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Zr-based amorphous alloy matrix composites reinforced with tantalum continuous fibers were fabricated by liquid pressing process, and their microstructures and mechanical properties were investigated. About 60 vol.% of tantalum fibers were homogeneously distributed inside the amorphous matrix, which contained a small amount of polygonal crystalline particles. The ductility of the tantalum-continuous-fiberreinforced composite under tensile or compressive loading was dramatically improved over that of the monolithic amorphous alloy, while maintaining high strength. The consequential observation of the tensile deformation and fracture behavior of the composite showed the formation of multiple shear bands and multiple necking, crack deflection in the amorphous matrix, and obstruction of crack propagation by ductile fibers, thereby resulting in very high tensile elongation of 7.2%. These findings suggested that the liquid pressing process was useful for the development of amorphous matrix composites with improved ductility.

keyword : composite, amorphous alloy, Liquid pressing process, multiple shear bands

Creep behavior of the squeeze infiltrated AS52 Mg matrix composites reinforced with 15 vol% of aluminum borate whiskers(Al18B4O33w) fabricated squeeze infiltration method was investigated. Microstructure of the composites was observed as uniformly distributed reinforcement in the matrix without any particular defects of casting pores etc.. Creep test was carried out at the temperature of 150 and 200℃ under the applied stress range of 60~120 MPa. The creep resistance of the composite was significantly improved comparing with the unreinforced AS52 Mg alloy. The creep behavior of composites might be interpreted with the substructure invariant model successfully for the composite. Threshold stress of the composite exist for the creep deformation of the composite. The analysis of the creep behavior of the composite with threshold stress indicated that creep deformation was controlled by the lattice diffusion process of AS52 Mg matrix at given effective stresses and temperatures. Activation energy was also calculated to check lattice diffusion controlled creep behavior of the composite.

keyword : AS52 Mg alloy, Aluminum borate whisker, composites, squeeze infiltration method, creep test, substructure invariant model, threshold stress, stress exponent, activation energy, Lattice diffusion control creep

By using electrodeposition, we developed a new method to produce Ni/Invar bimetal sheets, which have been used for the present study to investigate the texture evolution during annealing. The grains of electrodeposited Ni were columnar, while those of electrodeposited Fe-Ni alloy were nanocrystalline. These different parts of the bimetal underwent different evolution of textures and microstructures during annealing. In the nanocrystalline Invar, the asdeposited textures were of fiber-type characterized by strong <100>//ND and weak <111>//ND components, and the occurrence of grain growth resulted in the strong development of the <111>//ND fiber texture with the minor <100> // ND components. On the other hand, in the columnar-structured Ni part, the as-deposited <110>//ND fiber texture transformed to the <112>//ND fiber texture due to recrystallization occurring above 550℃. The development of microtextures which took place during annealing in the Ni/Invar interfacial regions was investigated by using the OIM analysis, and discussed in terms of the effect of atomic diffusion across the interfaces.

keyword : Bimetal, Nanocrystalline Invar, Columnar Ni, Electrodeposition, Grain growth, Texture

The effect of dewpoints on annealing behavior and coating characteristics such as wettability and galvannealing kinetics was studied by annealing 0.3wt%Si-0.1~0.4wt% Mn added interstitial-free high strength steels(IF-HSS). The 0.3wt%Si-0.1wt%Mn steel exhibited good wettability with molten zinc and galvannealing kinetics after annealing when the dewpoint of H2-N2 mixed gas was above -20℃. It is shown that the wettability and galvannealing kinetics are directly related to the coverage of the external(surface) oxide formed by selective oxidation during annealing. At N2-15%H2 annealing atmosphere, the increase of dewpoint results in a gradual transition from external to internal selective oxidation. The decrease of external oxidation of alloying elements with a concurrent increase of their subsurface enrichment in the substrate, showing a larger surface area that was free of oxide particles, contributed to the improved wettability and galvannealing kinetics. On the other hand, the corresponding wettability and galvannealing kinetics were deteriorated with the dewpoints below -20℃. The continuous oxide layer of network and/or film type was formed on the steel surface, leading to the poor wettability and galvannealing kinetics. It causes a high contact angle between annealed surface and molten zinc and plays an interrupting role in interdiffusion of Zn and Fe during galvannealing process.

keyword : dewpoint, internal oxidation, external oxidation, hot-dip galvannealed steel(GA), wettability, galvannealing kinetic, selective oxidation, IF high strength steel containing Si and Mn

