Metastable solidification in undercooled liquid droplets of Fe-Ni based soft-magnetic alloys under terrestrial and microgravity conditions

Microstructure evolution and metastable phase formation in undercooled melts of Fe-Ni based soft magnetic alloys were studied by the electromagnetic levitation technique in ground-based experiments and under microgravity during parabolic flight campaigns. Discontinuous changes in the microstructure were observed in samples of a commercial soft magnetic alloy quenched at distinct melt undercooling ΔT. The results were successfully interpreted within the framework of the dendrite breakup model. No metastable phase formation was detected in commercial soft magnetic alloys which possess higher Ni contents. Under microgravity conditions the lifetime of the metastable bcc phase formed for Fe90Ni10 beyond a critical melt undercooling increases. The surface tension of the levitating droplets under microgravity was determined from high speed video recordings of the oscillations of the droplets. The value obtained, σ = 1.90 ± 0.01 Nm−1, agrees well with values from the literature.