Effects of Mn addition on mechanical properties, fracture surface, and electrochemical corrosion resistance of CoCrFeNiAl high-entropy alloys

High-entropy alloys consisting of CoCrFeNiAl as the major elements and 2-5 at% Mn as the minor element were prepared using a vacuum arc melting method. The crystalline structures of the prepared alloys were identified by x-ray diffraction. Moreover, the mechanical properties of the alloys were examined under quasi-static (10⁻¹, 10⁻² and 10⁻³s⁻¹) and dynamic (3000, 4000, and 5000 s⁻¹) loading conditions using a universal testing machine and split-Hopkinson pressure bar system, respectively. The experimental results showed that, for all of the HEA alloys, the flow stress and strain rate sensitivity coefficient increased with increasing strain rate. Among all the alloys, that with 3 at% Mn exhibited the best mechanical properties. A significant loss in plasticity was observed as the Mn content increased to 5 at%. The scanning electron microscope observations showed that the favorable mechanical properties of the alloy with 3 at% Mn were the result of a compact dimple structure, which enhanced the toughness. The HEA with 5 at% Mn showed the best electrochemical corrosion resistance among all the alloys due to the formation of dendritic structures at the grain boundaries.