Mechanical properties and corrosion resistance characterization of a novel Co36Fe36Cr18Ni10 high-entropy alloy for bioimplants compared to 316L alloy

Abstract

The high strength, ductility, and corrosion resistance of alloys are highly desirable functional materials for biomedical applications. Multi-component alloys with a single face-centered-cubic (fcc) phase structure can provide superior ductility, while microstructures such as twins and stacking faults (SF) can be incorporated into the matrix to improve the strength of the alloy without damaging plasticity. Here, we have developed a single-fcc phase alloy Co36Fe36Cr18Ni10 with low stacking faults energy, which can effectively produce annealed twins by recrystallization annealing after cold rolling. The microstructure and mechanical properties of Co36Fe36Cr18Ni10 compared to commercial 316L alloy was methodically investigated by EBSD, TEM, and tensile testing. The results reveal that the Co36Fe36Cr18Ni10 alloy contains more twin boundaries and a high density of nano-twins and SFs in the microstructure, which effectively improve the strength of Co36Fe36Cr18Ni10 alloy meanwhile maintaining a similar ductility to commercial 316L. The corrosion behavior of Co36Fe36Cr18Ni10 and 316L in simulated body fluids has been investigated using electrochemical characterization, indicated that compared to 316L ss, pitting in Co36Fe36Cr18Ni10 alloys is easily inhibited and rapid re-passivation, meanwhile the twin boundaries were effective in weakening the formation of corrosion pits and impeded the expansion of corrosion crack. Compare the surfaces of the two alloys after passivation, apart from the Cr2O3/Cr(OH)3 contained in the passive film, the interactions between Co and other components in the passivation film produce more indissoluble substances with a lower enthalpy of formation that will enhance the passive film stability of Co36Fe36Cr18Ni10 alloy.