抄録
The microstructural change during the formation of semiconductive FeSi2 (β-phase) from FeSi (e-phase) and Fe2Si5 (α-phase) two metallic compounds by isothermal heating at 1123 K in Mn-doped Fe-66.7at%Si alloys which were prepared by both melting-solidification and sintering processes was firstly investigated, paying attention to the following peculiar phenomenon; some ε-phase particles were covered with β-phase layer and the others were not in solidified alloy. Secondly, the cause for the acceleration of β-phase formation rate by the addition of Pd was investigated. It was found that there were two kinds of α-phases; the one (α ?? ) decomposed to β- and Si phases by the eutectoid reaction and the other (αs) did not by the heating for up to 180 ks. The formations of two kinds of band-shaped regions which were caused by both these two kinds of α-phases and the eutectic reaction of the liquid were judged to be the causes for the peculiar phenomenon. The acceleration of β-phase formation rate by addition of Pd was attributed to both the increase of the α, -phase amount ratio and the acceleration of the eutectoid reaction of a, phase. In the consideration on non-shrinkage of α-phase particles inside test piece, a new hypothesis of "vacancy extinction in the core of core-rim structure" which stops the vacancy supply to the core/rim interface or the reaction at the core/rim interface was proposed.
