Estudo da resistência à corrosão e mecânica do ferro ARMCO na solução de Hank após processamento por torção sob alta pressão (High-Pressure Torsion)

Abstract

It is well established that iron (Fe) is a promising material for use in biomedical applications. However, it exhibits a very slow corrosion rate when present in physiological media, which can make it incompatible for application as degradable implants. In this work, pure iron processed by HPT (High-Pressure Torsion), which is a technique that consists of applying high pressure to the material together with the torsion, thus producing highly plastically deformed materials with ultrafine grains, was subjected to different temperatures annealing process. The influence of the grain size of the iron on the chemical and mechanical properties of the samples was evaluated. For that, tests were carried out to analyze the corrosion resistance in Hank's solution (static immersion, potentiodynamic polarization, and electrochemical impedance spectroscopy) and the mechanical properties (compression and microhardness) of the material under study, relating them to the iron microstructure, which was evaluated using scanning electron microscopy coupled with X-ray dispersive energy spectroscopy and X-ray diffraction. The material obtained ultrafine particle sizes of about 5 µm at 200 nm. Flow tensions greater than 1GPa were obtained in samples of ultrafine grain, enabling the production of load-bearing implants with smaller dimensions. Samples with ultrafine grain sizes exhibited very low corrosion rates (about 0.016 mm.year-1) and when immersed for 28 days in Hank's solution they developed a homogeneous surface layer of corrosion products containing hydroxyapatite. Processing by severe plastic deformation followed by annealing can produce pure iron with improved mechanical properties and slower biodegradability.