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Various Cu-Zr binary amorphous alloys, which exhibit different strains and atomic packing densities, were synthesized to investigate the crucial factor governing the degree of the plasticity. It was found that there is a linear proportion between the atomic packing density and the plasticity such that amorphous alloys with lower packing density exhibited higher plasticity and vice versa. Considering that the plasticity of the amorphous alloy is closely related to the facility of the structural rearrangement during the process of loading, the role played by the atomic packing density on the plasticity can be quantified by measuring the effective activation energy for overall crystallization. Indeed, there was an inverse proportionality between the packing density (i.e. plasticity) and the activation energy for overall crystallization. Herein, we report that the origin of the plasticity exhibited by monolithic amorphous alloys lies in the characteristics of the atomic packing state, which can be quantified by the effective activation energy for overall crystallization.

keyword : amorphous alloys, packing density, plasticity, activation energy

Dynamic deformation behavior of an ultra-fine-grained dual phase steel fabricated by equal channel angular pressing (ECAP) was investigated and compared with that of an ECAP`ed ultra-fine-grained conventional low-carbon steel. Tensile and dynamic torsional tests were conducted on these two steels, and the deformed microstructures were observed to investigate the deformation behavior under dynamic loading. The ECAP`ed conventional steel consisted of very fine, elongated ferrite-pearlite grains of ~0.5 μm in size, and the ECAP`ed dual phase steel specimen consisted of ferrite-martensite grains of ~1 μm in size. The dynamic torsional test results indicated that maximum shear stress of the dual phase steel was lower than that of the conventional steel, but that fracture shear strain was higher in the dual phase steel. Some adiabatic shear bands were observed at the gage center of the dynamically deformed torsional specimen of the conventional steel, although they were not found in the dual phase steel. These results suggested that the ECAP`ed ultra-fine-grained dual phase steel could be a good way to increase the fracture resistance under dynamic loading as the formation of adiabatic shear bands was reduced or prevented.

keyword : dynamic torsional test, ultra-fine-grained dual phase steel, equal channel angular pressing, ECAP, adiabatic shear band

In these days, T/P91 steel is widely used for boiler tubes of ultra super critical (USC) power plants. However, the usage is greatly restricted by the embrittlement observed in the steel. In this study, microstructural analyses with various mechanical tests were performed to determine the embrittlement mechanism in T/P91 (Modified 9Cr-lMo-V-Nb). As a result, a mechanism of embrittlement based on the stabilization of martensite was found in the steel, when it was quenched to and retained for two hours at a temperature between Ms and Mf, and then air-cooled. The severity of the embrittlement is believed to depend on the carbon content and the volume fraction of the fresh martensite which has been formed during the air-cooling. The above mechanism well explained the experimental results including the pre and post heat-treatment effect on the embrittlement.

keyword : embrittlement, T/P91 steel, isothermal heat-treatment, martensite

The dependence of creep properties on directionally solidified(DS) grain size has been studied. The DB buckets have been manufactured in commercial scale by two different DB growing directions from airfoil and root. From the buckets two grain sizes of coarse (9-12 mm) and fine(3-5 mm) were selected for the tensile and creep tests. Creep tests have been fulfilled to study the dependence of the mechanical properties on the DB grain size in one bucket and the dependence of the crystal directions in the other. The results are (1) at room temperature the fine showed about 3% higher yield strength than the coarse. Especially the longitudinal direction of the bucket had about 26% higher yield and tensile strengths than the transverse. On the contrary (2) at the high temperatures between 600-982℃ the coarse showed about 3% higher strength than the fine. But the longitudinal and transverse showed no differences at the strengths. (3) At 982℃ and low stress range the creep rupture life increased strongly with decreasing stress. (4) Increasing temperature, ductility has been drastically enhanced. Concluded that the microstmcture and creep properties are interdependent.

