On features in viscosity polytherms of Fe-B hypereutectic melts and their development in crystallization kinetics of rapidly quenched ribbons

An abnormal viscosity change (its decrease) has been revealed in the viscosity polytherms of the amorphysing Fe_81.5B_18.5 and Fe₇₉B₂₁ melts in the vicinity of 1420–1460 °C and 1380–1420 °C, respectively. They are caused by the change of the short-range order structure of the melts. The maintenance of the high-temperature state of the liquid phase down to solidification temperatures results in its viscosity hysteresis. It was found out that the quenching temperature rise results in an increase of the volume fraction of amorphous phase in rapidly quenched ribbons. It has been proven that crystallization of the ribbons obtained proceeds by the eutectic mechanism resulting in α-Fe and tetragonal Fe₃B^T formation. The kinetics of the process depends on the initial melt temperature and correlates with the anomalies in their viscosity temperature dependences.