Achieving superior mechanical properties over a wide temperature range in NiCoVTa medium-entropy alloy via semi-coherent nanolamellar structure

This study introduces a diffusion-rate-adaptive strategy for designing a high-performance NiCoV_0.9Ta_0.1 medium-entropy alloy (MEA) strengthened by semi-coherent κ-phase nanolamellae, achieving exceptional strength-ductility synergy across a wide temperature range (77–923 K). Guided by an Integrated Computational Materials Engineering (ICME) approach that combines Calculation of Phase Diagram (CALPHAD) and Density Functional Theory (DFT), Ta addition is screened for sluggish diffusion to effectively restricts κ-lath thickening, leading to the formation of a nanoscale semi-coherent lamellar structure. The resulting ultrahigh strength originates from the substantial strengthening effect of the nanolamellar structure, coupled with synergistic contributions from grain size strengthening and resistance stress from the matrix. Furthermore, the formation of coherent nanoscale L1₂ precipitates during elevated temperature deformation compensates for the strength loss observed at 923 K. The remarkable strain hardening behavior arises from the interaction between κ laths and dislocations, i.e., initial dislocation pile-ups at the κ laths enhancing the hardening rates, while subsequent dislocation shearing and stacking faults (SFs) activation in the κ laths relieving stress concentrations, synergistically stabilizing plastic deformation. Additionally, deformation-induced dislocation substructures, including 9R phases, nanotwins, and dislocation tangles, contribute to the high level of strain hardening between 77 K and 723 K. At 923 K, dense SFs, generated through the interaction of L1₂ precipitates with dislocations in the matrix, facilitate Lomer-Cottrell locks formation and shear κ laths, resulting in anomalous hardening. This work establishes a diffusion-rate-mediated semi-coherent nanolamellar structure design paradigm for advanced M/HEAs, with significant promise for extreme‑temperature applications.