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Fracture toughness of RS/PM Al-8.5%Fe-1.3%V 1.7%Si alloy decreases with increasing temperature and decreasing loading rate. Low toughness cracking is associated with single size of shallow dimples, while that with high toughness case is associated with bimodal distribution of dimples. Thermomechanical processing (TMP) has been performed on extruded Al-Fe-V-Si alloys to improve elevated temperature fracture toughness and toughness isotropy. Substantial improvement in toughness isotropy is obtained with TMP by homogenization of microstructure. K_k, however, tends to decrease with rolling reduction at 25 and 175℃. A decrease in fracture toughness with TMP is believed to be related to the microstructural changes occurred during rolling reduction. Fracture is by microvoid processes at all temperature ; reduced toughness correlates with changed void shape from spherical to irregular. It is believed that increased temperature reduces work and strain rate hardening between growing primary voids, leading to intravoid instability and coalescence at lowered strain. Decreased strain rate hardening is attributed to increased mobile dislocation density due to dislocation emission and detrapping from dispersoids in dynamically recovered dislocation-source-free grains.

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The structure, mechanical property and thermal stability of rapidly solidified aluminum-transition metal (=Fe, Co, Zr) alloy system were investigated. The structure was changed from Al phase to amorphous one through a mixed structure consisted of Al and amorphous phases with solute content. The amorphous single phase was formed at the Al-rich compositional range of Al=87-88at%. The crystallization temperature(T_x,) of amorphous Al_(88)Ni_(12-x)(Fe,Co)_x(X≤6at%) alloys was increased with the content of Fe or Co, indicating the thermal stabilization of the amorphous phase. Hardness (H_v,) and tensile fracture strength (σ_f) exhibited a maximum at the 5at% Fe or Co. On the other hand, aging treatment at temperature range less than 500K in amorphous Al_(88)Ni_9(Co,Fe)₃ alloys formed aluminum nanoparticles distributed homogeneously in an amorphous matrix. The H_v for the mixed phase alloy increased monotonically with the V_f. The σ_f showed a maximum at about 15%V_f and with further increase of the V_f decreased due to the embrittleness of the amorphous matrix. The increase is presumed because the Al particles act as an effective barrier to shear deformation of the amorphous matrix. The ultimate tensile fracture strength at elevated temperature less than 480K in an amorphous Al_(88)Ni_8Zr₃ alloy kept a high level more than 650㎫ and exhibited a large elongation of 25% at 440K. The large elongation can be explained by crystallization-induced plasticity.

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Peel strength of Cr/polyimde interfaces was measured on Cu/Cr/polyimide structures using T-peel test. Peel strength of Cr/BPDA-PDA interfaces decreased with increasing the thickness of Cu/Cr metal films to a critical value, and then increased with further increasing metal film thickness. When the thickness of Cu/Cr films was below a critical value, plastic bending of metal films mainly occurred during T-peel test. With metal films thicker than a critical thickness, however, plastic bending of polyimide films has been observed. A critical thickness of metal films, where transition from metal bending to polyimide bending occurred, became thinner with lower yield strength of metal films and with thicker polyimide film. Without depending on the plastic bending of metal or polyimide films, peel strength increased with increasing the peeling angle during T-peel test.

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The relationship between tensile and width strains during tensile testing has been studied for 99.99% aluminium, 70 : 30 brass and IF steel sheets. The data have been analyzed based on the conventional R-value, the instantaneous R-value and a linear regression R-value. The instantaneous R-value was found to be the most suitable method for characterizing the variation of the R-value or the plastic strain ratio. The instantaneous R-values of the aluminium and IF steel sheets were approximately constant, exhibiting a discontinuous increase at a strain of 5 to 6 percent. The instantaeous R-value of 70 : 30 brass sheet decreased continously with tensile strain. This variation was attributed to the texture variation with tensile strain.

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The effects of Al content and alloying elements on the crystallographic factors and the mechanical Properties of Ti-(47-54)Al and Ti-48Al-(1-3)M (M=Cr, Mn) intermetallic compounds have been investigated using optical microscopy, scanning electron microscopy, X-ray diffractometry, and compression testing. The γ grain size of heat-treated cast structure decreases with the decrease of Al content and the addition of Cr(or Mn). This is primarily due to the refinement of as-cast structure. In the heat-treated cast structure, the inhomogeneity of γ grain size is also related to the second phase particles, which are located within the dendrite core region. The variation of lattice parameters and tetragonality of γ phase as, a function of Al content shows a larger slope for the Ti-rich side than that for the Al-rich side in reference to the stoichiometric composition. This is believed to be primarily due to the difference of anti-site defect type. The hardness of Y phase is enhanced with the increase of the degree of non-stoichiometry. The variation of hardness is insensitive to the type of anti-site defect. The yield stresses of alloys containing Cr(or Mn) are mainly strengthened by the refinement of γ grain size. The ductility of γ-TiAl base intermetallic compounds depends primarily on the tetragonality rather than the unit cell volume change of γ phase.

