Formation mechanism of calcium phosphate coating on a plasma electrolytic oxidized magnesium and its corrosion behavior in simulated body fluids

A calcium phosphate coating is fabricated on the surface of plasma electrolytic oxidized (PEO) magnesium by using cathodic electrodeposition. The deposition temperature affects not only the morphology, thickness and composition of the coating, but also the corrosion behavior of the coated substrate. The phase compositions evolve from calcium hydrogen phosphate dihydrate (DCPD) to mixture of DCPD + hydroxyapatite (HA), mixture of octacalcium phosphate (OCP) and HA and only HA with the increase of the deposition temperature. The PEO Mg coated with DCPD and HA shows excellent corrosion resistance and degradable property within 90 days of immersion in simulated body fluid, since the hybrid coating has special structural characteristics and confers superior stability at the coating/substrate interface.