Equal Channel Angular Extrusion (ECAE) Processing of Tau-MnAl Magnets

Tau-MnAl 磁体的等通道角挤压 (ECAE) 加工

• 批准号: 1852529
• 负责人: Ian Baker
• 金额: $ 41.89万
• 依托单位: Dartmouth College
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-04-01 至 2023-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1852529&HistoricalAwards=false
• 关键词: Equal; Channel; Angular; Extrusion; ECAE

Demand for high-performance permanent magnets is increasing rapidly for applications such as wind turbine generators and motors in both electric and hybrid cars. This market is served by rare earth (RE) magnets based on neodymium-iron-boron and samarium-cobalt. RE magnets are not without issues; they can chip, suffer thermal shock, and can suffer grain boundary corrosion. However, their biggest problems are: price volatility; that China largely controls the RE metals market; and that the extraction of RE metals creates severe environmental degradation. The compound MnAl has been of interest as a permanent magnet since the early 1960s. It has a theoretical energy product (a measure of its magnetic strength) between that of traditional AlNiCo magnets and RE magnets with a value comparable to that of bonded neodymium-iron-boron magnets. Further, it does not suffer from the issues associated with RE magnets, and potentially has the lowest cost per unit energy product of any permanent magnet. The magnetic properties of MnAl are affected by the numerous types of defects present, but how these defects affect the magnetic properties and under what conditions these defects occur is unknown. In this project, we will determine both the conditions under which defects and second phases form during processing of MnAl and how these control the magnetic properties. The expectation is that superior magnetic properties can be obtained by carefully manipulating the defect structure. While the work focuses on MnAl, understanding the relationship between the occurrence of defects, their production and their relationship to the magnetic properties in MnAl will be useful for understanding similar behavior in the related compounds MnBi, MnGa, NiFe, PtFe and CoPt, all of which are of interest as hard magnets. The project includes the training of both a Ph.D. student and several undergraduates in state-of-the-art techniques.Tau-MnAl is a metastable phase that transforms from the high temperature epsilon phase, during which anti-phase boundaries (APBs), twins, stacking faults and dislocations are created. Depending on the processing conditions, the equilibrium beta and gamma 2 phases can also form. The fundamental difficulty with improving the magnetic properties of tau-MnAl is that there is no clear understanding on how they depend on the defect structure. The grain size can also influence the magnetic properties either directly or by affecting the beta and gamma 2 phases arrangement and defect formation. Our aim is to understand both the conditions under which APBs, twins, stacking faults, dislocations and second phases form during processing of tau-MnAl and how these control the magnetic properties. The local chemistry will also be explored at high resolution using atom probe tomography via collaboration with Dr. Baptiste Gault, Max-Planck-Institut fur Eisenforschung, Germany. Our working hypothesis is that we need a strong, c-axis alignment and a low density of APBs, twins and stacking faults (which locally disorder the material) for a high saturation magnetization, while a low density of APBs, twins and stacking faults but a high dislocation density are required for a high coercivity. It is thought that a fine distribution of beta and gamma 2 phases will also contribute to a high coercivity through magnetic domain wall pinning. While the work focuses on MnAl, understanding the relationship between the occurrence of defects, their production and their relationship to the magnetic properties in MnAl will be useful for understanding similar behavior in the related compounds MnBi, MnGa, NiFe, PtFe and CoPt, all of which are of interest as hard magnets. The project will include training of both a Ph.D. student and several undergraduates in state-of-the-art techniques.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.

高性能永磁体的需求正在迅速增加，用于风力发电机和电动汽车和混合动力汽车的电机等应用。这个市场是由基于钕铁硼和钐钴的稀土磁体服务的。稀土磁铁并非没有问题；它们会碎裂，承受热冲击，还会遭受晶界腐蚀。然而，它们最大的问题是：价格波动；中国在很大程度上控制着可再生金属市场；稀土金属的提取会造成严重的环境退化。自20世纪60年代初以来，化合物MnAl作为永磁体一直引起人们的兴趣。它的理论能量积（衡量其磁性强度）介于传统铝镍钴磁铁和稀土磁铁之间，其价值与结合钕铁硼磁铁相当。此外，它不会受到与RE磁铁相关的问题的困扰，并且可能具有任何永磁体中单位能量产品的最低成本。MnAl的磁性能受到多种缺陷的影响，但这些缺陷如何影响磁性能以及在什么条件下发生这些缺陷尚不清楚。在这个项目中，我们将确定缺陷和第二相在MnAl加工过程中形成的条件，以及它们如何控制磁性能。期望通过仔细操纵缺陷结构可以获得优越的磁性能。虽然工作的重点是MnAl，但了解MnAl中缺陷的发生，它们的产生及其与磁性能的关系将有助于理解相关化合物MnBi， MnGa, NiFe， PtFe和CoPt的类似行为，所有这些都是感兴趣的硬磁体。该项目包括对一名博士生和几名本科生进行最先进技术的培训。Tau-MnAl是由高温epsilon相转变而成的亚稳相，在此过程中会产生反相边界（apb）、孪晶、层错和位错。根据加工条件的不同，还可以形成平衡的β和γ 2相。提高tau-MnAl磁性能的根本困难在于对它们如何依赖于缺陷结构没有明确的认识。晶粒尺寸也可以直接或通过影响β和γ 2相排列和缺陷形成来影响磁性能。我们的目的是了解在tau-MnAl加工过程中apb、孪晶、层错、位错和第二相形成的条件，以及它们如何控制磁性能。当地的化学也将通过与德国马克斯普朗克研究所的Baptiste Gault博士合作，以高分辨率使用原子探针断层扫描进行探索。我们的工作假设是，我们需要强的c轴对准和低密度的apb、孪晶和层错（使材料局部无序）来获得高饱和磁化，而低密度的apb、孪晶和层错但高位错密度是高矫顽力所需的。认为β和γ 2相的精细分布也有助于通过磁畴壁钉钉获得高矫顽力。虽然工作的重点是MnAl，但了解MnAl中缺陷的发生，它们的产生及其与磁性能的关系将有助于理解相关化合物MnBi， MnGa, NiFe， PtFe和CoPt的类似行为，所有这些都是感兴趣的硬磁体。该项目将包括对一名博士生和几名本科生进行最先进技术的培训。该奖项反映了美国国家科学基金会的法定使命，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。

项目成果

The phase transformation behavior of Mn-Al rare-earth-free permanent magnets

• DOI: 10.1016/j.jmmm.2023.171331
• 发表时间: 2023-09
• 期刊: Journal of Magnetism and Magnetic Materials
• 影响因子: 2.7
• 作者: Thomas Keller;Dylan Barbagallo;Natalya Sheremetyeva;Tushar Kanti Gosh;Katherine S. Shanks;G. Hautier;Ian Baker

Manganese-based permanent magnet materials

• DOI: 10.1016/j.pmatsci.2021.100872
• 发表时间: 2021-09
• 期刊: Progress in Materials Science
• 影响因子: 37.4
• 作者: Thomas Keller;I. Baker