The synthesis and hydration of Calcium Sulfo Aluminate[3CaO·3Al2O3·CaSO4(C4A3S), CSA cement utilizing secondary steelmaking refining slags is studied for recycling the discarded steel plant wastes to meet the environmental requrations imposed on the steel industry. Raw materials of secondary refining slag, lime sludge, gypsum and bauxite were prepared to be sintered at 1,250℃. The sintered samples were hydrated for 1, 3 and 7 days to evaluate the mineralogical and physico-mechanical properties. The hydration products evaluated with the aid of SEM and XRD analyses confirmed the formation and the continuing growth of ettringite phase with the further hydration times, which plays a role in developing the early strength and the expansion properties of cements. The physico-mechanical properties of hydrated CSA products employing the recycled steelmaking refining slags determined in terms of compressive strength and linear expansion of hydrated products are found to be superior to those of the Ordinary Portland Cement(OPC) or the other commercial CSA cements.

keyword : CSA(C4A3S), ettringite, secondary steelmaking refining slag, hydration

Contact materials are used in many electrical devices. Ag-Cd alloy has been widely used in electrical part, because Ag-Cd alloy has a good wear resistance and stable contact resistance. But nowadays Ag-Cd alloy isn`t being used because of environmental challenges. Currently new research is being done on (Ag-SnO2 and Ag-SnO2-In2O3) as an alternative solution to fix any remainly environmental challenges. However In2O3 is more expensive and Ag-Sn alloy has low wear resistance. According to our research data Zn has a similar physical and chemical property. In this work, so we changed and optimized the Zn oxide to over 4 and added Sn oxide ratio 0.5, 1.0, 1.5wt%. Conclusions from the data recorded from the experiment of Ag-ZnO-SnO2 are as follows.

keyword : contact material, internal oxidation, oxide particle, Ag-Zn, rapid solidification process

Compression deformation behaviors at high temperature as a function of temperature and strain rate were investigated in the 6061 aluminum alloy, which is used for automobile wheel. Compression tests were carried out in the range of temperatures 300~475℃ and strain rate 10-3~10-1sec-1. By analyzing these results, strain rate sensitivity, deformation temperature sensitivity, the efficiency of power dissipation, Ziegler`s instability criterion, etc were calculated, which were plastic deformation instability parameters as suggested by Ziegler, Malas, etc. Furthermore, deformation processing map was drawn by introducing dynamic materials model (DMM) and Ziegler`s Continuum Criteria. This processing map was evaluated by relating the deformation instability conditions and the real microstructures. As a result, the optimum forging condition for the automobile wheel with the 6061 aluminum alloy was designed at temperature 450℃, strain rate 1.0×10-1 sec-1. It was also confirmed by DEFORM finite element analysis tool with simulation process.

keyword : 6061 aluminum alloy, forging, deformation processing map, deformation instability

High purity Fe thin films were prepared by the ion beam deposition method with 56Fe+ions on the Si substrate at the room temperature. The Fe thin films were deposited at the ion energy of 50 eV and 100 eV. Microstructural properties were investigated on the atomic scale using high-resolution transmission electron microscopy (HRTEM). It was found that the Fe thin film obtained with the energy of 50 eV having an excellent corrosion resistance consists of the amorphous layer of~15 nm in thickness and the bcc crystalline layer of about 30 nm in grain size, while the thin film obtained with the energy of 100 eV having a poor corrosion resistance consists of little amorphous layer and the defective crystalline layer. Furthermore the crystal structures and arrangements of the oxide layers formed on the Fe thin films were analyzed by processing of the HRTEM images. It was concluded that the corrosion behavior of Fe thin films relates to the surface morphology and the crystalline structure as well as the degree of purification.

keyword : Fe thin film, ion beam deposition, high-resolution transmission electron microscopy, corrosion resistance, amorphous Layer

Metallic nanostructures have great potential for bio-chemical sensor applications due to the excitation of localized surface plasmon and its sensitive response to environmental change. Unlike the commonly explored absorption based sensing, the optical scattering provides single particle detection scheme. For the localized surface plasmon resonance spectroscopy, the metallic nanostructures with controlled shape and size have been usually fabricated on adhesion-layer pre-coated transparent glass substrates. In this study, we calculated the optical scattering properties of plasmonic Au nanodisc using a discrete dipole approximation method and analyzed the effect of adhesion layer on them. Our result also indicates that there is a trade-off between the surface plasmon damping and the capability of supporting nanostructures in determining the optimal thickness of adhesion layer. Marginal thickness of Ti adhesion layer for supporting Au nanostructures fabricated on a silica glass substrate was experimentally analyzed by an adhesion strength test using a nano-indentation technique.

keyword : Localized surface plasmon resonance, adhesion Layer, discrete dipole approximation, effective medium approximation