Microstructural evolution, mechanical properties and corrosion mechanisms of additively manufactured biodegradable Zn-Cu alloys

Additively manufactured (AM) biodegradable zinc (Zn) alloys constitute an important branch of orthopedic implants because of their moderate degradation properties and bone-mimicking mechanical properties. In this paper, the microstructure evolution and corrosion mechanism of zinc-copper (Zn-Cu) alloy prepared by the laser-powder-bed-fusion (L-PBF) additive manufacturing method were investigated. Alloying with Cu significantly increases the ultimate tensile strength (UTS) of unalloyed Zn, but the UTS and ductility of unalloyed Zn and Zn-2Cu decrease with increasing laser energy density. Unalloyed Zn has a dendritic microstructure, while Zn-2Cu alloy has a peritectic microstructure. The formation of round peritectic grains is due to the low temperature gradient of unalloyed Zn during the AM. Zn-2Cu samples exhibited higher corrosion rates, addressing the problem of slow degradation of unalloyed Zn. The grain size distribution influences the corrosion behavior of the material. It enhances the corrosion rates of materials with fine grains in a non-passivating environment. However, the 100% extracts of Zn-2Cu samples exhibited greater values of cellular activity compared to unalloyed Zn samples, thus confirming their better cytocompatibility. This work demonstrates the great potential to design and modulate biodegradable Zn alloys to fulfill clinical needs by using AM technology.