Phase transformation in an n-type FeSi/sub 2/ processed by mechanical alloying

N-type Fe/sub 0.98/Co/sub 0.02/Si/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 /spl beta/-FeSi/sub 2/ phase by subsequent isothermal annealing. However, as-consolidated iron silicides consisted of untransformed mixture of /spl alpha/-Fe/sub 2/Si/sub 5/ and /spl epsiv/-FeSi phases. Isothermal annealing has been carried out to induce the transformation to a thermoelectric semiconducting /spl beta/-FeSi/sub 2/ phase. The transformation behavior of /spl beta/-FeSi/sub 2/ was investigated a modified TGA, SEM and XRD analyses. Isothermal annealing at 830/spl deg/C in vacuum led to the /spl beta/-FeSi/sub 2/ phase transformation, but some residual metallic /spl alpha/- and /spl epsiv/-phases were unavoidable. Microstructures of iron silicides were investigated using SEM. Microharness before and after isothermal annealing was evaluated and correlated with the phase transformation as well as thermoelectric properties.