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FE-MILC(Field Enhanced Metal Induced Lateral crystallization) growth rate of amorphous silicon thin film and its microstructure were intensively investigated. In the case of applying E-field, the growth rate was drastically increased toward (+) pole direction, while the growth rate toward (-) pole was decreased. It was revealed that the microstructure of MILC area was changed by applying E-field and its direcction, which was investigated by FE(Feild-Emission)-SEM. These Phenomena can be explained by hopping model of Ni ion and Ni vacancy in the NiSi_(2) phase and its interface at the front pf MILC region. (Received February 2, 2004)

keyword : MILC, FE-MILC, Ni ion Ni Vacancy Hopping Model, FE-SEM, Polycrystalline silicon

Dynamic deformation and fracture behavior of ultra-fine-grained low-carbon steels fabricated by equal channel angular pressing (ECAP) was investigated in this study. Dynamic torsional tests were conducted on four steel specimens, two of which were annealed after ECAP, using a torsional Kolsky bar, and then the test data were compared via microstructures, tensile properties, and fracture mode. The ECAP`ed specimen consisted of very he, elongated grains of -0.5 μm in size, which were slightly coarsened and had an equiaxed shape after annealing. The dynamic torsional test results indicated that maximum shear stress decreased, while fracture shear strain increased, with increasing annealing time. Some adiabatic shear bands were observed at the gage center of the dynamically deformed torsional specimen, and their width was smaller in the ECAP`ed specimen than in the 1-hr annealed specimen, although they were not found in the 24-hr annealed specimen. Ultra-he, equiaxed grains of 0.05-0.3 μm in size were formed inside the adiabatic shear band, and their boundaries had characteristics of high-angle grain boundaries. These phenomena were explained by dynamic recovery and recrystallization due to the highly localized plastic deformation and temperature rise inside the adiabatic shear band. (Received February 11, 2004)

keyword : Dynamic torsional test, Ultra-fine-grained low-carbon steel, Equal channel angular pressing, ECAP, Adiabatic shear band, Annealing

This study is concerned with the effects of microstructure on inverse fracture in the hammer-impacted region during drop-weight tear test(DWTT) of three high-toughness API X70 pipeline steels. Pressed notch or Chevron notch DWTT and Charpy V-notch impact test were conducted on the rolled steel specimens, and the results were discussed in comparison with the data obtained from tensile and Charpy impact tests of pre-strained specimens. In the hammer-impacted region of the DWTT specimens, cleavage-type inverse fracture appeared, and its fracture area was correlated well with upper shelf energy (USE) obtained from the Charpy impact test and with microstructure. The steel specimens having higher USE or having coarse polygonal ferrite had the larger inverse fracture area than those having lower USE or having fine acicular ferrite because of the larger compressive pre-strain induced by work hardening of the hammer-impacted region. These results were confirmed by relating to the Charpy impact test data of pre-strained steel specimens. (Received January 19, 2004)

keyword : High-toughness pipeline steel, Inverse fracture, Drop-weight tear test, DWTT, API RP 5L3 specification

Effects of aging treatment at 700℃ on high temperature strength of Nb containing ferritic stainless steels were compared with those of Nb free steels. Hot tensile tests were carried out at 700℃ after the aging for different aging times using Gleeble 1500. The high temperature strength of Nb free steels decreased with increasing aging time mainly due to grain growth. However, the reduction of the high temperature strength in Nb (0.38 wt％) containing steels occurred by Nb precipitation. It was observed that Fe₂Nb(Laves phase), NbC, NbN and Fe₃Nb₃C were precipitated out in 0.01C-0.38Nb steel, while only NbC, NbN was formed in 0.03C-0.38Nb steel during the aging at 700℃. This was well agreed with the calculated equilibrium fraction of precipitates. The coarsening rate of Fe₂Nb was measured faster than that of NbC. Coarse Fe₂Nb particles formed during the aging were very detrimental to high temperature strength. However, fine Fe₂Nb precipitates formed during the tensile test contributed to high temperature strength in 0.01C-0.38Nb steel.

keyword : Ferritic stainless steels, High temperature strength, Nb precipitation

Sliding wear behavior of 7075 Al alloy matrix composites was investigated. Reinforcements of the composite were SiC, TiC, and B_(4)C particles with various size and volume fractions. Sliding wear tests were carried out in an ambient atmosphere using a pin-on-disk wear tester with various loads of 5N-150N against a bearing steel ball counterpart. The composites showed higher wear resistance than the monolithic matrix alloy. Sliding wear of the composites proceeded by a grinding mechanism at low loads and by a delamination of a deformed layer at high loads. Wear resistance of the composites increased with the size and volume fraction of the reinforcements, and the increase was more significant at high applied loads. Deformation of the matrix was found to control the wear at high loads. The effect of heat treatment and reinforcement variation including size, volume fraction and species on the wear was discussed in connectin with the deformation of the matrix. (Received September 19, 2003)

