High entropy effect on structure and properties of (Fe,Co,Ni,Cr)-B amorphous alloys

We examined high entropy (HE) effect on the formation, structure, thermal stability, mechanical properties and corrosion behavior for (Fe,Co,Ni,Cr)100-xBx (x = 18-26) amorphous alloys in comparison with Fe100-xBx amorphous alloys. The as-quenched structure consists of an amorphous single phase for the 18-24%B alloys, and amorphous + tetragonal Cr5B3 phases for the 26%B alloy. The broad diffraction peak position due to amorphous phase shifts to a higher wave vector side with increasing B content for the HE alloys, while that of the Fe-B alloys changes to the lower wave vector side, indicating the distinct difference in disordered atomic structure between the HE alloys and the binary alloys. All the as-spun HEA ribbons exhibit good bending ductility in spite of the coexistence with their crystalline phases, being different from the brittle nature for the 26%B binary alloy. The crystallization temperature (Tx) and Vickers hardness (Hv) increase with increasing B content, show maximum values of 803 K and 1130, respectively, at 22%B and then decrease to 793 K and 1070, respectively at 26%B, being different from the nearly constant Tx and almost linear increase in Hv with increasing B content for the Fe100-xBx alloys. The corrosion resistance in NaCl, H2SO4 and HCl solutions evaluated by potential and anode current density is much better for the HE alloys as compared with the Fe-B alloys. Thus, the Tx, Hv, bending ductility and corrosion resistance for the HE amorphous alloys containing more than 20 at%B are much superior to those for the Fe-B amorphous alloys. The fully crystallized structure consists of fcc + FeB + Fe2B + Cr5B3 phase for the HE 22-26 at%B alloys and bcc-Fe + Fe2B for the Fe-B alloys. The significant improvement of the fundamental properties caused by the HE component modification is presumably due to the formation of Cr-B pair with higher B-rich components. The improved properties in conjunction with the change in the disordered structure for the HE amorphous alloys provide an opportunity of developing a new functional material by alloy design to HE type compositions.