Fabrication and characterization of nanostructured hydroxyapatite (HA)/ yttria stabilized zirconia (YSZ) composite coatings with various contents of yttria

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Salehi, Sahar ; Fathi, M. H. ; Raeissi, K.:
Fabrication and characterization of nanostructured hydroxyapatite (HA)/ yttria stabilized zirconia (YSZ) composite coatings with various contents of yttria.
In: Journal of Advanced Materials in Engineering. Bd. 29 (2010) Heft 1 . - S. 31-43.
ISSN 2423-5733

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Abstract

The addition of ZrO2 particles to the HA coating has received considerable attention because ZrO2 particles increase the bonding strength between HA coating and substrate. In this study, nanostructured hydroxyapatite (HA)/yttria stabilized zirconia (YSZ) coatings were prepared by a sol–gel method. It was found that at 950ºC, the dominant phases were HA and tetragonal (t)-zirconia in 3YSZ, cubic (c)-zirconia in 8 YSZ and t-c-Zirconia in 5YSZ phases with the small amounts of β-tricalcium phosphate (β-TCP) and CaZrO3. The crystallite size of the coating was about ~20-30 nm for tetragonal and cubic zirconia grain size and 40-80 nm for hydroxyapatite grain size. Crack-free and homogeneous HA/YSZ composite coatings were obtained with no observable defects. In vitro evaluation in 0.9% NaCl showed that Ca2+ dissolution rate of composite coatings was lower than that of pure HA coatings. The decrease in electrochemical performance of these coated samples in comparison with the uncoated type 316L St.St could be associated with chloride ion and water penetration into the coating, transport of ions through the coating, and the subsequent electrochemical reactions at the coating–metal interface.