Seog Hyeon Ryu, Jeong Tae Kim, Y.T. Keum
Abstract: The initiation and growth of internal defects usually cause the failure of long term operated structural components at high temperature. Therefore, by investigating the internal defects of material, the integrity of the system can be maintained and the unexpected failure can be prevented. The main purpose of this study is to investigate the possibility of the application of ultrasound to the measurement and estimation of the creep damage. In this study, the phased array ultrasound and backward ultrasound were employed to detect the internal defects caused by creep. Using the newly developed P92 steel, both creep and NDE ultrasound tests were performed. The results of defect inspection were checked by microstructure examination. Reliable information on the size and position of crack were obtained and successful estimation of the amount of micro-voids and their distribution proved to be obtainable by the ultrasound inspection technique. The width of the creep degraded zone was confirmed by the width of ultrasonic signal, and the severity of degradation was confirmed by ultrasonic amplitude.
Authors: Tamaz Eterashvili, M. Vardosanidze
Abstract: The microcrack tip plastic zone sizes in austenitic steels are measured using REM and interference microscope. It is shown that the plastic zone size varies from 300µm to 350µm. The importance of determining this parameter is discussed. Based on the analysis of the conventional continuum equations of linear-elastic approach a simple formula is derived for calculation of plastic zone size, R=d E/2π σF, establishing relation between the plastic zone radius (R), microcrack width (d), elasticity modulus (E) and the yield strength of the material (σF). The measured values of plastic zone size are in a good agreement with those reported in literature, and calculated by the above formula.
Authors: H.D. Joo, J.S. Kim, C.W. Bark, J.Y. Kim, Yang Mo Koo, Nobumichi Tamura
Abstract: In-situ measurement of local orientation and strain Has Been carried out for a copperpolycrystals under a uniaxial loading using a synchrotron x-ray microdiffraction method at the Advanced Light Source. The heterogeneities of deformation-induced microstructure within single grains were observed. There were differences in the selection of simultaneously acting slip systems among neighboring volume elements within a grain.
Authors: J.H. Lee, H.J. Oh, Y. Jeong, Y.J. Lee, J.S. Kim, C.-S. Chi
Abstract: The anodic titanium dioxide (TiO2) films for photocatalyst were prepared by anodization in acid solution. The characteristics of surface layer and the photocatalytic efficiency of the anodic film have been investigated. The chemical states of anodic film were analyzed using XPS, and the photocatalytic efficiency was evaluated by the degradation rate of aniline blue. From XPS results the component elements of the electrolyte, P and S, were observed in the anodic film, which were incorporated from the electrolyte into the oxide layer during anodization. The porous TiO2 film exhibited high photocatalytic efficiency for degradation of aniline blue.
Authors: Kee Do Woo, S.W. Kim, Dong Ki Kim
Abstract: It is convenient to analyze the distribution of boron in high carbon steel with boron, simply using neutron-induced radiography with a neutron fluency of 1.9 x 1013 [cm-2]. It was revealed by the neutron-induced radiography that the distribution of boron was dependent on boron contents, graphitizing temperature and time. The density of boron track increased with increasing boron contents. But the density of the boron track and graphite in high carbon steel graphitized at 700°C is higher than that of high carbon steel graphitized at 750°C. The density of graphite in high carbon steel also depends upon the content of boron and the graphitizing temperature. The shape of the boron track was changed from sphere to rod type when annealed at 800°C, in steel containing 50ppm of boron, due to different phases of boride. The distribution of boron segregation or boronrich precipitates in high carbon steel was well documented with a neutron-induced radiography, but the direct relationship between graphite and boron was not clarified by it. Furthermore, the analysis of electron probe X-ray microanalyzer (EPMA) also showed that the high amount of boron coexisted with carbon in graphite in high carbon steel.
Authors: Z.J. Ding, H.M. Li, X. Sun
Abstract: Topographic imaging of materials by a scanning electron microscope (SEM), using the secondary electrons and backscattered electrons escaped from the surface under a primary electron beam bombardment as image signals, has been a very important technique in application to material sciences and the related fields. In this work we have developed a new parallel Monte Carlo simulation program to calculate SEM images especially for an inhomogeneous sample with a complex structure, which may be constructed with some basic geometrical shapes containing different materials. The ray-tracing arithmetic is employed to obtain the corrected electron flight step length for electrons across the interface of different zones containing distinct elements. We have done simulations for several specimens with artificial structures at the nm level. The results illustrate some new characters of image contrast, demonstrating the applicability of this image simulation technique to the characterization of nano-scale structure.
Authors: Yong Gang Luo, Linda Zou, Eric Hu
Abstract: The porous TiO2 pellets were prepared based on pigment grade titaina, P25 titania powder and titanium(IV) butoxide. The characterization was done with X-Ray diffraction, scanning electron microscopy and BET measurements. The result shows that TiO2 pellets by using titanium(IV) butoxide with some addictive have the best surface porosity, with specific surface area of 196.9m2/g. For pigment grade titania and P25 titania powder, it is still effective to enhance the surface area after reassembling. The surface area increased from 11.6 to 29.2 m2/g for pigment grade titania and from 50 to 84.4 m2/g for P25 titania powder. Furthermore, it has been investigated on how to optimize and get the highest surface area by controlling the sintering temperature, reaction temperature, pH of solution, and the amount of alcohol and addictive of surfactant during preparation. The experimental photocatalytic degradation of acetone and toluene was performed using titania pellets made from P25 titania powder.
Authors: Sun Keun Hwang, D.H. Jang, B.D. Ko, Beong Bok Hwang
Abstract: Numerical simulations are applied to investigate the simultaneous radial-forward extrusion process in a combined extrusion such as subsequent radial-forward extrusion after radial extrusion. Design factors for the process such as gap height, deflection angle into annular gap and frictional condition are employed in the analysis. The analysis is focused to see the influence of design factors on the maximum force requirement for the forming process. One of the selected simulation results is compared with the experiments in terms of load-stroke relationships. The pressure distributions exerted on the die-wall interfaces are also investigated to reveal if the tooling system is safe, especially the die set. The plastic stress-strain relationship is derived analytically from the material constants used in elastic deformation analysis. It is revealed from the simulation results that the influence of the deflection angle on the maximum force requirement for the process is greatest among design parameters. AA 6063 alloy is selected as a model material for the analyses in this study.

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