Characterization of nano precipitate phase in an as-extruded Zn-Cu alloy

Zn-Cu-based alloys are an important alloy series and show promising application prospect for biodegradable cardiovascular stents due to their excellent anti-self-aging property and combination of strength and ductility as well as good biocompatibility. Generally, nano-precipitates are an effective way to strengthen these alloys. In Zn-Cu-based alloys, only the second phases with submicron or micron size were observed in previous investigations. Here nanosized precipitates in an as-extruded Zn-2.0wt.%Cu alloy were first characterized using transmission electron microscopy, and identified as the ε (CuZn₄) phase enriched Cu element with a hexagonal structure, which present with a rod shape and are symmetrically distributed along the ${\left[02\overline{2}1\right]}_{\eta }$ direction at a specific angle with the basal plane of the matrix. The nano-precipitates exhibit an approximately coherent interface with the matrix. The shape and orientation relationship with the matrix of these nano-precipitates were analyzed based on free energy minimization.