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The effect of transition metals on the glass forming ability, GFA, has been investigated in Fe_(75-x)Si_(10)B_(15) Mx(M=Cr, Mn, Co, Ni, Ti, Zr, Nb, Ta, x=2.5, 5.0at%) alloy wires. The effect of transition metals on the critical diameter of an amorphous wire was different according to the group of the periodic table. The amorphous wire with the largest critical diameter of 270 ㎛ was obtained in the Fe_(72. 5)Si_(10)B_(15)Ta(2 5) alloy. Although the GFA increased with atomic size difference and decreased with average outer electron concentration of transition metals, considerable scattering of data was shown in these relations. The GFA increased in good accordance with the boride and the silicide formation enthalpy of transition metals up to a certain level of the enthalpy, then rapidly decreased over that enthalpy level. It is thought that the enthalpies of formation of the transition metal boride and the silicide are more effective factors than the atomic size difference or the average outer electron concentration to explain the effect of the transition metals on the CFA in the Fe-Si-B alloys.

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Microstructural characteristics of Ti_(50)Ni_(50-x)Fe_x(x=0, 1, 2, 5 at%) processed by self-propagating high temperature synthesis method(SHS method) have been investigated in the present study. Ti_(50)Ni_(50-x)Fe_x(x=0, 1, 2, 5) processed by SHS method consists of TiNi and NiTi₂. Amount of NiTi₂ increases with increase of Fe content. The TiNi phase has an intermediate phase structure which exhibits extra reflections in the electron diffraction patterns. Therefore, high temperature B2 structure transforms into the intermediate phase structure during SHS processing. Several types of extra reflections such as 1/2<1 0 0>, 1/2<1 1 0>, 1/4<2 1 0> are superimposed on the B2 structure reflections. The transformation into the intermediate phase structure results in the formation of 50∼200 ㎚ scale microdomain structure in TiNi phase. The transformation into the intermediate structure occurs at lower temperature with heat treatment at high temperature or with increasing Fe content. Thus, no intermediate structure phases are observed after heat treatment at 900℃ for 7 hours.

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Transformation sequence and subsequent solute redistribution behaviors of Fe-15Cr-5V-1.2C alloy during solidification have been discussed. Specimens were quenched interruptly, as they were solidified and transformed. Primary δ-ferrite was not completely transformed into γ-austenite during δ→γ peritectic reaction. During the peritectic reaction V was enriched to the retained δ-ferrite, but Cr was not. When the retained δ-ferrite was directly changed into α-ferrite. V was diffused from δ-ferrite into the surrounding γ-austenite due to the decrease of V-solubility in the α-ferrite. As heating the as-cast specimen up to 1000℃, precipitated iron complex carbides were dissolved into the newly formed γ-austenite. The iron carbides were inferred as M_(23)C_6 carbides from the mole fraction change of each phases existing at the heating temperatures and microstructure change with increasing heating temperatures.

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The main objective of this study is to apply the internal variable theory of structural superplasticity proposed recently to the room temperature superplastic deformation of a two phase Pb-Sn eutectic alloy. A series of load relaxation and tensile tests were conducted on Pb-62 wt.% Sn eutectic and its constituent single phase alloys at room temperature and the results were analyzed based on the theory proposed. The flow curve of superplastic Pb-Sn eutectic alloy obtained from load relaxation test was shown to consist of the contributions from garin or phase boundary sliding (GBS/PBS) and the accommodating plastic deformation of grain matrix. The boundary sliding behavior of Pb-Sn eutectic alloy could be described as a viscous flow process characterized by the power index value of M_g = 0.5. This value is much less than that of quasi-single phase Al alloys, such as 7475 Al and 8090 Al-Li alloys. Strain rate range within which boundary sliding is predominant deformation mechanism was obtained as roughly 7×10^(-7) /s≤ε≤10^(-4)/s in superplastic Pb-Sn eutectic alloy used in this study. By carefully examining deformed surfaces of tensile test specimens of eutectic and its constituent single phase alloys, following results were also obtained. The existence of Pb rich phase is indispensable to the superplastic deformation of the Pb-Sn eutectic alloy and the onset of α/β interphase boundary sliding is responsible for the smaller value of the parameter M_g.

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The microstructural features of MA956 friction welds were examined using optical microscopy, STEM and EDS. The results of this investigation have confirmed that friction welding has a major influence on the microstructural features of MA953. The friction weld zone is considered as three distinct microstructural region, namely, region R I containing recrystallized grains, region R II where the grains were reoriented by the upsetting pressure and unaffected base material(region R III). The friction welding operation substantially alters the particle chemistry, dimensions and shape in the joint region. The number of Al-rich or Ti-rich particles is substantially decreased and large irregularly-shape particles are formed. It is postulated that the clustering of Y₂O₃ dispersoids, Al₂O₃ and Ti(C, N) particles is promoted by high strain rate superplastic behavior in the region immediately adjacent to the contact surface. The shape of elongated particles observed in friction welded joints, the variation in chemical composition across particles and the substantial increase in particle dimensions at the periphery of welded samples are all consistent with the proposed particle agglomeration mechanism.

