Designing nanoparticles-strengthened high-entropy alloys with simultaneously enhanced strength-ductility synergy at both room and elevated temperatures

Developing microstructurally stable alloys with the outstanding strength-ductility combination at both room temperature and elevated temperatures is highly desirable for advanced structural applications, which, however, still remains challenging despite years of efforts. In this study, leveraging on the computation-aided thermodynamic modeling, novel high-strength Ni_39.9Co₂₀Fe_30-xCr_xAl₆Ti₄B_0.1 (x = 0, 10, 15, and 20 at.%) high-entropy alloys (HEAs) were rationally designed, which maintained a stable coherent precipitation microstructure when continually substitute Fe with Cr. The structural features, mechanical properties, and underlying deformation micro-mechanisms were systematically investigated. We found that Cr mostly partitions into the face-centered-cubic (FCC) matrix relative to the L1₂-type nanoparticles. The increased Cr concentration substantially decreases the stacking fault energy (SFE) of the matrix and results in the stacking-fault-prevailed deformation behaviors, thereby producing simultaneously enhanced strength and ductility at room temperature. By contrast, when tested at 600 °C, the Cr-free HEA suffers from an extremely brittle fracture along grain boundaries caused by environmental oxidation damages. Interestingly, with Cr doping up to 20 at.%, such a serve intergranular embrittlement can be completely eliminated due to the increased oxidation resistance, leading to a distinct brittle-to-ductile transition (from 3.4 to 25.2%) at a high strength level of ∼ 1136 MPa. These findings will give new insights into the controllable design of novel high-performance HEAs for achieving target microstructures and superior property combinations.