Masami Onishi1, Yoshinori Wakamatsu1, Terunori Sasaki2 and Manabu Sagara1
1Department of Metallurgy, The Kyushu Institute of Technology, Kita-Kyushu
Formation kinetics of intermetallic compounds in Fe-Zn mixed powder compacts was investigated in relation to the expansion behavior of the compacts at 259 to 340°C. The ζ phase of a cone shape, which has a non-equilibrium composition ranging from the δ 1 to the ζ phase is first formed at the interface between iron and zinc particles, then the conical crystal grows into zinc particles. After the appearance of the Γ and ζ phases the composition of the ζ phase becomes the equilibrium one. Although the compacts expand as long as one of the three phases grows continuously by diffusion of zinc from the zinc particles to the compounds, the growth of the conical ζ phase having a non-equilibrium composition gives rise to the maximum expansion rate. This phenomenon arises mainly from a one-sided diffusion of zinc into the conical crystal.
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