Effect of pulse current on structure and adhesion of apatite electrochemically deposited onto titanium substrates

Apatite films were deposited onto titanium (Ti) metal substrates by an electrodeposition method under a pulse current. Metastable calcium phosphate solution was used as the electrolyte. The ion concentration of the solution was 1.5 times that of human body fluid, but the solution did not contain magnesium ions at 36.5 °C. We used an average current density of 0.01 A/cm² and current-on time (T_ON) equal to current-off time (T_OFF) of 10 ms, 100 ms, 1 s, and 15 s. The adhesive strength between apatite and Ti substrates were relatively high at T_ON = T_OFF = 10 ms. lt is considered that small calcium phosphate (C-P) crystals with low crystallinity were deposited on the Ti surface without reacting with other C-P crystals, H₂O, and HCO₃^- in the surrounding environment. This resulted in relaxation of the lattice mismatch and enhancement of the adhesive strength between the apatite crystals and Ti substrates.