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Rapidly solidified Cu-based ribbons with different alloying elements were investigated to replace the conventional Ag-based filler metals. Characteristics and microstructures of the brazed joint have been studied by TEM, SEM, DTA and X-ray diffractometer. The microstructures of the melt-spun Cu-Sn-Ni-P-Si alloys were basically in amorphous state. Si additions to Cu-base alloys showed positive effect on the depression of melting point as well as on the suppression of precipitation during brazing. The results indicated that the joining characteristics of the commercialized MBF-2005 alloy could be improved by substituting silicon for phosphorus in part.

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The Changes in microstructure during melting and solidification of YBa₂Cu₃O_(7-x) were observed and YBa₂Cu₃O_(7-x) wires were fabricated by the melt textured growth method. The YBa₂Cu₃O_(7-x) phase, when heated at 1050℃ for 10 min., was decomposed to Y₂BaCuO_5 and liquid phase. When the Y₂BaCuO_5 and liquid were cooled to form YBa₂Cu₃O_(7-x), the Y₂BaCuO_5 particles dispersed in the liquid grew fast while the growth rate of the entrapped particles in the YBa₂Cu₃O_(7-x) phase was negligible. Even after the completion of the peritectic reaction, Y₂BaCuO_5 particles remained within the YBa₂Cu₃O_(7-x) grains. Slower cooling rate during and after the peritectic reaction resulted in the larger YBa₂Cu₃O_(7-x) grain size. The transition temperatures of 85K and 79K were obtained at the cooling rates of 9℃/hr and 2℃/hr, respectively. However the wire obtained at 1℃/hr did not show superconductivity at the liquid nitrogen temperature of 77K.

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Simulation study employing metal thermal cycle simulator (MTCS) has been performed to investigate a correlation between the microstructure and fracture properties of the heat affected zone (HAZ) in welded HY-100 steel. Charpy impact energy dropped from 210 J to about 125 J after the first thermal cycle in the range of peak temperature (T_P¹) of 800℃∼1100℃, and decreased rapidly above 1100℃, down to 60 J for T_P¹=1350℃. Decreased Charpy impact energy of T_P¹=1350℃ appears to be due to the change of microstructure from tempered martensite to mixture of fresh martensite and fresh lower bainite. Impact transition temperature increased by the amount of 70℃ after thermal cycle simulation of T_P¹=1350℃, namely -50℃ in HAZ and -120℃ in HY-100 steel. Evaluation of Charpy impact result, after the second thermal cycle in the range of peak temperature (T_P²) of 700℃∼1300℃, revealed that the fracture properties of HAZ are not affected significantly by second thermal cycle in HY-100 steel.

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The mechanical alloying behaviours of Ti＋Al powder mixtures (Ti_(50)Al_(50)) and Ti_(25)Al_(75) have been investigated using various ball milling methods: attrition, vibratory, planetary and conventional horizontal milling. The morphological evolution of the powders was strongly dependent upon the milling methods. For Ti_(50)Al_(50) composition, an amorphization took place in the final stage of the milling where cold welded coarse powders were refined to the particle size of less than 30㎛. For Ti_(25)Al_(75) composition, both amorphous and metastable Al₃Ti phases were formed during the mechanical alloying, and the amount of the amorphous phase increased with increasing the milling time.

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Elemental Ti＋Al powder mixtures ((Ti_(50)Al_(50)) have been mechanically alloyed (MA) to obtain amorphous and/or nanocrystalline powders using a conventional horizontal ball milling. The MA metastable powders were then vacuum hot pressed(VHP) at 1000℃ for 1 hour, followed by an annealing at 1200℃ for 8 hours. Very fine microstructures were retained after the hot pressing and the subsequent annealing, less than 1㎛ in grain size. The result obtained by a compression testing on the annealed specimens shows a good combination of fracture strength and ductility as compared to cast specimen. Very fine grain structure might be the major cause of the property improvement.

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The present study is concered with the processing of ultra-fine steels by thermo-mechanical processes and the grain refinement mechanism. Three steels were deformed at high strain rates using a pilot plant rolling mill, and exhibited good tensile properties and low temperature impact toughness, although they contained only about 0.01% carbon. Especially in the Ni added steel, room temperature tensile strength reached to 850 MPa, and Charpy impact energy at -120℃ showed 78J, indicating the potent effect of Ni addition. Although the microstructure was identified to be mainly acicular ferrite by optical microscopy, TEM microstructures of ultra-fine steels were composed of very fine and highly dislocated grains whose shapes were changed from elongated to equiaxed ones as alloying elements were added. The formation of this microstructure might be explained by a possible mechanism, i.e., a repeated dynamic strain-induced transformation mechanism. These findings suggest that ultra-low carbon steels with high strength and toughness can be processed by grain refining combined with microalloying.

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The experimental results for the fabrication of TiC powder from TiO₂by self-combustion reaction are summerized as follows; 1) The mole ratio of Mg was the greatest affecting factor in the reaction and the mole ratio of C, particle size of Mg, mixing times affected the reaction as well. 2) MgO and Mg were completely removed by leaching in the 20% HCl solution. 3) The TiC powders had a spherical shape and the particle size was 0.3-0.4 microns with a narrow distribution. 4) Purity of manufactured TiC powder was about 99.925 weight percent.

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The effect of alloying element of Cu on tensile properties and SCC behaviors in 20Cr7Ni3Mo duplex stainless steel with fibrous structure have been investigated. The SCC resistance of the steel was examined by means of SSRT test. The steel with ferrite content of 31∼36% possessed superior tensile properties, corrosion and SCC resistances. Additive element, Cu, improved SCC resistance to NaCl solution, but not to hot MgCl₂solution.

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This research was performed to investigate the effect of thermo-mechanical cycling (TMC) treatment on the shape memory effect (SME) of Fe-10Mn-9Cr-8Ni-5Si (wt.%) alloy. Various TMC parameters were systematically changed to study the influence of individual parameter on the SME, and to find the optimum processing condition for the best SME of the alloy. The amount of prestrain and the annealing time were the important parameters for controlling the SME, and the best shape recovery was observed at the condition of 4% prestrain and 873K/60min. annealing. It was ascertained by microstructural observation that the improvement of the SME was primarily due to the introduction of a number of defect structure such as stacking faults and dislocations. These defects increased yield stress for γ matrix, and probably acted as a favorable nucleation site for ε martensite formation.

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A study was undertaken to investigate the effect of cooling rate, deformation temperature and thermomehanical treatment on shape memory capacity in an Fe-12Mn-10Cr-8Ni-6Si(wt.%) alloy. Among the several specimens which were cooled at different cooling rate from the single γ phase region, water quenched specimens showed the best shape memory effect, presumably due to the high amount of stacking fault and the lack of thermally induced martensite plates. The amount of shape recovery increased with decreasing deformation temperature for all the cooling conditions. When the deformation temperature range was near the Ms temperature (about 77K), shape recovery capacity was good regardless of cooling paths. In addition, a thermomechanical treatment (4% prestrain followed by annealing at 873K for 1 hr) on water quenched specimens was found to enhance ultimate tensile strength, yield strength and shape memory capacity compared to those of water quenched specimens. The improvement of shape memory capacity of thermomechanically treated specimens seemed to be attributed to the increase in yield strength and the shift of M_d temperature from 320K to 400K.

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