Electrochemical deposition of hydroxyapatite on beta-Ti-40Nb

Beta-phase alloys like Ti-40Nb with outstanding elastic properties are promising new materials for implant applications. For the generation of bioactive surface states electrodeposition of hydroxyapatite (Hap) was conducted on alloy substrates in a water-based electrolyte with 6.1 × 10− 4 M Ca(NO3)2 and 3.6 × 10− 4 M NH4H2PO4 and results were compared with those obtained for cp2-Ti. The impact of electrolyte temperature and of different chemical pre-treatments of the alloy surface, i.e. etching in piranha solution and alkali treatment, on the cyclic polarization behavior and on the potentiostaticly generated deposit characteristics were assessed. At all adjusted surface states the high Nb content of the beta-phase alloy alters passivity by incorporation of oxidized Nb species in the Ti oxide film, but this has no significant impact on the cathodic reduction steps of the complex deposition process. On Ti-40Nb single-phase microcrystalline Ca10(PO4)6OH2 (Hap) with preferred {002} orientation grows. Increasing the electrolyte temperature from 333 K to 353 K yields accelerated Hap growth rates and a morphology change from plate-like to needle-like. At 353 K on mechanically ground Ti-40Nb, adhesive layers with a mean thickness of 1–2 μm precipitate. Chemical pre-treatments of the alloy surface yield small variations of the Hap coating morphology.