Characterization of Electrolytic Al[sub 2]O[sub 3]/CaP Composite Coatings on Pure Titanium

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Abstract
Electrolytic composite coatings of calcium phosphate (CaP) and Al2O3Al2O3 were successfully deposited on titanium substrates in the mixed solution of Ca(NO3)2Ca(NO3)2 and NH4H2PO4NH4H2PO4 and subsequently in Al(NO3)3Al(NO3)3 aqueous solution, respectively. After annealing at 400°C for 4 h in air, the coated specimens were evaluated by electrochemical polarization and immersion tests in Hank’s solution, hardness test, scratch test, surface morphology observations, and X-ray diffraction analyses. The corrosion resistance, hardness, and adhesion strength of the CaP-coated film were improved, and the oxidation of Ti was also effectively retarded in air by the subsequent electrolytic deposition of Al2O3.Al2O3. Phase transformations of CaP-coated and Al2O3/CaPAl2O3/CaP -coated specimens were further identified in detail. The initial dissolution of hydroxyapatite (HA) with (002) preferred orientation and final reprecipitation of randomly oriented HA were found after immersion tests in Hank’s solution. © 2002 The Electrochemical Society. All rights reserved.