Magnetron sputtered freestanding MgAg films with ultra-low corrosion rate

Abstract

Magnesium based alloys are of great interest for temporary medical applications. In order to tailor the corrosion rate, Mg is often alloyed with other elements for the envisaged application as a biodegradable medical implant. In this study 10 µm thick freestanding MgAg thin film samples with varied Ag concentrations (nominal 2-10 wt%) are presented. These films could have the potential as scaffolds, e.g. in neurological applications. The films are fabricated by a combination of UV lithography, sacrificial layer technique and magnetron sputtering, where the latter allows the fabrication of supersaturated metastable alloys. After removing the sacrificial layer, the released freestanding thin film samples are investigated. The corrosion properties are determined using potentiodynamic polarization measurements in Hanks' balanced salt solution. The microstructure investigations are done by X-ray diffraction and scanning transmission electron microscopy. The results obtained show that it is possible using magnetron sputtering to achieve supersaturated materials with up to 6 wt% Ag which show a significant decrease in the corrosion rate compared to pure Mg by a factor of approximately three (0.04 ± 0.01 mm/yr compared to 0.12 ± 0.02 mm/yr). STATEMENT OF SIGNIFICANCE: In this study magnetron sputtered freestanding MgAg films with a Ag concentration of 2-10 wt% were investigated in terms of corrosion properties and microstructure. The 10 µm thick films were produced by a combination of UV lithography and magnetron sputtering, the latter allows the fabrication of supersaturated alloys. It was possible to fabricate participate free materials up to 6 wt% Ag, which showed a decrease in the corrosion rate by the factor of 3 compared to pure Mg. For materials with 10 wt% it was not possible to obtain single phasematerials, in this case the corrosion rate was increased by a factor of approximately 20 compared to pure Mg due to the formation of galvanic cells.

Keywords: Biodegradable; Corrosion; Magnetron sputtering; MgAg alloy; Microstructure.