In order to obtain ultrafine Nd-Fe-B powder, a spray-dried precursor was treated by reduction-diffusion (R/D) process. And, unlike the conventional R/D process, calcium reduction that is a crucial step for the formati...In order to obtain ultrafine Nd-Fe-B powder, a spray-dried precursor was treated by reduction-diffusion (R/D) process. And, unlike the conventional R/D process, calcium reduction that is a crucial step for the formation of Nd2Fe14B was performed without conglomerating the precursor with Ca powder. By adopting this modified process, it is possible to synthesize the hard magnetic Nd2Fe14B at the reaction temperature as low as 850 ℃. The average size of Nd2Fe14B particles that are uniformly distributed in the optimally treated powder was <<1 μm. Most Nd2Fe14B particles were enclosed with thin layers of Nd-rich phase. Typical magnetic properties of such powder without eliminating impurity CaO were iHc=～5.9 kOe, Br=～5.5 kG, and (BH)max=～6 MGOe.展开更多
The arrangements of the easy magnetization axis [001] of columnar Nd2Fe14B crystals in the laser scanned layer on anisotropic sintered Nd15Fe77B8 magnets were investigated by XRD and the Bitter method. The results sho...The arrangements of the easy magnetization axis [001] of columnar Nd2Fe14B crystals in the laser scanned layer on anisotropic sintered Nd15Fe77B8 magnets were investigated by XRD and the Bitter method. The results show that the common effects of both the heat flux and the substrate magnetization orientation constrain the columnar Nd2Fe14B solidified from the laser melting pool to form the c-axis texture orientated with the same direction as that of the substrate, when the geometric relationship between the heat flux in the laser scanning layer and c-axis texture orientation of the substrate is perpendicular to each other, and if the laser scanning velocity is no less than 25 mm·min-1. The c-axes of columnar Nd2Fe14B crystals are no longer randomly distributed in the plane normal to their preferential growing direction as they are randomly done in both ingots cooled by water-cooling copper mould and directionally solidified Nd-Fe-B rods.展开更多
用扫描电镜 (SEM )观察了Nd Fe B磁粉颗粒之间的磁团聚现象。对呈自然松散状态的Nd Fe B磁粉的磁化曲线测量结果表明 ,磁团聚现象是造成Nd Fe B磁粉难以充分取向的重要原因。用有限元数值分析方法对Nd Fe B磁粉颗粒之间的磁团聚相互作...用扫描电镜 (SEM )观察了Nd Fe B磁粉颗粒之间的磁团聚现象。对呈自然松散状态的Nd Fe B磁粉的磁化曲线测量结果表明 ,磁团聚现象是造成Nd Fe B磁粉难以充分取向的重要原因。用有限元数值分析方法对Nd Fe B磁粉颗粒之间的磁团聚相互作用进行了模拟计算。结果表明 ,随着Nd Fe B粉末颗粒间距的减小 ,颗粒之间的磁团聚作用力明显增大。当Nd Fe B粉末中存在α Fe时 ,颗粒之间的磁团聚作用力明显高于无α Fe时的磁团聚力。由于大部分有效取向外磁场被磁团聚效应抵消了 ,用通常的取向外磁场 (≤ 2 .0T)难以使Nd Fe B磁粉充分取向。展开更多
本文研究了添加微量元素Si对HDDR工艺制备各向异性Nd Fe Co B Si系永磁磁粉的磁性能和磁粉结构的影响。研究结果表明 :添加Si可以显著地提高磁粉的矫顽力和各向异性 ,Si的添加可以细化晶粒 ,还能使反磁化畴难以形核 ,因而磁粉的矫顽力...本文研究了添加微量元素Si对HDDR工艺制备各向异性Nd Fe Co B Si系永磁磁粉的磁性能和磁粉结构的影响。研究结果表明 :添加Si可以显著地提高磁粉的矫顽力和各向异性 ,Si的添加可以细化晶粒 ,还能使反磁化畴难以形核 ,因而磁粉的矫顽力较高。目前对于添加Si的Nd Fe展开更多
文摘In order to obtain ultrafine Nd-Fe-B powder, a spray-dried precursor was treated by reduction-diffusion (R/D) process. And, unlike the conventional R/D process, calcium reduction that is a crucial step for the formation of Nd2Fe14B was performed without conglomerating the precursor with Ca powder. By adopting this modified process, it is possible to synthesize the hard magnetic Nd2Fe14B at the reaction temperature as low as 850 ℃. The average size of Nd2Fe14B particles that are uniformly distributed in the optimally treated powder was <<1 μm. Most Nd2Fe14B particles were enclosed with thin layers of Nd-rich phase. Typical magnetic properties of such powder without eliminating impurity CaO were iHc=～5.9 kOe, Br=～5.5 kG, and (BH)max=～6 MGOe.
基金This work was financially supported by the Zhejiang Provincial Natural Science Fund of China (No.M503096) and by Ministry of Science and Technology (No.2004CCA04000).
文摘The arrangements of the easy magnetization axis [001] of columnar Nd2Fe14B crystals in the laser scanned layer on anisotropic sintered Nd15Fe77B8 magnets were investigated by XRD and the Bitter method. The results show that the common effects of both the heat flux and the substrate magnetization orientation constrain the columnar Nd2Fe14B solidified from the laser melting pool to form the c-axis texture orientated with the same direction as that of the substrate, when the geometric relationship between the heat flux in the laser scanning layer and c-axis texture orientation of the substrate is perpendicular to each other, and if the laser scanning velocity is no less than 25 mm·min-1. The c-axes of columnar Nd2Fe14B crystals are no longer randomly distributed in the plane normal to their preferential growing direction as they are randomly done in both ingots cooled by water-cooling copper mould and directionally solidified Nd-Fe-B rods.
文摘用扫描电镜 (SEM )观察了Nd Fe B磁粉颗粒之间的磁团聚现象。对呈自然松散状态的Nd Fe B磁粉的磁化曲线测量结果表明 ,磁团聚现象是造成Nd Fe B磁粉难以充分取向的重要原因。用有限元数值分析方法对Nd Fe B磁粉颗粒之间的磁团聚相互作用进行了模拟计算。结果表明 ,随着Nd Fe B粉末颗粒间距的减小 ,颗粒之间的磁团聚作用力明显增大。当Nd Fe B粉末中存在α Fe时 ,颗粒之间的磁团聚作用力明显高于无α Fe时的磁团聚力。由于大部分有效取向外磁场被磁团聚效应抵消了 ,用通常的取向外磁场 (≤ 2 .0T)难以使Nd Fe B磁粉充分取向。
