Degradation behavior of austenite, ferrite, and martensite present in biodegradable Fe-based alloys in three protein-rich pseudo-physiological solutions

This study investigates the degradation behavior of three distinct Fe-based alloys immersed in three pseudo-physiological solutions. These alloys, which have varied Mn and C contents, include a commercially available Fe-0.15C alloy, namely Fe–C, and two newly developed alloys, that is Fe–5Mn-0.2C (namely Fe–5Mn) and Fe–18Mn-0.6C (namely Fe–18Mn). The aim was to understand the effect of alloying elements and the testing solution on the in-vitro degradation behavior of these Fe-based materials. Static immersion degradation and potentiodynamic corrosion tests were carried out using three pseudo-physiological solutions with albumin supply, that is modified Hanks’ saline solution (MHSS), phosphate buffered saline solution (PBS), and sodium chloride solution (NaCl). After two weeks of static immersion, the results revealed that Fe–5Mn, characterized by a mixture of ferrite and martensite, showed the highest degradation rate, while Fe–C, composed solely of ferrite, showed the lowest rate of degradation. The predominant degradation products in MHSS and PBS were phosphates and carbonates. In PBS, these products formed a remarkably stable protective layer on the surface, contributing to the lowest degradation rate. In contrast, porous hydroxides appeared as the main degradation products for samples immersed in NaCl solution, leading to the highest degradation rate. These results provided important insights into the customization of Fe–Mn–C alloys for a range of biomedical applications, meeting a variety of clinical requirements, and highlighting the considerable potential of Fe–Mn–C alloys for biomedical applications.