Disordered atomic column state in Fe-Mo alloys

Changes in crystallographic features during the (bcc-->bcc+C14 structure) reaction have been investigated for Fe-Mo alloys containing around 10 at. % Mo by transmission electron microscopy. The metastable bcc Fe-Mo alloys were annealed at the relatively low temperature of 1023 K in order to elucidate the details of the structural change in the initial stage. The annealing led to the appearance of precipitates in the bcc matrix, which did not have the C14 structure even after 1000 h of annealing. The structure of the precipitate was basically characterized by a disordered arrangement of distorted decagonal columns. The column was composed of distorted icosahedral clusters connected one-dimensionally. In addition, annealing was found to cause an increase in the number of C14 configurations for the local arrangement of these decagonal columns.