Phase transformation in an n-type FeSi{sub}2 processes by mechanical alloying

摘要

N-type Fe{sub}0.98Co{sub}0.02Si{sub}2 powders have been produced by mechanical alloying process and consolidated by vacuum hot pressing. As-milled powders were in a metastable state and fully transformed to β-FeSi{sub}2 phase by subsequent isothermal annealing. However, as-consolidated iron suicides consisted of untransformed mixture of α-Fe{sub}2Si{sub}5 and ε-FeSi phases. Isothermal annealing has been carried out to induce the transformation to a thermoelectric semiconducting β-FeSi{sub}2 phase. The transformation behavior of β-FeSi{sub}2 was investigated a modified TGA, SEM and XRD analyses. Isothermal annealing at 830 °C in vacuum led to the β-FeSi{sub}2 phase transformation, but some residual metallic β- and ε-phases were unavoidable. Microstructures of iron suicides were investigated using SEM. Microharness before and after isothermal annealing was evaluated and correlated with the phase transformation as well as thermoelectric properties.