Thermoelectric properties of nearly single-phase ¢-FeSi2 alloys fabricated by gas-atomized powder sintering

Abstract

Thermoelectric alloys having nearly ¢-FeSi2 single-phase microstructure were fabricated by sintering gas-atomized powders using the hot pressing. Since the ¢-FeSi2 phase is formed by the peritectoid reaction between ¾-FeSi and ¡-Fe2Si5 phases, the reaction rate for the completion of ¢-FeSi2 phase transition strongly depends on the diffusion path length which is governed by the morphology and size of solidified microstructure consisting of ¾ and ¡ phases. It has been indicated by the wedge drop cast using arc melting that producing fine and fully eutectic microstructure by rapid solidification is quite effective for the completion of ¢-FeSi2 phase transition. An argon gas atomization process was chosen as a rapid solidification technique to produce fine and homogeneous alloy powder having fully ¾ and ¡ eutectic microstructure, which was turned out to be beneficial for the formation of ¢-FeSi2 single-phase microstructure by a short time annealing even within 30 minutes at 1073 K for the gas-atomized powders with the averaged particles size of 20 µm and under in diameter. Thermoelectric properties were evaluated for these nearly single-phase ¢-FeSi2 sintered alloys with the addition of doping elements, n-type Co and p-type Mn, 1.67 at% respectively. The absolute value of Seebeck coefficient and electrical conductivity are higher in a p-type Mn alloy than an n-type Co alloy.