强磁场下新型Fe-Si-B纳米晶软磁合金形成机制及性能研究

As a most potential soft magnetic material, nanocrystalline soft magnetic alloys show advanced soft magnetic properties, such as high magnetization, high permeability and low losses. The nanocrystalline soft magnetic materials are usually fabricated by partially crystallizing from parent amorphous alloys. In order to improve the soft magnetic properties, the non-ferromagnetic elements usually be added to the master amorphous alloy before the crystallization process: Copper enhances the nucleation of the bcc grains while niobium or phosphor impedes coarsening of crystalline. However, the addition of non-ferromagnetic elements will degrade the saturation magnetization. In the present subject, the high magnetic field will be introduced to the nanocrystllization process of amorphous soft magnetic materials. The high magnetic field can promote the nanocrystallization of bcc grains by introduction of magnetic energy and impede grains growth by influences on the atomic diffusion. Starting with the Fe84Si4B12 alloy, as well as the substitution of Fe atoms by Co atoms, the present subject will study the effects of high magnetic field both on the driving force of nucleation and on the diffusion process of atoms during the primary crystallization. It is aimed to establish the mechanism of nanocrystallization under high magnetic field, imply the relationship among the alloy composition, microstructure and soft magnetic properties. The magnetic-field-inducedanisotropies will also be investigated in the present work, which will help to interpret the exchange coupled mechanism of nanocrystalline soft materials annealed under high magnetic field. The research results will support fruitful experiments and theories for the investigation of high performance nanocrystalline soft magnetic materials in the future.

纳米晶软磁合金兼有高饱和磁感应强度、高磁导率、低损耗等优异的软磁性能，是软磁材料开发的新方向。当前主要采用非晶合金晶化方法制备纳米晶软磁材料，通过添加Cu、Nb或P元素促进纳米晶化过程中α-Fe相形核并抑制其生长提高软磁性能。但添加非磁性元素会降低纳米晶软磁材料的饱和磁感应强度。本项目把强磁场引入到软磁非晶合金的纳米晶化过程中，利用强磁场的磁化能及对元素扩散的影响，促进纳米晶形核并细化晶粒，替代非磁性元素添加的方法，制备具有超高性能的纳米晶软磁合金。本项目将以新型Fe84Si4B12为起始合金，并通过Co元素部分替代Fe元素，研究强磁场对纳米晶形核驱动力和原子扩散行为的影响，建立强磁场下的纳米晶软磁合金形成机制；阐明强磁场下纳米晶软磁合金成分、组织与软磁性能之间的关系；分析强磁场退火后合金的磁致各向异性，揭示强磁场下制备态纳米晶软磁合金的交换耦合机制。为开发高性能纳米晶合金提供理论支持。

非晶合金晶化后，形成的非晶/纳米晶软磁复合材料不仅具有Fe基非晶合金的高Bs和Co基非晶合金的高磁导率、低损耗特性，关键高温稳定性大为提高，成为软磁材料研发的重要方向。制备具有优异性能的纳米晶软磁合金需要提高析出相α-Fe的形核质点并且控制其尺寸生长。通常添加非磁性元素Cu和Nb实现纳米晶软磁合金的组织控制，Cu原子团聚形成α-Fe相的形核质点，Nb原子抑制α-Fe的快速长大。纳米晶合金的软磁机制：即纳米晶粒磁矩通过非晶基体进行交换耦合，且强烈依赖于纳米晶粒直径。因此，提高纳米晶析出相数量和抑制纳米晶粒长大成为开发具有优异软性能纳米晶合金的必要条件。而饱和磁感应强度的提高需要尽可能增加铁磁性元素，减少Nb、Cu等非铁磁性元素。这样，在饱和磁感应强度和软磁性能之间存在必然的矛盾，成为开发具有更高性能纳米晶软磁合金的瓶颈问题。均恒强磁场能够将高强度的能量无接触地传递到物质的原子尺度，从而改变原子的排列、匹配和迁移等行为。本研究通过对FeSiB及FeSiBNbCu合金进行强磁场下退火研究发现。强磁场下退火可以显著提高α-Fe相的形核质点，且减小α-Fe相的过分长大，具有与非金属元素Cu和Nb添加类似的作用，同时显著提高合金饱和磁感应强度。强磁场作用下析出的α-Fe具有磁化能降低了形核需要的能垒因此形核速率提高，而强磁场作用下Si元素在α-Fe相中含量增加，绝大多数Si元素从非晶基体迁移到α-Fe相中，这种元素扩散抑制了α-Fe相的长大。通过对完全非晶结构的GdCoCuAl合金进行成分调整，发现对于单一非晶结构，元素成分的调整改变软磁合计饱和磁感应强度，而对于非晶/纳米晶复合材料，晶化相的形成可以显著提高合金的饱和磁感应强度。因此研究证实强磁场可以控制FeSi非晶合金纳米晶化过程，优化合金组织提高性能，是制备高性能纳米晶软磁合金的有效手段。通过本项目的研究，发现以下重要研究结论：1.磁性相析出时，强磁场提供的磁化能可以显著降低析出相形核能垒，降低形核半径，增加形核率。2.FeSi系列合金在强磁场退火时，α-Fe相的生长速率显著变慢，其原因为磁场作用下，α-Fe中Si元素含量增加，非晶基体中Si元素含量减少，Si元素需要完成从非晶基体到α-Fe的迁移，因此生长速率显著降低。3.当成分固定时，纳米晶软磁非晶的饱和磁感应强度随析出α-Fe的增加而增加，完全非晶随成分变化而变化。