Sputtered, micro structured freestanding FeMn foils as biodegradable materialPart of:
The most prominent candidates for biodegradable metals are magnesium and iron. The advantages of iron in comparison to magnesium are the higher strength and good X-ray visibility which is essential during the implementation of the implant. However in vivo studies have shown an insufficient degradation rate. Thus the task for iron based biodegradable material is either to accelerate the degradation rate or increase the strength which would allow the usage of thinner structures and as a consequence relativizes the low corrosion rate. In order to achieve this FeMn alloys were shown being a promising candidate material. Even the investigations of alternative fabrication methods are of great interest in order to tailor the material properties due to the variation of the microstructure.
In the present study magnetron sputtering in combination with lithography techniques was used in order to fabricate freestanding, micro structured FeMn foils. To adjust the microstructure, the foils were annealed under reducing atmosphere. The microstructure was investigated by SEM, STEM, EDX and XRD. Furthermore, uniaxial tensile tests were performed on behalf of the mechanical characterization. The in vitro corrosion rates were determined with weight loss immersion tests and electrochemical polarization measurements. Additionally, the magnetic properties were measured via VSM
The foils showed a fine grained structure and a tensile strength of 712 MPa which is approximately by the factor of two higher compared to the sputtered pure iron reference material. Due to the TWIP (twinning induced plasticity) effect even the ductility is improved while the corrosion rate shows comparable values. Since the annealed foils exist in the austenitic, and antiferromagnetic γ-phase, an additional advantage of the FeMn foils, is the low magnetic saturation polarization of 0.003 T compared to iron with 1.978 T. This enhances the MRI compatibility of the material.