Microstructures of FeSi₂ based thermoelectric materials prepared by rapid solidification and hot pressing

FeSi₂ based thermoelectric materials have been prepared by melt spinning and vacuum hot pressing. Most of the rapidly solidified (melt spinning) powders are thin flakes with a thickness less than 0.1 mm. Scanning electron microscope (SEM) surface profiles show there are further finer grain structures with the characteristic size of about 100 nm in a flake. The samples obtained by hot uniaxial pressing (HUP) in vacuum have densities higher than 90% the theoretical density of the materials. It was found by SEM observations that the microstructures are very different for vertical and parallel sections of the HUP samples. X-ray diffraction (XRD)analyses show there are some texture features in the samples. It is considered that the textures of the samples are originated from the orientation of the flakes that tended to align perpendicular to the hot press axis. WSi₂ was introduced into the powders unexpectedly during melting process before the rapid solidification, but it makes the microstructures more easily to be explained.