高Bs纳米晶合金的非均匀结构衍化及对磁性能的影响研究

For nanocrystalline soft-magnetic alloys, formation of uniform microstructure with fine grain size and even distribution is crucial for obtaining excellent magnetic properties. The original α-Fe nucleis precipitated during the solidification process plays an important role in increasing the density and refining the size of grains for high Bs nanocrystalline alloys. However, the difference of the cooling rate and supercooling degree in solidification process will inevitably results in the non-uniform distribution of original nuclei in the cross-sectional direction. It is hence difficult to obtain a uniform microstructure through the conventional heat treatment process, which led to the deterioration of magnetic properties. In this project, the non-uniform structure derivation and its influence to the magnetic performance of high Fe content FeSiBCu alloys will be revealed. First, the formation mechanism and influencing factors of the original nucleis and clusters in quenched ribbon will be deeply studied, and the thermodynamics and kinetics analysis will clarify the formation mechanism of the original nucleis and clusters. Second, application of the rapid heating device to study the influence of original nucleis and clusters in different layers during crystallization process will help us understand the formation mechanism of the new nucleis and its competitive relations with original nucleis. Finally, characterization of the microstructure and macroscopic magnetic structures of the ribbons after heat treatment will be performed to associate the non-uniform microstructure with the magnetic properties. This project will contributes to a better understanding of the non-uniform structure everlution process of high Bs nanocrystalline alloys, which of great significance to promote the production and application.

纳米晶合金获得优异磁性能的关键是形成晶粒细小及分布均匀的微观结构。高Bs纳米晶合金淬态带材中的α-Fe晶核在提高晶粒密度和细化晶粒方面具有重要作用。然而，由于冷却速度的不同，带材横截面方向原生晶核和团簇分布不均匀，常规的热处理工艺难以得到均匀的微观结构，导致磁性能恶化。本项目拟以FeSiBCu系纳米晶合金的非均匀结构衍化及对磁性能的影响为研究对象，深入研究淬态带材中原生晶核和团簇形成机理及影响因素，并进行热力学和动力学分析，建立其形成机制；借助快速加热热处理装置研究不同晶化阶段带材各层中晶核和团簇的微观结构衍化，弄清新生晶核的形成机制及其与原生晶核的竞争关系；表征热处理后带材的微观结构、微观磁结构及宏观磁性能，建立微观结构不均匀性与磁性能的关联，阐明高Bs纳米晶软磁合金的非均匀结构衍化微观机制。本研究对高Bs纳米晶合金的生产和应用具有重要指导意义。

纳米晶合金具有高饱和磁感应强度、高磁导率、低损耗和低磁致伸缩系数等优点，是变压器和电机等能源传输和转换领域应用的理想软磁材料。然而，当前其生产和应用仍然存在严重障碍，常规制带和热处理方法难以获得均匀的纳米晶结构和优异的磁性能，微观结构非均匀性的形成机制也不清楚。本项目从微观结构衍化规律入手，研究晶核形成和晶粒长大的条件和影响因素，重点探索了结构衍化过程的非均匀性及对磁性能的影响，从而指导优化了合金成分和制备条件。项目实施完全按照计划进行，系统深入，进展顺利。首先，以计划的FeSiBCu系合金为研究对象，通过调整铜辊转速，成功实现了带材横截面方向的初晶相的梯度调控，并结合冷却速度梯度分析建立了初晶相的形成条件；然后，研究了热处理过程中带材的不同形核和晶体长大方式，分析了瞬态核壳结构的形成机制和其对晶粒生长过程的影响，揭示了高晶粒生长速度下的竞争晶粒细化机制的作用本质。之后，将非均匀晶化机制拓展到FeSiB(P,C)Cu系列合金中，进行了更普适的研究，探索了各组元及多组合间的协同作用对淬态带材微观结构和晶化过程的影响，并总结出了高Bs纳米晶软磁合金的成分设计新方法，提出了不含Cu元素的新型高Bs纳米晶合金设计新机制，开发了热稳定性和磁性能同步提高的新成分和热处理工艺，发现调控临界非晶形成能力效应是解决高Bs纳米晶合金软磁性能的关键，建立了合金成分-热处理工艺-微观结构-磁性能的关联机制；最后，在新晶化调控机制和成分设计方法的指导下，设计了具有优异杂质兼容性的FeSiBPCCu系合金，实现了工业原料制备，解决了高Bs纳米合金工业化生产的关键障碍。在本项目的支持下，发表了19篇高水平的SCI论文，申请了6项国家发明专利，其中2项先进成果已经开始进行中试，可望实现生产和应用；此外，还培养了2名博士生和4名合培硕士生，其中4人被评为优秀毕业生。