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The compressive deformation behavior under dynamic loading was investigated using a high performance servo-hydraulic machine in order to evaluate experimentally impact absorption energies of extruded aluminum tubing for space frame. Dynamic compression tests were conducted for three extruded aluminum tubing whose thicknesses were 1.5 ㎜, 2.0 ㎜, and 3.0 ㎜, and then the test data were compared via observation of deformation mode. The results indicated that the dynamic deformation behavior correlated well with load-displacement curve data, i.e., the number of peaks formed by the compression-resistant force matched with the number of plastic hinges formed during compression. In the tubing with thickness of 3.0 ㎜, the number of plastic hinges decreased, and bending occurred seriously. This leaded to drop in impact absorption energies per unit cross-sectional area since energies could not be absorbed effectively upon bending. These findings suggested that in order to improve impact absorption energies of the extruded aluminum tubing for space frame, their thickness less than 3.0 ㎜ and the design of their cross-section for promoting folding instead of bending were recommended.

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The p-type BiS_(0. 5)Sb_(1. 5)Te₃ thermoelectric materials were fabricated by hot pressing with various starting powders (size of 44 to 149 ㎛). Hot pressing was performed at temperature ranged from 380 to 450℃ and pressures of 100 to 200 MPa. The microstructure, mechanical properties, and thermoelectric properties of the materials were investigated. Optical microscopy and scanning electron microscopy were used to investigate the detailed microstructure. The microstructure showed fine grains elongated along the pressing direction. The figure of merit increased with increasing the hot pressing temperature and pressure due to the increase in carrier mobility and the decrease in lattice thermal conductivity. The materials, fabricated with starting podwers of 44∼75 ㎛ at 420℃, 200 MPa, showed the highest value of figure of merit (2.69×10^(-3)/K).

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Bi₂(Te_(0. 95)Se_(0. 05)₃ alloy powders have been fabricated by mechanical alloying process, and thermoelectric properties of the hot pressed Bi₂(Te_(0. 95)Se_(0. 05)₃have been investigated. Formation of Bi₂(Te_(0. 95)Se_(0. 05)₃ alloy powders was completed by mechanical alloying of the as-mixed Bi, Te, and Se granules of ∼3.6 ㎜ size for 2 hours at ball-to-material ratio of 5 : 1. Bi₂(Te_(0. 95)Se_(0. 05)₃, fabricated by mechanical alloying and hot pressed for 30minutes in vacuum at temperatures ranged from 300℃ to 550℃, exhibited n-type conduction without addition of donor dopant. When hot pressed at 550℃, figure of merit at 300K was 1.14×10^(-3)/K.

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Effects of electrolysis conditions on the microstructure and mechanical properties of copper electro-formed layer have been investigated using the copper sulfate. Electroforming was conducted at bath temperature of 25 to 55℃ and current density of 3∼20A/d㎡ for 10 hours on silver mirror-treated silicon rubber. The microstructure of copper layer was found to be dependent upon the electrolysis condition. The microstructural observation revealed that fine grains in the copper electroformed layer were formed in low current density and at bath temperatures of 25∼35℃. The tensile strength and elongation of copper electroformed layer tended to increase with decreasing bath temperature, and the peak tensile strength showed 380 MPa at bath temperature of 25℃. The tensile strength showed the highest value of 300 MPa at 7A/d㎡ of current density, and decreased when the current density increased above 7A/ d㎡. The Ni coating, with a thickness of 20 ㎛, on the copper electroformed layer improved microhardness(Hv) significantly and tensile strength slightly because the thickness of the Ni coating is thin.

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The computer simulation model was established to verify the applicability of smelting reduction concepts to converter slag which becomes an issue on the environmental and recycling aspects. The computer simulation model provides the following results. The utilization of latent energy of converter slag after tap is a very effective and reasonable method for saving energy. Also, the increase of post combustion ratio and heat transfer efficiency are effective ways in saving energy. But in order to increase PCR, recovery efficiency of post combustion energy has to be higher than 85% HTC to satisfy both refractory life and energy efficiency. Coke is a most useful fuel source because it shows low dependence to post combustion ratio and low hydrogen content. In the present process, the quality of hot metal would be expected to be at a similar level with that of the blast furnace. The utilization of scrap was also possible to maximize the advantages of the present process which were high temperature and chemical dilution with hot metal. In the case of scrap, energy consumption increases slightly due to preheating of scrap. Consequently, the concept of the present process provides one possibility of integrating recyclable waste materials such as converter slag, coke oven dust, life terminated acidic refractory, scrap by smelting reduction process.

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