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A study on the electrorefining of an impure uranium containing zirconium and neodymium at 500℃ by KCl-LiCl fused salt electrolysis was performed. The reduction potentials of uranium and neodymium were 0.12V and 0.64V.(vs. Ag/AgCl electrode), respectively. When a 1wt.%Nd of uranium was added as an impurity, 0.001wt% Nd was deposited onto the cathode below 0.5V after electrolysis. When a 10.5wt.% Zr of uranium was added to liquid cadmium anode as an impurity, zirconium was evaporated as ZrCl₄, at 500℃ during electrolysis, and consequently uranium was deposited onto the cathode as a purity of 99.98wt.% U. The morphology of purified uranium was appeared as dendritic structure. The activity coefficient of metallic neodymium for the displacement reaction of UCl₃+Nd_(cd)=NdCl₃+U_(cd), was calculated to be 3.67×10^(-10) at 500℃.

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Polished and thin sections from used graphite-bonded CaO-stabilized zirconia submerged entry nozzles were observed under the optical microscopes and by means of the electron optics. A new mechanism for the excessive slagline attack is advanced as follows: Once graphite dissolves in the metal, the slag comes in contact with zirconia particles embedded in the graphite bond which have been receded in contour. The graphite bond reduces SiO₂, Na₂O, MgO and probably B₂O₃ in the mold flux to SiO, Na, Mg and B. The gaseous products diffuse into ZrO₂ particles through their pores and oxidize to form low-melting compounds with the CaO, thus destabilizing the zirconia. In addition, the compounds etch grain boundaries, resulting in loose particles with well-defined roundness. Fresh slag penetrates the weakened particles and breaks them down into pieces, which are, in turn, dispersed into the slag. When the slag reaches the graphite-rich region, the metal replaces the slag. The process then repeats itself.

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Alumina-copper substrate was fabricated by active metal brazing with Ag-Cu-Zr alloy. The microstructure of the Al₂O₃/Cu pint was investigated by using SEM, EDX and EPMA. The bond strength for the bulk shaped pint was evaluated by shear test. The reaction product was identified as ZrO₂ with a monoclinic structure. The reaction layer thickness was nearly constant(∼4㎛) in the brazing temperature range of 785-850℃ because the content of Zr in the brazing alloy was consumed in the reaction with bonded copper. The shape of the brazement was irregular and also the width of the brazement was decreased with increasing the temperature because of the diffusion of Cu in the filler metal. The joint strength was abruptly decreased at the brazing temperature higher than 800℃ due to a decrease in the width of the brazement. The pint of a brazement with ∼140㎛ width, which was formed by brazing at 800℃ for 30min, showed the highest fracture strength(∼96㎫). In the alumina-copper substrate, the fillet width and morphology of the pint edge strongly affected the physical properties of the joint. To obtain a sound substrate pint, the brazing temperature lower than 800℃ was required. The substrate brazed at 745℃ did not form the crack during 50 thermal cyclic fatigue.

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This work is the basic research on the tailored blank laser welding of automobile low carbon steel sheets. The materials used were low carbon steel sheets for automotive bodies, which were welded together in equal thickness(0.9㎜/0.9㎜). In order to make a practical application of the tailored blank laser welding, conditions for laser welding should be optimised. Experiments were carried out by applying the Taguchi method. The advantage of the application of Taguchi method (calculated by S/N(Signal to Noise) ratio) is to reduce the amount of experiments and is to estimate the interaction between various parameters. Optical microscopy, SEM, TEM and XRD analysis were performed to observe the microstructures in the fusion zone and to determine the phase and solidification mode. The microstructure of fusion zone was consisted of fine grains with dendrites due to rapid solidification (cooling rate was estimated to 10⁴K/s). The fusion zone had a mixed phases of quasi-polygonal ferrite, martensite and undefined phase which had a transformation temperature between that of quasi-polygonal ferrite and martensite. Since an important property of the laser welded tailored blank is formability, the formability of the base metal and welded specimens were examined through tensile test, dome height test and microhardness test. The elongation and LDH of welded specimens were found to be more than 80% of the base metal. Optimum laser welding conditions could ensure reasonable formability for the laser welded tailored blank (automobile low C steel sheet).

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This work is the basic research on the tailored blank laser welding between different thickness automobile low carbon steel sheets. The materials used were low carbon steel sheets for automotive bodies, which were welded together in different thickness(0.9㎜/2.0㎜). In order to make a practical application of the tailored blank laser welding method in automobile industry, optimum conditions for laser welding should be obtained. Experiments were carried out and analysed by applying the Taguchi method. Optical microscopy, SEM, TEM and XRD analysis were performed to observe the microstructures in the fusion zone. In 0.9/2.0 welding, the proportion of lower transformation temperature phases has found to be increased in comparision to the 0.9/0.9 welding. Since an important property of tailored blank laser welding method is formability, the formability of the base metal and welded specimens were examined through tensile test, dome height test, microhardness test. The elongation and LDH of welded specimens were more than 70% of the base metal in the case of 0.9/2.0 welding.

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