Yamamoto, Koji, Sugiyama, Suguru, Nakamura, Yoshiteru, Jinbo, Itaru, Ozawa, Shunpei, Kuribayashi, Kazuhiko, 山本 晃司, 杉山 卓, 仲村 良輝, 神保 至, 小澤 俊平, 栗林 一彦, Yamamoto, Koji, Sugiyama, Suguru, Nakamura, Yoshiteru, Jinbo, Itaru, Ozawa, Shunpei, Kuribayashi, Kazuhiko, 山本 晃司, 杉山 卓, 仲村 良輝, 神保 至, 小澤 俊平, and 栗林 一彦
The melt of Fe-66.7 percent Si ejected into a drop tube was undercooled and solidified during the free fall. The microstructures of the spherical samples with various diameters that accumulated at the bottom of the drop tube were observed and analyzed by scanning electron microscopy (SEM), x-ray diffraction (XRD) and differential thermal analysis (DTA). The microstructure of the sample, the diameter of which is from 600 micrometer to 1,000 micrometer, consisted of the pro-eutectic primary Fe2Si5(alpha) phase and the subsequent eutectic phase of alpha and FeSi(epsilon), though the epsilon phase has to grow as the pro-eutectic primary phase according to the phase diagram. In the samples with diameters smaller than 600 micrometer, however, consisted the microstructure of small epsilon phase and fine eutectic. The fine eutectic in the sample with the diameter smaller than 600 micrometer can be easily transformed to a single phase of FeSi2(beta) by short time annealing such as for 10 minutes at 1,100 K, that is 100 times shorter than the value reported previously in the unidirectionally solidified sample.