Ta-induced strengthening of CoCrNi-AlTi medium-entropy alloys via nanoscale heterogeneous coherent precipitate

Nano-precipitate strengthened medium-entropy alloys (MEAs) with good strength elongation combinations are crucial for structural applications. This study demonstrated Ta-induced strengthening of CoCrNi-AlTi MEAs using nanoscale heterogeneous coherent precipitates. The density of coherent nanolamellar phases in (CoCr0.5-Ni1.5)86Al10Ti4 alloys can be increased with recrystallisation heat treatment, although this enhances the ductility of the alloy by up to 26.57 % the strength attained is only 733 MPa. However, addition of 2 at. % of Ta to (CoCr0.5Ni1.5)86Al10Ti4 MEAs enhances the mechanical properties, and the resulting yield strength, ultimate tensile strength, and acceptable elongation are 1385 MPa, 1690 MPa, and 7.44 %, respectively at room tem-perature. Thus, Ta-addition and aging treatments increase the yield stress by 89 %. This is attributed to the coexistence of nanoscale lamellar, heterogeneous, and continuous precipitates in the incompletely recrystallized grains. Therefore, this study serves as a reference for developing correlations between the microstructure evo-lution and property design of L12-gamma ' precipitation-strengthened MEAs.