Understanding microstructural evolution and soft magnetic properties in nanocrystallized metallic glass Fe68.5Cu1Nb3Si18.5B9

Abstract

Microstructural evolution during nanocrystallization of amorphous metallic glass Fe68.5Si18.5Nb3B9Cu1 has been studied. The effect of microstructural features of nanocrystalline phases on soft magnetic properties have been evaluated and rationalized with existing theoretical models. The TEM and XRD studies have shown the presence of single Fe3Si nanocrystalline phase at 550 °C (size range 13–16 nm) and three nanocrystalline phases Fe3Si, Fe3B, and Fe2B at 800 °C (size range 18–100 nm). Increase in annealing time at 800 °C resulted in decomposition of metastable Fe3B phase to equilibrium Fe2B phase. Positron annihilation spectroscopy revealed the presence of nanovoids in amorphous samples. Theoretical estimations showed that these nanovoids were having free volume equivalent to that of a vacancy defect consisting of five or more atoms vacancy cluster present in the amorphous samples. Nature of interfaces associated with nanocrystalline phases could be characterized using positron annihilation spectroscopy. This study showed that metallic nanoparticles have very low concentration of thermal vacancies. Effects of nature of phases, particle density, and nanoparticle size on saturation magnetization and coercivity have been studied.