回火温度对NdCeFeB烧结磁体微观结构及磁性能的影响

Influence of annealing temperature on the microstructure and magnetic properties of sintered NdCeFeB magnet

采用双主相工艺制备了名义成分为Di_(26.8)Ce_(5.6)Fe_(bal)Al_(0.3)Cu_(0.2)Co_(1.0)B_(1.0)的烧结磁体,烧结后分别在440℃、470℃、500℃、530℃进行不同温度回火处理。结果表明,磁体剩磁在回火前后基本没有变化,但是磁体矫顽力却对回火温度较为敏感:在440℃回火时矫顽力最高,达到1091 k A/m;在530℃回火时矫顽力最低,为936 k A/m。对比各样品回火前后的背散射像发现,440℃回火后微观结构并没有明显变化,当温度提高至470℃以上时晶界相变得连续且团块晶界相占比变大。EDS点分析和XRD结果显示,随着回火温度提高,晶界相中Ce含量逐步增高,且富Ce相及CeFe_(2)相衍射峰区域明显,而Nd_(2)Fe_(14)B主相占比逐步减少。富Ce合金的DSC分析结果发现,在424℃左右出现吸热峰,很可能是富Ce与CeFe_(2)相产生的相变点。晶界中Ce含量的提高可能降低各主相晶粒外延区的各向异性场,从而降低磁体矫顽力。

In the present work,the sintered magnet with the nominal composition of Di_(26.8)Ce_(5.6)FebalAl_(0.3)Cu_(0.2)Co_(1.0)B_(1.0) is fabricated through dual-main-phase process.The magnets are annealed at different temperatures from 440 to 530℃.It shows that the magnet remanence almost remains the same after annealing,but the coercivity shows relatively high sensitivity to the annealing temperature,with the maximum and minimum coercivity of 1091 k A/m and 936 k A/m annealed at 440℃ and 530℃,respectively.The backscatter images of the samples before and after annealing at 440℃ show that there is no obvious microstructure change,but as the temperature raises above 470℃,the grain boundary phase gradually become more continuous and the proportion of triple-junction grain boundary phase increases.EDS and XRD results show that with the increase of annealing temperature,the Ce content in the grain boundary phase increases gradually,and the existence of Ce-rich phase and Ce Fe_(2) phase peaks became more and more obvious,while the proportion of Nd_(2)Fe_(14)B main phase decreases gradually.The DSC curve of Ce-rich alloys shows an endothermic peak at 424℃,which is the possible phase transformation point of Ce-rich and CeFe_(2) phases.The increase of Ce content in the grain boundary may reduce the anisotropy field of the outer regions of the main phase grains,thus reducing the coercivity of the magnet.