Fe-Co
Samples of the Fe-Co alloys showed formation of a metastable bcc phase when undercooled below a composition dependent critical temperature in electromagnetic levitation experiments. The solidus temperature of the metastable phase was measured from the experiments and the metastable phase diagram was fitted to these values by manually adjusting two parameters in a thermodynamic database for Fe-Co from the literature.
Temperature-time profiles
Droplets of Fe-Co alloys were undercooled using the electromagnetic levitation technique. Temperature-time profiles revealed that above a critical undercooling, a metastable phase formed on solidification which transformed back to the equilibrium phase during recalescence. This becomes apparent by a small plateau in the temperature-time profiles from which the solidus (Ts) and liquidus (Tl) temperatures of the metastable d-ferrite phase are derived.
Metastable Fe-Co phase diagram
A metastable phase diagram for Fe-Co was calculated by extending the liquidus and solidus lines of the d-ferrite (bcc) phase beyond the equilibrium composition range. Two parameters in the thermodynamic database were then altered so that the metastable solidus line fitted well to the metastable solidus temperature measured from the levitation experiments. The adjusted database was shown to have good agreement with both equilibrium and metastable experimental data and the parameters for bcc Co were shown to be reasonable.