Untra-fine-grained equiatomic CoCrNi medium entropy alloys with high density stacking faults and strengthening mechanisms

R Yang and LJ Yang and TM Wang and QH Wang, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 870, 144880 (2023).

DOI: 10.1016/j.msea.2023.144880

This study introduces a powder metallurgy route (a combination of mechanical alloying (MA) and spark plasma sintering) to enhance the mechanical properties of equiatomic CoCrNi medium-entropy alloys (MEAs) using multiple strengthening mechanisms. The yield strength of MEA with an average grain size of 0.41 pm produced by MA is 777 +/- 21 MPa, which is 121% higher than that of MEA with grains of 4.55 pm prepared from com-mercial powders. Additionally, the yield strength of the untra-fine- grained alloy is 231% higher than that of the one produced by casting. Such an enhancement of the strength is attributed to the coordination of the ultra-fine grains, twins, and high-density stacking faults. Moreover, the influence of twins and stacking faults was inves-tigated using molecular dynamic simulations. The intersection of ultra-high density stacking faults generates many immobile dislocation locks and separates the grains into several small parts, leading to a dynamic grain -refinement effect. These findings indicate that MA is an effective way to produce MEAs with superior strength.

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