Effect of duty cycle on preparation and corrosion behavior of electrodeposited calcium phosphate coatings on AZ91

Highlights: • CaP coating were prepared on AZ91 alloy by pulse electrodeposition method. • Morphology and phase of CaP coatings were studied by thermodynamic analysis. • The most homogeneous pure HA was obtained with the duty cycle value of 0.10. • The coating deposited at the duty cycle of 0.10 has the best barrier properties. - Abstract: In present work, calcium phosphate coatings on AZ91 substrate were prepared by pulse electrodeposition at different duty cycle (0.05, 0.10, 0.15, 0.20) in the mixed solution of 0.1 M Ca(NO₃)₂ and 0.06 M NH₄H₂PO₄ at 60 °C. Phase composition and corrosion behavior of the as-deposited coatings were studied. Results showed that the calcium phosphate coatings had a grass-like structure. As the duty cycle increased, phase composition of the coatings changed from hydroxyapatite (HA) to mixture of HA and dicalcium phosphate dihydrate (DCPD). The adhesion of strength between the coatings and the substrate were higher than 10 MPa. Potentiodynamic polarization test and electrochemical impedance spectroscopy test in simulated body fluid (SBF) indicated that the samples deposited with calcium phosphate coatings exhibited better corrosion resistance as compared with the bare AZ91 alloy.