Enhancing controlled and uniform degradation of Fe by incorporating Mg and Zn aimed for bio-degradable material applications

Abstract

In this study, combinatorial development of three nanostructured thin film systems, i.e., Fe87Mg9Zn4 (FMZ-1), Fe74Mg19Zn7 (FMZ-2), and Fe60Mg30Zn10 (FMZ-3), are employed via magnetron sputtering and their degradation pattern is studied in Phosphate Buffered Saline (PBS) solution. Controlled and uniform degradation of Fe is observed with the addition of Mg and Zn, which are crucial for temporary biodegradable implants. The structural characterization of the three samples demonstrates a crystalline structure of Fe87Mg9Zn4, a partially amorphous structure of Fe74Mg19Zn7, and a substitutional solid solution of bcc-Fe-Mg in Fe60Mg30Zn10 sample. Potentiodynamic polarization test reveals higher degradation tendency with the addition of Mg and Zn in the samples compared to pure Fe, as validated by more negative corrosion potentials and higher corrosion current densities. Samples with higher Mg and Zn contents (FMZ-2 and FMZ-3) exhibiting lower charge transfer resistance, as extracted from electrochemical impedance spectroscopy (EIS), also indicates higher corrosion rate compared to Pure Fe. Time-dependent EIS demonstrates gradual decrease in impedance values, representing controlled degradation of the samples upon exposure in PBS solution. Scanning Electron Microscopy (SEM) confirms uniform degradation pattern of FMZ-2 and FMZ-3 samples compared to FMZ-1 after 12 h and 24 h immersion in PBS solution. Finally, the X-ray Photoelectron Spectroscopy (XPS) depicts the formation of oxides, hydroxides, and phosphates of Fe, Mg, and Zn as corrosion products. The higher degradation tendency of the co-sputtered samples is ascribed to the combined role of chemical composition and non-equilibrium nanostructures.