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

钕铁硼（Nd-Fe-B）磁体具有优异的磁性能，已广泛应用于计算机设备和声学设备等各种应用中。Nd_2Fe_<14>B金属间化合物相具有大的饱和磁化强度和高的磁晶各向异性场，这是该磁体的优越性来源。由于Nd_2Fe_<14>B相是通过γ-Fe相与残余液相的包埋反应生成的，因此，在铸造合金中，α-Fe相不可避免地以软磁相的形式残留下来，从而降低了磁体的硬磁性能。本实验中，作为抑制包晶反应的新技术之一，我们尝试了无容器工艺，即通过过冷熔体的快速淬火来形成不含α-Fe的Nd_Fe_<14>B相。本研究的目的是探索从下冷器近终形铸造磁体的可能性 ...更多信息 2003年，建立了急冷系统，掌握了近终形铸造的技术。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，在滴样中含有大量的Nd_2Fe_（<17>B_x）亚稳相。2005年，人们对Nd_2Fe_ B_x的亚稳相变<17>进行<14>了精确的研究。结果表明，Nd_2Fe_<17>B_x向Nd_2Fe_<14>B的扩散相变是快速的，这是由于晶间富Nd相的低熔化温度增强了溶质原子的扩散，这意味着与急冷系统相结合可以实现磁体的近终形铸造。在直径较大的样品中，<14>由亚稳态Nd_2Fe_ B_x分解得到的Nd_2Fe_ B和γ-Fe双相珠光体组织<17>有望成为纳米复合结构磁体的主要候选者之一。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