( 中國科學(xué)院 電工研究所應(yīng)用超導(dǎo)重點實驗室，北京 100080)
摘 要: 在3種不同凝固條件下， 制備了Bi-Mn合金， 研究了合金中MnBi相織構(gòu)組織隨磁感應(yīng)強度和凝固時間的演化。結(jié)果表明， 合金從265~355 ℃的固液兩相區(qū)凝固時， 隨1.0 T磁場中凝固時間的延長， 取向棒狀MnBi晶粒沿磁場方向聚合長大，長徑比增大約50％； 合金從355~446 ℃的固液兩相區(qū)凝固時， 隨外磁場強度的增大（最大達10.0 T）和凝固時間的增加，取向片狀MnBi晶粒沿磁場方向聚合長大， 形成疏松不規(guī)則的粗大棒狀晶粒； 合金從完全熔化狀態(tài)凝固時， 以0.15 ℃/s的速度冷卻可以獲得MnBi相織構(gòu)組織， 以0.015 ℃/s或更小的速度冷卻則不能； 延長磁場中Bi-Mn合金的凝固時間不能有效提高材料的剩磁性能。
關(guān)鍵字: 金屬凝固； 磁取向； 強磁場； Bi-Mn合金； MnBi相
YAN Lu-guang
（ CAS Laboratory of Applied Superconductivity, Institute of Electrical Engineering,
Chinese Academy of Sciences, Beijing 100080, China）
Abstract: Bi-Mn alloys were prepared under three different solidification conditions respectively. The microstructure evolutions of magnetic aligned MnBi grains were investigated experimentally in dependence on magnetic flux density and solidified time. The results show that, solidifying from mushy zone between 265 ℃ and 355 ℃ in an 1.0 T magnetic field, the aligned rod-like MnBi grains congregate and grow up along the direction of magnetic field with the increase of solidified time so that the mean ratio of long axis to diameter of the grains increases about 50%; solidifying from mushy zone between 355 ℃ and 446 ℃, the aligned oblate-shaped MnBi grains also congregate and grow up along the direction of magnetic field with the increase of magnetic flux density (up to 10.0 T) and solidified time, while several huge rod-like MnBi grains appear, which are irregular and loose; solidifying from molten state, the textured structure of MnBi phase can form at a cooling rate of 0.15 ℃/s, but can not at 0.015 ℃/s or slower. The remanence of Bi-Mn alloys can hardly be enhanced by prolongating solidified time in a magnetic field.
Key words: metal solidification; magnetic alignment; high static magnetic field; Bi-Mn alloy; MnBi phase
