Preparation Of Fluorinated HA Coatings And Quality Evaluation System

Hydroxyapatite (HA) is considered the preferred biological coating materials owing to ts excellent biocompatibility. As the only method approved by US Food and Drug Administration (FDA), plasma sprayed biological ceramic coating is always the research hotspot. The preparation of metal-based HA coatings has been widely used in clinical practice. But with the younger trend of replacement surgery patients and the improvement of living standards, people have the higher requirements of the implant. Thus, to produce high-performance coatings and improve the quality of the implant has a broad development prospects.There are many technologies to prepare bio-ceramic coatings. In addition to the conventional plasma spraying, laser cladding technology has been developed rapidly. This dissertation focuses on the plasma spraying/laser cladding composite technology to prepare the composite coating, mixing hydroxyapatite (HA) powder and titanium (Ti) powder as the material to prepare the transition layer by laser cladding and using hydroxyapatite (HA) powder and calcium fluoride (CaF2) to prepare the plasma sprayed ceramic layer. Through adjusting the content of CaF2 powder, the FHA coatings with different F content are produced. Scanning Electron Microscopy/Energy Dispersive Spectroscopy (SEM/EDS), X-ray diffraction analysis (XRD) and tensile test are applied to characterize the performance of the coating, the simulated body fluid (SBF) immersion experiments are used to study the bioactivity of the coatings. The main work and achievement are as follows:1.The optimal parameters of laser cladding, the laser power is 1200W, the scanning speed is 200 mm/s. Under this condition, the temperature of the coating and substrate metallurgical bond reached the required temperature conditions, therefore the prepared coating and the substrate achieved a good metallurgical bond. Besides a small amount of CaO, TCP and other material, the main components of the intermediate layer is CaTiO3. On one hand CaTiO3 and other ceramic nhase heln to imnrove the bondine strength of the coatine on the other hand due to the thermal expansion coefficient of the intermediate layer between the ceramic layer and the substrate, it is conducive to produce a better quality of the prepared ceramic coating.2.Fluorinated hydroxyapatite prepared by plasma sprayed, with the addition of F replaces the OH portion, Generated Ca-F bond energy is greater than the Ca-OH bond energy and crystal structure becomes smaller. Prepared in the plasma spraying conditions at the high temperature and then cooled to room temperature. Due to the contraction in the crystal structure of the ceramic coating FHA, it resulted in a micro-cracks between the grains. The coating surface cracks increasingly with the increase of F element content.3.Combination the method of Plasma spraying and laser cladding, fluorine-containing HA coating was prepared to increase the mechanical interlocking effect between the coating and the substrate. Internal bond energy was improved by adding F elements, making the coating bond strength from 20. IMPa increased to 28.4MPa.4. Simulated body fluid (SBF) soaking experiments show that adding F element can greatly improve the biological activity of the coating. Apatite formed on the surface of HAO (Ca10(PO4)6(OH)2) coating was significantly less than the fluorinated hydroxyapatite (FHA0.5, FHA1.0, FHA1.5, FHA2.0. the formulas of this four labels are Ca10(PO4)6F0.5(OH)1.5, Ca10(PO4)6F1(OH)1, Ca10(PO4)6F1.5(OH)0.5, Ca10(PO4)6F2) coatings’surface and nucleation formed exhibits petaloid. With the increase of F elements, the growth direction of apatite on the coating surface has changed. When the F content reach the maximum (FHA2.0) that the changes become the most obvious. Original growth direction of the crystal nucleus covered the surface of the coating is random. With the nuclei continues to grow, for more ions was adsorbed, the growth direction is perpendicular to the coating surface slightly.5.After four hours heat treatment at 800℃, the coating composition is more homogeneous, and the number of nuclei on the surface is larger than which is not heat-treated, and add to the limited number of ions on the surface, the size of the nuclei is smaller than the surface of the coating which is not heat-treated.6.Based on the failure modes in real life by orthopedic implants, the quality of coating can be evaluate by:bond strength, HA crystallinity, coating hardness, elastic modulus, fracture toughness, the coating porosity. Depending on the number of different failure modes, AHP method is employed to determine the weight of each index. The result is:Bond strength: 0.206, HA crystallinity:0.534, coating hardness:0.073, elastic modulus:0.025, fracture toughness:0.062, coating porosity:0.1. Taking hip implant coatings for example, evaluation principles are developed, so overall quality evaluation index S of coating can be expressed as follows: S=0.206X1+0.534X2+0.073X3+0.025X4+0.062X5+0.1X6X1,X2,X3,X4,X5,X6 are bonding strength, HA crystallinity, coating hardness, elastic modulus, fracture toughness, coating porosity rate’s score.