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Chemical short-range order (CSRO) is a typical microstructural characteristic commonly found in multi-principal element alloys (MPEAs). For MPEAs with the face-centered cubic (FCC) structure, the presence of CSRO has been verified and characterized meticulously by using electron microscope. However, it is still challenging to reveal the effect of CSRO structure on the deformation microstructure and micromechanical behavior of those alloys. By applying atomic scale simulations, this study explores the micromechanical behavior of an equiatomic CoCrNi medium entropy alloy with random solid solution and three different degrees of CSRO under plane strain compression, respectively. The results show that CSRO can effectively promote planar slip of dislocations in the FCC matrix and elevate flow stress of the alloy. The planar slip and stacking of partial dislocations then lead to the formation of hexagonal-close-packed (HCP) structure lamellae. CSRO also modulates the morphology of dislocations. When dislocations cut through CSRO, it hinders the movement of dislocations while being destroyed by atomic plastic flow, causing CSRO and atomic clusters at the interface of the matrix to embed each other and generate antiphase boundaries which can significantly enhance the bulk yield strength. These findings provide fundamental insights into the interaction between CSRO and dislocations in CoCrNi MEA, guiding the design of MPEAs with superior combinations of strength and ductility. [Display omitted] • Interaction between chemical short-range order (CSRO) and dislocations in the CoCrNi MEA is unraveled. • Deformation mechanisms depend on the degree of CSRO. • Plastic deformation deteriorates CSRO. The more significant the CSRO, the easier it is to be destroyed with deformation. [ABSTRACT FROM AUTHOR]

Refractory high-entropy alloys (RHEAs) with superior mechanical properties have been considered as a potential next-generation candidate for high-temperature structural materials. However, the structural stability of RHEAs at high temperatures is still noncommittal so far. Especially, the Al containing RHEAs with coherent BCC/B2 microstructure usually form intermetallic phases following short/long term aging at elevated temperatures, which deteriorate the mechanical performance. In this work, we systematically determine the microstructural evolution, including intergranular precipitates, BCC/B2 morphology, and corresponding mechanical properties changes of the Nb 40 Ti 25 Al 15 V 10 Ta 5 Hf 3 W 2 RHEA from 923 K to 1123 K. The density of antiphase domain boundaries (APBs) in the RHEA after aging at 923 K is significantly higher than at 1023 K and 1123 K. Only a low volume fraction of tetragonal (Nb, Hf) 2 Al phase precipitates along grain boundaries after aging at 1123 K. However, the microhardness and yield strengths of the RHEA after aging at 923 K - 1123 K are close to those of the as-cast RHEA, which proves that the APBs and low-density (Nb, Hf) 2 Al precipitates have a negligible effect on the mechanical performance of the RHEA. Therefore, the Nb 40 Ti 25 Al 15 V 10 Ta 5 Hf 3 W 2 RHEA exhibits superior structural stability from 923 K to 1123 K, which also imparts the mechanical stability. This work guides towards tailoring the composition and microstructure of RHEAs for even better high-temperature mechanical performance. • The microstructural evolution of Nb 40 Ti 25 Al 15 V 10 Ta 5 Hf 3 W 2 has been explored. • APBs have a negligible effect on the mechanical performance of the RHEA. • Hf-rich segregations appear along GBs and in the matrix after aging at 1123 K. • Tetragonal (Nb, Hf) 2 Al phase precipitates along GBs after aging at 1123 K. • The RHEA shows superior structural and mechanical stability from 923 K to 1123 K. [ABSTRACT FROM AUTHOR]