Polyphosphate assisted hydrothermal synthesis of hydroxyapatite coating on Mg alloys: Enhanced mechanical properties and corrosion resistance

Hydrothermal fabrication of hydroxyapatite coatings on Mg alloys has been extensively developed in recent years. However, the applicability of the samples is generally restricted by the porous nature and the brittleness coating. In this work, ammonium polyphosphate was selected as an additive of the hydrothermal synthesis process. A compact microstructure was obtained under the interlocking effect of the polyelectrolytes. The results from nanoindentation, scratch tests, electrochemical analysis, and immersion experiments revealed that the newly developed coating exhibited enhanced mechanical properties and corrosion resistance. Moreover, the role of PPA in the hydrothermal process was illustrated in a schematic figure. •Hydrothermal method was used to prepare a uniform polyphosphate-apatite coating.•The particles in the composite coating could be interlocked by polyphosphate.•The composite coating exhibited enhanced anticorrosion effect for the Mg alloy.