Supersaturated solid solution enhanced biodegradable Zn-Mn alloys prepared by mechanical alloying and selective laser melting

Abstract

Zn-Mn alloys have been recognized as promising biodegradable metals due to moderate degradation and good osteogenesis. However, the alloying content of Mn has been severely limited by the low solid solubility (0.8 wt%) in conventional preparation process to avoid the excessive formation of brittle intermetallics. In this work, supersaturated solid solution was achieved in Zn-Mn alloys via mechanical alloying (MA) and selective laser melting (SLM). During MA process, the mixed Zn and Mn powders experienced repeated welding and fracturing, which resulted in refined grains and abundant crystal defects that stored extra energy. This could reduce the energy barrier of interatomic diffusion and induce the rapid diffusion of Mn atoms, leading to supersaturated solid solution with ∼3.6 wt% Mn homogeneously dissolved in Zn lattices. Moreover, the rapid solidification process of SLM effectively maintained the metastable supersaturated structure. In addition, the Zn-15Mn alloys prepared by MA and SLM were composed of fine equiaxed grains (∼4.34 µm) and high content of high-angle grain boundaries (54.8%). Owing to solution strengthening and grain refinement, the Zn-15Mn alloy prepared by MA and SLM exhibited a compressive yield strength of 178 MPa which was 2.8 times and 1.6 times those of pure Zn and Zn-15Mn alloy without MA process, respectively, as well as a more ductile fracture. Meanwhile, the Zn-Mn alloys exhibited accelerated degradation and comparable cytocompatibility to pure Zn. These findings indicated that the combined process of MA and SLM may be an efficient strategy for the preparation of alloys characterized by supersaturated solid solution and refined grain structure.