Magnetic property-texture relationships in galfenol rolled sheet stacks

Abstract

Recent results in the area of galfenol (iron-gallium) alloy rolled sheet have yielded significant Goss ({110}<001>∥ rolling direction [RD]) texture development and large strain values, > 250 ppm. Goss-textured grain growth is promoted by the use of a grain boundary pinning second-phase particle. After multistage rolling and subsequent heat treatment, Goss grain areas as large as 125 cm2 develop in the RD–transverse direction (TD) plane. Goss grain <100> directions are typically within 15° of the RD inside these grains. Fully processed sheets were sectioned and bonded together to produce laminated stacks. Grain oriented and nongrain oriented stacks were characterized magnetically. Plotting strain data against H-field for both an Oriented Stack (OS) and a Nonoriented Stack (NonOS) yielded saturation stain values of 215 ppm and 70 ppm, at 48.3 MPa prestress, respectively. Magnetostrictive strain coefficient, d33, values of 20 nm/A and 4 nm/A were calculated for the OS and NonOS, respectively. Saturation magnetization values were found to be 1.3 T and 1.2 T for the OS and NonOS. Electron Backscatter Diffraction (EBSD) analysis was performed on cross sections of each laminated stack. EBSD mapping showed a large relative disparity in average grain size, taken from cross sections, of 470 μm and 84 μm for the OS and NonOS. Pole figures, contoured at a half-width of 10°, were analyzed and clearly show a high degree of Goss texture in the OS and a lack of any strong texture in the NonOS. The OS generated a maximum Multiple of Mean Uniform Density value > 16 while the NonOS produced a value < 2.