Microstructure, mechanical properties and creep behaviour of extruded Zn-xLi (x = 0.1, 0.3 and 0.4) alloys for biodegradable vascular stent applications

Zn–Li alloys have been shown to be promising for biodegradable vascular stent applications due to their favourable biocompatibility and superior strength. This work presents a thorough evaluation of the microstructure, room temperature mechanical properties and human body temperature creep behaviour of hot-extruded Zn-xLi (x = 0.1, 0.3 and 0.4) alloys. All alloys show typical basal texture after the extrusion but the recrystallized grains are much finer with increasing Li content. Consequently, not only the room temperature yield and tensile strengths but also the elongation to fracture is significantly increased with increasing Li content. However, increasing Li content has an adverse effect on the creep resistance at human body temperature. Moreover, there is a transition in the operative creep mechanism from dislocation creep in the Zn-0.1Li alloy to grain boundary sliding in the Zn-0.3Li and Zn-0.4Li alloys. The observed mechanical behaviour in these alloys can be well related to the grain size effect, i.e. strengthening to softening by grain boundaries with decreasing strain rate. This work suggests that grain size of biodegradable zinc alloys should be optimized in order to achieve a balance between room temperature mechanical properties and human body temperature creep resistance.