Highly Ductile Zn-2Fe-WC Nanocomposite as Biodegradable Material

Abstract

Zinc (Zn) has been widely investigated as a biodegradable metal for orthopedic implants and vascular stents due to its ideal corrosion in vivo and biocompatibility. However, pure Zn lacks adequate mechanical properties for load-bearing applications. Alloying elements, such as iron (Fe), have been shown to improve the strength significantly, but at the cost of compromised ductility and corrosion rate. In this study, tungsten carbide (WC) nanoparticles were incorporated into the Zn-2Fe alloy system for strengthening, microstructure modification, and ductility enhancement. Thermally stable WC nanoparticles modified the intermetallic ζ-FeZn₁₃ interface morphology from faceted to non-faceted. Consequently, WC nanoparticles simultaneously enhance mechanical strength and ductility while maintaining a reasonable corrosion rate. Overall, this novel Zn-Fe-WC nanocomposite could be used as biodegradable material for biomedical applications where pure Zn is inadequate.

Fig. 1.

Schematics of Zn-Fe-WC nanocomposite manufacturing

Fig. 2.

Microstructure of Zn-2Fe-8 vol pct WC. (a) The microstructure image of Zn-2Fe-WC under SEM at low magnification. Brighter phases indicated the high-density nanoparticle pseudo-clusters. (b) The microstructure image of Zn-2Fe-WC under SEM at high magnification, showing the good distribution of WC nanoparticles inside the pseudo-clusters. (c) SEM image of Zn-2Fe-WC after grain etching, showing nanoparticles modified the formation of FeZn₁₃. (d) EDS point scannings were performed on places shown in (c), indicating nanoparticles were likely to stay in Zn-rich phase

Fig. 3.

(a) and (b) Zn-2Fe optical images after etching, yellow phases indicated the faceted intermetallic precipitate (ζ-FeZn₁₃). (c) and (d) Zn-2Fe-WC optical images after etching, intermetallic phases showed non-faceted morphology and the black spots indicated the nanoparticle pseudo-clusters

Fig. 4.

Proposed schematic of the solidification process for Zn-2Fe and Zn-2Fe-WC at stages I–III

Fig. 5.

XRD results of Zn-2Fe and Zn-2Fe-WC

Fig. 6.

Vickers microhardness of Zn-2Fe and Zn-2Fe-WC compared with pure Zinc sample (n = 8)

Fig. 7.

(a) Representative stress-strain curve from the tensile test of cast Zn-2Fe, cast Zn-2Fe-WC. (b) Average values of yield strength, ultimate tensile strength, and elongation to failure (n = 3)

Fig. 8.

The fracture surface of as-cast Zn-2Fe and as-cast Zn-2Fe-WC are shown in (a, b) and (c, d), respectively

Fig. 9.

UTS vs. elongation to failure for as-cast biocompatible and biodegradable zinc alloys. As-cast Zn-2Fe-WC stands out due to the significantly improved ductility

Fig. 10.

Immersion test result: cumulative ion releases of Zn and Fe after 4 weeks in SBF