磁场对Bi-Mn合金两相区中MnBi相凝固组织的影响

EFFECTS OF A STATIC MAGNETIC FIELD ON SOLIDIFICATION STRUCTURE OF MnBi PHASE IN SEMI-SOLIDIFIED Bi-Mn ALLOY

将 Ｂｉ－３％Ｍｎ和Ｂｉ－６％Ｍｎ合金加热至固液两相区内低于 ＭｎＢｉ相 Ｃｕｒｉｅ点的温度，保温 ３０ ｍｉｎ后在一定条 件下降温凝固，施加 ０－１．０ Ｔ磁场． 结果表明，磁场对 ＭｎＢｉ相凝固组织和材料磁性能有明显的影响 ． Ｂｉ－Ｍｎ合金在固液 两相区恒温时，ＭｎＢｉ晶体在大于 ０．１ Ｔ的磁场作用下沿磁场方向定向排列和优先长大、定向排列因子 Ｔ 随外磁场强度的增大 而提高 在磁场作用下的降温凝固过程中、沿磁场方向ＭｎＢｉ晶体长度增加，其平均长度随磁场的增大和合金在磁场中凝固时间 的延长而增加． 此外，磁取向试样具有明显的磁各向异性，平行定向排列方向的剩磁显著增强，而垂直方向的磁性很弱． 从铁磁性 ＭｎＢｉ晶体的磁各向异性和磁化晶体之间磁相互作用出发，建立了ＭｎＢｉ晶体在磁场中取向和优先长大的理论模型，并利用该模 型对实验结果进行了讨论．

Influences of a static magnetic field (0-1.0 T) on the solidification structure and magnetic property of the semi-solidified Bi-3%Mn and Bi-6%Mn alloys have been investigated. In the present of the magnetic field, the alloys were maintained at semi-solid state for a certain time and then solidified. It was shown that alignment and preferential growth of MnBi crystals along the applied field occurred. The alignment degree of MnBi was increased with the increase of the applied field, and the mean length of elongated MnBi crystals was increased with the increase of the applied field and the prolongation of solidification time. Moreover, the remained magnetic flux intensity along the aligned direction of Bi-Mn alloys in the case with a magnetic field was found to be strongly anisotropic and nearly double of that without magnetic field. A model was proposed to explain the alignment and preferential growth of ferromagnetic MnBi crystals in a magnetic field in terms of the magnetic anisotropism and the interaction between the crystals.