采用传统的粉末冶金方法制备了名义成分为Nd_(28)Dy_2Fe_(68.6)B_1Ga_(0.2)Nb_(0.2)的烧结钕铁硼磁体,并研究了烧结钕铁硼磁体Nd_(28)Dy_2Fe_(68.6)B_1Ga_(0.2)Nb_(0.2)晶粒的细化和磁体晶界相演化之间的关系。通过细化磁粉粒度,制备出了平均晶粒尺寸分别是8.22,4.69,3.60和3.12μm的4种磁体。结果表明,磁体平均晶粒尺寸为3.60μm时对应的磁体的磁性能最好:最大磁能积(BH)m=389.93 k J·m^(-3),内禀矫顽力Hcj=1282.79 k A·m^(-1)。从磁体的微观形貌观察发现,随着磁体平均晶粒尺寸的减小,磁体中角隅晶界相的尺寸减小,条带状晶界相的比例增大,使更多的富Nd相参与到隔断主相晶粒之间的磁交换耦合中来,磁体矫顽力提高。磁粉粒径细化之后,磁粉颗粒的形貌更加规则、均一,取向时受到的摩擦力减小,提高了磁体的剩磁和取向度。但是随着平均晶粒尺寸从3.60到3.12μm的进一步减小,富Nd相发生了团聚,且分布不均匀,导致磁体矫顽力降低;磁体中的富Nd相增多并团聚,导致了磁体在烧结过程中由于液相较多而使主相晶粒发生了偏转,而且导致了磁体取向度降低,进而导致剩磁的减小。
In this paper, the magnetic Nd–Fe–B particles of different sizes were conducted under vacuum by the hot pressing, then cooled quickly to room temperature. Finally hot deformation was performed to get the anisotropy Nd–Fe–B magnet at a deformation rate of 70 % in the protection of argon atmosphere. NIM-2000 was used for the measurement of hysteresis loop of the samples. Meanwhile, scanning electron microscopy(SEM) was used to observe the surface morphology of the magnetic particles with different sizes and hot-deformed magnets, energy spectrum analyzer to analyze the composition of magnetic particles. The effect of magnetic particle sizes on the microstructure and magnetic properties of the hot-deformed anisotropic magnet was investigated. Anisotropic hot-deformed magnets produced from the maximum particle size of 200–350 lm have the highest magnetic properties of Br= 1.465 T, Hcj=1,157 k Aám-1,(BH)max= 425 k Jám-3.
Xu-Chao WangMing-Gang ZhuWei LiYan-Feng LiBin LaiAn Du
The strip-casting technique plays an important role in fabricating high coercivity sintered magnet. In this paper, we investigate the phase constitution and the microstructure of rapidly solidified Ce–Fe–B alloy fabricated by strip-casting.We find that the Ce2Fe14 B phase coexists with Fe, Fe2 B, and CeFe2 phases in the Ce–Fe–B strips. The eutectic structure consisting of Fe and Fe2 B is encased in Ce2Fe14 B grains, which is blocked by the CeFe2 grains at triple junctions, indicating that the microstructure of Ce–Fe–B strip is characteristic of a peritectic solidification. Thermal analysis indicates that the large supercooling of Ce2Fe14 B results in the residual Fe and Fe2 B. The microstructural optimization in Ce–Fe–B strips without Fe and Fe2 B could be achieved by a heat treatment of 1000?C.
The relationship between the microstructure and magnetic properties of Nd-Fe-B sintered magnet compressed by shock wave with 6.26 GPa≤p≤7.16 GPa was investigated.It reveals that Nd-Fe-B magnets show a demagnetization behavior after compressed by shock wave.The intergranular fracture is the main occurring phe-nomenon in the shock wave-compressed magnets.The coercivity of the shock wave-compressed Nd-Fe-B magnets could be recovered after repeating the annealing process.It suggests that only the morphology change just like the intergranular fracture occurs,and there is no structural change in the grain boundary phase in the shock wave-compressed magnet.Matrix phase grain interconnection,microcracks and pores,and alterant orientation relationship between matrix phase and grain boundaries phase are con-sidered as induced factors of demagnetization.
Ming-Gang ZhuYan-Feng LiWei LiLi-Yun ZhengDong ZhouHai-Bo FengLang ChenAn Du
