Band Structure Formation in Peritectic Fe-Co and Fe-Ni Alloys

Abstract

In this paper, band structure formation in peritectic Fe–18.0 at%Co and Fe–4.4 at%Ni alloys is reported. Bridgman type directional solidification experiments were performed, and an island band structure was observed in both of these alloys under low velocity solidification conditions. Solid composition profiles along the growth direction in this band region were determined with electron probe measurements. The solute concentration increased during δ growth, and after an abrupt increase for phase change, it decreased during γ growth. It then decreased abruptly for the phase change to δ. Repetition of this process formed bands. Composition profiles calculated by the convection model were compared with these experimental results, suggesting that island bands form by a mechanism similar to that assumed in the model for discrete bands. Furthermore, the nucleation condition in this model was extended. Applying the nucleation constitutional undercooling criterion, a new calculation was developed. The mechanism of band structure formation is discussed in the light of these results.