발간논문

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Vol.29, No.7, 688 ~ 695, 1991
Title
Microstructure and Magnetic property of Unidirectionally Solidified Bi / MnBi Eutectic Alloy
김기배K . B . Kim, 조순형S . H . Cho, 심진섭J . S . Shim, 박종완J . Y . Park, 이호인H . I . Lee, 나형용H . Y . Ra, 윤의박E . P . Yoon
Abstract
Microstructure and magnetic property correlations have been sought for unidirectionally solidified Bi/MnBi eutectic alloys. The growth rate was varied from 0.5 to 60 ㎝/h and the temperature gradient was varied from 56 to 256 K/㎝. Annealing for 60 hours at 248℃ was necessary for enhancing the magnetic property. The MnBi phase morphology under various growth conditions was characterized by four types;rod, trinangular, V letter and broken lamellar type. The slope of a logarithmic plot of MnBi phase spacing with respect to growth rate was 0.5148, which was nearly in agreement with the theoretical slope of a nf/nf eutectic alloy. This means the MnBi phase to be independent of temperature gradient. The coercivity of the Bi/MnBi eutectic alloy solidified unidirectionally were greatly imporved by annealing. This seems to be caused by the transformation of the MnBi phase from HTP to LTP. The more increased the growth rate, the more the intrinsic coercivity improved. As a result, the maximum intrinsic coercivity of 27.8 kOe was obtained at the growth rate of 60 ㎝/h.
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