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

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.

Automated summary

This study introduces a powder metallurgy route to enhance the mechanical properties of equiatomic CoCrNi medium-entropy alloys using multiple strengthening mechanisms. The yield strength of the alloy produced by mechanical alloying is significantly higher than that of alloys prepared from commercial powders or casting. The coordination of ultra-fine grains, twins, and high-density stacking faults contributes to the enhanced strength. Molecular dynamic simulations further demonstrate the influence of twins and stacking faults on the grain refinement effect. These findings highlight the effectiveness of mechanical alloying in producing MEAs with superior strength.