Near-net Shape Casting of Rare-earth Iron Magnet from Undercooled Melt

Nd-Fe-B(NdFeB)磁体具有优异的磁性能，在计算机设备、声学设备等领域有着广泛的应用。这种磁体的优越性源于Nd2Fe14&Gt；B金属间化合物相具有较大的饱和磁化强度和较高的磁晶各向异性。由于Nd2Fe14&Gt；B相是先包晶的γ-Fe相与残余液发生包晶反应而形成的铁磁性相，在铸造合金中，α-Fe相不可避免地以软磁相的形式存在，降低了磁体的硬磁性能。在本实验中，作为抑制包晶反应的新技术之一，尝试了无容器处理，其中过冷熔体的快速淬火有望形成不含α-Fe的NdFe14&Gt；B相。本研究的目的是探索从底盘…中近净成形铸造磁体的可能性。2003年建立了水花淬火系统，建立了近终形铸造工艺。2004年，为了阐明显微组织与过冷度之间的关系，进行了落管实验。实验结果表明，在滴入的样品中，有大量的Nd2Fe&lt；17&Gt；Bx相作为亚稳定相存在。2005年，我们对亚稳态Nd2Fe17&gt；B_x向稳定的Nd2Fe14&gt；B的相变进行了精确的研究。结果表明，Nd2Fe&lt；17&gt；Bx向Nd2Fe&lt；14&gt；B的扩散相转变速度很快，这是因为晶界保留的富Nd相由于熔化温度较低而提高了溶质原子的扩散系数，这意味着与片状淬火系统相结合，可以从过冷熔体中近净地浇注磁体。在直径较大的样品中，由亚稳Nd2Fe&lt；17&gt；Bx分解而成的Nd2Fe&lt；14&gt；B和γ-Fe双相珠光体组织有望成为纳米复合组织磁体的主要候选者之一。较少

Neodymium-iron-boron (Nd-Fe-B) magnets with excellent magnetic properties have been widely used in various applications such as computer devices and acoustic equipment. The superiority of the magnets originates from the Nd_2Fe_<14>B intermetallicphase, which has a large saturation magnetization and a high magnetocrystalline anisotropy field. Because the ferromagnetic Nd_2Fe_<14>B phase is formed via the peritectic reaction between the pro-peritectic γ-Fe phase and the residual liquid, in the casting alloy, the α-Fe phase inevitably remains as a soft-magnetic phase, deteriorating the hard magnetic properties of magnets. In the present experiment, as one of novel techniques to suppress the peritectic reaction, containerless processing has been tried, in which the rapid quenching of the undercooled melt is expected to form the Nd_Fe_<14>B phase free from the α-Fe. The objective of the present study is to explore the possibility of the near-net shape casting of a magnet from the undercoole … More d melt.In 2003, a splat quenching system was built up and the know-how to perform the near-net shape casting was established. In 2004, in order to elucidate the relationship between the microstructure and the undercooling, the drop-tube experiment was carried out. The experimental results show that, in the as-dropped sample, a large amount of the Nd_2Fe_<17>B_x was contained as a metastable phase. In 2005, the phase transformation from the metastable Nd_2Fe_<17>B_x into stable Nd_2Fe_<14>B was precisely investigated. The results show that the diffusive phase transformation from Nd_2Fe_<17>B_x into Nd_2Fe_<14>B was rapid, because the Nd-rich phase retained at the intergranular region enhanced the diffusivity of the solute atom due to its low melting temperature, implying that the combination with the splat quenching system enables the near-net shape casting of a magnet from the undercooled melt. In the sample with relatively large diameter, the Nd_2Fe_<14>B and γ-Fe dual-phase pearlite-like microstructure that was decomposed from the metastable Nd_2Fe_<17>B_x can be expected to be one of the prominent candidates for a magnet with nano-composite microstructures. Less