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

技术：这项工作考察了添加W和Mo后Fe的磁致伸缩显著增强，以及局域原子环境、短程有序化和结构缺陷如何显著影响Fe-W、Fe-Mo、FeGa和其他α-Fe基磁致伸缩合金单晶的磁致伸缩。PI和他的同事们早些时候已经证明，在低磁场下，添加Ga到Fe会导致磁致伸缩的大幅增加，而且这些合金是坚固的和有韧性的。在最近的一项工作中，Pi和他的同事们发现，随着W和Mo的添加到Fe中，磁致伸缩显著增加。按原子计算，延性Fe-4.4%W合金的磁致伸缩应变与Fe-20 at.%Ga和Fe-27.5 at.%Ga合金的磁致伸缩应变相当。正在进行的研究还表明，由结构变化和缺陷引入的内部不均匀应变在决定这些合金的磁致伸缩方面所起的作用比人们所认识的要大得多。长期目标是更好地了解铁和铁合金的磁致伸缩，并制定具有吸引人的磁致伸缩和机械性能的合金的设计指南。作为这项工作的一部分，这项工作将侧重于详细研究(A)bcc相二元Fe-W和Fe-Mo合金单晶的磁致伸缩和三元添加的影响，(B)揭示近邻原子间距离的局部原子环境的表征及其如何影响Fe合金的磁致伸缩，(C)热处理如何改变Fe-W，Fe-Mo和Fe-Ga合金的短程有序，以及它如何影响磁致伸缩，以及(D)定义明确的晶体缺陷及其分布对磁致伸缩的影响。要检查的缺陷包括通过受控单晶变形引入的位错结构，以及通过沉淀硬化处理引入的共格第二相。设想的工作包括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-性能关联。将使用透射电子显微镜来表征缺陷。使用同步辐射光源的扩展X射线吸收精细光谱(EXAFS)测量将用于探测局部原子环境，并确定平均原子间距离、邻近原子的配位数和类型以及邻近原子距离的均方无序。弹性测量将使用共振超声波谱技术进行。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、短程有序性和结构缺陷。非技术性：这项工作将进一步加深设计和开发用于传感器和执行器应用的新一代廉价和高性能低场磁致伸缩合金的知识。这项工作将(I)导致两名研究生的博士论文，(Ii)为本科生和高中生提供研究机会，(Iii)作为一种教育元素，吸引本科生学习冶金工程，特别是女性和代表性不足的少数民族学生，以及(Iv)加强磁性材料、金属加工和物理冶金的本科生和研究生课程。除了为更科学地了解铁合金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，用于声传感器和执行器以及磁机械设备，这些设备非常坚固耐用，在广泛的国防和商业应用中具有重要意义，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气延迟线。

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.