Influence of ultrasonic field during micro-arc oxidation on the structure and properties of calcium phosphate coatings

The study of the influence of applied external ultrasound (US) field with varied power of 35 or 100 W during the micro-arc oxidation (MAO) processing on the thickness growth, surface roughness, porosity, sizes of structural elements and structural-phase states of the calcium phosphate (CaP) coatings on the titanium surface was performed. It was shown that the US transmittance through the electrolyte for 10 min of MAO processing had led to the increase of the coating thickness from 50 to 60 mu m, the surface roughness from 3 to 4.5 mu m, and the cross-section porosity from 27 to 40%. However, under the action of external US there was a destruction of structural elements (spheres with pores) on the coating surface and a filling of pores' spaces by fragments. That led to the decrease of the surface porosity from 30 to 12%. It was revealed by X-ray diffraction (XRD) that all types of the CaP coatings deposited under external US field and without it were in X-ray amorphous state. However, applied US field had led to the increase of the coating crystallinity with incorporation of CaHPO4 and beta-Ca2P2O7 phases.