Effects of Al and Ti co-doping on the strength-ductility- corrosion resistance of CoCrFeNi-AlTi high-entropy alloys

In order to design and develop new marine structural materials with a balance of strength-toughness-corrosion resistance, in this work, the synergistic effects of Al and Ti on the microstructure, mechanical and corrosion resistance properties of CoCrFeNi(Al0.3Ti0.2)x high-entropy alloys were systematically investigated. With the addition of Al and Ti, the L12-γ' phase formed in the alloys significantly improves the mechanical properties, but excessive addition will lead to the formation of Al-Ti-rich B2 phase structure, which reduces the ductility of the alloy. For the corrosion resistance of the alloys in 3.5 wt. % NaCl solution, the increase of Al and Ti contents improves the stability of the passive film, while effectively reduces the corrosion current density and passivation current density of the alloys. However, the precipitation with a large number of strengthening phases aggravates the segregation of elements, resulting in a decrease in the pitting corrosion resistance and the resistance to the pit propagation of the alloy. In addition, compared with conventional structural alloys, the L12-strengthened dual-phase CoCrFeNiAl0.15Ti0.1 high-entropy alloy possesses an excellent balance of strength-toughness-corrosion resistance. This work also provides guidance for the future development of high-performance high-entropy alloy systems for marine engineering.