The Effects of Alloying and Severe Plastic Deformation on the Room- Temperature Creep Response of Zn-Based Biodegradable Alloys

In recent years, considerable research has focused on using zinc (Zn) alloys for the production of biodegradable implants, mainly because they exhibit lower corrosion rates compared to other biodegradable systems, such as magnesium (Mg)- and iron (Fe)-based alloys. However, pure Zn suffers from poor mechanical properties and pronounced creep at human body temperature, limiting its potential use in biomedical applications. Alloying and severe plastic deformation (SPD), including equal channel angular pressing (ECAP), are known to be effective approaches for improving mechanical properties of pure Zn. Nevertheless, the effects of these two processes on the creep behavior of Zn-based alloys have rarely been investigated in the literature. Therefore, the present work aims to compare the room-temperature creep behavior of pure Zn and a Zn-۱Mg alloy under homogenized conditions, as well as a Zn-۱Mg-۰.۲Y alloy in both the as-cast and after ECAP-processed states. Shear punch creep test (SPCT) was used for evaluating creep behavior. The results demonstrated that the creep resistance of the homogenized Zn-۱Mg alloy increased significantly compared to pure Zn. The creep rates of pure Zn and the Zn-۱Mg alloy under a shear stress of ۶۰ MPa were found to be ۵.۷۲ x ۱۰^-۸ s⁻¹ and ۸.۶۲ × ۱۰^-۸ s⁻¹, respectively. In addition, the stress exponent for both pure Zn and the Zn-۱Mg alloy was found to be within the range associated with five-power-law creep. Specifically, the stress exponent was calculated to be approximately ۶.۲ for pure Zn and ۷.۱ for the Zn-۱Mg alloy. The improved creep resistance of the homogenized Zn-۱Mg alloy was primarily attributed to the formation of Mg۲Zn precipitates at the grain boundaries. Moreover, comparing the creep behavior of the Zn-۱Mg-۰.۲Y alloy in the as-cast state and after ۴ passes of ECAP showed that the ECAP processing remarkably enhanced the creep resistance of the as-cast alloy. The creep rates of the as-cast and ECAP-processed samples under a shear stress of ۱۲۰ MPa were measured to be ۱.۷۷ × ۱۰^-۵ s⁻¹ and ۱.۲۶ x ۱۰^-۵ s⁻¹, respectively. Furthermore, the stress exponent was determined to be approximately ۶.۸ for the as-cast state and ۷.۲ for the ECAP-processed sample, suggesting that the grain refinement achieved during ECAP was likely responsible for the enhanced creep resistance in the dislocation creep mechanism.

کلیدواژه ها:

Creep ، Mechanical properties ، Shear punch creep test ، Zinc alloys