Influence of Structural Ordering and Defects on the Magnetostriction in Strong and Ductile Fe-Based Alloys with Large Low-Field Magnetostriction

【非技术摘要】这项工作涉及到在外加磁场下表现出应变的合金，或在施加应力时表现出磁化变化的合金。这些材料用于部署空间天线结构、风能和海洋能源收集系统、纳米定位系统和许多其他应用，使它们成为经济上重要的一类金属材料。基于铁和镓金属的合金已被证明是一种有吸引力的替代品，这类合金的进一步发展需要一个关于合金元素、结构和缺陷如何影响成分-结构-性能相关性的大型数据库。这个项目解决了这些重要问题。该项目将进一步提高知识水平，使设计和开发用于传感器和执行器应用的新一代廉价高性能合金成为可能。该项目将进一步教育和培训本科生和研究生，并增加妇女和代表性不足的少数民族学生的研究机会。该项目还将在广泛的应用中产生重大影响，这些应用将利用这些无稀土、强、韧性、低成本和高性能的传感器和执行器材料。本项目研究了FeGa和其他α - fe基磁致伸缩合金单晶的近程有序、远程有序和结构位错如何显著影响磁致伸缩。我们在早期的工作中已经表明，在低外加磁场下，向铁中添加Ga会导致磁致伸缩的大幅增加，并且这些合金具有很强的韧性。正在进行的研究还表明，由结构变化和缺陷引起的内部不均匀应变在确定这些合金的磁致伸缩方面的作用比人们所认识到的要大得多。长期目标是提高对铁和铁合金的磁致伸缩的理解，并制定具有吸引磁致伸缩和机械性能的合金设计指南。作为这项工作的一部分，拟议的工作将侧重于详细检查(a)热处理如何改变短程顺序以及它如何影响Fe-Ga， Fe-Al和Fe-Si合金的磁致伸缩；(b)相干第二相对内部应变调制的影响及其对磁致伸缩的影响(c)在控制单晶变形的情况下引入的特定位错结构中定义明确的晶体缺陷对磁致伸缩的影响以及(d)微细胞图案的干涉对比成像以及有序的第二相区域和位错阵列如何影响它们。设想的工作包括通过真空电弧熔炼制备合金，使用Bridgman技术生长单晶，结构评估，磁性和磁致伸缩测量以及结构-成分-性能相关性。将使用透射电子显微镜对缺陷进行表征和分析。弹性测量将使用共振超声光谱技术进行。通过theta -2 x射线衍射扫描、摇摆曲线扫描和x射线形貌测量来评估晶体取向、近程有序和结构缺陷。

Non-Technical AbstractThis work deals with alloys that exhibit strain in response to an applied magnetic field or change in magnetization with application of stress. Use of these materials for deploying antenna structures in space, wind and ocean energy harvesting systems, nanopositioning systems and numerous other applications make them an economically important class of metallic materials. Alloys based on Iron and Gallium metals have been demonstrated to be an attractive alternative and further development of this class of alloys requires a large data base of how alloying elements, structure and defects influence composition-structure-property correlations. This project addresses these important issues. The project will further the knowledge that will enable the design and development of a new generation of inexpensive and high performance alloys for use in sensor and actuator applications. The project will further the education and training of undergraduate and graduate students and enhance research opportunities for women and underrepresented minority students. The project will also have a great impact in a wide range of applications that will utilize these rare-earth free, strong, ductile, low cost and high performance sensor and actuator materials. Technical Abstract The project examines how short-range ordering, long-range ordering and structural dislocations can dramatically influence the magnetostriction in FeGa, and other alpha-Fe based magnetostrictive alloy single crystals. We have shown in earlier work that the addition of Ga to Fe results in a large increase in magnetostriction at low applied magnetic fields and that these alloys are strong and ductile. Ongoing investigations also suggest that internal inhomogeneous strains introduced by the structural changes and defects play a much greater role than has been appreciated in determining the magnetostriction in these alloys. The long-term objectives are to gain an improved understanding of magnetostriction in Fe and Fe alloys and formulate the guidelines for the design of alloys with attractive magnetostrictive and mechanical properties. As a part of this effort, the proposed work will focus on a detailed examination of (a) how short range order is changed with thermal treatments and how it influences magnetostriction in Fe-Ga, Fe-Al and Fe-Si alloys, (b) influence of coherent second phases on the internal strain modulations and how it affects magnetostriction (c) the effect of well-defined crystal defects in particular dislocation structures introduced with controlled single crystal deformation on magnetostriction and (d) Interference contrast imaging of microcellular patterns and how they are influenced by the ordered second phases regions and dislocation arrays. The work envisaged involves alloy preparation by vacuum arc-melting, single crystal growth using Bridgman technique, structural evaluation, magnetic and magnetostriction measurements, and structure-composition-property correlations. Characterization and analysis of the defects will be carried out using transmission electron microscopy. Elastic measurements will be made using the resonance ultrasound spectroscopy technique. Theta-2 theta x-ray diffraction scans, rocking curve scans and x-ray topography measurements will be performed to assess the crystal orientation, short range order and the structural defects.