Effects of Ta microalloying on the microstructure and mechanical properties of L12-strengthened CoCrFeNi–AlTi high-entropy alloys

In this work, the effects of Ta element microalloying on the microstructure and mechanical properties of CoCrFeNi–AlTi precipitation-strengthened high-entropy alloys were systematically studied. For CoCrFeNiAl0.15Ti0.1Ta0.015 high-entropy alloy, the microalloying of Ta can aggressively partition into the L12-γ′ phase, promote the continuous precipitation of the γ′ phase, and reduce the content of Al and Ti in the FCC matrix, resulting in a large lattice mismatch between the FCC and the γ′ phase. Moreover, the high-volume fraction of fine γ′ phase caused by Ta addition hinders grain boundary migration and dislocation movement, leading to a decrease in recrystallization and grain coarsening. The mechanical tensile tests show that the addition of Ta element (1 wt%) in the CoCrFeNiAl0.15Ti0.1 alloy can significantly improve the mechanical properties of the alloy due to the more effective precipitation strengthening effect and fine grain strengthening effect, in which the yield strength and ultimate tensile strength are increased by 17.6% and 8.2%, respectively, reaching 992.5 MPa and 1281.1 MPa. It was further confirmed through first-principle calculations that Ta tends to dissolve in the γ′ precipitates, which can effectively enhance the mechanical properties of the γ′ precipitates. This work provides a reference for the future design of L12-γ' precipitation-strengthened high-entropy alloys with ideal properties.