Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
1548483 | Progress in Natural Science: Materials International | 2012 | 5 Pages |
Undercooled Fe75Ni25 melts were phase-seeded by a high purity iron. It was found that above a critical undercooling, ΔTc=135 K, a metastable δ phase (b.c.c) solidifies from the iron-seeded melts instead of a thermodynamically stable γ phase (f.c.c). While undercooling of the melt (ΔT) is below ΔTc, solidification of the γ phase prevails in the iron-seeded melts. For the undercooled melts subjected to spontaneous nucleation, the γ phase always solidifies. After solidification, the as-solidified γ phase transforms completely to martensite; whereas the as-solidified metastable δ phase partially transforms to the γ phase, and then to martensite. The untransformed δ phase retains as α-ferrite particles in the microstructures. Based on the classical nucleation theory, catalytic nucleation of the metastable δ phase in the phase-seeded undercooled Fe75Ni25 melts was analyzed. It was quantitatively demonstrated that when ΔT>ΔTc, the formation of the δ phase can be ascribed to a better catalytic effect of the iron on its nucleation than that on the nucleation of the γ phase.