Superior synergy of strength and ductility under dynamic tensile loading in the Si-metalloid-substituted multi-principal element alloys

Résumé fourni par la source

A series of single-phase FCC multi-principal element alloys with compositions of (CoCrFeNi) 100-x Si x (x = 4, 8, 12, at.%) were designed and fabricated. The tensile responses were systematically investigated under quasi-static and dynamic-loading conditions at both room and cryogenic temperatures. The results show that increasing Si content simultaneously enhances yield strength and uniform elongation under all testing conditions. The density of geometrically necessary dislocations after deformation increases with increasing Si content. Under dynamic-loading at room temperature, the Si 12 MPEA also achieves an outstanding strength–ductility synergy: a yield strength of 0.8 GPa and a uniform elongation of ∼90 %. This superior performance originates from two synergistic effects: the formation of high-density stacking faults, which inhibits the dynamic recovery of dislocations and alleviates strain localization; and the martensitic transformation product dominated by nanoscale lamellar structures, which avoids the interfacial strain mismatch at phase boundaries and local mechanical instability induced by rapid and large-scale martensitic transformation. The above dual effects jointly promote sustained strain hardening, and ultimately endow the alloy with extraordinary ductility. Furthermore, a constitutive model incorporating mechanisms of dislocation slip, twinning, and martensitic transformation was developed. This model successfully predicts the flow behavior of the (CoCrFeNi) 88 Si 12 alloys under various conditions.

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