高压冶金雾化气淬工艺制备钐铁氮粉体的基础研究

The current technologies of fabricating Sm-Fe-N system permanent magnet alloy powders involve three major steps: Sm-Fe alloy preparation, crushing and milling, and nitriding at 450~500℃. The deficiencies of this technology are high energy consumption, low efficiency, hard control on the formation of α-Fe and Sm-rich phase, and nonuniform distribution of nitrogen element, which significantly affect the magnetic properties of powders manufactured. In this project, a novel technology of producing Sm2Fe17Nx alloy powder by atomizing and gas quenching under high pressure condition was proposed based on some preliminary tests. The characteristics of the new technology include accurate controlling nitrogen content in the whole high-pressure process, atomizing of liquid nitride-bearing alloys, rapid solidification of over-cooled liquid alloy by high pressure gas quenching, and phase transformation controlling through adjusting temperature and pressure. This project mainly investigate the effects of temperature, pressure, and cooling process on the microsctructure of solid alloy powders and on the Sm2Fe17Nx phase constituent control. The nitriding and atomizing mechanism of liquid Sm-Fe alloy in high pressure nitrogen atmosphere, the effect of process parameters of cooling by high-pressure and high-density gas on Sm2Fe17Nx alloy powder forming during gas quenching, cooling and over-cooled rapid solidification of alloy droplet are also examined. The Sm2Fe17Nx alloy powder with excellent magnetic properties will be produced using a high-pressure atomizing and gas quenching equipment designed and developed by ourselves. The project is not only a theoretical research but also a promising application with great prospect and important stategic significance. The achivement of this project will lay a foundation for the efficient, stable and low-cost production of high-performence SmFeN permanent magnetic materials.

现有钐铁氮永磁材料粉体制备一般为钐铁合金制备—破碎制粉—450~500℃低温氮化处理三个步骤，能耗高、效率低、易出现α-Fe和富钐相、氮分布不均匀，直接影响粉体磁性能。鉴于此，申请者提出了高压冶金雾化气淬法制取钐铁氮粉体的新方法，并开展了初步试验，特点为全程高压调控氮含量、含氮液态合金雾化、高压气淬过冷骤凝、温度与压力控制相变。本项目主要研究钐铁合金液态增氮机制，高压条件下含氮液态合金的雾化特点，分析液滴气淬过冷骤凝和冷却过程中，高压高密度气体冷却参数对钐铁氮合金粉体形成的影响，探索温度、压力、冷却曲线对固体合金粉体微观结构和Sm2Fe17Nx等相组成的控制规律，在自主研发的高压冶金雾化气淬实验设备上制备出高性能的钐铁氮粉体。本项目既有科学研究价值，又具有很好的应用前景和重要的战略意义，项目成果将为高效、稳定、低成本生产高性能钐铁氮永磁材料奠定基础。

现有钐铁氮永磁材料粉体制备一般为钐铁合金制备—破碎制粉—450~500℃低温氮化处理三个步骤，能耗高、效率低、易出现α-Fe和富钐相、氮分布不均匀，直接影响粉体磁性能。鉴于此，本文提出了高压冶金雾化气淬法制取钐铁氮粉体的新方法，通过钐铁合金熔液中氮溶解度等热力学和增氮速度等动力学研究，确定了液态合金高压气氛熔炼增氮的压力、温度和底吹参数等因素的控制条件。根据液态合金高压气氛中雾化工艺研究，设计并改进了雾化元器件的尺寸和布置形式。通过模拟研究合金雾滴凝固、冷却过程中的成分变化和相变规律，确定了气氛压力、温度、冷却强度的控制工艺。通过添加Zr、Nb合金元素研究在熔体快冷过程相组成及微观形貌的影响规律，得出添加元素可以有效细化快冷后的微观组织结构；根据EET理论开展了氮化钐铁合金机理的价电子结构的微观分析；并对气雾化参数对钐铁（氮）合金粉体制备过程的影响进行研究，优化了高压气雾化制备钐铁（氮）粉体的实验参数，揭示了钐铁合金熔滴的凝固机理，最终确定了最佳的雾化、腔室、喷铸压力参数分别是3 MPa、0.3 MPa、0.6 MPa。最后采用高压冶金雾化气淬法在自主研发的高压冶金雾化气淬实验设备上制备出尺寸及表面光洁的Sm2Fe17Nx粉体，找到了最优的钐铁合金粉体粒径为40 μm，此时氮化处理后合金的氮含量可达到1.58%。当合金成分为Sm2Fe17ZrNb0.4时，高压雾化粉体平均粒度仅为13.8 μm，球形度提高。这为制备其他不同相结构的钐铁氮粉体提供理论支持。本项目既有科学研究价值，又具有很好的应用前景和重要的战略意义，项目成果将为高效、稳定、低成本生产高性能钐铁氮永磁材料奠定基础。