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Authors: B.J. Kim, K.S. Park, J.S. Ryu, Young Hoon Moon
Abstract: Aluminum alloys have a high potential for weight reduction in automotive and other applications, but they have a relatively low tubular hydroformability at room temperature. Hot working processes are commonly used for bulk metal forming, such as forging and rolling, but rare in sheet metal forming like hydroforming. The hydroformability of aluminum alloys can however be enhanced significantly at elevated temperatures. In this study, the hydroformability of aluminum alloys at elevated temperatures has therefore been investigated by using a specially designed induction heating system. The formability characteristics at high temperatures were obtained by a T-fitting forming test as well as a free bulge test. The effects of the process parameters such as an internal pressure and temperature on tubular forming limits have mainly been investigated and the results are presented in this paper
Authors: B.S. Ham, Beong Bok Hwang, D.H. Jang
Abstract: The yield criterion describing asymmetric behavior of powdered metal compacts in tension and compression is introduced by modifying that used for sintered powdered metals. The plasticity theory related to the modified yield criterion is reviewed and summarized for a powdered metal compact. The constitutive equation is applied to the variational principle and its discritization is also introduced. Axisymmetric die pressings with copper powders were performed to see the deformation mechanics of hollow three-level parts. The simulation includes two different types of multiple-motion tooling compaction of a Class IV part of hollow three-level component. Predictions are made for density distributions, load-stroke relationships, average density as function of height, pressure distributions along the die-walls and punches, average compact densities at each level, and energy consumption for each pressing. The information from simulation can be used to synthesize the various punch motions in a multiple action tooling system.
Authors: Woong Ho Bang, C.S. Kang, J.H. Park, Kyu Hwan Oh
Abstract: Under a high-pressure condition, the wear characteristics of alloyed and unalloyed ductile cast iron were investigated. Mn, Cu, Si and Mo were chosen as alloying elements, and their effects on mechanical properties of hardness and toughness were correlated with wear properties. In most cases, high-pressure wear of alloyed and unalloyed DCI were sequentially developed by mild wear region followed by severe wear. The transition of wear mode was indicated by the drastic increase of friction coefficient and wear rate. The observation of worn surface at mild-wear region suggested that wear had been concentrated at graphite phases, whereas severe wear mode damaged both of graphite and matrix. It was found that DCI alloyed with Si-Mo exhibited the most prominent resistance to the beginning of severe wear while the toughness of DCI was also a crucial factor.
Authors: Y.R. Yoo, H.Y. Chang, Yong Bum Park, Y.S. Park, Tai Joo Chung, Young Sik Kim
Abstract: In general, thermal treatment at 500oC ~ 900oC ranges depending upon alloy composition of stainless steels can sensitize the steels and promote the intergranular cracking, and their intergranular corrosion resistance is decreased. These behaviors seem to be related to the change of microstructures. So, heat treatment at that temperature range should be avoided in fabrication, especially welding of stainless steels. In this work, it is focused on the effect of thermal treatment on caustic stress corrosion cracking of super austenitic stainless steel - S32050 The low temperature thermal treatment increased greatly the resistance to caustic SCC than those of annealed specimen. This enhancement might be closely related to the reduction of residual stress and slightly large grain, but its resistance was not affected by the anodic polarization behavior.
Authors: Il Ho Kim, S.I. Kwun
Abstract: The oxidation characteristics of a Ni-20Cr-20Fe-5Nb-1Y2O3 alloy and a Ni-20Cr- 20Fe-5Nb alloy both with ultra-fine grains were compared with those of commercial Inconel 718 and PM1000 alloys. The oxidation resistance of the Ni-20Cr-20Fe-5Nb-1Y2O3 alloy was superior to that of both the Ni-20Cr-20Fe-5Nb and commercial Inconel 718 alloys. This was attributed to the suppression of successive oxidation via the oxide formed during the oxidation of the ODS (oxide dispersion strengthening) alloy. It was confirmed that the prior powder boundary is the site where the oxide grows continuously during ODS alloy oxidation.
Authors: Gopal S. Upadhyaya, Emeritus Fellow
Abstract: The detailed knowledge of structure of materials whether crystalline or noncrystalline, is essential in fully understanding its impact on materials engineering. By structure, we mean structure at any scale from electronic to macro. The properties, processing and performance of materials are directly interwoven with the structure. In the present paper the whole strategy of materials engineering education keeping in view structure in the centre has been developed. Pedagogically such a treatment is most sound.
Authors: Jeff T.M. de Hosson, Hans A. De Raedt
Abstract: This paper aims at applying advanced transmission electron microscopy (TEM) to functional materials, such as ultra-soft magnetic films for high-frequency inductors, to reveal the structure-property relationship. The ultimate goal is to delineate a more quantitative way to obtain information of the magnetic induction and local magnetization. Nano-crystalline Fe-Zr-N films have been prepared by DC magnetron reactive sputtering with a thickness between 50 and 500 nm. Conventional TEM and selected area diffraction (SAD), reveal crystallites of sizes ranging between 2 and 30 nm. The films showed a granular or hillock type of roughness with an rms amplitude of 5 nm. In particular this paper concentrates on an analysis of phase maps in electron holography and intensity maps in Lorentz transmission electron microscopy including the thickness variation over the sample. For a particular statistical description of the roughness and values for the roughness it is shown that analytical expressions can be obtained. We demonstrate that starting from the concept of the vector potential in classical electrodynamics these results can be achieved assuming independent stationary Gaussian distributions for the height correlation functions.
Authors: L.M. Liu, Shao Qing Wang, Heng Qiang Ye
Abstract: We employ density functional calculations to investigate the doped Al/TiC interfaces. The effects of different segregation atoms are discussed. The results show that the different transition metal atoms have different effects on the adhesion. Results of analysis of atom size and electronic structure have shown that both atom size and activity of the doped atom influence on the adhesion. Our results are consistent with other results of doped metal-oxide interface.
Authors: Yan Rong Li, Jin Long Li, Ying Zhang, Xin Wu Deng, Fan Yang, Wei Dong Fei
Abstract: Well-ordered self-assembled SrTiO3 thin film, as a template for complex oxide quantum wires, was fabricated on LaAlO3 (100) single crystal substrates with laser molecular beam epitaxy. The self-assembled growth was in-situ monitored by reflective high energy electron diffraction. The morphology evolutions of the films as a function of thickness were studied by ex-situ atomic force microscopy. As the thickness of the films increased from 3.875nm to 46.5nm gradually, the compressive stress-induced SrTiO3 films exhibited a periodic well-ordered ripple structure, which formed a unique nanoassembled template for the fabrication of quantum wires. Small angle X-ray scattering technique was employed to investigate the structure. Symmetric satellite peaks were discovered, indicating the well-ordered superstructure. In contrast, the similar superstructure was not observed during the growth of the tensile stress-induced LaAlO3 films on SrTiO3 substrates. The Compressive stress was considered as the main reason of the self-assembled growth, and systematical elucidation about strain mechanism was discussed. These results might provide an efficient method for the controllable formation of well-aligned template of quantum wire for complex oxide with desirable structure via proper modulation of strains.
Authors: Y.Y. Zhao
Abstract: A model has been developed for the velocity and temperature evolution of a metal alloy droplet with travel distance in centrifugal atomisation. The droplet velocity decreases rapidly with increasing travel distance. The degree of droplet cooling at a certain travel distance decreases with increasing droplet velocity, increasing diameter and decreasing temperature, and is also affected by the droplet physical properties. The solidification of the droplets is largely dependent upon the latent heat removal.

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