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.
PI: Sivaraman Guruswamy, University of Utah NSF DMR-Award # 0854166 Project Outcomes Report for the General Public (POR) For the Period March 1, 2009-February 28, 2013 Magnetostrictive materials exhibit a reversible change in length in response to an applied magnetic field and changes in magnetic properties on the application of stress. The PI and collaborators discovered a large increase in magnetostriction of iron even with small applied magnetic fields. This discovery coupled with good mechanical properties and low costs of FeGa alloys make them very attractive in numerous actuator, sensor, active device, and energy harvesting (from wind, ocean and other vibration sources). This discovery also opened up the possibility of obtaining larger magnetostriction values in other low-cost ductile Fe- based alloys containing alloying elements that are less expensive and more abundant. The long-term objectives of the work carried out in this project were 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. The project led to several important scientific findings and good societal impact. Large magnetostrictions were also discovered in Fe-W and Fe-Mo alloys. The work showed that the nature of local strain fields in alloy crystal lattice introduced from the presence of solutes, dislocations, coherent second phases, incoherent precipitates and dispersions influence magnetostriction in FeGa, FeW and other magnetostrictive alloys. Controlling inhomogeneous elastic strains introduced by modifying local atomic spacing by solutes and defects such as dislocations is key to controlling the magnetostriction. These findings open up a new window of possibilities for using inexpensive non-rare-earth additions to Fe and controlling defects in order to obtain large magnetostrictive strains at low fields, and strong and ductile alloys. This is a significant contribution to a fundamental understanding of magnetostriction and towards alloy design for sensor and actuators with major implications from both scientific and commercial perspectives. Several avenues for the training and professional development of graduate and undergraduate students were provided by the scope of the project and the unique and complete range of experimental capabilities in the laboratory that range from alloy synthesis, single crystal growth and directional solidification, magnetic, magnetostrictive and physical property characterization, to prototype device development. Graduate students had the opportunities to attend several training courses and conferences enhancing their theoretical and experimental skills and publish 9 journal and conference proceeding with several under preparation. The project also supported laboratory experience of undergraduate and graduate students in at least four of the courses. Th eproject also helped enhance the facilities with the acquisition of new instrumentation. All the students who worked on this project and graduated with PhD degrees have now filled important technical positions (Gavin Garside -Senior Engineer at ATI-Wah Chang; Biswadeep Saha and M. Ramanthan, Senior Engineers at INTEL; and Chai Ren- post-doctoral fellow at the University of Utah) meeting the needs for highly trained technical personnel in industry and a research university. With an excellent combination of strain levels obtainable, low cost, low hysteresis, high strength, good ductility, and high elastic modulus (several times that of Terfenol-D), the alloys that have been already identified under this program can be considered for use in for many new and existing applications, and can compete with giant magnetostrictive Terfenol (Rare-earth based iron alloys) alloys and piezoelectric materials, especially those involving rugged environments. One major application that is emerging is the large-scale energy harvesting such as in wind and ocean energy harvesting using these inexpensive magnetostrictive alloys. The alloys are of great defense and commercial interest for use in numerous magnetomechanical devices and in acoustic sensors and actuators, particularly in applications involving tensile or impact loading. The numerous defense and commercial applications include underwater sonar devices, micro-electro-mechanical system (MEMS) devices, active structural systems for dampening seismic waves and other mechanical vibrations, strain gages, torque sensors for automobiles and other systems, positioning devices, microphones, and electrical delay lines. Low cost of these alloys can bring them to the market place in the immediate future.
