Opracowanie metody otrzymywania nowych bezszwowych rurek z bioabsorbowalnych stopów Zn- Mg przy użyciu wyciskania hydrostatycznego

In recent years, due to the biodegradation properties of zinc alloys with Mg, Mn, and Sr micro additives, their new potential applications have appeared in medicine for the production of temporary implants. Magnesium is the most popular zinc alloying additive due to its high biocompatibility, and of particular interest are hypoeutectic Zn-Mg alloys due to their best combination of strength and plasticity. Hence, Zn-Mg alloys have become the preferred candidate material for bioabsorbable cardiac stents or bone implants. The main obstacle for their future application was insufficient mechanical properties. As demonstrated in our previous studies, an unconventional deformation method such as hydrostatic extrusion at ambient temperature has become helpful in this regard. It allows achieving mechanical properties better than conventional methods which fulfil requirements for stent applications. Manufacturing of minitubes is a next challenge in the further development of biodegradable cardiac stents. The proposed hydrostatic extrusion process is characterized by triaxial compressive stresses in the deformation zone. It allows deformation of brittle and difficult-to-deform materials without the use of increased temperature, which is unfeasible using classical plastic processing methods such as conventional extrusion, rolling or drawing. Moreover, the favorable flow regime obtained by using low-angle dies makes possible hydrostatic extrusion of complex shapes with small cross-sections, such as seamless tubes. This project includes the hydrostatic extrusion of minitubes of two selected Zn alloys with the additive of Mg <0.5%, and their comparison with properties of Zn tubes manufactured in the same way, and with rods of similar composition. The project aims to analyze the effect of plastic deformation by hydrostatic extrusion on the production of seamless tubes made of a biocompatible zinc-magnesium alloy with mechanical and corrosion properties enabling their potential use in bioabsorbable stents. The optimization object will be the final parameters of plastic deformation by the cold hydrostatic extrusion method, including the tube geometry, deformation degree, tool geometry (dies and pins), deformation rate, and lubrication method. It is expected that the application of the hydrostatic extrusion method will allow, in addition to significantly increasing the mechanical properties, to obtain a homogeneous fine-grained microstructure in the tube walls. The plastic working parameters will be optimized based on the study of mechanical properties and the scanning and transmission electron microscopy methods. In particular, the application of the orientation microscopy technique in TEM and SEM will allow for quantitative analysis of the microstructure as well as the nature and distribution of second phases and grain boundaries, which have a significant impact on the mechanical properties and corrosion characteristics of alloys. Corrosion tests under dynamic conditions will be carried out to examine the deformation impact on the nature of manufactured tubes' corrosion. Investigations into the manufacturing processes for high-strength and ductile seamless tubes of Zn-Mg alloys by cold hydrostatic extrusion and characterization of mechanisms leading to their strengthening have not been undertaken so far and constitute a novel approach to the issue of technological processes of deformation of hard-deformable engineering materials.