Combinatorial screening of microstructure, hardness and biodegradable behaviour of Magnesium-Scandium thin film alloys

A Mg-Sc thin film library was produced by thermal evaporation technique focusing on a compositional spread of Sc up to 20 at.%. Microstructural investigations were carried out by scanning electron microscopy (SEM), grazing incidence X-ray diffraction (GIXRD) and atomic force microscopy (AFM) and the results demonstrated that a single-phase Mg-Sc solid solution was maintained across the library with no trace of binary intermetallic phases within the GIXRD resolution limits. An increase in Sc concentrations led to a gradual amorphization and smoothening of the surface. Nanoindentation tests revealed that the hardness of Mg showed enhancements up to around 10 at.% of Sc, above which it decreased. Electrochemical characterizations were conducted through scanning droplet cell microscopy (SDCM) performed at specific Sc concentrations in both, 0.9% NaCl and simulated body fluid (SBF). Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests showed that increasing Sc concentrations shifted the corrosion potential toward positive direction and improved the corrosion resistance of Mg-Sc thin films. The alloy with the highest Sc content (20 at.%) exhibited an exceptionally high corrosion resistance in the SBF due to the synergistic effects between the partial amorphous structure and complex ions from SBF.