Effect of boron content on microstructure evolution and crystallization behavior of Fe7(CoNi)93-xBx (x=15, 18, 21) eutectic high-entropy alloys

Abstract

The effect of boron content on microstructure evolution, glass-forming ability and crystallization behavior of Fe7(CoNi)93-xBx (x = 15, 18, 21) eutectic high-entropy alloys (EHEAs) was investigated. Bulk Fe7(CoNi)93-xBx EHEAs and ribbons were prepared by vacuum frequency induction melting furnace and melt-spinning method, respectively. The results show that the microstructure of as-cast hypoeutectic Fe7(CoNi)78B15 alloy consists of primary (Fe, Co, Ni) dendrite and lamellar eutectic. The eutectic Fe7(CoNi)75B18 alloy shows a fully lamellar eutectic structure consisting of (Fe, Co, Ni) phase and B-rich phase. The microstructure of hypereutectic Fe7(CoNi)72B21 alloy exhibits primary B-rich dendrite and lamellar eutectic. The as-spun Fe7(CoNi)75B18 and Fe7(CoNi)72B21 alloys show an amorphous structure. By comparison, the hypereutectic Fe7(CoNi)72B21 alloy shows an excellent glass-forming ability and thermal stability, which is attributed to the increase of crystallization activation energy induced by B addition. In addition, the increase of B addition inhibits the crystallization behavior, which is caused by the formation of stable covalent bonds between boron and other elements. This work provides an alternative route for the preparation of metallic glass by introducing the non-metallic boron component.