Enabling L10 Ordering in Bulk FeNi Alloys and an Alternative for Nd2Fe14B- Based Permanent Magnets

基于NdFeB的磁体在风力米尔斯、电动车辆中的DC马达和许多其它关键技术中的使用需求增加。稀土（RE）元素的高成本和对进口Nd和其他稀土元素的严重依赖使得用由更丰富的元素制成的低成本磁体替代NdFeB磁体成为迫切的经济和国家安全需求。 特定FeNi合金中Ni和Fe原子的特定类型的有序排列提供了与NdFeB磁体相当的强大磁性能。 虽然在陨石中已经观察到具有这种有序排列的Fe和Ni原子的FeNi合金，但迄今为止在地球上制造这种合金的努力尚未成功。这是因为这种排列只有在300摄氏度以下才稳定，但在这些温度下，实现有序晶体所需的原子跳跃将需要数百万年。该项目研究（i）使用独特的方法在FeNi单晶中引入大量的晶体缺陷，以及（ii）如何使用它们来增加原子跳跃率并在实际时间范围内获得所需的结构。这项工作也揭示了陨石中形成这种有序排列的FeNi合金的操作机制。最大限度地减少目前对可再生能源进口的依赖的战略需要强调了拟议研究的影响。该项目培训了几名研究生和本科生，加强了几门课程的课程内容，并改善了研究设施。在高中生、女性和代表性不足的学生群体以及更广泛的社区中开展了外联工作。技术概述对用于风力米尔斯、电动汽车直流电机和许多其他关键技术的钕铁硼磁体的需求日益增加。稀土元素的高成本和对进口Nd和其他稀土元素的严重依赖，使得用更丰富的元素制成的低成本磁体替代NdFeB磁体成为迫切的经济和国家安全需求。具有L10有序晶体结构的等原子FeNi合金相提供了与NdFeB磁体相当的强大永磁性能。虽然在中子辐照的FeNi单晶和小行星中观察到了这种相，但由于其约320摄氏度的低临界有序温度和因此的低扩散动力学，它无法以块状形式进行陆地合成。该项目通过在低于临界有序化温度的温度下增强扩散动力学来克服FeNi合金中L10长程有序化的障碍。这是通过增加位错密度和非平衡空位浓度，通过极端变形和合金添加，增强扩散动力学。采用垂直布里奇曼晶体生长技术生长了FeNi单晶。位错和其他缺陷密度的特征在于使用X射线衍射和扫描透射电子显微镜。使用漫散射峰和超晶格峰的X-射线衍射图中的短和长范围的顺序进行检查。有序和本地原子环境也使用扩展的X射线精细光谱（EXAFS）检查。振动样品磁强计用于评估磁性能。这项工作还阐明了在陨石中形成这种有序相的FeNi合金的运作机制。减少目前对稀土元素或稀土磁体进口的依赖的战略需要强调了拟议研究的影响。该项目培训了几名研究生和本科生，加强了几门课程的教学内容，并改善了大学的研究设施。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

NON-TECHNICAL SUMMARYNdFeB based magnets are in increased demand for use in wind mills, DC motors in electric vehicles and numerous other key technologies. The high cost of rare-earth (RE) elements and heavy reliance on imports of Nd and other rare-earth elements make the replacement of NdFeB magnets with low-cost magnets made of more abundant elements an urgent economic and national security need. A specific type of ordered arrangement of Ni and Fe atoms in a specific FeNi alloy provides powerful magnetic properties comparable to that of NdFeB magnets. While an FeNi alloy with such an ordered arrangement of Fe and Ni atoms has been observed in meteorites, efforts to make such an alloy on the earth has so far been unsuccessful. This is because such an arrangement is stable only below 300 degree Centigrade, but at these temperatures, the atomic jumps needed to achieve the ordered crystals will require millions of years. This project investigates (i) introduction of extensive amount of crystal defects in FeNi single crystals using a unique approach and (ii) how they can be used to increase the atomic jump rates and obtain the desired structure in a practical time frame. This work also sheds light on the operating mechanism in meteorites to form this ordered arrangement in the FeNi alloy. Strategic need to minimize the current reliance on RE imports underscores the impact of the proposed research. The project trains several graduate and undergraduate students, enhances course content in several courses, and improves research facilities. Outreach efforts are made to high school students, female and under-represented student groups, and the broader community.TECHNICAL SUMMARYThere is an increasing demand for NdFeB based magnets for use in wind mills, DC motors in electric vehicles and numerous other key technologies. The high cost of rare-earth elements and heavy reliance on the imports of Nd and other rare-earth elements make the replacement of NdFeB magnets with low-cost magnets made of more abundant elements an urgent economic and national security need. Equiatomic FeNi alloy phase with L10 ordered crystal structure provides powerful permanent magnet properties comparable to NdFeB magnets. While this phase has been observed in neutron irradiated FeNi single crystals and asteroids, it has defied terrestrial synthesis in bulk form due to its low critical ordering temperature of around 320 degree centigrade and consequently low diffusion kinetics. This project overcomes the barrier for L10 long-range ordering in FeNi alloy by enhancing diffusion kinetics at temperatures below the critical ordering temperature. This is achieved by increasing the dislocation density and nonequilibrium vacancy concentration through extreme deformation and by alloying additions that enhance diffusion kinetics. FeNi single crystals are grown using the vertical Bridgman crystal growth technique. Dislocation and other defect densities are characterized using x-ray diffraction and scanning transmission electron microscopy. Short- and long-range order are examined using diffuse scattering peaks and superlattice peaks in the x-ray diffraction patterns. Ordering and local atomic environments are also examined using extended x-ray fine spectrum (EXAFS). Vibrating sample magnetometry is used to assess the magnetic properties. The work also elucidates the operating mechanism in meteorites to form this ordered phase in the FeNi alloy. Strategic need to minimize the current reliance on rare-earth element or rare-earth magnet imports underscores the impact of the proposed research. The project trains several graduate and undergraduate students, enhances course content in several courses, and improves university research facilities. Outreach efforts are made to high school students, female and under-represented student groups, and to the broader community.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.