| Because hydroxyapatite(Ca10?PO4?6?OH?2,HA)is chemically similar to the inorganic component of the bone matrix and teeth,synthetic HA is widely used in bone surgery and dental application based on its outstanding cytocompatibility and osteoconductivity.It is known that the thermal expansion coefficient of the HA(13.3×10-6/K)coating is higher than that of the Ti(8.4×10-6/K)substrate.So,the HA coating prepared by APS has low bonding strength with Ti substrate,which affects its long-term application in vivo.In addition,the low physiochemical stability of an HA coating in human body fluid reduces its long-term stabilization and limits its practical clinical application.In view of the above problems,fluorohydroxyapatite and calcium silicate?FHA-CS?composite coatings were prepared by suspension plasma spraying?SPS?technology based on their individual characteristics,such as the high bonding strength between CS and Ti matrix,relatively stable structure and low solubility of FHA.The morphology,composition and microstructure of the as-sprayed coatings were evaluated by SEM?LSCM?XPS and XRD.Their mechanical properties?hardness and bond strength?,chemical stability and biological properties were investigated.The purpose of this work was to develop a new biological coating material with excellent biological activity,good chemical stability and high bonding strength,which had potential applications in orthopedics and dentistry.The main results were as follows:1. FHA nanopowders were synthesized by chemical coprecipitation.The optimum proportion of suspension for spraying was determined as solid phase?FHA/CS,15 wt.%?,dispersant?ammonium polyacrylate,1.5 wt.%?and solvent?distilled water,83.5 wt.%?.The best spraying process were spraying current of 700 A,spraying distance of 40 mm and flow rate of 32 ml/min.2. Five coatings with different compositions,including FHA,70%FHA+30%CS ?F7C3?,50%FHA+50%CS?F5C5?,30%FHA+70%?F3C7?and CS,were prepared by SPS technique.The XRD analysis presented that the major phase of coatings were FHA and?-CS.In addition,the trace phases included?-TCP,Ca O and Si O2.The changing trends of the peak intensities of the main phases were consistent with their designed contents in the coatings.The FHA-CS composite coatings prepared by SPS showed a good combination with the substrate,and no transverse cracks were found at the interfaces.But,among these coatings,a small amount of pores and microcracks could be observed.The thicknesses of the coatings ranged from 75 to 92 um with porosities of 7.4-8.3%.3. The mechanical properties of FHA-CS composite coatings showed that the microhardness of the coatings increased with the increase of FHA content,and the bonding strength increased with the increase of CS content.The results of solubility test showed containing the FHA component was lower,suggesting a higher chemical stability.The corrosion resistance,antibacterial properties and apatite-forming ability of the composite coating?F7C3?were similar to that of the single FHA coating.4. In order to further combine the characteristics of FHA and CS and optimize the comprehensive properties of the coating,FHA-CS gradient structure coating was prepared on Ti substrate by SPS technique.The results showed that the gradient coating was consistent with the expected composition continuous transition.The thickness of the coating was about 150 um,and had a rough and porous surface.The pores in the coating were evenly distributed and there was no vertical crack through the coating.5. The design of FHA-CS gradient structure further improved the bonding strength of the coating,reached 29.2 MPa,which was about 20%higher than the single FHA coating.The gradient coating showed excellent solubility resistance.And the presence of FHA component on the surface of the coating effectively improved the chemical stability of the coating.In addition,the gradient coating also showed excellent biological and antibacterial properties. |
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