Growth kinetics and microstructure transition of undercooled Fe7(CoNi)75B18 eutectic muti-principal element alloy

Abstract

The mechanism of rapid solidification behavior of eutectic muti-principal element alloys (EMPEAs) is an eye-catching field. In this study, the novel Fe7(CoNi)75B18 EMPEA was undercooled via rapid solidification and B2O3 glass purification method and the maximum undercooling up to 190 K was achieved. A clear microstructure evolution path was identified with the undercooling: fully regular eutectic → primary dendrite and regular eutectic → primary dendrite and divorced eutectic. The orientation relationship (OR) between the primary (Fe, Co, Ni) phase and secondary B-rich phase was revealed both at low and medium undercoolings by electron backscatter diffraction (EBSD) analysis. The results show that the OR disappears at high undercooling (190 K) owing to the microstructure fragment and rotation during the post-recalescence. Furthermore, the growth velocity exponentially raised with the increase of undercooling. The maximum growth velocity of the primary phase was 1.152×10−1 m/s, which is significantly lower than binary alloys due to the sluggish kinetics effect of EMPEAs. This study helps to understand the solidification kinetics and microstructure transition of the novel EMPEA and has important implications for controlling the solidification process of more complex alloys.