A strong and ductile NiCoCr-based medium-entropy alloy strengthened by coherent nanoparticles with superb thermal-stability

Abstract

• A novel strong yet ductile (NiCoCr) 92 Al 6 Ta 2 MEA strengthened by nanoscale coherent L1 2 -precipitate was designed. • The multi-strengthening in particular the pronounced precipitate-hardening confers a good strength-ductility balance in this alloy. • A unique particle-features-dependent plastic mechanism of the matrix in this alloy was revealed. • This alloy displayed an extraordinarily superior coarsening resistance of nanoparticles as compared to typical superalloys and reported M/HEAs. In this work, we designed a novel NiCoCr-based medium-entropy alloy (MEA) strengthened by coherent L1 2 -nanoparticles, i.e., (NiCoCr) 92 Al 6 Ta 2 (at.%). The strengthening and deformation mechanisms of the material and the coarsening kinetics of the coherent precipitates were systematically investigated. The results indicated that giant precipitation hardening and its synergy with other strengthening contributors confer on the aged material a yield strength as high as 1.0 GPa. Moreover, a unique particle-features-dependent plasticity mechanism was revealed in this alloy. That is, the alloy with a lower volume fraction, denser distribution, and finer particles mainly deformed by dislocation planar slip, otherwise, stack-faults-mediated plasticity was favored, rationalized by the cooperative/competitive effect of stack-fault energy, spatial confinement, and applied stress. Furthermore, the coarsening behavior of precipitate followed a modified Lifshitz–Slyozov–Wagner (LSW) model, and the nanoparticles displayed remarkably superior thermal stability compared to most traditional superalloys and reported multicomponent alloys. The superb coarsening resistance of precipitate originated from the coupled effect of intrinsic sluggish diffusion in multi-principal alloys and the dual-roles of Ta species as a precipitate stabilizer. This work provides a new pathway to develop strong-yet-ductile multicomponent alloys as promising candidates for high-temperature applications.