注射成形纯铁软磁材料的δ相烧结致密化机理

High density is the first condition with excellent magnetic properties for iron-based soft magnetic materials. How to improve the density of iron-based soft magnetic materials is the key problem to bring the advantage of powder metallurgy on the production of soft magnetic parts into full play. In this project, a new idea that delta phase sintering densification of injection molded soft magnetic materials has presented. Using carbonyl iron as powder, the influences of raw material powder, injection molding technology, sintering process on the density, microstructure and magnetic properties of pure iron were systematically investigated. The sintering kinetics, mass transfer process and grain growth kinetics, the diffusion rate and the change of lattice constant of delta phase transformation point of injection molded iron were deeply analyzed. The material transfer mechanism was studied. Based on this, the delta phase sintering densification mechanism of injection molded pure iron was illuminated. The relationship between microstructure and magnetic performance (magnetic permeability, magnetic induction intensity, coercive force, etc.) of injection molded pure iron was established. The results provide experimental basis and theoretical support for the high performance of pure iron and iron-based soft magnetic materials fabricated by powder injection molding.

高致密度是保证铁基软磁材料具备良好磁性能的重要条件。如何提高铁基软磁材料的密度，已成为应用粉末冶金技术制造铁基软磁材料零部件的关键难题。本项目提出注射成形软磁材料δ相烧结致密化的新思路，以羰基铁粉为研究对象，系统考察粉末原料、注射成形工艺、烧结工艺等对纯铁软磁材料的致密度、微观组织结构与软磁性能的影响规律，深入分析烧结动力学、烧结传质过程、晶粒生长动力学和δ相相变点的扩散速率、晶格常数的变化，弄清烧结过程中物质迁移机制，阐明注射成形纯铁软磁的δ相烧结致密化机理，厘清微观组织与磁性能（磁导率、磁感应强度、矫顽力等）之间的构性关系，为粉末注射成形制备高性能纯铁及铁基软磁零部件提供实验依据和理论支持。

纯铁软磁材料因具较高的饱和磁感应强度和居里温度及资源丰富、环境负荷低等优点，已成为计算技术、仪表、电力、电子和汽车工业等领域不可缺少的材料。随着时代的进步和产业的迅速发展，各种仪器设备日趋小型化、复杂化和多样化，且对外形尺寸的要求越来越精细，对元器件的软磁性能要求越来越高。金属注射成形技术应用于纯铁软磁性材料的制备及其复杂形状零件的生产，可望实现软磁材料产品的低成本、高性能、小型化和大批量规模化生产，还可提高其磁路设计的自由度。但目前由于注射成形制备的软磁材料致密度较低，导致其软磁性能明显劣于铸锻加工制备的软磁材料，无法满足高性能磁路元器件中的应用要求。本项目提出将δ相烧结应用于注射成形纯铁软磁材料的新思路，所制备的注射成形纯铁软磁材料的致密度明显提高。并以纯铁软磁材料为研究对象，以羰基铁粉为原料，系统考察了粉末原料、注射成形工艺和烧结工艺等对纯铁软磁材料的致密度、微观组织结构与磁性能的影响，深入分析了烧结动力学、烧结传质过程和晶粒生长动力学、δ相相变点的扩散速率的变化，阐明了注射成形纯铁软磁材料的δ相烧结致密化机理，归纳总结了微观组织与磁性能之间的构性关系，并将其应用到其它注射成形铁系软磁合金（如Fe-Co，Fe-Si，Fe-P等）的制备，提高了其致密度和软磁性能。在1450摄氏度烧结6小时，可以制备出接近全致密(>99.9%)，磁感应强度B6000=1.81T，矫顽力Hc=20.6A/m，最大磁导率µm=17400的纯铁软磁材料，此性能与铸造纯铁软磁性能相当。为获得全致密、高性能的注射成形纯铁软磁材料和设计新的高性能注射成形铁基软磁材料提供实验依据和理论基础，以满足我国电子元器件对高性能、精密及复杂形状铁基软磁零部件的迫切需求，对拓展粉末冶金软磁材料的应用具有重要的科学意义和实用价值。