ABNORMAL GRAIN GROWTH IN MAGNETOSTRICTIVE GALFENOL ROLLED SHEET
Flatau, Alison B
MetadataShow full item record
Highly textured Fe-Ga (Galfenol) rolled sheet with Cube (100)<100> or Goss (110)<100> preferred orientation is under investigation to provide easy magnetization, enhanced magnetostrictive performance and a cost-effective option for production of these alloys for use in applications as sensors and actuators. In this study, 1-2.5% NbC added Galfenol rolled sheet was used because NbC particles enhance the rollability of and abnormal grain growth (AGG) in polycrystalline Galfenol rolled sheet. Driving forces, due to grain boundary energy, surface energy, deformation energy and magnetic fields are generally considered to explain grain growth phenomena. In this dissertation, the effect on grain boundary energy for influencing AGG was studied for the case of high temperature annealing at 1200°C. Both Coincident Site Lattice (CSL) and High Energy Grain Boundary (HEGB) models were investigated as possible mechanisms to explain the contribution of grain boundary energy to Goss-textured AGG. Results support the HEGB model as a suitable model for the observed development of Goss-textured AGG in Galfenol rolled sheet. Next, the effect of deformation energy on AGG was studied by using tension annealing and strain annealing methods in the temperature range of 900°C to 1100°C. This study was built on results from studies of grain boundary energy on other alloys. For the tension annealing investigation, Galfenol rolled sheet was simultaneously subjected to tensile loading during high temperature annealing. No AGG was observed from the tension annealing method. For the strain-annealing investigation, homogeneously recrystallized Galfenol rolled sheet with a taper was subjected to tensile loading under different strain rates and post-strain high temperature anneal conditions to investigate the resultant grain growth phenomena. Different grain growth modes, including Cube- and Goss-textured AGG, were observed in this study. Assessment of the extent of AGG resulting from these was conducted using Electron Backscattering Diffraction (EBSD) patterns that were captured and analyzed using Orientation Imaging Microscope (OIM) software to obtain Inverse Pole Figures (IPF) and Orientation Distribution Function (ODF). Additionally, Ga loss, which lowers the magnetostrictive properties, under different conditions was investigated by Electron Probe Micro Analyzer (EPMA). No significant Ga loss was observed during the annealing process at 1000°C, however, about 2% Ga loss was observed during the annealing process at 1100°C and 1200°C in the areas with a high density of grain boundaries.