Influência do processamento por torção sob alta pressão no comportamento em corrosão do magnésio e suas ligas para aplicação como material biodegradável

Abstract

Due to its good combination of mechanical, biological, and electrochemical properties, magnesium has shown great potential for use in biodegradable implants. Severe plastic deformation processes have proven promising in achieving appropriate mechanical properties and a controlled, homogeneous degradation rate for the development of magnesium-based biodegradable implants and their alloys. This study evaluates the corrosion behavior of magnesium and its alloys in simulated body fluid over long immersion periods after being processed by High Pressure Torsion (HPT), a technique that enables the formation of an ultrafine-grained microstructure. The adopted methodology involved literature data analysis, structural characterization, mechanical testing, and immersion tests in Hank’s solution to evaluate corrosion rates through mass loss, complemented by X-ray tomography and hydrogen evolution analysis after long immersion periods in solution. The results indicate that pure magnesium and its alloys show a significant improvement in mechanical properties and corrosion resistance when subjected to HPT processing. The Mg-1%Zn-0.5%Ca and Mg-4%Y 3%RE alloys exhibited a tendency for localized deformation during HPT, with non-uniform grain refinement and severe localized corrosion. The Mg-1%Zn, Mg-4%Li-1%Y, and Mg-8%Li 1%Y alloys maintained structural integrity after immersion, despite the observed points of localized corrosion. Pure magnesium demonstrated good corrosion resistance and maintained its integrity after 28 days of immersion. The conclusions highlight that grain refinement of magnesium through HPT results in a more homogeneous and refined grain microstructure, improving both mechanical properties and corrosion resistance with increased immersion time. The corrosion rate is affected by deformation heterogeneity, particularly in areas near the center and edges of the HPT-processed discs. The effect of grain structure on the corrosion rate is attributed to a transition from localized corrosion mechanisms (coarse grains) to uniform corrosion (fine and ultrafine grains). Finally, HPT proves to be more effective than other processing techniques for grain refinement and structural homogenization. Corrosion resistance tends to increase with grain size reduction, and the best combinations of mechanical strength and corrosion resistance are observed in magnesium and alloys processed by HPT with ultrafine grains.