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Sb-InSb eutectic alloys containing 26∼34 wt%In were unidirectionally solidified at a temperature gradient of 57℃ and in the range of growth rate 1.2 × 10^(-4)∼1.2 × 10^(-1)㎝/s in order to investigate the coupled region and halo formation. A symmetric coupled region, widened remarkably in the range of lower growth rates, was obtained in the present f-f type eutectic system. The area fraction of primary phase increased gradually with an increase of growth rate upto 1.2 × 10^(-1)㎝/s, but it decreased considerably by quenching, implying a widening of the coupled region in the range of growth rates corresponding to quenching. Halo formation was observed around both Sb and InSb primary phases. Halo fraction was independent of alloy composition, and its dependence on the growth rate revealed the same trend as in the primary phase fraction.
The relationship between the microstructures and some their related material properties was investigated in order to design the best suitable microstructure of the Ag-Cu electrical contact alloy. The Ag-Cu eutectic alloy was unidirectionally solidified in order to obtain an anisotropic microstructure. Some part of such unidirectionally solidified eutectic alloy has undergone also the rolling deformation to get the more elongated microstructure, characterizing the more anisotropic microstructural features. The specimen of a unidirectionally solidified eutectic structure has shown the better properties in regard to its application on electrical contact than the others. Furthermore its properties relevant to the contact performance was able to be improved by an appropriate rolling deformation. The specimen of the narrower lamellar spacing obtained by rolling deformation in direction to unidirectional solidification has shonw the best properties among the various types of the specimens investigated in this study. Possible explanation on the experimental result was also carried out.
It was investigated, whether high speed steel part could be directly fabricated to near net shape by normal P/M process, ie. powder mixing, compacting and sintering procedure. Fe-, W-, Cr₃C₂and VC powders, whose composition is equivalent to the commercial T1 grade high speed steel, were thoroughly mixed in ball mill, and compacted into a disc-type specimens of 10㎜ diameter and about 5㎜ height at a hydraulic pressure of 5.5 ton/㎠. This compact was sintered in alumina tube furnace at temperature between 1220℃ and 1340℃, both in H₂ atmosphere and in vacuum for various sintering time. The fully densified structure could be obtained only by the sintering at the temperature above 1340℃, or by prolonging the sintering time at 1320℃. The heat treatment behavior of a directly sintered P/M HSS was similar to that of a wrought HSS, so far as the alloying components were fully homogenized during sintering process. The microstructure of the sintered, quenched or tempered high speed steel was also observed in order to elucidate the relationship between the structure and properties of the sintered high speed steel. It could be cautiously concluded that the directly sintered HSS. prepared by normal sintering process could be used supplementary for the production of near net shape HSS part, so far as the more finer Fe-powder would be used and the sintering might be carried out at the optimal temperature.
An investigation was carried out on the possibility whether metal powder injection moulding using sieve size powders instead of ultrafine carbonyl powders could be applied to the fabrication of high performance Ni-Mo-steel sintered parts. The debinding was performed by employing two step debinding process. The higher the green density and the shorter the presintering time, the higher sintered density of the injection moulded parts could be obtained in Fe-5Ni-3Mo-0.2B-0.4P alloy steel. The injection moulded parts with the relative sintered density above 97% could be obtained by following three step process; debinding, presintering at 650℃ for Omin, sintering at 1230℃ for 1h. The hardness and UTS of the sintered MIM part at 1230℃ for 1 and 3h were 40HRc, 272±19MPa and 44HRc, 458±9MPa, respectively.