Rapid solidification of non-stoichiometric intermetallic compounds: Modeling and experimental verification

The thermodynamic extremal principle was applied to model of rapid solidification of non-stoichiometric intermetallic compounds and the Co-xat.%Si alloys (x = 50, 53, 55) were undercooled to test the model. It is the model with but not the model without solute drag that can be derived self-consistently in thermodynamics. Unique dual sluggish and abrupt growth stages were found in undercooled Co-53 at.%Si and Co-55 at.%Si alloys. The first (second) sluggish stage is solute-controlled (thermal-controlled). The first (second) abrupt growth stage is ascribed to the sharp occurrence of solute trapping (inverted partitioning) and disorder trapping that initiates the transition from solute-controlled (thermal-controlled) to thermal-controlled (kinetic-controlled) growth. Since the predictions by the current (previous) model with (without) solute drag predicted well (deviate drastically from) the experimental results, solute drag was suggested be significant upon rapid solidification. The current work solved such an open problem, i.e. solute drag in solidification, and is helpful for not only understanding the non-equilibrium phenomena that is of theoretical importance but also controlling the non-equilibrium microstructures that is of technological importance.