Ultrafine Cellular Eutectic Biodegradable Zn–Ge Alloys Fabricated by Laser Powder Bed Fusion: Process Manipulation and Performance Improvement

Zn has been recognized as a promising biodegradable metal for its good biocompatibility and favorable biodegradability. However, it has always struggled with poor mechanical properties, which restrict its application prospects as a bone implant. In the present study, the laser powder bed fusion (LPBF) process was applied to fabricate biodegradable Zn-Ge eutectic alloys for mechanical reinforcement. The effects of volumetric energy density on the relative density and surface roughness of LPBF-fabricated (LPBF-ed) Zn-Ge alloys were investigated by orthogonal tests, which contributed to an optimal relative density >99.5%. Because of the differences in growth rates of constituent phases under nonequilibrium solidification, the LPBF-ed Zn-Ge alloys exhibited a distinctive ultrafine cellular structure (∼1.2 μm), where the α-Zn matrix was surrounded by a Zn-Ge network eutectic via semicoherent interface. Meanwhile, the size of the Zn-Ge eutectic phase was also significantly refined owing to the ultrafast cooling and high temperature gradient of the LPBF process. Moreover, the Ge-doping was found to enable heterogeneous nucleation and significantly refine the grain size within the LPBF-ed Zn-Ge alloys, especially in the Zn-3Ge alloy. Consequently, the LPBF-ed Zn-3Ge alloy presented substantially improved yield strength (156.81 ± 7.47 MPa) and ultimate tensile strength (178.61 ± 6.41 MPa) owing to the numerous semicoherent interfaces induced by refined eutectic structure. Furthermore, the LPBF-ed Zn-Ge alloys also demonstrated good cytocompatibility, as well as appropriate degradation rates (0.265 ± 0.010 mm/y for LPBF-ed Zn-3Ge alloy) owing to the microbattery effect and the barrier effect. Accordingly, these findings indicated the promising application of the LPBF-ed ultrafine cellular eutectic structure in the mechanical reinforcement of biodegradable Zn alloys.