定向凝固NdFeB永磁合金中包晶相的取向生长研究

Orientation Growth of Peritectic Phase in Directionally Solidified NdFeB Permanent Magnet Alloys

选取NdFeB稀土永磁合金作为研究对象,采用Bridgman定向凝固工艺,将Bitter粉纹磁畴图像与X射线衍射分析方法相结合,系统研究定向凝固过程中金属间化合物包晶相Nd2Fe14B(T1相)的生长形态及取向变化规律。研究表明:定向凝固过程中包晶T1相的形态及择优生长方向与合金成分及凝固速率有关。凝固速率较低时(小于10μm·s-1),包晶T1相以典型的小平面方式生长,表现出强的晶体学特性。随着凝固速率增大,T1相晶粒逐渐细化,T1相生长界面出现粗糙化趋势;Nd11.76Fe82.36B5.88合金在1μm·s-1凝固速率下,T1相的易磁化轴[001]方向几乎沿热流方向,这与T1相沿a轴[100]方向择优生长的传统解释有很大不同;Nd13.5Fe79.75B6.75合金中T1相的轴向择优取向随凝固速率的增加逐渐偏离c轴而转向a轴,其原因可能是凝固速率的增加引起T1相沿[100]和[001]方向的生长驱动力即生长速率的改变。

Directional solidification experiments were performed on the NdFeB rare earth permanent magnets. The solidification be- haviors of the intermetallic compound Nd2 Fe14 B （ T1 ） phase were analyzed by X-ray diffraction （XRD） analysis method and Bitter magnetic domain observation. The resuhs showed that the morphology and the preferred orientation of Nd2Fe14 B were related to the composition and solidification rate. At lower solidification rates （less than 10 μm·s-1 ） , T1 phase grew with a faceted interface and ex- hibited a high tendency of the anisotropic growth. With the increase of the growth rate, the Ti grain became refined, and the growth in- terface of T~ phase tended to be roughened. The axial preferred orientation of Tt phase was close to the direction of the easy magnetiza- tion axis, i.e. c-axis [ 001 ] during directional solidification Nd11. 76 Fe82. 36 B5. 88 alloy. In addition, the preferred orientation of T1 phase gradually deviated from the c-axis [ 001 ] to a-axis [ 1001 with increased solidification rate in Nd13.5 Fe79.75 B6. 75 alloy. The reason might be that the solidification rate changed the driving forces, i.e. the growth rates in the [ 100] and [001 ] directions of the T1 phase.