keyword : blade, macrostructure, tensile strength, creep

Penetration of nitrogen into commercial pure titanium by plasma immersion ion implantation has been carried out to develop wear resistant titanium materials in the present investigation. X-ray diffraction analysis indicates that the nitrogen implanted specimens consist of titanium nitrides and titanium phases. Nanoindentation hardness variations in the nitrogen implanted specimens as a function of depth from the surface are quite different from those in the unimplanted ones, showing significantly higher value of nanoindentation hardness in the near-surface of the nitrogen implanted ones. Profilometer measurements of wear track on the dry sliding wear tested specimens show that the wear resistance can be most improved by nitrogen implantation at anenergy of 30 keV to a dose of 6 × 10(17) N2+ ions/cm2 into commercial pure titanium in the present study. Higher value of nanoindentation hardness in the near-surface of the nitrogen implanted specimens to cause microploughing wear may be one of the main reasons for showing the most improvement of the wear resistance of the commercial pure titanium by plasma immersion ion implantation within the investigated ranges.

keyword : wear-resistant titanium materials, nanoindentation hardness, microploughing wear

Expansion agents of cable grout in post-tension concrete structure were used to improve the corrosion properties of steel cable. The corrosion behavior of cable grout in 3 wt.% NaCl solution was investigated by accelerated corrosion test using potentiostatic test and electrochemical impedance spectroscopy (EIS) at room temperature. In this paper, the corrosion resistance of the pozzolanic admixture and nonmetallic expansion agent mixture was compared with that of aluminum powder expansion agent. Results obtained from accelerated corrosion test showed that pozzolanic admixture reduced diffusion and permeability to chloride ions, and increased the corrosion resistance of cable grout. The cable embedded in grout with aluminum powder expansion agent was more corroded than that in grout with nonmetallic expansion agent. The EIS results revealed that (Rfilm + Rct) value of grout with pozzolanic admixture and nonmetallic expansion agent mixture was higher than the value of grout with aluminum powder expansion agent after cracking.

keyword : cable grout, corrosion resistance, potentiostatic test, EIS, chloride

The objective of this study is to investigate the reaction behavior of cobalt with molten zinc. Pure cobalt specimen was immersion tested in the molten pure zinc bath at 460℃, 490℃ and 520℃. For the understanding of degradation processes, specimens were analyzed with scanning electron microscope (SEM) and energy dispersive spectrum (EDS), and electrochemical stripping method. After immersion of Co in a molten zinc bath at 460℃ to 520℃ four kinds of Co-Zn intermetallic compound layers, β1, γ, γ1, and γ2 were formed on the Co matrix, which was confirmed by both microstructural observation and electrochemical stripping method. According to the Co-Zn binary phase diagram they were all the possible intermetallic compounds at the temperatures of experimental conditions. The relationship between weight loss after immersion tests and immersion time followed typical parabolic rate law. Rate controlling step for this reaction was analyzed as the inter-diffusion process of Co & Zn atoms through β1 compound layer and the activation energy for the process was csalculated to be 214.9 kJ/mole.

keyword : Co-binder, molten-Zn, immersion test in Zinc, parabolic rate Law, β1 phase, diffusion process

The effects of Mo under-layer thickness on the hillock formation and microstructure of AI films for interconnects of TFT-LCD have been investigated. The density and size of hillock on AI films were successfully reduced by applying Mo under-layer between Al and SiO2 substrate, because Mo under-layer improved (111) textured growth and grain size of Al film. The optimum thickness of Mo was 30 nm for reducing the hillock formation. In addition, the hillock density and size of Al films were more dominantly dependent on the grain size of Al rather than (111) textured growth of Al. The (111) textured growth and grain size of Al films increased with increasing Mo thickness up to 30 nm, however, the grain size of Al with 50 nm thick Mo decreased due to the increase of Mo surface roughness.

keyword : pure Al interconnects, Mo under-Layer, hillock formation

Ultrathin silicon oxides were grown in SC-1, H2O2 and ozonated water (O3 in DI water) in order to investigate the hydrophilicity and stability of each grown oxide layers. Thickness of oxide and contact angle were measured, and oxide layers were characterized by using and X-ray photoelectron spectroscopy (XPS). It is found that oxides grown in ozonated water revealed thicker layer, faster oxidation rate and better thickness uniformity (3%) compared to those grown in SC-1 or H2O2. Analysis of XPS also showed that relative intensity of SiO2 peak on the surface grown in ozonated water was stronger than that grown in SC-1 or H2O2. It is concluded that superior hydrophilic oxide grown in ozonated water is due to the faster formation of stable oxide layers.

keyword : ozone, SC-1, oxide film, XPS, contact angle