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

Abstract

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 (CoCr0.5Ni1.5)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 temperature. 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 evolution and property design of L12-γ′ precipitation-strengthened MEAs.