Aluminum and titanium alloyed non-equiatomic Co-Fe-Ni medium-entropy alloy with ultra high strength and hardness

High-entropy alloys are a new class of multi-component alloys, which demonstrate outstanding strength-ductility combination, significant expanding the alloy design space in metallurgical research. However, the yield strength levels, are still low when compared with other high strength materials. Here, the non-equiatomic design concept was employed to improve the yield strength of the CoFeNi alloy through adjusting the Al and Ti element. Gigapascal compressive yield strength and relative good ductility were obtained in the FCC + L1(2)+BCC structured high-entropy alloys system. In addition, the superiority of adding Al and Ti simultaneously in micromechanical behaviors was investigated during nano-indentation tests at room temperature. The strength increment is owing to various complementary strengthening mechanisms, including solid solution strengthening, Hall-Petch strengthening, and precipitation strengthening, which have been quantitatively calculated.

Automated summary

By adjusting the elements Al and Ti through the non-equiatomic design concept, the yield strength of high-entropy alloys can be improved. High gigapascal compressive yield strength and relatively good ductility were achieved in the FCC + L1(2)+BCC structured high-entropy alloys system. The addition of Al and Ti simultaneously showed superior micromechanical behaviors and contributed to the strength increment through multiple strengthening mechanisms.