Abstract
The enhancement of thermoelectric properties of p-type β-FeSi2 doped with Mn and Al by mechanical alloying (MA) was described. The pre-mixed powder of nominal composition Fe30Si70 transforms to a homogeneous β-FeSi2 phase in the as milled condition. The appropriate milling time of a powder for sintering was around 720 ks at which the powder consists of very fine Fe and Si crystals in the as milled condition. Specimens prepared by hot pressing from MA powder showed lower thermal conductivity, higher figure of merit and hence higher conversion efficiency than those prepared from ingot metallurgy. This was mostly due to the small grain size obtained by MA. Phase formation sequence in MA powder was discussed in conjunction with thin films. The formation sequence of β-FeSi2 from the mixture of Fe and Si powders via ε-FeSi observed in MA powder and thin films of Fe with a Si substrate can be explained with the proposed two rules when the non-stable phases at room temperature were excluded. The possibility of the influence of MA energy on the phase formation sequence was also pointed out.
