Effect of Ti Content on Microstructure and Mechanical Properties of the Co_39.2Ni_39.2Al_21.6-xTi_xDual-phase High Entropy Alloys

Three dual phase high entropy alloys with a composition of Co_39.2Ni_39.2Al_21.6-xTi_x(x=2, 4, and 6) are prepared in this work. All the three alloys display an FCC-B2 dual phase structure. Dispersed nanoscale L1₂ ordered precipitate phases are presented in FCC, and lath-like L1₀ martensite presented in B2 phase. With the increase of Ti content, the volume fractions of FCC and L1₂ phases and size of L1₂ phase increase, and the volume fraction of B2 phase decreases. The Co_39.2Ni_39.2Al_15.6Ti₆ alloy shows the most excellent combination of strength and ductility. The high strength and plasticity come from the stress induced martensitic transformation in the B2 phase during the deformation process, and the high work hardening rate provided by the L1₂ ordered precipitate phase in the FCC phase. This work provides a theoretical reference for designing the microstructure of the dual phase high entropy alloys through alloying to enhance their comprehensive mechanical properties.