Thermoelectric Properties of Nearly Single-Phase β-FeSi₂ Alloys Fabricated by Gas-Atomized Powder Sintering

抄録

Thermoelectric alloys having nearly β-FeSi₂ single-phase microstructure were fabricated by sintering gas-atomized powders using the hot pressing. Since the β-FeSi₂ phase is formed by the peritectoid reaction between ε-FeSi and α-Fe₂Si₅ phases, the reaction rate for the completion of β-FeSi₂ phase transition strongly depends on the diffusion path length which is governed by the morphology and size of solidified microstructure consisting of ε and α 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 β-FeSi₂ phase transition. An argon gas atomization process was chosen as a rapid solidification technique to produce fine and homogeneous alloy powder having fully ε and α eutectic microstructure, which was turned out to be beneficial for the formation of β-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 β-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.