Ab initio study of precipitate stability in an Mg–Zn–Zr–Y alloy and its effects on corrosion, antimicrobial and in vitro biocompatibility

Abstract

Magnesium (Mg) alloy has long been projected as a degradable biomaterial with a special focus on its corrosion behaviour, mechanical properties and biocompatibility. In this study, we developed an Mg–5Zn–0.5Zr–0.9Y alloy and studied the effects of Mg₇Zn₃ and Mg₂₄Y₅ precipitates on its mechanical, corrosion, antimicrobial, and in vitro biocompatibility properties. The cast specimen exhibited a continuous network of Mg₇Zn₃ precipitates and a weaker basal texture, which adversely affected the mechanical and corrosion properties. The application of thermomechanical treatment preferentially dissolutes the Mg₇Zn₃ precipitate network compared to the Mg₂₄Y₅ precipitate owing to its lower cohesive energy, lower enthalpy of formation and lower bonding electrons, as calculated using the first principle study. This resulted in a significant reduction in the volta potential difference between the precipitates and the matrix, which simultaneously improved corrosion resistance and ductility. Moreover, the increased area fraction of Mg₂₄Y₅ fine precipitates in the forged specimen contributed to its enhanced corrosion resistance. DFT calculations indicated a lower total density of state (DOS) value near the Fermi energy level of Mg₂₄Y₅, which retarded electron loss capability and thereby reduced the corrosion rate. The higher corrosion resistance of the forged sample was due to lower defect density, as determined through Mott–Schottky analysis. All samples exhibited excellent antimicrobial properties against Gram-negative E. coli bacteria. Improved degradation properties of the forged specimen enhanced cell viability and alkaline phosphatase activity against MC3T3-E1 cells, indicating its non-toxic nature.