A novel complex-structure Co-free Cr-Fe-Ni-Al-Si-Ti-Cu high entropy alloy with outstanding mechanical properties in as-cast and cold-rolled states

In this paper, a novel Co-free CrFeNiAl_0.28Si_0.09Ti_0.02Cu_0.01 high entropy alloy (HEA) was designed and fabricated by casting. It is found that, this as-cast HEA has complex multi-phase microstructure including fine FCC sideplates with ultrafine wheathead-like substructures, as well as nano-precipitates in the fine BCC inter-sideplate regions. Further, it shows excellent comprehensive mechanical properties combining ultimate tensile strength (UTS) of over 1.2 GPa and plasticity of ∼22% in as-cast state, while cold rolling with the reduction rate of 60% further increases UTS to ∼1.7 GPa and maintain good plasticity. Moreover, it is found that the formation of FCC sideplates in this HEA in as-cast state is possibly resulted from solid-state phase transformation. Besides, dislocation and heterogeneous structure play important roles in mechanical properties of this HEA under different fabrication conditions. This work provides a novel route in the design of high-performance low-cost HEAs that could be fabricated in simple ways, which is beneficial for further application and development of this series of advanced materials.