Characterization of electrodeposited calcium phosphate coatings by complementary scanning electron microscopy and scanning-transmission electron microscopy associated to X-ray microanalysis

Abstract Calcium phosphate (CaP) coatings on Ti6Al4V substrate were elaborated by electrodeposition at different current densities (2, 5 and 10 mA/cm 2 ). The surface morphology and the chemical composition of the coatings were characterized by scanning electron microscopy associated to X-ray microanalysis (SEM-EDXS). However, these CaP coatings are irregular specimens (rough surface, porosity, variable thickness), so the SEM-EDXS analysis becomes limited. Therefore, we carried out an experimental procedure to minimize these effects which is based on global analysis by SEM-EDXS confirmed by a nanometer scale analysis using scanning transmission electron microscopy associated to X-ray microanalysis. Moreover, phase analysis was performed by X-ray diffraction in order to corroborate the chemical characterization and to identify the different calcium phosphate phases as a function of current density. The results showed that at 2 mA/cm 2 current density, the coating is composed of an octacalcium phosphate: Ca 8 H 2 (PO 4 ) 6 and its amorphous phase called OCPam. At 5 mA/cm 2 , the coating is a mix of calcium deficient hydroxyapatite (Ca-def HAP): Ca 10 − x (HPO 4 ) x (PO 4 ) 6 − x (OH) 2 − x with 0  2 , the coating is mainly composed of an amorphous phase of Ca-def HAPam. Furthermore, cathodic reaction mechanisms of electrolytic CaP coatings on Ti6Al4V are proposed to explain the different kinds of calcium phosphate obtained.