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

University Of Utah, Salt Lake City UT

Investigators

Abstract

Non-Technical Abstract This 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.