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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。
NdFeB rare earth permanent magnetic alloys were selected as the research object. The Bridgman directional solidification process was used to combine Bitter grain morphology with X-ray diffraction analysis to systematically study the effect of Nd2Fe14B (T1 phase) intermetallic compound peritectic phase during directional solidification Growth morphology and orientation changes. The results show that the morphology and preferred growth direction of peritectic T1 phase are related to alloy composition and solidification rate during directional solidification. When the solidification rate is low (less than 10μm · s-1), the peritectic T1 phase grows in a typical faceted manner and exhibits strong crystallographic properties. With the increase of the solidification rate, the grain size of T1 phase is gradually refined and the growth phase of T1 phase appears the tendency of roughening. When the solidification rate of Nd11.76Fe82.36B5.88 alloy is 1μm · s-1, the easy magnetization axis [001] ] Direction is almost along the direction of heat flow, which is very different from the traditional interpretation of preferential growth of T1 along the a-axis [100] direction. The axial preferred orientation of T1 phase in Nd13.5Fe79.75B6.75 alloy deviates gradually with the increase of solidification rate c axis to a-axis. The reason may be that the increase of the solidification rate causes the growth driving force of the T1 phase along the [100] and [001] directions, ie, the change of the growth rate.