Effect of High-Pressure Torsion on Microstructure, Mechanical and Operational Properties of Zn-1%Mg-0.1%Ca Alloy

A study of the effect of high-pressure torsion (HPT) on the structure, phase composition, corrosion resistance, mechanical properties and bioactivity in vitro of Zn-1%Mg-0.1%Ca alloy was performed. It was shown that HPT leads to refinement of the alloy microstructure with the formation of recrystallized α-Zn grains with an average size of 750 ± 30 nm, and grains of a mixture of different phases with a size of 38 ± 7 nm. In addition, precipitation of Ca-enriched particles ~20 nm in size was observed. X-ray phase analysis showed that the Zn-1%Mg-0.1%Ca alloy consists of five phases (Zn, Mg2Zn11, MgZn2, CaZn11 and CaZn13), whose volume fraction does not change after HPT. It was found that HPT does not lead to a deterioration in the corrosion resistance of the alloy. At the same time, HPT leads to an increase in the yield stress of the alloy from 135 ± 13 to 356 ± 15 MPa, the ultimate tensile strength from 154 ± 5 to 416 ± 31 MPa, and the ductility from 0.4 ± 0.1 to 5.5 ± 2.8%. No significant increase in hemolytic activity, bactericidal activity, and the ability to colonize the surface of the alloy by cells was revealed during the conducted studies. Additionally, there was no significant difference in these parameters in comparison with the control. However, HPT contributes to a decrease in the cytotoxicity of the alloy by an average of 10% compared to the annealed alloy. The conducted studies allow us to conclude that the Zn-1%Mg-0.1%Ca alloy is promising material for the development of biodegradable orthopedic medical implants.