Design and microstructural development of a new eutectic Fe-Co-Ni-B multi-principal element alloy system

A new eutectic Fe-Co-Ni-B multi-principal element alloy system was designed. Microstructure evolution and mechanical properties of the Fe-Co-Ni-B alloys with varied content of Fe and B were investigated. For the Fe-x(CoNi)(84-x)B-16 alloys, it is found that the eutectic structure transforms from anomalous to lamellar, further to rod, and then to faceted dendrite, which was attributed to the transition of crystal structure of B-rich intermetallic phase from orthogonal to tetragonal as the Fe content increases. For the Fe-7(CoNi)(93-y)B-y alloys, the primary phase changes from (Fe, Co, Ni)-rich FCC solid solution to B-rich intermetallic with the increase of B content. The Fe-7(CoNi)(75)B-18 shows fully lamellar structure consisted of (Fe, Co, Ni)-rich phase and boron-rich phase with cubic and orthogonal crystal structures respectively. It is also found that the compressive strength and hardness of Fe-7(CoNi)(93-y)B-y alloys increase significantly but the plasticity decreases as B increases. The introduction of non-metallic element B as principal component provides a new idea for the design of eutectic high entropy alloy. (C) 2021 Published by Elsevier B.V.