The Effect of Field Annealing on Highly Textured Polycrystalline Galfenol Strips

Iron-Gallium alloys (Galfenol) possess a body centered cubic (BCC) alpha-Fe structure with the gallium atoms substituted throughout the lattice structure. Polycrystalline metals are often isotropic due to their overall random crystallographic orientation, however single crystal and strongly textured polycrystalline BCC metals exhibit a high degree of anisotropy in their physical characteristics. Galfenol has an anisotropic magnetostriction with the maximum performance achieved in the lang100rang direction. Previous field annealing experiments on polycrystalline Galfenol strips have shown a great disparity in the results. This paper uses EBSD to examine the influence of crystal orientation of grains on magnetostriction under various stresses to determine if the disparity is due to the number and/or orientation of the crystals comprising the strip. The saturation magnetostrictions and elastic moduli for each grain are predicted based on the crystal angle measured using EBSD, and the averaged maximum magnetostriction for each sample is calculated with the force balanced between each grain in a sample. The experimental saturation magnetostrictions at 700 Oe agree well with the calculated results. The highest built-in uniaxial anisotropy after magnetic annealing is about 1 kJ/m³ and all the samples in this study showed performance improvement after field annealing.