Investigation on microstructures, mechanical properties and in vitro corrosion behavior of novel biodegradable Zn-2Cu-0.01Ti-xLi alloys

Abstract

The poor mechanical properties of pure Zn almost exclude the possibility of using it as biodegradable implant material. Therefore, alloy design and process strategy of biodegradable Zn alloys have been the focus of attention. In this work, novel biodegradable Zn-2Cu-0.01Ti-xLi (x = 0, 0.1 and 0.38) alloys were designed and fabricated (cast, annealed and extruded) to investigate their microstructures, mechanical properties and corrosion behavior. The results showed that primary ɛ-CuZn4 particles and eutectic TiZn16 phase are formed in all the as-cast alloys. However, the size and volume fraction of the primary particles in the Zn-2Cu-0.01Ti-0.38Li alloy are significantly increased. Also, wavy lamellar β-LiZn4 phase precipitates from the Zn matrix of this alloy. In the as-annealed microstructures, secondary lath-like ɛ-CuZn4 phase is formed around the primary ɛ-CuZn4 particles in the Zn-2Cu-0.01Ti and Zn-2Cu-0.01Ti-0.1Li alloys. The above phases are broken, crushed or elongated in the as-extruded alloys, playing a crucial role in enhancing their strength. All the as-cast alloys show inferior mechanical properties, especially poor ductility. By contrast, the as-extruded alloys exhibit significantly improved mechanical properties. The as-extruded Zn-2Cu-0.01Ti alloy has elongation of up to 130 ± 5.60%, exhibiting ultrahigh tensile ductility. The as-extruded Zn-2Cu-0.01Ti-0.38Li alloy possesses tensile yield strength, ultimate tensile strength, tensile elongation, compression yield strength, and ultimate compression strength of 408 ± 16.6 MPa, 431 ± 7.9 MPa, 68 ± 4.05%, 393 ± 13.2 MPa and 1030 ± 25.2 MPa, respectively, showing the best comprehensive mechanical properties. Both electrochemical and in vitro immersion corrosion tests show that the Zn-2Cu-0.01Ti and Zn-2Cu-0.01Ti-0.38Li alloys have the highest and lowest corrosion rates, respectively. Adding Ti and Li to Zn-Cu alloy can reduce and improve its corrosion resistance, respectively.