Temperature-dependent microstructural evolutions and deformation mechanisms of (Ni2Co2FeCr)92Al4Nb4 high-entropy alloys

Precipitation-strengthened high-entropy alloys (HEAs) with tailored phase structures are expected to possess excellent strength-ductility combinations for advanced structural applications. In this work, we systematically studied the microstructural evolutions and mechanical behaviors of (Ni2Co2FeCr)(92)Al4Nb4 HEAs at different aging temperatures (700-900 C). It was revealed that only spherical L1(2) phase existed in the specimen peak-aged at 700 C without other precipitates, while in the specimen peak-aged at 800 C, irregular precipitation of epsilon phase appeared on the grain boundaries in addition to the intragranular L1(2) phase. In strong contrast, upon peak aging at 900 C. the fine interleaving Widmanstatten-type epsilon phase with an ordered hexagonal structure (D019) became the dominated precipitate. We further revealed that the coherent L1(2) phase provided a more effective strengthening effect than that of the epsilon phase, leading to the highest yield strength of ~950 MPa in the alloy peak-aged at 700 C. The stacking faults shearing of L12 phase and the planar dislocations shearing of epsilon phase were identified as the main deformation mechanisms of the specimens peak-aged at 700 and 900 C, respectively. Interestingly, the epsilon phase was determined to have certain plastic deformability, enabling the 900 C peak-aged alloy to exhibit excellent tensile ductility. These findings would provide valuable guidelines for the design of precipitation-strengthened HEAs with optimized microstructures and superior mechanical properties. (C) 2022 Elsevier B.V. All rights reserved.

Automated summary

In this study, the microstructural evolution and mechanical behavior of (Ni2Co2FeCr)(92)Al4Nb4 HEAs alloy at different aging temperatures were systematically investigated. The results showed that the aging temperature had a significant impact on the phase structure and mechanical properties of the alloy.