Patterns of formation of micro-arc calcium phosphate coatings on different types of metal substrates

The development of novel materials for traumatology and orthopedics is the major focus of current research in the field of medical materials science. Bioinert titanium alloys continue to be widely used for the production of medical implants, while new-generation materials based on bioresorbable magnesium alloys are also gaining popularity. A promising method for modifying the surface of these implants is through the formation of biocoatings using the micro-arc oxidation (MAO) technique. Comparative studies of the formation patterns of micro-arc calcium phosphate (CaP) coatings on the surface of titanium VT1-0, Ti-40 wt.% Nb and magnesium Mg-0.8 wt.% Ca alloys were carried out in this work. The morphology of the coatings, their microstructure, and phase composition were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and powder X-ray diffraction (XRD) methods. It is established that the MAO process on magnesium substrates is characterized by the highest value of the initial current density, equal to 0.68 A / cm2. The thickness of the non-porous transition oxide layer of MgO is almost 10 times higher than the thickness of oxide layers for coatings on titanium alloys. CaP coatings deposited on magnesium substrates have the highest values of thickness, roughness and adhesion strength, equal to 118 μm, 8.8 μm, and 19.2 N, respectively. The reasons for the differences in the MAO processes implemented on titanium and magnesium alloys, as well as in the properties of the resulting coatings, are the different types of conductivity and the different electrophysical properties of titanium, niobium, and magnesium oxides that make up the transition oxide layer between the coating and the substrate.

1. Institute of Strength Physics and Materials Science, Siberian Branch of the Russian Academy of Sciences - Government research assignment for ISPMS SB RAS, project FWRW-2021-0007