keyword : Sliding wear, MMCs, SiC, TiC, B4C, 7075 Al alloy, T6 heat treatment

Diamond-like carbon (DLC) films have several advantages in applications such as high hardness, chemical inertness, low friction and electrical insulation. Furthermore, DLC-coated STS 316L films have been reported to have a good biocompatibility, such as the absence of inflammatory response. Thus, corrosion resistance is the first consideration for the biomaterials to be used in the body. DLC films have been deposited onto substrates of STB 316L for artificial hip joints using r.f PACVD (plasma-assisted chemical vapor deposition) with C_(6)H_(6) and mixture of C_(6)H_(6) and SiH_(4) as the process gases. Three kinds of DLC-coated films were prepared as a function of diverse bias voltage and Si incorporation. Corrosion behavior of DLC films was investigated by electrochemical techniques (potentiodynamic polarization test and electrochemical impedance spectroscopy) and surface analyses (atomic force microscopy and scanning electron microscopy). The electrolyte used in his test was a 0.89％NaCl solution of pH 7.4 at temperature 37℃. Electrochemical measurements showed that DLC films with higher bias voltage and Si incorporation could improve corrosion resistance in the simulated body fluid environment. (Received December 5, 2003)

keyword : Hip joint, DLC, Porosity, SEM, AFM, EIS

High velocity oxy-fuel sprayed 34Co-32Ni-22Cr-10Al-0.4Ir coatings were oxidized between 1000 and 1200℃ in air, and the oxide scales were investigated by XRD, SEM/EDS, and EPMA. The unoxidized coatings consisted mainly of γ-Ni_(3)Al, with some y-Ni and a meager amount of Cr_(2)O_(3). The major oxide formed on the coatings was α-Al_(2)O_(3). Additionally, spinels of CoCr_(2)O_(4) and CoAl_(2)O_(4) coexisted. Neither Ni- nor Ir-xoides were detected by XRD owing to thermodynamic nobility that resist oxidation or their small amount in the oxide scale. Iridium seemed to deter the formation of sound oxide scales. (Received November 17, 2003)

keyword : NiCoCrAlIr, Thermal barrier coating, High velocity oxy-fuel spraying

Paint coating process on steel sheet has to be carried out for producing prepainted steel sheet by continuous process. After coating process, drying processes are needed. Temperature control of oven system directly affects on the product quality, such as, a coherence of coating and state of surface. In this study, heat transfer coefficients were calculated by 3-dimensional heat flow analysis from hot wind of nozzle to steel sheet and values of PMT(Peak Metal Temperature) of steel sheets were predicted by adapting that value to 2-dimensional analysis and using the coefficients. Conditions of numerical analysis were obtained from orthogonal arrary which is known as Taguchi method. Coefficients of heat transfer coefficient equation were derived from the second order regression model. By comparing numerical analysis with experimental results, the accuracy of numerical analysis was verified. Moreover we analyzed the effect of various conditon of factors, such as velocity and thickness of steel sheet, temperature of hot wind and the type of steel sheet. (Received December 17, 2003)

keyword : PMT prediction, Drying process, Heat transfer coefficient, Numerical analysis, Orthogonal arrary

"he removal of lead from electric arc furnace (EAF) dust is important in the process for recovering zinc by a reduction-volatilization method. In this study, experiments on kinetics of the volatilization reaction of lead by chlorine components as NaCl and KCl contained in the EAF dust were carried out in the temperature range of 973 to 1223 K under an air atmosphere using a weight-loss technique. As a result, the volatilization ratio of lead was about 99.0% at the temperature of 1223 K and the reaction time of 180 min. Jander equation was found to fit well the volatilization reaction rate over the entire temperature range. The volatilization reaction of lead is rate controlled by solid-solid diffusion. An activation energy of 175 kJ/mol(41.8 kcal/mol) was obtained. (Received January 8, 2004)

keyword : EAF dust, Reduction-volatilization, Lead, Zinc

The separation and extraction of copper from waste water solutions by the liquid surfactant membrane process using LM84 as an extractant and Span 80 as a surfactant were investigated . In extraction, the extraction rate of copper was greatly accelerated by the presence of sodium acetate and with the increase of pH in the aqueous feed solution. The optimum concentrations of LIX84 and Span 80 in the membrane phase were 7-10 vol. % and 2.5-3vol. %, respectively. Experiments also showed that the concentration ratio of copper was greatly enhanced with the decrease of the ratio of V_(e) and V_(w) and with the decreasing of A/O ratio. After the extraction process, the concentration of copper in the raffinate solution reduced to 1-2 ppm, and the concentration of copper in the internal aqueous solution increased to 20 gll. (Received February 11, 2004)

keyword : Copper, Extraction, LIX84, Span80, Liquid surfactant membrane