Enhancement of magnetic properties by controlling structures

本研究旨在通过控制稀土永磁和磁致伸缩合金的凝固组织和热处理组织，为显著提高稀土永磁和磁致伸缩合金的磁性能提供指导。对于Nd-Fe-B系永磁合金，增加Nd_2Fe_ B相的含量<14>是提高磁性能的必要条件。因此，将初始成分范围扩大到γ-Fe代替Nd_2Fe_ B初晶的稳定相范围<14>，并<14>应用考虑相选择准则的最新枝晶生长理论对Nd_2Fe_ B亚稳相进行了预测。（TbDy）Fe_2合金具有优良的磁致伸缩性能，在传感器和驱动器材料等方面有着广泛的应用。为了获得更高的性能，有必要研究（TbDy）Fe_2Laves相的凝固行为、晶体生长和磁致伸缩性能，从而获得具有良好微结构控制的晶体 关于我们 Nd-Fe-B系中的Se选择采用快淬技术制备了近化学计量比的Nd-Fe-B合金。实现了Nd_2Fe_ B的晶化<14>。阐明了其与合金成分、凝固速度的关系。在此基础上，<14>根据枝晶生长理论，定量预测了Nd_2Fe_ B和γ-Fe之间的相选择。2.<111>取向Tb-Dy-Fe单晶的生长Tb-Dy-Fe合金的磁致伸缩具有高度的各向异性，沿着其方向的磁致伸缩性能最好<111>。然而，<111>根据以往的研究，定向单晶的生长是非常困难的。在本研究中，<111>Tb-Dy-Fe单晶体的生长成功地与择优生长和孪晶再入阶梯生长机制仔细考虑。3<111>.（TbDy）Fe_2晶体磁致伸缩性能的表征对<112>-、<110>-和<111>-取向Tb-Dy-Fe晶体的磁致伸缩性能进行了测量。发现晶体的性能<110>比通常使用的<112>晶体高。在单晶中<111>，获得了世界上最大的磁致伸缩跳跃和最低的饱和磁场

This research aims to present a guide line to improve significantly magnetic properties of rare earth permanent magnets and magnetostrictive alloys by controlling solidified and heat-treated structures. For Nd-Fe-B permanent magnetic alloys, increasing of amount of Nd_2Fe_<14>B phases is necessary to enhance magnetic properties. Therefore an initial composition range is expanded to a stable phase range of primary crystallization of gamma-Fe instead of Nd_2Fe_<14>B and also prediction of metastable Nd_2Fe_<14>B is made by using a recent dendritic growth theory considered with phase selection criterion. (TbDy) Fe_2 alloy has excellent magnetostrictive properties and thus exhibits extensive applications such as being transducer and actuator materials. To achieve higher properties, it is necessary to investigate the solidification behavior, crystal growth and magnetostrictive performance of the (TbDy) Fe_2 Laves phase, and thus obtain the crystals with well controlled microstructures.1.Pha … More se selection in the Nd-Fe-B systemNear-stoichiometric Nd-Fe-B alloys were prepared with a rapid solidification method using melt-spinning technique. Crystallization of the metastable Nd_2Fe_<14>B was realized. Its relationships of to alloy composition, solidification velocity was clarified. Furthermore, the phase selection between the Nd_2Fe_<14>B and gamma-Fe was quantitatively predicted on the basis of a dendritic growth theory.2.Growth of <111>-oriented Tb-Dy-Fe single crystalMagnetostriction of the Tb-Dy-Fe alloy is highly anisotropic with the best properties along its <111> directions. However, growth of <111>-oriented single crystal was very difficult according to previous studies. In the present research, <111>-oriented Tb-Dy-Fe single crystals were grown successfully with a careful consideration on the preferred growth and twinned re-entrant stepped growth mechanism. Furthermore, the effects of alloy composition and growth conditions on the <111> growth were clarified.3.Characterization of the magnetostrictive properties of the (TbDy) Fe_2 crystalsThe magnetistrictive properties of <112>-, <110>- and <111>-oriented Tb-Dy-Fe crystals were measured. Higher properties were found in the <110> crystals than usually used <112> one. In the <111> single crystals, the largest magnetostrictive jump and the lowest saturation magnetic field in the world were obtained Less