Microstructures and thermoelectric properties of Co-doped iron disilicides prepared by rapid solidification and hot pressing

Abstract

Iron disilicide based alloys Fe 0.94Co 0.06Si 2.00 were prepared by rapid solidification and hot uniaxial pressing. The effects of pre-annealing of the powders and hot pressing temperature on the microstructures and thermoelectric properties were investigated. X-ray diffraction and scanning electron microscopy show that after pre-annealing at 800 °C for only 2 h, the high temperature phases (α-Fe 2Si 5 and ɛ-FeSi) in the rapidly solidified powders have been completely transformed to β-FeSi 2 phase, while the fine grain structures were maintained. It is found that the grain growth during hot pressing was successfully suppressed for the pre-annealed samples, especially at a lower pressing temperature of 880 °C. The Seebeck coefficient was markedly enhanced by the pre-annealing treatment, also by a lower pressing temperature, while both the electrical conductivity and the thermal conductivity were decreased by them. The maximum dimensionless figure of merit ZT = 0.25 at 908 K was obtained for Fe 0.94Co 0.06Si 2.00, which is pre-annealed, followed by hot pressing at 880 °C with 70 MPa for 30 min.