Tunable nucleation process of nano-sized NaZn13-type and α-(Fe,Si) phases by doping boron in La–Fe–Si alloys during rapid solidification

Abstract

The effect of a small dose of boron-doping on the nucleation process of nano-sized 1:13 phase (NaZn13-type phase) and α-(Fe,Si) phase of the La–Fe–Si alloys during the rapid solidification was investigated. The simulation of classical nucleation theory indicates a competitive nucleation relationship between 1:13 and α-(Fe,Si) phases during the rapid solidification. Compared to the La–Fe–Si alloys undoped with boron atom, the undercooled temperature change (ΔT) for the same nucleation rate conditions of the 1:13 and α-Fe phases was significantly decreased from 673 K (x = 0) to 639 K (x = 0.3) during the rapid solidification of La–Fe–Si–B alloys. The analysis of the microstructure and phase structure of the La–Fe–Si alloys ribbons by scanning electron microscope , x-ray diffraction, and transmission electron microscope also concludes that the doping of boron promoted the formation of the 1:13 phase. The results of this study have considerable meaning for the engineering application of magnetic refrigeration materials (La–Fe–Si) in the future.