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KMID : 0381919950250030090
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Korean Journal of Microscopy
1995 Volume.25 No. 3 p.90 ~ p.98
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Transformation Behaviour of High Temperature Thermoelectric $FeSi_2$
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Eun Young-Hyo
Min Byoung-Gue
Lee Dong-Hi
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Abstract
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In the Fe-Si system, a mixture of a($Fe_{2}Si_5$) - and ${\epsilon}$(FeSi)-composition powders was sintered and heat-treated subsequently at various temperatures and time to get thermoelectric ${\beta}$-phase($FeSi_2$) compacts. The different transformational sequences depending on the heat treating temperature were found through the investigation into phase transformation and microstructural development. That is, a rapid eutectoid decomposition of ${\alpha}{\to}{\beta}+Si$ occurred together with a accompanying slow reaction between the dispersed Si formed by above decomposition and the preexisted ${\epsilon}$ phase at temperatures below $830^{\circ}C$. The unreacted Si and the micropores formed due to the density change upon the transformation coarsened as heat treating time elapsed. At temperatures above $880^{\circ}C$, however, transformation was proceeded by a peritectoid reaction of ${\alpha}+{\epsilon}{\to}{\beta}$. It took at least 200min. to achieve 90% volume fracion of transformed ${\beta}$ phase, and the growth of micro-pores was also observed in this transformational sequence with prolonged heat treating time.
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KEYWORD
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Thermoelectric $FeSi_2$, ${\beta}$ phase, Transformational sequence, Eutectoid decomposition, Peritectoid reaction
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