A new complex-regular eutectic in the Fe7(CoNiMn)93-xBx high entropy alloys

Abstract

Phase constituents and solidification microstructures of as-cast Fe7(CoNiMn)93-xBx (x = 9, 13) HEAs were investigated via electron backscattered diffraction and transmission electron microscopy. It was observed that the phase constituents contain an FCC1 solid solution and an M23B6 compound. The microstructure of hypoeutectic Fe7(CoNiMn)84B9 high-entropy alloy consists of primary face-centered-cubic (FCC1) dendrite and trigonal-shaped complex-regular eutectic, and that of Fe7(CoNiMn)80B13 eutectic high-entropy alloy is fully consisted of trigonal-shaped complex-regular eutectic. The formation of this rare complex-regular eutectic is attributed to the preferential growth of M23B6 in a trigonal-shaped trunk due to its crystallography anisotropy. In addition, the FCC1 eutectic phase has a cube-on-cube orientation relationship with the M23B6 phase where the same orientation but different lattice constants for them leads to the appearance of misfit dislocations at the interface, which enhances the strength of materials. The compression strength for Fe7(CoNiMn)80B13 eutectic high-entropy alloy is higher than that of hypoeutectic Fe7(CoNiMn)84B9 high-entropy alloy.