Structure-Composition-Magnetostriction Correlations in Strong and Ductile Fe-Based Alloys with large Low-Field Magnetostriction

技术支持：本文研究了添加W和Mo对Fe磁致伸缩性能的增强作用，以及局部原子环境、短程有序和结构缺陷对Fe-W、Fe-Mo、FeGa等α-Fe基磁致伸缩合金单晶磁致伸缩性能的影响。PI及其同事早先已经表明，向Fe中添加Ga导致在低施加磁场下磁致伸缩的大幅增加，并且这些合金是坚固且可延展的。在最近的一项工作中，PI和同事发现，在Fe中加入W和Mo后，磁致伸缩大大增加。韧性Fe-4.4%W合金中实现的磁致伸缩应变的大小，在每个原子的基础上，与Fe-20at. % Ga和Fe-27.5原子%镓合金单晶。正在进行的调查还表明，内部不均匀的应变引入的结构变化和缺陷发挥更大的作用比已经认识到在确定这些合金的磁致伸缩。长期目标是获得铁和铁合金的磁致伸缩的更好的理解，并制定有吸引力的磁致伸缩和机械性能的合金设计的指导方针。作为这项努力的一部分，本论文的工作重点是：（a）体心立方相二元Fe-W和Fe-Mo合金单晶的磁致伸缩和三元添加物的影响（B）揭示近邻原子间距离的局部原子环境的表征以及它们如何影响Fe合金的磁致伸缩（c）在Fe-W、Fe-Mo和Fe-Ga合金中，短程有序是如何随热处理而改变的，以及它是如何影响磁致伸缩的，以及（d）定义明确的晶体缺陷及其分布对磁致伸缩的影响。要检查的缺陷包括位错结构引入控制单晶变形，并通过沉淀硬化处理引入共格第二相。设想的工作包括真空电弧熔炼合金制备，单晶生长使用布里奇曼技术，结构评价，磁性和磁致伸缩测量，和结构-成分-性能的相关性。透射电子显微镜将用于表征缺陷。扩展X射线吸收精细谱（EXAFS）测量使用同步辐射源将用于探测局部原子环境，并确定平均原子间距离，配位数和相邻原子的类型，以及相邻距离的均方无序。将使用共振超声光谱技术进行弹性测量。将进行X射线衍射扫描、摇摆曲线扫描和X射线形貌测量，以评估晶体取向、短程有序和结构缺陷。非技术性：这项工作将进一步的知识，将使设计和开发新一代的廉价和高性能的低场磁致伸缩合金用于传感器和执行器的应用。（一）将导致博士学位。该项目的目的是：（i）为两名研究生撰写论文;（ii）为本科生和高中生提供研究机会;（iii）作为一种教育手段，吸引本科生，特别是女性和代表性不足的少数民族学生学习冶金工程;（iv）加强磁性材料、金属加工和物理冶金学方面的本科生和研究生课程。除了为更科学地理解铁合金中的磁致伸缩提供基础外，这项工作还将导致开发廉价和高性能的合金，用于声学传感器和致动器以及磁力机械设备，这些设备非常坚固，并且在广泛的国防和商业应用中感兴趣，包括纳米定位设备，MEMS设备，声纳设备，主动减振设备，负载和扭矩传感器以及电延迟线。

TECHNICAL: This work examines the large enhancements in the magnetostriction of Fe with W and Mo additions, and how local atomic environment, short range ordering and structural defects can dramatically influence the magnetostriction in Fe-W, Fe-Mo, FeGa, and other alpha-Fe based magnetostrictive alloy single crystals. PI and co-workers have earlier shown 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. In a recent work, PI and coworkers have discovered a large increase in magnetostriction with W and Mo additions to Fe. The magnitude of magnetostrictive strain achieved in ductile Fe-4.4% W alloys, on a per atom basis, is comparable to that obtained in Fe-20 at.% Ga and Fe-27.5 at.% Ga alloy single crystals. 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 work will focus on detailed examinations of (a) magnetostriction in bcc phase binary Fe-W and Fe-Mo alloy single crystals and the influence of ternary additions (b) the characterization of local atomic environments that shed light on near-neighbor interatomic distances and how they influence the magnetostriction in Fe alloys (c) how short range order is changed with thermal treatments and how it influences magnetostriction in Fe-W, Fe-Mo and Fe-Ga alloys, and (d) the effect of well-defined crystal defects and their distribution on magnetostriction. The defects to be examined include dislocation structures introduced with controlled single crystal deformation, and coherent second phases introduced through precipitation hardening treatments. 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. Transmission electron microscopy will be used to characterize the defects. Extended X-ray absorption Fine Spectrum (EXAFS) measurements using a synchrotron radiation source will be used to probe the local atomic environments and determine the mean inter-atomic distances, coordination number and type of neighboring atom, and mean-square disorder of neighbor distance. Elastic measurements will be made using the resonance ultrasound spectroscopy technique. 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. NON-TECHNICAL: The work will further the knowledge that will enable the design and development of a new generation of inexpensive and high performance low-field magnetostrictive alloys for use in sensor and actuator applications. The work will (i) lead to Ph.D. dissertations of two graduate students, (ii) provide research opportunities for undergraduate and high school students, (iii) be used as an educational element to attract undergraduate students to metallurgical engineering, in particular women and underrepresented minority students, and (iv) enhance the undergraduate- and graduate-courses in Magnetic Materials, Metals Processing and Physical Metallurgy. Besides providing a basis for a more scientific understanding of magnetostriction in Fe alloys, this work will lead to the development of inexpensive and high performance alloys for use in acoustic sensors and actuators and magnetomechanical devices that are very rugged and of interest in a wide range of defense and commercial applications that would include nano-positioning devices, MEMS devices, sonar devices, active vibration damping devices, load and torque sensors, and electrical delay lines.