Enhancement of magnetic properties by controlling structures

点击翻译按钮获取中文摘要

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