Hydroxyapatite-coated metals: Interfacial reactions during sintering

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Journal Article
Journal of Materials Science: Materials in Medicine, 2005, 16 (2), pp. 101 - 106
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Electrophoretic deposition (EPD) is a low cost flexible process for producing HA coatings on metal implants. Its main limitation is that it requires heating the coated implant in order to densify the HA. HA typically sinters at a temperature below 1150°C, but metal implants are degraded above 1000°C. Further, the metal induces the decomposition of the HA coating upon sintering. Recent developments have enabled EPD of metathesis-synthesised uncalcined HA which sinters at ∼ 1000°C. The effects of temperature on HA-coated Ti, Ti6Al4V, and 316L stainless steel were investigated for dual coatings of metathesis HA sintered at 1000°C. The use of dual HA coatings (coat, sinter, coat, sinter) enabled decomposition to be confined to the "undercoat" (HA layer 1), with the surface coating decomposition free. The tensile strength of the three metals was not significantly affected by the high sintering temperatures (925°C < T < 1000°C). XRD/SEM/EDS analyses of the interfacial zones revealed that 316L had a negligible HA:metal interfacial zone (∼1 μm) while HA:Ti and HA:Ti6Al4V had large interfacial zones (>10 μm) comprising a TiO2 oxidation zone and a CaTiO3 reaction zone. © 2005 Springer Science + Business Media, Inc.
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