Preparation And Properties Of Nanostructured Hydroxyapatite Coating On Titanium Alloy By Microwave Synthesizing

Hydroxyapatite(HA, Ca₁₀（PO₄）₆（OH）₂) coating prepared on Ti6Al4V substrate is aexcellent substitute material for bones and teeth in orthopedics and dental surgery, Whichboth have the excellent mechanical property of metal materials and biological propertiesof coating materials. microwave heating emerges as a new synthesizing technology, whichcan significantly shorten the sintering time and get obtain nanocrystals. Here, in this study,we reports a novel hybrid sol-gel and microwave synthesizing method to producenanostructured HA films on Ti6Al4V substrate with sound bond strength and intra-filmstrength. The phase structure, micro structure, bonding strength and biological propertiesof coatings were analyzed with scanning electron microscopy （SEM）, X-ray diffraction（XRD）, scratch tester and cell adhesion.Sol of good stability and high purity was prepared by mixing calcium nitrate （1mol/L）and phosphorus pentoxide （0.5mol/L） in absolute ethyl alcohol, followed by the additionof ammonia to adjust pH to8.Orthogonal experiment shows the bond strength of the coatings was significantlyaffected by synthesizing parameters. The order of the factors: oxygen content of theatmosphere＞synthesizing time＞synthesizing temperature. The moderate oxygencontent（10.5%）, the moderate treatment temperature（600℃） and the longer sintering time（90min）produced the nano-structed HA films with excellent bond strength, as theoptimal microwave synthesizing parameters.Interfacial bonding mechanism analysis. The interface between the coating and thesubstrate consists of three parts, respectively, on two flanks of the HA coating and theTi6Al4V substrate, while the middle of the oxide film. In the beginning of the microwavesynthesizing, the bonding strength between HA coating and oxide film is much higherthan that between oxide film and Ti6Al4V substrate. For these titanium dioxides with astrong microwave absorption ability, which would generate the heat necessary forsintering of the HA film on to the metal substrate with microwave processing. On theother hand, it will lead to an rapid growth of oxide film and a decline in bond strength with the Ti6Al4V substrate. There is a critical thickness（Tc） of the oxide film. If thethickness is at or near Tc, we will get a high bond strength. Orthogonal experiment showsthe moderate oxygen content（10.5%）, the lower treatment temperature（600℃） and thelonger sintering time（90min）can make the thichness of oxide film close to the Tc.The result of cell adhesion experiment shows that nanostructed HA coating is moreconducive to the osteoblast adhesion than smooth Ti6Al4V. Nanostructed HA coatingsynthesized by microwave can improve biological properties of materials.